Patent Application
20160037090
1. Field of the Invention
The present invention relates to a finder system and an optical apparatus using the same, which are particularly suitable for a photographic camera, a video camera, and the like that enable a user to observe a subject image formed on a reticle and an image formed on a display element via a common eyepiece unit.
2. Description of the Related Art
Hitherto, there has been proposed a camera capable of displaying an image of a display element on an optical finder in a superimposed manner or in a switching manner via a common eyepiece unit. In Japanese Patent No. 4154022, there is disclosed a finder in which a half mirror or a dichroic mirror is evaporated on an optical surface between a pentaprism and an eyepiece optical system so that a user is enabled to observe a range-finding frame that is superimposed on a subject image formed on a reticle. Further, in Japanese Patent Application Laid-Open No. 2007-264029, there is disclosed a finder in which an optical path combining member is used so that a user is enabled to observe a display of a display element that is superimposed from a subject-side surface of a pentaprism.
The finder disclosed in Japanese Patent No. 4154022 assumes that a display system displays a range-finding frame with an angle of field that is about half the field of view of the finder. When the angle of field of the display system is increased to approximately 0.8 times as large as the field of view of the finder, the display system is upsized by 10 mm or more in a height direction.
In the finder disclosed in Japanese Patent Application Laid-Open No. 2007-264029, a panel is far from an eyepiece frame, and hence the image to be displayed on the display element is small. Further, the camera is upsized in a subject direction, and hence it is difficult to mount a large-aperture photographing lens to the camera.
In order to achieve the above-mentioned object, according to one embodiment of the present invention, there is provided a finder system, including: an observation optical system configured to convert a subject image formed on a predetermined surface into an erect image via an erect image forming member, and cause the erect image to be transmitted through a first optical surface that is inclined with respect to an optical axis, thereby observing the erect image via an eyepiece lens; and a display optical system configured to cause an image indicating display information of a display member to be reflected on the first optical surface, thereby observing the image via the eyepiece lens in the same field of view as the subject image. The display optical system includes, between the display member and the eyepiece lens: an optical member including at least two reflection surfaces; and a lens unit having a positive refractive power, the optical member and the lens unit being arranged along an optical path from the display member side to the eyepiece lens side in the stated order.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Exemplary embodiments of the present invention are hereinafter described with reference to the drawings.
On the other hand, light from a display member 9 configured to display information on photography passes through an optical member 10 and a first lens unit 11 as a lens unit having a positive refractive power, and then passes through an optical surface 6a that is a light input surface of the prism 6. After that, the light is reflected by two optical surfaces 6b (second optical surface) and 6c (first optical surface) of the prism 6 in the stated order, which are inclined in different directions with respect to the optical axis Fa of the observation optical system. The light is then transmitted through the optical surface 6b, and passes through the eyepiece lens 8 to reach the eyes of the observer, thereby enabling the observer to observe the information on photography in the same field of view as that of the subject image. The above-mentioned components serve as a display optical system in the finder system. The first lens unit 11 may be formed of a single positive lens, or may be formed of a plurality of lenses. The first lens unit 11 only needs to have a positive refractive power as a whole.
Now,
The image displayed on the display member 9 in a live view is enlarged by the first lens unit 11, and passes through the prisms 6 and 7 and the eyepiece lens 8 to reach the eyes of the observer. Viewing of photographed images and displaying of menus are also possible via the display member 9 after the mirror-up. In this manner, the camera as the optical apparatus having the finder system mounted thereon according to this embodiment enables the observer to observe the subject image formed on the reticle 3 as well as a subject image, photographed images, and various kinds of menus displayed in a live view through the same eyepiece lens.
Now,
Neither of the optical axis Fa of the observation optical system and the optical axis Fb of the display optical system is included in the same plane. Specifically, in
Further, in the finder system according to this embodiment, a focal length f1 of the first lens unit 11 and a focal length f of the eyepiece lens 8 at −1 diopter satisfy Conditional Expression (1).
0.3<f1/f<1.0 (1)
Conditional Expression (1) is a condition for enlargedly observing an image of the display member 9 with a wide angle of field while preventing the finder system from being upsized in the height direction. When f1/f falls below Conditional Expression (1), the focal length of the first lens unit 11 is too short, and hence the distance between the display member 9 and the optical surface 6a of the prism 6 is too narrow. As a result, the internal reflection in the optical member 10 occurs only once, thus failing to optimize the position of the display member 9.
On the other hand, when f1/f exceeds Conditional Expression (1), the focal length of the first lens unit is too long, and hence the distance between the display member 9 and the optical surface 6a of the prism 6 is too long. As a result, the display member 9 is too far from the observer, and the observer cannot see the image of the display member 9 with a wide angle of field.
Further, in the finder system according to this embodiment, when a diagonal length of the display member 9 is represented by L1 and a diagonal length of the display member 9 on an observation surface is represented by L, the diagonal lengths L1 and L satisfy Conditional Expression (2).
1.2<(f1/f)×(L/L1)<1.5 (2)
Conditional Expression (2) is a condition for enlargedly observing an image of the display member 9 with a wide angle of field while preventing the finder system from being upsized in the height direction. When (f1/f)×(L/L1) falls below Conditional Expression (2), the focal length of the first lens unit 11 is too short, and hence the distance between the display member 9 and the optical surface 6a of the prism 6 is too narrow. As a result, the internal reflection in the optical member 10 occurs only once, thus failing to optimize the position of the display member 9. On the other hand, when (f1/f)×(L/L1) exceeds Conditional Expression (2), the focal length of the first lens unit is too long, and hence the distance between the display member 9 and the optical surface 6a of the prism 6 is too long. As a result, the display member 9 is too far from the observer, and the observer cannot see the image of the display member 9 with a wide angle of field.
Further, in the finder system according to this embodiment, the angle formed between the normal to the display member 9 and the central axis of the first lens unit 11 is represented by θ, the angle θ satisfies Conditional Expression (3).
40°<θ<75° (3)
Conditional Expression (3) is a condition for preventing the finder system from being upsized in the height direction. When θ falls below Conditional Expression (3), the light beam from the display member 9 cannot satisfy the condition of total reflection on an optical surface 10a (
Further, in the finder system according to this embodiment, an optical surface 10b (
The optical surface 6c (first optical surface) of the prism 6 serves as a half mirror or a dichroic mirror. The optical surface 6b (second optical surface) of the prism 6 may serve as a half mirror or a dichroic mirror, but the following is preferred.
Specifically, an air gap of from approximately 10 μm to approximately 100 μm is formed between the prisms 6 and 7 so that a light beam from the optical surface 6a is totally reflected but a light beam reflected from the optical surface 6c enters the optical surface 6b at less than a critical angle and is transmitted through the optical surface 6b, and hence light beam loss can be minimized. As a result, the optical finder can be maintained bright, and as illustrated in
Now, Numerical Examples of the present invention are described. Note that, in the values described below, ω represents an apparent field of view (half angle of field) at −1 diopter (standard diopter). Further, in the values indicating lens data, “ri” represents a paraxial radius of curvature of the i-th surface counted from an object side with reference to the reticle, and “di” represents an axial surface distance between the i-th surface and the (i+1)th surface counted from the object side.
Further, “Ni” represents a refractive index for d-line (wavelength=578.6 nm) of the i-th glass material counted from the object side, and “νi” represents an Abbe number for d-line of the i-th glass material counted from the object side. Note that, in the values described below, the unit of the length described is [mm] unless otherwise specified. However, the same optical characteristic of the optical system can be obtained even when the values are proportionally enlarged or proportionally reduced, and hence the unit is not limited to [mm] and may be another appropriate unit. Note that, in each of Numerical Examples, the surfaces described as “Rotationally Symmetric Aspherical Surface” in the field of “Parasitic Curvature Radius” have a rotationally symmetric aspherical shape defined by Expression 1.
Note that, in the above expression (Expression 1), x represents a distance from the apex of the lens surface in the optical axis direction, h represents a height in the direction perpendicular to the optical axis, R represents a paraxial radius of curvature at the apex of the lens surface, k represents a conic constant, and c2, c4, c6, c8, and c10 represent polynomial coefficients. In the values indicating aspherical coefficients, “E−i” represents an exponential notation using 10 as its base, that is, “10−i”.
Further, in each of Numerical Examples, the surfaces described as “Rotationally Asymmetric Aspherical Surface” in the field of “Parasitic Curvature Radius” have a rotationally asymmetric aspherical shape defined by Expression 2.
x=c
20
y
2
+c
02
z
2
+c
30
y
3
+c
12
yz
2
+c
40
y
4
+c
22
y
2
z
2
+c
04
z
4
+c
50
y
5
+c
32
y
3
z
2
+c
34
yz
4
+c
60
y
6
+c
42
y
4
z
2
+c
24
y
2
z
4
+c
06
z
6
+c
70
y
7
+c
52
y
5
z
2
+c
34
y
3
z
4
+c
16
yz
6
+c
80
y
8
+c
62
y
6
z
2
+c
44
y
4
z
4
+c
26
y
2
z
6
+c
08
z
8
+c
90
y
9
+c
72
y
7
z
2
+c
54
y
5
z
4
+c
36
y
3
z
6
+c
18
yz
8
+c
100
y
10
+c
82
y
8
z
2
+c
64
y
6
z
4
+c
46
y
4
z
6
+c
28
y
2
z
8
+c
010
z
10 (Expression 2)
Note that, in Expression 2, as illustrated in
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2014-158591, filed Aug. 4, 2014, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-158591 | Aug 2014 | JP | national |
