Finder optical system

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a real image mode finder optical system suitable for use in a lens shutter camera or an electronic still camera which is constructed so that a photographing optical system is independent of a finder optical system, and in particular, to a real image mode finder optical system which has a large angle of emergence and is best adapted for mounting to a compact camera.

2. Description of Related Art

In general, finders constructed to be independent of photographing optical systems, used in lens shutter cameras, are roughly divided into two classes: virtual image mode finders and real image mode finders.

The virtual image mode finder has the advantage that an image erecting optical system is not required, but has the disadvantage that since an entrance pupil is located at the same position as an observer's pupil, the diameter of a front lens must be increased or the area of a visual field is not defined. An Albada finder of this type allows the area of the visual field to be definitely set, but has the problem that a half mirror coating is applied to the surface of a lens and thus the transmittance of the lens is reduced or flare is increased.

In contrast to this, the real image mode finder is such that the position of the entrance pupil can be located on the object side, and hence the diameter of the front lens can be decreased. Moreover, by placing a field frame in the proximity of the imaging position of an objective lens, the area of the visual field can be defined without reducing the transmittance.

A conventional real image mode finder, however, dose not provide a sufficient angle of apparent visual field (hereinafter referred to as an angle of emergence). Specifically, an object to be observed can be viewed only in small size. Thus, when the object is a person, there is the problem that it is difficult to view the expression of the person. A finder with a relatively large angle of emergence is disclosed, for example, in each of Japanese Patent Preliminary Publication Nos. Hei 6-51201 and Hei 11-242167. However, even such a finder does not provide a sufficiently large angle of emergence.

A so-called telescope has a large angle of emergence. However, the telescope, which has a high magnification, namely a small angle of visual field, cannot be applied to a finder constructed to be independent of the photographing optical system, used in a common lens shutter camera which has a wide angle of view.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide a real image mode finder optical system in which the angle of emergence can be increased and compactness can be attained.

In order to achieve this object, the real image mode finder optical system according to the present invention is constructed to be independent of the photographing optical system and has, in order from the object side, an objective optical system with a positive refracting power, a field frame located in the proximity of the imaging position of the objective optical system, and an eyepiece optical system with a positive refracting power. The real image mode finder optical system includes an image erecting means, and the focal length of the objective optical system can be made shorter than that of the eyepiece optical system. In this case, the real image mode finder optical system satisfies the following condition:

0.52<mh/fe<1 (1)

where mh is the maximum width of the field frame and fe is the focal length of the eyepiece optical system.

The real image mode finder optical system according to the present invention is constructed to be independent of the photographing optical system and has, in order from the object side, an objective optical system with a positive refracting power, a field frame located in the proximity of the imaging position of the objective optical system, and an eyepiece optical system with a positive refracting power. The real image mode finder optical system includes an image erecting means, the objective optical system includes three of reflecting surfaces of the image erecting means, and the eyepiece-optical system includes one of reflecting surfaces of the image erecting means so that an image is erected through four reflecting surfaces comprised of three reflecting surfaces of the objective optical system and one reflecting surface of the eyepiece optical system. The focal length of the objective optical system is variable, and when the magnification of the finder optical system is changed, at least two lens units are moved along different paths. The focal length of the objective optical system at the wide-angle position thereof is shorter than that of the eyepiece optical system. In this case, the real image mode finder optical system satisfies Condition (1).

The real image mode finder optical system according to the present invention is constructed to be independent of the photographing optical system and has, in order from the object side, an objective optical system with a positive refracting power, a field frame located in the proximity of the imaging position of the objective optical system, and an eyepiece optical system with a positive refracting power. The real image mode finder optical system includes an image erecting means, the objective optical system includes three of reflecting surfaces of the image erecting means, and the eyepiece optical system includes one of reflecting surfaces of the image erecting means so that an image is erected through four reflecting surfaces comprised of three reflecting surfaces of the objective optical system and one reflecting surface of the eyepiece optical system. The focal length of the objective optical system is variable, and when the magnification of the finder optical system is changed, at least two lens units are moved along different paths. The focal length of the objective optical system at the wide-angle position thereof is shorter than that of the eyepiece optical system. The image erecting means including the three reflecting surfaces is constructed with two prisms so that each of the prisms has at least one reflecting surface and one of the entrance surface and the exit surface of each prism is configured as a curved surface with finite curvature.

This and other objects as well as the features and advantages of the present invention will become apparent from the following detailed description of the preferred embodiments when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing of a first embodiment of the real image mode finder optical system according to the present invention;

FIG. 2 is a plan view of the real image mode finder optical system of FIG. 1;

FIG. 3 is a side view of the real image mode finder optical system of FIG. 1;

FIG. 4 is an explanatory view of a field frame used in the real image mode finder optical system of the first embodiment;

FIGS. 5A, 5B, and 5C are sectional views showing arrangements, developed along the optical axis, at wide-angle, middle, and telephoto positions, respectively, of the real image mode finder optical system in the first embodiment;

FIGS. 6A, 6B, 6C, and 6D are diagrams showing aberration characteristics at the wide-angle position of the real image mode finder optical system in the first embodiment;

FIGS. 7A, 7B, 7C, and 7D are diagrams showing aberration characteristics at the middle position of the real image mode finder optical system in the first embodiment;

FIGS. 8A, 8B, 8C, and 8D are diagrams showing aberration characteristics at the telephoto position of the real image mode finder optical system in the first embodiment;

FIGS. 9A, 9B, and 9C are sectional views showing arrangements, developed along the optical axis, at wide-angle, middle, and telephoto positions, respectively, of the real image mode finder optical system in a second embodiment;

FIGS. 10A, 10B, 10C, and 10D are diagrams showing aberration characteristics at the wide-angle position of the real image mode finder optical system in the second embodiment;

FIGS. 11A, 11B, 11C, and 11D are diagrams showing aberration characteristics at the middle position of the real image mode finder optical system in the second embodiment;

FIGS. 12A, 12B, 12C, and 12D are diagrams showing-aberration characteristics at the telephoto position of the real image mode finder optical system in the second embodiment;

FIGS. 13A, 13B, and 13C are sectional views showing arrangements developed along the optical axis, at wide-angle, middle, and telephoto positions, respectively, of the real image mode finder optical system in a third embodiment;

FIGS. 14A, 14B, 14C, and 14D are diagrams showing aberration characteristics at the wide-angle position of the real image mode finder optical system in the third embodiment;

FIGS. 15A, 15B, 15C, and 15D are diagrams showing aberration characteristics at the middle position of the real image mode finder optical system in the third embodiment;

FIGS. 16A, 16B, 16C, and 16D are diagrams showing aberration characteristics at the telephoto position of the real image mode finder optical system in the third embodiment;

FIGS. 17A, 17B, and 17C are sectional views showing arrangements, developed along the optical axis, at wide-angle, middle, and telephoto positions, respectively, of the real image mode finder optical system in a fourth embodiment;

FIGS. 18A, 18B, 18C, and 18D are diagrams showing aberration characteristics at the wide-angle position of the real image mode finder optical system in the fourth embodiment;

FIGS. 19A, 19B, 19C, and 19D are diagrams showing aberration characteristics at the middle position of the real image mode finder optical system in the fourth embodiment;

FIGS. 20A, 20B, 20C, and 20D are diagrams showing aberration characteristics at the telephoto position of the real image mode finder optical system in the fourth embodiment;

FIGS. 21A, 21B and 21C are sectional views showing arrangements, developed along the optical axis, at wide-angle, middle, and telephoto positions, respectively, of the real image mode finder optical system in a fifth embodiment;

FIGS. 22A, 22B, 22C, and 22D are diagrams showing aberration characteristics at the wide-angle position of the real image mode finder optical system in the fifth embodiment;

FIGS. 23A, 23B, 23C, and 23D are diagrams showing aberration characteristics at the middle position of the real image mode finder optical system in the fifth embodiment;

FIGS. 24A, 24B, 24C, and 24D are diagrams showing aberration characteristics at the telephoto position of the real image mode finder optical system in the fifth embodiment;

FIGS. 25A, 25B, 25C, and 25D are sectional views showing arrangements, developed along the optical axis, at wide-angle, middle, and telephoto positions and with respect to an eyepiece optical system, respectively, of the real image mode finder optical system in a sixth embodiment;

FIGS. 26A, 26B, 26C, and 26D are diagrams showing aberration characteristics at the wide-angle position of the real image mode finder optical system in the sixth embodiment;

FIGS. 27A, 27B, 27C, and 27D are diagrams showing aberration characteristics at the middle position of the real image mode finder optical system in the sixth embodiment;

FIGS. 28A, 28B, 28C, and 28D are diagrams showing aberration characteristics at the telephoto position of the real image mode finder optical system in the sixth embodiment;

FIGS. 29A, 29B, 29C, and 29D are diagrams showing aberration characteristics of the eyepiece optical system of the real image mode finder optical system in the sixth embodiment;

FIGS. 30A, 30B, 30C, and 30D are sectional views showing arrangements, developed along the optical axis, at wide-angle, middle, and telephoto positions and with respect to an eyepiece optical system, respectively, of the real image mode finder optical system in a seventh embodiment;

FIGS. 31A, 31B, 31C, and 31D are diagrams showing aberration characteristics at the wide-angle position of the real image mode finder optical system in the seventh embodiment;

FIGS. 32A, 32B, 32C, and 32D are diagrams showing aberration characteristics at the middle position of the real image mode finder optical system in the seventh embodiment;

FIGS. 33A, 33B, 33C, and 33D are diagrams showing aberration characteristics at the telephoto position of the real image mode finder optical system in the seventh embodiment;

FIGS. 34A, 34B, 34C, and 34D are diagrams showing aberration characteristics of the eyepiece optical system of the real image mode finder optical system in the seventh embodiment;

FIGS. 35A, 35B, 35C, and 35D are sectional views showing arrangements, developed along the optical axis, at wide-angle, middle, and telephoto positions and with respect to an eyepiece optical system, respectively, of the real image mode finder optical system in an eighth embodiment;

FIGS. 36A, 36B, 36C, and 36D are diagrams showing aberration characteristics at the wide-angle position of the real image mode finder optical system in the eighth embodiment;

FIGS. 37A, 37B, 37C, and 37D are diagrams showing aberration characteristics at the middle position of the real image mode finder optical system in the eighth embodiment;

FIGS. 38A, 38B, 38C, and 38D are diagrams showing aberration characteristics at the telephoto position of the real image mode finder optical system in the eighth embodiment;

FIGS. 39A, 39B, 39C, and 39D are diagrams showing aberration characteristics of the eyepiece optical system of the real image mode finder optical system in the eighth embodiment;

FIGS. 40A, 40B, 40C, and 40D are sectional views showing arrangements, developed along the optical axis, at wide-angle, middle, and telephoto positions and with respect to an eyepiece optical system, respectively, of the real image mode finder optical system in a ninth embodiment;

FIGS. 41A, 41B, 41C, and 41D are diagrams showing aberration characteristics at the wide-angle position of the real image mode finder optical system in the ninth embodiment;

FIGS. 42A, 42B, 42C, and 42D are diagrams showing aberration characteristics at the middle position of the real image mode finder optical system in the ninth embodiment;

FIGS. 43A, 43B, 43C, and 43D are diagrams showing aberration characteristics at the telephoto position of the real image mode finder optical system in the sixth embodiment;

FIGS. 44A, 44B, 44C, and 44D are diagrams showing aberration characteristics of the eyepiece optical system of the real image mode finder optical system in the ninth embodiment;

FIGS. 45A, 45B, 45C, and 45D are sectional views showing arrangements, developed along the optical axis, at wide-angle, middle, and telephoto positions and with respect to an eyepiece optical system, respectively, of the real image mode finder optical system in a tenth embodiment;

FIGS. 46A, 46B, 46C, and 46D are diagrams showing aberration characteristics at the wide-angle position of the real image mode finder optical system in the tenth embodiment;

FIGS. 47A, 47B, 47C, and 47D are diagrams showing aberration characteristics at the middle position of the real image mode finder optical system in the tenth embodiment;

FIGS. 48A, 48B, 48C, and 48D are diagrams showing aberration characteristics at the telephoto position of the real image mode finder optical system in the tenth embodiment;

FIGS. 49A, 49B, 49C, and 49D are diagrams showing aberration characteristics of the eyepiece optical system of the real image mode finder optical system in the tenth embodiment;

FIGS. 50A, 50B, 50C, and 50D are sectional views showing arrangements, developed along the optical axis, at wide-angle, middle, and telephoto positions and with respect to an eyepiece optical system, respectively, of the real image mode finder optical system in an eleventh embodiment;

FIGS. 51A, 51B, 51C, and 51D are diagrams showing aberration characteristics at the wide-angle position of the real image mode finder optical system in the eleventh embodiment;

FIGS. 52A, 52B, 52C, and 52D are diagrams showing aberration characteristics at the middle position of the real image mode finder optical system in the eleventh embodiment;

FIGS. 53A, 53B, 53C, and 53D are diagrams showing aberration characteristics at the telephoto position of the real image-mode finder optical system in the eleventh embodiment;

FIGS. 54A, 54B, 54C, and 54D are diagrams showing aberration characteristics of the eyepiece optical system of the real image mode finder optical system in the eleventh embodiment;

FIGS. 55A, 55B, and 55C are sectional views showing arrangements, developed along the optical axis, at wide-angle, middle, and telephoto positions, respectively, of the real image mode finder optical system in a twelfth embodiment;

FIGS. 56A, 56B, and 56C are sectional views showing arrangements, developed along the optical axis, at wide-angle, middle, and telephoto positions, respectively, of the real image mode finder optical system in a thirteenth embodiment;

FIGS. 57A, 57B, and 57C are sectional views showing arrangements, developed along the optical axis, at wide-angle, middle, and telephoto positions, respectively, of the real image mode finder optical system in a fourteenth embodiment;

FIGS. 58A, 58B, and 58C are sectional views showing arrangements, developed along the optical axis, at wide-angle, middle, and telephoto positions, respectively, of the real image mode finder optical system in a fifteenth embodiment,

FIGS. 59A, 59B, and 59C are sectional views showing arrangements, developed along the optical axis, at wide-angle, middle, and telephoto positions, respectively, of the real image mode finder optical system in a sixteenth embodiment;

FIGS. 60A, 60B, and 60C are sectional views showing arrangements, developed along the optical axis, at wide-angle, middle, and telephoto positions, respectively, of the real image mode finder optical system in a seventeenth embodiment;

FIGS. 61A, 61B, and 61C are sectional views showing arrangements, developed along the optical axis, at wide-angle, middle, and telephoto positions, respectively, of the real image mode finder optical system in an eighteenth embodiment;

FIGS. 62A, 62B, and 62C are sectional views showing arrangements, developed along the optical axis, at wide-angle, middle, and telephoto-positions, respectively, of the real image mode finder optical system in a nineteenth embodiment;

FIGS. 63A, 63B, and 63C are sectional views showing arrangements, developed along the optical axis, at wide-angle, middle, and telephoto positions, respectively, of the real image mode finder optical system in a twentieth embodiment;

FIGS. 64A, 64B, and 64C are sectional views showing arrangements, developed along the optical axis, at wide-angle, middle, and telephoto positions, respectively, of the real image mode finder optical system in a twenty-first embodiment;

FIG. 65 is a plan view of the real image mode finder optical system in the twenty-first embodiment;

FIG. 66 is a side view of the real image mode finder optical system of FIG. 65;

FIG. 67 is a rear view of the real image mode finder optical system of FIG. 65;

FIGS. 68A, 68B, and 68C are sectional views showing arrangements, developed along the optical axis, at wide-angle, middle, and telephoto positions, respectively, of the real image mode finder optical system in a twenty-second embodiment;

FIGS. 69A, 69B, and 69C are sectional views showing arrangements, developed along the optical axis, at wide-angle, middle, and telephoto positions, respectively, of the real image mode finder optical system in a twenty-third embodiment;

FIGS. 70A, 70B, and 70C are sectional views showing arrangements, developed along the optical axis, at wide-angle, middle, and telephoto positions, respectively, of the real image mode finder optical system in a twenty-fourth embodiment;

FIG. 71 is a front perspective view showing the appearance of an electronic camera in an embodiment of a photographing apparatus using the real image mode finder optical system of the present invention:

FIG. 72 is a rear perspective view of the electronic camera of FIG. 71;

FIG. 73 is a sectional view showing the structure of the electronic camera of FIG. 71; and

FIGS. 74A, 74, and 74C are sectional views showing arrangements, developed along the optical axis, at wide-angle, middle, and telephoto positions, respectively, of a photographing zoom lens used in a compact camera for a 35 mm film (the maximum image height of 21.6 mm).

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the present invention, when the objective optical system is designed to have the focal length shorter than that of the eyepiece optical system, the magnification of the real image mode finer optical system can be reduced to 1× or less, and as a result, the angle of visual field can be increased.

Condition (1) in the present invention is related to the angle of emergence. In order to increase the angle of emergence, it is only necessary to increase the size of an image obtained by the objective optical system, that is, the size of the field frame, or to reduce the focal length of the eyepiece optical system.

Below the lower limit of Condition (1), the image can be seen only in small size. On the other hand, beyond the upper limit of Condition (1), it becomes difficult to grasp the entire area of the visual field, for example, to quickly determine a picture composition.

By constructing the finder optical system to be independent of the photographing optical system, the value of a maximum width mh of the field frame can be set, irrespective of the size of an imaging plane. This is particularly advantageous for compact design of the eyepiece optical system and for the placement of an image erecting means.

It is favorable that the real image mode finder optical system of the present invention is constructed so that the focal length of the objective optical system is variable, and when the magnification of the finder is changed, at least two lens units are moved along different paths.

When the objective optical system is constructed so that its focal length can be changed, a constant angle of emergence can be obtained, without changing the size of the field frame, even when the magnification is changed.

When the angle of emergence is increased, the phenomenon of a so-called diopter shift will occur if the back focal position is shifted. However, when at least two lens units are moved along different paths to change the magnification, the back focal position of the objective optical system can be kept to be nearly constant.

It is desirable that the real image mode finder optical system of the present invention satisfies the following condition:

12.0 mm<fe<18.0 mm (2)

Condition (2) is provided for the purpose of ensuring a space for placing the image erecting means and compactness of the whole of the real image mode finder optical system in a state where Condition (1) is satisfied.

If the lower limit of Condition (2) is passed, a distance on the optical axis between the front principal point of the eyepiece optical system and the field frame will be reduced and at the same time, the finder magnification will be as low as 1× or less. Therefore, a distance on the optical axis between the rear principal point of the objective optical system and the field frame is also reduced, and it becomes difficult to place the image erecting means, which is not favorable.

On the other hand, beyond the upper limit of Condition (2), the maximum width mh of the field frame must be enlarged to increase the angle of emergence. In this case, the objective optical system becomes bulky and the balance between the angle of emergence and the size of the real image mode finder ceases to be kept, which is unfavorable.

It is more desirable that the real image mode finder optical system satisfies the following condition:

13.5 mm<fe<16.5 mm (3)

It is favorable that the real image mode finder optical system is constructed so that the objective optical system includes three reflecting surfaces of the image erecting means and the eyepiece optical system includes one reflecting surface of the image erecting means to erect an image with four reflecting surfaces comprised of the three reflecting surfaces of the objective optical system and the one reflecting surface of the eyepiece optical system.

Thus, according to the present invention, a real image mode finder optical system with a large angle of emergence can be constructed in a state where the arrangement of the eyepiece optical system is simplified.

It is favorable that the real image mode finder optical system of the present invention is constructed so that the objective optical system has the image erecting means including four reflecting surfaces to erect the image with the four reflecting surfaces of the objective optical system.

In this case, at least four reflecting surfaces are required for the image erecting means, and thus if the image erecting means is constructed with four reflecting surfaces, space efficiency can be improved. When the image erecting means is placed in the objective optical system, the burden of a space for placing the image erecting means to the eyepiece optical system is eliminated, and the eyepiece optical system can be constructed with a small number of lenses. Consequently, the focal length of the eyepiece optical system can be completely reduced, and aberration characteristics are easily improved. Thus, according to the present invention, a real image mode finder optical system with a large angle of emergence can be constructed in a state where the arrangement of the eyepiece optical system is simplified.

As mentioned above, when the objective optical system is designed to have the focal length shorter than that of the eyepiece optical system, the magnification of the real image mode finer optical system can be reduced to 1× or less, and as a result, the angle of visual field can be increased. Condition (1) in the present invention is related to the angle of emergence.

At least four reflecting surfaces are required for the image erecting means, and thus if the image erecting means is constructed with four reflecting surfaces, space efficiency can be improved. When three of four reflecting surfaces constituting the image erecting means are placed in the objective optical system, the burden of a space for placing the image erecting means to the eyepiece optical system is lessened, and the number of optical elements constituting the eyepiece optical system can be reduced. Thus, according to the present invention, the focal length of the eyepiece optical system can be completely reduced, and aberration characteristics are easily improved. Also, the objective optical system has a large number of lenses because of the magnification change, and hence can be designed to ensure a space for incorporating three reflecting surfaces in the objective optical system. Consequently, a real image mode finder optical system which has a large angle of emergence and is compact in design can be constructed in a state where the arrangement of the eyepiece optical system is simplified.

It is desirable that the real image mode finder optical system of the present invention is constructed so that the objective optical system comprises, in order from the object side, a first unit with a negative power, fixed or moved when the magnification is changed; a second unit with a positive power, moved when the magnification is changed; a third unit with a negative power, moved when the magnification is changed; and a fourth unit with a positive power, fixed when the magnification is change and including three reflecting surfaces.

According to the present invention, it becomes easy to achieve compactness of the whole of the real image mode finder optical system and to obtain favorable aberration and a large angle of emergence.

It is desirable that the real image mode finder optical system of the present invention is constructed so that the fourth unit includes at least one prism having at least one reflecting surface, and one of the entrance surface and the exit surface of the prism is configured as a curved surface with finite curvature.

According to the present invention, a lens function, such as a contribution to the focal length or correction for aberration, as the fourth unit of the objective optical system and an image erecting function can be exerted in the same space.

Furthermore, it is desirable that the real image mode finder optical: system of the present invention is constructed so that one of the reflecting-surfaces of the prism is configured as a totally reflecting surface.

If total reflection is utilized as far as possible with respect to the reflecting surfaces of the prism, the transmittance of the entire finder can be improved accordingly.

In the real image mode finder optical system, it is desirable that each of the first-unit, the second unit, and the third unit is constructed with a single lens.

According to the present invention, it becomes easy to achieve compactness of the whole of the real image mode finder optical system.

Moreover, it is desirable that the real image mode finder optical system of the present invention is constructed so that the eyepiece optical system includes optical elements having two lens functions, providing air spacing between them and has a positive refracting power as a whole.

In order to increase the angle of emergence, it is only necessary to increase the size of an image obtained by the objective optical system, that is, the size of the field frame, or to reduce the focal length of the eyepiece optical system. However, if the field frame is enlarged with respect to the focal length of the eyepiece optical system, the burden of correction for aberration to the eyepiece optical system will be increased, and it becomes difficult to hold good performance with a single lens. If three or more optical elements are used, it becomes difficult to obtain compactness of the whole of the real image mode finder optical system. Hence, in order to diminish the size of the entire system including the objective optical system, it is desirable to reduce the focal length of the eyepiece optical system. However, when the focal length of the eyepiece optical system is reduced, the distance on the optical axis between the front principal point of the eyepiece optical system and the field frame is diminished, and, for example, space for arranging the optical elements of the image erecting means is narrowed.

Thus, in view of good performance, space for placing the image erecting means, and compactness of the whole of the real image mode finder optical system, it is desirable that the eyepiece optical system, as mentioned above, is constructed with the optical elements having two lens functions, providing air spacing between them.

Furthermore, it is desirable that the real image mode finder optical system of the present invention is designed so that the eyepiece optical system includes, in order from the object side, a prism which has the lens function, at least, with respect to the exit surface and bears a part of an image erecting function and a single positive lens component.

As mentioned above, when an optical element on the field frame side of the eyepiece optical system is constructed with the prism which bears a part of the image erecting function, space can be effectively utilized. Moreover, when the lens function is imparted to the prism separated from the field frame, the degree of a contribution to the focal length of the eyepiece optical system is increased, and it becomes easy to reduce the focal length of the eyepiece optical system.

It is desirable that the real image mode finder optical system of the present invention is designed to impart the lens function to the entrance surface of the prism of the eyepiece optical system.

Since the entrance surface of the prism of the eyepiece optical system is located close to the field frame, the degree of a contribution to the focal length of the eyepiece optical system is low. However, correction for aberration, notably for distortion, and a pupil combination of the objective optical system and the eyepiece optical system are favorably compatible.

It is desirable that the real image mode finder optical system is designed so that the reflecting surface of the prism of the eyepiece optical system is configured as a totally reflecting surface.

As described above, when total reflection is utilized for the reflecting surface of the prism, the transmittance of the entire system of the finder can be improved accordingly.

It is desirable that the real image mode finder optical system of the present invention is constructed so that the positive lens of the eyepiece optical system is capable of making diopter adjustment in accordance with an observer's diopter.

According to the present invention, a change of the diopter required is obtained with a small amount of adjustment. Since the diopter can be adjusted by the positive lens, unlike an element in which the optical axis is bent as in the prism, the adjustment can be easily made.

In this case, it is favorable that the real image mode finder optical system of the present invention satisfies Condition (2).

It is more desirable that the real image mode finder optical system satisfies Condition (3).

The image erecting means including the three reflecting surfaces is constructed with two prisms so that each of the prisms has at least one reflecting surface and one of the entrance surface and the exit surface of each prism is configured as a curved surface with finite curvature.

When the image erecting means including the three reflecting surfaces of the objective optical system is constructed with two prisms so that one of the entrance surface and the exit surface of each prism has a curvature, a lens function, such as a contribution to the focal length or correction for aberration, and an image erecting function can be exerted in the same space.

At least four reflecting surfaces are required for the image erecting means, and thus if the image erecting means is constructed with four reflecting surfaces, space efficiency can be improved. When the image erecting means is placed in the objective optical system, the burden of a space for placing the image erecting means to the eyepiece optical system is eliminated, and the eyepiece optical system can be constructed with a small number of lenses. Consequently, the focal length of the eyepiece optical system can be completely reduced, and aberration characteristics are easily improved.

Also, the objective optical system has a large number of lenses because of the magnification change, and hence the image erecting means can be constructed with comparative ease.

It is desirable that the real image mode finder optical system of the present invention is constructed so that the objective optical system comprises, in order from the object side, s first unit with a negative refracting power, moved when the magnification is changed; a second unit with a positive refracting power, moved when the magnification is changed; a third unit with a negative refracting power, moved when the magnification is changed; and a fourth unit with a positive refracting power, fixed when the magnification is change and including four reflecting surfaces.

According to the present invention, it becomes easy to achieve compactness of the whole of the real image mode finder optical system and to obtain favorable aberration and a large angle of emergence. Also, the four reflecting surfaces of the fourth unit constitute the image erecting means.

In the real image mode finder optical system, it is desirable that the fourth unit includes two prisms so that each of the prisms has at least one reflecting surface and one of the entrance, surface and the exit surface of each prism is configured as a curved surface with finite curvature.

Furthermore, it is desirable that the real image mode finder optical system of the present invention is constructed so that one of the two prisms has totally reflecting surfaces.

As mentioned above, when total reflection is utilized as far as possible with respect to the reflecting surfaces of the prism, the transmittance of the entire finder can be improved accordingly.

In the real image mode finder optical system, it is desirable that each of the first unit, the second unit, and the third unit is constructed with a single lens.

According to the present invention, it becomes easy to achieve compactness of the whole of the real image mode finder optical system.

It is desirable that the real image mode finder optical system of the present invention is constructed so that the eyepiece optical system has a lens which is capable of making diopter adjustment to an observer's diopter.

According to the present invention, a change of the diopter required is obtained with a small amount of adjustment, with little deterioration of performance. Since the diopter can be adjusted by the lens, unlike an element in which the optical axis is bent as in the prism, the adjustment can be easily made.

In this case, it is favorable that the real image mode finder optical system of the present invention satisfies Condition (2).

In this case, it is more desirable that the real image mode finder optical system satisfies Condition (3).

At least four reflecting surfaces are required for the image erecting means, and thus if the image erecting means is constructed with four reflecting surfaces, space efficiency can be improved. When the image erecting means is placed in the objective optical system, the burden of a space for placing the image erecting means to the eyepiece optical system is eliminated, and the eyepiece optical system can be constructed with a small number of lenses. According to the present invention, the focal length of the eyepiece optical system can be completely reduced, and aberration characteristics are easily improved. Also, the objective optical system has a large number of lenses because of the magnification change, and hence the image erecting means can be constructed with comparative ease.

It is favorable that the photographing apparatus according to the present invention has the photographing optical system and the real image mode finder optical system which has been described.

When Condition (4) is satisfied, chromatic aberration of magnification produced in the eyepiece optical system can be suppressed.

When the objective optical system is designed to have the focal length shorter than that of the eyepiece optical system, the magnification of the real image mode finer optical system can be reduced to 1× or less, and as a result, the angle of visual field can be increased. Condition (1) in the present invention is related to the angle of emergence. In order to increase the angle of emergence, it is only necessary to increase the size of an image obtained by the objective optical system, that is, the size of the field frame, or to reduce the focal length of the eyepiece optical system.

When Condition (4) is satisfied, chromatic aberration of magnification produced in the eyepiece optical system can be suppressed.

It is desirable that the real image mode finder optical system of the present invention satisfies Condition (2).

It is more desirable that the real image mode finder optical system satisfies Condition (3).

At least four reflecting surfaces are required for the image erecting means, and thus if the image erecting means is constructed with four reflecting surfaces, space efficiency can be improved. When three of four reflecting surfaces constituting the image erecting means are placed in the objective optical system, the burden of a space for placing the image erecting means to the eyepiece optical system is lessened, and the number of optical elements constituting the eyepiece optical system can be reduced. Thus, according to the present invention, the focal length of the eyepiece optical system can be completely reduced, and aberration characteristics are easily improvised. In particular, where the focal length of the objective optical system is variable, the objective optical system, which has a large number of lenses, can be designed to ensure a space for incorporating three reflecting surfaces in the objective optical system. Consequently, a real image mode finder optical system which has a large angle of emergence and is compact in design can be constructed in a state where the arrangement of the eyepiece optical system is simplified.

At least four reflecting surfaces are required for the image erecting means, and thus if the image erecting means is constructed with four reflecting surfaces, space efficiency can be improved. When the image erecting means is placed in the objective optical system, the burden of a space for placing the image erecting means to the eyepiece optical system is eliminated, and the eyepiece optical system can be constructed with a small number of lenses. According to the present invention, the focal length of the eyepiece optical system can be completely reduced, and aberration characteristics are easily improved. In particular, where the focal length of the objective optical system is variable, the number of lenses constituting the objective optical system is large and hence the image erecting means can be constructed with comparative ease.

When the cemented lens component including the positive lens element and the negative lens element is placed on the observer's pupil side of the eyepiece optical system, chromatic aberration of magnification produced in the eyepiece optical system can be suppressed.

Also, by constructing the finder optical system to be independent of the photographing optical system, the value of a maximum width mh of the field frame can be set, irrespective of the size of an imaging plane. This is particularly advantageous for compact design of the eyepiece optical system and for the placement of an image erecting means.

When the objective optical system is designed to have the focal length shorter than that of the eyepiece optical system, the magnification of the real image mode: finer optical system can be reduced to 1× or less, and as a result, the angle of visual field can be increased. Condition (1) in the present invention is related to the angle of emergence. In order to increase the angle of emergence, it is only necessary to increase the size of an image obtained by the objective optical system, that is, the size of the field frame, or to reduce the focal length of the eyepiece optical system.

It is also favorable that the real image mode finder optical system of the present invention satisfies the following condition:

vp−vn>10 (5)

where vp is the Abbe's number of the positive lens element constituting the cemented lens component on the observer's pupil side of the eyepiece optical system and Vn is the Abbe's number of the negative lens element constituting the cemented lens component.

As mentioned above, when the finder optical system is designed to satisfy Condition (5), chromatic aberration of magnification produced in the eyepiece optical system can be suppressed.

It is more desirable that the real image mode finder optical system of the present invention satisfies the following condition:

vp−vn>20 (6)

It is favorable that that the photographing apparatus according to the present invention has the photographing optical system and the real image mode finder optical system which has been described.

Also, in the above description, where the reflecting surface is configured as a roof reflecting surface, it is assumed that the roof reflecting surface is constructed with two reflecting surfaces.

The real image mode finder optical system according to the present invention includes, in order from the object side, an objective optical system with a positive refracting power, a field frame located in the proximity of the imaging position of the objective optical system, and an eyepiece optical system with a positive refracting power. The real image mode finder optical system has an image erecting means, and the objective optical system includes, in order from the object side, a first unit with a negative refracting power, a second unit with a positive refracting power, a third unit with a negative refracting power, and a fourth unit with a positive refracting power so that the magnification of the finder is changed, ranging from the wide-angle position to the telephoto position, by simply moving the second unit toward the object side and the third unit toward the eyepiece optical system. In this case, the finder optical system satisfies Condition (2).

The real image mode finder optical system according to the present invention includes, in order from the object side, an objective optical system with a positive refracting power, a field frame located in the proximity of the imaging position of the objective optical system, and an eyepiece optical system with a positive refracting power. The real image mode finder optical system has an image erecting means and the objective optical system is capable of having the focal length shorter than that of the eyepiece optical system. The eyepiece optical system includes, in order from the object side, a prism unit with a positive refracting power and a lens unit with a positive refracting power so that a most field-frame-side surface of the prism unit with a positive refracting power has a positive refracting power and is configured as an aspherical surface with a negative refracting power on the periphery thereof.

In order to increase the angle of emergence, it is only necessary to increase the size of an image obtained by the objective optical system, that is, the size of the field frame, or to reduce the focal length of the eyepiece optical system. However, if the field frame is enlarged with respect to the focal length of the eyepiece optical system, the objective optical system must be also enlarged. Moreover, since the burden of correction for aberration to the eyepiece optical system will be increased, it becomes difficult that good performance of the eyepiece optical system and compactness due to a simple arrangement are compatible with each other. Thus, in order to keep the size of the finder compact and increase the angle of emergence, it is desirable to reduce the focal length of the eyepiece optical system.

However, when the focal length of the eyepiece optical system is reduced, the distance on the optical axis between the front principal point of the eyepiece optical system and the field frame is diminished, and, for example, space for arranging the optical elements of the image erecting means is narrowed. Consequently, it is necessary that the back focal distance of the objective optical system is increased to place the image erecting means there.

Thus, in the present invention, the objective optical system is designed to have, in order to the object side, the first unit with a negative refracting power, the second unit with a positive refracting power, the third unit with a negative refracting power, and the fourth unit with a positive refracting power. In this way, the back focal distance of the objective optical system is increased.

When the objective optical system is constructed as mentioned above, the focal length of the eyepiece optical system can be reduced, and a real image mode finder optical system which has a large angle of emergence and is compact in design can be obtained.

Condition (2) defines a condition for maintaining the balance of size between the angle of emergence and the finder. Below the lower limit of Condition (2), the distance on the optical axis between the front principal point of the eyepiece optical system and the field frame is reduced, and it becomes difficult to ensure the space for placing the image erecting means. In addition, a diopter shift due to the position shift of the field frame in the direction of the optical axis is increased.

On the other hand, beyond the upper limit of Condition (2), the objective optical system becomes bulky because the image formed by objective optical system must be enlarged to increase the angle of emergence. Consequently, the balance between the angle of emergence and the size of the finder ceases to be kept, which is unfavorable.

When the magnification of the finder is changed, it is necessary that a variable magnification function is chiefly imparted to one of at least two moving lens units and a diopter correcting function involved in the magnification change is chiefly imparted to the other. In this case, the amount of movement of the lens unit having the variable magnification function becomes larger than that of the lens unit having the diopter correcting function, and a mechanism for movement is liable to be complicated and oversized.

Thus, in the present invention, the finder optical system is constructed so that the magnification is changed, ranging from the wide-angle position to the telephoto position, by simply moving the second unit toward the object side and the third unit toward the eyepiece side.

By doing so, both the variable magnification function and the diopter correcting function can be shared between the second unit and the third unit. Hence, the amount of movement of each of the second and third units where the magnification is change can be kept to a minimum, and compactness of the mechanism for movement is obtained.

In this case, it is more desirable that the real image mode finder optical system satisfies Condition (3).

As mentioned above, in order to increase the angle of emergence, it is only necessary to increase the size of an image obtained by the objective optical system, that is, the size of the field frame, or to reduce the focal length of the eyepiece optical system. However, if the field frame is enlarged with respect to the focal length of the eyepiece optical system, the objective optical system must be also enlarged. Moreover, since the burden of correction for aberration to the eyepiece optical system will be increased, it becomes difficult that good performance of the eyepiece optical system and compactness due to a simple arrangement are compatible with each other. Thus, in order to keep the size of the finder compact and increase the angle of emergence, it is desirable to reduce the focal length of the eyepiece optical system.

Condition (1) is related to the angle of emergence. Below the lower limit of Condition (1), the image can be seen only in small size. On the other hand, beyond the upper limit of Condition (1), it becomes difficult to grasp the entire area of the visual field, for example, to quickly determine a picture composition.

When the magnification of the finder is changed, it is necessary that the variable magnification function is chiefly imparted to one of at least two moving lens units and the diopter correcting function involved in the magnification change is chiefly imparted to the other. In this case, the amount of movement of the lens unit having the variable magnification function becomes larger than that of the lens unit having the diopter correcting function, and a mechanism for movement is liable to be complicated and oversized.

As described above, when the objective optical system is designed to have the focal length shorter than that of the eyepiece optical system, the magnification of the real image mode finer optical system can be reduced to 1× or less, and as a result, the angle of visual field can be increased.

When the eyepiece optical system is designed to have the prism unit, a part of the image erecting means can be shared to the eyepiece optical system, and space can be effectively utilized. When the eyepiece optical system is constructed with the unit having a positive refracting power, the diopter can be adjusted in accordance with the observer's diopter.

In order to keep the size of the finder compact and increase the angle of emergence, it is desirable to reduce the focal length of the eyepiece optical system. Further, in order to reduce the focal length of the eyepiece optical system, it is desirable to increase the positive refracting power of the optical element constituting the eyepiece optical system.

However, if the most field-frame-side surface of the eyepiece optical system is configured so that the positive refracting power is increased, and a marginal beam in the proximity of the field frame is rendered nearly parallel to the optical axis, the size of the eyepiece optical system in its radial direction will be increased. On the other hand, if the most field-frame-side surface of the eyepiece optical system is configured so that the positive refracting power is increased, and at the same time, the size of the eyepiece optical system in its radial direction is diminished, the angle of inclination will be increased. Consequently, the marginal beam of the first unit at the wide-angle position is separated from the optical axis, and hence the diameter of the first unit must be enlarged.

Thus, when the most field-frame-side surface of the eyepiece optical system has a positive refracting power and is configured as an aspherical surface with a negative refracting power on its periphery, the diameter of the first-unit can be diminished. Moreover, correction for aberration, notably for distortion, is favorably compatible with a pupil combination of the objective optical system and the eyepiece optical system, notably in an off-axis.

In the real image mode finder optical system of the present invention, it is desirable that the eyepiece optical system includes, in order from the object side, a prism unit with a positive refracting power and a lens unit with a positive refracting power so that a most field-frame-side surface of the prism unit with a positive refracting power has a positive refracting power and is configured as an aspherical surface with a negative refracting power on its periphery.

As mentioned above, when the eyepiece optical system is designed to have the prism unit, a part of the image erecting means can be shared to the eyepiece optical system, and space can be effectively utilized. When the eyepiece optical system is constructed with the lens unit having a positive refracting power, the diopter can be adjusted in accordance with the observer's diopter.

In order to reduce the focal length of the eyepiece optical system, it is desirable to increase the positive refracting power of the optical element constituting the eyepiece optical system.

However, if the most field-frame-side surface of the eyepiece optical system is configured so that the positive refracting power is increased, and a marginal beam in the proximity of the field frame is rendered nearly-parallel to the optical axis, the size of the eyepiece optical system in its radial direction will be increased. On the other hand, if the most field-frame-side surface of the eyepiece optical system is configured so that the positive refracting power is increased, and at the same time, the size of the eyepiece optical system in its radial direction is diminished, the angle of inclination will be increased. Consequently, the marginal beam of the first unit at the wide-angle position is separated from the optical axis, and hence the diameter of the first unit must be enlarged.

Thus, when the most field-frame-side surface of the eyepiece optical system has a positive refracting power and is configured as an aspherical surface with a negative refracting power on its periphery, the diameter of the first unit can be diminished. Moreover, correction for aberration, notably for distortion, is favorably compatible with a pupil combination of the objective optical system and the eyepiece optical system, notably in an off-axis.

In the real image mode finder optical system of the present invention, it is favorable that the negative refracting power on the periphery of the most field-frame-side surface of the prism unit with a positive refracting power satisfies the following condition:

−0.7(1/mm)<φ(mh/2)<0(1/mm) (8)

where φ(mh/2) is a refracting power at a height mh/2 in a direction normal to the optical axis of the aspherical surface.

As described above, when Condition (8) is satisfied, the negative refracting power on the periphery of the most field-frame-side surface of the positive prism unit can be optimized.

Also, a refracting power φ(y) at a height y of the aspherical surface is obtained as follows. When z is taken as the coordinate in the direction of the optical axis, y is taken as the coordinate normal to the optical axis, r denotes the radius of curvature, K denotes a conic constant, and A₄, A₆, A₈, and A₁₀denote aspherical coefficients, the configuration of the aspherical surface is expressed by the following equation:

z=(y²/r)/[1+√{square root over ({1−(1+K)(y/r)²})}{square root over ({1−(1+K)(y/r)²})}]+A₄y₄+A₆y⁶+A₈y⁸+A₁₀y¹⁰

Also, first-order differential dz/dy and second-order differential d²z/dy²are given from the following formulas:

dz/dy=(y/r)/[√{square root over ({1−(1+K)(y/r)²})}{square root over ({1−(1+K)(y/r)²})}]+4A₄y³+6A₆y⁵+8A₈y⁷+10A₁₀y⁹
d²z/dy²=(1/r)/[{1−(1+K)(y/r)²}^3/2]+12A₄y²+30A₆y⁴+56A₈y⁶+90A₁₀y⁸

In this case, the refracting power φ(y) at the height y of the aspherical surface is obtained from the following formula:

φ(y)=(n₂−n₁)/r_asp

where n₁is the refractive index of the aspherical surface on the object side thereof and n₂is the refractive index on the image side.

Also, r_aspis defined as

r_asp=[{1+(dz/dy)²}^3/2]/(d²z/dy²)

It is favorable that the real image mode finder optical system of the present invention is constructed so that the objective optical system has at least two lens units, the focal length of the objective optical system is variable, and when the magnification is changed, the at least two lens units are moved along different paths.

It is favorable that the photographing apparatus according to the present invention has the photographing optical system and the real image mode finder optical system which has been described.

Also, in the above description, where the reflecting surface is configured as a roof reflecting surface, it is assumed that the roof reflecting surface is constructed with two reflecting surfaces.

The real image mode finder optical system according to the present invention includes, in order from the object side, an objective optical system which has a positive refracting power and changes the magnification of the finder, a field frame located in the proximity of the imaging position of the objective optical system, and an eyepiece optical system with a positive refracting power. The real image mode finder optical system has an image erecting means, and the objective optical system includes, in order from the object side, a front unit with a negative refracting power and a rear unit with a positive refracting power. The front unit is constructed with a plurality of lens units so that the magnification is changed, ranging from the wide-angle position to the telephoto position, by moving at least two of the plurality of lens units. The rear unit is constructed with a plurality of prism units with positive refracting powers so that at least one of surfaces opposite to one another, of the plurality of prism units is configured to be convex.

The real image mode finder optical system according to the present invention includes, in order from the object side, an objective optical system which has a positive refracting power and changes the magnification of the finder, a field frame located in the proximity of the imaging position of the objective optical system, and an eyepiece optical system with a positive refracting power. The real image mode finder optical system has an image erecting means, and the objective optical system includes, in order from the object side, a first unit with a negative refracting power, a second unit with a positive refracting power, a third unit with a negative refracting power, and a fourth unit with a positive refracting power. The fourth unit is comprised of a fourth front sub-unit with a positive refracting power and a fourth rear sub-unit with a positive refracting power, and the magnification is changed, ranging from the wide-angle position to the telephoto position, by moving the second unit and the third unit. Each of the first, second, and third units is constructed with a lens, and each of the fourth front and rear sub-units is constructed with a prism so that at least one of surfaces opposite to each other, of the fourth front and rear sub-units is configured to be convex.

In the above construction, the real image mode finder optical system is such that the fourth front sub-unit is comprised of a single prism and has a single reflecting surface.

In order to increase the angle of emergence, it is only necessary to increase the size of an image obtained by the objective optical system, that is, the size of the field frame, or to reduce the focal length of the eyepiece optical system. However, if the field frame is enlarged with respect to the focal length of the eyepiece optical system, the objective optical system must be also enlarged. Moreover, since the burden of correction for aberration to the eyepiece optical system will be increased, it becomes difficult that good performance of the eyepiece optical system and compactness due to a simple arrangement are compatible with each other. Thus, in order to keep the size of the finder compact and increase the angle of emergence, it is desirable to reduce the focal length of the eyepiece optical system.

However, when the focal length of the eyepiece optical system is reduced, the distance on the optical axis between the front principal point of the eyepiece optical system and the field frame is diminished, and, for example, space for arranging the optical elements of the image erecting means is narrowed, so that the reflecting surface to be placed is limited to one. Consequently, it is necessary that the back focal distance of the objective optical system is increased to place the image erecting means there.

Thus, in the present invention, the objective optical system is designed to have, in order to the object side, a front unit with a negative refracting power, including a plurality of lens units and changing the magnification by moving at least two lens units thereof and a rear unit with a positive refracting power comprised of a plurality of prism units with positive refracting powers.

As mentioned above, when the objective optical system is designed to be of a retrofocus type, the back focal distance of the objective optical system can be increased. Moreover, when the rear unit with a positive refracting power is constructed with the prism units, the image erecting means can be shared. Thus, according to the present invention, the focal length of the eyepiece optical system can be reduced, and a real image mode finder optical system which has a large angle of emergence and is compact in design can be achieved.

In the case where the variable magnification ratio of the finder optical system is increased to particularly extend the variable magnification range to the wide-angle side, a high refracting power is required for the rear unit with a positive refracting power. The inclination of the marginal beam with respect to the optical axis where the magnification is changed at the wide-angle position is large immediately after the beam emerges from the front unit with a negative refracting power. Hence, in order to make this inclined beam parallel in the proximity of the field frame, a great positive refracting power is required on the rear side of the front unit with a negative refracting power. In this case, it is desirable that the great positive refracting power is shared among a plurality of surfaces because the performance of the objective optical system is improved.

The rear unit with a positive refracting power comprised of a plurality of prism units with positive refracting powers is placed on the eyepiece side of the front unit with a negative refracting power, and at least one of surfaces opposite to one another, of the plurality of prism units with positive refracting powers is configured to be convex. By doing so, the positive refracting power can be shared to the entrance or exit surface of each of the plurality of prism units with positive refracting powers, and thus the performance of the objective optical system can be improved.

When the magnification is changed by moving at least two lens units, the variable magnification function and the diopter correcting function involved in the magnification change can be exercised.

When the angle of emergence is increased, the diopter shift is liable to occur. However, by moving at least two lens units of the front unit, the diopter shift involved in the magnification change can be corrected.

However, when the focal length of the eyepiece optical system is reduced, the distance on the optical axis between the front principal point of the eyepiece optical system and the field frame is diminished, and, for example, space for arranging the optical elements of the image erecting means is narrowed, so that the reflecting surface to be placed is limited to one. Consequently, it is necessary that the back focal distance of the objective optical system is increased to place the image erecting means there.

Thus, in the present invention, the objective optical system is designed to have, in order to the object side, the first unit with a negative refracting power, the second unit with a positive refracting power, the third unit with a negative refracting power, and the fourth unit with a positive refracting power so that the fourth unit includes the fourth front sub-unit with a positive refracting power and the fourth rear sub-unit with a positive refracting power.

As described above, when the positive refracting power is imparted to each of the fourth front sub-unit and the fourth rear sub-unit, the back focal distance of the objective optical system can be increased. Moreover, when the fourth front and rear subunits are constructed with prisms, the function of the image erecting means can be shared. Thus, according to the present invention, the focal length of the eyepiece optical system can be reduced, and a real image mode finder optical system which has a large angle of emergence and is compact in design can be obtained.

In the case where In the case where the variable magnification ratio of the finder optical system is increased to particularly extend the variable magnification range to the wide-angle side, high refracting powers are required for the units with positive refracting powers on the eyepiece side of the third unit. The inclination of the marginal beam with respect to the optical axis where the magnification is changed at the wide-angle position is large immediately after the beam emerges from the front unit with a negative refracting power. Hence, in order to make this inclined beam parallel in the proximity of the field frame, a great positive refracting power is required on the rear side of the front unit with a negative refracting power. In this case, it is desirable that the great positive refracting power is shared among a plurality of surfaces because the performance of the objective optical system is improved.

When the prism units of the fourth front and rear sub-units with two positive refracting powers are arranged on the eyepiece side of the third unit and at least one of opposite surfaces of the fourth front and rear sub-units is configured to be convex, the positive refracting power can be shared to at least one of opposite surfaces of the fourth front and rear sub-units, and hence the performance of the objective optical system can be improved.

When the magnification is changed by moving at least two units, the variable magnification function and the diopter correcting function involved in the magnification change can be exercised.

When the angle of emergence is increased, the diopter shift is liable to occur. However, by moving the second and third units, the diopter shift involved in the magnification change can be corrected.

In order that the thickness of a camera is reduced to provide a compact camera, it is desirable that a position where the most object-side optical axis of the image erecting means, that is, the position of a reflecting surface, is brought close to the object side. When the magnification is changed, the image erecting means remains fixed and thereby the arrangement of the finder is simplified. Thus, it is desirable that the fourth front sub-unit with a positive refracting power has a reflecting surface.

On the other hand, in order to increase the back focal distance of the objective optical system, it is desired that most of the reflecting surfaces having positive refracting powers shared between the fourth front and rear sub-units are arranged together at a distance away from the field frame.

When the objective optical system is constructed so that the fourth front sub-unit has a single reflecting surface as mentioned above, the opposite surfaces of the fourth front and rear sub-units can be arranged along the length of the fourth front sub-unit including one reflecting surface. Consequently, compactness of the camera and the back focal distance of the objective optical system can be ensured.

In the real image mode finder optical system of the present invention, it is favorable that the fourth rear sub-unit is constructed with a single prism and has two reflecting surfaces.

It is favorable that the real image mode finder optical system of the present invention satisfies the following condition:

−1.0<MG45<−0.5 (9)

where MG45 is a combined imaging magnification of the fourth front sub-unit and a fourth rear sub-unit at an object distance of 3 m.

When Condition (9) is satisfied, the balance between performance and size of the objective optical system can be held. Below the lower limit of Condition (9), a combined refracting power of the first, second, and third units must be increased, and thus the fluctuation of aberration becomes heavy by movement of the second and third units for changing the magnification. On the other hand, beyond the upper limit of Condition (9), a combined refracting power of the first, second, and third units must be reduced, and thus the diameter of the first unit will be particularly enlarged.

When the magnification is changed over the range from the wide-angle position to the telephoto position, it is favorable that the real image mode finder optical system satisfies the following condition:

−1.2<β3 <−0.8 (10)

where β3 is the imaging magnification of the third unit in a state where the imaging magnification of the second unit is −1× at an object distance of 3 m.

The second and third units bear the variable magnification function and the diopter correcting function, but if the diopter correction is not completely made, the diopter shift will be produced. In particular, when the angle of emergence is increased, the diopter shift is liable to occur.

In the real image mode finder optical system of the present invention, it is favorable that the second unit is constructed with a single lens and satisfies the following condition:

−0.6<SF2<0.6 (11)

- where SF2=(r3+r4)/(r3−r4), which is the shape factor of the second unit, r3 is the radius of curvature of the object-side surface of the second unit, and r4 is the radius of curvature of the eyepiece-side surface of the second unit.

When the finder optical system is designed to satisfy Condition (11), the fluctuation of performance where the magnification is changed can be suppressed. If the upper or lower limit of Condition (11) is passed, the fluctuation of aberration where the magnification is changed becomes heavy.

In the real image mode finder optical system of the present invention, it is desirable that each of the second and third units is constructed with a single lens and satisfies the following condition:

−1.9<f2/f3<−1.0 (12)

where f2 is the focal length of the second unit and f3 is the focal length of the third unit.

Condition (12) defines a condition relative to the refracting powers of the second and third units for suppressing a change in performance where the magnification is changed. Below the lower limit of Condition (12), the refracting power of the third unit is increased, and the fluctuation of aberration where the magnification is changed becomes heavy. Beyond the upper limit of Condition (12), the refracting power of the second unit is increased, and the fluctuation of aberration where the magnification is changed becomes heavy.

It is favorable that the real image mode finder optical system of the present invention satisfies the following conditions at the same time:

−1.0<fw/fFw<−0.4 (13)
−1.0<f/fFT<−0.4 (14)

where fFw is a combined focal length of the front unit with a negative refracting power at the wide-angle position, fFT is a combined focal length of the front unit with a negative refracting power at the telephoto position, fw is the focal length of the objective optical system at the wide-angle position, and fT is the focal length of the objective optical system at the telephoto position.

When Conditions (13) and (14) are satisfied at the same time, the balance between the performance and the back focal distance of the objective optical system can be maintained. If the lower limit of Condition (13) or (14) is passed, a negative combined refracting power of the front unit will be strengthened, and thus the fluctuation of aberration caused by the movement of the second and third units for changing the magnification becomes heavy.

On the other hand, if the upper limit of Condition (13) or (14) is exceeded, the negative combined refracting power of the front unit will be diminished, and hence a long back focal distance caused by the retrofocus arrangement will cease to be completely obtainable.

It is desirable that the real image mode finder optical system of the present invention satisfies the following condition:

2.7<mT/mW<7.0 (15)

where mW is the finder magnification of the entire system at the wide-angle position and mT is the finder magnification of the entire system at the telephoto position.

The present invention provides a preferred zoom ratio in the real image mode finder optical system described above.

Below the lower limit of Condition (15), the performance of the finder optical system cannot be completely exercised. On the other hand, beyond the upper limit of Condition (15), the refracting power of each unit becomes too strong and aberration is liable to occur.

It is favorable that that the photographing apparatus according to the present invention has the photographing optical system and the real image mode finder optical system which has been described.

Also, in the above description, where the reflecting surface is configured as a roof reflecting surface, it is assumed that the roof reflecting surface is constructed with two reflecting surfaces.

The real image mode finder optical system according to the present invention includes, in order from the object side, an objective optical system which has a positive refracting power and changes the magnification of the finder, a field frame located in the proximity of the imaging position of the objective optical system, and an eyepiece optical system with a positive refracting power. The real image mode finder optical system has an image erecting means, and the objective optical system includes, in order from the object side, a first unit with a negative refracting power, a second unit with a positive refracting power, a third unit with a negative refracting power, and a fourth unit with a positive refracting power. The magnification is changed, ranging from the wide-angle position to the telephoto position, by simply moving the second unit toward the object side and the third unit toward the eyepiece side. A combined focal length of the first, second, and third units is negative, and when the magnification is changed over the range from the wide-angle position to the telephoto position, a combined imaging magnification of the second and third units is 1×.

In this case, it is favorable that the real image mode finder optical system constructed as mentioned above satisfies Condition (10).

Furthermore, in the real image mode finder optical system of the present invention, it is favorable that the second unit is constructed with a single lens and satisfies Condition (11).

As described above, in order to increase the angle of emergence, it is only necessary to increase the size of an image obtained by the objective optical system, that is, the size of the field frame, or to reduce the focal length of the eyepiece optical system. However, if the field frame is enlarged with respect to the focal length of the eyepiece optical system, the objective optical system must be also enlarged. Moreover, since the burden of correction for aberration to the eyepiece optical system will be increased, it becomes difficult that good performance of the eyepiece optical system and compactness due to a simple arrangement are compatible with each other. Thus, in order to keep the size of the finder compact and increase the angle of emergence, it is desirable to reduce the focal length of the eyepiece optical system.

However, when the focal length of the eyepiece optical system is reduced, the distance on the optical axis between the front principal point of the eyepiece optical system and the field frame is diminished, and, for example, space for arranging the optical elements of the image-erecting means is narrowed. Consequently, it is necessary that the back focal distance; of the objective optical system is increased to place the image erecting means there.

Thus, in the present invention, the objective optical system is designed to have, in order to the object side, the first unit with a negative refracting power, the second unit with a positive refracting power, the third unit with a negative refracting power, and the fourth unit with a positive refracting power so that the combined focal length of the first, second, and third units is negative.

By doing so, the objective optical system is arranged to be of a retrofocus type, and therefore, the back focal distance of the objective optical system can be increased. Thus, according to the present invention, the focal length of the eyepiece optical system can be reduced, and a real image mode finder optical system which has a large angle of emergence and is compact in design can be achieved.

By doing so, both the variable magnification function and the diopter correcting function can be shared between the second-unit and the third unit. Hence, the amount of movement of each of the second and third units where the magnification is change can be kept to a minimum, and compactness of the mechanism for movement is obtained.

In order to achieve compactness of the objective optical system, it is only necessary to increase the refracting power of each of the second and third units for changing the magnification. In this case, however, the fluctuation of aberration where the magnification is changed becomes heavy.

Here, in the whole range in which the magnification is changed, if an attempt is made so that the combined imaging magnification of the second and third units becomes lower than 1×, there is a tendency that the refracting power of the third unit is increased. In this case, since the refracting power of the first unit must be diminished, the diameter of the first unit must be increased.

On the other hand, if an attempt is made so that the combined imaging magnification of the second and third units becomes higher than 1×, there is a tendency that the refracting power of the second unit is increased. In this case, since the refracting power of the first unit must be increased, the diopter shift caused by a change of space between the first and second units becomes particularly considerable.

Thus, if the combined imaging magnification of the second and third units is changed so that it becomes 1×, the balance between the performance and the size of the objective optical system can be optimized.

When the finder optical system is designed to satisfy Condition (10), a state where the imaging magnification of the second unit is −1× at an object distance of 3 m practically coincides with a state where the imaging magnification of the third unit is −1× at an object distance of 3 m when the magnification is changed over the range from the wide-angle position to the telephoto position. As a result, diopter correction can be favorably made over the whole range in which the magnification is changed. When the finder optical system is designed to satisfy Condition (11), the fluctuation of performance where the magnification is changed can be suppressed. If the upper or lower limit of Condition (11) is passed, the fluctuation of aberration where the magnification is changed becomes heavy.

In the real image mode finder optical system of the present invention, it is favorable that each of the second and third units is constructed with a single lens and satisfies Condition (12).

It is favorable that the real image mode finder optical system of the present invention satisfies the following conditions at the same time:

−1.0<fw/fw123<−0.4 (16)
−1.0<fT/fT123<−0.4 (17)

where fw123 is a combined focal length of the first, second, and third units at the wide-angle position and fT123 is a combined focal length of the first, second, and third units at the telephoto position.

When Conditions (16) and (17) are satisfied at the same time, the balance between the performance and the back focal distance of the objective optical system can be maintained. If the lower limit of Condition (16) or (17) is passed, a negative combined refracting power of each of the first, second, and third units will be strengthened, and thus the fluctuation of aberration caused by the movement of the second and third units for changing the magnification becomes heavy.

On the other hand, if the upper limit of Condition (16) or (17) is exceeded, the negative combined refracting power of each of the first, second, and third units will be diminished, and hence a long back focal distance caused by the retrofocus arrangement will cease to be completely obtainable.

It is favorable that the real image mode finder optical system is constructed so that when the magnification is changed over the range from the wide-angle position to the telephoto position, the fourth unit remains fixed.

By doing so, the number of units to be moved can be lessened, and cost can be reduced accordingly.

In the real image mode finder optical system of the present invention, it is favorable that the fourth unit is constructed with two optical units with positive refracting powers.

In the case where the variable magnification ratio of the finder optical system is increased to particularly extend the variable magnification range to the wide-angle side, a high refracting power is required for the unit with a positive refracting power on the eyepiece side of the third unit. The inclination of the marginal beam with respect to the optical axis where the magnification is changed at the wide-angle position is large immediately after the beam emerges from the third unit. Hence, in order to make this inclined beam parallel in the proximity of the field frame, a great positive refracting power is required on the rear side of the third unit. In this case, it is desirable that the great positive refracting power, is shared among a plurality of surfaces because the performance of the objective optical system is improved.

As explained above, when the two optical units with positive refracting powers are arranged on the eyepiece side of the third unit, the lens function can be shared between opposite surfaces of the two optical units with positive refracting powers, and hence the performance of the objective optical system can be improved.

In the real image mode finder optical system of the present invention, it is favorable that the fourth unit has a plurality of reflecting surfaces.

Thus, when at least half of the image erecting function is shared to the objective optical system, an increase in thickness along the optical axis of incidence of the objective optical system can be suppressed and at the same time, the distance between an intermediate image and an eyepiece is reduced. Consequently, a finder which has a large angle of emergence can be obtained.

In the real image mode finder optical system of the present invention, it is favorable that the two optical units are prisms having reflecting surfaces.

When at least half of the image erecting function is shared to the objective optical system, an increase in thickness along the optical axis of incidence of the objective optical system can be suppressed and at the same time, the distance between an intermediate image and an eyepiece is reduced. Consequently, a finder which has a large angle of emergence can be obtained.

It is favorable that the real image mode finder optical system is constructed so that the magnification is changed, ranging from the wide-angle position to the telephoto position, by moving the first unit as well.

The second and third units bear the variable magnification function and the diopter correcting function, but if the diopter correction is not completely made, the diopter shift will be produced.

Where the units for changing the magnification are obstructed with only the second and third units, diopter correction cannot be favorably made over the whole range in which the magnification is changed, unless a state where the imaging magnification of the second unit is −1× practically coincides with a state where the imaging magnification of the third unit is −1× when the magnification is changed over the range from the wide-angle position to the telephoto position.

However, when the first unit is also moved to change the magnification, restrictions on imaging magnifications of the second and third units are eliminated, and the performance of the objective optical system can be easily improved.

The real image mode finder optical system of the present invention may be constructed so that when the magnification is changed over the range from the wide-angle position to the telephoto position, the first unit remains fixed.

By doing so, the number of units to be moved can be lessened, and cost can be reduced accordingly.

In this case, it is favorable that the real image mode finder optical system of the present invention satisfies Condition (15).

The present invention provides a preferred zoom ratio in the real image mode finder optical system described above.

It is favorable that that the photographing apparatus according to the present invention has the photographing optical system and the real image mode finder optical system which has been described.

Also, in the above description, where the reflecting surface is configured as a roof reflecting surface, it is assumed that the roof reflecting surface is constructed with two reflecting surfaces.

In accordance with the drawings and numerical data, the embodiments of the real image mode finder optical system of the present invention will be explained below.

In any of the embodiments, the real image mode finder optical system includes, in order from the object side, an objective optical system with a positive refracting power, a field frame placed in the proximity of the imaging position of the objective optical system, and an eyepiece optical system with a positive refracting power, and has an image erecting means.

First Embodiment

In the real image mode finder optical system of this embodiment, as shown in FIGS. 1–3 and 5A–5C, the objective optical system includes, in order from the object side, a first unit G1 with a negative refracting power, a second unit G2 with a positive refracting power, a third unit G3 with a negative refracting power, and a fourth unit G4 with a positive refracting power, and has a positive refracting power as a whole.

The fourth unit G4 is constructed with two prisms P1 and P2. The eyepiece optical system is constructed with a prism P and a positive lens E1 and has a positive refracting power as a whole. Also, in FIG. 5A, symbol EP represents an eyepoint.

The image erecting means includes the prisms P1 and P2 and the prism P. In the real image mode finder optical system of the first embodiment, an intermediate image formed by the objective optical system is interposed between the prism P2 and the prism P, and the field frame, such as that shown in FIG. 4, is provided in the proximity of its imaging position.

The magnification of the finder is changed in the range from the wide-angle position to the telephoto position by fixing the first unit G1 and the fourth unit G4 and by moving the second unit G2 and the third-unit G3 along the optical axis.

Each of the first unit G1, the second unit G2, and the third unit G3 is constructed with a single lens. The entrance surface and the exit surface of the prism P1 and the entrance surface of the prism P2 have finite curvatures. The entrance surface and the exit surface of the prism P also have finite curvatures.

The prisms P1 and P2 and the prism P, as shown in FIGS. 1–3, are provided with reflecting surfaces P1₁, P2₁, P2₂, and P₁along the optical path so that the optical axis is bent to erect an image. Specifically, as shown in FIG. 3, the reflecting surface P1₁provided in the prism P1 bends the optical axis in a Y-Z plane; as shown in FIGS. 2 and 3, the two reflecting surfaces P2₁and P2₂provided in the prism P2 bend the optical axis in the Y-Z plane and an X-Z plane in this order from the object side; and as shown in FIG. 2, the reflecting surface P₁provided in the prism P bends the optical axis in the X-Z plane. In this way, an erect image is obtained. Also, the arrangement of the reflecting surfaces is based on that of a Porro prism. Angles made with the optical axis bent by the reflecting surfaces are such that, for example, the angles of the optical axis bent by the reflecting surfaces P1₁and P₁of the prism P1 and the prism P are smaller than 90 degrees and the angles of the optical axis bent by the reflecting surfaces P2₁and P2₂of the prism P2 are larger than 90 degrees. The reflecting surfaces P1₁and P₁of the prism P1 and the prism P are coated with metal films, such as silver and aluminum. The reflecting surfaces P2₁and P2₂of the prism P2 utilize total reflection.

However, the ways of bending the optical axis through the prisms and the angles of the optical axis bent by the reflecting surfaces are not limited to the above description. For example, the angle of the optical axis bent by the most field-frame-side reflecting surface P2₂of the prism P2 may be made smaller than 90 degrees so that this reflecting surface is coated with a metal film. Moreover, the angle of the optical axis bent by, the reflecting surface, P₁of the prism P2 may also be made larger than 90 degrees so that this reflecting surface utilizes total reflection.

The positive, lens E1 is constructed so that diopter adjustment can be made in accordance with an observer's diopter.

Also, aberration characteristics in the first embodiment are shown in FIGS. 6A–6D, 7A–7D, and 8A–8D.

Subsequently, numerical data of optical members constituting the real image mode finder optical system according to the first embodiment are shown below. In the numerical data of the first embodiment, m denotes a finder magnification; ω denotes a field angle; f denotes the focal length of the objective optical system; r₁, r₂, . . . represent radii of curvature of the surfaces of individual lenses or prisms; d₁, d₂, . . . represent thicknesses of individual lenses or prisms or spaces therebetween; n_d1, n_d2, . . . represent refractive indices of individual lenses or prisms; and v_d1, v_d2, . . . represent Abbe's numbers of individual lenses or prisms; mh represents the maximum width of the field frame; fe represents the focal length of the eyepiece optical system; f123 represents a combined focal length of the first to third units; m23 represents a combined imaging magnification of the second and third units where an object distance is 3 m; m2 represents an imaging magnification of the second unit at the middle position where the object distance is 3 m; and m3 represents an imaging magnification of the third unit at the middle position where the object distance is 3 m.

Also, the configuration of the aspherical surface, as already described, is expressed by the following equation:

z=(y²/r)/[1+√{square root over ({1−(1+K)(y/r)²})}{square root over ({1−(1+K)(y/r)²})}]+A₄y₄+A₆y⁶+A₈y⁸+A₁₀y¹⁰

These symbols are also applied to the embodiments to be described later.

Numerical data 1

Wide-angle position
Middle position
Telephoto position

m
0.536
1.016
2.075

ω (°)
33.541
17.525
8.746

f (mm)
8.047
15.253
31.147

Pupil dia. (mm) 4.000

r₁= 83.6172

d₁= 1.0000
n_d1= 1.58423
ν_d1= 30.49

r₂= 10.0913 (aspherical)

d₂= D2 (variable)

r₃= 10.3392 (aspherical)

d₃= 4.3149
n_d3= 1.52542
ν_d3= 55.78

r₄= −21.0217 (aspherical)

d₄= D2 (variable)

r₅= −10.0239 (aspherical)

d₅= 1.0000
n_d5= 1.58425
ν_d5= 30.35

r₆= 10.3239 (aspherical)

d₆= D6 (variable)

r₇= 11.2869

d₇= 9.9000
n_d7= 1.52542
ν_d7= 55.78

r₈= −23.2085 (aspherical)

d₈= 0.5000

r₉= 15.7633 (aspherical)

d₉= 22.5495
n_d9= 1.52542
ν_d9= 55.78

r₁₀= ∞

d₁₀= 2.2605

r₁₁= ∞ (field frame)

d₁₁= 2.5500

r₁₂= 15.9503 (aspherical)

d₁₂= 15.5600
n_d12= 1.52542
ν_d12= 55.78

r₁₃= −38.8890

d₁₃= 1.7500

r₁₄= 25.2612

d₁₄= 5.3200
n_d14= 1.52542
ν_d14= 55.78

r₁₅= −16.9795 (aspherical)

d₁₅= 17.0491

r₁₆= ∞ (eyepoint)

Aspherical coefficients

Second surface

K = −1.2950

A₄= 2.10279 × 10⁻⁶
A₆= −2.71836 × 10⁻⁷
A₈= 1.45499 × 10⁻⁹

Third surface

K = −0.2610

A₄= −9.12395 × 10⁻⁵
A₆= −3.93632 × 10⁻⁷
A₈= −6.31136 × 10⁻⁹

Fourth surface

K = −0.0224

A₄= 8.97235 × 10⁻⁵
A₆= −4.73271 × 10⁻⁷
A₈= −1.37810 × 10⁻⁹

Fifth surface

K = 0.2143

A₄= 6.18253 × 10⁻⁴
A₆= −3.45137 × 10⁻⁵
A₈= 7.99836 × 10⁻⁷

Sixth surface

K = −0.0423

A₄= 1.66996 × 10⁻⁶
A₆= −2.60860 × 10⁻⁵
A₈= 6.01778 × 10⁻⁷

Eighth surface

K = 0.1568

A₄= 2.22420 × 10⁻⁴
A₆= −1.28141 × 10⁻⁶
A₈= 3.95727 × 10⁻⁸

Ninth surface

K = 0.0140

A₄= −1.11940 × 10⁻⁵
A₆= −1.42736 × 10⁻⁶

Twelfth surface

K = 0.0000

A₄= −1.19998 × 10⁻³
A₆= 1.07234 × 10⁻⁵

Fifteenth surface

K = 0.0000

A₄= 4.29178 × 10⁻⁵
A₆= 1.34232 × 10⁻⁷

Zoom data

Wide-angle

position
Middle position
Telephoto position

D2
11.6242
7.1879
3.4246

D4
1.2500
8.2976
16.2705

D6
7.8209
5.2097
1.0000

mh = 10.139 mm

f123
−10.436
−19.857
−41.578

m23
0.529
1.000
2.044

m2

−1.000

m3

−1.000

Condition (9) MG45
−0.773
−0.775
−0.776

Conditions (1), (7) mh/fe
= 0.676

Conditions (2), (3) fe
= 15.009 mm

Condition (8) φ (mh/2)
= −0.377955 (l/mm)

Condition (10) β3
= −1.000

Condition (11) SF2
= −0.341

Condition (12) f2/f3
= −1.619

Condition (13) fw/fFw
= −0.771

Condition (14) fT/fFT
= −0.749

Condition (15) mT/mW
= 3.871

Condition (16) fw/fw123
= −0.771

Condition (17) fT/fT123
= −0.749

Second Embodiment

In the real image mode finder optical system of this embodiment, as shown in FIGS. 9A–9C, the objective optical system includes, in order from the object side, the first unit G1 with a negative refracting power, the second unit G2 with a positive refracting power, the third unit G3 with a negative refracting power, and the fourth unit G4 with a positive refracting power, and has a positive refracting power as a whole.

The fourth unit G4 is constructed with a positive lens L and the prism P1. The eyepiece optical system is constructed with a prism P and a positive lens E1 and has a positive refracting power as a whole.

The image erecting means includes the prism P1 and the prism P. In the real image mode finder optical system of the second embodiment, the intermediate image formed by the objective optical system is interposed between the prism P1 and the prism P, and the field frame, such as that shown in FIG. 4, is provided in the proximity of its imaging position.

The magnification of the finder is changed in the range from the wide angle position to the telephoto position by fixing the fourth unit G4 and by moving the first unit G1, the second unit G2, and the third unit G3 along the optical axis.

Each of the first unit G1 the second unit G2, and the third unit G3 is constructed with a single lens. The entrance surface and the exit surface of the prism P1 have finite curvatures. The entrance surface and the exit surface of the prism P also have finite curvatures.

The prism P1 and the prism P are provided with reflecting surfaces along the optical path so that the optical axis is bent to obtain an erect image. For example, the prism P1 is provided with three reflecting surfaces (for bending the optical axis twice in the Y-Z plane and once in the X-Z plane in this order from the object side) and the prism P is provided with one reflecting surface (for bending the optical axis in the X-Z plane) to erect the image. Also, the arrangement of the reflecting surfaces is based on that of a Porro prism. Angles made with the optical axis bent by the reflecting surfaces are such that, for example, the angle of the optical axis bent by one reflecting surface of the prism P1 is smaller than 90 degrees and the angles of the optical axis bent by the remaining two reflecting surfaces are larger than 90 degrees, while the angle of the optical axis bent by the reflecting surface of the prism P is smaller than 90 degrees. The reflecting surfaces making angles smaller than 90 degrees are coated with metal films, such as silver and aluminum. The reflecting surfaces of angles larger than 90 degrees utilize total reflection. However, the angles of the optical axis bent by the reflecting surfaces are not limited to the above description. For example, the angle of the optical axis bent by the most field-frame-side reflecting surface of the prism P1 may be made smaller than 90 degrees so that this reflecting surface is coated with a metal film. Moreover, the angle of the optical axis bent by the reflecting surface of the prism P may also be made larger than 90 degrees so that this reflecting surface utilizes total reflection.

The positive lens E1 is constructed so that diopter adjustment can be made in accordance with an observer's diopter.

Also, aberration characteristics in the second embodiment are shown in FIGS. 10A–10D, 11A–11D, and 12A–12D.

Subsequently, numerical data of optical members constituting the real image mode finder optical system according to the second embodiment are shown below.

Numerical data 2

Wide-angle position
Middle position
Telephoto position

m
0.685
1.176
2.016

ω (°)
26.680
15.434
8.985

f (mm)
10.290
17.649
30.256

Pupil dia. (mm) 4.000

r₁= 37.0457

d₁= 1.0000
n_d1= 1.58423
ν_d1= 30.49

r₂= 9.2320 (aspherical)

d₂= D2 (variable)

r₃= 9.5256 (aspherical)

d₃= 4.4760
d₂₃= 1.49241
ν_d3= 57.66

r₄= −22.0049

d₄= D4 (variable)

r₅= −10.2911

d₅= 0.7000
n_d5= 1.58423
ν_d5= 30.49

r₆= 9.8912 (aspherical)

d₆= D6 (variable)

r₇= 36.5176

d₇= 3.5263
n_d7= 1.52542
ν_d7= 55.78

r₈−11.2570 (aspherical)

d₈= 0.5000

r₉= 17.5358

d₉= 29.0967
n_d9= 1.52542
ν_d9= 55.78

r₁₀= −218.6484

d₁₀= 2.7527

r₁₁= ∞ (field frame)

d₁₁= 2.9177

r₁₂= 19.1732 (aspherical)

d₁₂= 17.0445
n_d12= 1.52542
ν_d12= 55.78

r₁₃= −20.5269

d₁₃= 1.4765

r₁₄= 39.9369 (aspherical)

d₁₄= 3.4455
n_d14= 1.52542
ν_d14= 55.78

r₁₅= −20.1555 (aspherical)

d₁₅= 15.7651

r₁₆= ∞ (eyepoint)

Aspherical coefficients

Second surface

K = −1.3017

A₄= 4.40512 × 10⁻⁵
A₆= 1.04845 × 10⁻⁶
A₈= −4.86973 × 10⁻⁹

Third surface

K = −0.1847

A₄= −1.74316 × 10⁻⁴
A₆= −2.38197 × 10⁻⁷
A₈= −6.24988 × 10⁻⁹

Sixth surface

K = −0.0683

A₄= −4.82178 × 10⁻⁴
A₆= 3.96724 × 10⁻⁶
A₈= −3.64804 × 10⁻⁸

Eighth surface

K = 0.1808

A₄= 9.81681 × 10⁻⁵
A₆= 8.46115 × 10⁻⁷
A₈= 8.50642 × 10⁻⁹

Twelfth surface

K = 0.0000

A₄= −5.68528 × 10⁻⁴
A₆= −1.76882 × 10⁻⁷

Fourteenth surface

K = 0.0000

A₄= −5.49243 × 10⁻⁵
A₆= 1.22082 × 10⁻⁶

Fifteenth surface

K = 0.0000

A₄= −2.37429 × 10⁻⁵
A₆= 1.03731 × 10⁻⁶

Zoom data

Wide-angle position
Middle position
Telephoto position

D2
11.6070
8.0586
4.1006

D4
1.1067
7.0086
13.2454

D6
6.3793
4.0397
1.6737

mh = 9.765 mm

Conditions (1), (7) mh/fe
= 0.650

Conditions (2), (3) fe
= 15.011 mm

Third Embodiment

In the real image mode finder optical system of this embodiment, as shown in FIGS. 13A–13C, the objective optical system includes, in order from the object side, the first unit G1 with a negative refracting power, the second unit G2 with a positive refracting power, the third unit G3 with a negative refracting power, and a fourth unit G4 with a positive refracting power, and has a positive refracting power as a whole.

The fourth unit G4 is constructed with two prisms P1 and P2. The eyepiece optical system is constructed with a negative lens L1 and the positive lens E1 and has a positive refracting power as a whole.

The image erecting means includes the prisms P1 and P2. In the real image mode finder optical system of the third embodiment, the intermediate image formed by the objective optical system is interposed between the prism P2 and the negative lens L1, and the field frame, such as that shown in FIG. 4, is placed in the proximity of its imaging position.

Each of the first unit G1, the second unit G2, and the third unit G3 is constructed with a single lens. The entrance surface and the exit surface of each of the prisms P1 and P2 have finite curvatures.

The prisms P1 and P2 are provided with reflecting surfaces along the optical path so that the optical axis is bent to obtain an erect image. For example, the prism P1 is provided with one reflecting surface (for bending the optical axis in the Y-Z plane) and the prism P2 is provided with three reflecting surfaces (for bending the optical axis once in the Y-Z plane and twice in the X-Z plane in this order from the object side) to erect the image. Also, the arrangement of the reflecting surfaces is based on that of a Porro prism. Angles made with the optical axis bent by the reflecting surfaces are such that, for example, the angle of the optical axis bent by the reflecting surface of the prism P1 is smaller than 90 degrees, while the angles of the optical axis bent by two reflecting surfaces of the prism P2 are larger than 90 degrees and the angle of the optical axis bent by the remaining one reflecting surface is smaller than 90 degrees. The reflecting surfaces making angles smaller than 90 degrees are coated with metal films, such as silver and aluminum. The reflecting surfaces of angles larger than 90 degrees utilize total reflection. The positive lens E1 is constructed so that diopter adjustment can be made in accordance with an observer's diopter.

Also, aberration characteristics in the third embodiment are shown in FIGS. 14A–14D, 15A–15D, and 16A–16D.

Subsequently, numerical data of optical members constituting the real image mode finder optical system according to the third embodiment are shown below.

Numerical data 3

Wide-angle position
Middle position
Telephoto position

m
0.692
1.181
2.018

ω (°)
26.656
15.374
8.976

f (mm)
10.375
17.709
30.248

Pupil dia. (mm) 4.000

r₁= −37.0118

d₁= 1.6264
n_d1= 1.58423
ν_d1= 30.49

r₂= 15.0266 (aspherical)

d₂= D2 (variable)

r₃= 13.6624 (aspherical)

d₃= 4.2776
n_d3= 1.49241
ν_d3= 57.66

r₄= −19.7350

d₄= D4 (variable)

r₅= −23.9768

d₅= 0.6800
n_d5= 1.58423
ν_d5= 30.49

r₆= 15.4052 (aspherical)

d₆= D6 (variable)

r₇= 64.0979

d₇= 14.4273
n_d7= 1.52542
ν_d7= 55.78

r₈= −16.0524 (aspherical)

d₈= 0.5000

r₉= 46.4363

d₉= 39.5267
n_d9= 1.52542
ν_d9= 55.78

r₁₀= −21.0120

d₁₀= 3.7943

r₁₁= ∞ (field frame)

d₁₁= 6.9095

r₁₂= −9.9877 (aspherical)

d₁₂= 3.6912
n_d12= 1.58423
ν_d12= 30.49

r₁₃= −15.7572

d₁₃= 0.9421

r₁₄= 19.1293 (aspherical)

d₁₄= 7.8836
n_d14= 1.52542
ν_d14= 55.78

r₁₅= −10.9574 (aspherical)

d₁₅= 15.7651

r₁₆= ∞ (eyepoint)

Aspherical coefficients

Second surface

K = −1.3019

A₄= −1.08535 × 10⁻⁴
A₆= 1.48477 × 10⁻⁶
A₈= −7.37060 × 10⁻⁹

Third surface

K = −0.1784

A₄= −1.38562 × 10⁻⁴
A₆= 1.91486 × 10⁻⁷
A₈= −9.59282 × 10⁻¹⁰

Sixth surface

K = −0.0760

A₄= −4.70450 × 10⁻⁵
A₆= −2.11500 × 10⁻⁶
A₈= 3.61544 × 10⁻⁸

Eighth surface

K = 0.1930

A₄= 4.06798 × 10⁻⁵
A₆= −8.51164 × 10⁻⁸
A₈= 3.41981 × 10⁻⁹

Twelfth surface

K = 0.0000

A₄= −4.97284 × 10⁻⁴
A₆= −5.19125 × 10⁻⁶

Fourteenth surface

K = 0.0000

A₄= 1.11128 × 10⁻⁴
A₆= −2.84749 × 10⁻⁶

Fifteenth surface

K = 0.0000

A₄= 1.70029 × 10⁻⁴
A₆= −6.56818 × 10⁻⁷

Zoom data

Wide-angle position
Middle position
Telephoto position

D2
25.7084
12.8854
7.7602

D4
1.0000
9.0863
19.8650

D6
2.8644
5.0585
1.4948

mh = 9.621 mm

Conditions (1), (7) mh/fe
= 0.642

Conditions (2), (3) fe
= 14.990 mm

Fourth Embodiment

In the real image mode finder optical system of this embodiment, as shown in FIGS. 17A–17C, the objective optical system includes, in order from the object side, the first unit G1 with a negative refracting power, the second unit G2 with a positive refracting power, the third unit G3 with a negative refracting power, and a fourth unit G4 with a positive refracting power, and has a positive refracting power as a whole.

The fourth unit G4 is constructed with two prisms P1 and P2. The eyepiece optical system is constructed with the negative lens L1 and the positive lens E1 and has a positive refracting power as a whole.

The image erecting means includes the prisms P1 and P2. In the real image mode finder optical system of the fourth embodiment, the intermediate image formed by the objective optical system is interposed between the prism P2 and the negative lens L1, and the field frame, such as that shown in FIG. 4, is placed in the proximity of its imaging position.

Also, aberration characteristics in the fourth embodiment are shown in FIGS. 18A–18D, 19A–19D, and 20A–20D.

Subsequently, numerical data of optical members constituting the real image mode finder optical system according to the fourth embodiment are shown below.

Numerical data 4

Wide-angle position
Middle position
Telephoto position

m
0.574
0.980
1.680

ω (°)
26.946
15.541
9.003

f (mm)
8.612
14.706
25.218

Pupil dia. (mm) 4.000

r₁= −27.7265

d₁= 0.7033
n_d1= 1.58423
ν_d1= 30.49

r₂= 12.5528 (aspherical)

d₂= D2 (variable)

r₃= 11.3610 (aspherical)

d₃= 3.8444
n_d3= 1.49241
ν_d3= 57.66

r₄= = −15.8341

d₄= D4 (variable)

r₅= 18.1098

d₅= 0.7000
n_d5= 1.58423
ν_d5= 30.49

r₆= 11.6071 (aspherical)

d₆= D6 (variable)

r₇= 53.8289

d₇= 12.8726
n_d7= 1.52542
ν_d7= 55.78

r₈= −14.5655 (aspherical)

d₈= 1.0000

r₉= 23.4433

d₉= 34.8807
n_d9= 1.52542
ν_d9= 55.78

r₁₀= −28.7418

d₁₀= 1.4329

r₁₁= ∞ (field frame)

d₁₁= 6.9526

r₁₂= −12.6182 (aspherical)

d₁₂= 3.6221
n_d12= 1.58423
ν_d12= 30.49

r₁₃= −15.2579

d₁₃= 31.1803

r₁₄= 24.0716 (aspherical)

d₁₄= 8.3376
n_d14= 1.52542
ν_d14= 55.78

r₁₅= −11.3348 (aspherical)

d₁₅= 15.7651

r₁₆= ∞ (eyepoint)

Aspherical coefficients

Second surface

K = −1.3022

A₄= −2.00833 × 10⁻⁴
A₆= 3.41784 × 10⁻⁶
A₈= −1.63261 × 10⁻⁸

Third surface

K = −0.1825

A₄= −2.54261 × 10⁻⁴
A₆= 5.60513 × 10⁻⁷
A₈= −3.79136 × 10⁻⁹

Sixth surface

K = −0.0762

A₄= −1.57743 × 10⁻⁴
A₆= −3.09431 × 10⁻⁶
A₈= 4.76542 × 10⁻⁸

Eighth surface

K = 0.1928

A₄= 4.63808 × 10⁻⁵
A₆= −2.97595 × 10⁻⁷
A₈= 8.60163 × 10⁻⁹

Twelfth surface

K = 0.0000

A₄= −6.08556 × 10⁻⁴
A₆= −8.85765 × 10⁻⁶

Fourteenth surface

K = 0.0000

A₄= 1.52011 × 10⁻⁴
A₆= −1.19503 × 10⁻⁶

Fifteenth surface

K = 0.0000

A₄= 1.06106 × 10⁻⁴
A₆= 8.55846 × 10⁻⁷

Zoom data

Wide-angle position
Middle position
Telephoto position

D2
21.4497
10.4751
6.4304

D4
1.0000
7.7777
16.8353

D6
1.9906
3.8269
1.3800

mh = 8.107 mm

Conditions (1), (7) mh/fe
= 0.540

Conditions (2), (3) fe
= 15.010 mm

Fifth Embodiment

In the real image mode finder optical system of this embodiment, as shown in FIGS. 21A–21C, the objective optical system includes, in order from the object side, the first unit G1 with a negative refracting power, the second unit G2 with a positive refracting power, the third unit G3 with a negative refracting power, and a fourth unit G4 with a positive refracting power, and has a positive refracting power as a whole.

The image erecting means includes the prisms P1 and P2. In the real image mode finder optical system of the fifth embodiment, the intermediate image formed by the objective optical system is interposed between the prism P2 and the negative lens L1, and the field frame, such as that shown in FIG. 4, is placed in the proximity of its imaging position.

The magnification of the finder is changed in the range from the wide-angle position to the telephoto position by fixing the fourth unit G4 and by moving the first unit G1, the second unit G2, and the third unit G3 along the optical axis. Each of the first unit G1, the second unit G2, and the third unit G3 is constructed with a single lens. The entrance surface and the exit surface of each of the prisms P1 and P2 have finite curvatures.

Also, aberration characteristics in the fifth embodiment are shown in FIGS. 22A–22D, 23A–23D, and 24A–24D.

Subsequently, numerical data of optical members constituting the real image mode finder optical system according to the fifth embodiment are shown below.

Numerical data 5

Wide-angle position
Middle position
Telephoto position

m
0.873
1.293
2.418

ω (°)
24.751
16.220
8.611

f (mm)
13.110
19.409
36.290

Pupil dia. (mm) 4.000

r₁= −39.3543

d₁= 2.0000
n_d1= 1.58423
ν_d1= 30.49

r_{2 = 20.1886 (aspherical)}

d₂= D2 (variable)

r₃= 17.8228 (aspherical)

d₃= 4.5550
nd₃= 1.49241
ν_d3= 57.66

r₄= −20.6969

d₄= D4 (variable)

r₅= −26.5948

d₅= 0.9712
n_d5= 1.58423
ν_d5= 30.49

r_{6 = 21.3842 (aspherical)}

d₆= D6 (variable)

r₇= 49.7469

d₇= 16.0933
n_d7= 1.52542
ν_d7= 55.78

r₈= −23.8038 (aspherical)

d₈= 0.6446

r₉= 38.3198

d₉= 43.7612
n_d9= 1.52542
ν_d9= 55.78

r₁₀= −63.9202

d₁₀= 2.7501

r₁₁= ∞ (field frame)

d₁₁= 7.1509

r₁₂= −7.9810 (aspherical)

d₁₂= 3.6432
n_d12= 1.58423
ν_d12= 30.49

r₁₃= −11.3215

d₁₃= 1.2765

r₁₄= 16.6904 (aspherical)

d₁₄= 7.6344
n_d14= 1.52542
ν_d14= 55.78

r₁₅= −13.2210 (aspherical)

d₁₅= 15.7651

r₁₆= ∞ (eyepoint)

Aspherical coefficients

Second surface

K = −1.3021

A₄= −3.80325 × 10⁻⁵
A₆= 5.97449 × 10⁻⁷
A₈= −2.67271 × 10⁻⁹

Third surface

K = −0.1774

A₄= −7.61365 × 10⁻⁵
A₆= 1.22273 × 10⁻⁷
A₈= −3.41547 × 10⁻¹⁰

Sixth surface

K = −0.0759

A₄= −3.60399 × 10⁻⁵
A₆= −1.18573 × 10⁻⁷
A₈= 9.28811 × 10⁻¹⁰

Eighth surface

K = 0.1900

A₄= 1.33964 × 10⁻⁵
A₆= 5.39206 × 10⁻⁸
A₈= −9.03386 × 10⁻¹¹

Twelfth surface

K = 0.0000

A₄= −2.69230 × 10⁻⁴
A₆= −2.03083 × 10⁻⁶

Fourteenth surface

K = 0.0000

A₄= 8.14903 × 10⁻⁵
A₆= −1.34641 × 10⁻⁶

Fifteenth surface

K = 0.0000

A₄= 1.81061 × 10⁻⁴
A₆= −6.24901 × 10⁻⁷

Zoom data

Wide-angle position
Middle position
Telephoto position

D2
29.0804
15.7590
8.2552

D4
1.0000
8.0891
22.1773

D6
3.1755
8.1368
2.0110

mh = 11.006 mm

Conditions (1), (7) mh/fe
= 0.733

Conditions (2), (3) fe
= 15.010 mm

Sixth Embodiment

The arrangement of this embodiment is similar to that of the first embodiment described with reference to FIGS. 1–4. FIGS. 25A–25D show the arrangement of the sixth embodiment. In this embodiment, low-dispersion glass is used for the positive lens E1 to suppress chromatic aberration of magnification produced in the eyepiece optical system.

Also, aberration characteristics in the sixth embodiment are shown in FIGS. 26A–26D, 27A–27D, 28A–28D, and 29A–29D.

Subsequently, numerical data of optical members constituting the real image mode finder optical system according to the sixth embodiment are shown below.

Numberical data 6

Wide-angle position
Middle position
Telephoto position

m
0.743
1.016
2.072

ω (°)
23.854
17.511
8.739

f (mm)
11.156
15.252
31.104

Pupil dia. (mm) 4.000

r₁= 81.9112

d₁= 1.0000
n_d1= 1.58423
ν_d1= 30.49

r₂= 10.0742 (aspherical)

d₂= D2 (variable)

r₃= 10.3535 (aspherical)

d₃= 4.3238
n_d3= 1.52542
ν_d3= 55.78

r₄= −20.9984 (aspherical)

d₄= D4 (variable)

r₅= −10.0333 (aspherical)

d₅= 1.0000
n_d5= 1.58425
ν_d5= 30.35

r₆= 10.3333 (aspherical)

d₆= D6 (variable)

r₇= 11.3130

d₇= 9.9000
n_d7= 1.52542
ν_d7= 55.78

r₈= −23.1581 (aspherical)

d₈= 0.5000

r₉= 15.7417 (aspherical)

d₉= 22.5485
n_d9= 1.52542
ν_d9= 55.78

r₁₀= ∞

d₁₀= 2.2615

r₁₁= ∞ (field frame)

d₁₁= 2.5500

r₁₂= 15.2310 (aspherical)

d₁₂= 15.5600
n_d12= 1.52542
ν_d12= 55.78

r₁₃= −39.1300

d₁₃= 1.7500

r₁₄= 24.5529

d₁₄= 5.3200
n_d14= 1.49700
ν_d14= 81.54

r₁₅= −15.8669 (aspherical)

d₁₅= 17.0491

r₁₆= ∞ (eyepoint)

Aspherical coefficients

Second surface

K = −1.2950

A₄= 5.82582 × 10⁻⁶
A₆= −2.91852 × 10⁻⁷
A₈= 1.53866 × 10⁻⁹

Third surface

K = −0.2618

A₄= −8.99427 × 10⁻⁵
A₆= −3.14079 × 10⁻⁷
A₈= −8.23133 × 10⁻⁹

Fourth surface

K = −0.0224

A₄= 8.74333 × 10⁻⁵
A₆= −3.77249 × 10⁻⁷
A₈= −3.31925 × 10⁻⁹

Fifth surface

K = 0.2138

A₄= 6.11164 × 10⁻⁴
A₆= −3.28266 × 10⁻⁵
A₈= 7.55363 × 10⁻⁷

Sixth surface

K = −0.0425

A₄= 2.44411 × 10⁻⁵
A₆= −2.80434 × 10⁻⁵
A₈= 6.70880 × 10⁻⁷

Eighth surface

K = 0.1564

A₄= 2.36396 × 10⁻⁴
A₆= −1.54507 × 10⁻⁶
A₈= 3.28513 × 10⁻⁸

Ninth surface

K = 0.0138

A₄= 7.48388 × 10⁻⁶
A₆−1.90449 × 10⁻⁶

Twelfth surface

K = 0.0000

A₄= −1.19998 × 10⁻³
A₆= 1.07234 × 10⁻⁵

Fifteenth surface

K = 0.0000

A₄= 5.20019 × 10⁻⁵
A₆= 1.50643 × 10⁻⁷

Zoom data

Wide-angle position
Middle position
Telephoto position

D2
9.1623
7.1846
3.4243

D4
4.9049
8.2975
16.2619

D6
6.6190
5.2041
1.0000

mh = 10.121 mm

Conditions (1), (7) mh/fe
= 0.674

Condition (4) ν
= 81.54

Conditions (2), (3) fe
= 15.010 mm

Seventh Embodiment

In the real image mode finder optical system of this embodiment, as shown in FIGS. 30A–30D, the objective optical system includes, in order from the object side, a first unit G1 with a negative refracting power, a second unit G2 with a positive refracting power, a third unit G3 with a negative refracting power, and a fourth unit G4 with a positive refracting power, and has a positive refracting power as a whole.

The fourth unit G4 is constructed with two prisms P1 and P2. The eyepiece optical system is constructed with the prism P and the positive lens E1 and has a positive refracting power as a whole.

The image erecting means includes the prisms P1 and P2 and the prism P. In the real image mode finder optical system of the seventh embodiment, the intermediate image formed by the objective optical system is interposed between the prism P2 and the prism P, and the field frame, such as that shown in FIG. 4, is provided in the proximity of its imaging position.

Each of the first unit G1, the second unit G2, and the third unit G3 is constructed with a single lens. The entrance surface and the exit surface of the prism P1 and the entrance surface of the prism P2 have finite curvatures, that is, are configured as lens surfaces. The entrance surface and the exit surface of the prism P also have finite curvatures.

The prisms P1 and P2 and the prism P, as in the first embodiment shown in FIGS. 1–3, are provided with the reflecting surfaces along the optical path so that the optical axis is bent to erect an image. For example, one reflecting surface provided in the prism P1 bends the optical axis in the Y-Z plane; two reflecting surfaces provided in the prism P2 bend the optical axis in the Y-Z plane and the X-Z plane in this order from the object side; and one reflecting surface provided in the prism P bends the optical axis in the X-Z plane. In this way, an erect image is obtained. Also, the arrangement of the reflecting surfaces is based on that of a Porro prism. Angles made with the optical axis bent by the reflecting surfaces are such that, for example, the angles of the optical axis bent by the reflecting surfaces of the prism P1 and the prism P are smaller than 90 degrees and the angles of the optical axis bent by the two reflecting surfaces of the prism P2 are larger than 90 degrees. The reflecting surfaces of the prism P1 and the prism P are coated with metal films, such as silver and aluminum. The two reflecting surfaces of the prism P2 utilize total reflection.

However, the ways of bending the optical axis through the prisms and the angles of the optical axis bent by the reflecting surfaces are not limited to the above description. For example, the angle of the optical axis bent by the most field-frame-side reflecting surface of the prism P2 may be made smaller than 90 degrees so that this reflecting surface is coated with a metal film. Moreover, the angle of the optical axis bent by the reflecting surface of the prism P may also be made larger than 90 degrees so that this reflecting surface utilizes total reflection.

The positive lens E1 is constructed so that diopter adjustment can be made in accordance with an observer's diopter.

Also, aberration characteristics in the seventh embodiment are shown in FIGS. 31A–31D, 32A–32D, 33A–33D, and 34A–34D.

Subsequently, numerical data of optical members constituting the real image mode finder optical system according to the seventh embodiment are shown below.

Numerical data 7

Wide-angle position
Middle position
Telephoto position

m
0.743
1.015
2.070

ω (°)
23.875
17.526
8.746

f (mm)
11.146
15.237
31.075

Pupil dia. (mm) 4.000

r₁= 81.9602

d₁= 1.0000
n_d1= 1.58423
ν_d1= 30.49

r₂= 10.0611 (aspherical)

d₂= D2 (variable)

r₃= 10.3753 (aspherical)

d₃= 4.3253
n_d3= 1.52542
ν_d3= 55.78

r₄= −20.8601 (aspherical)

d₄= D4 (variable)

r₅= −10.0315 (aspherical)

d₅= 1.0000
n_d5= 1.58425
ν_d5= 30.35

r₆= 10.3315 (aspherical)

d₆= D6

r₇= 11.2984

d₇= 9.9000
n_d7= 1.52542
ν_d7= 55.78

r₈= −23.0708 (aspherical)

d₈= 0.5000

r₉= 15.8095 (aspherical)

d₉= 22.5530
n_d9= 1.52542
ν_d9= 55.78

r₁₀= ∞

d₁₀= 2.2570

r₁₁= ∞ (field frame)

d₁₁= 2.5500

r₁₂= 15.4188 (aspherical)

d₁₂= 15.5600
n_d12= 1.52542
ν_d12= 55.78

r₁₃= −37.3902

d₁₃= 1.7500

r₁₄= 20.4078

d₁₄= 5.3200
n_d14= 1.43389
ν_d14= 95.15

r₁₅= −14.4726 (aspherical)

d₁₅= 17.0491

r₁₆= ∞ (eyepoint)

Aspherical coefficients

Second surface

K = −1.2949

A₄= 6.66017 × 10⁻⁶
A₆= −2.62591 × 10⁻⁷
A₈= 1.12121 × 10⁻⁹

Third surface

K = −0.2625

A₄= −7.97190 × 10⁻⁵
A₆= −6.29748 × 10⁻⁷
A₈= −1.17464 × 10⁻⁹

Fourth surface

K = −0.0226

A₄= 9.61346 × 10⁻⁵
A₆= −6.24988 × 10⁻⁷
A₈= −2.63996 × 10⁻⁹

Fifth surface

K = 0.2132

A₄= 6.22361 × 10⁻⁴
A₆= −3.35122 × 10⁻⁵
A₈= 7.43683 × 10⁻⁷

Sixth surface

K = −0.0427

A₄= 3.84712 × 10⁻⁵
A₆= −2.91300 × 10⁻⁵
A₈= 6.92795 × 10⁻⁷

Eighth surface

K = 0.1561

A₄= 2.24263 × 10⁻⁴
A₆= −1.03011 × 10⁻⁶
A₈= 3.32247 × 10⁻⁸

Ninth surface

K = 0.0135

A₄= −5.19982 × 10⁻⁶
A₆= −1.46612 × 10⁻⁶

Twelfth surface

K = 0.0000

A₄= −1.19998 × 10⁻³
A₆= 1.07234 × 10⁻⁵

Fifteenth surface

K = 0.0000

A₄= 7.35154 × 10⁻⁵
A₆= 2.26014 × 10⁻⁷

Zoom data

Wide-angle position
Middle position
Telephoto position

D2
9.1683
7.1925
3.4339

D4
4.8993
8.2891
16.2507

D6
6.6171
5.2031
1.0000

mh = 10.133 mm

Conditions (1), (7) mh/fe
= 0.675

Condition (4) ν
= 95.15

Conditions (2), (3) fe
= 15.010 mm

Eighth Embodiment

In the real image mode finder optical system of this embodiment, as shown in FIGS. 35A–35D, the objective optical system includes, in order from the object side, a first unit G1 with a negative refracting power, a second unit G2 with a positive refracting power, a third unit G3 with a negative refracting power, and a fourth unit G4 with a positive refracting power, and has a positive refracting power as a whole.

The fourth unit G4 is constructed with two prisms P1 and P2. The eyepiece optical system is constructed, with a cemented lens component CE comprised of a positive lens element CE1 and a negative lens element CE2 and has a positive refracting power as a whole.

The image erecting means includes the prisms P1 and P2 and the prism P. In the real image mode finder optical system of the eighth embodiment, the intermediate image formed by the objective optical system is interposed between the prism P2 and the prism P, and the field frame, such as that shown in FIG. 4, is provided in the proximity of its imaging position.

The prisms P1 and P2 and the prism P are provided with the reflecting surfaces along the optical path so that the optical axis is bent to erect an image. For example, the prism P1 is provided with one reflecting surface (for bending the optical axis in the Y-Z plane), the prism P2 is provided with two reflecting surfaces (for bending the optical axis in the Y-Z plane and the X-Z plane), and the prism P is provided with one reflecting surface (for bending the optical axis in the X-Z plane) to erect the image. Also, the arrangement of the reflecting surfaces is based on that of a Porro prism. Angles made with the optical axis bent by the reflecting surfaces are such that, for example, the angles of the optical axis bent by the reflecting surfaces of the prism P1 and the prism P are smaller than 90 degrees and the angles of the optical axis bent by the two reflecting surfaces of the prism P2 are larger than 90 degrees. The reflecting surfaces of the prism P1 and the prism P are coated with metal films, such as silver and aluminum. The two reflecting surfaces of the prism P2 utilize total reflection.

However, the ways of bending the optical axis through the prisms and the angles of the optical axis bent by the reflecting surfaces are not limited to the above description. For example, the angle of the optical axis bent by the most field-frame-side reflecting surface of the prism P2 may be made smaller than 90 degrees so that this reflecting surface is coated with a metal film. Moreover, the angle of the optical axis bent by the reflecting surface of the prism P may also be made larger than 90 degrees so that this reflecting surface utilizes total reflection.

The cemented lens component CE is constructed so that diopter adjustment can be made in accordance with an observer's diopter.

In the eighth embodiment, the cemented lens component CE including, in order from the object side, the positive lens element and the negative lens element is used to suppress the chromatic aberration of magnification produced in the eyepiece optical system.

Also, aberration characteristics in the eighth embodiment are shown in FIGS. 36A–36D, 37A–37D, 38A–38D, and 39A–39D.

Subsequently, numerical data of optical members constituting the real image mode finder optical system according to the eighth embodiment are shown below.

Numerical data 8

Wide-angle position
Middle position
Telephoto position

m
0.743
1.020
2.076

ω (°)
23.954
17.549
8.727

f (mm)
11.160
15.304
31.158

Pupil dia. (mm) 4.000

r₁= 75.9203

d₁= 1.0000
n_d1= 1.58423
ν_d1= 30.49

r₂= 10.0850 (aspherical)

d₂= D2 (variable)

r₃= 10.2485 (aspherical)

d₃= 4.2776
n_d3= 1.52542
ν_d3= 55.78

r₄= −21.9093

d₄= D4 (variable)

r₅= −10.0501 (aspherical)

d₅= 1.0000
n_d5= 1.58425
ν_d5= 30.35

r₆= 10.3501 (aspherical)

d₆= D6 (variable)

r₇= 11.5799

d₇= 9.9000
n_d7= 1.52542
ν_d7= 55.78

r₈= −21.8697 (aspherical)

d₈= 0.5000

r₉= 15.8360 (aspherical)

d₉= 22.6385
n_d9= 1.52542
ν_d9= 55.78

r₁₀= ∞

d₁₀= 2.1715

r₁₁= ∞ (field frame)

d₁₁= 2.5500

r₁₂= 18.8734 (aspherical)

d₁₂= 15.5600
n_d12= 1.52542
ν_d12= 55.78

r₁₃= −20.0934

d₁₃= 1.7500

r₁₄= 36.0448

d₁₄= 5.3393
n_d14= 1.52542
ν_d14= 55.78

r₁₅= −13.2074

d₁₅= 1.0000
n_d15= 1.58423
ν_d15= 30.49

r₁₆= −18.5585 (aspherical)

d₁₆= 17.0491

r₁₇= ∞ (eyepoint)

Aspherical coefficients

Second surface

K = −1.2950

A₄= −2.88906 × 10⁻⁵
A₆= 1.81910 × 10⁻⁷
A₈= −1.52765 × 10⁻⁹

Third surface

K = −0.2463

A₄= −1.12182 × 10⁻⁴
A₆= −6.22353 × 10⁻⁷
A₈= 2.82153 × 10⁻⁹

Fourth surface

K = −0.0226

A₄= 8.40588 × 10⁻⁵
A₆= −7.72274 × 10⁻⁷
A₈= 6.21797 × 10⁻⁹

Fifth surface

K = 0.2122

A₄= 1.04005 × 10⁻³
A₆= −6.22976 × 10⁻⁵
A₈= 1.48889 × 10⁻⁶

Sixth surface

K = −0.0428

A₄= 4.20510 × 10⁻⁴
A₆= −5.35363 × 10⁻⁵
A₈= 1.24406 × 10⁻⁶

Eighth surface

K = 0.1561

A₄= 2.78620 × 10⁻⁴
A₆= −1.75114 × 10⁻⁶
A₈= 1.84964 × 10⁻⁸

Ninth surface

K = 0.0138

A₄= 7.75842 × 10⁻⁵
A₆= −2.54066 × 10⁻⁶

Twelfth surface

K = 0.0000

A₄= −1.19998 × 10⁻³
A₆= 1.07234 × 10⁻⁵

Sixteenth surface

K = 0.0000

A₄= 1.54561 × 10⁻⁵
A₆= 6.06156 × 10⁻⁸

Zoom data

Wide-angle position
Middle position
Telephoto position

D2
9.1388
7.1293
3.3607

D4
4.9642
8.4021
16.3723

D6
6.6307
5.2010
0.9994

mh = 10.095 mm

Conditions (1), (7) mh/fe
= 0.673

Conditions (2), (3) fe
= 15.010 mm

Conditions (5), (6) νp − νn
= 25.29

Ninth Embodiment

In the real image mode finder optical system of this embodiment, as shown in FIGS. 40A–40D, the objective optical system includes, in order from the object side, a first unit G1 with a negative refracting power, a second unit G2 with a positive refracting power, a third unit G3 with a negative refracting power, and a fourth unit G4 with a positive refracting power, and has a positive refracting power as a whole.

The fourth unit G4 is constructed with two prisms P1 and P2. The eyepiece optical system is constructed with the cemented lens component CE comprised of the positive lens element CE1 and the negative lens element CE2 and has a positive refracting power as a whole.

The image erecting means includes the prisms P1 and P2 and the prism P. In the real image mode finder optical system of the ninth embodiment, the intermediate image formed by the objective optical system is interposed between the prism P2 and the prism P, and the field frame, such as that shown in FIG. 4, is provided in the proximity of its imaging position.

However, the ways of bending the optical axis through the prisms and the angles of the optical axis bent by the reflecting surfaces are not limited to the above description. For example, the angle of the optical axis bent by the most field-frame-side reflecting surface of the prism P2 may be made smaller than 90 degrees so that this reflecting surface is coated with a metal film. Moreover, the angle of the optical axis bent by the reflecting surface of the prism P may also be made larger than 90 degrees so that this reflecting surface utilizes total reflection.

The cemented lens component CE is constructed so that diopter adjustment can be made in accordance with an observer's diopter.

In the ninth embodiment, the cemented lens component CE including, in order from the object side, the positive lens element and the negative lens element is used to suppress the chromatic aberration of magnification produced in the eyepiece optical system.

Also, aberration characteristics in the ninth embodiment are shown in FIGS. 41A–41D, 42A–42D, 43A–43D, and 44A–44D.

Subsequently, numerical data of optical members constituting the real image mode finder optical system according to the ninth embodiment are shown below.

Numerical data 9

Wide-angle position
Middle position
Telephoto position

m
0.745
1.019
2.078

ω (°)
23.864
17.523
8.748

f (mm)
11.179
15.288
31.185

Pupil dia. (mm) 4.000

r₁= 83.1968

d₁= 1.0000
n_d1=1.58423
ν_d1= 30.49

r₂= 10.0574 (aspherical)

d₂= D2 (variable)

r₃= 10.4051 (aspherical)

d₃= 4.3247
n_d3= 1.52542
ν_d3= 55.78

r₄= −20.6708 (aspherical)

d₄= D4 (variable)

r₅= −10.0283 (aspherical)

d₅= 1.0000
n_d5= 1.58425
ν_d5= 30.35

r₆= 10.3283 (aspherical)

d₆= D6 (variable)

r₇= 11.0837

d₇= 9.9000
n_d7= 1.52542
ν_d7= 55.78

r₈= −23.2992 (aspherical)

d₈= 0.5000

r₉= 16.1348 (aspherical)

d₉= 22.5851
n_d9= 1.52542
ν_d9= 55.78

r₁₀= ∞

d₁₀= 2.2249

r₁₁= ∞ (field frame)

d₁₁= 2.5500

r₁₂= 15.1194 (aspherical)

d₁₂= 15.5600
n_d12= 1.52542
ν_d12= 55.78

r₁₃= −32.9857

d₁₃= 1.7500

r₁₄= 22.3114

d₁₄= 1.0000
n_d14= 1.58423
ν_d14= 30.49

r₁₅= 13.0456

d₁₅= 5.4129
n_d15= 1.52542
ν_d15= 55.78

r₁₆= −18.6581 (aspherical)

d₁₆= 17.0491

r₁₇= ∞ (eyepiece)

Aspherical coefficients

Second surface

K = −1.2945

A₄= 9.89743 × 10⁻⁶
A₆= −4.30715 × 10⁻⁷
A₈= 2.58833 × 10⁻⁹

Third surface

K = −0.2627

A₄= −6.69210 × 10⁻⁵
A₆= −9.19006 × 10⁻⁷
A₈= 6.64337 × 10⁻¹⁰

Fourth surface

K = −0.0228

A₄= 1.06273 × 10⁻⁴
A₆= −8.28362 × 10⁻⁷
A₈= 3.85729 × 10⁻⁹

Fifth surface

K = 0.2133

A₄= 6.06366 × 10⁻⁴
A₆= −2.97302 × 10⁻⁵
A₈= 5.98935 × 10⁻⁷

Sixth surface

K = −0.0427

A₄= 4.82034 × 10⁻⁵
A₆= −2.89969 × 10⁻⁵
A₈= 6.72146 × 10⁻⁷

Eighth surface

K = 0.1560

A₄= 2.50445 × 10⁻⁴
A₆= −1.47471 × 10⁻⁶
A₈= 4.11057 × 10⁻⁸

Ninth surface

K = 0.0136

A₄= 5.39717 × 10⁻⁶
A₆= −1.68771 × 10⁻⁶

Twelfth surface

K = 0.0000

A₄= −1.19998 × 10⁻³
A₆= 1.07234 × 10⁻⁵

Sixteenth surface

K = 0.0000

A₄= 3.44659 × 10⁻⁵
A₆= 1.08095 × 10⁻⁷

Zoom data

Wide-angle position
Middle position
Telephoto position

D2
9.1868
7.2088
3.4518

D4
4.8856
8.2783
16.2383

D6
6.6129
5.1982
0.9952

mh = 10.217 mm

Conditions (1), (7) mh/fe
= 0.681

Conditions (2), (3) fe
= 15.006 mm

Conditions (5), (6) νp − νn
= 25.29

Tenth Embodiment

In the real image mode finder optical system of this embodiment, as shown in FIGS. 45A–45D, the objective optical system includes, in order from the object side, the first unit G1 with a negative refracting power, the second unit G2 with a positive refracting power, the third unit G3 with a negative refracting power, and a fourth unit G4 with a positive refracting power, and has a positive refracting power as a whole.

The image erecting means includes the prisms P1 and P2. In the real image mode finder optical system of the tenth embodiment, the intermediate image formed by the objective optical system is interposed between the prism P2 and the negative lens L1, and the field frame, such as that shown in FIG. 4, is placed in the proximity of its imaging position.

In the tenth embodiment, low-dispersion glass is used for the positive lens E1 to suppress chromatic aberration of magnification produced in the eyepiece optical system.

Also, aberration characteristics in the tenth embodiment are shown in FIGS. 46A–46D, 47A–47D, 48A–48D, and 49A–49D.

Subsequently, numerical data of optical members constituting the real image mode finder optical system according to the tenth embodiment are shown below.

Numerical data 10

Wide-angle position
Middle position
Telephoto position

m
0.686
1.177
2.019

ω (°)
26.700
15.294
8.889

f (mm)
10.290
17.650
30.261

Pupil dia. (mm) 4.000

r₁= −35.4073

d₁= 1.3547
n_d1= 1.58423
ν_d1= 30.49

r₂= 15.7324 (aspherical)

d₂= D2 (variable)

r₃= 14.1173 (aspherical)

d₃= 4.2036
n_d3= 1.49241
ν_d3= 57.66

r₄= −19.7136

d₄= D4 (variable)

r₅= −21.3268

d₅= 1.0000
n_d5= 1.58423
ν_d5= 30.49

r₆= 15.4585 (aspherical)

r₆= D6 (variable)

r₇= 47.9547

d₇= 14.7087
n_d7= 1.52542
ν_d7= 55.78

r₈−16.9222 (aspherical)

d₈= 0.5000

r₉= 40.5011

d₉= 39.7256
n_d91.52542
ν_d9= 55.78

r₁₀= −22.4670

d₁₀= 4.0295

r₁₁= ∞ field frame)

d₁₁= 7.6484

r₁₂= −6.8411 (aspherical)

d₁₂= 3.0616
n_d12= 1.58423
ν_d12= 30.49

r₁₃= −9.5101

d₁₃= 1.9354

r₁₄= 16.4813

d₁₄= 5.2395
n_d14= 1.49700
ν_d14= 81.54

r₁₅= −12.4181 (aspherical)

d₁₅= 15.7651

r₁₆= ∞ (eyepoint)

Aspherical coefficients

Second surface

K = −1.3019

A₄= −1.03082 × 10⁻⁴
A₆= 1.18309 × 10⁻⁶
A₈= −3.69689 × 10⁻⁹

Third surface

K = −0.1784

A₄= −1.31901 × 10⁻⁴
A₆= 1.62576 × 10⁻⁷
A₈= −5.25998 × 10⁻¹⁰

Sixth surface

K = −0.0760

A₄= −7.29856 × 10⁻⁵
A₆= −1.57784 × 10⁻⁶
A₈= 2.85950 × 10⁻⁸

Eighth surface

K = 0.1940

A₄= 3.47928 × 10⁻⁵
A₆= 5.46298 × 10⁻⁸
A₈= 1.40140 × 10⁻⁹

Twelfth surface

K = 0.0000

A₄= −2.29965 × 10⁻⁴
A₆= −5.49255 × 10⁻⁶

Fifteenth surface

K = 0.0000

A₄= 1.23613 × 10⁻⁴
A₆= 7.32239 × 10⁻⁷

Zoom data

Wide-angle position
Middle position
Telephoto position

D2
25.8585
12.8666
7.9000

D4
1.0000
9.3310
20.3050

D6
3.2733
5.0026
1.7063

mh = 9.539 mm

Conditions (1), (7) mh/fe
= 0.636

Condition (4) ν
= 81.54

Conditions (2), (3) fe
= 14.990 mm

Eleventh Embodiment

In the real image mode finder optical system of this embodiment, as shown in FIGS. 50A–50D, the objective optical system includes, in order from the object side, the first unit G1 with a negative refracting power, the second unit 62 with a positive refracting power, the third unit 63 with a negative refracting power, and a fourth unit 64 with a positive refracting power, and has a positive refracting power as a whole.

The fourth unit 64 is constructed with two prisms P1 and P2. The eyepiece optical system is constructed with the negative lens L1 and the cemented lens component CE comprised of the negative lens element CE 2 and the positive lens element CE1, and has a positive refracting power as a whole.

The image erecting means includes the prisms P1 and P2. In the real image mode finder optical system of the eleventh embodiment, the intermediate image formed by the objective optical system is interposed between the prism P2 and the negative lens L1, and the field frame, such as that shown in FIG. 4, is placed in the proximity of its imaging position.

The magnification of the finder is changed in the range from the wide-angle position to the telephoto position by fixing the fourth unit 64 and by moving the first unit G1, the second unit G2, and the third unit G3 along the optical axis.

The prisms P1 and P2 are provided with reflecting surfaces along the optical path so that the optical axis is bent to obtain an erect image. For example, the prism P1 is provided with one reflecting surface (for bending the optical axis in the Y-Z plane) and the prism P2 is provided with three reflecting surfaces (for bending the optical axis once in the Y-Z plane and twice in the X-Z plane in this order from the object side) to erect the image. Also, the arrangement of the reflecting surfaces is based on that of a Porro prism. Angles made with the optical axis bent by the reflecting surfaces are such that, for example, the angle of the optical axis bent by the reflecting surface of the prism P1 is smaller than 90 degrees, while the angles of the optical axis bent by two reflecting surfaces of the prism P2 are larger than 90 degrees and the angle of the optical axis bent by the remaining one reflecting surface is smaller than 90 degrees. The reflecting surfaces making angles smaller than 90 degrees are coated with metal films, such as silver and aluminum. The reflecting surfaces of angles larger than 90 degrees utilize total reflection. The cemented lens component CE is constructed so that diopter adjustment can be made in accordance with an observer's diopter.

In the eleventh embodiment, the cemented lens component CE including, in order from the object side, the negative lens element and the positive lens element is used to suppress the chromatic aberration of magnification produced in the eyepiece optical system.

Also, aberration characteristics in the eleventh embodiment are shown in FIGS. 51A–51D, 52A–52D, 53A–53D, and 54–54D.

Subsequently, numerical data of optical members constituting the real image mode finder optical system according to the eleventh embodiment are shown below.

Numerical data 11

Wide-angle position
Middle position
Telephoto position

m
0.685
1.175
2.016

ω (°)
26.509
15.216
8.803

f (mm)
10.289
17.629
30.259

Pupil dia.
4.000

(mm)

r₁= −31.2936

d₁= 1.3442
n_d1= 1.58423
υ_d1= 30.49

r₂= 16.8814 (aspherical)

d₂= D2 (variable)

r₃= 14.1167 (aspherical)

d₃= 4.5120
n_d3= 1.49241
υ_d3= 57.66

r₄= −20.4840

d₄= D4 (variable)

r₅= −20.2406

d₅= 0.9963
n_d5= 1.58423
υ_d5= 30.49

r₆= 14.9676 (aspherical)

d₆= D6 (variable)

r₇= 41.4899

d₇= 14.6927
n_d7= 1.52542
υ_d7= 55.78

r₈= −17.9428 (aspherical)

d₈= 0.5000

r₉= 34.5533

d₉= 39.7402
n_d9= 1.52542
υ_d9= 55.78

r₁₀= −28.4392

d₁₀= 4.5510

r₁₁= ∞ (field frame)

d₁₁= 7.9719

r₁₂= −9.6322 (aspherical)

d₁₂= 3.1829
n_d12= 1.58423
υ_d12= 30.49

r₁₃= −10.6815

d₁₃= 1.6105

r₁₄= 19.4893

d₁₄= 1.0000
n_d14= 1.58423
υ_d14= 30.49

r₁₅= 13.6490

d₁₅= 5.4672
n_d15= 1.49241
υ_d15= 57.66

r₁₆= −12.4053 (aspherical)

d₁₆= 15.7651

r₁₇= ∞ (eyepoint)

Aspherical coefficients

Second surface

K = −1.3018

A₄= −1.08269 × 10⁻⁴
A₆= 9.30175 × 10⁻⁷
A₈= −1.42679 × 10⁻⁹

Third surface

K = −0.1791

A₄= −1.31719 × 10⁻⁴
A₆= 1.67274 × 10⁻⁷
A₈= −6.28754 × 10⁻¹⁰

Sixth surface

K = −0.0761

A₄= −1.10385 × 10⁻⁴
A₆= −3.75495 × 10⁻⁷
A₈= 2.90075 × 10⁻⁹

Eighth surface

K = 0.1945

A₄= 3.40022 × 10⁻⁵
A₆= −8.32444 × 10⁻⁸
A₈= 2.90545 × 10⁻⁹

Twelfth surface

K = 0.0000

A₄= −2.80853 × 10⁻⁴
A₆= −6.97108 × 10⁻⁶

Sixteenth surface

K = 0.0000

A₄= 3.07353 × 10⁻⁵
A₆= 9.18614 × 10⁻⁷

Zoom data

Wide-angle position
Middle position
Telephoto position

D2
25.8073
13.2103
8.2556

D4
0.9957
9.3832
20.5408

D6
3.5101
4.5817
1.6440

mh = 9.486 mm

Conditions (1), (7) mh/fe = 0.632

Conditions (2), (3) fe = 15.010 mm

Conditions (5), (6) υp − υn = 27.17

Twelfth Embodiment

The real image mode finder optical system of this embodiment, as shown in FIGS. 55A–55C, has nearly the same arrangement as that of the first embodiment with the exception of lens data.

Subsequently, numerical data of optical members constituting the real image mode finder optical system according to the twelfth embodiment are shown below.

Numerical data 12

Wide-angle position
Middle position
Telephoto position

m
0.530
1.007
2.050

ω (°)
33.694
17.618
8.796

f (mm)
8.482
16.100
32.782

Pupil dia.
4.000

(mm)

r₁= 52.6894

d₁= 1.0000
n_d1= 1.58423
υ_d1= 30.49

r₂= 9.9227 (aspherical)

d₂= D2 (variable)

r₃= 10.2741 (aspherical)

d₃= 4.2589
n_d3= 1.52542
υ_d3= 55.78

r₄= −23.8681 (aspherical)

d₄= D4 (variable)

r₅= −10.3480 (aspherical)

d₅= 1.0000
n_d5= 1.58425
υ_d5= 30.35

r₆= 10.6480 (aspherical)

d₆= D6 (variable)

r₇= 11.1372

d₇= 9.9000
n_d7= 1.52542
υ_d7= 55.78

r₈= −26.1339 (aspherical)

d₈= 0.5000

r₉= 15.5869 (aspherical)

d₉= 22.3572
n_d9= 1.52542
υ_d9= 55.78

r₁₀= ∞

d₁₀= 2.4528

r₁₁= ∞ (field frame)

d₁₁= 3.0665

r₁₂= 15.8132 (aspherical)

d₁₂= 15.9408
n_d12= 1.52542
υ_d12= 55.78

r₁₃= −75.7570

d₁₃= 2.0915

r₁₄= 27.2996

d₁₄= 4.8098
n_d14= 1.52542
υ_d14= 55.78

r₁₅= −16.0615 (aspherical)

d₁₅= −16.8220

r₁₆= ∞ (eyepoint)

Aspherical coefficients

Second surface

K = −1.2951

A₄= 2.66909 × 10⁻⁵
A₆= −2.25605 × 10⁻⁷
A₈= 9.99104 × 10⁻¹¹

Third surface

K = −0.2614

A₄= −8.86459 × 10⁻⁵
A₆= −2.02523 × 10⁻⁷
A₈= −5.25729 × 10⁻⁹

Fourth surface

K = −0.0224

A₄= 6.51575 × 10⁻⁵
A₆= −1.53327 × 10⁻⁷
A₈= −1.18392 × 10⁻⁹

Fifth surface

K = 0.2138

A₄= 4.33241 × 10⁻⁴
A₆= −1.93785 × 10⁻⁵
A₈= 4.02985 × 10⁻⁷

Sixth surface

K = −0.0427

A₄= 9.91769 × 10⁻⁵
A₆= −1.51811 × 10⁻⁵
A₈= 3.40669 × 10⁻⁷

Eighth surface

K = 0.1565

A₄= 2.28575 × 10⁻⁴
A₆= −1.22359 × 10⁻⁷
A₈= 3.27751 × 10⁻⁸

Ninth surface

K = 0.0140

A₄= 4.56644 × 10⁻⁶
A₆= −9.81069 × 10⁻⁷

Twelfth surface

K = 0.0000

A₄= −7.24335 × 10⁻⁴
A₆= 3.64409 × 10⁻⁶

Fifteenth surface

K = 0.0000

A₄= 4.99493 × 10⁻⁵
A₆= 9.74998 × 10⁻⁸

Zoom data

Wide-angle
Middle
Telephoto

position
position
position

D2
11.4582
6.8773
3.0038

D4
1.2808
8.5674
16.7674

D6
8.0121
5.3064
0.9799

mh = 10.692 mm

f123
−11.144
−21.243
−44.469

m23
0.529
1.000
2.038

m2

−1.000

m3

−1.000

Condition (9) MG45
−0.763
−0.765
−0.767

Conditions (1), (7) mh/fe =
0.669

Conditions (2), (3) fe =
15.991 mm

Condition (8) φ(mh/2) =
−0.406970 (l/mm)

Condition (10) β3 =
−1.000

Condition (11) SF2 =
−0.389

Condition (12) f2/f3 =
−1.618

Condition (13) fw/fFw =
−0.761

Condition (14) fT/fFT =
−0.737

Condition (15) mT/mW =
3.865

Condition (16) fw/fw123 =
−0.761

Condition (17) fT/fT123 =
−0.737

Thirteenth Embodiment

The real image mode finder optical system of this embodiment, as shown in FIGS. 56A–56C, has nearly the same arrangement as that of the first embodiment with the exception of lens data.

Subsequently, numerical data of optical members constituting the real image mode finder optical system according to the thirteenth embodiment are shown below.

Numerical data 13

Wide-angle position
Middle position
Telephoto position

m
0.533
1.007
2.050

ω (°)
33.897
17.661
8.803

f (mm)
7.468
14.111
28.722

Pupil dia. (mm) 4.000

r₁= 166.7316

d₁= 1.0000
n_d1= 1.58423
ν_d1= 30.49

r₂= 10.3218 (aspherical)

d₂= D2 (variable)

r₃= 10.2841 (aspherical)

d₃= 4.3636
n_d3= 1.52542
ν_d3= 55.78

r₄= −19.9166 (aspherical)

d₄= D4 (variable)

r₅= −9.8214 (aspherical)

d₅= 1.0000
n_d5= 1.58425
ν_d5= 30.35

r₆= 10.1214 (aspherical)

d₆= D6 (variable)

r₇= 13.2873

d₇= 9.9000
n_d7= 1.52542
ν_d7= 55.78

r₈= −17.5762 (aspherical)

d₈= 0.5000

r₉= 15.4406 (aspherical)

d₉= 22.6932
n_d9= 1.52542
ν_d9= 55.78

r₁₀= ∞

d₁₀= 2.1168

r₁₁= ∞ (field frame)

d₁₁= 2.4325

r₁₂= 28.5591 (aspherical)

d₁₂= 14.7924
n_d12= 1.52542
ν_d12= 55.78

r₁₃= −24.5754

d₁₃= 1.2620

r₁₄= 27.5003

d₁₄= 4.1395
n_d14= 1.52542
ν_d14= 55.78

r₁₅= −16.2956 (aspherical)

d₁₅= 16.6524

r₁₆= ∞ (eyepoint)

Aspherical coefficients

Second surface

K = −1.2951

A₄= −9.85470 × 10⁻⁶
A₆= −3.31289 × 10⁻⁷
A₈= 3.00060 × 10⁻⁹

Third surface

K = −0.2607

A₄= −9.27092 × 10⁻⁵
A₆= −8.01222 × 10⁻⁷
A₈= 2.80942 × 10⁻⁹

Fourth surface

K = −0.0224

A₄= 1.02300 × 10⁻⁴
A₆= 7.73167 × 10⁻⁷
A₈= 5.82839 × 10⁻⁹

Fifth surface

K = 0.2137

A₄= 5.86855 × 10⁻⁴
A₆= −2.95943 × 10⁻⁵
A₈= 6.45936 × 10⁻⁷

Sixth surface

K = −0.0425

A₄= −2.30372 × 10⁻⁵
A₆= −2.55725 × 10⁻⁵
A₈= 6.22366 × 10⁻⁷

Eighth surface

K = 0.1564

A₄= 1.56106 × 10⁻⁴
A₆= −7.63871 × 10⁻⁸
A₈= 4.09536 × 10⁻⁹

Ninth surface

K = 0.0137

A₄= 9.52536 × 10⁻⁷
A₆= −1.05084 × 10⁻⁶

Twelfth surface

K = 0.0000

A₄= −1.23450 × 10⁻³
A₆= 1.00000 × 10⁻⁵

Fifteenth surface

K = 0.0000

A₄= 3.90391 × 10⁻⁵
A₆= 1.54761 × 10⁻⁷

Zoom data

Wide-angle

position
Middle position
Telephoto position

D2
11.7540
7.4253
3.7541

D4
1.2500
8.1247
15.8923

D6
7.6424
5.0964
1.0000

mh = 9.279 mm

f123
−10.011
−18.982
−39.511

m23
0.531
1.000
2.036

m2

−1.000

m3

−1.000

Condition (9) MG45
−0.748
−0.749
−0.751

Conditions (1), (7) mh/fe
= 0.662

Conditions (2), (3) fe
= 14.010 mm

Condition (8) φ (mh/2)
= −0.395473 (l/mm)

Condition (10) β3
= −1.000

Condition (11) SF2
= −0.319

Condition (12) f2/f3
= −1.622

Condition (13) fw/fFw
= −0.746

Condition (14) fT/fFT
= −0.727

Condition (15) mT/mW
= 3.846

Condition (16) fw/fw123
= −0.746

Condition (17) fT/fT123
= −0.727

Fourteenth Embodiment

The real image mode finder optical system of this embodiment, as shown in FIGS. 57A–57C, has nearly the same arrangement as that of the first embodiment with the exception of lens data.

Subsequently, numerical data of optical members constituting the real image mode finder optical system according to the fourteenth embodiment are shown below.

Numerical data 14

Wide-angle position
Middle position
Telephoto position

m
0.530
1.011
2.054

ω (°)
33.791
17.591
8.810

f (mm)
7.962
15.170
30.830

Pupil dia. (mm) 4.000

r₁= 82.9717

d₁= 1.0000
n_d1= 1.58425
ν_d1= 30.35

r₂= 10.0913 (aspherical)

d₂= D2 (variable)

r₃= 10.3969 (aspherical)

d₃= 4.2911
n_d3= 1.52542
ν_d3= 55.78

r₄= −21.6082 (aspherical)

d₄= D4 (variable)

r₅= −11.4300

d₅= 1.0000
n_d5= 1.58425
ν_d5= 30.35

r₆= 9.3984 (aspherical)

d₆= D6 (variable)

r₇= 11.1076

d₇= 9.9000
n_d7= 1.52542
ν_d7= 55.78

r₈= −24.3057 (aspherical)

d₈= 0.5000

r₉= 15.7603 (aspherical)

d₉= 22.4265
n_d9= 1.52542
ν_d9= 55.78

r₁₀= ∞

d₁₀= 2.2691

r₁₁= ∞ (field frame)

d₁₁= 2.5500

r₁₂= 15.9134 (aspherical)

d₁₂= 15.5881
n_d12= 1.52542
ν_d12= 55.78

r₁₃= −39.1000

d₁₃= 1.7582

r₁₄= 25.7997 (aspherical)

d₁₄= 5.1865
n_d14= 1.52542
ν_d14= 55.78

r₁₅= −16.7689 (aspherical)

d₁₅= 16.8782

r₁₆= ∞ (eyepoint)

Aspherical coefficients

Second surface

K = −1.2943

A₄= −9.84819 × 10⁻⁶
A₆= −2.39182 × 10⁻⁸
A₈= 4.94427 × 10⁻¹⁰

Third surface

K = −0.2438

A₄= −1.13792 × 10⁻⁴
A₆= −6.83279 × 10⁻⁸
A₈= −6.63089 × 10⁻⁹

Fourth surface

K = −0.0218

A₄= 6.76356 × 10⁻⁵
A₆= −1.19790 × 10⁻⁷
A₈= −2.64472 × 10⁻⁹

Sixth surface

K = −0.0422

A₄= −5.28848 × 10⁻⁴
A₆= 2.13243 × 10⁻⁶
A₈= 1.98353 × 10⁻⁸

Eighth surface

K = 0.1608

A₄= 1.86541 × 10⁻⁴
A₆= 1.81579 × 10⁻⁷
A₈= 3.74182 × 10⁻⁸

Ninth surface

K = 0.0115

A₄= −3.79724 × 10⁻⁵
A₆= −6.23075 × 10⁻⁷

Twelfth surface

K = 0.0000

A₄= −1.19998 × 10⁻³
A₆= 1.07234 × 10⁻⁵

Fourteenth surface

K = 0.0000

A₄= 1.76029 × 10⁻⁵
A₆= 3.42514 × 10⁻⁷

Fifteenth surface

K = 0.0000

A₄= 6.14363 × 10⁻⁵
A₆= 4.37825 × 10⁻⁷

Zoom data

Wide-angle

position
Middle position
Telephoto position

D2
12.0419
7.5075
3.7196

D4
1.1332
8.3326
16.3538

D6
7.8982
5.2332
1.0000

mh = 10.098 mm

f123
−10.392
−19.874
−41.387

m23
0.526
1.000
2.034

m2

−1.000

m3

−1.000

Condition (9) MG45
−0.768
−0.770
−0.772

Conditions (1), (7) mh/fe
= 0.673

Conditions (2), (3) fe
= 15.010 mm

Condition (8) φ (mh/2)
= −0.377550 (l/mm)

Condition (10) β3
= −1.000

Condition (11) SF2
= −0.350

Condition (12) f2/f3
= −1.615

Condition (13) fw/fFw
= −0.766

Condition (14) fT/fFT
= −0.745

Condition (15) mT/mW
= 3.872

Condition (16) fw/fw123
= −0.766

Condition (17) fT/fT123
= −0.745

Fifteenth Embodiment

The real image mode finder optical system of this embodiment, as shown in FIGS. 58A–58C, has nearly the same arrangement as that of the first embodiment with the exception of lens data.

Subsequently, numerical data of optical members constituting the real image mode finder optical system according to the fifteenth embodiment are shown below.

Numerical data 15

Wide-angle position
Middle position
Telephoto position

m
0.429
0.813
1.663

ω (°)
33.665
17.724
8.889

f (mm)
7.384
13.997
28.641

Pupil dia. (mm) 4.000

r₁= 107.4567

d₁= 1.0000
n_d1= 1.58423
ν_d1= 30.49

r₂= 10.2589 (aspherical)

d₂= D2 (variable)

r₃= 10.2029 (aspherical)

d₃= 4.4631
n_d3= 1.52542
ν_d3= 55.78

r₄= −20.4728 (aspherical)

d₄= D4 (variable)

r₅= −9.3096 (aspherical)

d₅= 1.0000
n_d5= 1.58425
ν_d5= 30.35

r₆= 10.3604 (aspherical)

d₆= D6 (variable)

r₇= 16.9815

d₇= 9.9000
n_d7= 1.52542
ν_d7= 55.78

r₈= −13.8071 (aspherical)

d₈= 0.5000

r₉= 15.6162 (aspherical)

d₉= 22.4902
n_d9= 1.52542
ν_d9= 55.78

r₁₀= ∞

d₁₀= 2.3198

r₁₁= ∞ (field frame)

d₁₁= 3.8080

r₁₂= 24.6624 (aspherical)

d₁₂= 15.9445
n_d12= 1.52542
ν_d12= 55.78

r₁₃= −144.7239

d₁₃= 2.0644

r₁₄= 37.1434

d₁₄= 4.1276
n_d14= 1.52542
ν_d14= 55.78

r₁₅= −14.1033 (aspherical)

d₁₅= 16.7947

r₁₆= ∞ (eyepoint)

Aspherical coefficients

Second surface

K = −1.2993

A₄= 5.71536 × 10⁻⁵
A₆= −1.74731 × 10⁻⁶
A₈= 9.48321 × 10⁻⁹

Third surface

K = −0.2562

A₄= −1.82646 × 10⁻⁵
A₆= −1.79005 × 10⁻⁶
A₈= 5.13165 × 10⁻⁹

Fourth surface

K = −0.0200

A₄= 1.47200 × 10⁻⁴
A₆= −1.56976 × 10⁻⁶
A₈= 1.27897 × 10⁻⁸

Fifth surface

K = 0.2127

A₄= 5.41270 × 10⁻⁴
A₆= −3.32639 × 10⁻⁵
A₈= 5.81147 × 10⁻⁷

Sixth surface

K = −0.0433

A₄= −1.09499 × 10⁻⁴
A₆= −2.68424 × 10⁻⁵
A₈= 6.74415 × 10⁻⁷

Eighth surface

K = 0.1546

A₄= 2.00697 × 10⁻⁴
A₆= −1.61566 × 10⁻⁶
A₈= −3.13569 × 10⁻⁹

Ninth surface

K = 0.0164

A₄= 6.95918 × 10⁻⁵
A₆= −2.13186 × 10⁻⁶

Twelfth surface

K = 0.0000

A₄= −4.54314 × 10⁻⁴
A₆= −3.43968 × 10⁻⁶

Fifteenth surface

K = 0.0000

A₄= 4.97954 × 10⁻⁵
A₆= 1.10003 × 10⁻⁷

Zoom data

Wide-angle

position
Middle position
Telephoto position

D2
11.2714
6.9682
3.2721

D4
1.6105
8.4616
16.2351

D6
7.6649
5.1170
1.0397

mh = 9.349 mm

f123
−10.318
−19.605
−41.020

m23
0.530
1.000
2.042

m2

−1.000

m3

−1.000

Condition (9) MG45
−0.717
−0.720
−0.722

Conditions (1), (7) mh/fe
= 0.543

Conditions (2), (3) fe
= 17.226 mm

Condition (8) φ (mh/2)
= −0.390191 (l/mm)

Condition (10) β3
= −1.000

Condition (11) SF2
= −0.335

Condition (12) f2/f3
= −1.656

Condition (13) fw/fFw
= −0.716

Condition (14) fT/fFT
= −0.698

Condition (15) mT/mW
= 3.879

Condition (16) fw/fw123
= −0.716

Condition (17) fT/fT123
= −0.698

@

The real image mode finder optical system of this embodiment, as shown in FIGS. 59A–59C, has nearly the same arrangement as that of the first embodiment with the exception of lens data.

Subsequently, numerical data of optical members constituting the real image mode finder optical system according to the sixteenth embodiment are shown below.

Numerical data 16

Wide-angle position
Middle position
Telephoto position

m
0.429
0.809
2.024

ω (°)
33.860
17.674
7.199

f (mm)
7.439
14.047
35.124

Pupil dia. (mm) 4.000

r₁= 244.6491

d₁= 1.0000
n_d1= 1.58423
ν_d1= 30.49

r₂= 10.7182 (aspherical)

d₂= D2 (variable)

r₃= 9.8239 (aspherical)

d₃= 4.5281
n_d3= 1.52542
ν_d3= 55.78

r₄= −19.6580 (aspherical)

d₄= D4 (variable)

r₅= −9.4259 (aspherical)

d₅= 1.0000
n_d5= 1.58425
ν_d5= 30.35

r₆= 9.7259 (aspherical)

d₆= D6 (variable)

r₇= 13.6837

d₇= 9.9000
n_d7= 1.52542
ν_d7= 55.78

r₈= −17.5090 (aspherical)

d₈= 0.5000

r₉= 15.6690 (aspherical)

d₉= 22.4657
n_d9= 1.52542
ν_d9= 55.78

r₁₀= ∞

d₁₀= 2.3443

r₁₁= ∞ (field frame)

d₁₁= 4.2463

r₁₂= 24.2774 (aspherical)

d₁₂= 15.9476
n_d12= 1.52542
ν_d12= 55.78

r₁₃= −225.2944

d₁₃= 2.0463

r₁₄= 37.1333

d₁₄= 3.6458
n_d14= 1.52542
ν_d14= 55.78

r₁₅= −14.1787 (aspherical)

d₁₅= 16.8295

r₁₆= ∞ (eyepoint)

Aspherical coefficients

Second surface

K = −1.3022

A₄= 1.94109 × 10⁻⁵
A₆= −1.53742 × 10⁻⁶
A₈= 9.18621 × 10⁻⁹

Third surface

K = −0.2549

A₄= −7.62311 × 10⁻⁵
A₆= −2.11044 × 10⁻⁶
A₈= 9.22506 × 10⁻⁹

Fourth surface

K = −0.0175

A₄= 1.18065 × 10⁻⁴
A₆= −1.28525 × 10⁻⁶
A₈= 1.15858 × 10⁻⁸

Fifth surface

K = 0.2594

A₄= 7.73262 × 10⁻⁴
A₆= = −4.07569 × 10⁻⁵
A₈= 6.35774 × 10⁻⁷

Sixth surface

K = −0.0434

A₄= 2.49683 × 10⁻⁵
A₆= −3.63701 × 10⁻⁵
A₈= 8.31505 × 10⁻⁷

Eighth surface

K = 0.1534

A₄= 1.67581 × 10⁻⁴
A₆= −1.34210 × 10⁻⁶
A₈= 5.76435 × 10⁻⁹

Ninth surface

K = 0.0177

A₄= 9.17386 × 10⁻⁶
A₆= −1.80151 × 10⁻⁶

Twelfth surface

K = 0.0000

A₄= −3.02442 × 10⁻⁴
A₆= −2.91068 × 10⁻⁶

Fifteenth surface

K = 0.0000

A₄= 5.38216 × 10⁻⁵
A₆= 6.59977 × 10⁻⁸

Zoom data

Wide-angle

position
Middle position
Telephoto position

D2
10.3532
6.2169
1.8288

D4
1.2500
7.8558
17.6530

D6
8.8787
6.4091
1.0000

mh = 9.259 mm

f123
−10.214
−19.332
−50.207

m23
0.532
1.000
2.500

m2

−1.000

m3

−1.000

Condition (9) MG45
−0.730
−0.732
−0.735

Conditions (1), (7) mh/fe
= 0.534

Conditions (2), (3) fe
= 17.354 mm

Condition (8) φ (mh/2)
= −0.263294 (l/mm)

Condition (10) β3
= −1.000

Condition (11) SF2
= −0.334

Condition (12) f2/f3
= −1.638

Condition (13) fw/fFw
= −0.728

Condition (14) fT/fFT
= −0.700

Condition (15) mT/mW
= 4.722

Condition (16) fw/fw123
= −0.728

Condition (17) fT/fT123
= −0.700

Seventeenth Embodiment

The real image mode finder optical system of this embodiment, as shown in FIGS. 60A–60C, has nearly the same arrangement as that of the first embodiment with the exception of lens data.

Subsequently, numerical data of optical members constituting the real image mode finder optical system according to the seventeenth embodiment are shown below.

Numerical data 17

Wide-angle position
Middle position
Telephoto position

m
0.427
0.806
2.149

ω (°)
34.100
17.683
6.723

f (mm)
7.358
13.901
37.053

Pupil dia. (mm) 4.000

r₁= −713.7698

d₁= 1.0000
n_d1= 1.58423
ν_d1= 30.49

r₂= 11.0797 (aspherical)

d₂= D2 (variable)

r₃= 9.7135 (aspherical)

d₃= 4.6200
n_d3= 1.52542
ν_d3= 55.78

r₄= −18.4096 (aspherical)

d₄= D4 (variable)

r₅= −9.1335 (aspherical)

d₅= 1.0000
n_d5= 1.58425
ν_d5= 30.35

r₆= 9.4327 (aspherical)

d₆= D6 (variable)

r₇= 13.0353

d₇= 9.9000
n_d7= 1.52542
ν_d7= 55.78

r₈= −18.2574 (aspherical)

d₈= 0.5000

r₉= 15.8017 (aspherical)

d₉= 22.4291
n_d9= 1.52542
ν_d9= 55.78

r₁₀= ∞

d₁₀= 2.3809

r₁₁= ∞ (field frame)

d₁₁= 4.1914

r₁₂= 23.7178 (aspherical)

d₁₂= 15.9419
n_d12= 1.52542
ν_d12= 55.78

r₁₃= −188.7242

d₁₃= 2.0225

r₁₄= 38.0414

d₁₄= 3.6351
n_d14= 1.52542
ν_d14= 55.78

r₁₅= −14.0922 (aspherical)

d₁₅= 16.8589

r₁₆= ∞ (eyepoint)

Aspherical coefficients

Second surface

K = −1.3025

A₄= −3.21798 × 10⁻⁵
A₆= −7.78889 × 10⁻⁷
A₈= 5.08606 × 10⁻⁹

Third surface

K = −0.2547

A₄= −1.33313 × 10⁻⁴
A₆= −1.48099 × 10⁻⁶
A₈= 7.55992 × 10⁻⁹

Fourth surface

K = −0.0172

A₄= 1.11743 × 10⁻⁴
A₆= −9.24392 × 10⁻⁷
A₈= 9.33552 × 10⁻⁹

Fifth surface

K = 0.2714

A₄= 1.27697 × 10⁻³
A₆= −8.18736 × 10⁻⁵
A₈= 1.94631 × 10⁻⁶

Sixth surface

K = −0.0432

A₄= 3.65213 × 10⁻⁴
A₆= −6.62961 × 10⁻⁵
A₈= 1.63076 × 10⁻⁶

Eighth surface

K = 0.1534

A₄= 1.31305 × 10⁻⁴
A₆= −7.77237 × 10⁻⁷
A₈= 1.72405 × 10⁻⁸

Ninth surface

K = 0.0176

A₄= −4.34110 × 10⁻⁵
A₆= −9.40302 × 10⁻⁷

Twelfth surface

K = 0.0000

A₄= −2.47396 × 10⁻⁴
A₆= −3.97394 × 10⁻⁶

Fifteenth surface

K = 0.0000

A₄= 5.72418 × 10⁻⁵
A₆= 3.57168 × 10⁻⁸

Zoom data

Wide-angle

position
Middle position
Telephoto position

D2
10.0156
5.9870
1.4776

D4
1.2500
7.6739
17.9124

D6
9.1244
6.7292
1.0000

mh = 9.156 mm

f123
−9.916
−18.774
−52.236

m23
0.532
1.000
2.667

m2

−1.000

m3

−1.000

Condition (9) MG45
−0.744
−0.746
−0.748

Conditions (1), (7) mh/fe
= 0.531

Conditions (2), (3) fe
= 17.239 mm

Condition (8) φ (mh/2)
= −0.251090 (l/mm)

Condition (10) β3
= −1.000

Condition (11) SF2
= −0.309

Condition (12) f2/f3
= −1.647

Condition (13) fw/fFw
= −0.742

Condition (14) fT/fFT
= −0.709

Condition (15) mT/mW
= 5.035

Condition (16) fw/fw123
= −0.742

Condition (17) fT/fT123
= −0.709

Eighteenth Embodiment

The real image mode finder optical system of this embodiment, as shown in FIGS. 61A–61C, has nearly the same arrangement as that of the first embodiment with the exception of lens data.

Subsequently, numerical data of optical members constituting the real image mode finder optical system according to the eighteenth embodiment are shown below.

Numerical data 18

Wide-angle position
Middle position
Telephoto position

m
0.435
0.824
1.691

ω (°)
33.426
17.596
8.847

f (mm)
7.656
14.498
29.743

Pupil dia. (mm) 4.000

r₁= 99.5495

d₁= 1.0000
n_d1= 1.58423
ν_d1= 30.49

r₂= 10.1706 (aspherical)

d₂= D2 (variable)

r₃= 10.3729 (aspherical)

d₃= 4.4126
n_d3= 1.52542
ν_d3= 55.78

r₄= −19.6559 (aspherical)

d₄= D4 (aspherical)

r₅= −9.5997 (aspherical)

d₅= 1.0000
n_d5= 1.58425
ν_d5= 30.35

r₆= 9.8997 (aspherical)

d₆= D6 (variable)

r₇= 14.3933

d₇= 9.9000
n_d7= 1.52542
ν_d7= 55.78

r₈= −15.6309 (aspherical)

d₈= 0.5000

r₉= 15.7116 (aspherical)

d₉= 22.4940
n_d9= 1.52542
ν_d9= 55.78

r₁₀= ∞

d₁₀= 2.3160

r₁₁= ∞ (field frame)

d₁₁= 3.6826

r₁₂= 27.7932 (aspherical)

d₁₂= 16.0681
n_d12= 1.52542
ν_d12= 55.78

r₁₃= −173.7673

d₁₃= 2.3552

r₁₄= 35.5235

d₁₄= 4.0389
n_d14= 1.52542
ν_d14= 55.78

r₁₅= −14.3073 (aspherical)

d₁₅= 22.5403

r₁₆= ∞ (eyepoint)

Aspherical coefficients

Second surface

K = −1.3005

A₄= 6.14835 × 10⁻⁵
A₆= −1.68311 × 10⁻⁶
A₈= 8.77195 × 10⁻⁹

Third surface

K = −0.2546

A₄= −2.04009 × 10⁻⁶
A₆= −1.97626 × 10⁻⁶
A₈= 8.97003 × 10⁻⁹

Fourth surface

K = −0.0188

A₄= 1.56534 × 10⁻⁴
A₆= −1.56324 × 10⁻⁶
A₈= 1.26722 × 10⁻⁸

Fifth surface

K = 0.2126

A₄= 4.66912 × 10⁻⁴
A₆= −3.86240 × 10⁻⁵
A₈= 1.14314 × 10⁻⁶

Sixth surface

K = −0.0436

A₄= −2.20422 × 10⁻⁴
A₆= −2.72889 × 10⁻⁵
A₈= 8.43830 × 10⁻⁷

Eighth surface

K = 0.1534

A₄= 2.24324 × 10⁻⁴
A₆= −3.90532 × 10⁻⁶
A₈= 2.12435 × 10⁻⁸

Ninth surface

K = 0.0178

A₄= 4.50620 × 10⁻⁵
A₆= −3.09867 × 10−6

Twelfth surface

K = 0.0000

A₄= −7.56343 × 10⁻⁴
A₆= 8.42941 × 10⁻⁷

Fifteenth surface

K = 0.0000

A₄= 3.82666 × 10⁻⁵
A₆= 2.37037 × 10⁻⁷

Zoom data

Wide-angle

position
Middle position
Telephoto position

D2
11.1798
6.8982
3.2011

D4
1.7379
8.5495
16.3243

D6
7.6797
5.1496
1.0719

mh = 9.800 mm

f123
−10.319
−19.589
−41.128

m23
0.530
1.000
2.048

m2

−1.000

m3

−1.000

Condition (9) MG45
−0.744
−0.746
−0.749

Conditions (1), (7) mh/fe
= 0.557

Conditions (2), (3) fe
= 17.593 mm

Condition (8) φ (mh/2)
= −0.484313 (l/mm)

Condition (10) β3
= −1.000

Condition (11) SF2
= −0.309

Condition (12) f2/f3
= −1.663

Condition (13) fw/fFw
= −0.742

Condition (14) fT/fFT
= −0.723

Condition (15) mT/mW
= 3.885

Condition (16) fw/fw123
= −0.742

Condition (17) fT/fT123
= −0.723

Nineteenth Embodiment

In the real image mode finder optical system of this embodiment, as shown in FIGS. 62A–62C, the objective optical system includes, in order from the object side, the first unit G1 with a negative refracting power, the second unit G2 with a positive refracting power, the third unit G3 with a negative refracting power, and the fourth unit G4 with a positive refracting power, and has a positive refracting power as a whole.

The fourth unit G4 is constructed with two prisms P1 and P2. The eyepiece optical system is constructed with the prism P and the positive lens E1 and has a positive refracting power as a whole.

The image erecting means includes the prisms P1 and P2 and the prism P. In the real image mode finder optical system of the nineteenth embodiment, the intermediate image formed by the objective optical system is interposed between the prism P2 and the prism P1 and the field frame, such as that shown in FIG. 4, is provided in the proximity of its imaging position.

The magnification of the finder is changed in the range from the wide-angle position to the telephoto position by fixing the fourth unit G4 and by moving the first unit 0G, the second unit G2, and the third unit G3 along the optical axis. In this case, the second unit G2 is simply moved toward the object side, and the third unit G3 toward the eyepiece side.

Each of the first unit G1, the second unit G2, and the third unit G3 is constructed with a single lens. The entrance surface and the exit surface of the prism P1 and the entrance surface of the prism P2 have curvatures. The entrance surface and the exit surface of the prism P also have curvatures.

The prisms P1 and P2 and the prism P are provided with the same reflecting surfaces as the reflecting surfaces P1₁, P2₁, P2₂, and P₁in the first embodiment shown in FIGS. 1–3, along the optical path, so that the optical axis is bent to erect an image. For example, one reflecting surface provided in the prism P1 bends the optical axis in the Y-Z plane; two reflecting surfaces provided in the prism P2 bend the optical axis in the Y-Z plane and the X-Z plane in this order from the object side; and one reflecting surface provided in the prism P bends the optical axis in the X-Z plane. In this way, an erect image is obtained. Also, the arrangement of the reflecting surfaces is based on that of a Porro prism. Angles made with the optical axis bent by the reflecting surfaces are such that, for example, the angles of the optical axis bent by the reflecting surfaces of the prism P1 and the prism P are smaller than 90 degrees and the angles of the optical axis bent by the reflecting surfaces of the prism P2 are larger than 90 degrees. The reflecting surfaces of the prism P1 and the prism P are coated with metal films, such as silver and aluminum. The two-reflecting surfaces of the prism P2 utilize total reflection.

However, the ways of bending the optical axis through the prisms and the angles of the optical axis bent by the reflecting surfaces are not limited to the above description. For example, the angle of the optical axis bent by the most field-frame-side reflecting surface of the prism P2 may be made smaller than 90 degrees so that this reflecting surface is coated with a metal film. Moreover, the angle of the optical axis bent by the reflecting surface of the prism P may also be made larger than 90 degrees so that this reflecting surface utilizes total reflection.

The positive lens E1 is constructed so that diopter adjustment can be made in accordance with an observer's diopter.

Subsequently, numerical data of optical members constituting the real image mode finder optical system according to the nineteenth embodiment are shown below.

Numerical data 19

Wide-angle position
Middle position
Telephoto position

m
0.528
1.033
2.073

ω (°)
33.663
17.287
8.778

f (mm)
7.927
15.503
31.114

Pupil dia. (mm) 4.000

r₁= 38.8071

d₁= 1.0000
n_d1= 1.58423
ν_d1= 30.49

r₂= 8.9754 (aspherical)

d₂= D2 (variable)

r₃= 9.9087 (aspherical)

d₃= 4.3628
n_d3= 1.52542
ν_d3= 55.78

r₄= −23.7155 (aspherical)

d₄= D4 (variable)

r₅= −10.0428 (aspherical)

d₅= 1.0000
n_d5= 1.58425
ν_d5= 30.35

r₆= 10.3428 (aspherical)

d₆= D6 (variable)

r₇= 11.5157

d₇= 9.9000
n_d7= 1.52542
ν_d7= 55.78

r₈= −22.7435 (aspherical)

d₈= 0.5000

r₉= 15.4370 (aspherical)

d₉= 22.2718
n_d9= 1.52542
ν_d9= 55.78

r₁₀= ∞

d₁₀= 2.1155

r₁₁= ∞ (field frame)

d₁₁= 2.3895

r₁₂= 18.2155 (aspherical)

d₁₂= 15.5672
n_d121.52542
ν_d12= 55.78

r₁₃= −36.4337

d₁₃= 1.8054

r₁₄= 26.1660

d₁₄= 4.9762
n_d14= 1.53542
ν_d14= 55.78

r₁₅= −16.4971 (aspherical)

d₁₅= 16.9055

r₁₆= ∞ (eyepoint)

Aspherical coefficients

Second surface

K = −1.2947

A₄= 2.38204 × 10⁻⁵
A₆= 4.87600 × 10⁻⁷
A₈= −3.73584 × 10⁻⁹

Third surface

K = −0.2620

A₄= −1.35699 × 10⁻⁴
A₆= 4.65011 × 10⁻⁷
A₈= −1.87327 × 10⁻⁸

Fourth surface

K = −0.0225

A₄= 4.04582 × 10⁻⁵
A₆= 7.12976 × 10⁻⁸
A₈= −9.76450 × 10⁻⁹

Fifth surface

K = 0.2139

A₄= 6.19005 × 10⁻⁴
A₆= −3.14679 × 10⁻⁵
A₈= 7.58697 × 10⁻⁷

Sixth surface

K = −0.0424

A₄= 4.58626 × 10⁻⁵
A₆= −2.40512 × 10⁻⁵
A₈= 5.34729 × 10⁻⁷

Eighth surface

K = 0.1566

A₄= 2.05649 × 10⁻⁴
A₆= 2.93949 × 10⁻⁷
A₈= 2.68796 × 10⁻⁸

Ninth surface

K = 0.0143

A₄= 7.12313 × 10⁻⁶
A₆= −6.74794 × 10⁻⁷

Twelfth surface

K = 0.0000

A₄= −1.15138 × 10³
A₆= 8.42829 × 10⁻⁶

Fifteenth surface

K = 0.0000

A₄= 4.56110 × 10⁻⁵
A₆= 1.18793 × 10⁻⁷

Zoom data

Wide-angle

position
Middle position
Telephoto position

D2
11.7539
7.0573
3.4654

D4
1.2500
8.5614
16.1337

D6
8.1857
5.3729
1.0000

mh = 10.076 mm

f123
−10.700
−21.016
−43.277

m23
0.529
1.032
2.072

m2

−1.000

m3

−1.032

Condition (9) MG45
−0.743
−0.744
−0.746

Conditions (1), (7) mh/fe
= 0.671

Conditions (2), (3) fe
= 15.009 mm

Condition (8) φ (mh/2)
= −0.451821 (l/mm)

Condition (10) β3
= −1.032

Condition (11) SF2
= −0.411

Condition (12) f2/f3
= −1.625

Condition (13) fw/fFw
= −0.741

Condition (14) fT/fFT
= −0.719

Condition (15) mT/mW
= 3.925

Condition (16) fw/fw123
= −0.741

Condition (17) fT/fT123
= −0.719

Twentieth Embodiment

The real image mode finder optical system of this embodiment, as shown in FIGS. 63A–63C, has nearly the same arrangement as that of the nineteenth embodiment with the exception of lens data. A substantial difference with the nineteenth embodiment is that the exit surface of the prism P2 has a curvature in twentieth embodiment.

Subsequently, numerical data of optical members constituting the real image mode finder optical system according to the twentieth embodiment are shown below.

Numerical data 20

Wide-angle position
Middle position
Telephoto position

m
0.557
1.038
2.023

ω (°)
32.360
17.517
9.010

f (mm)
8.356
15.584
30.363

Pupil dia. (mm) 4.000

r₁= 59.2465

d₁= 1.0000
n_d1= 1.58423
ν_d1= 30.49

r₂= 8.3310 (aspherical)

d₂= D2 (variable)

r₃= 8.3856 (aspherical)

d₃= 4.1672
n_d3= 1.49241
ν_d3= 57.66

r₄= −17.8798

d₄= D4 (variable)

r₅= −13.7008

d₅= 0.7000
n_d5= 1.58423
ν_d5= 30.49

r₆= 8.6409 (aspherical)

d₆= D6 (variable)

r₇= 11.7739

d₇= 9.8661
n_d7= 1.52542
ν_d7= 55.78

r₈= −29.5195 (aspherical)

d₈= 1.0000

r₉= 15.0708

d₉= 22.3752
n_d9= 1.52542
ν_d9= 55.78

r₁₀= −416.8001

d₁₀= 2.0410

r₁₁= ∞ (field frame)

d₁₁= 2.4340

r₁₂= 15.7244 (aspherical)

d₁₂= 18.3578
n_d12= 1.52542
ν_d12= 55.78

r₁₃= −20.5538

d₁₃= 1.2739

r₁₄= 30.8079 (aspherical)

d₁₄= 3.4263
n_d14= 1.52542
ν_d14= 55.78

r₁₅= −24.2754 (aspherical)

d₁₅= 15.7651

r₁₆= ∞ (eyepoint)

Aspherical coefficients

Second surface

K = −1.3070

A₄= −5.42129 × 10⁻⁵
A₆= 2.66433 × 10⁻⁶
A₈= −1.96586 × 10⁻⁸

Third surface

K = −0.2445

A₄= −3.33944 × 10⁻⁴
A₆= 3.11379 × 10⁻⁷
A₈= −1.64750 × 10⁻⁸

Sixth surface

K = −0.0650

A₄= −5.31385 × 10⁻⁴
A₆= 4.99350 × 10⁻⁶
A₈= −6.09994 × 10⁻⁸

Eighth surface

K = 0.1673

A₄= 2.10857 × 10⁻⁴
A₆= 1.83918 × 10⁻⁷
A₈= 3.12747 × 10⁻⁸

Twelfth surface

K = 0.0000

A₄= −1.45924 × 10⁻³
A₆= 1.59291 × 10⁻⁵

Fourteenth

K = 0.0000

A₄= 7.03020 × 10⁻⁵
A₆= 4.89240 × 10⁻⁷

Fifteenth

K = 0.0000

A₄= 8.28668 × 10⁻⁵
A₆= 3.99233 × 10⁻⁷

Zoom data

Wide-angle

position
Middle position
Telephoto position

D2
11.8115
7.0078
2.9081

D4
1.0094
6.6799
14.3532

D6
7.7860
4.6744
1.0000

mh= 9.992 mm

f123
−12.274
−23.044
−46.120

m23
0.734
1.370
2.676

m2

−1.000

m3

−1.370

Condition (9) MG45
−0.683
−0.683
−0.683

Conditions (1), (7) mh/fe
= 0.666

Conditions (2), (3) fe
= 15.010 mm

Condition (8) φ (mh/2)
= −0.322195 (l/mm)

Condition (10) β3
= −1.370

Condition (11) SF2
= −0.361

Condition (12) f2/f3
= −1.364

Condition (13) fw/fFw
= −0.681

Condition (14) fT/fFT
= −0.658

Condition (15) mT/mW
= 3.634

Condition (16) fw/fw123
= −0.681

Condition (17) fT/fT123
= −0.658

Twenty-First Embodiment

In the real image mode finder optical system of this embodiment, as shown in FIGS. 64A–64C, the objective optical system includes, in order from the object side, the first unit G1 with a negative refracting power, the second unit G2 with a positive refracting power, the third unit G3 with a negative refracting power, and the fourth unit G4 with a positive refracting power, and has a positive refracting power as a whole.

The fourth unit G4 is constructed with two prisms P1 and P2. The eyepiece optical system is constructed with the prism P and the positive lens E1 and has a positive refracting power as a whole.

The image erecting means includes the prisms P1 and P2 and the prism P. In the real image mode finder optical system of the twenty-first embodiment, the intermediate image formed by the objective optical system is interposed between the prism P2 and the positive lens E1, and the field frame, such as that shown in FIG. 4, is provided in the proximity of its imaging position.

The magnification of the finder is changed in the range from the wide-angle position to the telephoto position by fixing the first unit G1 and the fourth unit G4 and by simply moving the second unit G2 toward the object side and the third unit G3 toward the eyepiece side along the optical axis.

Each of the first unit G1, the second unit G2, and the third unit G3 is constructed with a single lens. The entrance surface and the exit surface of the prism P1 and the entrance surface of the prism P2 have curvatures. The entrance surface and the exit surface of the prism P also have curvatures.

The prisms P1 and P2 and the prism P, as shown in FIGS. 65–67, are provided with reflecting surfaces P₁, P2₁, P2₂, and P₁along the optical path so that the optical axis is bent to erect an image. Specifically, as shown in FIG. 66, the reflecting surface P1₁provided in the prism P1 bends the optical axis in a Y-Z plane; as shown in FIG. 67, the two reflecting surfaces P2₁and P2₂provided in the prism P2 bend the optical axis twice in the X-Y plane in this order from the object side; and as shown in FIG. 66, the reflecting surface P₁provided in the prism P bends the optical axis in the Y-Z plane. In this way, an erect image is obtained. Also, the arrangement of the reflecting surfaces is based on that of a Porro prism. Angles made with the optical axis bent by the reflecting surfaces are 90 degrees. The reflecting surfaces P1₁, P2₁, and P2₂of the prism P1 and the prism P2 are coated with metal films, such as silver and aluminum. The reflecting surface P₁of the prism P utilizes total reflection.

However, the ways of bending the optical axis through the prisms and the angles of the optical axis bent by the reflecting surfaces are not limited to the above description. For example, the angle of the optical axis bent by one reflecting surface of the prism P2 may be made smaller than 90 degrees so that this reflecting surface is coated with a metal film. Moreover, the angle of the optical axis bent by the other reflecting surface of the prism P2 may also be made larger than 90 degrees so that this reflecting surface utilizes total reflection.

The positive lens E1 is constructed so that diopter adjustment can be made in accordance with an observer's diopter.

Subsequently, numerical data of optical members constituting the real image mode finder optical system according to the twenty-first embodiment are shown below.

Numerical data 21

Wide-angle
Middle
Telephoto

position
position
position

m
0.394
0.659
1.049

ω (°)
32.118
19.007
12.091

f (mm)
6.866
11.492
18.288

Pupil dia. (mm) 5.000

r₁= −59.3919

d₁= 1.0000
n_d1= 1.58423
υ_d1= 30.49

r₂= 10.3748 8 (aspherical)

d₂= D2 (variable)

r₃= 14.1522 (aspherical)

d₃= 3.7000
n_d3= 1.52542
υ_d3= 55.78

r₄= −9.2660 (aspherical)

d₄= D4 (variable)

r₅= −7.5095 (aspherical)

d₅= 1.0000
n_d5= 1.58425
υ_d5= 30.35

r₆= 13.7636

d₆= D6 (variable)

r₇= 20.3870

d₇= 10.0000
n_d7= 1.52542
υ_d7= 55.78

r₈= −13.4385 (aspherical)

d₈= 0.4000

r₉= 12.4702 (aspherical)

d₉= 22.0000
n_d9= 1.52542
υ_d9= 55.78

r₁₀= ∞

d₁₀= 2.0000

r₁₁= ∞ (field frame)

d₁₁= 7.9991

r₁₂= 18.8914 (aspherical)

d₁₂= 3.1688
n_d12= 1.52542
υ_d12= 55.78

r₁₃= −15.1681

d₁₃= 2.0000

r₁₄= −13.4956 (aspherical)

d₁₄= 12.2000
n_d14= 1.52542
υ_d14= 55.78

r₁₅= −10.7971 (aspherical)

d₁₅= 13.5000

r₁₆= ∞ (eyepoint)

Aspherical coefficients

Second surface

K = −1.8801

A₄= 8.93195 × 10⁻⁵
A₆= −1.59803 × 10⁻⁵
A₈= 2.26734 × 10⁻⁷

Third surface

K = −26.0761

A₄= 8.01991 × 10⁻⁴
A₆= =1.09865 × 10⁻⁴
A₈= 4.19307 × 10⁻⁶

A₁₀= −1.65929 × 10⁻⁷

Fourth surface

K = 0.7079

A₄= 1.90150 × 10⁻⁴
A₆= −3.87917 × 10⁻⁵
A₈= 8.76025 × 10⁻⁷

A₁₀= −3.24756 × 10⁻⁸

Fifth surface

K = −0.4742

A₄= 4.50016 × 10⁻⁴
A₆= 4.48738 × 10⁻⁵
A₈= −3.79556 × 10⁻⁶

Eighth surface

K = 0.8140

A₄= −1.12430 × 10⁻³
A₆= 5.37408 × 10⁻⁵
A₈= −1.01121 × 10⁻⁶

Ninth surface

K = −2.4434

A₄= −1.05938 × 10⁻³
A₆= 4.60167 × 10⁻⁵
A₈= −8.38383 × 10⁻⁷

Twelfth surface

K = 0.0000

A₄= 4.97477 × 10⁻⁴
A₆= −3.14535 × 10⁻⁵
A₈= −3.04078 × 10⁻⁸

Fourteenth surface

K = 0.0000

A₄= −8.27827 × 10⁻⁴
A₆= 5.41341 × 10⁻⁵
A₈= −6.06561 × 10⁻⁷

Fifteenth surface

K = 0.0000

A₄= −4.89807 × 10⁻⁶
A₆= 7.07749 × 10⁻⁶
A₈= −9.70475 × 10⁻⁸

Zoom data

D2
8.2666
5.9354
3.4477

D4
0.8000
5.6220
10.2589

D6
5.3399
2.8492
0.7000

mh = 8.240 mm

f123
−9.787
−16.419
−26.311

m23
0.651
1.088
1.729

m2

−1.000

m3

−1.088

Condition (9)
MG45
−0.703
−0.704
−0.705

Conditions (1), (7)
mh/fe
= 0.473

Conditions (2), (3)
fe
= 17.434 mm

Condition (10)
β3
= −1.088

Condition (11)
SF2
= 0.209

Condition (12)
f2/f3
= −1.379

Condition (13)
fw/fFw
= −0.702

Condition (14)
fT/fFT
= −0.695

Condition (15)
mT/mW
= 2.663

Condition (16)
fw/fw123
= −0.702

Condition (17)
fT/fT123
= −0.695

Twenty-Second Embodiment

In the real image mode finder optical system of this embodiment, as shown in FIGS. 68A–68C, the objective optical system includes, in order from the object side, the first unit G1 with a negative refracting power, the second unit G2 with a positive refracting power, the third unit G3 with a negative refracting power, and the fourth unit G4 with a positive refracting power, and has a positive refracting power as a whole.

The fourth unit G4 is constructed with the positive lens L1 and the prism P1. The eyepiece optical system is constructed with the prism P and the positive lens E1 and has a positive refracting power as a whole.

Each of the first unit G1, the second unit G2, and the third unit G3 is constructed with a single lens. The entrance surface of the prism P1 has a curvature. The entrance surface and the exit surface of the prism P also have curvatures. The prism P1 and the prism P are provided with reflecting surfaces along the optical path so that the optical axis is bent to obtain an erect image. For example, the prism P1 is provided with three reflecting surfaces for bending the optical axis twice in the Y-Z plane and once in the X-Z plane in this order from the object side, and the prism P is provided with one reflecting surface for bending the optical axis in the X-Z plane to erect the image. Also, the arrangement of the reflecting surfaces is based on that of a Porro prism. Angles made with the optical axis bent by the reflecting surfaces are such that, for example, the angle of the optical axis bent by one reflecting surface of the prism P1 is smaller than 90 degrees and the angles of the optical axis bent by the remaining two reflecting surfaces are larger than 90 degrees, while the angle of the optical axis bent by the reflecting surface of the prism P is smaller than 90 degrees. The reflecting surfaces making angles smaller than 90 degrees are coated with metal films, such as silver and aluminum. The reflecting surfaces of angles larger than 90 degrees utilize total reflection.

However, the angles of the optical axis bent by the reflecting surfaces are not limited to the above description. For example, the angle of the optical axis bent by the most field-frame-side reflecting surface of the prism P1 may be made smaller than 90 degrees so that this reflecting surface is coated with a metal film. Moreover, the angle of the optical axis bent by the reflecting surface of the prism P may also be made larger than 90 degrees so that this reflecting surface utilizes total reflection.

The positive lens E1 is constructed so that diopter adjustment can be made in accordance with an observer's diopter.

Subsequently, numerical data of optical members constituting the real image mode finder optical system according to the twenty-second embodiment are shown below.

Numerical data 22

Wide-angle
Middle
Telephoto

position
position
position

m
0.710
1.045
2.031

ω (°)
26.166
17.592
9.011

f (mm)
10.647
15.663
30.438

Pupil dia. (mm) 4.000

r₁= 94.9717

d₁= 0.9721
n_d1= 1.58423
υ_d1= 30.49

r₂= 9.3965 (aspherical)

d₂= D2 (variable)

r₃= 9.8091 (aspherical)

d₃= 4.2874
n_d3= 1.52542
υ_d3= 55.78

r₄= −25.4274 (aspherical)

d₄= D4 (variable)

r₅= −16.9121

d₅= 1.0000
n_d5= 1.58423
υ_d5= 30.49

r₆= 15.2040 (aspherical)

d₆= D6 (variable)

r₇= 40.9744

d₇= 3.5824
n_d7= 1.52542
υ_d7= 55.78

r₈= −14.7461 (aspherical)

d₈= 0.5000

r₉= 21.4998 (aspherical)

d₉= 28.4133
n_d9= 1.52542
υ_d9= 55.78

r₁₀= ∞

d₁₀= 1.8195

r₁₁= ∞ (field frame)

d₁₁= 2.3065

r₁₂= 15.5002 (aspherical)

d₁₂= 15.7893
n_d12= 1.52542
υ_d12= 55.78

r₁₃= −35.0088

d₁₃= 1.9666

r₁₄= 27.5692 (aspherical)

d₁₄= 5.0860
n_d14= 1.52542
υ_d14= 55.78

r₁₅= −16.2713 (aspherical)

d₁₅= 16.9035

r₁₆= ∞ (eyepoint)

Aspherical coefficients

Second surface

K = −1.2960

A₄= 2.42034 × 10⁻⁵
A₆= −4.03294 × 10⁻⁷
A₈= −3.85761 × 10⁻¹⁰

Third surface

K = −0.2523

A₄= −1.40079 × 10⁻⁴
A₆= 9.09631 × 10⁻⁸
A₈= −7.25698 × 10⁻⁹

Fourth surface

K = −0.0226

A₄= 2.34829 × 10⁻⁵
A₆= 6.60458 × 10⁻⁷
A₈= −6.09388 × 10⁻⁹

Sixth surface

K = −0.0504

A₄= −1.07083 × 10⁻⁴
A₆= 1.32744 × 10⁻⁶
A₈= −4.22406 × 10⁻⁹

Eighth surface

K = 0.1637

A₄= 5.89020 × 10⁻⁵
A₆= 2.51165 × 10⁻⁷
A₈= 1.03528 × 10⁻⁸

Ninth surface

K = 0.0039

A₄= −3.04882 × 10⁻⁶
A₆= 4.78283 × 10⁻⁷

Twelfth surface

K = 0.0000

A₄= −1.19998 × 10⁻³
A₆= 1.07234 × 10⁻⁵

Fourteenth surface

K = 0.0000

A₄= 3.35581 × 10⁻⁵
A₆= −1.60128 × 10⁻⁷

Fifteenth surface

K = 0.0000

A₄= 7.31972 × 10⁻⁵
A₆= 9.93972 × 10⁻⁹

Zoom data

D2
8.3076
6.0828
3.0961

D4
1.1490
6.5799
16.8299

D6
11.9688
8.7628
1.4995

mh = 9.844 mm

f123
−21.628
−32.011
−64.323

m23
1.204
1.771
3.458

m2

−1.328

m3

−1.333

Condition (9)
MG45
−0.495
−0.495
−0.495

Conditions (1), (7)
mh/fe
= 0.657

Conditions (2), (3)
fe
= 14.990 mm

Condition (11)
SF2
= −0.443

Condition (12)
F2/f3
= −1.038

Condition (13)
fw/fFw
= −0.492

Condition (14)
fT/fFT
= −0.473

Condition (15)
mT/mW
= 2.859

Condition (16)
fw/fw123
= −0.492

Condition (17)
fT/fT123
= −0.473

Twenty-Third Embodiment

The real image mode finder optical system of this embodiment, as shown in FIGS. 69A–69C, has nearly the same arrangement as that of the twenty-first embodiment with the exception of lens data.

Subsequently, numerical data of optical members constituting the real image mode finder optical system according to the twenty-third embodiment are shown below.

Numerical data 23

Wide-angle
Middle
Telephoto

position
position
position

m
0.574
0.905
1.568

ω (°)
24.652
15.498
8.841

f (mm)
10.617
16.725
28.996

Pupil dia. (mm) 4.000

r₁= −920.9537

d₁= 1.0000
n_d1= 1.58423
υ_d1= 30.49

r₂= 9.9330 (aspherical)

d₂= D2 (variable)

r₃= 9.6882 (aspherical)

d₃= 4.1510
n_d3= 1.52542
υ_d3= 55.78

r₄= −23.0106 (aspherical)

d₄= D4 (variable)

r₅= −14.4812 (aspherical)

d₅= 1.0000
n_d5= 1.58425
υ_d5= 30.35

r₆= 14.7812 (aspherical)

d₆= D6 (variable)

r₇= 11.6881

d₇= 10.4000
n_d7= 1.52542
υ_d7= 55.78

r₈= −44.1162 (aspherical)

d₈= 0.5000

r₉= 19.0394 (aspherical)

d₉= 21.0918
n_d9= 1.52542
υ_d9= 55.78

r₁₀= ∞

d₁₀= 2.9577

r₁₁= ∞ (field frame)

d₁₁= 8.6051

r₁₂= 18.8914 (aspherical)

d₁₂= 3.0466
n_d12= 1.52542
υ_d12= 55.78

r₁₃= −19.3762

d₁₃= 2.5000

r₁₄= 22.1615 (aspherical)

d₁₄= 14.0000
n_d14= 1.52542
υ_d14= 55.78

r₁₅= −13.1330 (aspherical)

d₁₅= 16.9541

r₁₆= ∞ (eyepoint)

Aspherical coefficients

Second surface

K = −1.2958

A₄= −1.37883 × 10⁻⁴
A₆= 3.49813 × 10⁻⁶
A₈= −2.85996 × 10⁻⁸

Third surface

K = −0.2610

A₄= −2.84178 × 10⁻⁴
A₆= 2.18425 × 10⁻⁶
A₈= 1.89724 × 10⁻⁸

Fourth surface

K = −0.0222

A₄= −3.94404 × 10⁻⁵
A₆= 2.36146 × 10⁻⁶
A₈= 1.07129 × 10⁻⁸

Fifth surface

K = 0.2136

A₄= 7.49839 × 10⁻⁴
A₆= −3.41182 × 10⁻⁵
A₈= 9.01815 × 10⁻⁷

Sixth surface

K = −0.0419

A₄= 6.33920 × 10⁻⁴
A₆= −3.96052 × 10⁻⁵
A₈= 1.13002 × 10⁻⁶

Eighth surface

K = 0.1567

A₄= 1.02994 × 10⁻⁴
A₆= 3.46598 × 10⁻⁶
A₈= 6.31270 × 10⁻⁹

Ninth surface

K = 0.0129

A₄= −6.13561 × 10⁻⁵
A₆= 1.96098 × 10⁻⁶

Twelfth surface

K = 0.0000

A₄= −1.14754 × 10⁻⁴
A₆= 2.96268 × 10⁻⁶
A₈= −4.33585 × 10⁻⁸

Fourteenth surface

K = 0.0000

A₄= −1.44350 × 10⁻⁴
A₆= −3.21946 × 10⁻⁶
A₈= 6.14512 × 10⁻⁸

Fifteenth surface

K = 0.0000

A₄= −7.32422 × 10⁻⁶
A₆= 5.88495 × 10⁻⁷
A₈= −9.09150 × 10⁻¹⁰

Zoom data

D2
8.4479
5.9380
3.5969

D4
2.3409
8.3613
16.2888

D6
10.0702
6.5597
0.9733

mh = 9.332 mm

f123
−20.012
−31.646
−56.048

m23
1.168
1.864
3.229

m2

−1.365

m3

−1.365

Condition (9)
MG45
−0.533
−0.535
−0.537

Conditions (1), (7)
mh/fe
= 0.505

Conditions (2), (3)
fe
= 18.490 mm

Condition (11)
SF2
= −0.407

Condition (12)
F2/f3
= −1.097

Condition (13)
fw/fFw
= −0.530

Condition (14)
fT/fFT
= −0.517

Condition (15)
mT/mW
= 2.731

Condition (16)
fw/fw123
= −0.530

Condition (17)
fT/fT123
= −0.517

Twenty-Fourth Embodment

In the real image mode finder optical system of this embodiment, as shown in FIGS. 70A–70C, the objective optical system includes, in order from the object side, the first unit G6 with a negative refracting power, the second unit G2 with a positive refracting power, the third unit G3 with a negative refracting power, and the fourth unit G4 with a positive refracting power, and has a positive refracting power as a whole.

The fourth unit G4 is constructed with the positive lens L1 and the prism P1. The eyepiece optical system is constructed with the positive lens E1 and the prism P and has a positive refracting power as a whole.

The image erecting means includes the prism P1 and the prism P. In the real image mode finder optical system of the twenty-fourth embodiment, the intermediate image formed by the objective optical system is interposed between the prism P1 and the positive lens E1, and the field frame, such as that shown in FIG. 4, is provided in the proximity of its imaging position.

However, the ways of bending the optical axis through the prisms and the angles of the optical axis bent by the reflecting surfaces are not limited to the above description. For example, the angle of the optical axis bent by the most field-frame-side reflecting surface of the prism P1 may be made smaller than 90 degrees so that this reflecting surface is coated with a metal film. Moreover, the angle of the optical axis bent by the second reflecting surface, from the field frame side, of the prism P1 may also be made larger than 90 degrees so that this reflecting surface utilizes total reflection.

The positive lens E1 is constructed so that diopter adjustment can be made in accordance with an observer's diopter.

Subsequently, numerical data of optical members constituting the real image mode finder optical system according to the twenty-fourth embodiment are shown below.

Numerical data 24

Wide-angle
Middle
Telephoto

position
position
position

m
0.457
0.775
1.602

ω (°)
30.208
17.858
8.701

f (mm)
8.505
14.412
29.797

Pupil dia. (mm) 4.000

r₁= 75.2465

d₁= 1.0000
n_d1= 1.58423
υ_d1= 30.49

r₂= 8.8816 (aspherical)

d₂= D2 (variable)

r₃= 10.2728 (aspherical)

d₃= 4.1473
n_d3= 1.52542
υ_d3= 55.78

r₄= −18.0037 (aspherical)

d₄= D4 (variable)

r₅= −10.0864 (aspherical)

d₅= 1.0000
n_d5= 1.58425
υ_d5= 30.35

r₆= 10.3864 (aspherical)

d₆= D6 (variable)

r₇= 19.6921

d₇= 4.3014
n_d7= 1.52542
υ_d7= 55.78

r₈= −13.1461 (aspherical)

d₈= 0.5000

r₉= 21.4624 (aspherical)

d₉= 27.5577
n_d9= 1.52542
υ_d9= 55.78

r₁₀= ∞

d₁₀= 2.1330

r₁₁= ∞ (field frame)

d₁₁= 8.3794

r₁₂= 18.8914 (aspherical)

d₁₂= 3.1249
n_d12= 1.52542
υ_d12= 55.78

r₁₃= −18.8429

d₁₃= 2.5000

r₁₄= −19.8984 (aspherical)

d₁₄= 14.0000
n_d14= 1.52542
υ_d14= 55.78

r₁₅= −12.6982 (aspherical)

d₁₅= 16.9541

r₁₆= ∞ (eyepoint)

Aspherical coefficients

Second surface

K = −1.2958

A₄= 3.44925 × 10⁻⁶
A₆= 4.20426 × 10⁻⁷
A₈= −7.66223 × 10⁻⁹

Third surface

K = −0.2616

A₄= −2.70426 × 10⁻⁴
A₆= 1.77644 × 10⁻⁶
A₈= −2.00847 × 10⁻⁷

Fourth surface

K = −0.0223

A₄= −7.38297 × 10⁻⁵
A₆= 6.70806 × 10⁻⁷
A₈= −1.54652 × 10⁻⁷

Fifth surface

K = 0.2135

A₄= 3.49998 × 10⁻⁴
A₆= −1.71207 × 10⁻⁵
A₈= 3.68862 × 10⁻⁷

Sixth surface

K = −0.0430

A₄= −1.78394 × 10⁻⁴
A₆= −7.98576 × 10⁻⁶
A₈= 1.76981 × 10⁻⁷

Eighth surface

K = 0.1579

A₄= 4.99038 × 10⁻⁶
A₆= 8.82927 × 10⁻⁷
A₈= 1.18585 × 10⁻⁸

Ninth surface

K = 0.0120

A₄= −1.28730 × 10⁻⁴
A₆= 5.21275 × 10⁻⁷

Twelfth surface

K = 0.0000

A₄= −2.49634 × 10⁻⁴
A₆= 1.72455 × 10⁻⁷
A₈= 2.31794 × 10⁻⁹

Fourteenth surface

K = 0.0000

A₄= 8.06332 × 10⁻⁶
A₆= 4.07603 × 10⁻⁷
A₈= −1.41628 × 10⁻⁸

Fifteenth surface

K = 0.0000

A₄= 3.96776 × 10⁻⁵
A₆= 5.11111 × 10⁻⁸
A₈= −1.38979 × 10⁻¹⁰

Zoom data

D2
11.4348
8.0329
4.3575

D4
1.2500
6.8862
14.8224

D6
8.1779
5.9436
1.6828

mh = 9.391 mm

f123
−10.255
−17.402
−36.720

m23
0.592
1.000
2.070

m2

−1.000

m3

−1.000

Condition (9)
MG45
−0.831
−0.834
−0.837

Conditions (1), (7)
mh/fe
= 0.505

Conditions (2), (3)
fe
= 18.603 mm

Condition (8)
φ(mh/2)
= −0.118345 (1/mm)

Condition (10)
β3
= −1.000

Condition (11)
SF2
= −0.273

Condition (12)
F2/f3
= −1.524

Condition (13)
fw/fFw
= −0.829

Condition (14)
fT/fFT
= −0.811

Condition (15)
mT/mW
= 3.503

Condition (16)
fw/fw123
= −0.829

Condition (17)
fT/fT123
= −0.811

The real image mode finder optical system according to the present invention constructed as mentoned above can be used in any of various photographing apparatuses, such as compact cameras, for example, 35 mm film cameras and APS film cameras; digital cameras using electronic image sensors, for example, CCDs and CMOS sensors; and video movies. A specific application example of this finder optical system will be described below.

FIGS. 71–73 show an example of an electromic camera incorporating the real image mode finder optical system of the present invention.

As shown in FIGS. 71–73, an electronic camera 200 includes a photographing optical system 202 having a photpgraphing optical path 201, a finder optical system 204 of the present invention having a finder optical path 203, a release button 205, a stroboscopic lamp 206, and a liquid crystal display monitor 207. When the release button 205 provided on the upper surface of the electronic camera 200 is pushd, photographing is performed through the photographing optical system 202 in association with the release button 205. An object image formed by the photographing optical system 202 falls on an image senser chip 209, such as a CCD, through various filters 208, such as an IR (infrared) cutoff filter and a low-pass filter.

The object image received by the image sensor chip 209 is displayed, as an electronic image, on the liquid crystal display monitor 207 provided on the back surface of the electronic camera 200 through a processing means 211 electrically connected with terminals 210. The processing means 211 controls a recording means 212 for recording the object image received by the image sensor chip 209 as electronic information. The recording means 212 is electrocally connected with the processing means 211. Also, the recording means 212 may be replaced with a device for writing the record in a recording medium, such as a floppy disk, a smart medium, or memory card.

Where the photographing optical system 202 is constructed as a zoom lens, the finder optical system 204 having the finder optical path 203 may use the real image mode finder optical system of any of the above embodiments. Where the photographing optical system 202 is a single focus optical system, the objective optical system in the finder optical system 204 may be replaced with a single focus objective optical system in which a photographing area can be observed.

For the image erecting means, any means which is capable of erecting an image, not to speak of the Porro prism, is satisfactory. For example, when a roof reflecting surface is used as the image erecting means so that the objective optical system includes the roof reflecting surface and one planar reflecting surface and the eyepiece optical system includes one planar reflecting surface, compactness of the entire camera can be achieved. The reflecting surfaces are not limited to planar surfaces and may be configured as curved surfaces.

Even when a photographing film is used instead of the image sensor chip 209, a compact film camera with an excellent view can be obtained.

FIGS. 74A–74C show a specific example of a photographing zoom lens used in a compact camera for a 35 mm film (the maximum image height of 21.6 mm).

The photographing zoom lens includes, in order from the object side, the first unit G1 with a positive refracting power; the second unit G2 with a negative refracting power, having an aperture stop S which is variable in aperture diameter, at the most object-side position; and the third unit G3 with a negative refracting power. When the magnification of the finder is changed in the range from the wide-angle position to the telephoto position, a space between the first unit and the second unit is continuously widened, and a space between the second unit and the third unit is contunuously narrowed, so that the first unit and the third unit are integrally constructed and the first unit, the second unit, and the third unit are continuously moved toward the object side, thereby forming the object image on a film surface.

Subsequently, numerical data of optical members constituting the photographing zoom lens are shown below. In the numerical data, f represents the focal length of the photographing zoom lens, ω represents a half angle of view, Fno represents an F-number, and bf represents a back focal distance. Other symbols are the same as those used in the numerical data of the embodiments.

Numerical data (photographing zoom lens)

Wide-angle position
Middle position
Telephoto position

f(mm)
29.31
72.87
135.00

ω (°)
28.3
16.1
9.0

Fno
4.1
6.8
11.5

bf (mm)
9.47732
31.48343
71.3185

r₁= −180.6198

d₁= 1.2001
n_d1= 1.76182
υ_d1= 26.52

r₂= 180.6198

d₂= 0.2286

r₃= 21.6168

d₃= 3.1212
n_d3= 1.49700
υ_d3= 81.54

r₄= −380.8986

d₄= D4 (variable)

r₅= ∞ (stop)

d₅= 1.0000

r₆= −16.3795

d₆= 1.0004
n_d6= 1.77250
υ_d6= 49.60

r₇= 12.8963

d₇= 3.1001
n_d7= 1.72825
υ_d7= 28.46

r₈= −134.5936

d₈= 0.4702

r₉= 31.9527

d₉= 3.3010
n_d9= 1.56016
υ_d9= 60.30

r₁₀= −24.8940 (aspherical)

d₁₀= 0.7899

r₁₁= −80.7304

d₁₁= 1.0020
n_d11= 1.80518
υ_d11= 25.43

r₁₂= 21.6465

d₁₂= 4.0740
n_d12= 1.69680
υ_d12= 55.53

r₁₃= −17.2293

d₁₃= D13 (variable)

r₁₄= −48.1099 (aspherical)

d₁₄= 0.2501
n_d14= 1.52288
υ_d14= 52.50

r₁₅= −65.5251

d₁₅= 1.3535
n_d15= 1.80610
υ_d15= 40.95

r₁₆= 47.5056

d₁₆= 0.2911

r₁₇= 41.0817

d₁₇= 3.5899
n_d17= 1.80518
υ_d17= 25.43

r₁₈= −76.4471

d₁₈= 3.8912

r₁₉= −14.7089

d₁₉= 1.6801
n_d19= 1.69680
υ_d19= 55.53

r₂₀= −488.7372

d₂₀= D20 (variable)

r₂₁= ∞ (film surface)

Aspherical coefficients

Tenth surface

K = 1.5373

A₄= 8.3473 × 10⁻⁵
A₆= 5.1702 × 10⁻⁷
A₈= −1.3021 × 10⁻⁸

A₁₀= 1.5962 × 10⁻¹⁰

Fourteenth surface

K = −18.4065

A₄= 2.4223 × 10⁻⁵
A₆= 1.3956 × 10⁻⁷
A₈= −1.8237 × 10⁻¹⁰

A₁₀= 3.9911 × 10⁻¹²

Zoom data

When an infinite object point is focused:

D4
3.6815
10.0332
14.0700

D13
11.5705
5.2188
1.1820

D20
9.4773
31.4834
71.3185

When the object point distance is 0.6 m:

D4
2.3504
8.3489
11.9918

D13
12.9016
6.9031
3.2602

D20
9.4773
31.4834
71.3185

Number	Date	Country	Kind
2000-122413	Apr 2000	JP	national
2000-127652	Apr 2000	JP	national
2000-159584	May 2000	JP	national
2000-166523	May 2000	JP	national
2000-172018	Jun 2000	JP	national

Number	Name	Date	Kind
6041193	Aoki	Mar 2000	A
6175455	Kato et al.	Jan 2001	B1
6411783	Takase et al.	Jun 2002	B2
6515797	Koyama	Feb 2003	B2
6671461	Tochigi	Dec 2003	B2
6862411	Tochigi	Mar 2005	B2
6865032	Hankawa et al.	Mar 2005	B2

Number	Date	Country
06-051201	Feb 1994	JP
08-136806	May 1996	JP
09-211547	Aug 1997	JP
10-206933	Aug 1998	JP
11-242167	Sep 1999	JP

	Number	Date	Country
Parent	10687911	Oct 2003	US
Child	11009084		US
Parent	09836391	Apr 2001	US
Child	10687911		US

Finder optical system

Information

Patent Number

Date Filed

Date Issued

Inventors

Original Assignees

Examiners

Agents

CPC

US Classifications

Field of Search

US

International Classifications

Term Extension

Abstract

Description

Claims

Priority Claims (5)

Parent Case Info

US Referenced Citations (7)

Foreign Referenced Citations (5)

Related Publications (1)

Divisions (2)