JPH10186454A - Prism - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a prism capable of taking light in a condensing lens for photometry as efficiently as possible. SOLUTION: A plane parallel plate 22 is stuck to the back surface of a pentagonal prism 20. The surface of the plate 22 is a 1st light emitting surface 22 opposed to the ocular 12a of a finder 12. The upper part of the prism 20 than the plate 22 is a 2nd light emitting surface 23 opposed to the condensing lens 15 of an optical system for photometry. Namely, the 1st emitting surface 22 is projected from the 2nd emitting surface.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a pentaprism for a single-lens reflex camera, for example.

[0002]

2. Description of the Related Art Conventionally, a pentaprism of a single-lens reflex camera used as a part of a photometric optical system is known. That is, a light receiving element for photometry is provided on the back of this pentaprism and near the eyepiece of the finder optical system, and a condenser lens is provided between the back and the light receiving element. The transmitted light is reflected in the pentaprism, exits from the back surface, and enters the light receiving element, whereby the photometric value of the subject image is detected.

[0003] At least the portion facing the eyepiece and the portion facing the condenser lens of the finder optical system on the back surface of the pentaprism must be transmissive surfaces.
The transmitting surface is usually formed by polishing, but it is very difficult to polish a stepped surface, so the part facing the eyepiece and the condensing lens, that is, most of the back of the pentaprism is formed as a plane. Is done.

[0004]

However, in order to make the pentaprism as small as possible, the size of the back surface is limited, and most of the back surface faces the eyepiece of the finder optical system. That is, the light-measuring condenser lens is disposed at the end of the rear surface, and therefore, conventionally, it is not possible to secure a sufficient area of the portion facing the light-measuring light-collecting lens. There is a problem that the light receiving amount of the element becomes small and it is difficult to improve the detection accuracy of the photometric value.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a prism which can take in light as efficiently as possible into a photometric condenser lens.

[0006]

In the prism according to the present invention, the second exit surface facing the condenser lens of the photometric optical system is more concave than the first exit surface facing the eyepiece of the finder. It is characterized by having.

The first exit surface is, for example, the surface of a plane-parallel plate adhered to a part of the surface of the prism. In this case,
The second exit surface is formed at a portion of the prism surface where the parallel flat plate is not attached.

The second exit surface is formed, for example, by forming a transparent plate having at least one surface as a transmission surface on a wall surface formed by grinding a part of the surface of the prism so that the transmission surface is on the front side. It may be formed by attaching with a light transmitting adhesive. In this case, it is preferable that the adhesive does not substantially shrink when cured.

[0009] The prism is formed of, for example, glass,
It is also used as a pentaprism for single-lens reflex cameras.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a view showing a pentaprism of a single-lens reflex camera to which the first embodiment of the present invention is applied, and this pentaprism is formed of glass.

The focus plate 11 faces the lower surface of the pentaprism 20, that is, the entrance surface 21, and the eyepiece 12a of the finder 12 faces the first exit surface 22 formed on the back surface of the pentaprism 20. A condenser lens 15 is provided in an opening 14 formed above a housing 13 of the finder 12, and a light receiving element 16 for detecting a photometric value is provided behind the opening 14. The condenser lens 15 faces a second emission surface 23 formed above the first emission surface 22. That is, the pentaprism 20
Is used as a part of the photometric optical system in addition to the finder optical system.

As shown in FIGS. 2 to 4, the back surface of the pentaprism 20 is substantially triangular, and a trapezoidal parallel plane plate 25 is adhered to the center of the pentaprism 20 with a light transmitting adhesive. The surface of the plane-parallel plate 25 is the first emission surface 22. The oblique side of the trapezoid of the parallel plane plate 25 coincides with the oblique side of the triangle on the back of the pentaprism 20, and on the back of the pentaprism 20, above the parallel plane 25,
That is, the second emission surface 23 having a shape similar to the triangle on the back surface is formed in a portion where the parallel plane plate 25 is not stuck. Below the parallel plane plate 25, a trapezoidal concave portion 24 that is elongated in the horizontal direction is formed.

As described above, the condenser lens 1 of the photometric optical system
The first emission surface 22 facing the projection 5 projects more than the second emission surface 23 facing the eyepiece 12a of the finder. First and second exit surfaces 22, 23 and recess 24
Is a polished surface, that is, a transmission surface, but the wall surface of the concave portion 24 may be a rubbed surface (non-polished surface).

In the conventional apparatus, as shown in FIG. 5, the exit surface 42 has the same plane as the portion where the condenser lens 15 of the photometric optical system faces and the portion where the eyepiece 12a of the finder 12 faces. , The recess 24 below the exit surface 42.
Are formed. Comparing the pentaprism 40 of FIG. 5 with the pentaprism 20 of FIG. 1, the distances from the tips S of the pentaprisms 40 and 20 to the emission surfaces 42 and 22 are equal to each other. The condenser lens 15 is located behind the first exit surface 22 in FIG. For this reason, the area of the exit surface facing the condenser lens 15 is relatively small, and the amount of light received by the light receiving element 16 is not sufficient.

On the other hand, in the present embodiment, the second light exit surface 23 is more concave than the first light exit surface 22, and the second light exit surface 23 is lower than the light exit surface 42 of the conventional pentaprism 40. It is located on the front side, that is, to the left in FIG. The reason why the second exit surface 23 can be recessed in this way is as follows.
As shown in FIG. 6, light required as a finder light beam is a portion surrounded by two-dot chain lines K and L. For example, a hatched portion M does not adversely affect the finder even if the prism is cut. It is. The reason why the first emission surface 22 should be relatively protruded is to prevent stray light (indicated by a one-dot chain line J in FIG. 5) from being reflected into the prism.

As described above, according to the present embodiment, the condenser lens 15 and the light receiving element 16 can be relatively arranged on the pentaprism 20 side. As a result, the area of the exit surface facing the condenser lens 15 becomes relatively large, and the light receiving element 16 can efficiently guide the light to the condenser lens 15 and can perform photometry with lower luminance. Becomes

FIG. 7 is a view showing a pentaprism of a single-lens reflex camera to which the second embodiment of the present invention is applied.
8 to 10 show the pentaprism.

In this embodiment, a first concave portion 26 having a triangular shape is formed near the vertex of the back surface of the pentaprism 20, and a second concave portion 24 having a horizontally elongated trapezoid is formed at a lower portion of the back surface. Are formed. That is, a trapezoidal convex portion is formed between the concave portions 26 and 24, and the surface of the convex portion serves as the first emission surface 22. The recesses 26 and 24 are formed by grinding, and are rubbed (non-polished) surfaces.

On the triangular wall surface of the first concave portion 26, a back surface 32 of a glass transparent plate 31 having a triangle slightly smaller than the wall surface is adhered. At least the front surface 33 of the transparent plate 31 is a transmission surface (polished surface), but the back surface 32 may be a transmission surface or a rubbed surface (non-polished surface). The adhesive used to bond the transparent plate 31 to the recess 26 must have light transmittance, and preferably does not substantially shrink when cured.

As described above, the transparent plate 31 whose surface 33 is a transmission surface is attached to the wall surface of the recess 26 via the light-transmitting adhesive, thereby forming a transmission surface in the recess 26. The condensing lens 15 of the photometric optical system is
1 is provided. Therefore, light with little disturbance enters the light receiving element 16 for photometry.

As described above, in the present embodiment, since the transparent plate 31 having a thickness smaller than the depth of the concave portion 23 and having a surface 33 as a transmission surface is attached to the wall surface of the concave portion 23 of the pentaprism 20, The optical lens 15 is disposed substantially within the recess 23. Accordingly, a sufficient amount of light for detecting the photometric value of the subject image is guided to the light receiving element 16, and photometry can be performed with high accuracy. In addition, since the present embodiment is configured to obtain the transmission surface by attaching the thin transparent plate 31, the polishing process for the surface of the pentaprism 20 can be reduced as much as possible, and the pentaprism 20 is provided on and around the pentaprism 20. The manufacturing cost of the optical system can be reduced.

Although the above embodiment is an example in which the present invention is applied to a pentaprism, the present invention is not limited to a prism shape.

[0023]

As described above, according to the present invention, light can be taken in as efficiently as possible into the condensing lens for photometry.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing a pentaprism to which a first embodiment of the present invention is applied and a configuration around the pentaprism.

FIG. 2 is a side view showing the pentaprism of the first embodiment.

FIG. 3 is a perspective view of the pentaprism of the first embodiment as viewed from an oblique direction.

FIG. 4 is a perspective view of the pentaprism according to the first embodiment as viewed from behind.

FIG. 5 is a partial cross-sectional view showing a conventional pentaprism and its peripheral configuration.

FIG. 6 is a diagram showing a light beam in a pentaprism.

FIG. 7 is a partial cross-sectional view illustrating a pentaprism to which a second embodiment of the present invention is applied and a configuration around the pentaprism.

FIG. 8 is a side view illustrating a pentaprism according to a second embodiment.

FIG. 9 is an exploded perspective view showing a pentaprism and a transparent plate according to a second embodiment.

FIG. 10 is a perspective view of a pentaprism according to a second embodiment as viewed from behind.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 12 Finder 12a Eyepiece 15 Condensing lens 20 Pentaprism 22 First emission surface 23 Second emission surface

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] November 17, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0013

[Correction method] Change

[Correction contents]

As described above, the eyepiece 12 of the finder
The first emission surface 22 facing the light-collecting optical system a
It projects beyond the second exit surface 23 facing the lens 15 . First and second exit surfaces 22, 23 and recess 24
Is a polished surface, that is, a transmission surface, but the wall surface of the concave portion 24 may be a rubbed surface (non-polished surface).

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0021

[Correction method] Change

[Correction contents]

[0021] In this embodiment as described above, the wall surface of the recessed portion 26 of the pentagonal prism 20, thinner than the depth of the recess 26, and the surface 33 is adhered to the transparent plate 31 is a transmission surface, collecting Optical lens 15 is disposed substantially within recess 26 . Accordingly, a sufficient amount of light for detecting the photometric value of the subject image is guided to the light receiving element 16, and photometry can be performed with high accuracy. In addition, since the present embodiment is configured to obtain the transmission surface by attaching the thin transparent plate 31, the polishing process for the surface of the pentaprism 20 can be reduced as much as possible, and the pentaprism 20 is provided on and around the pentaprism 20. The manufacturing cost of the optical system can be reduced.

Claims (6)

[Claims] A first finder facing an eyepiece of the finder;
And a second surface facing the condenser lens of the photometric optical system.
And a second emission surface is recessed from the first emission surface. 2. The method according to claim 1, wherein the first exit surface is a surface of a plane parallel plate adhered to a part of the surface of the prism, and the second exit surface is a surface of the plane parallel plate of the prism. 2. The method according to claim 1, wherein the adhesive layer is formed on a portion that is not adhered.
Prism. 3. A light-transmitting adhesive having a transparent plate having at least one transparent surface on a wall surface formed by grinding a part of the surface of the prism so that the transparent surface is on the front side. 2. The prism according to claim 1, wherein the second emission surface is formed by being attached with an agent. 3. 4. The prism according to claim 1, wherein the adhesive does not substantially shrink when cured. 5. The prism according to claim 1, wherein the prism is formed of glass. 6. The prism according to claim 1, wherein the prism is a pentaprism of a single-lens reflex camera.