JPS6330614B2 - - Google Patents

Description

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

Conventionally, the split prism focus plate used in the viewfinder of single-lens reflex cameras has two prisms with inclination angles in opposite directions. The optical images created by the two objects appear to match, but when they are out of focus, the optical images appear to be out of alignment. A major drawback of this split prism focus plate is that when the aperture ratio of the photographing lens becomes smaller, the optical image becomes darker, which is the so-called "shadowing phenomenon."

In order to prevent this "shadowing phenomenon", these two
Methods have been proposed such as reducing the inclination angle of each prism, providing a flat portion, or arranging prisms with two types of inclination angles in the shape of a diffraction grating.

However, if the tilt angle is made smaller, the amount of deviation of the optical image relative to the amount of defocus becomes smaller, and the focus discrimination performance deteriorates. Further, if a flat portion is provided, the amount of light that does not contribute to focus determination will increase, and the focus determination performance will also deteriorate. 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 and randomly arranging them as a whole. The objective is to solve the above problems by creating an optical image that does not give a strange feeling.

The present invention will be explained below with reference to the drawings.

FIG. 1 is a conceptual diagram showing the "shadowing phenomenon" caused by a conventional split prism reticle.

When the light emitted from the photographic lens 1 is incident on the split prism 3 formed on the focusing plate 2, it is split into two directions by the two prisms. If the aperture ratio of the photographic lens 1 is above a certain value, the two separated light beams will overlap each other, and the "shadowing phenomenon" will not occur. However, if the aperture ratio is small, as shown in Figure 1. The overlapping portion of these two light beams disappears, and the light does not enter the eyepiece lens 4 and the eye 5, causing a "shading phenomenon."

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

With the split prism dividing line 6 as a boundary, a large number of micro prisms having different inclination directions are arranged in the upper half and the lower half. The micro prisms are composed of two types: prisms 7 and 9 with large inclination angles and prisms 8 and 10 with small inclination angles.
Moreover, these micro prisms are randomly arranged as a whole. With this configuration, when the aperture ratio of the photographic lens becomes small, a "shading phenomenon" occurs for the small prisms 7 and 9 with large inclination angles, but for the small prisms 8 and 10 with small inclination angles. In contrast, a clear optical image is visible. 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 the angle of the diffracted light also apparently widens, resulting in a random blurred image when the prism is out of focus. Therefore,
It is possible to create a viewfinder image that does not look strange.

In FIG. 2, the vertical direction is shaped like a diffraction grating, but the vertical direction may also be random. Further, in FIGS. 2 and 3, the prisms 7 and 9 with large inclination angles and the prisms 8 and 10 with small inclination angles are arranged alternately, but they do not need to be arranged alternately as long as they are arranged randomly as a whole. Furthermore, the second
In the embodiment shown in FIGS. 3 and 3, it is assumed that the prism is composed of prisms having two types of inclination angles, but a more natural optical image can be obtained if there are two or more types of inclination angles.

As described above, the present invention provides two
Since this is a split prism focusing plate in which multiple tiny prisms of different sizes or larger are arranged randomly as a whole, and the angles of inclination are opposite to each other on both sides of one split dividing line, the aperture ratio of the photographing lens is Even when the lens size is small, no apparent "shading" phenomenon occurs, and a randomly blurred image is obtained when the lens is out of focus, so a finder image that does not give any strange feeling can be obtained.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the "shading phenomenon" that occurs when a conventional split prism focus plate is used. FIG. 2 is a diagram showing an embodiment of the present invention.
FIG. 3 is a partially enlarged view of the embodiment shown in FIG. 2. 1...Photographing lens, 2...Focal plate, 3...Split prism, 4...Eyepiece, 5...Eye, 6...Split prism division line, 7, 9...Minute prism with large inclination angle, 8, 10...Inclination angle A small microprism.

Claims (1)

[Claims] 1. A plurality of micro prisms of two or more types with different inclination angles are arranged randomly as a whole, and the directions of the inclination angles are opposite to each other on both sides of one split dividing line. A camera's split prism focus plate.