Patent Application
20130342907
This invention claims the benefit of Japanese Patent Application Nos. 2009-127260, 2009-127261, 2009-127262 and 2009-127263 which are hereby incorporated by reference.
The present invention relates to a lens system that is used for an optical apparatus such as a digital still camera.
As a focusing method for a high zoom ratio optical system, a front lens feed method for feeding a lens group disposed closest to the object (e.g. see Japanese Laid-Open Patent Publication No. H11-258504) and an internal focusing method (e.g. see Japanese Laid-Open Patent Publication No. 2004-212612) have been known.
However if focusing is attempted using the conventional front lens feed method, the support mechanism and driver mechanism of the focusing lens group tend to be large, since the large and heavy lens group that is disposed closest to the object is normally moved. The total length of the lens system also tends to increase upon focusing on an object at close distance.
If the conventional internal focusing method is used, an advantage is that the support mechanism and drive mechanism of the focusing lens group can be compact, since the focusing lens group is a second or subsequent lens group, which is lighter than the first lens group disposed closest to the object. However in the case of the internal focusing method, the focusing mechanism tends to become complicated, since focusing cannot be performed on objects at a same photographic distance with a same feed amount throughout the entire zooming range from the wide angle end state to the telephoto end state.
Further, in order to prevent a photographic error due to an image blur caused by hand motion, it is desired that the above mentioned high zoom ratio zoom lens has an image blur correction function, which corrects an image blur on the image plane by setting all or a part of one lens group, out of the lens group constituting the lens system, as a shift lens group, and shifting the shift lens group so as to have a component approximately orthogonal to the optical axis, according to a value that is output by a detection system for detecting a blur of the lens system. Generally for a shift lens group, it is preferable to select a lens group located near a diaphragm where the abaxial flux of light passes near the optical axis upon zooming, so as to minimize the performance deterioration during lens shift.
Moreover many optical systems with high zoom ratios have a vibration proof function for correcting an image blur on an image plane by decentering all or a part of one lens group, out of the lens groups constituting the lens system, as a shift lens group, in order to prevent photographic errors due to an image blur caused by hand motion. However if a lens group which moves during zooming, is decentered for the purpose of vibration proofing as in the case of a conventional optical system, the optical performance may dramatically drop, which makes it impossible to obtain good images.
It is an object of the present invention to provide a lens system, an optical apparatus and a manufacturing method which can simultaneously implement a decrease in the total length of the lens system, and simplification of the focusing mechanism by appropriately setting the arrangement of the focusing lens group.
It is another object of the present invention to provide a lens system, an optical apparatus and a manufacturing method which can shift images, having an excellent image forming performance even if the shift lens group is shifted, by appropriately setting the arrangement of the shift lens group and aperture stop.
It is still another object of the present invention to provide a lens system, an optical apparatus and a manufacturing method which can minimize the influence of decentering so as to prevent the deterioration of performance.
A first aspect of the present invention is a lens system comprising, in order from an object, a first lens group having positive refractive power, and second to fourth lens groups, wherein the first lens group includes a front portion lens group, and a rear portion lens group disposed to an image side of the front portion lens group with an air distance therebetween, and performs focusing by shifting the rear portion lens group in an optical axis direction, and the fourth lens group includes, in order from the object, a negative lens, a positive lens, a negative lens and an aperture stop, and is fixed in the optical axis direction with respect to an image plane upon zooming from a wide angle end state to a telephoto end state.
In the first aspect of the present invention, it is preferable that the fourth lens group has, in order from the object, a cemented lens of a negative lens and a positive lens, a negative lens and an aperture stop.
In the first aspect of the present invention, it is preferable that the fourth lens group has, in order from the object, a cemented lens of a negative lens having a concave surface facing the object and a positive lens having a concave surface facing the Image, a negative lens having a concave surface facing the object, and an aperture stop.
In the first aspect of the present invention, it is preferable that the fourth lens group has negative refractive power.
In the first aspect of the present invention, it is preferable that the conditional expression 1.30<ft/f1b<3.10 is satisfied, where ft denotes a focal length of the total lens system in the telephoto end state, and f1b denotes a focal length of the rear portion lens group of the first lens group.
In the first aspect of the present invention, it is preferable that the second lens group has negative refractive power.
In the first aspect of the present invention, it is preferable that the conditional expression 0.23<|f2/f4|<0.88 is satisfied, where f2 denotes a focal length of the second lens group and f4 denotes a focal length of the fourth lens group.
In the first aspect of the present invention, it is preferable that at least one of the front portion lens group and the rear portion lens group of the first lens group has positive refractive power.
In the first aspect of the present invention, it is preferable that the rear portion lens group of the first lens group has positive refractive power.
In the first aspect of the present invention, it is preferable that the conditional expression 0.90<TL/f1b<2.48 is satisfied, where TL denotes a total length of the lens system in the telephoto end state, and f1b denotes a focal length of the rear portion lens group of the first lens group.
In the first aspect of the present invention, it is preferable that the first lens group is fixed in the optical axis direction with respect to the image plane upon focusing on infinity in zooming from the wide angle end state to the telephoto end state.
In the first aspect of the present invention, it is preferable that the fourth lens group is fixed in the optical axis direction with respect to the image plane upon zooming from the wide angle end state to the telephoto end state.
In the first aspect of the present invention, it is preferable that the conditional expression 0.59<TL/ft<0.70 is satisfied, where TL denotes a total length of the lens system in the telephoto end state, and ft denotes a focal length of the total lens system in the telephoto end state.
In the first aspect of the present invention, it is preferable that the third lens group has positive refractive power.
In the first aspect of the present invention, it is preferable that the third lens group has at least one aspherical surface.
In the first aspect of the present invention, it is preferable that all or a part of the fourth lens group is shifted so as to have a component orthogonal to the optical axis.
It is preferable that the first aspect of the present invention has a fifth lens group and a sixth lens group which are disposed to an image side of the fourth lens group, wherein the first lens group has positive refractive power, the second lens group has negative refractive power, the third lens group has positive refractive power, the fourth lens group has negative refractive power, the fifth lens group has positive refractive power, and the sixth lens group has negative refractive power.
It is preferable that the first aspect of the present invention has a fifth lens group which is disposed to an image side of the fourth lens group, wherein the fifth lens group has positive refractive power.
In this case, it is preferable that the conditional expression 0.40<|f2/f5|<1.00 is satisfied, where f2 denotes a focal length of the second lens group, and f5 denotes a focal length of the fifth lens group.
It is also preferable that the fifth lens group, in order from the object, a positive lens component, a negative lens component, and a positive lens component, and the aperture stop is disposed to the object side of the fifth lens group.
It is also preferable that the fifth lens group further comprises, in order from the object, a cemented lens of a positive lens and a negative lens, and a positive lens.
It is also preferable that the fifth lens group has at least one aspherical surface.
It is also preferable that this lens system has a sixth lens group which is disposed to an image side of the fifth lens group, and the sixth lens group has negative refractive power.
An optical apparatus according to the present invention is an optical apparatus having a lens system for forming an image of an object on a predetermined image plane, wherein the lens system is the lens system according to the first aspect of the present invention.
A second aspect of the present invention is a lens system having, in order from an object, an “a” lens group having positive refractive power, a “b” lens group having negative refractive power, and a “c” lens group having positive refractive power, wherein an aperture stop is disposed between the “b” lens group and the “c” lens group, and all or a part of the “b” lens group is shifted so as to have a component orthogonal to the optical axis.
In the second aspect of the present invention, it is preferable that the “b” lens group is fixed in an optical axis direction with respect to an image plane upon zooming from a wide angle end state to a telephoto end state.
In the second aspect of the present invention, it is preferable that the aperture stop is integrated with the “b” lens group upon zooming from the wide angle end state to the telephoto end state.
In the second aspect of the present invention, it is preferable that the “b” lens group is a fourth lens group from the object side.
In the second aspect of the present invention, it is preferable that a second lens group, which is the second lens group from the object side, has negative refractive power, and the conditional expression 0.43<(−f2)/fc<1.00 is satisfied, where f2 denotes a focal length of the second lens group, and fc denotes a focal length of the “c” lens group.
In the second aspect of the present invention, it is preferable that the second lens group, which is the second lens group from the object side, has negative refractive power, and the conditional expression 0.23<(−f2)/(−fb)<0.88 is satisfied, where f2 denotes a focal length of the second lens group, and fb denotes a focal length of the “b” lens group.
In the second aspect of the present invention, it is preferable that a first lens group, which is disposed closest to the object, includes a front portion lens group, and a rear portion lens group disposed to an image side of the front portion lens group with an air distance therebetween.
In this case, it is preferable that the conditional expression 1.30<ft/f1b<3.10 is satisfied, where ft denotes a focal length of the total lens system in the telephoto end state, and f1b denotes a focal length of the rear portion lens group of the first lens group.
It is also preferable that focusing is performed by shifting the rear portion lens group of the first lens group in the optical axis direction.
An optical apparatus according to the present invention is an optical apparatus having a lens system for forming an image of an object on a predetermined image plane, wherein the lens system is the lens system according to the second aspect of the present invention.
A third aspect of the present invention is a lens system comprising, in order from an object, first to fifth lens groups, wherein the first lens group includes a front portion lens group, and a rear portion lens group disposed to an image side of the front portion lens group with an air distance therebetween, and performs focusing by shifting the rear portion lens group in an optical axis direction, and the fifth lens group includes, in order from the object, a positive lens component, a negative lens component and a positive lens component, and an aperture stop is disposed to the object side of the fifth lens group.
A fourth aspect of the present invention is a lens system comprising, in order from an object, first to fifth lens groups, wherein the first lens group is divided into at least two subgroups, a front portion lens group, which is a subgroup closest to the object our of the subgroups, has positive refractive power, and focusing is performed by shifting a rear portion lens group, which is a subgroup closest to an image out of the subgroups, in an optical axis direction, and the conditional expression 0.59<TL/ft<0.70 is satisfied, where TL denotes a total length of the lens system in a telephoto end state, and ft denotes a focal length of the total lens system in the telephoto end state.
Now configuration of a manufacturing method according to the present invention will be described.
A first manufacturing method of the present invention is a manufacturing method for a lens system which comprises, in order from an object, a first lens group having positive refractive power, and second to fourth lens groups, wherein operation is confirmed after each lens is assembled in a lens barrel so that the first lens group includes a front portion lens group, and a rear portion lens group disposed to an image side of the front portion lens group with an air distance therebetween, and performs focusing by shifting the rear portion lens group in an optical axis direction, and the fourth lens group includes, in order from the object, a negative lens, a positive lens, a negative lens and an aperture stop, and is fixed in the optical axis direction with respect to an image plane upon zooming from a wide angle end state to a telephoto end state.
In this manufacturing method, it is preferable that the fourth lens group further has, in order from the object, a cemented lens of a negative lens and a positive lens, a negative lens, and an aperture stop.
In the first manufacturing method, it is preferable that the conditional expression 1.30<ft/f1b<3.10 is satisfied, where ft denotes a focal length of the total lens system in the telephoto end state, and f1b denotes a focal length of the rear portion lens group of the first lens group.
In the first manufacturing method, it is preferable that the following conditional expression 0.23<|f2/f4|<0.88 is satisfied, where f2 denotes a focal length of the second lens group and f4 denotes a focal length of the fourth lens group.
A second manufacturing method of the present invention is a manufacturing method for a lens system which has, in order from an object, an “a” lens group having positive refractive power, a “b” lens group having negative refractive power, and a “c” lens group having positive refractive power, wherein operation is confirmed after each lens is assembled in a lens barrel so that an aperture stop is disposed between the “b” lens group and the “c” lens group, and all or a part of the “b” lens group is shifted so as to have a component orthogonal to the optical axis.
A third manufacturing method of the present invention is a manufacturing method for a lens system which comprises, in order from an object, first to fifth lens groups, wherein operation is confirmed after each lens is assembled in a lens barrel so that the first lens group includes a front portion lens group, and a rear portion lens group disposed to an image side of the front portion lens group with an air distance therebetween, and performs focusing by shifting the rear portion lens group in an optical axis direction, the fifth lens group includes, in order from the object, a positive lens component, a negative lens component, and a positive lens component, and an aperture stop is disposed to the object side of the fifth lens group.
A fourth manufacturing method of the present invention is a manufacturing method for a lens system which comprises, in order from an object, first to fifth lens groups, wherein operation is confirmed after each lens is assembled in a lens barrel so that the first lens group is divided into at least two subgroups, a front portion lens group, which is a subgroup closest to the object out of the subgroups, has positive refractive power, focusing is performed by shifting a rear portion lens group, which is a subgroup closest to an image out of the subgroups, in an optical axis direction, and the conditional expression 0.59<TL/ft>0.70 is satisfied, where TL denotes a total length of the lens system in a telephoto end state, and ft denotes a focal length of the total lens system in the telephoto end state.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only and thus are not limitative of the present invention.
A lens system according to a first embodiment group of the present invention will now be described with reference to the drawings. A lens system of the present embodiment has, in order from an object, at least a first lens group having positive refractive power and second to fourth lens groups, wherein the first lens group has a front portion lens group, and a rear portion lens group disposed to an image side of the front portion lens group with an air distance therebetween, and performs focusing by shifting the rear portion lens group in the optical axis direction, and the fourth lens group has, in order from the object, a negative lens, a positive lens, a negative lens and an aperture stop, and is fixed in the optical axis direction with respect to the image plane upon zooming from the wide angle end state to the telephoto end state.
In the case of the lens system of the present embodiment, which is comprised of a plurality of lens groups, an optical system having a high zoom ratio can be easily constructed. Since the first lens group has positive refractive power, a decrease in total length and a correction of distortion can be implemented in a balanced manner. The first lens group is divided into at least two groups, that is the front portion lens group and the rear portion lens group disposed to the image side of the front portion lens group with an air distance therebetween, and focusing is performed using the rear portion lens group, therefore the focusing mechanism can be simplified, and as a result, focusing speed can be increased. At the same time, a close distance fluctuation of spherical aberration and curvature of field due to focusing can be minimized. Further, objects in a same photographic distance can be focused on with a same feed amount throughout the entire zooming area from the wide angle end state to the telephoto end state. The fourth lens group has, in order from the object, a negative lens, a positive lens, a negative lens and an aperture lens, and is fixed in the optical axis direction with respect to the image plane upon zooming from the wide angle end state to the telephoto end state, whereby the spherical aberration and curvature of field can be corrected well. Disposing the aperture stop to the image side of the fourth lens group, like the case of the present embodiment, makes it easier to correct distortion. And disposing the diaphragm closer to a lens mount than an image blur correction mechanism can simplify the diaphragm mechanism.
In the lens system according to the present embodiment, it is preferable that the fourth lens group has, in order from the object, a cemented lens of a negative lens and a positive lens, a negative lens, and an aperture stop, in order to correct the spherical aberration and curvature of field well.
In the lens system according to the present embodiment, it is preferable that the fourth lens group has, in order from the object, a cemented lens of a negative lens having a concave surface facing the object and a positive lens having a concave surface facing the image, a negative lens having a concave surface facing the object, and an aperture stop, in order to correct the spherical aberration and curvature of field well.
In the lens system according to the present embodiment, it is preferable that the fourth lens group has negative refractive power in order to correct the spherical aberration well.
In the lens system according to the present embodiment, it is preferable that the following conditional expression (1) is satisfied, where ft denotes a focal length of the total lens system in the telephoto end state, and f1b denotes a focal length of the rear portion lens group of the first lens group.
1.30<ft/f1b<3.10 (1)
The conditional expression (1) is a conditional expression for specifying an appropriate range of the ratio of the focal length of the total lens system in the telephoto end state and the focal length of the rear portion lens group of the first lens group that is disposed closest to the image. If the upper limit of the conditional expression (1) is exceeded, the refractive power of the rear portion lens group becomes relatively high. As a result, an aberration fluctuation of the coma aberration and a curvature of field upon focusing increases, which is not desirable. If the lower limit of the conditional expression (1) is not reached, the refractive power of the rear portion lens group becomes relatively low. This is advantageous in terms of aberration correction, but increase the shift distance of the focusing lens group, which makes it difficult to balance decreasing size and increase performance. As a result, the total lens length increases, which runs against the intention of the present invention, and is therefore not desirable.
In order to ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (1) to 2.95. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (1) to 2.80. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (1) to 2.65.
In order to ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (1) to 1.50. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (1) to 1.70. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (1) to 1.90.
In the lens group according to the present embodiment, it is preferable that the second lens group has negative refractive power, in order to correct the coma aberration and curvature of field well.
In the lens system according to the present embodiment, it is preferable that the following conditional expression (2) is satisfied, where f2 denotes a focal length of the second lens group, and f4 denotes a focal length of the fourth lens group.
0.23<|f2/f4|<0.88 (2)
The conditional expression (2) is a conditional expression for specifying an appropriate range of the ratio of the focal lengths of the second lens group and the fourth lens group. If the upper limit of the conditional expression (2) is exceeded, the refractive power of the second lens group becomes relatively low, and the fluctuation of the coma aberration generated in the second lens group upon zooming increases. The refractive power of the fourth lens group becomes relatively high, and the shift distance increases upon zooming, and a fluctuation of curvature of field generated in the fourth lens group increases. As a result, it becomes difficult to suppress the deterioration of performance in the total zooming range from the wide angle end state to the telephoto end state.
If the lower limit of the conditional expression (2) is not reached, the refractive power of the second lens group becomes relatively high, and correction of coma aberration becomes insufficient. Since the second lens group cannot contribute efficiently to zooming, a high zoom ratio, about 4 times or more, cannot be secured. Further, the refractive power of the fourth lens group becomes relatively low, and spherical aberration and curvature of field, which are generated in the fourth lens group, increase excessively, which makes it difficult to achieve the object of the present invention, that is, implementing excellent optical performance.
In order to ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (2) to 0.80. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (2) to 0.75. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (2) to 0.70.
In order to ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (2) to 0.30. In order to further ensure the effect of the present invention, it is preferable to set the lower limit of the conditional expression (2) to 0.35. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (2) to 0.40.
It is preferable that the lens system according to the present embodiment has a fifth lens group which is disposed to the image side of the fourth lens group, and the following conditional expression (3) is satisfied, where f2 denotes a focal length of the second lens group, and f5 denotes a focal length of the fifth lens group.
0.40<|f2/f5|<1.00 (3)
The conditional expression (3) is a conditional expression for specifying an appropriate range of the ratio of the focal lengths of the second lens group and the fifth lens group. If the upper limit of the conditional expression (3) is exceeded, the refractive power of the second lens group becomes relatively low, and the fluctuation of the coma aberration generated in the second lens group upon zooming increases. The refractive power of the fifth lens group becomes relatively high, and the shift distance increases upon zooming, and a fluctuation of spherical aberration generated in the fifth lens group increases. As a result, it becomes difficult to suppress the deterioration of performance in the total zooming range from the wide angle end state to the telephoto end state.
If the lower limit of the conditional expression (3) is not reached, the refractive power of the second lens group becomes relatively high, and since the second lens group cannot contribute efficiently to zooming, high zoom ratio, about four times or more, cannot be secured. Further, the refractive power of the fifth lens group becomes relatively low, and spherical aberration and coma aberration, which are generated in the fifth lens group, increased excessively, which makes it difficult to achieve the objective of the present invention, that is, implementing excellent optical performance.
In order to ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (3) to 0.95. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (3) to 0.90. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (3) to 0.85.
In order to ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (3) to 0.50. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (3) to 0.55. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (3) to 0.60.
In the lens system according to the present embodiment, it is preferable that at least one of the front portion lens group and the rear portion lens group of the first lens group has positive refractive power. In order to decrease the total length and minimize the generation of distortion, it is preferable that the front portion lens group of the first lens group has positive refractive power. In order to minimize close distance fluctuation of the spherical aberration and curvature of field due to focusing, it is preferable that the rear portion lens group of the first lens group has positive refractive power.
In the lens system according to the present embodiment, it is preferable that the following conditional expression (4) is satisfied, where TL denotes a total length of the lens system in the telephoto end state, and f1b denotes a focal length of the rear portion lens group of the first lens group.
0.90<TL/f1b>2.48 (4)
The conditional expression (4) is a conditional expression for specifying an appropriate range of the ratio of the total length of the lens system and the focal length of the rear portion lens group of the first lens group which is disposed closest to the object. If the upper limit of the conditional expression (4) is exceeded, the refractive power of the rear portion lens group becomes relatively high. As a result, aberration fluctuation of coma aberration and curvature of field upon focusing increases, which is not desirable. If the lower limit of the conditional expression (4) is not reached, the refractive power of the rear portion lens group becomes relatively low. This is advantageous in terms of aberration correction, but increases the shift distance of the focusing lens group, which makes it difficult to balance decreasing size and increasing performance. As a result, the total lens length increases, which runs against the intention of the present invention, and is therefore not desirable.
In order to ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (4) to 2.20. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (4) to 1.90. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (4) to 1.75.
In order to ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (4) to 1.00. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (4) to 1.10. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (4) to 1.20.
In the lens system according to the present embodiment, it is preferable that the first lens group is fixed in the optical axis direction with respect to the image plane upon focusing on infinity in zooming from the wide angle end state to the telephoto end state in order to reduce performance deterioration due to decentering, and particularly to minimize deterioration of curvature of field and implement good optical performance.
It is preferable that the lens system according to the present embodiment has a fifth lens group and a sixth lens group which are disposed to the image side of the fourth lens group, wherein the first lens group has positive refractive power, the second lens group has negative refractive power, the third lens group has positive refractive power, the fourth lens group has negative refractive power, the fifth lens group has positive refractive power, and the sixth lens group has negative refractive power, in order to correct spherical aberration, coma aberration and curvature of field well, and implement excellent optical performance with high zoom ratio.
In the lens system according to the present embodiment, it is preferable that all or a part of the fourth lens group is shifted so as to have a component orthogonal to the optical axis, and thereby image blur on the image plane is corrected when motion blur is generated, in order to correct the image well during lens shift, and spherical aberration, sine condition and Petzval sum are corrected well. The spherical aberration and sine condition are corrected for suppressing decentering coma aberration which is generated in the center area of the screen when the shift lens group is shifted approximately orthogonal to the optical axis. The Petzval sum is corrected for suppressing curvature of field which is generated in the peripheral area of the screen when the shift lens group is shifted approximately orthogonal to the optical axis.
If the user presses a release button, which is not illustrated, the quick return mirror 3 is retracted out of the optical path, and the light from the object, which is not illustrated, collected by the camera lens 1, forms an object image on a picture element 7. Thereby the light from the object is imaged by the picture element 7, and is recorded in a memory, which is not illustrated, as the object image. In this way, the user can photograph the object by this camera CAM. The camera CAM shown in
The configuration of the digital single lens reflex camera CAM is the same for all the embodiments herein below.
Each example (Example 1 to Example 5) in the first embodiment group will now be described with reference to the drawings.
The configuration of the lens system and relative shift relationship upon zooming shown in
In each example, an aspherical surface is given by the following expression (a) where y is a height in a direction perpendicular to the optical axis, S (y) is a distance (sag amount) from a tangential plane of a vertex of each aspherical surface at height y to each aspherical surface along the optical axis, r is a radius of curvature of the reference spherical surface (paraxial radius of curvature), κ is a conical coefficient, and Cn is an aspherical coefficient of the n-th order. In each example, the aspherical coefficient C2 of the second order is 0, and description thereof is omitted. “E-n” means “×10−n”. For example, 1.234 E−05=1.234×10−5.
In each example, the values of the parameters are listed in the tables (Tables 1, 6, 11, 16 and 21). In [All Parameters] in the tables, f denotes a focal length of the total system, F. NO. denotes an F number, and 2ω denotes an angle of view. The total lens length indicates a distance from the first surface of the lens surface to the image plane I on the optical axis upon focusing on infinity. In [Lens Data], a surface number denotes a sequence of the lens surface from the object, along the light traveling direction, r denotes a radius of curvature of each lens surface, d denotes a surface distance, that is a distance from each optical surface to the next optical surface (or image plane) on the optical axis, nd denotes a refractive index at the d-line (wavelength: 587.6 nm), and vd is an Abbe number at the d-line (wavelength: 587.6 nm). “*” is attached to the surface number if the lens surface is aspherical, and a paraxial radius of curvature is shown in the column of the radius of curvature r. “0.0000” of the radius of curvature indicates a plane or aperture. The refractive index of air “1.00000” is omitted. [Lens group focal length data] shows a first surface and the focal length of each group.
In [Aspherical Data] (Tables 2, 7, 12, 17 and 22), R denotes a vertex radius of curvature, K denotes a conical coefficient, and C4 to C10 denote a value of each aspherical constant. [Variable distance data] (Tables 3, 8, 13, 18 and 23) shows variable distance upon focusing on infinity in each focal distance when the lens system is in the wide angle end state, intermediate focal length state, and telephoto end state. In [Focusing lens group shift distance] (Tables 4, 9, 14, 19 and 24), f denotes a focal length, and Δ1b denotes a shift distance of the rear portion lens group G1b upon close distance focusing (photographic distance 1.8 m) (the direction of shift to the object is defined as a positive direction). In [conditional expression correspondence value] (Tables 5, 10, 15, 20 and 25), values corresponding to the above mentioned conditional expressions (1) to (4) are shown.
“mm” is normally used for the unit of focal length, radius of curvature, surface distance and other lengths in all the parameter values herein below. However the unit is not limited to “mm”, but another appropriate unit can be used instead, since an equivalent optical performance is obtained even if an optical system is proportionally expanded or proportionally reduced.
The above description is the same for all the examples shown herein below.
Example 1 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a biconvex lens are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a biconvex lens L31, a cemented negative lens L32 in which a biconvex lens and a biconcave lens are cemented, and a positive meniscus lens L33 having a convex surface facing the object.
The fourth lens group G4 has, in order from the object, a cemented negative lens L41 in which a negative meniscus lens having a convex surface facing the object and a positive meniscus lens having a convex surface facing the object are cemented, and a negative meniscus lens L42 having a convex surface facing the object. In this example, all or a part of the fourth lens group G4 shift as a shift lens group, so as to have a component in an approximately orthogonal to the optical axis.
The fifth lens group G5 has, in order from the object, a biconvex lens L51, and a cemented positive lens L52 in which a biconvex lens and a negative meniscus lens having a convex surface facing the image are cemented.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The image plane I is formed on a picture element, which is not illustrated, and the picture element is constituted by a CCD, CMOS or the like (description on the image plane I is the same for the examples herein below).
The aperture stop S is disposed closest to the image in the fourth lens group G4, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 1 are shown in Table 1.
In Example 1, the twenty first and twenty ninth lens surfaces are aspherical. Table 2 shows the [Aspherical data].
In Example 1, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d33 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 3 shows the [Variable distance data].
Table 4 shows the [Focusing lens group shift distance] in Example 1.
Table 5 shows the [Conditional expression correspondence value] in Example 1.
In each graph showing aberrations, FNO denotes an F number, A denotes a half angle of view, and H0 denotes an object height with respect to each image height. In the graphs showing spherical aberration, a value of the F number corresponding to a maximum aperture is shown, in the graphs showing astigmatism and distortion, a maximum value of the image height is shown respectively, and in the graphs showing coma aberration, a value of each image height is shown. In the graph showing astigmatism, a solid line indicates a sagittal image surface, and a broken line indicates a meridional image surface. This description on graphs showing aberrations is the same for the other examples, for which description is omitted.
As each graph showing aberrations indicates, according to Example 1, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
Example 2 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a biconvex lens are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a biconvex lens L31, a cemented positive lens L32 in which a biconvex lens and a biconcave lens are cemented, and a positive meniscus lens L33 having a convex surface facing the object.
The fourth lens group G4 has, in order from the object, a cemented negative lens L41 in which a negative meniscus lens having a convex surface facing the object and a positive meniscus lens having a convex surface facing the object are cemented, and a negative meniscus lens L42 having a convex surface facing the object. In this example, all or a part of the fourth lens group G4 shift as a shift lens group, so as to have a component in an approximately orthogonal to the optical axis.
The fifth lens group G5 has, in order from the object, a biconvex lens L51, and a cemented positive lens L52 in which a biconvex lens and a negative meniscus lens having a convex surface facing the image are cemented.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The aperture stop S is disposed closest to the image in the fourth lens group G4, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 2 are shown in Table 6.
In Example 2, the twenty first and twenty ninth lens surfaces are aspherical. Table 7 shows the [Aspherical data].
In Example 2, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d33 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 8 shows the [Variable distance data].
Table 9 shows the [Focusing lens group shift distance] in Example 2.
Table 10 shows the [Conditional expression correspondence value] in Example 2.
As each graph showing aberrations indicates, according to Example 2, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
Example 3 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a biconvex lens are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a positive meniscus lens L31 having a convex surface facing the object, a cemented positive lens L32 in which a biconvex lens and a biconcave lens are cemented, and a positive meniscus lens L33 having a convex surface facing the object.
The fourth lens group G4 has, in order from the object, a cemented negative lens L41 in which a negative meniscus lens having a convex surface facing the object and a positive meniscus lens having a convex surface facing the object are cemented, and a negative meniscus lens L42 having a convex surface facing the object.
The fifth lens group G5 has, in order from the object, a cemented positive lens L51 in which a biconvex lens and a negative meniscus lens having a convex surface facing the image are cemented, and a biconvex lens L52.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The aperture stop S is disposed closest to the image in the fourth lens group G4, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 3 are shown in Table 11.
In Example 3, the twenty first and thirty second lens surfaces are aspherical. Table 12 shows the [Aspherical data].
In Example 3, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d33 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 13 shows the [Variable distance data].
Table 14 shows the [Focusing lens group shift distance] in Example 3.
Table 15 shows the [Conditional expression correspondence value] in Example 3.
As each graph showing aberrations indicates, according to Example 3, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
Example 4 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a biconvex lens are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a positive meniscus lens L31 having a convex surface facing the object, a cemented positive lens L32 in which a biconvex lens and a biconcave lens are cemented, and a positive meniscus lens L33 having a convex surface facing the object.
The fourth lens group G4 has, in order from the object, a cemented negative lens L41 in which a negative meniscus lens having a convex surface facing the object and a positive meniscus lens having a convex surface facing the object are cemented, and a negative meniscus lens L42 having a convex surface facing the object.
The fifth lens group G5 has, in order from the object, a cemented positive lens L51 in which a biconvex lens and a negative meniscus lens having a convex surface facing the image are cemented, and a biconvex lens L52.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The aperture stop S is disposed closest to the image in the fourth lens group G4, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 4 are shown in Table 16.
In Example 4, the twenty first and thirty second lens surfaces are aspherical. Table 17 shows the [Aspherical data].
In Example 4, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d33 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 18 shows the [Variable distance data].
Table 19 shows the [Focusing lens group shift distance] in Example 4.
Table 20 shows the [Conditional expression correspondence value] in Example 4.
As each graph showing aberrations indicates, according to Example 1, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
Example 5 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a biconvex lens are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a positive meniscus lens L31 having a convex surface facing the object, a cemented positive lens L32 in which a biconvex lens and a biconcave lens are cemented, and a positive meniscus lens L33 having a convex surface facing the object.
The fourth lens group G4 has, in order from the object, a cemented negative lens L41 in which a negative meniscus lens having a convex surface facing the object and a positive meniscus lens having a convex surface facing the object are cemented, and a negative meniscus lens L42 having a convex surface facing the object.
The fifth lens group G5 has, in order from the object, a cemented positive lens L51 in which a biconvex lens and a negative meniscus lens having a convex surface facing the image are cemented, and a biconvex lens L52.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The aperture stop S is disposed closest to the image in the fourth lens group G4, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 5 are shown in Table 21.
In Example 5, the twenty first and thirty second lens surfaces are aspherical. Table 22 shows the [Aspherical data].
In Example 5, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d33 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 23 shows the [Variable distance data]. In the table, the direction of shift to the object is defined as a positive direction.
Table 24 shows the [Focusing lens group shift distance] in Example 5. In the table, the direction of shift to the object is defined as a positive direction.
Table 25 shows the [Conditional expression correspondence value] in Example 5.
As each graph showing aberrations indicates, according to Example 5, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
As described above, according to the present embodiment, a lens system which can provide high image forming performance while simultaneously implementing a decrease in the total length of the lens system and simplification of the focusing mechanism, and an optical apparatus having this lens system and a manufacturing method thereof, can be provided.
A lens system according to a second embodiment group will now be described with reference to the drawings. A lens system of the present embodiment has, in order from an object, an “a” lens group having positive refractive power, a “b” lens group having negative refractive power, and a “c” lens group having positive refractive power, wherein an aperture stop is disposed between the “b” lens group and the “c” lens group, and all or a part of the “b” lens group is shifted so as to have a component orthogonal to the optical axis.
Having a plurality of lens groups makes it easier to construct an optical system with a high zoom ratio. Disposing the aperture stop between the “b” lens group and the “c” lens group makes it easier to correct distortion. Disposing the diaphragm in a position closer to the lens mount than the image blur correction mechanism, that is, a position closer to the image side of the “b” lens group that is a shift lens group, can simplify the diaphragm mechanism.
In the lens system according to the present embodiment, it is preferable that all or a part of the “b” lens group is shifted so as to have a component orthogonal to the optical axis, and therefore image blur on the image plane is corrected when motion blur is generated, in order to correct the image well during lens shift, and spherical aberration, sine condition and Petzval sum are corrected well. The spherical aberration and sine condition are corrected for suppressing decentering coma aberration which is generated in the center area of the screen when the shift lens group is shifted approximately orthogonal to the optical axis. The Petzval sum is corrected for suppressing curvature of field which is generated in the peripheral area of the screen when the shift lens group is shifted approximately orthogonal to the optical axis.
In the lens system according to the present embodiment, it is preferable that the “b” lens group is fixed in the optical axis direction with respect to the image plane upon zooming from the wide angle end state to the telephoto end state in order to reduce performance deterioration due to decentering, particularly to minimize deterioration of curvature of field, and implement good optical performance.
In the lens system according to the present embodiment, it is preferable that the aperture stop is integrated with the “b” lens group upon zooming from the wide angle end state to the telephoto end state, since distortion can be corrected well and disposing the aperture stop closer to the lens mount, than the image blur correction mechanism, simplifies the diaphragm mechanism.
In the lens system according to the present embodiment, it is preferable that the “b” lens group is the fourth lens group from the object side, in order to reduce performance deterioration due to decentering, particularly to minimize deterioration of the curvature of field, and implement good optical performance.
In the lens system according to the present embodiment, it is preferable that a second lens group, which is the second lens group from the object side, has negative refractive power, and the following expression (5) is satisfied, where f2 denotes a focal length of the second lens group, and fc denotes a focal length of the “c” lens group.
0.43<(−f2)/fc<1.00 (5)
The conditional expression (5) is a conditional expression for specifying an appropriate range of the ratio of the focal lengths of the second lens group and the “c” lens group. If the upper limit of the conditional expression (5) is exceeded, the refractive power of the second lens group becomes relatively low, and the fluctuation of the coma aberration generated in the second lens group upon zooming increases. The refractive power of the “c” lens group becomes relatively high, and the shift distance increases upon zooming, and a fluctuation of spherical aberration generated in the “c” lens group increases. As a result, it becomes difficult to suppress the deterioration of performance in the total zooming range from the wide angle end state to the telephoto end state.
If the lower limit of the conditional expression (5) is not reached, the refractive power of the second lens group becomes relatively high, and the second lens group cannot contribute efficiently to zooming, and as a result, a high zoom ratio, about four times or more, cannot be secured. Further, the refractive power of the “c” lens group becomes relatively low, and spherical aberration and coma aberration, which are generated in the “c” lens group, increase excessively, which makes it difficult to achieve the object of the present invention, that is, implementing excellent optical performance.
In order to ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (5) to 0.95. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (5) to 0.90. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (5) to 0.85.
In order to ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (5) to 0.50. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (5) to 0.55. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (5) to 0.60.
In the lens system according to the present embodiment, it is preferable that a second lens group, which is the second lens group from the object side, has negative refractive power, and the following conditional expression (6) is satisfied, where f2 denotes a focal length of the second lens group, and fb denotes a focal length of the “b” lens group.
0.23<(−f2)/(−fb)<0.88 (6)
The conditional expression (6) is a conditional expression for specifying an appropriate range of the ratio of the focal lengths of the second lens group and the “b” lens group. If the upper limit of the conditional expression (6) is exceeded, the refractive power of the second lens group becomes relatively low, and the fluctuation of the coma aberration generated in the second lens group upon zooming increases. The refractive power of the “b” lens group becomes relatively high, and the shift distance increases upon zooming, and a fluctuation of curvature of field generated in the “b” lens group increases. As a result, it becomes difficult to suppress the deterioration of performance in the total zooming range from the wide angle end state to the telephoto end state.
If the lower limit of the conditional expression (6) is not reached, the refractive power of the second lens group becomes relatively high, and correction of coma aberration becomes insufficient. Since the second lens group cannot contribute efficiently to zooming, a high zoom ratio, about four times or more, cannot be secured. Further, the refractive power of the “b” lens group becomes relatively low, and spherical aberration and curvature of field, which are generated in the “b” lens group, increase excessively, which makes it difficult to achieve the object of the present invention, that is, implementing excellent optical performance.
In order to ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (6) to 0.80. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (6) to 0.75. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (6) to 0.70.
In order to ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (6) to 0.30. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (6) to 0.35. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (6) to 0.40.
In the lens system according to the present embodiment, it is preferable that a first lens group, which is disposed closest to the object, has at least a front portion lens group, and a rear portion lens group disposed to an image side of the front portion lens group with an air distance therebetween, in order to correct distortion well.
In the lens system according to the present embodiment, it is preferable that the following conditional expression (7) is satisfied, where ft denotes a focal length of the total lens system in the telephoto end state, and f1b denotes a focal length of the rear portion lens group of the first lens group.
1.30<ft/f1b<3.10 (7)
The conditional expression (7) is a conditional expression for specifying an appropriate range of the ratio of the focal length of the total lens system in the telephoto end state and the focal length of the rear portion lens group of the lens group that is disposed closest to the object. If the upper limit of the conditional expression (7) is exceeded, the refractive power of the rear portion lens group becomes relatively high. As a result, an aberration fluctuation of the coma aberration and a curvature of field upon focusing increases, which is not desirable. If the lower limit of the conditional expression (7) is not reached, the refractive power of the rear portion lens group becomes relatively low. This is advantageous in terms of aberration correction, but increase the shift distance of the focusing lens group, which makes it difficult to balance decreasing size and increase performance. As a result, the total lens length increases, which runs against the intention of the present invention, and is therefore not desirable.
In order to ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (7) to 2.95. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (7) to 2.80. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (7) to 2.65.
In order to ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (7) to 1.50. In order to further ensure the effect of the present embodiment, it is more preferable to set the lower limit of the conditional expression (7) to 1.70. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (7) to 1.90.
In the lens system according to the present embodiment, it is preferable that focusing is performed by shifting the rear portion lens group of the first lens group in the optical axis direction, in order to simplify the focusing mechanism, and minimize the short distance fluctuation of the spherical aberration and curvature of field due to focusing.
In the lens system according to the present embodiment, it is preferable that at least one of the front portion lens group and the rear portion lens group of the first lens group has positive refractive power. It is preferable that the front portion lens group has positive refractive power in order to decrease the total length thereof, and minimize the generation of distortion. It is preferable that the rear portion lens group has positive refractive power in order to minimize close distance fluctuation of spherical aberration and curvature of field due to focusing.
In the lens system according to the present embodiment, it is preferable that the first lens group disposed closest to the object is fixed in the optical axis direction with respect to the image plane upon focusing on infinity in zooming from the wide angle end state to the telephoto end state in order to reduce performance deterioration due to decentering, particularly to minimize deterioration of curvature of field and implement good optical performance.
In the lens system according to the present embodiment, it is preferable that the lens system has, in order from the object, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, a fourth lens group having negative refractive power, a fifth lens group having positive refractive power, and a sixth lens group having negative refractive power, in order to correct spherical aberration, coma aberration and curvature of field well, and implement excellent optical performance with high zoom ratio.
In the lens system according to the present embodiment, it is preferable that the following conditional expression (8) is satisfied, where TL denotes a total length of the lens system in the telephoto end state, and f1b denotes a focal length of the rear portion lens group of the first lens group.
0.90<TL/f1b<2.48 (8)
The conditional expression (8) is a conditional expression for specifying an appropriate range of the ratio of the total length of the lens system and the focal length of the rear portion lens group of the first lens group. If the upper limit of the conditional expression (8) is exceeded, the refractive power of the rear portion lens group becomes relatively high. As a result, an aberration fluctuation of the coma aberration and a curvature of field upon focusing increases, which is not desirable. If the lower limit of the conditional expression (8) is not reached, the refractive power of the rear portion lens group becomes relatively low. This is advantageous in terms of aberration correction, but increase the shift distance of the focusing lens group, which makes it difficult to balance decreasing size and increase performance. As a result, the total lens length increases, which runs against the intention of the present invention, and is therefore not desirable.
In order to ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (8) to 2.20. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (8) to 1.90. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (8) to 1.75.
In order to ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (8) to 1.00. In order to further ensure the effect of the present invention, it is preferable to set the lower limit of the conditional expression (8) to 1.10. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (8) to 1.20.
Each example (Example 6 to Example 13) in the second embodiment group will now be described with reference to the drawings. For the lens systems according to these examples as well, allocation of refractive power and a shifting state of each lens group upon changing of the focal length state from the wide angle end state (W) to the telephoto end state (T) are shown in
Example 6 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a positive meniscus lens having a convex surface facing the object are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a positive meniscus lens L31 having a convex surface facing the object, a cemented negative lens L32 in which a biconvex lens and a biconcave lens are cemented, and a positive meniscus lens L33 having a convex surface facing the object.
The fourth lens group G4 has, in order from the object, a cemented negative lens L41 in which a negative meniscus lens having a convex surface facing the object and a positive meniscus lens having a convex surface facing the object are cemented, and a negative meniscus lens L42 having a convex surface facing the object. In this example, all or a part of the fourth lens group G4 shift as a shift lens group, so as to have a component in an approximately orthogonal to the optical axis.
The fifth lens group G5 has, in order from the object, a biconvex lens L51, and a cemented positive lens L52 in which a biconvex lens and a negative meniscus lens having a convex surface facing the image are cemented.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The image plane I is formed on a picture element, which is not illustrated, and the picture element is constituted by a CCD, CMOS or the like (description on the image plane I is the same for the examples herein below).
The aperture stop S is disposed between the fourth lens group G4 and the fifth lens group G5, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 6 are shown in Table 26.
In Example 6, the twenty first and twenty ninth lens surfaces are aspherical. Table 27 shows the [Aspherical data].
In Example 6, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d33 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 28 shows the [Variable distance data].
Table 29 shows the [Focusing lens group shift distance] in Example 6.
Table 30 shows the [Conditional expression correspondence value] in Example 6.
In each graph showing aberrations, FNO denotes an F number, A denotes a half angle of view, and H0 denotes an object height with respect to each image height. In the graphs showing spherical aberration, a value of the F number corresponding to a maximum aperture is shown, in the graphs showing astigmatism and distortion, a maximum value of the image height is shown respectively, and in the graphs showing coma aberration, a value of each image height is shown. In the graph showing astigmatism, a solid line indicates a sagittal image surface, and a broken line indicates a meridional image surface. This description on graphs showing aberrations is the same for the other examples, for which description is omitted.
As each graph showing aberrations indicates, according to Example 6, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
Example 7 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a biconvex lens are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a biconvex lens L31, a cemented positive lens L32 in which a biconvex lens and a biconcave lens are cemented, and a positive meniscus lens L33 having a convex surface facing the object.
The fourth lens group G4 has, in order from the object, a cemented negative lens L41 in which a negative meniscus lens having a convex surface facing the object and a positive meniscus lens having a convex surface facing the object are cemented, and a negative meniscus lens L42 having a convex surface facing the object. In this example, all or a part of the fourth lens group G4 shift as a shift lens group, so as to have a component in an approximately orthogonal to the optical axis.
The fifth lens group G5 has, in order from the object, a biconvex lens L51, and a cemented positive lens L52 in which a biconvex lens and a negative meniscus lens having a convex surface facing the image are cemented.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The aperture stop S is disposed between the fourth lens group G4 and the fifth lens group G5, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 7 are shown in Table 31.
In Example 7, the twenty first and twenty ninth lens surfaces are aspherical. Table 32 shows the [Aspherical data].
In Example 7, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d33 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 33 shows the [Variable distance data].
Table 34 shows the [Focusing lens group shift distance] in Example 7.
Table 35 shows the [Conditional expression correspondence value] in Example 7.
As each graph showing aberrations indicates, according to Example 7, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
Example 8 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a biconvex lens are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a positive meniscus lens L31 having a convex surface facing the object, a cemented positive lens L32 in which a biconvex lens and a biconcave lens are cemented, and a positive meniscus lens L33 having a convex surface facing the object.
The fourth lens group G4 has, in order from the object, a cemented negative lens L41 in which a negative meniscus lens having a convex surface facing the object and a positive meniscus lens having a convex surface facing the object are cemented, and a negative meniscus lens L42 having a convex surface facing the object. In this example, all or a part of the fourth lens group G4 shift as a shift lens group, so as to have a component in an approximately orthogonal to the optical axis.
The fifth lens group G5 has, in order from the object, a cemented positive lens L51 in which a biconvex lens and a negative meniscus lens having a convex surface facing the image are cemented, and a biconvex lens L52.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The aperture stop S is disposed between the fourth lens group G4 and the fifth lens group G5, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 8 are shown in Table 36.
In Example 8, the twenty first and thirty second lens surfaces are aspherical. Table 37 shows the [Aspherical data].
In Example 8, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d33 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 38 shows the [Variable distance data].
Table 39 shows the [Focusing lens group shift distance] in Example 8.
Table 40 shows the [Conditional expression correspondence value] in Example 8.
As each graph showing aberrations indicates, according to Example 8, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
Example 9 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a biconvex lens are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a positive meniscus lens L31 having a convex surface facing the object, a cemented positive lens L32 in which a biconvex lens and a biconcave lens are cemented, and a positive meniscus lens L33 having a convex surface facing the object.
The fourth lens group G4 has, in order from the object, a negative meniscus lens L41 having a convex surface facing the object, and a cemented negative lens L42 in which a negative meniscus lens having a convex surface facing the object and a positive meniscus lens having a convex surface facing the object are cemented. In this example, all or a part of the fourth lens group G4 shift as a shift lens group, so as to have a component in an approximately orthogonal to the optical axis.
The fifth lens group G5 has, in order from the object, a cemented positive lens L51 in which a biconvex lens and a negative meniscus lens having a convex surface facing the image are cemented, and a biconvex lens L52.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The aperture stop S is disposed between the fourth lens group G4 and the fifth lens group G5, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 9 are shown in Table 41.
In Example 9, the twenty first and thirty second lens surfaces are aspherical. Table 42 shows the [Aspherical data].
In Example 9, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d33 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 43 shows the [Variable distance data].
Table 44 shows the [Focusing lens group shift distance] in Example 9.
Table 45 shows the [Conditional expression correspondence value] in Example 9.
As each graph showing aberrations indicates, according to Example 9, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
Example 10 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a biconvex lens are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a biconvex lens L31, a cemented positive lens L32 in which a biconvex lens and a biconcave lens are cemented, and a positive meniscus lens L33 having a convex surface facing the object.
The fourth lens group G4 has, in order from the object, a negative meniscus lens L41 having a convex surface facing the object, and a cemented negative lens L42 in which a biconcave lens and a positive meniscus lens having a convex surface facing the object are cemented. In this example, all or a part of the fourth lens group G4 shift as a shift lens group, so as to have a component in an approximately orthogonal to the optical axis.
The fifth lens group G5 has, in order from the object, a cemented positive lens L51 in which a biconvex lens and a biconcave lens are cemented, and a biconvex lens L52.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The aperture stop S is disposed between the fourth lens group G4 and the fifth lens group G5, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 10 are shown in Table 46.
In Example 10, the twenty first and thirty second lens surfaces are aspherical. Table 47 shows the [Aspherical data].
In Example 10, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d33 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 48 shows the [Variable distance data].
Table 49 shows the [Focusing lens group shift distance] in Example 10.
Table 50 shows the [Conditional expression correspondence value] in Example 10.
As each graph showing aberrations indicates, according to Example 10, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
Example 11 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a biconvex lens are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a biconvex lens L31, a cemented positive lens L32 in which a biconvex lens and a biconcave lens are cemented, and a biconvex lens L33.
The fourth lens group G4 has, in order from the object, a negative meniscus lens L41 having a convex surface facing the object, and a cemented negative lens L42 in which a biconcave lens and a positive meniscus lens having a convex surface facing the object are cemented. In this example, all or a part of the fourth lens group G4 shift as a shift lens group, so as to have a component in an approximately orthogonal to the optical axis.
The fifth lens group G5 has, in order from the object, a positive meniscus lens L51 having a convex surface facing the object, a biconcave lens L52, and a biconvex lens L53.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The aperture stop S is disposed between the fourth lens group G4 and the fifth lens group G5, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 11 are shown in Table 51.
In Example 11, the twenty first and thirty third lens surfaces are aspherical. Table 52 shows the [Aspherical data].
In Example 11, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d34 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 53 shows the [Variable distance data].
Table 54 shows the [Focusing lens group shift distance] in Example 11.
Table 55 shows the [Conditional expression correspondence value] in Example 11.
As each graph showing aberrations indicates, according to Example 11, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
Example 12 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a biconvex lens are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a biconvex lens L31, a cemented positive lens L32 in which a biconvex lens and a biconcave lens are cemented, and a biconvex lens L33.
The fourth lens group G4 has, in order from the object, a negative meniscus lens L41 having a convex surface facing the object, and a cemented negative lens L42 in which a biconcave lens and a positive meniscus lens having a convex surface facing the object are cemented. In this example, all or a part of the fourth lens group G4 shift as a shift lens group, so as to have a component in an approximately orthogonal to the optical axis.
The fifth lens group G5 has, in order from the object, a biconvex lens L51, a negative meniscus lens L52 having a convex surface facing the image, and a biconvex lens L53.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The aperture stop S is disposed between the fourth lens group G4 and the fifth lens group G5, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 12 are shown in Table 56.
In Example 12, the twenty first and thirty third lens surfaces are aspherical. Table 57 shows the [Aspherical data].
In Example 12, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d34 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 58 shows the [Variable distance data].
Table 59 shows the [Focusing lens group shift distance] in Example 12.
Table 60 shows the [Conditional expression correspondence value] in Example 12.
As each graph showing aberrations indicates, according to Example 12, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
Example 13 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a biconvex lens are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a biconvex lens L31, a cemented positive lens L32 in which a biconvex lens and a biconcave lens are cemented, and a positive meniscus lens L33 having a convex surface facing the object.
The fourth lens group G4 has, in order from the object, a negative meniscus lens L41 having a convex surface facing the object, and a cemented negative lens L42 in which a biconcave lens and a positive meniscus lens having a convex surface facing the object are cemented. In this example, all or a part of the fourth lens group G4 shift as a shift lens group, so as to have a component in an approximately orthogonal to the optical axis.
The fifth lens group G5 has, in order from the object, a positive meniscus lens L51 having a convex surface facing the object, a biconcave lens L52, and a biconvex lens L53.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The aperture stop S is disposed between the fourth lens group G4 and the fifth lens group G5, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 13 are shown in Table 61.
In Example 13, the thirty third lens surface is aspherical. Table 62 shows the [Aspherical data].
In Example 13, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d34 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 63 shows the [Variable distance data].
Table 64 shows the [Focusing lens group shift distance] in Example 13.
Table 65 shows the [Conditional expression correspondence value] in Example 13.
As each graph showing aberrations indicates, according to Example 13, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
As described above, the present embodiment can provide a lens system, an optical apparatus and a manufacturing method which can shift images, having an excellent image forming performing even if the shift lens group is shifted, since the arrangement of the shift lens group and aperture stop is appropriately set.
A lens system according to a third embodiment group will now be described with reference to the drawings. A lens system of the present embodiment has, in order from an object, at least first to fifth lens groups, wherein the first lens group has a front portion lens group, and a rear portion lens group disposed to an image side of the front portion lens group with an air distance therebetween, and performs focusing by shifting the rear portion lens group in the optical axis direction, the fifth lens group has, in order from the object, a positive lens component, a negative lens component, and a positive lens component, and the aperture stop is disposed to the object side of the fifth lens group.
In the case of the lens system of the present embodiment, which is comprised of five or more lens groups, an optical system having a high zoom ratio can be easily constructed. Since the first lens group which is disposed closest to the object has a front portion lens group and the rear portion lens group disposed to the image side of the front portion lens group with an air distance therebetween, and focusing is performed using the rear portion lens group out of these two subgroups, the focusing mechanism can be simplified and a close distance fluctuation of spherical aberration and curvature of field due to focusing can be minimized. Further, objects in the same photographic distance can be focused with a same feed amount throughout the entire zooming area from the wide angle end state to the telephoto end state. The fifth lens group has, in order from the object, a positive lens component, a negative lens component, and a positive lens component, so the spherical aberration and curvature of field can be corrected well. The aperture stop is disposed to the object side of the fifth lens group, so distortion can be corrected easily. The spherical aberration and coma aberration which are generated in the fifth lens group alone can also be corrected well.
In the lens system according to the present embodiment, it is preferable that the fifth lens group has, in order from the object, a positive lens, a negative lens and a positive lens, in order to correct the spherical aberration and coma aberration well.
In the lens system according to the present embodiment, it is preferable that the fifth lens group has, in order from the object, a cemented lens of a positive lens and a negative lens, and a positive lens, in order to correct the spherical aberration and coma aberration well.
In the lens system according to the present embodiment, it is preferable that the fourth lens group is fixed in the optical axis direction with respect to the image plane upon zooming from the wide angle end state to the telephoto end state, in order to reduce performance deterioration due to decentering, particularly a drop in curvature of field.
Another lens system according to the present embodiment has, in order from the object, at least first to fifth lens groups, wherein the fourth lens group is fixed in the optical axis direction with respect to the image plane upon zooming from the wide angle end state to the telephoto end state, and the fifth lens group has at least one aspherical surface. In the case of the lens system according to the present embodiment, which is comprised of five or more lens groups, an optical system having a high zoom ratio can be easily constructed. Since the fourth lens group is fixed with respect to the image plane upon changing of the lens position from the wide angle end state to the telephoto end state, decentering is decreased. Further, a drop in performance due to decentering, particularly curvature of field, is reduced, so good performance can be implemented. Disposing at least one aspherical surface in the fifth lens group improves correction of coma aberration. Particularly a drop in performance of coma aberration due to decentering can be reduced.
In the lens system according to the present embodiment, it is preferable that the third lens group has at least one aspherical surface, in order to correct the spherical aberration and coma aberration well, and particularly to reduce a drop in performance of coma aberration due to decentering.
In the lens system according to the present embodiment, it is preferable that the aperture stop is disposed between the fourth lens group and the fifth lens group. By this configuration, distortion can be corrected well. Disposing the aperture stop closer to the lens mount than the image blur correction mechanism simplifies the diaphragm mechanism.
In the lens system according to the present embodiment, it is preferable that the aperture stop is integrated with the fourth lens group upon zooming from the wide angle end state to the telephoto end state. By this configuration, distortion can be corrected well. Disposing the aperture stop closer to the lens mount than the image blur correction mechanism simplifies the diaphragm mechanism.
In the lens system according to the present embodiment, it is preferable that the third lens group has positive refractive power, in order to correct the spherical aberration and coma aberration well.
In the lens system according to the present embodiment, it is preferable that the fourth lens group has negative refractive power, in order to correct the spherical aberration well.
In the lens system according to the present embodiment, it is preferable that the fifth lens group has positive refractive power, in order to correct coma aberration and curvature of field well.
In the lens system according to the present embodiment, it is preferable that all or a part of the fourth lens group is shifted so as to have a component orthogonal to the optical axis, and therefore image blur on the image plane is corrected when motion blur is generated, in order to correct the image well during lens shift, and spherical aberration, sine condition and Petzval sum are corrected well. The spherical aberration and sine condition are corrected for suppressing decentering coma aberration which is generated in the center area of the screen when the shift lens group is shifted approximately orthogonal to the optical axis. The Petzval sum is corrected for suppressing curvature of field which is generated in the peripheral area of the screen when the shift lens group is shifted approximately orthogonal to the optical axis.
In the lens system according to the present embodiment, it is preferable that both the second lens group and the fourth lens group have negative refractive power, and the following conditional expression (9) is satisfied, where f2 denotes a focal length of the second lens group, and f4 denotes a focal length of the fourth lens group.
0.23<(−f2)/(−f4)<0.88 (9)
The conditional expression (9) is a conditional expression for specifying an appropriate range of the ratio of the focal lengths of the second lens group and the “c” lens group. If the upper limit of the conditional expression (9) is exceeded, the refractive power of the second lens group becomes relatively low, and the fluctuation of the coma aberration generated in the second lens group upon zooming increases. The refractive power of the fourth lens group becomes relatively high, and the shift distance increases upon zooming, and a fluctuation of curvature of field generated in the fourth lens group increases. As a result, it becomes difficult to suppress the deterioration of performance in the total zooming range from the wide angle end state to the telephoto end state.
If the lower limit of the conditional expression (9) is not reached, the refractive power of the second lens group becomes relatively high, and correction of coma aberration becomes insufficient. Since the second lens group cannot contribute efficiently to zooming, a high zoom ratio, about four times or more, cannot be secured. Further, the refractive power of the fourth lens group becomes relatively low, and the spherical aberration and curvature of field, which are generated in the fourth lens group, increase excessively, which makes it difficult to achieve the object of the present invention, that is, implementing excellent optical performance.
In order to ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (9) to 0.80. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (9) to 0.75. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (9) to 0.70.
In order to ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (9) to 0.30. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (9) to 0.35. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (9) to 0.40.
In the lens system according to the present embodiment, it is preferable that the second lens group has negative refractive power, the fifth lens group has positive refractive power, and the following conditional expression (10) is satisfied, where f2 denotes a focal length of the second lens group, and f5 denotes a focal length of the fifth lens group.
0.43<(−f2)/f5<1.00 (10)
The conditional expression (10) is a conditional expression for specifying an appropriate range of the ratio of the focal lengths of the second lens group and the fifth lens group. If the upper limit of the conditional expression (10) is exceeded, the refractive power of the second lens group becomes relatively low, and the fluctuation of the coma aberration generated in the second lens group upon zooming increases. The refractive power of the fifth lens group becomes relatively high, and the shift distance increases upon zooming, and a fluctuation of spherical aberration generated in the fifth lens group increases. As a result, it becomes difficult to suppress the deterioration of performance in the total zooming range from the wide angle end state to the telephoto end state.
If the lower limit of the conditional expression (10) is not reached, the refractive power of the second lens group becomes relatively high, and since the second lens group cannot contribute efficiently to zooming, high zoom ratio, about four times or more, cannot be secured. Further, the refractive power of the fifth lens group becomes relatively low, and spherical aberration and curvature of field, which are generated in the fifth lens group, increased excessively, which makes it difficult to achieve the objective of the present invention, that is, implementing excellent optical performance.
In order to ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (10) to 0.95. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (10) to 0.90. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (10) to 0.85.
In order to ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (10) to 0.50. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (10) to 0.55. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (10) to 0.60.
In the lens system according to the present embodiment, it is preferable that the first lens group has positive refractive power in order to implement both correction of distortion and decrease in the total length of the lens system.
In the lens system according to the present embodiment, it is preferable that the first lens group has, at least a front portion lens group, and a rear portion lens group disposed to the image side of the front portion lens group with an air distance therebetween, in order to implement both correction of distortion and decrease in the total length of the lens system.
In the lens system according to the present embodiment, it is preferable that focusing is performed by shifting the rear portion lens group of the first lens group in the optical axis direction, in order to simplify the focusing mechanism and minimize the close distance fluctuation of the spherical aberration and curvature of field due to focusing.
In the lens system according to the present embodiment, it is preferable that at least one of the front portion lens group and the rear portion lens group of the first lens group has positive refractive power. It is preferable that the front portion lens group of the first lens group has positive refractive power, in order to decrease the total length thereof and minimize the generation of distortion. It is preferable that the rear portion lens group of the first lens group has positive refractive power, in order to minimize close distance fluctuation of spherical aberration and curvature of field due to focusing.
In the lens system according to the present embodiment, it is preferable that the following conditional expression (11) is satisfied, where ft denotes a focal length of the total lens system in the telephoto end state, and f1b denotes a focal length of the rear portion lens group of the first lens group.
1.30<ft/f1b<3.10 (11)
The conditional expression (11) is a conditional expression for specifying an appropriate range of the ratio of the focal length of the total lens system in the telephoto end state and the focal length of the rear portion lens group of the first lens group that is disposed closest to the image. If the upper limit of the conditional expression (11) is exceeded, the refractive power of the rear portion lens group becomes relatively high. As a result, an aberration fluctuation of the coma aberration and a curvature of field upon focusing increases, which is not desirable. If the lower limit of the conditional expression (11) is not reached, the refractive power of the rear portion lens group becomes relatively low. This is advantageous in terms of aberration correction, but increase the shift distance of the focusing lens group, which makes it difficult to balance decreasing size and increase performance. As a result, the total lens length increases, which runs against the intention of the present invention, and is therefore not desirable.
In order to ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (11) to 2.95. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (11) to 2.80. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (11) to 2.65.
In order to ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (11) to 1.50. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (11) to 1.70. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (11) to 1.90.
In the lens system according to the present embodiment, it is preferable that the following conditional expression (12) is satisfied, where TL denotes a total length of the lens system in the telephoto end state, and f1b denotes a focal length of the rear portion lens group of the first lens group.
0.90<TL/f1b<2.48 (12)
The conditional expression (12) is a conditional expression for specifying an appropriate range of the ratio of the total length of the lens system and the focal length of the rear portion lens group of the first lens group that is disposed closest to the object. If the upper limit of the conditional expression (12) is exceeded, the refractive power of the rear portion lens group becomes relatively high. As a result, an aberration fluctuation of the coma aberration and a curvature of field upon focusing increases, which is not desirable. If the lower limit of the conditional expression (12) is not reached, the refractive power of the rear portion lens group becomes relatively low. This is advantageous in terms of aberration correction, but increase the shift distance of the focusing lens group, which makes it difficult to balance decreasing size and increase performance. As a result, the total lens length increases, which runs against the intention of the present invention, and is therefore not desirable.
In order to ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (12) to 2.20. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (12) to 1.90. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (12) to 1.75.
In order to ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (12) to 1.00. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (12) to 1.10. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (12) to 1.20.
In the lens system according to the present embodiment, it is preferable that the first lens group is fixed in the optical axis direction with respect to the image plane upon focusing on infinity in zooming from the wide angle end state to the telephoto end state, in order to reduce performance deterioration due to decentering, particularly to minimize deterioration of curvature of field, and implement good optical performance.
It is preferable that the lens system according to the present embodiment further has a sixth lens group that is disposed to the image side of the fifth lens group, wherein the first lens group has positive refractive power, the second lens group has negative refractive power, the third lens group has positive refractive power, the fourth lens group has negative refractive power, the fifth lens group has positive refractive power, and the sixth lens group has negative refractive power, in order to correct spherical aberration, coma aberration and curvature of field well, and implement excellent optical performance with high zoom ratio.
It is preferable that the lens system according to the present embodiment further has a fifth lens group and a sixth lens group which are disposed to the image side of the fourth lens group, wherein the first lens group has positive refractive power, the second lens group has negative refractive power, the third lens group has positive refractive power, the fourth lens group has negative refractive power, the fifth lens group has positive refractive power, and the sixth lens group has negative refractive power, in order to correct spherical aberration, coma aberration and curvature of field well, and implement excellent optical performance with high zoom ratio.
Each example (Example 14 to Example 22) in the third embodiment group will now be described with reference to the drawings. For the lens systems according to these examples as well, allocation of refractive power and a shifting state of each lens group upon changing of the focal length state from the wide angle end state (W) to the telephoto end state (T) are shown in
Example 14 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a biconvex lens are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a positive meniscus lens L31 having a convex surface facing the object, a cemented positive lens L32 in which a biconvex lens and a biconcave lens are cemented, and a positive meniscus lens L33 having a convex surface facing the object.
The fourth lens group G4 has, in order from the object, a cemented negative lens L41 in which a negative meniscus lens having a convex surface facing the object and a positive meniscus lens having a convex surface facing the object are cemented, and a negative meniscus lens L42 having a convex surface facing the object. In this example, all or a part of the fourth lens group G4 shift as a shift lens group, so as to have a component in an approximately orthogonal to the optical axis.
The fifth lens group G5 has, in order from the object, a cemented positive lens L51 in which a biconvex lens and a negative meniscus lens having a convex surface facing the image are cemented, and a biconvex lens L52.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The image plane I is formed on a picture element, which is not illustrated, and the picture element is constituted by a CCD, CMOS or the like (description on the image plane I is the same for the examples herein below).
The aperture stop S is disposed closest to the image in the fourth lens group G4, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 14 are shown in Table 66.
In Example 14, the twenty first and thirty second lens surfaces are aspherical. Table 67 shows the [Aspherical data].
In Example 14, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d33 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 68 shows the [Variable distance data].
Table 69 shows the [Focusing lens group shift distance] in Example 14.
Table 70 shows the [Conditional expression correspondence value] in Example 14.
In each graph showing aberrations, FNO denotes an F number, A denotes a half angle of view, and H0 denotes an object height with respect to each image height. In the graphs showing spherical aberration, a value of the F number corresponding to a maximum aperture is shown, in the graphs showing astigmatism and distortion, a maximum value of the image height is shown respectively, and in the graphs showing coma aberration, a value of each image height is shown. In the graph showing astigmatism, a solid line indicates a sagittal image surface, and a broken line indicates a meridional image surface. This description on graphs showing aberrations is the same for the other examples, for which description is omitted.
As each graph showing aberrations indicates, according to Example 14, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
Example 15 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a biconvex lens are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a positive meniscus lens L31 having a convex surface facing the object, a cemented positive lens L32 in which a biconvex lens and a biconcave lens are cemented, and a positive meniscus lens L33 having a convex surface facing the object.
The fourth lens group G4 has, in order from the object, a cemented negative lens L41 in which a negative meniscus lens having a convex surface facing the object and a positive meniscus lens having a convex surface facing the object are cemented, and a negative meniscus lens L42 having a convex surface facing the object. In this example, all or a part of the fourth lens group G4 shift as a shift lens group, so as to have a component in an approximately orthogonal to the optical axis.
The fifth lens group G5 has, in order from the object, a cemented positive lens L51 in which a biconvex lens and a negative meniscus lens having a convex surface facing the image are cemented, and a biconvex lens L52.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The aperture stop S is disposed closest to the image in the fourth lens group G4, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 15 are shown in Table 71.
In Example 15, the twenty first and thirty second lens surfaces are aspherical. Table 72 shows the [Aspherical data].
In Example 15, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d33 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 73 shows the [Variable distance data].
Table 74 shows the [Focusing lens group shift distance] in Example 15.
Table 75 shows the [Conditional expression correspondence value] in Example 15.
As each graph showing aberrations indicates, according to Example 15, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
Example 16 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a biconvex lens are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a positive meniscus lens L31 having a convex surface facing the object, a cemented positive lens L32 in which a biconvex lens and a biconcave lens are cemented, and a positive meniscus lens L33 having a convex surface facing the object.
The fourth lens group G4 has, in order from the object, a negative meniscus lens L41 having a convex surface facing the object, and a cemented negative lens L42 in which a negative meniscus lens having a convex surface facing the object and a positive meniscus lens having a convex surface facing the object are cemented.
The fifth lens group G5 has, in order from the object, a cemented positive lens L51 in which a biconvex lens and a negative meniscus lens having a convex surface facing the image are cemented, and a biconvex lens L52.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The aperture stop S is disposed closest to the image in the fourth lens group G4, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 16 are shown in Table 76.
In Example 16, the twenty first and thirty second lens surfaces are aspherical. Table 77 shows the [Aspherical data].
In Example 16, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d33 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 78 shows the [Variable distance data].
Table 79 shows the [Focusing lens group shift distance] in Example 16.
Table 80 shows the [Conditional expression correspondence value] in Example 16.
As each graph showing aberrations indicates, according to Example 16, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
Example 17 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a biconvex lens are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a biconvex lens L31, a cemented positive lens L32 in which a biconvex lens and a biconcave lens are cemented, and a positive meniscus lens L33 having a convex surface facing the object.
The fourth lens group G4 has, in order from the object, a cemented negative lens L41 in which a negative meniscus lens having a convex surface facing the object and a positive meniscus lens having a convex surface facing the object are cemented, and a negative meniscus lens L42 having a convex surface facing the object. In this example, all or a part of the fourth lens group G4 shift as a shift lens group, so as to have a component in an approximately orthogonal to the optical axis.
The fourth lens group G4 has, in order from the object, a negative meniscus lens L41 having a convex surface facing the object, and a cemented negative lens L42 in which a biconcave lens and a positive meniscus lens having a convex surface facing the object are cemented.
The fifth lens group G5 has, in order from the object, a cemented positive lens L51 in which a biconvex lens and a biconcave lens are cemented, and a biconvex lens L52.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The aperture stop S is disposed closest to the image in the fourth lens group G4, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 17 are shown in Table 81.
In Example 17, the twenty first and thirty second lens surfaces are aspherical. Table 82 shows the [Aspherical data].
In Example 17, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d33 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 83 shows the [Variable distance data].
Table 84 shows the [Focusing lens group shift distance] in Example 17.
Table 85 shows the [Conditional expression correspondence value] in Example 17.
As each graph showing aberrations indicates, according to Example 17, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
Example 18 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a biconvex lens are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a biconvex lens L31, a cemented positive lens L32 in which a biconvex lens and a biconcave lens are cemented, and a biconvex lens L33.
The fourth lens group G4 has, in order from the object, a negative meniscus lens L41 having a convex surface facing the object, and a cemented negative lens L42 in which a biconcave lens and a positive meniscus lens having a convex surface facing the object are cemented.
The fifth lens group G5 has, in order from the object, a positive meniscus lens L51 having a convex surface facing the object, a biconcave lens L52, and a biconvex lens L53.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The aperture stop S is disposed closest to the image in the fourth lens group G4, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 18 are shown in Table 86.
In Example 18, the twenty first and thirty third lens surfaces are aspherical. Table 87 shows the [Aspherical data].
In Example 18, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d34 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 88 shows the [Variable distance data].
Table 89 shows the [Focusing lens group shift distance] in Example 18.
Table 90 shows the [Conditional expression correspondence value] in Example 18.
As each graph showing aberrations indicates, according to Example 18, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
Example 19 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a biconvex lens are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a biconvex lens L31, a cemented positive lens L32 in which a biconvex lens and a biconcave lens are cemented, and a biconvex lens L33.
The fourth lens group G4 has, in order from the object, a negative meniscus lens L41 having a convex surface facing the object, and a cemented negative lens L42 in which a biconcave lens and a positive meniscus lens having a convex surface facing the object are cemented.
The fifth lens group G5 has, in order from the object, a biconvex lens L51, a negative meniscus lens L52 having a convex surface facing the image, and a biconvex lens L53.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The aperture stop S is disposed closest to the image in the fourth lens group G4, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 19 are shown in Table 91.
In Example 19, the twenty first and thirty third lens surfaces are aspherical. Table 92 shows the [Aspherical data].
In Example 19, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d34 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 93 shows the [Variable distance data].
Table 94 shows the [Focusing lens group shift distance] in Example 19. In the table, the direction of shift to the object is defined as a positive direction.
Table 95 shows the [Conditional expression correspondence value] in Example 19.
As each graph showing aberrations indicates, according to Example 19, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
Example 20 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a biconvex lens are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a biconvex lens L31, a cemented positive lens L32 in which a biconvex lens and a biconcave lens are cemented, and a positive meniscus lens L33 having a convex surface facing the object.
The fourth lens group G4 has, in order from the object, a cemented negative lens L41 in which a negative meniscus lens having a convex surface facing the object and a positive meniscus lens having a convex surface facing the object are cemented, and a negative meniscus lens L42 having a convex surface facing the object. In this example, all or a part of the fourth lens group G4 shift as a shift lens group, so as to have a component in an approximately orthogonal to the optical axis.
The fourth lens group G4 has, in order from the object, a negative meniscus lens L41 having a convex surface facing the object, and a cemented negative lens L42 in which a biconcave lens and a positive meniscus lens having a convex surface facing the object are cemented.
The fifth lens group G5 has, in order from the object, a positive meniscus lens L51 having a convex surface facing the object, a biconcave lens L52, and a biconvex lens L53.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The aperture stop S is disposed closest to the image in the fourth lens group G4, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 20 are shown in Table 96.
In Example 20, the thirty third lens surface is aspherical. Table 97 shows the [Aspherical data].
In Example 20, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d34 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 98 shows the [Variable distance data].
Table 99 shows the [Focusing lens group shift distance] in Example 20. In the table, the direction of shift to the object is defined as a positive direction.
Table 100 shows the [Conditional expression correspondence value] in Example 20.
As each graph showing aberrations indicates, according to Example 20, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
Example 21 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a biconvex lens are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a biconvex lens L31, a cemented positive lens L32 in which a biconvex lens and a biconcave lens are cemented, and a positive meniscus lens L33 having a convex surface facing the object.
The fourth lens group G4 has, in order from the object, a cemented negative lens L41 in which a negative meniscus lens having a convex surface facing the object and a positive meniscus lens having a convex surface facing the object are cemented, and a negative meniscus lens L42 having a convex surface facing the object. In this example, all or a part of the fourth lens group G4 shift as a shift lens group, so as to have a component in an approximately orthogonal to the optical axis.
The fourth lens group G4 has, in order from the object, a cemented negative lens L41 in which a negative meniscus lens having a convex surface facing the object and a positive meniscus lens having a convex surface facing the object are cemented, and a negative meniscus lens L42 having a convex surface facing the object. In this example, all or a part of the fourth lens group G4 shift as a shift lens group, so as to have a component in an approximately orthogonal to the optical axis.
The fifth lens group G5 has, in order from the object, a biconvex lens L51, and a cemented positive lens L52 in which a biconvex lens and a negative meniscus lens having a convex surface facing the image are cemented.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The aperture stop S is disposed closest to the image in the fourth lens group G4, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 21 are shown in Table 101.
In Example 21, the twenty first and twenty ninth lens surfaces are aspherical. Table 102 shows the [Aspherical data].
In Example 21, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d33 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 103 shows the [Variable distance data].
Table 104 shows the [Focusing lens group shift distance] in Example 21.
Table 105 shows the [Conditional expression correspondence value] in Example 21.
As each graph showing aberrations indicates, according to Example 21, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
Example 22 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a positive meniscus lens having a convex surface facing the object are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a biconvex lens L31, a cemented positive lens L32 in which a positive meniscus lens having a convex surface facing the object and a negative meniscus lens having a convex surface facing the object are cemented, and a biconvex lens L33.
The fourth lens group G4 has, in order from the object, a negative meniscus lens L41 having a convex surface facing the object, and a cemented negative lens L42 in which a biconcave lens and a positive meniscus lens having a convex surface facing the object are cemented.
The fifth lens group G5 has, in order from the object, a positive meniscus lens L51 having a convex surface facing the object, a negative meniscus lens L52 having a convex surface facing the object, and a biconvex lens L53.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The aperture stop S is disposed closest to the image in the fourth lens group G4, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 22 are shown in Table 106.
In Example 22, the sixteenth and twenty ninth lens surfaces are aspherical. Table 107 shows the [Aspherical data].
In Example 22, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d34 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 108 shows the [Variable distance data].
Table 109 shows the [Focusing lens group shift distance] in Example 22.
Table 110 shows the [Conditional expression correspondence value] in Example 22.
As each graph showing aberrations indicates, according to Example 22, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
As described above, according to the present embodiment, a lens system which can achieve high image forming performance while simultaneously implementing a decrease in the total length of the lens system and simplification of the focusing mechanism, an optical apparatus having this lens system, and a manufacturing method thereof, can be provided. At the same time, a lens system, an optical apparatus and a manufacturing method which can minimize the influence of decentering, so as to prevent the deterioration of performance, can be provided.
A lens system according to the fourth embodiment group will now be described with reference to the drawings. A lens system of the present embodiment has, in order from an object, at least first to fifth lens groups, wherein the first lens group disposed closest to the object is divided into at least two subgroups, a front portion lens group, which is a subgroup closest to the object side out of the subgroups, has positive refractive power, and focusing is performed by shifting a rear portion lens group, which is a subgroup closest to an image out of the subgroups.
In the case of the lens system of the present embodiment, which is comprised of five or more lens groups, an optical system having a high zoom ratio can be easily constructed. Since the first lens group which is disposed closest to the object is divided into at least two subgroups and the front portion lens group, which is a subgroup closest to the object, has positive refractive power, a decrease in the total length of the lens system and correction of distortion can be balanced. Further, focusing is performed using the rear portion lens group, which is a subgroup closest to the image, so the focusing mechanism can be simplified, and as a result, the focusing speed can be increased. At the same time, close distance fluctuation of spherical aberration and curvature of field due to focusing can be minimized. Also objects in a same photographic distance can be focused on with a same feed amount throughout the entire zooming area from the wide angle end state to the telephoto end state.
In the lens system of the present embodiment having the above configuration, the following conditional expression (13) is satisfied, where TL denotes a total length of the lens system in the telephoto end state, and ft denotes a focal length of the total lens system in the telephoto end state.
0.59<TL/ft<0.70 (13)
The conditional expression (13) is a conditional expression for specifying an appropriate range of the ratio of the total length of the lens system and the focal length of the total lens system in the telephoto end state. If the upper limit of the conditional expression (13) is exceeded, this is advantageous in terms of aberration correction (mainly spherical aberration and coma aberration), but the total length of the lens system increases, which makes it difficult to balance decreasing size and increasing performance. If the lower limit of the conditional expression (13) is not reached, this is advantageous in terms of decreasing size, but spherical aberration, coma aberration and curvature of field, which are generated in the lens system, cannot be corrected well, which is not desirable. It also becomes difficult to increase the back focus.
In order to ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (13) to 0.69. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (13) to 0.68. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (13) to 0.67.
In order to ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (13) to 0.60. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (13) to 0.61. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (13) to 0.62.
In the lens system according to the present embodiment, it is preferable that the first lens group has positive refractive power, in order to implement both correction of distortion and decreasing the total length.
In the lens system according to the present embodiment, it is preferable that the rear portion lens group of the first lens group has positive refractive power, in order to minimize the close distance fluctuation of the spherical aberration and curvature of field due to focusing.
In the lens system according to the present embodiment, it is preferable that the first lens group is fixed in the optical axis direction with respect to the image plane upon focusing on infinity in zooming from the wide angle end state to the telephoto end state, in order to reduce performance deterioration due to decentering, particularly to minimize deterioration of curvature of field, and implement good optical performance.
In the lens system according to the present embodiment, it is preferable that the following conditional expression (14) is satisfied, where ft denotes a focal length of the total lens system in the telephoto end state, and f1b denotes a focal length of the rear portion lens group of the first lens group.
0.10<ft/f1b<3.74 (14)
The conditional expression (14) is a conditional expression for specifying an appropriate range of the ratio of the focal length of the total lens system in the telephoto end state and the focal length of the rear portion lens group of the first lens group. If the upper limit of the conditional expression (14) is exceeded, the refractive power of the rear portion lens group becomes relatively high. As a result, an aberration fluctuation of the coma aberration and a curvature of field upon focusing increases, which is not desirable. If the lower limit of the conditional expression (14) is not reached, the refractive power of the rear portion lens group becomes relatively low. This is advantageous in terms of aberration correction, but increase the shift distance of the focusing lens group, which makes it difficult to balance decreasing size and increase performance. As a result, the total lens length increases, which runs against the intention of the present invention, and is therefore not desirable.
In order to ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (14) to 3.40. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (14) to 3.10. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (14) to 2.80.
In order to ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (14) to 0.35. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (14) to 0.65. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (14) to 0.95.
In the lens system according to the present embodiment, it is preferable that the following conditional expression (15) is satisfied, where TL denotes a total length of the lens system in the telephoto end state, and f1b denotes a focal length of the rear portion lens group of the first lens group.
0.03<TL/f1b<2.48 (15)
The conditional expression (15) is a conditional expression for specifying an appropriate range of the ratio of the total length of the lens system and the focal length of the rear portion lens group of the first lens group. If the upper limit of the conditional expression (15) is exceeded, the refractive power of the rear portion lens group becomes relatively high. As a result, an aberration fluctuation of the coma aberration and a curvature of field upon focusing increases, which is not desirable. If the lower limit of the conditional expression (15) is not reached, the refractive power of the rear portion lens group becomes relatively low. This is advantageous in terms of aberration correction, but increase the shift distance of the focusing lens group, which makes it difficult to balance decreasing size and increase performance. As a result, the total lens length increases, which runs against the intention of the present invention, and is therefore not desirable.
In order to ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (15) to 2.20. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (15) to 1.90. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (15) to 1.75.
In order to ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (15) to 0.20. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (15) to 0.45. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (15) to 0.70.
In the lens system according to the present embodiment, it is preferable that the second lens group has negative refractive power, in order to correct coma aberration and curvature of field well.
In the lens system according to the present embodiment, it is preferable that the following conditional expression (16) is satisfied, where f2 denotes a focal length of the second lens group, and f4 denotes a focal length of the fourth lens group.
0.23<|f2/f4|<0.88 (16)
The conditional expression (16) is a conditional expression for specifying an appropriate range of the ratio of the focal lengths of the second lens group and the fourth lens group. If the upper limit of the conditional expression (16) is exceeded, the refractive power of the second lens group becomes relatively low, and correction of coma aberration becomes insufficient. Since the second lens group cannot contribute efficiently to zooming, a high zoom ratio, about four times or more, cannot be secured. Further, the refractive power of the fourth lens group becomes relatively high, and spherical aberration and curvature of field, which are generated in the fourth lens group, increase excessively, which makes it difficult to achieve the object of the present invention, that is, implementing excellent optical performance.
If the lower limit of the conditional expression (16) is not reached, the refractive power of the second lens group becomes relatively high, and fluctuation of coma aberration generated in the second lens group upon zooming increases. Also the refractive power of the fourth lens group becomes relatively low, and shift distance upon zooming increases, and fluctuation of curvature of field generated in the fourth lens group increases. As a result, it becomes difficult to suppress the deterioration of performance in the total zoom range from the wide angle end state to the telephoto end state.
In order to ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (16) to 0.80. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (16) to 0.75. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (16) to 0.70.
In order to ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (16) to 0.30. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (16) to 0.35. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (16) to 0.40.
In the lens system according to the present embodiment, it is preferable that the following conditional expression (17) is satisfied, where f2 denotes a focal length of the second lens group, and f5 denotes a focal length of the fifth lens group.
0.40<|f2/f5|<1.00 (17)
The conditional expression (17) is a conditional expression for specifying an appropriate range of the ratio of the focal lengths of the second lens group and the fifth lens group. If the upper limit of the conditional expression (17) is exceeded, the refractive power of the second lens group becomes relatively low, and since the second lens group cannot contribute efficiently to zooming, the zoom ratio, about four times or more, cannot be secured. Further, the refractive power of the fifth lens group becomes relatively high, and spherical aberration and coma aberration, which are generated in the fifth lens group, increase excessively, which makes it difficult to achieve the object of the present invention, that is, implementing excellent optical performance.
If the lower limit of the conditional expression (17) is not reached, the refractive power of the second lens group becomes relatively high, and fluctuation of coma aberration generated in the second lens group upon zooming increases. Also the refractive power of the fifth lens group becomes relatively low, and shift distance upon zooming increases, and fluctuation of spherical aberration generated in the fifth lens group increases. As a result, it becomes difficult to suppress the deterioration of performance in the total zoom range from the wide angle end state to the telephoto end state.
In order to ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (17) to 0.95. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (17) to 0.90. In order to further ensure the effect of the present embodiment, it is preferable to set the upper limit of the conditional expression (17) to 0.85.
In order to ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (17) to 0.50. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (17) to 0.55. In order to further ensure the effect of the present embodiment, it is preferable to set the lower limit of the conditional expression (17) to 0.60.
In the lens system according to the present embodiment, it is preferable that the fourth lens group is fixed in the optical axis direction with respect to the image plane upon zooming from the wide angle end state to the telephoto end state in order to reduce performance deterioration due to decentering, particularly to minimize deterioration of curvature of field, and implement good optical performance.
It is preferable that the lens system according to the present embodiment has, in order from the object, a first lens group having positive refractive power, a second lens group having negative refractive power, a third lens group having positive refractive power, a fourth lens group having negative refractive power, and a fifth lens group having positive refractive power, in order to correct spherical aberration, coma aberration and curvature of field well, and implement excellent optical performance with high zoom ratio.
It is preferable that the lens system according to the present embodiment has a sixth lens group having negative refractive power, which is disposed to the image side of the fifth lens group, in order to correct spherical aberration, coma aberration and curvature of field well, and implement excellent optical performance with high zoom ratio.
Each example (Example 23 to Example 27) in the fourth embodiment group will now be described with reference to the drawings. For the lens systems according to these examples as well, allocation of refractive power and a shifting state of each lens group upon changing of the focal length state from the wide angle end state (W) to the telephoto end state (T) are shown in
Example 23 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a positive meniscus lens having a convex surface facing the object are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a biconvex lens L31, a cemented negative lens L32 in which a positive meniscus lens having a convex surface facing the object and a negative meniscus lens having a convex surface facing the object are cemented, and a biconvex lens L33.
The fourth lens group G4 has, in order from the object, a negative meniscus lens L41 having a convex surface facing the object, and a cemented negative lens L42 in which a biconcave lens and a positive meniscus lens having a convex surface facing the object are cemented. In this example, all or a part of the fourth lens group G4 shift as a shift lens group, so as to have a component in an approximately orthogonal to the optical axis.
The fifth lens group G5 has, in order from the object, a positive meniscus lens L51 having a convex surface facing the object, a negative meniscus lens L52 having a convex surface facing the object, and a biconvex lens L53.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The image plane I is formed on a picture element, which is not illustrated, and the picture element is constituted by a CCD, CMOS or the like (description on the image plane I is the same for the examples herein below).
The aperture stop S is disposed closest to the image in the fourth lens group G4, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 23 are shown in Table 111.
In Example 23, the sixteenth and thirty third lens surfaces are aspherical. Table 112 shows the [Aspherical data].
In Example 23, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d34 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 113 shows the [Variable distance data].
Table 114 shows the [Focusing lens group shift distance] in Example 23.
Table 115 shows the [Conditional expression correspondence value] in Example 23.
In each graph showing aberrations, FNO denotes an F number, A denotes a half angle of view, and H0 denotes an object height with respect to each image height. In the graphs showing spherical aberration, a value of the F number corresponding to a maximum aperture is shown, in the graphs showing astigmatism and distortion, a maximum value of the image height is shown respectively, and in the graphs showing coma aberration, a value of each image height is shown. In the graph showing astigmatism, a solid line indicates a sagittal image surface, and a broken line indicates a meridional image surface. This description on graphs showing aberrations is the same for the other examples, for which description is omitted.
As each graph showing aberrations indicates, according to Example 23, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
Example 24 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a biconvex lens are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a biconvex lens L31, a cemented positive lens L32 in which a biconvex lens and a biconcave lens are cemented, and a biconvex lens L33.
The fourth lens group G4 has, in order from the object, a negative meniscus lens L41 having a convex surface facing the object, and a cemented negative lens L42 in which a biconcave lens and a positive meniscus lens having a convex surface facing the object are cemented.
The fifth lens group G5 has, in order from the object, a positive meniscus lens L51 having a convex surface facing the object, a negative meniscus lens L52 having a convex surface facing the object, and a biconvex lens L53.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The aperture stop S is disposed closest to the image in the fourth lens group G4, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 24 are shown in Table 116.
In Example 24, the twenty ninth lens surface is aspherical. Table 117 shows the [Aspherical data].
In Example 24, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d34 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 118 shows the [Variable distance data].
Table 119 shows the [Focusing lens group shift distance] in Example 24.
Table 120 shows the [Conditional expression correspondence value] in Example 24.
As each graph showing aberrations indicates, according to Example 24, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
Example 25 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a biconvex lens are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a biconvex lens L31, a cemented positive lens L32 in which a biconvex lens and a biconcave lens are cemented, and a biconvex lens L33.
The fourth lens group G4 has, in order from the object, a negative meniscus lens L41 having a convex surface facing the object, and a cemented negative lens L42 in which a biconcave lens and a positive meniscus lens having a convex surface facing the object are cemented.
The fifth lens group G5 has, in order from the object, a positive meniscus lens L51 having a convex surface facing the object, a negative meniscus lens L52 having a convex surface facing the object, and a biconvex lens L53.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The aperture stop S is disposed closest to the image in the fourth lens group G4, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 25 are shown in Table 121.
In Example 25, the twenty ninth lens surface is aspherical. Table 122 shows the [Aspherical data].
In Example 25, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d34 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 123 shows the [Variable distance data].
Table 124 shows the [Focusing lens group shift distance] in Example 25.
Table 125 shows the [Conditional expression correspondence value] in Example 25.
As each graph showing aberrations indicates, according to Example 25, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
Example 26 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a biconvex lens are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a biconvex lens L31, a cemented positive lens L32 in which a biconvex lens and a biconcave lens are cemented, and a positive meniscus lens L33 having a convex surface facing the object.
The fourth lens group G4 has, in order from the object, a negative meniscus lens L41 having a convex surface facing the object, and a cemented negative lens L42 in which a biconcave lens and a positive meniscus lens having a convex surface facing the object are cemented.
The fifth lens group G5 has, in order from the object, a positive meniscus lens L51 having a convex surface facing the object, a negative meniscus lens L52 having a convex surface facing the object, and a biconvex lens L53.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The aperture stop S is disposed closest to the image in the fourth lens group G4, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 26 are shown in Table 126.
In Example 26, the twenty ninth lens surface is aspherical. Table 127 shows the [Aspherical data].
In Example 26, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d34 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 128 shows the [Variable distance data].
Table 129 shows the [Focusing lens group shift distance] in Example 26.
Table 130 shows the [Conditional expression correspondence value] in Example 26.
As each graph showing aberrations indicates, according to Example 26, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
Example 27 will now be described with reference to
The second lens group G2 has, in order from the object, a negative meniscus lens L21 having a convex surface facing the object, a cemented negative lens L22 in which a biconcave lens and a positive meniscus lens having a convex surface facing the object are cemented, and a biconcave lens L23.
The third lens group G3 has, in order from the object, a biconvex lens L31, a cemented positive lens L32 in which a biconvex lens and a biconcave lens are cemented, and a positive meniscus lens L33 having a convex surface facing the object.
The fourth lens group G4 has, in order from the object, a negative meniscus lens L41 having a convex surface facing the object, and a cemented negative lens L42 in which a biconcave lens and a positive meniscus lens having a convex surface facing the object are cemented.
The fifth lens group G5 has, in order from the object, a positive meniscus lens L51 having a convex surface facing the object, a negative meniscus lens L52 having a convex surface facing the object, and a biconvex lens L53.
The sixth lens group G6 has, in order from the object, a cemented negative lens L61 in which a biconcave lens and a biconvex lens are cemented.
The aperture stop S is disposed closest to the image in the fourth lens group G4, and is fixed with respect to the image plane I upon zooming from the wide angle end state to the telephoto end state.
Parameter values of Example 131 are shown in Table 27.
In Example 27, the twenty ninth lens surface is aspherical. Table 132 shows the [Aspherical data].
In Example 27, the axial air distance d5 between the front portion lens group G1a and the rear portion lens group G1b, the axial air distance d8 between the first lens group G1 and the second lens group G2, the axial air distance d15 between the second lens group G2 and the third lens group G3, the axial air distance d22 between the third lens group G3 and the fourth lens group G4, the axial air distance d28 between the fourth lens group G4 and the fifth lens group G5, the axial air distance d34 between the fifth lens group G5 and the sixth lens group G6, and the back focus Bf, change upon zooming. Table 133 shows the [Variable distance data].
Table 134 shows the [Focusing lens group shift distance] in Example 27.
Table 135 shows the [Conditional expression correspondence value] in Example 27.
As each graph showing aberrations indicates, according to Example 27, various aberrations are corrected well in each focal length state, from the wide angle end state to the telephoto end state, implementing excellent image forming performance.
Now a manufacturing method for the lens system with the Above configuration will be described with reference to
First a manufacturing method for the lens system according to the first embodiment group will be described with reference to
Now a manufacturing method for the lens system according to the second embodiment group will be described with reference to
Now a manufacturing method for the lens system according to the third embodiment group will be described with reference to
Now the manufacturing method for the lens system according to the third embodiment group will be described with reference to
In the above mentioned first to fourth embodiment groups, the following content can be used if necessary within a range where the optical performance is not diminished.
In the above examples, a six-lens group configuration was shown, but the present invention can be applied to another group configuration, such as a five-lens group or a seven-lens group. A configuration having an additional lens or a lens group which is disposed closest to the object, or a configuration having an additional lens or a lens group which is disposed closest to the image, can also be used. A lens group refers to a portion having at least one lens isolated by an air distance which changes upon zooming.
A focusing lens group, for focusing on an object from infinity to a close distance by shifting a single or a plurality of lens group(s), or a partial lens group in the optical axis direction, may be used. This focusing lens group can be applied to auto focus, and is also appropriate for driving a motor for auto focus (e.g. ultrasonic motor). It is particularly preferable to use the rear portion lens group G1b as the focusing lens group.
A lens group or a partial lens group may be constructed as a vibration proof lens group, which corrects image blur generated due to hand motion, by shifting the lens group or the partial lens group so as to have a component orthogonal to the optical axis, or rotating (oscillating) the lens or the partial lens group in the plane direction including the optical axis. It is particularly desirable to construct at least a part of the fourth lens group G4 as the vibration proof lens group.
Each lens surface can be spherical or a plane, or aspherical. If the lens surface is spherical or a plane, a lens can be easily processed, assembled or adjusted, and deterioration of optical performance due to errors in processing, assembly and adjustment can be prevented, which is desirable. Also even if the image plane is shifted, deterioration of writing performance is minor, which is desirable. If the lens surface is aspherical, this aspherical surface can be any of an aspherical surface generated by grinding, a glass mold aspherical surface in which glass is formed to be an aspherical shape using a die, or a composite type aspherical surface in which resin is formed in an aspherical shape on the surface of the glass. Each lens surface may be a diffraction surface, and each lens may be a refractive index distributed lens (GRIN lens) or a plastic lens.
It is preferable that the aperture stop S is disposed near the fourth lens group G4 (image side of the fourth lens group G4 in the present embodiment), but a lens frame may take over this part, without disposing an independent element as the aperture stop.
An anti-reflection film which has high transmittance in a wide wavelength range may be formed on each lens surface in order to decrease flares and ghosts, and to implement high optical performance with high contrast.
The zoom ratio of the lens system of the present embodiment is about 4 to 5, and the focal length thereof in the telephoto end state is 300 mm or more.
In the lens system of the present embodiment, it is preferable that the fourth lens group G4 has one positive lens component and two negative lens components. It is preferable to dispose the lens components in a sequence of negative, positive and negative, in order from the object, with an air distance therebetween.
Embodiments were described with configuration requirements, in order to assist in understanding the present invention, but needless to say, the present invention is not limited to these embodiments.
The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-127260 | May 2009 | JP | national |
| 2009-127261 | May 2009 | JP | national |
| 2009-127262 | May 2009 | JP | national |
| 2009-127263 | May 2009 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 12788292 | May 2010 | US |
| Child | 13875546 | US |
