JP2000321626A - Reticle for finder optical system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reticle capable of brightening the whole screen without causing the deterioration of an image forming function. SOLUTION: As for the reticle, a diffusion surface is constituted by arranging a large number of plural kinds of random pattern structure P40 to P42. The random pattern structure P40 to P42 is constituted of plural fine rectangular elements E1 to E4 with four kinds of height, and the rectangular elements E1 to E4 are irregularly arranged so as to constitute plural kinds of diffraction gratings having different grating pitches. The ratio of the high frequency component of the grating pitch is made larger as the random pattern structure P41 and P42 positioned further away from the optical axis AX of a finder optical system.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reticle for a finder optical system, and more particularly to a reticle mounted on a finder of a single-lens reflex camera.

[0002]

2. Description of the Related Art The viewfinder of a general single-lens reflex camera reflects light from a photographing lens with a main mirror.
An image is formed on a focusing screen having a diffusion function. Since the reticle is located at a position optically equivalent to the film surface, it passes through a pentaprism or eyepiece.
By observing the image formation state of the finder screen formed on the reticle, the image formation state on the film surface can be known.

FIG. 7 shows a conventional example of a focusing screen. A Fresnel lens surface (S1) is formed on the photographing lens (not shown) side of this reticle, and {AX: the optical axis of the Fresnel lens surface (S1)}, and a diffusing surface ( S2) is formed.
The Fresnel lens surface (S1) has a condenser power for guiding off-axis light entering the outermost periphery of the finder screen to the pupil (that is, adjusting the pupil). The light from the taking lens is deflected by the Fresnel lens surface (S1) and then forms an image on the diffusion surface (S2). Such a reticle configuration is generally known. For example, in Japanese Patent Application Laid-Open No. 8-129205, a directional pattern and a non-directional pattern are superposed to form a diffusion surface (S2), and A diffusion plate having a Fresnel lens surface (S1) has been proposed.

[0004]

As shown in FIG. 7, when the Fresnel lens surface (S1) and the diffusion surface (S2) are located apart from each other, the combination of the photographing lens and the Fresnel lens surface (S1) is formed. The imaging performance is the imaging performance on the diffusion surface (S2). Therefore, the Fresnel lens surface (S1) is
(For example, aberration performance). If the Fresnel lens surface (S1) is closer to the diffusion surface (S2), or if a Fresnel lens is formed on the diffusion surface (S2), the Fresnel lens surface
Since the orbicular zone of (S1) (that is, the concentric line) is observed through the eyepiece, this also causes deterioration of the imaging performance. Conversely, if the Fresnel lens surface (S1) is separated from the diffusing surface (S2), the aberration performance and the like will deteriorate, and the amount of light around the finder screen will decrease due to vignetting, resulting in darkness.

The present invention has been made in view of such circumstances, and has as its object to provide a reticle capable of brightening the entire screen without deteriorating the imaging performance.

[0006]

In order to achieve the above object, a reticle according to a first aspect of the present invention is a reticle for a finder optical system in which a plurality of random pattern structures are arranged to form a diffusion surface. Wherein the random pattern structure comprises a plurality of minute elements having a plurality of types of heights, and the elements are irregularly formed to form a plurality of types of diffraction gratings having different grating pitches. The random pattern structure located farther from the optical axis of the finder optical system has a higher ratio of the high frequency component of the grating pitch.

A reticle according to a second aspect of the present invention is characterized in that, in the configuration of the first aspect, the random pattern structures located at the same distance from the optical axis of the finder optical system have the same random pattern.

According to a third aspect of the present invention, in the reticle of the first aspect, a surface opposite to the surface on which the diffusion surface is provided is a flat surface.

According to a fourth aspect of the present invention, in the reticle according to the first aspect of the present invention, the height of the element is four or more.

According to a fifth aspect of the present invention, in the reticle of the first aspect, the adjacent random pattern structure satisfies the following conditional expression. h1max ≦ h2max, where h1max: the maximum height of the element in the random pattern structure near the optical axis of the finder optical system, h2max: the maximum height of the element in the random pattern structure far from the optical axis of the finder optical system, is there.

The reticle according to a sixth aspect of the present invention is the reticle according to the fifth aspect, wherein the number of element types in the random pattern structure far from the optical axis of the finder optical system is different from the optical axis of the finder optical system. The number of the heights of the elements in the random pattern structure on the side closer to is equal to or more than the number of types.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A reticle embodying the present invention will be described below with reference to the drawings. FIG. 2 shows a finder optical system on which the embodiment of the focusing screen is mounted. The finder optical system includes an objective lens (TL), a reticle (FS), an eyepiece (SL), and the like. Pupil (FS) pupil (EP)
A diffusion surface (FSa) having a diffusion function is formed on the side surface, and the surface opposite to the surface on which the diffusion surface (FSa) is provided {that is, the side surface of the objective lens (TL)} is flat. I have.
Light emitted from the objective lens (TL) is diffused on the focusing screen (FS).
(FSa). The diffused light (LA, LB) emitted from the image on the diffusion surface (FSa) passes through the eyepiece (SL) and enters the pupil (EP). Since the diffusing surface (FSa) has condenser power, which will be described later, off-axis light that has entered the outermost periphery of the viewfinder screen is also directed to the center of the eyepiece (SL) as diffused light (LB) after imaging. Become.

The diffusing surface (FSa) of the reticle (FS) is formed by arranging a large number of different types of random pattern structures. The random pattern structure is composed of a plurality of minute rectangular elements having a plurality of types of heights, and the rectangular elements are arranged irregularly so as to form a plurality of types of diffraction gratings having different grating pitches. . The plurality of types of diffraction gratings are, for example, CGH (Compute
r Generated Hologram). When a plurality of periodic structures having different heights are superimposed on a plurality of periods in the CGH, a plurality of types of diffraction gratings having different grating pitches are formed, and as a result, the above random pattern structure in which rectangular elements are irregularly arranged is formed. You. Due to the plurality of superimposed periodicities, a large number of diffracted lights are densely generated within a predetermined angle, so that the brightness of the blur becomes uniform. Therefore, it is possible to generate a large blur with uniform brightness (that is, smooth and natural) and to brighten the finder screen.

As described above, the diffusion surface (FSa) is composed of a plurality of types of random pattern structures. The random pattern structure located farther from the optical axis (AX) of the finder optical system (ie, image height). The higher the value, the higher the ratio of the high frequency component of the grating pitch. That is, FIG.
As shown in the figure, the center area (AR0), intermediate area (AR1), and peripheral area (AR) of the finder screen centered on the optical axis (AX) position.
In the order of 2), the ratio of the high-frequency component of the grating pitch (that is, the diffraction grating having a small grating pitch) in the random pattern structure located in that region gradually increases.
And, since the random pattern structure located at the same distance from the optical axis (AX) (that is, the same image height) has the same random pattern, the same random pattern structure is on the same concentric circle centered on the optical axis (AX). Will be located. The same applies to the areas located between the areas (AR0, AR1, AR2).

FIG. 1 shows each region (AR0, AR1, AR1) of the diffusion surface (FSa).
2) shows the random pattern structure located in the middle. FIG. 1 (A)
Is a random pattern structure (P40) located in the center area (AR0) of the finder screen, FIG. 1 (B) is a random pattern structure (P41) located in the intermediate area (AR1), and FIG. 1 (C) is a peripheral area The random pattern structure (P42) located in (AR2) is shown. The optical axis (AX) of the finder optical system (Fig. 2)
Is located at the center of the random pattern structure (P40) shown in FIG. 1 (A), and (in the plane of the paper) of the random pattern structure (P41, P42) shown in FIGS. 1 (B) and (C). ) It is located above.

Any random pattern structure (P40-P42)
Also multiple small rectangular elements with four different heights
(E1, E2, E3, E4) and its rectangular element (E1
To E4) are irregularly arranged so as to constitute a plurality of types of diffraction gratings having different grating pitches. Each of the rectangular elements (E1 to E4) has a rectangular cross section parallel to the diffusion surface (FSa), and has a rectangular wave shape in a cross section perpendicular to the diffusion surface (FSa). Therefore, the plurality of types of diffraction gratings are constituted by phase type multi-level diffraction gratings having a binary structure of up to four levels.

In FIG. 1, the shading representing each rectangular element (E1 to E4) and the height h (μm) of each rectangular element (E1 to E4)
Is shown in Table 1 below. However, the material of the reticle (FS) is PMMA (polymethyl methacrylate), and its refractive index for e-ray: ne = 1.41414.

[0018]

[Table 1]

If the diffraction angle is θ, the wavelength is λ, and the grating pitch is Λ, the following equation holds: sin θ = λ / Λ. Diffusing surface
In (FSa), the ratio of the high-frequency component of the lattice pitch 大 き く increases as the random pattern structure is farther from the optical axis (AX). There is a concentric direction centered on (AX). Therefore, off-axis light incident on the diffusing surface (FSa) at a position farther from the optical axis (AX) can be bent more greatly, and guides off-axis light incident on the outermost periphery of the finder screen to the pupil (EP). Capacitor power is achieved. As described above, since the diffusion surface (FSa) has the condenser power, the Fresnel lens surface is unnecessary, and it is possible to brighten the entire finder screen without deteriorating the imaging performance.

It is desirable that there are four or more types of elements constituting the random pattern structure. FIG. 4 shows a random pattern structure (P81, P82) having eight kinds of element heights. FIG. 4A shows the intermediate region (AR
1) shows a random pattern structure (P81) located in the center, and FIG. 4B shows a random pattern structure (P82) located in the peripheral area (AR2). The optical axis (AX) of the finder optical system (FIG. 2) is located above (toward the paper) the random pattern structure (P81, P82) shown in FIGS. 4 (A) and 4 (B).

Any random pattern structure (P81, P82)
Also a plurality of small rectangular elements with eight different heights
(E1, E2, E3, E4, E5, E6, E7, E8), and the rectangular elements (E1 to E8) are irregularly arranged so as to form a plurality of types of diffraction gratings having different grating pitches. Have been. Each of the rectangular elements (E1 to E8) has a rectangular cross-sectional shape parallel to the diffusion surface (FSa), and has a rectangular wave shape in a cross-section perpendicular to the diffusion surface (FSa). Therefore, the plurality of types of diffraction gratings are constituted by phase-type multi-level diffraction gratings having a binary structure of up to eight levels.

In FIG. 4, the shading representing each rectangular element (E1 to E8) and the height h (μm) of each rectangular element (E1 to E8)
Is shown in Table 2 below. However, the material of the reticle (FS) is PMMA (polymethyl methacrylate), and its refractive index for e-ray: ne = 1.41414.

[0023]

[Table 2]

Although the condenser power is achieved by changing the grating pitch on the diffusing surface (FSa) of the reticle (FS) described above, a configuration may be employed in which the change in the maximum height of the element is used for the condenser power. . For example, it is desirable that adjacent random pattern structures satisfy the following conditional expression (I). h1max ≦ h2max (I) where h1max is the maximum height of the element in the random pattern structure on the side closer to the optical axis (AX) of the finder optical system, and h2max is random on the side farther from the optical axis (AX) of the finder optical system. The maximum height of an element in the pattern structure.

The diffusion surface (FSa) satisfying the conditional expression (I) is, for example, a random pattern structure (P4) shown in FIGS. 5A and 6A.
0) is located in the center area (AR0) of the viewfinder screen, and FIG.
6B and the random pattern structure (P82W) shown in FIG. 6B is arranged in the peripheral area (AR2). The optical axis (AX) of the finder optical system (FIG. 2) is shown in FIG.
Is located at the center of the random pattern structure (P40) shown in FIG.
(Toward the paper).

The random pattern structure (P40) comprises a plurality of minute rectangular elements (E1 to E4) having four different heights, and the random pattern structure (P82W) comprises a plurality of minute rectangular elements having eight different heights. It consists of simple rectangular elements (E1 to E8). The rectangular elements (E1 to E8) of any random pattern structure (P40, P82W) are arranged irregularly so as to constitute a plurality of types of diffraction gratings having different grating pitches,
Cross section parallel to the diffusion surface (FSa) is rectangular, diffusion surface (FSa)
The cross section perpendicular to the vertical axis forms a rectangular wave shape. Therefore, the plurality of types of diffraction gratings are constituted by a phase type multi-level diffraction grating having a binary structure gradually changing from a maximum of four levels to a maximum of eight levels from the central region (AR0) to the peripheral region (AR2). become.

In FIG. 6, the shading representing each rectangular element (E1 to E8) and the height h (μm) of each rectangular element (E1 to E8)
Is shown in Table 3 below. However, the material of the reticle (FS) is PMMA (polymethyl methacrylate), and its refractive index for e-ray: ne = 1.41414.

[0028]

[Table 3]

The random pattern structure (P4
0), the maximum height hmax = 0.83 μm, and the peripheral area (AR2)
In the random pattern structure (P82W), the maximum height hmax = 1.9
6 μm. From the central area (AR0) to the peripheral area (AR2), the height type of the rectangular element gradually changes from 4 to 8, and the maximum height hmax of the rectangular element also gradually changes. This satisfies conditional expression (I). When the diffraction angle is θ, the wavelength is λ, the grating pitch is Λ, and the height of the rectangular element is h,
The equation: sin θ = λ / Λ and the equation: h = λ / (n−1) hold, and the equation: sin θ = h (n−1) / Λ is obtained from these equations. Therefore, if the height h of the rectangular element doubles, sin θ also doubles. That is, by changing the height of the rectangular element, off-axis light incident on the diffusion surface (FSa) at a position farther from the optical axis (AX) can be bent more.

If the configuration is made so as to satisfy the conditional expression (I), a strong condenser power can be generated at the same grating pitch Λ, and the off-axis light incident on the outermost periphery of the finder screen can be generated by the condenser power by the pupil ( EP). Outside the range of the conditional expression (I), the grating pitch な け れ ば must be further reduced in order to generate strong capacitor power.
Production of a) becomes difficult.

The random pattern structure (P40) is composed of rectangular elements (E1 to E4) having four different heights, and the random pattern structure (P82W) is rectangular elements (E82) having eight different heights.
1 to E8), but the number of element height types in the random pattern structure on the side farther from the optical axis (AX) {for example, the peripheral area (AR2)} is closer to the optical axis (AX) ~ side
It is desirable that the number of heights of the elements in the random pattern structure of {for example, the central region (AR0)} be equal to or greater than the number of types. With this configuration, it is possible to prevent the diffraction efficiency from decreasing in the peripheral area (AR2) of the finder screen. If this condition is not satisfied, the diffraction efficiency is reduced in the peripheral area (AR2) of the finder screen, so that the area may be darkened or colored.

[0032]

As described above, according to the reticle according to the present invention, it is possible to brighten the entire screen without deteriorating the imaging performance.

[Brief description of the drawings]

FIG. 1 is a plan view showing a random pattern structure composed of four types of rectangular elements.

FIG. 2 is an optical configuration diagram schematically showing a finder optical system according to the embodiment.

FIG. 3 is a plan view showing a reticle in FIG. 2;

FIG. 4 is a plan view showing a random pattern structure including eight types of rectangular elements.

FIG. 5 is an enlarged cross-sectional view showing a main part of a random pattern structure in which the number of height types of rectangular elements differs depending on the image height position.

FIG. 6 is a plan view showing the random pattern structure of FIG. 5;

FIG. 7 is a sectional view showing a conventional focusing screen.

[Explanation of symbols]

 FS: Focusing plate FSa: Diffusing surface AR0: Central area AR1: Middle area AR2: Peripheral area P40 to P42: Random pattern structure P81, P82: Random pattern structure P82W: Random pattern structure E1 to E8: Rectangular element TL: Objective lens SL … Eyepiece EP… Eye AX… Optical axis

Claims (6)

[Claims] 1. A reticle for a finder optical system, wherein a diffusion surface is formed by arranging a plurality of types of random pattern structures, wherein the random pattern structure has a plurality of types of heights. Are arranged irregularly so as to form a plurality of types of diffraction gratings having different grating pitches, and the random pattern structure located farther from the optical axis of the finder optical system is ,
A reticle, wherein the ratio of the high frequency component of the grating pitch is large. 2. The reticle according to claim 1, wherein the random pattern structures located at the same distance from the optical axis of the finder optical system have the same random pattern. 3. The reticle according to claim 1, wherein the surface opposite to the surface on which the diffusion surface is provided is a flat surface. 4. The reticle according to claim 1, wherein the height of the element is four or more. 5. The reticle according to claim 1, wherein adjacent random pattern structures satisfy the following conditional expression: h1max ≦ h2max, where h1max: a random pattern closer to the optical axis of the finder optical system. H2max: maximum height of the element in the random pattern structure far from the optical axis of the finder optical system. 6. The number of element types in the random pattern structure on the side farther from the optical axis of the finder optical system is equal to or greater than the number of element height types in the random pattern structure on the side closer to the optical axis of the finder optical system. The reticle according to claim 5, wherein