JPS6285229A - Ttl light measuring device of single-lens reflex camera - Google Patents

Abstract

PURPOSE:To measure object light efficiently and to eliminate the difference of a light measurement area even when a lens is interchanged by dividing a submirror by a boundary line which runs on the intersection of the optical axis of a photographic lens and constituting >=2 areas which differ in reflection direction characteristics. CONSTITUTION:Rays of light 11 incident on a point P1 from a photodetecting element 6 are diffuse-reflected within a narrow range by the upper Fresnel mirror 41 of the submirror 4 to form an area 11b and rays of light 12 incident on a point P2 form an area 12b at a lower part 42 similarly. Then, rays of light guided from the photographic lens 1 to the photodetecting element 6 backward through the optical path are divided into four sections on the submirror 4 to become rays of light of the four uniform areas. Therefore, the object light is measured efficiently and even if there is a difference in F value of an interchangeable lens at open aperture or if the lens is stopped down, variation of the light measurement area in a picture plane is eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field of the Invention) The present invention relates to a TTL photometry device for a single-lens reflex camera, and in particular to a main mirror for a finder having a semi-transparent section and a light receiving system that transmits light that has passed through the semi-transmissive section. The present invention relates to a TTL photometry device equipped with a guiding sub-mirror.

(Background of the Invention) In this type of TTL photometry device, the light incident from the photographing lens is sent to the finder system by the main mirror, and the light passes through the semi-transparent part of this main mirror, is reflected by the sub-mirror, and is sent to the light receiving system. The light is divided into two parts. Most of the light incident from this photographic lens is sent to the finder system, so normally only a small amount of light is sent to the light receiving system.

Therefore, in such a photometry device, it is necessary for the submirror to efficiently guide the light that has passed through the semi-transparent part of the main mirror to the light receiving system. Further, in order to obtain linearity of the photometric output, it is desirable that the sub-mirror has a reflection characteristic such that the output of the light receiving element can be obtained in proportion to the size of the aperture of the aperture of the photographing lens.

By the way, a method of using a diffuse reflection surface as a sub-mirror of this type of photometric device has been proposed. FIGS. 9 and 10 illustrate how light from a photographing lens is taken in by a side light device using submirrors 3 having different diffusion characteristics. Here, in order to simplify the explanation, the traveling direction of light is assumed to be from the light receiving element 6 toward the exit pupil of the photographing lens 1. FIG. 9 shows a case where the sub-mirror 4 has a diffusion characteristic almost equal to that of a perfect diffuse reflection surface. In FIG. 9, a single light beam 21 emitted from the light-receiving element 6 is reflected at a point S on the sub-mirror 4 and is diffused in a substantially spherical strong distribution indicated by 21a. A portion of this diffused light 21a that goes toward the exit pupil of the photographic lens 1 becomes a light flux 21b shown by a dotted line. Tracing the direction of this light beam in the opposite direction, at point S on the submirror 4, the light receiving element 6 has the ability to receive light with the distribution shown by 21a. In this way, as shown in FIG. 9, the light receiving element 6 can evenly and uniformly receive the light from the exit pupil of the photographic lens 1 in the highly diffusive Zabu mirror 4 as shown in FIG. The drawback was that it was only partially used and was very inefficient.

FIG. 10 shows a photometric system in which the diffusivity of some of the submirrors 4 is lowered to improve efficiency. Note that when the diffusivity is lowered, the directivity increases. Therefore, in order to correctly reflect the light from the photographic lens 1 in the direction of the light receiving system, the sub-mirror 4 is a Fresnel mirror, and is additionally provided with diffusing properties. In FIG. 10, a single light beam 22 emitted from the light-receiving element 6 is diffused at a point t on the sub-mirror 4 with a distribution of intensity shown by a reflection gap 22a. Tracing the direction of this light beam in the opposite direction, at point t on the submirror 4, the light receiving element 6 is 22
It has the ability to receive light with the distribution shown by a.

The area that evenly and uniformly receives the light from the photographic lens 1 is a range 22b indicated by a dotted line, which is a roughly narrow range. In this way, when the diffusivity of the sub-mirror 4 is lowered as shown in FIG. 10, the light-receiving ability of the light-receiving element 6 is mostly used to take in the light from the photographing lens 1, so the efficiency is high, but the range in which light is evenly and clearly received is high. Since the aperture of the photographing lens 1 becomes narrower than the uniform light receiving range, there is a drawback that there is little change in the light reception output, that is, the linearity of the photometric output with respect to the aperture is poor.

Further, FIG. 11 shows a mechanism for determining the photometry area on the screen when a diffuse reflection surface as shown in FIG. 9 is used as a sub-mirror. In Figure 11, 1a and 1a
J indicates the exit pupil of a photographic lens with a small F number, and 1b and lb' indicate the exit pupil of a photographic lens with a large F number. As mentioned above, since the sub-mirror 4 evenly guides the light from the exit pupil of the photographic lens 1 to the light receiving element, the light measured at the lowest side of the film surface 7 comes from the upper ends 1a and 1b of the exit pupil of the photographic lens l. Similarly, the light measured at the uppermost side of the film surface 7 is the lower end 1a' and lb' of the photographic lens 1.
It becomes light from. Therefore, the photometric area on the screen is the area indicated by 7a for a taking lens with a small F number, and the area shown by 7b for a taking lens with a large F number. This has the disadvantage that in a camera with interchangeable lenses, the photometry area will differ if the lens has a different lt, and the photometry area will change if the photographic lens is stopped down and photometered. Particularly, methods called partial photometry and spot photometry that measure light on a small area of the screen pose a problem because the photometry area cannot be specified.

(Objective of the Invention) The present invention solves these drawbacks, has good linearity of photometric output, and can efficiently measure subject light. The purpose of the present invention is to provide an excellent TTL photometry device with no difference in photometry area.

(Summary of the Invention) The sub-mirror of the present invention is divided by a boundary line passing through a point that intersects with the optical axis of a photographing lens, and has two mirrors having different reflection direction characteristics.
Each divided region is configured to transmit light passing through a predetermined region extending from the center to the outer periphery of the exit pupil of the photographic lens, which is in the same positional relationship as the respective region with respect to the optical axis. The technical point is to guide the light to the light receiving means.

(Example) FIGS. 1 to 8 show an example of the present invention. TT in Figure 4
In the optical path diagram of the L photometer, the light that has passed through the photographing lens 1 is guided to the finder system 3 by the main mirror 2, and the light is guided to the light receiving system (light receiving lens 5, light receiving element 6) by the submirror.
) and the light guided by it. Most of the light that has passed through the photographic lens 1 is guided to the finder system 3, and the rest passes through the semi-transparent part of the main mirror 2, is reflected by the sub-mirror 4, and is guided to the light-receiving element 6 through the light-receiving lens 5.

FIG. 1 shows an enlarged view of the sub-mirror 4 shown in FIG. 4, which is composed of four Fresnel mirrors 41 to 44 each having minute irregularities at different centers, and these minute irregularities have relatively directivity. brings about sharp diffusivity. FIGS. 2 and 3 explain the photometric principle of a photometric device using this sub-mirror 4. FIG.

Figure 2 shows the upper part 41 and lower part 42 of the sub-mirror 4 in Figure 1.
This figure shows the reflection direction characteristics at . Although not shown, the left part 43 and right part 44 of the sub-mirror 4 have similar reflection characteristics.
The traveling direction of the light is from the light receiving element 6 side toward the exit pupil of the photographing lens 1. In FIG. 2, at the upper part 41 of the submirror 4 shown in FIG. 1, the light ray 11 incident on the point P1 on the submirror 4 from the light receiving element 6 is diffusely reflected in a narrow range with an intensity distribution indicated by lla. A region 11b is indicated by a dotted line in which the difference in intensity is relatively small in the diffusely reflected light 11a. Next, the submirror 4 in FIG.
Similarly, at the lower part 42 of the light-receiving element 6, the light [12 that enters the point P2 on the sub-mirror 4] is diffusely reflected in the distribution shown by 12a. Indicated. Here, the shape of the Fresnel mirror of the sub-mirror 4 is such that light from the light-receiving element 6 side is transmitted to the sub-mirror 4.
The upper part 41 of the sub-mirror 4 is shaped to have a reflection direction characteristic such that it is directed toward a point Q1 located outside the exit pupil of the photographic lens 1, and the lower part 42 of the sub-mirror 4 is all directed toward a point Q2. . If the light beam is traced in the reverse direction in FIG.
This shows that the point P2 on the sub-mirror 4 has the ability to almost uniformly receive the light in the area 11b, and similarly, the point P2 on the submirror 4 shows that it has the ability to almost uniformly receive the light in the area 12b. . In this way, the sub-mirror 4 is configured to guide different areas of light incident from the photographing lens 1 to the light-receiving element for each of the four divided parts. FIG. 3 shows a region where each of the parts 41 to 44 of the sub-mirror 4 uniformly guides light to the light receiving element 6 on the exit pupil of the photographing lens 1.

Areas 11b, 12b, 13 indicated by dotted lines in FIG.
b, 14b are respective parts 41, 42 of the submirror 4
, 43 and 44 form a region where light is guided to the light receiving element 6. As shown in FIG. 3, for example, the upper part 41 of the sub-mirror 4
The area where the submirror 4 effectively guides light to the light receiving element is smaller than the exit pupil of the photographic lens 1, as shown by llb, but the submirror 4 as a whole almost covers the exit pupil of the photographic lens 1. Since each region 11b to 14b is formed to cover the exit pupil from the center to the outer periphery, a photometric output corresponding to the size of the aperture of the aperture can be obtained immediately from the maximum aperture of the photographic lens 1. be able to.

FIG. 5 shows a mechanism for determining the photometry area in the vertical direction of the screen in the photometry device using the sub-mirror according to this embodiment. In FIG. 5, the upper part 4 of the sub-mirror 4
1, the area to be photometered on the exit pupil of the photographic lens 1 is 1lb, as described above. Of the light measured by the upper part 41 of the sub-mirror, the light that reaches the lowest part of the film surface 7 is:
The light passes through the upper end 1a of the exit pupil of the photographic lens 1 and passes through the lower end 4C of the upper part 41 of the sub-mirror 4. Among the light measured by the Fresnel mirror 41, the light that reaches the uppermost side of the film surface 7 passes through the center IC of the exit pupil of the photographic lens 1 and passes through the upper end 4a of the upper part 41 of the sub-mirror 4. Similarly, out of the light measured by the lower part 42 of the sub-mirror 4, the light that reaches the lowest part of the film surface 7 is the light that passes through the lower end 4b of the lower part 42 of the sub-mirror 4, at the center of the exit pupil of the photographing lens 1. becomes. In addition, the lower part 42 of the sub mirror 4
Of the light measured in , the light that reaches the uppermost side of the film surface 7 passes through the lower end 1 ar of the exit pupil of the photographing lens 1 and passes through the upper part 54 c of the lower part 42 of the sub-mirror 4 . Therefore, the light reflected by the soil portion 41 of the sub-mirror 4 is not shown in the figure (the area photometered by the Tokumitsu element 6 is the area 71a on the film surface 7 shown in the figure, and the light is reflected by the lower part 42 of the sub-mirror 4). The area where the light is side-lighted by the light receiving element 6 (not shown) is the area 71b on the film surface 7 shown in the figure, and the area 71 on the film surface 7 for both the areas 41 and 42 of the sub-mirror 4 is the area 71b on the film surface 7 shown in the figure. As shown in the figure, this area 71 is determined by the light that passes through the center IC of the photographing lens 1 and passes through the upper and lower ends 4a and 4b of the sub-mirror 4.The same applies to the left and right directions of the sub-mirror 4. In this way, the areas 11b, 12b, etc. cover the exit pupil of the photographic lens 1 from approximately the center to the outer periphery, and the areas that take in the light from the exit pupil of the photographic lens 1 and each area of the sub-mirror 4. Since each area of the sub-mirror 4 and the area for taking in light are configured so that they have the same positional relationship with respect to the optical axis and face each other, the photometry area 71 on the screen is always located at the center IC of the exit pupil of the photographing lens 1. Therefore, in the photometry device using submirror No. 4 according to the embodiment, the photometry area 71 is constant on both sides, regardless of the size of the exit pupil of the photographing lens, that is, regardless of the aperture F value of the interchangeable lens. can be obtained.

In reality, the position of the exit pupil differs depending on the focal length of the interchangeable lens, but the position of the exit pupil of the interchangeable lens of a general single-lens 7-lens camera is different for wide-angle lenses because the back focus is long, and for telephoto lenses. In order to shorten the total length of the lens, the difference in the position of the exit pupil is not as large as the difference in focal length, and if the position of the virtual exit pupil is set appropriately using the photometry system as in the example, the center of the exit pupil can be The light that passes through can be made to pass through the exit pupil of most interchangeable lenses, and differences in the photometric area of the screen due to differences in focal length can be ignored.

FIGS. 6 and 7 illustrate a method of setting the shape of the 7-Renel mirror in each part of the sub-mirror 4. FIG.

FIG. 6 shows the case of the upper part 41 of the sub-mirror 4, where a light-receiving lens 5' and the center point R' of its entrance pupil are assumed to be located symmetrically with the light-receiving lens 5 with the plane containing the sub-mirror 4 as a boundary. A lens 41' has the function of focusing the light emitted from the upper point Q1 on the exit pupil of the photographic lens 1 onto the R'.
is assumed to be the position of the submirror 4. If a Fresnel mirror equivalent to this lens 41' is placed at the submirror 4,
The light exiting from the point Q1 at the upper right of the exit pupil of the photographic lens 1 is condensed at the center point R of the entrance pupil of the light receiving lens 5. A Fresnel mirror equivalent to this lens 41' is composed of an annular reflecting surface centered at the intersection T1 of the straight line connecting Q1 and R' and the plane including the nub mirror.

FIG. 7 shows the case of the lower part 42 of the sub-mirror 4, in which there is a 7-Renel mirror that has the function of condensing the light emitted from the point Q2 at the lower part of the exit pupil of the photographing lens 1 to the center point R of the entrance pupil of the light-receiving lens 5. It is determined in the same manner as in FIG. And this Fresnel mirror is the above-mentioned Q2. ! : It is composed of an annular reflecting surface centered on the intersection T2 of the straight line connecting R' and the plane including the sub-mirror 4. Also, the left side 43 of the sub-mirror 4.
Similarly, for the right side 44, the points Q3. It functions as a Fresnel mirror that focuses the light from the right point Q4 onto the center point R of the entrance pupil of the light receiving lens 5.

FIG. 8 is an enlarged cross-section of the sub-mirror 4 in the embodiment of the present invention. In FIG. 7, the sub-mirror 4 is a Fresnel mirror with minute irregularities provided on its surface to achieve the required diffusion characteristics.

In addition, four points Q assumed on the exit pupil of the photographic lens 1,
, Q2. Q3. It is desirable that Q4 be a point equidistant q from the center 1c, but the appropriate distance may be determined depending on the required photometric characteristics. Furthermore, the present invention is not limited to the above-mentioned embodiments. For example, if the photometric area on the screen only needs to be constant in one direction, such as below or left and right, the sub mirror 4 can be placed at two locations, up and down or left and right. It is only necessary to divide the area into regions T. Further, the number of divided regions of the sub-mirror 4 may be determined depending on the required photometric characteristics.

(Effects of the Invention) As described above, according to the present invention, the open F
It is possible to provide an excellent photometry device in which the photometry area within the screen does not change even when there are differences in values or when narrowing down. Furthermore, the linearity and efficiency of the photometric output when stopped down are also excellent. In particular, in photometry methods with small photometry areas such as partial and spot metering, if the photometry area changes when changing an interchangeable lens or when stopping down, the photometry output value will change each time and will not remain constant. Although there was a drawback that a photograph could not be obtained, the above drawback can be solved by using the photometric device of the present invention.

Incidentally, if the present invention is configured as in the embodiment, the sub-mirror is a combination of Fresnel mirrors having a relatively directional diffusing effect and having minute irregularities consisting of two or more areas with different reflection directions. Because of this structure, it is possible to obtain a photometric characteristic with good linearity of photometric output with respect to the aperture with a simple configuration, and to provide a photometric device that efficiently captures the light of the subject and is effective even for subjects with low brightness. becomes possible.

[Brief explanation of drawings]

1 to 9 show examples of the present invention, in which FIG. 1 is a front view of the submirror, FIG. 2 is an explanatory diagram showing the reflection characteristics of the submirror, and FIG. 3 is the injection of the photographing lens by the submirror. An explanatory diagram showing how light is taken in from the pupil, Fig. 4 is a layout diagram of the optical system and light receiving system for photometry in the body of a single-lens reflex camera, and Fig. 5 is an illustration of the photometry area of the screen according to an embodiment of the present invention. FIGS. 6 and 7 are diagrams illustrating how the shape of the sub-mirror is determined, and FIG. 8 is an enlarged cross-sectional view of the sub-mirror. FIGS. 9 and 10 are explanatory diagrams showing the reflection characteristics of a conventional submirror having a diffusing surface, and FIG. 11 is a diagram showing a screen-like photometry area of a photometry system using a conventional submirror. (Explanation of symbols of main parts) 1...Photographing lens 2...Main mirror 4...Sub mirror 5...Light receiving lens 6...Light receiving element

Claims (1)

[Claims] (1) A main mirror that reflects the subject light that has passed through the photographic lens to the finder system and has a semi-transparent section through which the subject light can pass, and a mirror box that directs the subject light that has passed through the semi-transmissive section. In a TTL photometry device for a single-lens reflex camera, the submirror is divided by a boundary line passing through a point that intersects with the optical axis of the photographic lens, and the submirror is divided into two parts having different reflection direction characteristics.
Each divided region is configured to transmit light passing through a predetermined region extending from the center to the outer periphery of the exit pupil of the photographic lens, which is in the same positional relationship as the respective region with respect to the optical axis. A photometric device for a single-lens reflex camera, characterized in that the light is guided to the light receiving means.