JPS6155633A - Photometric device of single-lens reflex camera - Google Patents

Abstract

PURPOSE:To attain center preferential average photometry with respect to the photometric characteristic by changing stepwise the reflection factor of a half- transmission part, which branches the optical path in a prism, to adjust the photometric characteristic. CONSTITUTION:The luminous flux focused by a photographic lens 1 is reflected on a mirror 2 to form an image on a focusing screen 4, and this light is reflected on prisms 5 and 6 and is emitted from a surface S6 and reaches an eye 8 through an eyepiece lens 7. A half-transmission part 9 is provided on a surface S3 of the prism 5 to lead a part of the luminous flux to a photodetector 10. Since the reflection factor of the half-transmission part 9 is reduced stepwise toward a surface S1', the dense distribution of light under the center of the picture on the photometric sensitivity distribution is reduced to attain center preferential average photometry.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical system for a camera having a photometric device, and more particularly to an optical system suitable for an eye reflex camera or an electronic camera using an image pickup tube or a solid-state photographing element.

Conventionally, single-lens reflex cameras using silver halide film have achieved great development as they have an optimal structure for system development. A typical optical system is
The optical path of the photographing lens is branched by a quick return puller to become the finder optical path, and nine optical paths are split into one.
In this configuration, the light path is guided to a prism, the direction of the optical path is changed, the left and right sides of the screen are reversed, and the light is guided to the eyepiece.

Then, the so-called T that measures the light flux passing through the photographic lens
A photometric device that performs TL photometry is often placed on the bottom surface or exit surface of a pentagonal roof prism.

However, in recent finder optical systems in so-called electronic cameras using imaging bodies such as CCDs, the above-mentioned finder optical systems have become less desirable in terms of optical performance and construction. This is mainly due to the following reasons.

(b) For example, the effective screen of a 5-inch image pickup body is 35% smaller in diagonal length ratio than that of a film, so it is not possible to obtain the specified field of view ratio and field magnification using a conventional penta-roof prism. becomes difficult.

(b) A space must be provided at the rear of the image pickup body for arranging the electrical processing circuit, which increases the distance from the image plane of the photographic lens to the rearmost end of the camera. For this reason, the pupil position for observation of the finder optical system is set to KyJg behind the camera side.
This configuration is difficult to maintain optical performance.

Regarding the optical performance of (a) and (b) above, what is particularly important is the field of view magnification, which will be discussed below. In general, the larger the field of view magnification h is, the easier it is to observe as a pointing optical system, so it is preferable. The field of view magnification r is the standard focal length of the photographic lens.
o, the focal length of the eyepiece is f. Then = f, the field of view multiplication f.

In order to increase the ratio γ, it is necessary to decrease the focal length f0.

The eyepiece lens is arranged so that its front focal point is located near the image formation plane of the finder optical system, so the field magnification γ
In order to achieve high magnification, it is necessary to make the optical path length of the optical system from the focusing screen of the eyepiece optical system to the eyepiece lens to obtain a so-called erect normal image as small as possible. Now, temporarily change the focal length of the photographing lens to % inches so that it corresponds to a standard lens for the image pickup object.
12.5 mm, and the field magnification γ is 16, the focal length f of the eyepiece is 2 (L8).Therefore, in the conventional finder optical system using a penta roof prism, the field magnification r = α6 or more can be obtained. In this case, the optical path length from the focusing screen to the eyepiece must be approximately 20.8 mm, which is approximately equal to the focal length of the eyepiece.This means that the eyepiece can be placed as close as possible to the exit surface of the penta roof prism. This means that it is necessary to do this, and it is actually difficult because it conflicts with the desire to set the observation pupil behind the rear end of the camera due to the above-mentioned (mouth) condition.

The applicant of this patent previously proposed in Japanese Patent Application No. 59-126825 that the viewfinder optical system is designed to increase the field of view magnification of the finder, and the observation pupil is set behind the rear end of the camera, and the photometric element is This article describes a device that guides a portion of the finder light beam. However, since the structure of the finder optical system itself is designed to meet difficult requirements, there is little margin for satisfying other requirements, making it difficult to freely select photometric characteristics.

(Objective) The object of the present invention is to - provide a device for branching the optical path of the finder optical system of an eye reflex camera and guiding the light to a photometric element;
This allows the photometric characteristics to be shaped as desired.

The second purpose is to expand the field of view magnification and to branch the optical path of the finder, which moves the pupil to the rear of the camera body, to achieve photometry, and to change the photometry characteristics to center-weighted average photometry regardless of the position of the photometry element. This is what I did.

In order to achieve the above objects, the present invention provides a photographic lens that forms a subject image on an imaging body, and a finder that is optically coupled to the photographic lens and includes a prism that guides light through multiple internal reflections. , the light-transmitting surface has a light-transmitting surface that branches an optical path in the prism, and a photometric element that receives the light beam passing through the branched optical path, and the light-transmitting surface has a mirror finish in which the reflectance changes continuously or stepwise. The photometric characteristics are adjusted by changing the reflectance.

(Example) The present invention will be described in detail below with reference to FIG. In the figure,
1 has the function of forming an image of a subject with a photographing lens. 2
is a tights critter/mirror that has the function of guiding light to the viewfinder. The mirror 2 may be a semi-transparent mirror.

3 is the imaging surface of the solid-state imaging device. Reference numeral 4 denotes a focusing screen, which has, for example, a split prism in the center and a matte surface around the periphery, and is arranged at approximately the same position as the photographing surface 5 with respect to the mirror 2. A light beam subjected to an imaging action by the photographing lens 1 is reflected by the mirror 2 and forms an image on or near the focusing screen 4.

Combination prisms 5 and 6 have the function of changing the direction of the optical path, determining the positional relationship between the optical axis of the photographing lens 1 and the optical axis of the eyepiece lens 7, and reversing the left and right sides of the screen. The first prism 5 has a triangular prism shape, and the illustrated surface corresponds to the cross section.

Sl is an incident surface, S2 is a mirror-treated first reflective surface,
B and l are assumed to undergo total reflection or specular reflection on the second reflecting surface, and are surfaces that are extensions of the incident surface S1. Further, B5 is an output surface. 6 is the second prism, S4 is the entrance surface, S5/S5/
is a first reflective surface, which is a mirror-treated Dach surface. Bi2 is assumed to undergo total reflection or specular reflection on the second reflecting surface, and has nine surfaces extending from the incident surface S4. S6 is an exit surface. Further, the light emitted from the focusing screen 4 enters the first prism 50 incident surface S1 perpendicularly, and after being reflected by the first reflective surface S2 on which a reflective film is deposited, the light enters the incident surface S1 of the first prism 50.
The light is totally reflected or specularly reflected by the second reflecting surface B1/ which is the same surface as , and is emitted from the first grism 5 through the exit surface S5. After that, the light beam enters through the incident surface 84 of the second prism B, is reflected by the roof surface formed by the two third reflective surfaces S5 and fourth reflective surface B5' on which reflective films are deposited, and is further reflected on the same surface as the incident surface S4. After being reflected at the fifth reflecting surface B4t, the light is emitted substantially perpendicularly from the exit surface 86. The light beam emitted from the exit surface S6 passes through the eyepiece lens 7 and reaches the observation meK. Incidentally, the if prism 5 and the second prism 6 may be attached to each other, or may be arranged with a slight gap between them.

Next, a method for performing photometry in such a configuration will be described.

In the figure, the exit surface 85 of the first prism or the second prism
A semi-transparent part 9 is provided on either of the entrance surfaces 84 of the prism,
A light-receiving element disposed near the second reflective surface S1 that reflects a part of the luminous flux totally reflected by the second reflective surfaces B and I of the M1 prism toward the second reflective surface 611 and emits it from the second reflective surface 611. 10 and measure the light. However, since the light receiving element 10 and the focusing screen 4 are placed close to each other, if consideration is given to eliminating mechanical interference between the holding members, the position of the light receiving element cannot be brought close to the light-shift focusing screen. The problem caused by this K will be explained with reference to FIG. 2. Since the center of the light-receiving element 10 is located at the distance from the eyepiece lens υ, the photometric sensitivity distribution on the focusing screen is biased. At the same time, for convenience, we will show how the light rays emitted in various directions from the center point of the light receiving element are distributed on the 7 orcasing screen 4, and from this, the photometric sensitivity distribution is from the center of the screen. Showing a dense distribution at the bottom,
Bottom-weighted average metering. This is shown in FIG.

With the photometric sensitivity distribution shown in the same figure, the normal amount is also high in a bust shot scene of a typical person, since the face of the person in the scene is slightly above the center of the screen (Kt), so when the person is wearing black clothes, If the head is extremely over-exposed, or if you are wearing white clothes, it will be under-exposed), making it difficult to obtain optimal exposure.

To deal with this situation, the semi-transparent part 9 in Fig. 1 has a continuous or stepwise reflectance as shown in Fig. 4, and the semi-transparent part 9 in Fig.
Reflection surface B, the part close to r has a small reflectance.
are doing. With this configuration, the amount of reflected light in the lower portion gradually decreases, and the dense distribution of light rays below the center of the screen on the photometric sensitivity distribution can be reduced, providing an effect equivalent to center-weighted average photometry.

A film whose reflectance changes continuously is expensive, and a high degree of a is not necessarily required.

The semi-transparent film whose reflectance changes stepwise as shown in FIG. 4 can be easily manufactured, for example, by the following method. That is, when depositing a dielectric multilayer film onto a prism, a large number of masks having openings of different sizes are prepared, and the thickness and substance of the deposited film are changed for each mask, and the deposition is repeated in sequence. , a vapor deposited film is formed so that the reflectance changes stepwise. In this case, it is not necessary to regularly change the reflectance or the dimensions of the aperture of the mask, as long as the desired photometric sensitivity distribution is satisfied.

(Effects) As stated above, the present invention can transform the photometric distribution into a desired form, so when the prism in the viewfinder is adapted to the arrangement of the photographing system and camera itself, the photometric distribution will be different from the initial purpose. However, it has the effect of being able to adjust it freely.

A further advantage of the present invention is that the photometric element is less affected by reverse incident light that enters from the eyepiece side. Normally, as a means to prevent this, an eyepiece shutter placed near the eyepiece lens is used to solve the photometry error caused by reverse light, but the device is complicated and the operation is difficult.
It had the disadvantage of being stiff.

In the photometry method according to the present invention, most of the reverse incident light incident on the eyepiece side takes an optical path that goes backwards from the normal optical path of the finder optical system, so that the light flux incident on the incident surface S3 of the first prism is The light is totally reflected by the second reflecting surface B1r and does not reach the light receiving element 10, which has the advantage of not causing exposure errors.

[Brief explanation of the drawing]

FIG. 1 is an optical sectional view showing an embodiment of the present invention, FIG. 2 is an optical sectional view for explaining the photometric distribution depending on the shape of the prism, and FIG. 3 is the photometric distribution diagram. FIG. 4 is a perspective view showing a semi-transparent part according to the embodiment. In the figure, 1...Photographing lens 2...Quick return mirror 4...Focusing screen 5...First prism 6...Second prism 7...Eyepiece 9...Semi-transparent part 10 ...A light receiving element.

Claims (2)

[Claims] (1) A photographic lens that forms a subject image on an imaging body, a finder that is optically coupled to the photographic lens and includes a prism that guides light through multiple internal reflections, and an optical half that branches the optical path in the prism. It has a transmissive surface and a photometric element that receives the light beam passing through the branched optical path, and the semi-transmissive surface is formed by a mirror treatment in which the reflectance changes continuously or stepwise, and the reflectance changes continuously or stepwise. A photometric device for a single-lens reflex camera, characterized in that photometric characteristics are adjusted by. (2) A reflecting mirror is used to optically couple the finder to the photographing lens, and the prism has an entrance surface S_1 for vertically entering the reflected light from the reflecting mirror.
and the light reflected by the first reflecting surface S_2 and the second reflecting surface S_1' for reflecting and deflecting the light incident from the said incident surface so that it is reflected by the second reflecting surface S_1' which is an extension of the said incident surface. a first prism having an exit surface S_3 for emitting light; an entrance surface S_4 for entering the light emitted from the exit surface S_3 of the first prism; and the entrance surface S_
4, a roof-shaped third reflecting surface S_5, a fourth reflecting surface S_5', and the fifth
Output surface S for emitting the light reflected by the reflective surface S_4
_6, and the light semi-transmissive surface is located on the exit surface S_3 of the first prism or the entrance surface S_4 of the second prism, and
A part of the light reflected by the reflecting surface S_1' is transferred to the second reflecting surface S_
2. A photometric device for a single-lens reflex camera according to claim 1, wherein the reflectance of said semi-transparent surface decreases as it approaches said second reflecting surface S_1'.