JPS6132825A - Light metering device of single-lens reflex camera - Google Patents

Abstract

PURPOSE:To attain focal plane light metering and to reduce the phenomenon of a more decrease in the quantity of light at the peripheral part of a viewfinder visual field than at the center part by providing a light transmission body which has light metering elements made of an ASP diode provided in a radial pattern near the focal plane on the optical path of the single-lens reflex camera. CONSTITUTION:A glass plane plate 7 equipped with light meteringelements 8 is arranged more closely to a quick return mirror 2 than to a focal plate 4 so that the center of the radial pattern coincident with the center of a Fresnel lens. This arrangement allow light metering elements to be arranged directly nearby the focus of a photographic lens and further the light metering of the entire image plane or a light metering sensitivity distribution is selected relatively easily by forming the pattern in a desired shape. The light metering element 8 of ASP diodes measure the quantity of light when object light given an tendency to form an image by the photographic lens 1 is reflected by a quick return mirror 2 to form an object image on the focal plate 4 and their outputs are sent to an electric processing circuit through layered electrodes 8a and 8c.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a TTL photometry device for a single-lens reflex camera, and in particular uses an amorphous silicon photodiode (hereinafter abbreviated as ASP diode) as a photometry element.
This invention relates to a photometric device that takes advantage of the characteristics of

2. Description of the Related Art Conventionally, in photometric devices, a light receiving element is generally arranged on the exit surface of a pentagonal roof prism located in the observation optical path or on the bottom of the camera body. However, in the case of these arrangements, since photometry is performed at a location away from the focal plane of the photographic lens, there is a drawback that a photometric amount proportional to the F number of the photographic lens cannot be obtained.

There is also a known type of photometry device in which an optical element with a fine structure for light splitting is placed near the focusing plate, and a portion of the observation light is guided to a light receiving element provided outside the optical path. It has similar drawbacks due to its distance from the focal plane.

On the other hand, in recent years, ASP diodes have become more reliable, have become extremely thin films, can be formed by vapor deposition, and are
It has many advantages, such as the ability to form fine patterns with a width of about microns, and is attracting attention, but it also has limitations because it is not transparent.

An object of the present invention is to take advantage of the advantages of ASP diodes to achieve focal plane photometry.

The present invention has the effect of significantly alleviating the phenomenon in which the amount of light decreases at the periphery of the viewfinder field of view compared to the center, and even if a Fresnel lens is used as a condenser lens in the viewfinder system, moiré fringes may occur and the field of view may This has the effect of not causing problems such as making it difficult to see.

In the embodiment of the present invention, which will be described in detail below, a light-transmitting body in which photometric elements made of ASP diodes are arranged in a radial pattern is provided near the focal plane in the optical path of a single-lens reflex camera. A cross-sectional view of a single-lens reflex camera is shown. Number 1 is a photographic lens, which can be moved back and forth in the optical axis direction for focusing. Reference numeral 2 denotes a tie-in return mirror, which reflects photographic light to the finder system at an oblique position and allows the photographic light to form an image on film 3 at a retracted position. Reference numeral 4 denotes a focusing plate, which has a matte surface on the incident side, and a Fresnel groove formed around the optical axis on the output side. 5 is a pentagonal roof prism, 6 is an eyepiece lens, and the quick return mirror 2 onwards constitutes the finder system.

7 is a glass flat plate, and a photometric element 8 made of an ASP diode is deposited on the incident side. A schematic diagram of this ASP diode is shown in FIG. 2, where 8a and 80 are electrode layers, and 8b is a thin layer of the ASP diode.

Figures 3 and 4 depict the pattern of the photometric element formed by the ASP diode when viewed from above, and Figure 3 shows a pattern in which narrow bands close to the resolution of the eye are arranged in the radial direction. Figure 4 shows a pattern in which minute rhombuses are arranged in a radial manner in the longitudinal direction, and various modifications are possible, such as arranging ellipses in a row. It is sufficient if the pattern is dense and extends in the radial direction.

The glass flat plate 7 provided with the photometric element 8 is placed closer to the quick return mirror 2 than the focusing plate 4.

The lens shall be installed so that the center of the radial pattern coincides with the center of the Fresnel lens.

The above arrangement makes it possible to place the photometric element directly near the focal point of the photographic lens, and by shaping the pattern to the desired shape, it is possible to measure the entire screen or select the photometric sensitivity distribution relatively freely. I can do it.

The photometric element 8 of the ASP guideo measures the priority of the object light given the imaging tendency by the photographing lens 1 when it is reflected by the quick return mirror 2 and forms an object image on the focusing plate 4, and Electrode 8a.

It has a function of sending the output to an electrical processing circuit (not shown) via 8C. In addition, the glass flat plate 7 is placed below the matte surface of the focusing plate 4, so that the fine structure of the pattern is blurred by the scattering effect of the cloak surface, so that an observer looking through the finder can see the pattern clearly. This is to ensure that there is no such thing.

On the other hand, photographic lenses generally have low peripheral photoacidity in order to prevent performance deterioration at the periphery of the screen and to prevent the lens diameter from increasing. The cosine 4th power law is particularly effective with lenses with a high open F-number, and wide-angle lenses have a significant drop in peripheral light intensity. When you look through the viewfinder of a camera equipped with such a lens, the periphery appears darker than the center of the field of view.

On the other hand, the glass glass plate 7 with the above-mentioned pattern
When placed close to the focusing plate 4, the light in the center where the pattern is dense is blocked and reduced.

The surrounding area has a rough pattern, so it is not affected much.

Therefore, since the amount of light at the periphery increases relative to the center, visibility through the finder improves.

Furthermore, since most subjects are aligned to the center of the screen, it is preferable for the photometric sensitivity distribution to be center-weighted, but a pattern that is dense in the center and coarse in the periphery naturally satisfies this sensitivity distribution.

Furthermore, the pattern of the ASP diodes can be, for example, arranged in thin strips in concentric circles, but in that case, a Fresnel lens is used as the focusing plate, and if there is a mounting error between the center of the concentric circle and the center of the Fresnel lens, moiré may occur. Streaks appear and make the field of vision difficult to see.

In this respect, the pattern of this embodiment has no fear of generating moiré fringes, has a good viewfinder field of view, and can reduce the burden on processing accuracy and assembly accuracy.

As described above, the present invention has the effect of realizing focal plane photometry, and at the same time, corrects the peripheral light distortion of the viewfinder field of view, eliminates problems such as the occurrence of moiré fringes, and eliminates the problem of photometry sensitivity. This is an excellent invention that is effective in center-weighting the distribution.

[Brief explanation of the drawing]

FIG. 1 is an optical sectional view showing an embodiment of the present invention. Figure 2 is A
FIG. 3 is an enlarged sectional view showing the structure of the photometric element of the SP type electrode. FIGS. 3 and 4 are cross-sectional views showing pattern examples. In the figure, l is a photographic lens, 2 is a quick return mirror,
4 is a focusing plate, 7 is a flat glass plate, and 8 is a photometric element of an ASP (amorphous or silicon photo) diode.

Claims (4)

[Claims] (1) A photometric device for a single-lens reflex camera, characterized in that a light-transmitting body having photometric elements arranged in a pattern extending in the radial direction is disposed near the focusing plate in the optical path of the single-lens reflex camera. (2) The photometry device for a single-lens reflex camera according to claim 1, wherein the pattern is denser in the center than in the periphery. (3) A photometric device for a single-lens reflex camera according to claim 1, wherein the light transmitting body is arranged closer to the photographing lens than the focusing plate. (4) A photometric device for a single-lens reflex camera according to claim 1, wherein the pattern is orthogonal to the Fresnel groove of the focusing plate.