JP4981300B2 - Focus plate and optical viewfinder having the same - Google Patents

Description

The present invention is also suitable for focusing plate and the optical viewfinder with it using a microlens array for use in single lens reflex camera or the like to.

  Conventionally, a microlens array in which a large number of microlenses are arranged on a screen or a focusing screen has been used. Among these, for example, a screen made of a microlens array has the advantage of being brighter and less grainy in observation than a screen in which fine irregularities are transferred from a sanding surface of a mold.

  However, in the microlens array in which the microlenses are arranged periodically, the direction of the diffracted light is limited to a specific direction and the blur may be unnatural. In addition, when used together with a Fresnel lens, it causes interference with the ring zone structure of the Fresnel lens, and moire fringes are generated.

  For this reason, a microlens array has been proposed in which the above-described problems are solved by randomizing the arrangement of microlenses and minute recesses.

  Among these, various microlens arrays having a configuration in which microlenses are randomly arranged have been proposed (see Patent Document 1 and Non-Patent Document 1).

  In Patent Document 1, a microlens array in which a plurality of microlenses are formed irregularly or with a probability distribution regularity so as to be different from a basic pattern in which the vertex intervals of adjacent microlenses are all equally spaced L is used. Disclosure.

  Specifically, a microlens array is disclosed in which the vertex positions of all the microlenses are located within a predetermined circle centered on the vertex position in the basic pattern.

Non-Patent Document 1 discloses an ion exchange method in which a plurality of portions on a substrate made of multicomponent glass are increased in refractive index in a distributed state to form a plurality of lenses. And the microlens array of the structure which formed the microlens at random using this method is disclosed.
Japanese Patent Laid-Open No. 2003-4907 M.Oikawa, et al., Jpn.J.Appl.Phys.20 (4) L51-54,1918

  The microlens array disclosed in Patent Document 1 is free from the influence of diffracted light and the occurrence of moire fringes that are peculiar to a periodic regular array such as a basic pattern. In addition, the microlens array of Patent Document 1 does not cause local burrs caused by the vertices of adjacent microlenses being too far apart, and graininess due to this. Furthermore, there is a feature that a local feeling of omission due to local diffusion failure due to being too close does not occur.

  When this microlens array is used, for example, as a focusing screen for an optical viewfinder, there is little graininess, the influence of diffracted light peculiar to a regular array, and the occurrence of moire fringes.

  For this reason, it has a bright and clean appearance characteristic, and the reproducibility of each microlens shape is good, and an extremely excellent optical viewfinder can be obtained.

  However, in general, when a microlens array to which a random apex arrangement is applied is used in an optical finder, light rays incident on the end of each microlens are refracted differently by each microlens.

  As a result of this action, there are cases where light that enters the observer's pupil and light that deviates from the pupil are generated and are observed as local vignetting, that is, dark areas.

  In particular, this phenomenon becomes remarkable when a microlens array composed of dark microlenses having a large Fno is used.

The present invention aims to provide a focusing screen using a microlens array with less graininess in observation by arranging a plurality of microlenses randomly in a desired shape and appropriately setting the shape between the microlenses. And

Further, it is an object of the present invention to provide a focusing screen using a microlens array that has a small difference in refraction angle with respect to an incident light beam and has little local vignetting when used in an optical viewfinder, for example.

The present invention is a focusing screen using a microlens array, and the plurality of microlenses constituting the microlens array include a plurality of microlens arrays such that the surface vertex intervals of the adjacent microlenses are all equal intervals L. When a honeycomb structure in which microlenses are arranged is used as a basic pattern, the surface vertex positions of a plurality of microlenses are randomly positioned in a circle having a radius of 0.5 L or less centered on the surface vertex position in the basic pattern. The boundary areas in all directions of the plurality of microlenses are characterized by comprising curved surfaces having a surface curvature with a sign different from the surface curvature of the microlenses.

According to the present invention, it is possible to obtain a focusing screen using a microlens array with little graininess in observation.

In addition, according to the present invention, a focus plate using a microlens array having a small difference in refraction angle with respect to an incident light beam and having little local vignetting when used in, for example, an optical finder can be obtained.

  Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view showing the arrangement of the microlenses ML of the microlens array MLA according to the focusing screen having the microlens array according to the first embodiment of the present invention. In this embodiment, the microlenses ML are formed in a honeycomb shape and are periodically arranged regularly (basic pattern), and the surface vertices of the microlenses ML are displaced under certain conditions. It is arranged irregularly (randomly).

The plurality of boundary regions A1~A3 including all directions of the line La is made of the surface curvature of a different sign to the surface curvature of the lens surface of the microlens ML, as shown in FIG. 4 to be described later, is the width (W1 to W3) It is made from a song surface having (boundary portion).

A method for arranging the microlenses ML shown in FIG. 1 will be described with reference to FIG. In FIG. 2, when the microlenses ML are regularly arranged (basic pattern), the vertex (center) of each microlens is indicated by a dot G, and the interval between adjacent dots G (lens vertex interval) L is all. The equal interval L is set . This arrangement is called a basic pattern here.

  In the microlens array MLA of this embodiment, the position of each dot G in this basic pattern is set as a virtual grid point G. Then, the microlenses ML are arranged in a circle having a radius d centered on each grid point G shown in FIG. 2 so that the surface vertices are random (irregularly).

  In general, a microlens array in which microlenses are randomly arranged has excellent characteristics to solve the following problems (1) and (2) that occur when microlenses are periodically arranged.

  (1) The direction of the diffracted light is limited to a specific direction and the blur is unnatural.

  (2) When used in combination with a Fresnel lens, it causes interference with the ring zone structure of the Fresnel lens, resulting in moiré fringes.

  However, on the other hand, graininess may occur due to a difference in local diffusion intensity. This will be described with reference to FIGS.

  FIG. 6 is a cross-sectional view of a main part of the microlens array MLA in which the microlenses ML are arranged at equal intervals. The four microlenses ML in FIG. 6 are arranged so that the surface vertex intervals thereof are L, and the microlenses ML are arranged on the surface vertexes (grid points) G at equal intervals.

  FIG. 7 is a cross-sectional view of the main part of the microlens array MLA in which the microlenses ML are arranged with the surface vertices being randomly arranged. When the surface vertex position T of the microlens ML is displaced as compared with that in FIG. 6, the microlenses ML are arranged so that the surface vertex distances L1, L2, and L3 satisfy L3 <L1 <L2. L1, L2, and L3 are the surface vertex intervals in one direction of the microlens.

  In FIG. 7, rays 11 and 12 incident on the end portions Lb1 and Lb2 of the individual microlenses ML are indicated by dotted lines. In FIG. 7, although the light beam l1 incident on the end portion Lb1 of the microlens ML whose surface vertex interval of the microlens ML is L1 is refracted by the microlens ML, the Fno (F number) of the partial microlens is large. The refraction angle does not become large.

  On the other hand, the light beam l2 incident on the end portion Lb2 of the microlens ML whose surface vertex interval of the microlens ML is L2 is refracted by the microlens ML and has a small refraction angle because the Fno of the partial microlens ML is small. Become. By this optical action, the light beam l1 becomes a light beam incident on the observer's pupil, but the light beam l2 becomes a light beam that deviates from the pupil and is observed as a local vignetting, that is, a dark part.

  This phenomenon is particularly noticeable when a dark microlens with a large Fno is used.

  Therefore, the microlens ML of the present embodiment is configured such that the surface vertices are randomly arranged on the basis of a certain condition to reduce vignetting and eliminate graininess when used in an optical finder.

  Specifically, in the microlens array MLA shown in FIG. 1, the relationship is L = 0.02 mm and d = 0.15 × L.

  The focal length of each microlens ML is f = 0.08 mm. This is, for example, a specification that can be used as a focus plate (focal plate) suitable for a camera having an eyepiece with a focal length of about 80 mm when used in an optical viewfinder.

  FIG. 3 shows an arrangement example of the surface vertex position T of the microlens ML of the present embodiment. Here, the surface vertex interval L in the basic pattern serving as a reference and the focal length f of the microlens ML are appropriately selected according to the applied optical apparatus.

In the optical viewfinder with a focusing screen using a microlens array, it is required that the focal length of the generally eyepiece to reduce the shorter surface vertex distance L. Further, the brighter the Fno (F number) of the objective lens used, the shorter the focal length f of the microlens, and the smaller the Fno of the microlens ML is required.

In the present embodiment, the surface vertex positions T of all the microlenses ML are set so as to be located within a circle having a radius d centered on the surface vertex position in the basic pattern having a radius of 0.5 L or less. Note that the surface vertex position T of the microlens ML may be located 0.5 L away from the grid point G, or may be located on the grid point G.

In this case, the surface vertex interval P of the microlenses ML adjacent to each other is
0 ≦ P ≦ 2L
Will satisfy the following condition.

  In a general camera optical finder, it is required that the diffusion characteristics when light is incident are mainly in the range of ± 5 ° to ± 10 °. This is because the photographing lens of the camera has Fno in the range of about F2.8 to F5.6.

  In order to confirm the focus of the photographing lens, it is necessary that the light flux of the photographing lens reaches the eyes of the photographer regardless of whether the focus is in focus or not. For example, if attention is paid to one of the image points, the outermost rays in the light beam cone of the photographing lens are guided to the eyes of the photographer. It is necessary to reach the eyes of the photographer.

  For this purpose, the Fno of the microlens ML should be equal to the Fno of the corresponding photographing lens. Actually, Fno, which is optimal in terms of design, is selected in order to give priority to the brightness of the optical viewfinder or to support various types of interchangeable lenses such as a single-lens reflex camera. Therefore, it is desirable that the Fno of the microlens is in the range of F2.8 to F5.6.

  Also in this embodiment, the surface vertices of the microlenses ML are randomly distributed inside the circle having the radius d. For this reason, there is a possibility that Fno may differ as a result of fluctuations in the aperture diameter of each microlens ML.

  Therefore, it is considered that the interval L between the virtual grid points G, which is the center of the setting range of the surface vertex of the microlens ML, is equal to the aperture diameter of the microlens ML on average. If the focal length of the microlens ML is f (this is determined by the radius of curvature of the lens surface and is the same for all the microlenses ML), the average F number Fno = f / L. If this is set to about 2.8 to 5.6, diffusion characteristics suitable for an optical viewfinder of a camera can be obtained.

  When the surface vertex interval of each microlens ML is different and the surface vertex interval is wide, depending on the Fno of the microlens, an area suitable for an optical finder is locally exceeded, and vignetting and graininess are observed.

FIG. 4 is a cross-sectional view of a main part of the microlens array MLA in the focusing screen using the microlens array according to the first embodiment of the present invention.

In the present embodiment, the boundary areas A1 to A3 of the plurality of microlenses ML are composed of surfaces (boundary portions) having widths W1 to W3 having curvatures different from the surface curvatures of the microlenses ML. As a result, the vignetting ray indicated by the ray 12 in FIG. 7 is reduced, and the graininess is reduced.

  In FIG. 4, three surfaces A1 to A3 having widths W1 to W3 are exemplarily shown, but there are three or more.

  The light beam l2 shown in FIG. 4 does not receive the refraction action by the microlens ML by passing through the region indicated by the boundary portion A2. As a result, no vignetting of the light flux occurs, and the graininess is alleviated without producing a fine dark portion.

In this embodiment, when the width in the in- plane direction of the boundary portions A1 to A3 is W, and the vertex interval in the basic pattern is L,
L / 20 ≦ W ≦ L / 3 (1)
Satisfy the following conditions.

  Conditional expression (1) is for defining the width W of the boundary portion. Exceeding the upper limit value of conditional expression (1) is not good because a region with little refractive action increases and sufficient diffusion characteristics cannot be obtained. If the lower limit of conditional expression (1) is exceeded, a sufficient anti-vignetting effect cannot be obtained, which is not good.

  More preferably, the numerical range of conditional expression (1) is set as follows.

L / 10 ≦ W ≦ L / 6 (1a)
In this embodiment, each microlens ML is formed so that its surface vertex is random (irregularity) under a certain condition. However, the present invention is not limited to this, and has regularity with probability distribution. May be formed. For example, as an example of the method, there is a method in which a distribution model including a large number of coordinates according to a certain probability distribution is created, and coordinates are randomly selected from the distribution model.

Figure 5 is a principal block diagram showing a configuration of an optical viewfinder of a single-lens reflex camera provided with a focusing screen using a microlens array MLA of the present embodiment.

In the figure, the light beam from the subject passes through the photographing lens 11 and is reflected by the quick return mirror 12, and then an object image is formed on the focusing screen 13 made of a microlens array.

  The subject image formed on the focusing screen 13 is diffused by the microlens array, inverted by the pentaprism 14, and observed at the eye point 16 through the eyepiece 15 as an erect image.

  Diffusion by the microlens array is determined by the arrangement of the microlens array and the radius of the microlens, and affects the ease of focusing, the appearance of the blurred image, and the graininess of the focusing screen itself.

  By using the above-described microlens array for the focusing screen 13 as in this embodiment, the characteristics required for the focusing screen can be satisfactorily satisfied.

  In this embodiment, a microlens array having a specification suitable for a focusing plate used in an optical finder for a camera has been described. However, the present invention is not limited to a microlens array screen or a diffusion plate used in various optical devices. It is possible to apply to.

Arrangement of microlenses in the microlens array of Example 1 of the present invention Explanatory drawing which shows the grid arrangement | positioning of the basic pattern used as the reference | standard for determining the surface vertex arrangement | positioning of the microlens in the microlens array of Example 1 of this invention. Explanatory drawing which shows the random grid arrangement | positioning of the micro lens array of Example 1 of this invention. Sectional drawing of the principal part of the microlens array of Example 1 of this invention Explanatory drawing showing an optical viewfinder of a camera using a microlens array as a focusing screen Cross-sectional view of main parts of microlens array arranged at equal intervals Cross-sectional view of the main part of a microlens array to which random surface vertex arrangement is applied

Explanation of symbols

MLA micro lens array ML micro lens L vertex distance in basic pattern T vertex position of micro lens G grid point 11 photographing lens 12 quick return mirror 13 focusing plate 14 pentaprism 15 eyepiece

Claims (4)

A focusing plate using a microlens array, and the plurality of microlenses constituting the microlens array are arranged such that the surface vertex intervals of adjacent microlenses are all equally spaced L. When the formed honeycomb structure is used as a basic pattern, the surface vertex positions of a plurality of microlenses are randomly positioned within a circle having a radius of 0.5 L or less centered on the surface vertex position in the basic pattern. The focusing screen is characterized in that a boundary region in all directions of the plurality of microlenses is formed of a curved surface having a surface curvature with a sign different from the surface curvature of the microlenses. When the width in the in-plane direction of the microlens of the boundary region is W,
L / 20 ≦ W ≦ L / 3
The focusing screen according to claim 1, wherein the following condition is satisfied . An optical viewfinder comprising the focusing screen according to claim 1 . A camera comprising the optical viewfinder according to claim 3.

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