JPH05232548A - Prism finder - Google Patents

Abstract

PURPOSE:To excellently observe a finder image. CONSTITUTION:An image is formed on the display surface S2 of a display board 10b, and light from the display surface S2 is bent by a prism 20b and reflection mirrors 30b and 30c and guided toward a pupil E by oculars 40b and 40c. The display board 10b is inclined so that the optical axis AX of the oculars 40b and 40c may be aligned with a field direction having the highest contrast ratio in the center part of the display surface S2. The oculars 40b and 40c are adjusted so that the finder magnification at that time may be equal to or under unmagnification.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a prism finder, and more particularly to a prism finder suitable for a video camera.

[0002]

2. Description of the Related Art FIG. 5 shows a schematic structure of a conventionally known prism finder. This prism finder can be applied to a video camera or the like, and mainly includes a display plate 10a forming the display surface S1, a first prism 20a, a second prism 30a, and an eyepiece lens 40a.

A display plate 10a (AX in the figure is the optical axis of the eyepiece lens 40a) formed of a liquid crystal display device forms an image on the display surface S1. Then, the light beam emitted from the display surface S1 is refracted by the B surface 2 of the first prism 20a,
It is reflected by the A surface 1. The A surface 1 does not have to be a vapor deposition surface as long as an incident angle equal to or greater than the critical angle is secured, and may be an ordinary polished surface. However, in general, in view of downsizing and a prism finder system, the vapor deposition surface is There are many things that have become.

The light rays reflected by the A surface 1 of the first prism 20a reach the B surface 2 again. Since some light rays are incident from the display surface S1 on the B surface 2, an incident angle equal to or greater than the critical angle is set here for total reflection. Then, the light rays reflected by the B surface 2 are transmitted to the C surface 3 of the first prism 20a and the second surface.
After being refracted by the E surface 5 of the prism 30a, it is reflected by the D surface 4 and the E surface 5, and then emitted from the F surface 6. And
The eyepiece 40a magnifies the image to a desired finder magnification to form an image, which reaches the pupil. Therefore, the photographer can look into the finder from the direction perpendicular to the display surface S1.

The finder magnification is the eyepiece lens 4
When the angle formed by the pupil with respect to the image on the display surface S1 without passing through 0a is α ₁ and the angle formed by the pupil with respect to the image on the display surface S1 through the eyepiece lens 40a is α ₂ , α ₂
/ α ₁ .

[0006]

However, in the conventional example as shown in FIG. 5, the viewing angle characteristic of the display surface S1 is not taken into consideration. Therefore, when a display plate 10a having a viewing angle characteristic in which an element that affects the finder image such as contrast changes depending on the angle of inclination from the vertical direction with respect to the display surface S1, a good finder image is obtained. There is a problem that you cannot get it.

Further, since the above-mentioned conventional example is configured to form a magnified image, there is a problem that the screen becomes difficult to see when the display surface S1 is made to be observed relatively large. For example, when liquid crystal display is performed on the display surface S1, there arises a problem that pixels become rough.

The present invention has been made in view of these points, and an object of the present invention is to provide a prism finder in which a finder image is satisfactorily observed.

[0009]

In order to achieve the above object, the prism finder of the present invention comprises a display member for forming an image on the display surface and a reflecting surface for bending light from the display surface in a predetermined direction. In a prism finder including a prism having an eyepiece optical system that guides light emitted from the prism to a pupil, the display member is provided so that the viewing angle characteristics of the display surface match the optical axis of the eyepiece optical system. The feature is that it is inclined.

The viewing angle characteristic is, for example, an inclination of a viewing direction having the highest contrast ratio on the display surface from a direction perpendicular to the display surface.

Further, the prism finder of the present invention is
A prism finder including a display member that forms an image on the display surface, a prism having a reflecting surface that bends the light from the display surface in a predetermined direction, and an eyepiece optical system that guides the light emitted from the prism to the pupil. In, the angle formed by the pupil on the image on the display surface through the eyepiece optical system is equal to or smaller than the angle formed by the pupil on the image on the display surface without passing through the eyepiece. It has a feature.

[0012]

For example, the image formed on the display surface has a high contrast by tilting the display member so that the optical axis of the eyepiece optical system and the viewing direction with the highest contrast ratio on the display surface are aligned with each other. The finder image is formed in the best condition.

Further, if the finder magnification is equal to or smaller than 1: 1, for example, the roughness of pixels becomes inconspicuous.

[0014]

Embodiments of the prism finder of the present invention will be described below with reference to the drawings. FIG. 1 shows a schematic structure of the prism finder of this embodiment. As shown in the figure, the A ′ surface 11, B ′ surface 12 and C ′ surface 13 of the prism 20b correspond to the A surface 1, B surface 2 and C surface 3 of the first prism 20a shown in FIG. The D ′ surface 14 of the reflecting mirror 30b and the E ′ surface 15 of the reflecting mirror 30c are surfaces corresponding to the D surface 4 and the E surface 5 of the second prism 30a shown in FIG. 5, respectively, and have the same optical path as the conventional example. Is forming.

However, since the D ′ surface 14 and the E ′ surface 15 are divided into the reflection mirror 30b and the reflection mirror 30c, respectively,
There is no surface corresponding to the F surface 6 in FIG. In the prism 30a of FIG. 5, the surfaces on which the light flux emitted from the C surface 3 is incident (F surface 6 and E surface 5) are required to be polishing surfaces, but the polishing surfaces are eliminated. Cost reduction is possible.

By using the reflection mirrors 30b and 30c instead of the second prism 30a, the optical path portion between them is air. Therefore, although it goes against the size reduction, it does not hinder the viewfinder as a whole.

Next, the viewing angle characteristics of the display surface S2 of the display plate 20 used as a display member in this embodiment will be described with reference to FIG.

The display surface S2 has a viewing angle characteristic in which the contrast changes depending on the angle of inclination from the vertical direction with respect to the display surface S2. That is, as shown in FIG. 2, the upper and lower portions of the display surface S2 are respectively displayed on the upper surface SU of the display surface.
And the lower part SD of the display surface, the viewing angle characteristic of the display surface S2 of the display plate 20 is such that the viewing angle direction is such that the best contrast ratio is obtained with respect to the central portion of the display surface S2.
It is in a state of being inclined in the direction of θ ′ degrees toward the lower part SD of the display surface.

The allowable range of the contrast ratio is
There are θ degrees each from the direction inclined by θ ′ toward the display surface upper portion SU and the display surface lower portion SD (hereinafter, referred to as “vertical direction”). Further, the viewing angle characteristics of the display surface S2 in the left-right direction with respect to the up-down direction (hereinafter, referred to as “left-right direction”) have an allowable range that is sufficiently larger than θ degrees, so that a value corresponding to θ ′ degrees is However, the inclination in the left-right direction is 0 degree.
Since the viewing angle characteristics are directional in this way, in this embodiment, it is only necessary to consider the vertical direction.
Although FIG. 2 shows the viewing angle characteristics for the central portion of the display surface S2, it is assumed that this is the same for any portion of the display surface S2.

Since the display plate 10b has a vertical viewing angle characteristic as described above, as shown in FIG. 1, the display surface S2 is vertically inclined by θ'with respect to the B'plane of the prism 20b. The display surface S2 in the viewing direction having the highest contrast ratio with respect to the optical axis AX of the eyepieces 40b and 40c forming the eyepiece optical system.
Is tilted from the vertical direction. This inclination can be achieved by inclining the display plate 10b and aligning the optical axes AX of the eyepieces 40b and 40c with the viewing direction with the highest contrast ratio in the central portion of the display surface S2.

Further, as the shape of the prism 20b, a light ray from the edge of the upper display surface SU and a light ray from the edge of the lower display surface SD which are inclined by θ degrees with respect to the vertical direction of the B ′ surface 12 can be used. Is designed to be. By this,
It is possible to realize a prism finder that is suitable for the viewing angle characteristics of the display surface S2 and that does not waste. In addition, since the viewing angle characteristics have directionality as described above, it is not necessary to tilt the display surface S2 in the left-right direction.

In this way, the display plate 10b, the prism 20b and the eyepieces 40b and 40c constituting the display surface S2 are formed.
By determining the positional relationship and the configuration state with respect to the viewing angle characteristics of the display surface S2, it is possible to prevent deterioration of the finder image due to the viewing angle characteristics. According to this embodiment, the photographer can look into the finder from a direction substantially perpendicular to the display surface S2.

The viewfinder magnification is determined by the eyepieces 40b and 40c shown in FIG. FIG. 3 shows the optical relationship of the finder system by paraxial rays in the present embodiment forming a virtual image finder. In the figure, the respective optical values of paraxial rays can be derived by the following equations (1) to (4). f ₀ = (f ₁ · f ₂ ) / (f ₁ + f ₂ −D) (1) A = f ₀ · D / f ₂ (2) B = f ₀ · D / f ₁ (3) m = −f ₁ / f ₂ = Y / X (4) where, f ₀ : eyepiece lens 40b and eyepiece lens 40c
Synthesis of the focal length f _1: eyepiece 40b having a focal length f _2: the focal length of the eyepiece 40c m: finder magnification A: front principal point of the synthetic front principal point H and the eyepiece 40b H ₁
Interval B: Distance between composite rear principal point H ′ and rear principal point H ₂ ′ of eyepiece 40 c D: Rear principal point H ₁ ′ of eyepiece 40 _b and eyepiece 40
c is the distance between the front principal point H ₂ and X: the distance between the combining front principal point H and the display surface S2 Y: the distance between the combining rear principal point H ′ and the virtual image I. In addition, C in FIG. 3 represents the clear viewing distance.

As a method of designing the finder optical system, as shown in FIG. 4, when the virtual image I is seen directly from the eyepoint E, and when the display surface S2 is used to view the eyepieces 40b, 4b.
The eyepieces 40b and 40c will be designed so that the ratio of the respective angles Z when entering the eyepoint E through 0c becomes the desired finder magnification.

As described above, since the display surface S2 has the viewing angle characteristic that the contrast changes depending on the angle θ'inclined from the vertical direction with respect to the display surface S2, the display surface S2 is displayed according to the viewing angle characteristic. By changing the positional relationship between the surface S2 and the prism 20b (FIG. 1) and then determining the prism 20b to have a predetermined shape, it is possible to achieve compactness and obtain an optimum image that matches the viewing angle characteristics. You can do it.

Further, the positions of the pre-combination main point H and the post-combination main point H'of the eyepieces 40b and 40c are adjusted (FIG. 3),
By setting the viewfinder magnification m to about 1x or less,
The pixels of the finder image formed by the display plate 10b composed of the liquid crystal display device become fine. That is, the display surface S
Even when 2 is observed relatively large, the visibility of the image is improved. However, in the present embodiment, the display plate 10b having a large display surface S2 is used so that the finder magnification is kept low so that the observed finder image does not become small.

Although this embodiment is a viewfinder suitable for a video camera, it can be applied to a still camera such as a single-lens reflex camera if a focusing screen is used instead of the display plate 10b.

[0028]

As described above, the prism finder of the present invention has a viewing angle characteristic of the display surface with respect to the optical axis of the eyepiece optical system (for example, the viewing direction in the viewing direction with the highest contrast ratio on the display surface). Since the display member is inclined so that the inclination from the direction perpendicular to the display surface is matched, it is compatible with the display member that forms an image on the display surface, and the finder image is well observed. A finder can be realized.

Further, the prism finder of the present invention is
The angle at which the pupil is extended with respect to the image on the display surface through the eyepiece optical system is equal to or smaller than the angle at which the pupil is extended with respect to the image on the display surface without passing through the eyepiece lens, that is, the viewfinder magnification. By making it equal to or less than 1 ×, it is possible to realize a prism finder in which the pixels of the finder image are made fine and the image is easy to see even when the display surface is relatively large, and the finder image is well observed.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a diagram for explaining viewing angle characteristics of a display surface in an example of the present invention.

FIG. 3 is a diagram showing an optical relationship of a finder system by paraxial rays in an example of the present invention.

FIG. 4 is a diagram for explaining an example of a finder optical system designing method according to an embodiment of the present invention.

FIG. 5 is a view showing a conventional example of a prism finder.

[Explanation of symbols]

 10b ... Display plate 20b ... Prism 30b, 30c ... Reflection mirror 40b, 40c ... Eyepiece E ... Pupil S2 ... Display surface

Claims (3)

[Claims] 1. A display member for forming an image on a display surface, a prism having a reflecting surface for bending light from the display surface in a predetermined direction, and an eyepiece optical system for guiding light emitted from the prism to a pupil. In the prism finder, the display member is tilted so that the viewing angle characteristics of the display surface match the optical axis of the eyepiece optical system. 2. The prism finder according to claim 1, wherein the viewing angle characteristic is an inclination of a viewing direction having the highest contrast ratio on the display surface from a direction perpendicular to the display surface. 3. A display member for forming an image on a display surface, a prism having a reflecting surface for bending light from the display surface in a predetermined direction, and an eyepiece optical system for guiding light emitted from the prism to a pupil. In the prism finder consisting of, the angle at which the pupil on the image on the display surface through the eyepiece optical system is less than or equal to the angle at which the pupil on the image on the display surface does not pass through the eyepiece. A prism finder that is characterized by being