JPH0136181Y2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention is a reflection photometry device for a single-lens reflex camera.
This invention relates to a reflection photometry device for a single-lens reflex camera, which is provided with a photometry mirror for focus detection, and which reflects and guides subject light to a photoreceptor located at a position conjugate with the film.

In a single-lens reflex camera, a photometric mirror 2 is rotatably provided on the back side of an observation mirror 1, as shown in FIG. 1, for focus detection and the like. The photometric mirror 2 is designed to rotate in conjunction with the movement of the observation mirror 1, and before the shutter is released, the observation mirror 1 is positioned at a 45° angle within the photographing optical path as shown in the figure. Since the photometric mirror 2 is in the lowered position, at this time the photometric mirror 2 is in an open state behind the observation mirror 1 and approximately perpendicular to the observation mirror 1. The object light that has passed through the photographic lens 3 is reflected upward by the observation mirror 1 and guided to the focusing glass 4, pentaprism 5, and finder eyepiece 6 of the finder optical system, and some of the light is reflected from the observation mirror 1. 1, and is totally reflected by the photometric mirror 2, and is placed outside the lower photographic optical path at a position conjugate with the focusing glass 4 and the surface of the film 8. 7. Then, when the observation mirror 1 rotates and rises in the direction of the focusing glass 4 due to the release operation of the shutter, the photometry mirror 2 also moves its half mirror portion relative to the observation mirror 1. 1a, and both mirrors 1 and 2 stop horizontally in a folded state at positions 1A and 2A shown by dashed lines outside the photographing optical path, and at the same time the viewfinder eyepiece 6
Blocks reverse incident light from In this state, the subject light transmitted through the photographic lens 3 is imaged on the film 8 and photographed.

By the way, when performing focus detection using the photoreceptor 7, the photoreceptor 7 is attached to the film 8 as described above.
It is necessary to place it in a position conjugate with the plane of. For this purpose, if the photoreceptor 7 is arranged so that the position where the subject light passing through the photographic lens 3 forms an image on the surface of the film 8 and the position where the image forms on the light-receiving surface of the photoreceptor 7 coincide with each other, then , the photoreceptor 7 enters the photographing optical path and blocks the photographing light flux that has passed through the photographing lens 3. This tendency is particularly noticeable in single-lens reflex cameras that are small and low in height, and mirror devices that are designed to capture a sufficiently large amount of light.
Therefore, as shown in FIG. 2, in conventional devices of this type, in order to place the photoreceptor 7 outside the photographing optical path, the photometering mirror 2 is moved to a position in front of the film 8 at a certain distance. There is something I did. However, when the photometric mirror 2 is moved forward along the lens optical axis,
Since the amount of light components above the central optical axis incident on the photometric mirror 2 is reduced, in such a conventional device, the amount of received light is reduced, causing an imbalance in the photographing light flux. For this purpose, as shown in FIG. 3, the light that is imaged at the center of the film 8 is not photometered, but the light that is imaged at a position slightly below the center by the dimension D is transferred to the photoreceptor 7. Some devices are designed to measure light using the following methods. However, in this conventional device, there is a problem that the photometry position is shifted from the center of the viewfinder eyepiece 6, and in particular, in a camera with an interchangeable photographic lens 3, aberrations due to changes in the position of the exit pupil, etc.
Problems are expected to occur.

In view of the above-mentioned conventional problems, the purpose of the present invention is to form the reflective surface of the photometric mirror into a hyperboloid,
It is an object of the present invention to provide a reflection photometry device for a single-lens reflex camera by forming a long substantial optical path length to a photoreceptor for photometry located at a position optically conjugate with a film surface.

The present invention will be explained below with reference to illustrated embodiments.

FIG. 4 is a sectional view of a reflection photometry device showing an embodiment of the present invention. The observation mirror 11 is fixed to a movable mirror frame 14 rotatably provided on the side wall (not shown) of the mirror box by a support shaft 13, and the photometry mirror 12 is attached to the observation mirror 11.
It is fixed to a mirror support member 16 rotatably provided on the movable mirror frame 14 by a support shaft 15 behind the movable mirror frame 14 . When the movable mirror frame 14 approaches the focusing glass 4 and rises to the position 14A shown by the dashed line, the mirror support member 16 rotates so as to fold over the movable mirror frame 14, and the movable mirror frame 14 moves as shown in the figure. When the mirror support member 16 is lowered to the 45° angle position, the movable mirror 14
It is configured to rotate so as to open at a predetermined angle.

The shape of the reflecting surface of the photometric mirror 12 is formed into a convex shape that is a part of a hyperboloid. Therefore, the movable mirror frame 14 is located at a position 14 outside the photographing optical path.
In A, the subject light that focuses _F1 on the film 8 when it does not obstruct the light transmitted through the photographic lens 3 is:
As shown in the figure, when the movable mirror frame 14 is lowered and passes through the half mirror portion 11a of the observation mirror 11 and is totally reflected by the photometric mirror 12, this total reflected light from the object is reflected by the photometric mirror 12. film 8
The focal point _F2 is set at a position where the optical path length is substantially longer than the optical path length between the two. That is, the hyperboloid that is the surface shape of the reflective surface of the photometric mirror 12 is a hyperbola H ₁ expressed by x ² /a ² −y ² /b ² =1, shown by a solid line, as shown in FIG. One hyperbola of H ₂
It is a convex curved surface obtained by rotating H ₁ around the x-axis. In the hyperboloid consisting of this hyperbola H ₁ ,
An incident light beam condensed toward the focal point F ₁ inside the hyperbola H ₁ is reflected at an angle such that it converges toward the focal point F ₂ inside the other hyperbola H ₂ . Therefore,
At this time, in Fig. 5, the hyperbola of the above ray
than the length from above H ₁ to its focal point F ₁ , the hyperbola
It is clear that the optical path length from reflection at H ₁ to focal point F ₂ is sufficiently longer. Therefore, when arranging the photometric mirror 12 whose reflective surface is a hyperboloid, the focal point F ₁ of the hyperbola H ₁ of the mirror 12 is the focal point of the object light that has passed through the photographic lens 3 on the surface of the film 8. Match the center point that will be the image point,
Also, the focal point F ₂ of the hyperboloid H ₂ that is paired with this hyperboloid H ₁
is made to coincide with the center of the light-receiving surface of the photometric photoreceptor 17 outside the photographing optical path.

The photometric photoreceptor 17 is disposed below the movable mirror frame 14 and outside the photographing optical path at the focal point F ₂ of the hyperboloid H ₂ by an adjustable mounting mechanism. That is, an IC chip 18 constituting a photometry circuit, to which a photoreceptor 17 is integrally attached, is arranged on an electrical wiring board 19, and one end of the board 19 is connected to a fixing member 20 that is integrated with a fixed base plate. Support pin 2
1, the electrical wiring board 19 is rotatably held by
The other end is attached to a fixing threaded rod 23 fixed to the inner wall of the front plate of the light shielding member 22 by being held between two nuts 24 and 25. Photoreceptor 17 for photometry
is arranged in an inclined state facing the photometric mirror 12 by the substrate 19, and by adjusting the nuts 24 and 25 screwed onto the fixing threaded rod 23, the photoreceptor 17 is aligned with the substrate 19. The optical path length with the photometric mirror 12 and the same mirror 1 are integrated.
By changing the inclination angle with respect to 2, the focus of the subject light to be imaged on the film 8 can be correctly focused on the photoreceptor 17.
It can be tied at the top.

Since the reflective surface of the photometric mirror 12 has a hyperboloid shape, the light from the subject is reflected by the mirror 1.
All of the light reflected by the lens 2 is focused on a single point on the light-receiving surface of the photoreceptor 17 for photometry, and no spherical aberration due to the shape of the reflecting surface or aberration due to replacement of the photographing lens 3 occurs.

As described above, according to the reflection photometry device of the present invention, the reflection surface of the photometry mirror is formed into a hyperboloid, so that the photometry photoreceptor and photometry The effective optical path length with the mirror for photometry can be lengthened, and the photoreceptor for photometry can be placed in a position where it does not interfere with the photographic optical path, and the image formation condition is similar to that on the film surface without causing spherical aberration on the reflective surface. The image can be focused on a single point on the surface of the photoreceptor for photometry, improving focusing accuracy, and the amount of light from the subject is uniformly measured around the optical axis of the photographic lens, making it possible to It exhibits excellent effects such as enabling photometry even with dark lenses.

[Brief explanation of the drawing]

1 to 3 are sectional views of each example of a conventional reflection photometry device, FIG. 4 is a sectional view of an embodiment of a reflection photometry device showing an embodiment of the present invention, and FIG. FIG. 5 is a curve diagram illustrating a reflective surface of a photometric mirror of the reflective photometric device shown in FIG. 4 above. DESCRIPTION OF SYMBOLS 1, 11... Mirror for observation, 2, 12... Mirror for photometry, 1a, 11a... Half mirror part (translucent part), 3... Photographic lens, 7, 17... Light receiving part for photometry, 8... ...Film.

Claims (1)

[Claim for Utility Model Registration] An observation mirror for guiding light transmitted through the photographic lens to the viewfinder section is provided movably with respect to a fixed base plate such as a side wall of a mirror box, and the photographic lens and the observation mirror are A photometric mirror for guiding the light transmitted through the light-transmitting portion to a photometric photoreceptor disposed at a position optically conjugate with the film is provided behind the observation mirror so that it can move together with the observation mirror. In a reflection photometry device for a single-lens reflex camera, the reflection surface of the photometry mirror has a first focal point at the intersection of the optical axis of the photographic lens and the film surface, and a second focal point at the photoreceptor. formed 2
A reflection photometry device for a single-lens reflex camera, characterized in that the hyperboloid is one of the two hyperboloids on the first focus side.