JPS61109030A - Finder optical system - Google Patents

Abstract

PURPOSE:To obtain a high visual field rate and high visual field magnification and lead out even a photometry output by forming a finder image between two prisms and providing a light splitter, and converting the finder image into a regular erect image through the roof surface reflection of the 2nd prism. CONSTITUTION:Luminous flux passed through a photographic lens 1 is split into photographic luminous flux and finder luminous flux through a prism 10 having a translucent reflecting surface 2, and the finder luminous flux is reflected by a reflecting surface 4 on the same plane with the incidence surface 10-1 of the prism 10 to form the finder image on a focal plate 5 arranged at a position optically equivalent to an image pickup body 3. An observer observes it as the regular erect image through an ocular lens 6 after the reflection of a prism 11 having the roof surface. Further, the light splitter 301 having the translucent reflecting surface is arranged between the prisms 10 and 11 and reflected luminous flux from the translucent reflecting surface is guided to a photodetecting element 303. Thus, the high visual field rate and high visual field power are obtained and even the photometry output is led out.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a finder optical system, and more particularly to a simple finder optical system having a TTL optical photometer suitable for so-called electronic cameras that use an image pickup tube or a solid-state image sensor such as a COD. .

Conventionally, the finder optical system of a single-lens reflex camera for 35 m film has formed an erect finder image via a penta roof prism. This finder optical system has a ratio of the image taken on the film surface to the image observed by the finder optical system, that is, a field of view ratio of 90% or more, and a field magnification of α8 or more when a standard lens is attached. It has excellent performance.

On the other hand, electronic cameras that use recent image pickup bodies such as COD have smaller effective screens than conventional single-lens reflex cameras, and require a relatively large electronic circuit to connect to the image pickup body. are different.

For this reason, in order to obtain a finder optical system with a high field of view and high field of view magnification similar to that of a single-lens reflex camera in an electronic camera, the effective screen is small, so the optical path length of the finder system must be shortened accordingly. A short eyepiece is required.

In order to use an eyepiece with a short focal length in a finder system, it is necessary to shorten the distance from the focus plate where the finder image is formed to the eyepiece, that is, the optical path length, and use a prism with an erect image system. However, since the pentagonal roof prism has a long optical path length, the focal length of the eyepiece must be correspondingly long when using the pentagonal roof prism. For this reason, the pentagonal roof prism is not very suitable for obtaining a high field of view and high field of view magnification in the finder optical system of an electronic camera with a relatively small effective screen. In addition, when using a penta roof prism, the photometer can be placed in a part of the finder optical system, or if it is placed near the bottom of the penta roof prism to display information within the field of view of the finder, the finder optical system can be viewed from a wide angle. There is a tendency to become

SUMMARY OF THE INVENTION An object of the present invention is to provide a TTL optical finder optical system that is suitable for electronic cameras and the like with a relatively small effective screen and is capable of photometering a part of a subject with a small and simple configuration.

The main feature of the finder optical system for achieving the object of the present invention is that a first prism having a semi-transparent reflective surface is disposed on the image plane side of the photographing lens to divide the incident light beam into the photographing light beam and the finder light beam. , after passing through the photographic lens, the next light beam enters the person from the entrance surface of the agl prism, is reflected by the semi-transparent reflection surface, and is reflected by the reflection surface substantially on the same plane as the entrance surface, and then exits from the first prism. After t, the light is guided onto the first imaging surface to form a finder image, and a second prism having a dowel and a surface disposed behind the first imaging surface and a second
The viewfinder image is changed to an erect image by the eyepiece lens placed behind the exit surface of the prism, and the first
A light splitter having a semi-transparent reflective surface is disposed between the prism 1 and the 20th prism, and the reflected light beam from the semi-transparent reflective surface of the light splitter is guided to a light receiving element for photometry.

Next, one embodiment of the present invention will be described with reference to each drawing.

FIG. 1 is a schematic diagram of an optical system according to an embodiment of the present invention, and FIG. 2 is an explanatory diagram of a portion of FIG. 1.

In FIGS. 1 and 2, the light beam passing through the photographing lens 1 is divided into two by a first prism 10 having a semi-transparent reflective surface 2 for dividing the photographing light beam and the finder light beam. The light beam passes through the first prism lO and reaches the image pickup body 3. On the other hand, the finder light beam is reflected by the semi-transparent reflective surface 2 and then passes through the first prism 100.
It undergoes specular reflection or total reflection on the reflection surface 4 on the same plane as the entrance surface 10-1, exits from the exit surface 10-2 of the first prism 10, and is placed at a position optically equivalent to the imaging body 3. A finder image is formed on the first imaging plane 5 & on the focusing plate s. The observer observes the finder image on the primary imaging plane 5 through the eyepiece 6t through the reflection of the second prism 11 having a roof surface.

301 is a light splitter for photometry, and has a semi-transparent reflective surface 302 for light splitting. A part of the finder light flux is reflected by the semi-transparent reflective surface 302 and then reflected at the bottom L of the light splitter 301.
The light rays 1j and 1j undergo total internal reflection on the top surface, exit from the end surface, and are guided to the light receiving element 303K. The camera system performs an integral calculation on the amount of light obtained by the light receiving element 303 to determine appropriate exposure.

Here, the light splitter may also serve as a condenser lens for pupil alignment of the field image, and may also serve as a condenser lens.
A light splitter shown in FIG. 3 disclosed in Japanese Patent No. 106518 may be used. An example of its configuration is shown in FIG.

The light splitter shown in FIG. 3 is constructed by having a large number of grating line portions 305t-curvatures inside a parallel flat plate in order to guide the incident light beam in one direction.

In this way, in this embodiment, a finder image is formed between two prisms, and a light splitter for photometry is placed between the two prisms to measure part of the finder image using a simple configuration, thereby achieving highly accurate TTL photometry. is possible.

7 is a display element for displaying information in a part of the field of view of the finder. The display element 7 is placed close to the periphery of a field frame 8 that completely limits the size of the finder image on the first imaging plane 51, and the light flux from the display element 7 is directed to the incident surface of the second prism 11. 9, the Danault surface 12a, 12
It is reflected at b, exits from the exit surface 13, passes through the eyepiece lens 6t, and enters the observation pupil.

The narrow beam of light for this information display is rounded to pass outside the ninth beam of light for object image observation, and a space is provided between the entrance surface 9 and the exit surface 13 of the second prism 11. There is.

201 is a member 69 that holds the display element 7 and focus plate 5;
, on which a second prism is roughly placed. In the figure, the first imaging surface 5a and the display element surface are arranged on the same plane, but when the focal length of the eyepiece is shortened to achieve a high field of view magnification, the isotropic surface is often looks like the dotted line in the figure. Therefore, in order to make the viewfinder image and the image of the display element 7 have the same visibility in FIG. 2, it is preferable to raise the display element 70 surface to the eyepiece side from the first image forming surface 5a.

In this embodiment, the light splitter 301 is placed above the focusing plate 5 to create a space, so the position of the display element 7 can be set arbitrarily, and the display element 7 can be observed well. There is.

In the finder optical system IC in this embodiment, the second
For my friend who is creating an erect image system only by reflection from the roof surface of the prism 11, the optical path length inside the prism can be shortened compared to a penta roof prism, in other words, an eyepiece with a short focal length can be used. It is possible to easily achieve high field of view and high field of view magnification.

In this embodiment, since the finder image on the first image forming surface 5a is vertically and horizontally inverted, the display element 7 is moved upward and downward to the right and arranged in the alignment f-g.

In this embodiment, the first imaging plane 5a and the t-focal plate 5
It can also be used as the bottom surface of

In addition, in Example 9, when the light rays on the optical axis of the finder system enter and exit the two prisms, the configuration is such that they enter and exit perpendicularly, respectively, to maintain good optical performance of the finder image. preferred to do.

As described above, according to the present invention, a TTL optical finder optical system has a photometry device with a small and simple configuration that has a high field of view ratio and a high field of view magnification suitable for electronic cameras with relatively small effective screens. be able to achieve the goal.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of an optical system according to an embodiment of the present invention, and Figure 2 is! 1 is an explanatory diagram of a part of FIG. 1, and FIG. 3 is an explanatory diagram of a modified part of FIG. 2. In the figure, 1 is a photographing system, 2 is a transflective surface, 3 is an imaging body, 5 is a focus plate, 6 is an eyepiece, 7 is a display element, 8 is a light receiving element, 10#:t, the first prism, Ll is a second prism, and 301 is a light splitter.

Claims (2)

[Claims] (1) A first prism having a semi-transparent reflective surface for splitting the incident light beam into a photographing light beam and a finder light beam is arranged on the image plane side of the photographic lens, and the first prism out of the light beam passing through the photographic lens is arranged. A light flux that enters the prism from the incident surface and is reflected by the semi-transparent reflective surface is reflected by a reflective surface that is substantially coplanar with the incident surface and exits from the first prism, and then onto a first image forming surface. A second prism that guides light to form a finder image and has a roof surface placed behind the first image forming surface and an eyepiece placed behind the exit surface of the second prism to form the finder image. The first prism and the second prism are observed while changing to an erect image.
A finder optical system, characterized in that a light splitter having a semi-transparent reflective surface is disposed between the prism and the light splitter, and a reflected light beam from the semi-transparent reflective surface of the light splitter is guided to a light receiving element for photometry. (2) The finder optical system according to claim 1, characterized in that an information carrier for observing the finder image together with the finder image is disposed near the first imaging plane.