JPS6119017B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a viewfinder for a single-lens reflex camera, and more particularly to an eyepiece in this type of viewfinder. Conventionally, as an eyepiece lens for a viewfinder for a single-lens reflex camera, a composite positive laminated lens consisting of a convex lens and a concave lens laminated behind the exit surface of a penta roof prism has often been used. Due to the structure of the penta roof prism, the focal length of the eyepiece is approximately 70 mm, and therefore the magnification of the eyepiece is approximately 4 times when the focal plane is viewed at clear vision distance. However, in recent years, the area around the viewfinder of single-lens reflex cameras has incorporated a large number of various devices for photometry and distance measurement, so the area around the eyepiece, especially the lower part, has protruded backwards, making it difficult to look at the viewfinder from a distance from the eyepiece. Therefore, conventional eyepiece lenses had the disadvantage that the peripheral part of the viewfinder field of view became vignetted and darkened. To try to correct this drawback with a conventional type of eyepiece, there is no other way than to make the distance from the eyepiece to the eye point (eye relief) sufficiently large, or to lower the eyepiece back and bring it closer to the eye. There was no. In both cases, the penta-roof prism becomes larger due to the spread of the light beam, and the focal length of the eyepiece becomes correspondingly longer due to the increased optical path length, which has the drawback of reducing the magnification of the loupe. . An object of the present invention is to obtain a viewfinder for a single-lens reflex camera that can ensure sufficient eye relief without reducing the loupe magnification of the eyepiece, and can observe a bright image without vignetting up to the periphery of the viewfinder field of view. . The structure of the viewfinder for a single-lens reflex camera according to the present invention includes a focusing plate, a condenser lens, a penta roof prism, and an eyepiece lens. It is formed by a negative lens component placed separately. Hereinafter, the present invention will be explained based on examples. FIG. 1 shows a first embodiment of the invention. The light beams refracted and reflected by a photographic lens and a flip-up mirror (not shown) form an image on the focal plane 1a of the focusing plate 1, and then a condenser lens 2, a prism 3,
The lens passes through the pentagonal roof prism 4 and reaches an eyepiece 10 consisting of a positive lens component 5 and a negative lens component 6, and the image on the focal plane 1a is observed by the naked eye 7 placed on the eye point. The prism 4 is used for distance measurement or photometry using a half mirror 3a and the like provided therein. The shaded area 8 indicates information processing members such as an optical system for distance measurement or photometry, an electrical system, and hardware members. The positive lens component 5 constituting the eyepiece 10 is a composite positive bonded lens consisting of a biconvex positive lens and a negative lens, and the negative lens component 6 is a single negative lens. That is, the main objective of the present invention is to arrange the positive lens component 5 and the negative lens component 6 with a large air gap in the composition, so that the main surface of the entire eyepiece lens system 10 is directed forward, that is, the pentagonal roof prism 4. The purpose of this is to shorten the focal length of the eyepiece lens system by pushing it out to the side, thereby preventing a decrease in magnification of the loupe. This will be explained in more detail with reference to FIG.
In FIG. 2, only the main parts of the eyepiece system of the present invention are shown as a thin lens system with the direction reversed. f
_o and f _p indicate the focal lengths of the negative lens component 6 and the bonded positive lens component 5, respectively, and d is the interval when these are considered as thin lenses, that is, the principal point interval. A ray l incident parallel to the optical axis A from infinity is diverged by the negative lens component 6, then proceeds as if it were a ray emitted from the focal point Fn of the negative lens component 6, and is refracted by the positive lens component 5. The image is formed at the rear focal point F' of the eyepiece system. In reality, the focal plane 1a is located at the position of this rear focal point F'. In this case, f _e = f _o × β (-a) = (-f _o ) + d β = b/a x = b - f _e The following relational expression is derived. Here, f _e is the composite focal length of the eyepiece lens system, and β is the lateral magnification of the positive lens component 5. Further, (-a) and b indicate the object point and image distance with respect to the positive lens component 5, and x indicates the distance from the positive lens component 5 to the combined rear principal surface H' of the eyepiece system. That is, by configuring the eyepiece from two groups, the negative lens component 6 and the positive lens component 5,
x
By moving the lens by that amount, the composite focal length can be shortened by that amount, and the magnification of the loupe can be kept relatively high. In such a configuration of the present invention, in order to appropriate the power distribution and arrangement of each group, 0.6<f _p /f _e <0.9 (1) 1.3<|f _o /f _e |<10.0 (2) 0.05 It is necessary to satisfy <d/f _e <0.3 (3). d is the positive lens component 5
This is the principal point interval between the negative lens component 6 and the negative lens component 6. Equations (1) and (2) are conditions that respectively define the focal lengths of the positive lens component 5 and the negative lens component 6 in the eyepiece 10 system. When the upper limits of equations (1) and (2) are exceeded, f _p approaches f _e , so the main surface of the eyepiece combination system does not move forward much, and the power of f _o decreases, making it difficult to use conventional eyepieces. There will be no difference.
Furthermore, if the lower limit of equations (1) and (2) is exceeded, the powers of f _p and f _o become stronger, respectively, so the principal plane of the synthesis system comes forward, but it becomes difficult to correct aberrations, especially the curvature of field. It becomes difficult to correct the comatic aberration that accompanies this. Equation (3) is an equation that defines the principal surface distance d between the positive lens component 5 and the negative lens component 6. If the upper limit of equation (3) is exceeded, the distance between both lens components increases, which is advantageous for pushing the main surface of the entire eyepiece system forward, but it also corrects comatic aberration due to field curvature. This makes it difficult to sufficiently correct aberrations. If the lower limit of equation (3) is exceeded, it will be difficult to bring the main surface of the composite system forward, and there will be no difference from the conventional type of eyepiece, which will deviate from the purpose of the present invention. Further, in order to satisfactorily correct various aberrations, especially field curvature and coma aberration under the power distribution for moving the main surface of the eyepiece lens toward the front, that is, toward the pentagonal roof prism side, the following conditions are further satisfied. This is desirable. That is, the refractive surfaces of the negative lens component 6 and the bonded positive lens component 5 constituting the eyepiece 10 are designated r ₁ , r ₂ , ... r ₅ in order from the eye 7 side, and the negative lens component 6
When the shape factors SF _o and SF _p of positive lens component 5 are defined as SF _o = r ₂ + r ₁ / r ₂ - _{r 1} SF _p = r ₅ + r ₃ / r ₅ - r ₃ -2< SF _o <+2 (4) −2<SF _p <+1 (5) is satisfied. When the upper limit of equation (4) is exceeded, the curvature of field becomes excessively negative, and when the lower limit is exceeded, the opposite is true. Furthermore, when the upper limit of equation (5) is exceeded, the curvature of field becomes excessively negative, and when the lower limit is exceeded, the opposite is true. In the second embodiment shown in FIG. 3, the information processing member 8
The light rays from the eyepiece reach another information processing member 8a provided above the eyepiece. With this configuration, not only the space below the eyepiece but also the space above the eyepiece can be used for various information processing, making the air space between the positive and negative lens components forming the eyepiece effective. It can be used for. In the third embodiment shown in FIG. 4, a parallel plane glass 9 is arranged between the positive lens component 5 and the negative lens component 6. By providing an oblique semi-transparent mirror on this parallel plane glass 9, further optical information can be taken out from there, and by using this parallel plane glass 9 as a sharp cut filter, it will not adversely affect photometry etc. It is possible to control the backlight. The parallel plane glass 9 does not contradict the basic structure of the present invention, and represents a broader example of application. The specifications of the first, second, and third embodiments of the present invention are shown in Tables 1, 2, and 3 below, respectively.
As shown in the figure, the specifications in each table are listed in order from the viewing eye 7 side, and r ₁ , r ₂ , ...... are the radius of curvature of the refractive surface of each optical member, d ₁ , d ₂ , . . . represent the interval between each refractive surface, and nd and vd represent the refractive index and Atsube number of each optical member, respectively. Further, E and P in the table represent the distance from the top surface of the eyepiece to the eye point (eye relief).

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【table】

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[Table] Various aberration diagrams for each of the above embodiments are listed in order.
6 and 7. These aberration diagrams are
As shown in each of the above tables, each aberration amount is shown when ray tracing is performed from the eye side and aberration calculation is performed on the focal plane. As can be seen from the above specification table and each aberration diagram, each example has sufficient eye relief for finder observation, and various aberrations are corrected sufficiently well for practical use. As described above, according to the present invention, the main surface of the eyepiece system can be pushed out toward the pentagonal roof prism, so even if an information processing member with a large space is provided around the eyepiece, the focal length of the eyepiece system can be shortened. By keeping it this way, it is possible to prevent the magnification of the loupe from decreasing. Therefore, it is possible to provide a viewfinder for a single-lens reflex camera that effectively utilizes space without affecting the magnification of the loupe even if various members are placed around the eyepiece.

[Brief explanation of the drawing]

FIG. 1 shows a first embodiment of the present invention. FIG. 2 is a thin lens system layout diagram showing the basic configuration of the present invention. Third
Figures 4 and 4 show the second and third embodiments. 5th, 6th, 7th
The figures are various aberration diagrams of the first, second, and third embodiments, respectively. [Explanation of symbols of main parts], 1... focus plate, 2
...Condenser lens, 3... Prism, 4...
Penta roof prism, 5...Positive lens component, 6...
...Negative lens component, 10...Eyepiece, f _e ...
Focal length of the eyepiece, f _p ...focal length of the positive lens component, f _o ...focal length of the negative lens component, d
...The principal point spacing between the positive lens component and the negative lens component.

Claims (1)

[Claims] 1. A focusing plate, a condenser lens, a penta roof prism, and an eyepiece lens, and the eyepiece lens is arranged in order from the penta roof prism side to a positive lens component, and an air gap from the positive lens component. In the viewfinder for a single-lens reflex camera, the focal length of the eyepiece is fe, and the focal lengths of the positive lens component and the negative lens component constituting the eyepiece are fp, respectively. , fn, and the principal point interval between the positive lens component and the negative lens component is d, then 0.6<fp/fe<0.9 (1) 1.3<|fn/fe|<10.0 (2) 0.05<d/ A viewfinder for a single-lens reflex camera that satisfies the condition of fe<0.3 (3).