JPH0228844B2 - KAKUSANBAN - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a diffuser plate suitable for use in a focusing plate for single-lens reflex cameras, 8mm cameras, movie cameras, and the like.

Conventionally, acrylic matte surfaces with surface shapes and diffusion characteristics similar to those of ground glass have been used as focus plates for single-lens reflex cameras, etc., for wide-angle, standard, telephoto, and
It has been used as a standard reticle screen for a long time because it can be used relatively easily with super telephoto lenses. However, since the surface of such an acrylic mat surface is not smooth, a considerable amount of light is diffused outside the viewfinder window, and when the lens aperture is closed, the viewfinder suddenly becomes dark and grainy on the matte surface. It had drawbacks such as noticeable roughness (bumps like fine sand).

On the other hand, unlike the above-mentioned matte surface with random irregularities, there is a full-scale microlens focusing plate with a structure in which triangular pyramids and square pyramids are regularly arranged. When close to the open F-number, there is no vignetting due to vignetting and the image has brightness close to that of an aerial image.

However, because it has a regular structure, moiré fringes occur between objects that have periodic patterns and between the periodic structure of the Fresnel lens, making it difficult to see the viewfinder, and when the aperture is closed down, shadows suddenly appear. Because of this drawback, it is not used as a standard focusing plate, but is used as an exchange focusing plate exclusively for so-called close-up photography, copying, rapid photography, etc.

On the other hand, the applicant has developed a focusing plate for such a special purpose that maintains the characteristics of the above-mentioned full-scale microprism focusing plate, such as having a special bokeh, making it easy to measure distances, and being bright. We have discovered a method for manufacturing a new type of focusing plate that is entirely microlens-shaped, which alleviates the drawback that the brightness of the viewfinder suddenly dims above a certain FNo. (Patent Application No. 53-165092) If this method is used, as will be explained later, convex and/or concave microlenses with a diameter of about 10 to 30μ, which could not be obtained conventionally, as shown in Figures 4 and 6, can be obtained. A diffuser plate with a regular and densely arranged surface shape is obtained. When the diffuser plate obtained in this way was installed in a camera, it did not darken rapidly even when stopped down, and the bokeh was relatively similar to that of a matte lens.It was a bright and clear focusing plate with no graininess at all. It was confirmed that it was a screen. However, since this focusing plate basically has a diffraction grating structure (periodic structure), if the subject has a periodic structure, the concentric bits (usually 30~
50μ) and the pitch of the diffraction grating structure of the focusing plate is similar, moiré fringes occur and the finder image becomes difficult to see. If there is a large amount of 0th order diffracted light, when the lens is stopped down or when the aperture f/number is large to begin with, such as with a super telephoto lens, the shadow of the lens's pupil (diaphragm) will be seen directly, and the center of the viewfinder ( It was also confirmed that it could not be used as a standard focusing plate, as a bright spot appeared on the screen (as the eye moved), and the surrounding area appeared colored.

In view of the above points, the present invention takes advantage of the characteristics of the novel diffuser proposed by the applicant as described above, and provides a diffuser having standard characteristics that further reduces the moiré fringe phenomenon and coloring phenomenon. The purpose is to do.

On the other hand, the present applicant has proposed a mat surface that improves the noticeable graininess of the acrylic mat surface. (Unexamined Japanese Patent Publications No. 53-42726, No. 51755)
This diffuser plate is made using a manufacturing method that optically records a fine random speckled pattern (so-called speckle pattern) generated using coherent light such as a laser beam, and has a relatively regular size of about 5 to 15 μm. A large number of minute irregularities with smooth curved surfaces are formed in an irregular arrangement. A focus plate using this diffuser plate has a smooth uneven surface compared to the matte surface of the light, increasing brightness by up to 50%, and has the characteristic that graininess is relatively inconspicuous even when the aperture is narrowed down. are doing.

The present invention further reduces the graininess when the lens is stopped down, which is the only drawback of such an irregularly uneven diffuser plate, eliminates the moiré fringes and discoloration of a full-surface microlens-shaped diffuser plate, and improves both. To provide an ideal standard focusing plate having excellent features such as brightness, clearness, easy focusing, and no graininess.

By the way, focusing plates with finely roughened surfaces of the individual micro cones of the conventional full-surface microprism focusing plates have been commercially available, and in recent years, focusing plates with rounded tops of the cones and roughened surfaces arranged in a close-packed manner have become available. Boards are also commercially available.

Unlike that, the present invention has an irregular uneven structure in which microlens-like curved surfaces with a size of about 10 to several tens of micrometers are arranged periodically in two dimensions, and the microlens-like curved surfaces are connected by a smooth curved surface. By combining it in a complex manner with the novel full-surface microlens-like structure, a diffuser plate with unprecedented excellent characteristics can be obtained.

Embodiments of the present invention will be described below with reference to the drawings.
Conventionally, there has been no diffusion plate like the embodiment of the present invention described below, partly because the manufacturing method had not been invented, but what kind of lens arrangement and what kind of randomness could be combined? The problem was that it was unclear whether it was a good idea or not.

The applicant has conducted various studies and experiments, and has succeeded in finding several manufacturing methods and conditions. First, I will explain this point.

First, in the case of a full-surface microlens focusing plate, as shown in the cross-sectional view of the single-lens reflex finder optical system in Figure 1, when the matte surface 1 is closer to the imaging lens than the Fresnel lens 2 (in this case, the focus plate is If the pitch of the Fresnel lens is around 50μm,
On the other hand, moiré was not noticeable on the full-surface micropit plate, which had a periodic structure with a pitch of about 25 μm.

When the pitch of the Fresnel lens was about 30 μm, moiré was not noticeable on the full-surface microlens piston plate, which had a periodic structure with a pitch of about 16 μm.
Of course, distance measurement etc. would have been better with a finer pitch of about 10μm, but these can be used when the lens is stopped down, for example, when a lens with a focal length of 50 mm wide open F No. 1.4 is stopped down to about F8 or a focal length of 300 mm wide open F No. When using a .5.6 lens, the viewfinder appears colored.

Therefore, even if moiré does not occur with such a full-surface microlens pit plate, if coloration appears, it is possible to roughen the surface and weaken the periodic structure to eliminate the coloring phenomenon caused by diffraction phenomenon, and also to reduce the pitch of the periodic structure. is relatively rough and there is no coloring phenomenon, but if moire fringes appear between the microlens and the Fresnel lens, it was found that the contrast of the moire fringes could be weakened by further roughening the boundary surface between the microlenses and weakening the periodic structure. . That is, in order to eliminate moire fringes, it is desirable to roughen not only the curved surfaces of the convex portions of the lenses but also the curved surfaces of the concave portions that are the boundaries between the lenses. Furthermore, roughening the surface of the periodic uneven structure is in accordance with the gist of the present invention in the sense that it weakens the special bokeh and approaches the bokeh of a standard matte surface. However, it is not preferable to roughen the surface of ground glass at sharp angles, and as shown in Fig. 8, a smooth curved surface smaller than the pitch is formed on the surface of a regular lens-like curved surface array as shown in Figs. 4 and 6. It is desirable to randomly arrange the microlenses in order to maintain the brightness of the viewfinder.

The applicant has discovered several methods of manufacturing such preferable diffuser plates. Before entering into the explanation, an example of a manufacturing method of a diffuser plate having a regular array of microlens-like curved surfaces, which has already been filed by the applicant of the present invention, and its surface shape will be explained.

Figure 2 shows a creation device using an interference pattern generator using a laser.
The three lenses 7 _{1 to 3} are placed in the enlarged beam, and noise is removed at the convergence point 8 _{1 to 3} of the three convergent beams obtained by the three lenses. Install a pinhole for Assuming that the three pinholes are almost at the vertices of a regular triangle,
Two-dimensional interference fringes are produced in the space where the three beams of light emitted from the pinhole overlap, and their contour lines are as shown in FIG. In the figure, assuming that the intensity at the center surrounded by approximately concentric circles is 1, contour lines with intensities of 0.9, 0.8, . . . are drawn outward from there. In Fig. 2, for example, a holographic dry plate is placed at the position where the three beams of light are incident, and after exposure it is processed using the bleaching method known in this field. Distribution is possible. The unevenness distribution is shown in FIG. In the figure, the six mountain tops B ₁ to _{B 6} surrounding the central mountain top A form a substantially regular hexagon when connected. The peak-to-peak distance, for example AB ₁ , is determined depending on the spacing between the three pinholes in FIG. 2 and the distance from the pinhole to the recording material surface 10, and can be easily controlled from about 10μ to 40μ. Note that a size of about 10 μm to several tens of μm is preferable in order to maintain the performance of the diffuser plate.

In Fig. 2, the three lenses 7 _{1 to 3} become four, and therefore the convergent light sources 8 _{1 to 3} also become four, and if they form a square, the recording surface will look like the one shown in Fig. 5. Interference fringes (contour lines) are obtained, and by processing similar to the previous processing, an uneven surface as shown in FIG. 6 is obtained. In the figure, four peaks D 1 to D ₄ surrounding the central peak C are connected to form a substantially square shape. Depending on how the four pinholes are arranged, D ₁
~D ₄ can be either a rectangle or a diamond. When the recording material is a holographic dry plate, such irregularities are recorded as irregularities on the gelatin surface, and when a resist is used, the irregularities on the resist surface are recorded.

Using this as a master plate, a mold is made by electroforming and molded into plastic, making it possible to mass produce focusing plates. The surface of the molded focusing plate has a shape similar to that shown in FIG. 4 or FIG. 6.

Based on the above explanation, the method for manufacturing the focusing plate screen of the present invention will be described.

One is a purely optical method and the other is a semi-mechanical method.

The pure optical method is, for example, a method using an apparatus in which a speckle generating section is added to the optical system shown in FIG. 2, and an example thereof is shown in FIG. 7.

In the figure, reference numeral 13 denotes a lens whose peripheral part 14 is made of ground glass, and the recording surface 10 has three pinholes 8 _{1 to 3.} The spherical waves emitted from the lens 13 are converted into parallel light fluxes into three parallel light fluxes. , minute irregular speckled patterns (so-called speckle patterns) generated by the ground glass 14 on the periphery of the lens 13 simultaneously enter and interfere with each other, and are recorded as a pattern in which synchronous structures and random structures overlap. . In this case, the pitch of the interference fringes is determined by the distance between the three pinholes and the distance between the pinhole and the lens 13 (usually taken as the focal length of the lens).
The average size of the random structure is determined by the arrangement of the lens (more specifically, the diffusing surface of the lens) and the recording surface, that is, the shape of the diffusing surface and the distance between the lens recording surfaces, and therefore, it is determined by varying the ratio of the interference fringe distance to Can be adjusted in size.

The surface of the focusing plate, which is formed by forming a mold using the master plate and the uneven surface having the periodicity and random graininess recorded in this way by electroforming, is formed by the periodic microlens shown in Fig. 4, as shown in Fig. 8. This resulted in finer and smoother unevenness superimposed on the curved surface.

Another manufacturing method for the focus plate screen of the present invention is semi-mechanical. When the surface of the mold has a regular lens array with concavities and convexities reversed to those in FIG. 6, hard particles having a radius smaller than the frame inscribed in the concave surface of the mold are sprayed onto the surface of the mold. When glass beads with a diameter of 10μ are blown onto a lens array with a pitch of 16μ by honing, the surface of the mold with the concave and convex surfaces shown in Figure 6 inverted is covered with irregular concave curves.
When a focusing plate was molded using this mold, a surface with irregular minute convexities was obtained.

This method is called a semi-mechanical method because the mold having a surface in the form of a regular lens array was created based on an optical method.

It is also possible to make a mold for a micro fly-eye lens by stamping directly on a metal surface with a cutting tool with a spherical tip, but this method can also be used to roughen the surface, in which case it is completely mechanical. It can be said that it is a manufacturing method.

As described above, in the diffuser plate of the present invention, the smooth microlens-like curved surfaces are periodically arranged two-dimensionally and the boundaries between them are also connected by smooth curved surfaces, so even if the viewfinder is stopped down to a bright light, there will be no shadowing. Furthermore, because random minute irregularities are formed on the regular lens array surface, the image quality obtained when installed in the viewfinder is limited to moiré,
It was found that problems such as spots and coloring were reduced, and graininess did not deteriorate, making it an excellent focusing plate screen.

[Brief explanation of drawings]

Figure 1 is a schematic diagram of a diffuser plate incorporated into a camera, Figure 2 is a diagram showing the manufacturing method of a full-surface microlens-shaped diffuser plate, and Figures 3, 4, 5, and 6 are full-scale microlens-shaped diffuser plates. FIG. 7 is a diagram showing a method of manufacturing a diffuser plate according to an embodiment of the present invention, and FIG. 8 is an enlarged perspective view of a diffuser plate according to an embodiment of the present invention. In the figure, 3...laser light, 7 ₁ , 7 ₂ , 7 ₃ ...
...Lens, 10...Recording surface, 13...Lens, 1
4... Peripheral ground glass.

Claims (1)

[Claims] 1 It has a surface shape in which minute microlens-shaped curved surfaces are periodically arranged two-dimensionally and the microlens-shaped curved surfaces are connected by a smooth curved surface, and the microlens-shaped curved surfaces and the smooth curved surfaces A diffuser plate characterized by having irregularly arranged smooth unevenness formed on its top.