JPS6318174B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a speckle diffuser plate obtained by irradiating a diffuser plate such as ground glass with a coherent light beam and optically recording a speckle pattern formed by the light beam from the diffuser plate. be. As a diffuser plate in which a speckle pattern is optically recorded, there is one that utilizes the unevenness on the surface of a recording material obtained by illuminating the diffuser plate with coherent light, photographing it, developing it, and bleaching it. In order to use this diffuser plate as a uniform illumination device in holography, it is necessary to set the wavelength of the illumination light to λ so that the phase change after passing through the diffuser plate is λ/2 or less.
No. 48-17093. In addition, considering the observation area for use as a screen for a projector, and in particular to ensure that the light distribution characteristics are rotationally asymmetric, the optical system for photographing the speckle pattern is a so-called 4-F arrangement double diffraction optical system. JP-A-49-10265 describes the use of a spatial frequency filter in the speckle plane using the above system. These diffusion plates were of the uneven surface type, but there are also some that record the speckle pattern holographically (USP3708217), and others that record the speckle pattern as a volume type Gaboa hologram and use it as a viewer screen for a microsystem. . (D. Meyerhoter, Apul, Opt. 12

[9]
2180.) The diffuser plates obtained by optically recording speckle patterns in this manner will be collectively referred to as speckle diffusers. The present inventor believes that such a speckle diffuser plate is 35
It has been found that it is also effective as a viewfinder screen for mm still cameras, 8mm movie cameras, etc. Figure 1 shows one mode in which a speckle diffuser is used in a camera.
As a result, an image of the object is formed on the mat surface 10 of the focusing plate 4 via the mirror 2. Usually, a split prism or microprism 9 is provided at the center of the mat surface, and focusing is performed by adjusting the distance of the imaging lens while viewing the image of this part with the eye 8. When you turn off the shutter after focusing, the mirror 2 will rise to the top.
An image is exposed onto a film 3 located at a position conjugate to the matte surface with respect to the mirror 2. The conventional mat surface 10 was made by, for example, rough-sanding a metal surface and transferring it onto a plastic plate. As shown in the cross-sectional view of FIG. 2, the thus obtained pine surface has acute corners of the unevenness and irregular grains of the unevenness. As a result, as for optical characteristics, a lot of light is greatly deviated from the direction of incidence and is diffused, resulting in disadvantages such as dark images in the viewfinder, and when the aperture is closed, graininess becomes noticeable and the image becomes blurry. Ta. In conventional processing methods, a method was considered to make the sand mesh for roughing finer to eliminate this drawback, but as the height of the uneven peaks and the grain size become smaller, the amount of light transmitted through the mat surface increases, and the finder becomes smaller. The trade-off for the increased brightness was that it became difficult to measure distances on the pine surface. The necessity of distance measurement on the mat surface will be explained by returning to FIG. The split prism or microprism in the center of the mat face has a certain angle and therefore bends the incident light beam in a certain direction. Normally, single-lens reflex cameras have this angle of declination between 4° and
It is set at about 6°. Therefore, as an imaging lens, FNo.
When using a telephoto lens with a large angle, the angle of incidence of the light beam that enters the focusing plate 9 approaches 90 degrees, and if the light beam is bent by 4 to 6 degrees, it will exit the viewfinder optical system and will not reach the eye. It turns out. As a result, even if you use a bright lens with a small F No., if you close down the aperture to about F5.6 or F8, or if you use a lens with a large F No., the focusing plate 9 will not be able to measure the distance. Therefore, distance measurement will be performed using the mat surface 10. As you can see from the above explanation, the performance required for a matte surface for a camera is: 1. Brighter than a matte surface produced using conventional processing methods (eliminating sharp edges of unevenness) 2. Even with a lens with a large f/no., it has no graininess (The particle size of the unevenness is kept below the resolution limit of the eye, including the viewfinder optical system.) 3. As a diffusion characteristic, there is a sufficient amount of light that can be bent by at least 5 degrees with respect to the incident direction. etc. As a result of making and measuring various speckle diffusers, the inventor came to the conclusion that the speckle diffuser satisfies the above three conditions and can be used as a matte surface for cameras that is superior to matte surfaces produced by conventional methods. . FIG. 3 shows an embodiment of the method for manufacturing a diffuser plate of the present invention. In Figure 3, the laser light source, for example
A light beam 31 from a He-Ne laser is converted into a diverging spherical wave 33 using a microscope objective lens 32, and then converted into a converging spherical wave using a condenser lens 34 (a single lens is also acceptable).
A diffuser plate 37 made of ground glass or the like is illuminated through the light.
A well-known speckle pattern is generated in the light beams 91 to 94 emitted from the diffuser plate 37 and is recorded on the photosensitive material 100. When the photosensitive material 100 is a silver salt dry plate, a speckled pattern recorded using various known bleaching methods can be converted into a speckled pattern consisting of a change in refractive index or a speckled pattern consisting of a change in unevenness. . Photosensitive material 10
If 0 is a polymer sensitive material, such as a photoresist, it will be a recorded speckled pattern, that is, a change in unevenness. In FIG. 3, the average size of the individual speckles of the speckle pattern recorded on the photosensitive material 100 is determined by the shape 38 of the illumination area on the diffuser plate 37 due to the aperture 36.
and the distance from the diffuser plate 37 to the photosensitive material 100,
It is determined by the wavelength λ used. According to our experience, the use of annular apertures as shown in Figure 3 was most effective in making the graininess uniform. By varying the distance from the diffuser plate 37 to the photosensitive material 100, the average particle size is 10μ,
Various diffuser plates with a diameter of about 5μ and 3μ can be easily obtained. Further, when the speckle pattern recorded in this manner is converted into a change in unevenness, the shape and height of each mountain vary greatly depending on the type of photosensitive material used, the developing process, etc. Judging from an electron micrograph, the cross-sectional shape of the unevenness obtained by bleaching the silver salt photosensitive material is approximately as shown in FIG. 4. At this time, the height of one mountain was measured using an interference microscope, and the average particle size was about 10 μm, which was about 0.5 to 1 μm. FIG. 5 shows an example of the transmission orientation characteristics of the speckle diffuser plate thus obtained and the diffuser plate obtained by the conventional processing method. In FIG. 5, the solid line is a speckle diffuser plate, and the dotted line is a diffuser plate formed by a conventional processing method. Comparing Figures 2, 4, and 5 reveals the following. That is, the sharp peaks of the unevenness seen in the conventional diffuser plate (Fig. 2) are no longer present in the speckle diffuser plate (Fig. 4), and the speckle diffuser plate can be regarded as an array of microlenses of approximately the same size. Therefore, as shown in FIG. 5, the diffusion characteristics of the conventional diffuser plate are larger than those of the speckle diffuser plate in the area where the diffusion angle is large, resulting in a corresponding loss in the effective light quantity. When we actually conducted a panel test to check the visibility of the viewfinder by placing a speckle diffusion surface at position 10 in Figure 1, we found that the distance measurement accuracy was the same as that of the conventional matte surface, and the brightness was significantly improved. Ta. Furthermore, when the lens was stopped down, the graininess was hardly noticeable and a clear image was obtained. However, if the average particle size is about 10μ or more,
It was pointed out that the bokeh quality deteriorated. The resolution of the eye is about 10 lines/mm at the distance of clear vision, and the magnification of the finder optical system used at that time was about 5 times, so the resolution of the eye including the finder optical system is
Approximately 50 lines/mm, pitch approximately 20μ. In other words, when the size of the speckle approaches the resolution limit of the eye including the viewfinder optical system, the bokeh becomes worse. This means that the average particle size must be kept below the resolution limit mentioned above. The panel test results showed that the visibility of the finder was good for speckles with an average particle size of 3μ or 5μ. As variously explained above, the present invention provides a matte surface for a camera finder having performance that was thought to be unattainable by conventional mechanical processing, by a method using optical means. . Additionally, various optical and mechanical copying techniques well known in the art can be used to control the properties of the resulting diffuser or to obtain large quantities of diffusers with the same properties.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment in which a speckled diffuser plate is applied to the viewfinder of a single-lens reflex camera, and Fig. 2 is a cross-sectional view of a conventional ground glass diffuser plate.
Fig. 3 is a diagram explaining the method for producing the speckle diffuser plate of the present invention, Fig. 4 is a cross-sectional view of the speckle diffuser plate produced by the production method shown in Fig. 3, and Fig. 5 is a characteristic diagram of the speckle diffuser plate. be. In the figure, 1 is an objective lens, 2 is a swing-up mirror, 3 is a film, 4 is a diffuser, 5 is a condenser lens, 6 is a pentaprism, 7 is an eyepiece, 9 is an eye, 31 is a coherent light beam, and 32 is a microscope objective. Lens, 33 is a diverging spherical wave, 34 is a condenser lens, 35 is a light shielding plate, 36 is an aperture, 37
38 is a diffuser plate, 38 is an illuminated area, 91 to 94 are emitted light beams, and 100 is a photosensitive material.

Claims (1)

[Claims] 1. A method for creating a diffuser plate in a camera viewfinder in which an object image is formed on a diffuser plate by an objective lens and this object image is observed through an observation optical system, the method comprising: When illuminating and directly recording speckles formed by the light flux emitted from the diffusing member on the surface of the photosensitive material, a predetermined aperture is used to control the speckle pattern reaching the surface of the photosensitive material, and a desired pattern is formed on the surface of the photosensitive material. A method for creating a diffuser plate characterized by recording a speckle pattern.