JPS58120230A - Focusing screen for camera - Google Patents

Abstract

PURPOSE:To obtain a finder image which does not give a feeling of disorder, by constituting each of a pair of argument elements of minute prisms having >=2 kinds of arguments and arranging these prisms at random as the whole. CONSTITUTION:Many minute prisms different in inclination direction are arranged in upper and lower halves with a split prism division line 6 as the boundary, respectively. Minute prisms consist of prisms 7 and 9 having a large inclination angle and prisms 8 and 10 having a small inclination angle, and they are arranged at random as the whole. By this constitution, the shading phenomenon is generated for prisms 7 and 9 having a large inclination angle but a non- shaded optical image is seen for prisms 8 and 10 having a small inclination angle when the aperture ratio of a photogrpahic lens is reduced. Since minute prisms are arranged at random, a random blurred image is obtained for out-of- focus, and consequently, the finder image which does not give a feeling of disorder is obained.

Description

DETAILED DESCRIPTION OF THE INVENTION The second invention relates to a split prism reticle in which fine prisms are arranged.

Conventionally, a split prism focus plate used in a part of the viewfinder of an eye reflex camera has two prisms with inclination angles in opposite directions, and when the focus is correct, the two prisms are The optical images created through the lens appear to match, but when they are out of focus, the optical images appear to be shifted. The major drawback of this split lens and focus plate is that when the aperture ratio of the photographing lens becomes smaller, the optical image becomes darker, which is the so-called "shading group image".3 This "shading phenomenon" can be prevented. In order to prevent this, methods have been proposed such as reducing the inclination angle of the two prisms, providing a flat portion, or arranging prisms with two different inclination angles in the shape of a diffraction grating.

However, if the tilt angle is made small, the amount of deviation of the optical image relative to the amount of defocus becomes small, and the focus discrimination performance deteriorates. Further, if a flat portion is provided, the amount of light that does not contribute to focus determination increases, and the focus determination performance also deteriorates. Furthermore, the method of arranging prisms having two types of inclination angles in the shape of a diffraction grating has the drawback that the optical image is doubled due to the influence of the diffracted light due to the shape of the diffraction grating, resulting in a regular blurred image, which is troublesome. be.

The present invention prevents the "shadowing phenomenon" by arranging prisms having two or more types of inclination angles, and by making the prisms small.

The purpose of this is to solve the J problem by creating an optical image that does not give a strange impression by disposing the optical image on the run rim as a whole.

The invention of JJ de: will be explained with reference to the drawings.

Figure 1 shows a conventional split prism focus plate.
FIG.

When the light emitted from the photographic lens 1 is incident on the split prism 3 formed on the focus plate 2, it is split into two directions by the two prisms. If the aperture ratio of the photographic lens 1 is greater than or equal to a certain value, the two separated beams will overlap each other.

Although "shadowing" does not occur, if the aperture ratio is small, there will be no overlap between the two beams, as shown in Figure 1: fp
-, the light does not enter the eyepiece lens 4 and the eye 5, and a "shading phenomenon" occurs.

FIG. 2 shows an embodiment of the present invention, and FIG. 3 shows a partially enlarged view of the embodiment.

A large number of micro prisms having different inclination directions are arranged in the upper and lower halves with the split prism dividing line 6 as a boundary. The small prisms have an inclination of S, a prism with a large angle of 7.9, and a prism with a small angle of inclination, 2 of 8,10.
If the lens is composed of two types of prisms, and these microprisms are arranged randomly as a whole, when the l'l diameter ratio of the photographic lens is small and one A "shading phenomenon" occurs for a small prism 7.9 with a large inclination angle, but an optical image without shading can be seen for a small prism 8°10 with a small inclination angle.

If the size of these minute prisms is made smaller than the value that can be resolved by the eye, focusing can be achieved although the overall brightness of the optical image will be darkened. In addition, since these micro prisms are arranged randomly as a whole, it is difficult to distinguish the arrangement structure, and since the angle of the diffracted light also apparently widens by -1, a random blurred image is obtained when the prism is out of focus. Therefore, it is possible to create a viewfinder image that does not give any strange feeling.

In FIG. 2, it is shaped like a diffraction grating in the 22 directions, but it may also be random in the IF direction. In addition, in FIGS. 2 and 3, prisms 7.9 with large inclination angles and prisms 8.10 with small inclination angles are arranged alternately.
Even if they are not arranged alternately, it is sufficient if they are arranged randomly as a whole. Furthermore, in the embodiment shown in FIGS. 2 and 3, it is assumed that the prism is composed of two types of inclination angles, but 11.2
If the type is E, a more natural optical image can be obtained.

As described above, the present invention provides split prisms in which a large number of two or more types of microprisms with different inclination angles are randomly arranged throughout the prism, and the inclination angles are reversed above and below the split dividing line. Because it is a focus plate, even if the aperture ratio of the photographic lens becomes small, "shading" does not occur, and when it is out of focus, a very blurry image is obtained, so you can obtain a viewfinder image that does not look strange. It will be done.

[Brief explanation of drawings]

The first figure is an explanatory diagram showing the "shading phenomenon" that occurs in l117 with a conventional split prism focus plate.
Figure 2 is a diagram showing one embodiment of the present invention. Third
The figure is a partially enlarged view of the embodiment shown in FIG. 2. 1 Photographing lens 2...Focal plate 3...Split 1 prism 11...Eyepiece 5...Eye 6 Split prism dividing line 7.9 Small prism with a large inclination angle 3,, l (1-(IQ) Small prism with small bevel Mine I Atop Z Illustrated 3 concave

Claims (1)

[Claims] 1. A split prism focus plate for a camera, wherein each of the pair of deflection angle elements is composed of minute prisms each having two or more types of deflection angles, and the minute prisms are arranged randomly as a whole.