JP2503485B2 - Focus plate and manufacturing method thereof - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a focusing screen for focusing a camera or the like and a manufacturing method of the focusing screen.

[Conventional technology]

As a focusing screen for a conventional single-lens reflex camera, a base material such as glass is roughened by sanding, a mold is taken from this and the unevenness of Y is transferred onto a plastic material, and this is used as a focusing screen. Is known. Further, Japanese Patent Laid-Open No. 58-60642 proposes a method in which a sanded rough surface is processed by etching or the like to eliminate a sharp angle portion to improve diffusion characteristics.

However, these focusing screens are highly evaluated for their natural bokeh, but even with dark lenses or bright lenses, when the aperture is narrowed down, the granularity of fine sand on the screen surface is recognized, and the appearance is poor. There was a drawback to do.

Such an effect is caused because the micro unevenness of the sanding surface or the surface processed based on it is extremely random in its shape (particle size, height) and arrangement.

On the other hand, Japanese Patent Laid-Open No. 55-90931 proposes a focusing screen having a structure in which microscopic irregularities (particle diameter, height) and arrangement are perfectly aligned and microlenses are periodically arranged.

While such a focusing screen has the excellent feature that even if the aperture is narrowed down, the graininess of fine sand does not appear on the screen, the direction of the diffracted light corresponds to the order of diffraction due to its periodic structure. However, since it is limited to a specific direction, there is a serious drawback that the blurring is not natural because of the multi-line blurring.

In order to solve the drawbacks of both types of focusing screens, a reticle pattern in which semi-regular figures are scattered is repeated by a step-and-repeat method to increase the area to make a mask original plate, and the mask pattern is smoothly applied to a photosensitive material. Japanese Unexamined Patent Publication (Kokai) No. 59-208536 discloses a method of recording as unevenness.

In this conventional example, for each dot forming the reticle pattern, the diameter, center position, and center interval of the circle are determined using random numbers. However, in the original picture created in this way, it is pointed out that the seam of the reticle becomes unnatural,
The following four embodiments have been described as methods for making the boundaries inconspicuous by the step-and-repeat method.

In the first example, as shown in FIG. 11, the reticle is divided into square cells, and even if it is cut at the boundary, it can be combined with the adjacent reticle to form one continuous opening. In the second example, as shown in FIG. 12, the square is replaced with a circle having the same area as the center of the first example as shown in FIG. 12. The third example is shown in FIG. Three circular openings with diameters of 20μ, 24μ, and 28μ, which are the same in the example and its center, are used, and the cuts of adjacent circles on the boundary line are aligned.

Further, in the fourth example, the boundary line is deformed by modifying the incomplete circle existing in the boundary area of FIG. 14 in which the unit patterns generated by the computer are arranged mechanically as shown in FIG. .

[Problems to be solved by the invention]

In the conventional example as described above, there is a drawback that a complicated treatment must be performed in order to match the cuts on the boundary line. Even in this case, in the first, second, and third examples, since the opening is cut on the boundary line, inconsistency of 1 μ order cannot be avoided during step and repeat, and this forms an incomplete circle. The effect of making the boundaries stand out was unavoidable.

Further, in this prior art example, since a random distribution is assumed from the beginning, there is a drawback that the randomness appears so strongly that the graininess like sanding due to the above-mentioned narrowing is easily washed.

The present invention has been made in view of such conventional problems, and an object thereof is to provide a focusing screen in which the boundaries are inconspicuous and the graininess and the bokeh are well-balanced, and the optimum random at that time is provided. However, the numerical value is limited.

[Means for solving problems]

In order to solve the above problems, in the present invention, a lattice point that gives a two-dimensional periodic structure is determined, a point with a slight variation is determined in the vicinity of this lattice point, and a predetermined point is centered on this point. Forming an opening of the size.

As a result, it is not necessary to consider the problem of seams such as in the conventional example at all, and assuming a two-dimensional periodic structure, the periodicity is slightly disturbed in the vicinity of the two-dimensional periodic structure. Since the directivity can be almost eliminated with respect to the diffracted light of higher order that does not appear, it is possible to obtain a diffusing plate with an improved bokeh as compared with the diffusing plate having a perfect period.

[Action]

The basic structure of the present invention will be described with reference to FIGS. 6 to 10. In order to clarify the principle and operation of the present invention, first, a focusing screen in which microlenses are arranged in a two-dimensional periodic structure will be described. Here, the term "microlens" is not limited to the case where the curved surface is spherical as shown in FIG. 6 (a), but is a generic term for a sine shape (b), a conical shape (c), and micro-raised shapes having similar shapes. .

As a method for changing the concentration distribution formed on the photosensitive material into a surface unevenness, a method using a photoresist as the photosensitive material and a method by bleaching a gelatin dry plate are well known and will not be described in detail here.

The light and shade distribution of the photosensitive material is formed by transferring the mask original plate.The method is to provide a gap of about 200 μ or less between the original plate and the photosensitive material even if the mask is brought into close contact with the mask and exposed to light so that the diffraction effect or Depending on the spread of the light source, the exposure may be performed by utilizing the blur or the reduced projection exposure may be performed. Hereinafter, the structure of the mask original plate, which is the point of the present invention, will be mainly described.

FIG. 7 shows an example of a mask original plate for making a focusing screen in which microlenses are periodically arranged. FIG. 8 shows a contour map showing the undulations of the matte surface of the focusing screen made from the original mask plate of FIG. Figure 7 shows pitch P ₀ and diameter
In which P _0/2 around the opening portion is illustrated case arranged in a hexagonal lattice, the center coordinates of each opening (X ', Y') is given by the following equation.

FIG. 7 shows the case where I = 1, 2, 3, 4; J = 1, 2, 3, 4.

The diffraction image of such a periodic grating is as shown in FIG. Therefore, when the point image is blurred, such multi-point blurring occurs, and when the line image is blurred, it becomes multi-line blurring, and the defocusing effect is poor.

In this case, the angle Δθ (FIG. 9) formed by each order of the diffracted light is given by assuming that the wavelength of the incident light is λ. Becomes FIG. 10 is a graph obtained by calculating the diffracted light intensity distribution in the angle region of θ _x to θ _{30 in} FIG. 9. Thus, little light comes between each diffraction order.

In the present invention, since the center coordinates of each aperture are slightly shifted from the period given by the formula, light is scattered in addition to the diffraction orders shown in FIGS. 9 and 10. ,
The unsightly bokeh is greatly reduced.

〔Example〕

Next, the contents of the present invention will be described with reference to the embodiments shown in FIGS. FIG. 2 is a plot of the center coordinates (X ', Y') of the periodic opening of FIG. Next, a region of width Δ (spread of Δ / 2 on one side) is set around this coordinate point (X ′, Y ′) and a new center coordinate point (X, Y) is created with appropriate variation in this region. To decide. (FIGS. 3 (a) and 3 (b)).

Any suitable method may be used for providing the appropriate variation, but for example, values may be generated at random within this area.

As Figure 1 is Δ / P ₀ = K, an example where the K = 0.25, the fourth diagram that calculated diffracted light intensity distribution in an angle region up to theta _x through? _{30 °} corresponding thereto Is.
Comparing FIG. 10 and FIG. 4, it is clear that the introduction of slight randomness weakens the directivity of the diffracted light and alleviates the bad blur effect.

 Next, the optimum range of randomness will be described.

Naturally, the larger the value of K, the greater the effect of introducing randomness. However, when K0.5 is reached, the distance between the peaks varies from half to 1.5 times the average pitch P, and the unevenness of the mat surface finally obtained is expressed by contour lines, as shown in FIG. Become. In such a case, the flat part increases and the 0th-order light increases and the diffusivity deteriorates. At the same time, a deep inclined part is formed to increase scattered light at a large angle, and a feeling of roughness like sand on the mat surface when narrowing down is obtained. It becomes easy to appear.

Therefore, the range in which the effect of the present invention can be recognized is required to be 0.1K0.5 ..., It is preferably about 0.1K0.4. It is most preferable that the graininess is 0.2K0.3 ... so that the graininess is not noticeable and the effect of improving the blurring effect is recognized.

Next, the difference in effect due to the difference in pitch P on the focusing screen will be described.

The pitch P on the focusing plate is equal to the pitch P ₀ of the original plate when the mask original plate is exposed at a one-to-one scale, but they are not equal in the case of reduction projection. Therefore, in order to distinguish between the two, the pitch of the microlenses on the focusing screen is represented by P.

By introducing the randomness of about K, the width Δφ of the phase difference variation in the n-th order diffracted light is Δφ = nλ ·
It becomes K. Therefore, as the diffracted light of higher order is affected by the randomness, the diffraction peak disappears. When the phase difference variation Δφ is about λ / 2 or more, a considerable effect is recognized.
Since it is considered that the diffraction peaks almost disappear at φλ, the effect is considerably recognized by introducing the randomness of about K is n1 / (2K) …… The diffraction order above is n1 / K ...... It is a diffraction order of a degree or more.

Applying the formula for the case of K = 0.25 results in n2. Actually comparing Fig. 10 (K = 0) and Fig. 4 (K = 0.25), the peak of n2 in Fig. 4 becomes considerably smaller, and in inverse proportion to this, the intermediate angular range where there is no peak in Fig. 10 Also, a mountain appears, and the directivity of diffraction is weakened.

In the case of a photographing lens having an open F value of 4, the incident light beam having a maximum incident angle with respect to the optical axis is about 7 °.

The reason that the first-order diffracted light is in the direction of 7 ° is P = 4μ when λ = 0.5μ, so that the effect of the randomness of the present invention is not recognized when P <4μ. F = 4, K =
The effect of the present invention begins to appear at 0.25 when the second-order diffracted light is 7
It can be said that it is at a pitch of about P = 8 μ, which falls within the range of °.

Strictly speaking, the optimum diffusion characteristic of the focusing screen changes depending on the open F value of the taking lens, but considering the versatility, the F value is 2.8.
It is often designed so that scattered light is distributed in the range of about 4 or so. Therefore, the range in which the effect of the present invention appears is about P> 8μ in some cases.
It can be said that 15μ has a considerable effect. The upper limit of the pitch is not limited by the above discussion, but in a normal single-lens reflex finder, the structure becomes visible when it is about 30 μ or more on the focusing screen, so the pitch of the microlens is less than this. Is preferred.

Next, a method for producing a mask original plate having such conditions will be described.

As a known example of a method for producing a mask original plate, Japanese Patent Laid-Open No. 59-
There is one described in 208536. In this document, an original plate in which a lens pattern is expanded and recorded by a step-and-repeat method is created, and a method for making the seam of the reticle boundary part inconspicuous in that case is described.

Immediately, since the pattern is randomly generated in this known example, the problem that the circular opening pattern is cut off at the reticle boundary part inevitably arises, and it is necessary to take measures as extended in the known example. . However, in the present invention, the periodic structure is premised, and since the center of the opening is slightly moved around the periodic structure, it is not necessary to make complicated consideration as in the known example, and the procedure is exactly the same as in the case of the periodic structure. It is possible to expand the pattern.

In other words, in the case of the periodic structure shown in FIG. 7, four openings are arranged in the X direction and four openings in the Y direction, but more generally, I _max pieces in the X direction and J _max pieces in the Y direction. Assuming that the openings are arranged according to the formula, and the pitch of the center of the openings is P ₀ , the amount of movement during step and repeat is P ₀ × in the X direction.
I _{max in} the Y direction Becomes

By doing so, the next start is naturally determined at the opening position shown by the dotted line in FIG. 7, and there is no need to worry about boundaries as in the known example. Further, in the case of FIG. 1 in which a slight randomness of the periodic structure is introduced as in the present invention, the values of I _max , J _max , and P ₀ determined by the periodic structure which is the premise thereof are used, and in the X direction, P ₀ × I _max , in the Y direction If you move it repeatedly, you can get the original pattern of the target pattern automatically. The circular opening shown by the dotted line in FIG. 1 indicates the position of the start of the next step thus determined.

As described above, in the method of the present invention, a slight variation is provided around the periodic structure on the assumption that it has a merit that no particular consideration is required regarding the joint at the time of step-id repeat as in the known example.

The basic periodic structure may be a tetragonal lattice, but it is preferable that the hexagonal lattice is densely packed and highly isotropic as shown in FIG. The diameter of the opening is 7th
In the figure, it is half the pitch P ₀ , but other values may be used.

In the above, the reticle pattern is repeated by the step-and-repeat method in the same manner as in the known example, and the case where the target original plate is formed is described, but even if there is no fundamental defect such as the opening being cut at the boundary, If there is a slight gap or jam during the and repeat,
On the original plate created in this way, a pattern that is dimly recognizable still occurs. In order to eliminate this, the amount of step and repeat must be adjusted very delicately.

In order to eliminate such problems, the area equivalent to the entire mat surface (24 mm × 36
It is most preferable to draw the opening in mm).
In fact, it is possible to draw an area of 50 mm x 50 mm or more at a stretch with electro beam exposure.

In addition, a minute unevenness is added by a vapor deposition method or a plating method to the focusing plate made using such an original plate or its mold or the dairy material surface on which the unevenness of the previous stage is formed, and then the mold is raised. It is also possible to make a natural focusing screen with a more uniform diffusivity by making a focusing screen.

In the above description, the range of the randomness of the microlens arrangement is described on the premise of the mask exposure method which is easy to introduce the randomness, but this is also applicable to the case of other matting methods. That is, it is also possible to mass-produce finder mats by forming microlenses on the mat master with an indenter in the arrangement having the above-mentioned randomness, and using the known transfer technique from the master. Therefore, the application of the randomness does not depend on the microlens forming method.

〔The invention's effect〕

As described above, according to the present invention, with respect to the arrangement of the microlenses on the focusing screen, the arrangement is made to have a slight randomness in the vicinity thereof on the assumption of the periodic structure, so that the graininess due to the narrowing is not conspicuous. In addition, it is possible to obtain a focusing screen having good characteristics in which the unnaturalness of the bokeh is not noticeable.

Further, since the present invention is premised on the periodic structure, there is also an effect that the problem of the reticle seam, which has been a problem in the known example, does not occur when the mask original plate is produced.

[Brief description of drawings]

1 to 5 are explanatory views for explaining the structure and the structure method of the focusing screen of the embodiment of the present invention, and FIG. 1 shows Δ / P = K in FIGS. 2 and 3. (= 0.2
5) is an explanatory view showing the mask original plate of the focusing plate in the case of 5), FIG. 2 is an explanatory view showing the central coordinates of the periodic openings of the mask original plate of FIG. 7, and FIG. , (B) are explanatory views showing the new center coordinates in which the center coordinates of FIG. 2 are varied in the area of the width Δ, and FIG. 4 shows the focus plate made by the mask original plate of FIG. FIG. 5 is an explanatory diagram showing the diffraction intensity distribution of the diffraction image, and FIG. 5 is a contour diagram showing the undulations of the matte surface of the focusing screen made from the mask original plate of FIG. 6 to 10 are explanatory views for explaining the structure and manufacturing method of the focusing screen which is the basis of the present invention, and FIGS. 6 (a) to (c) show the focusing screen of the present invention. FIG. 7 is an explanatory view showing a curved surface of a microlens, FIG. 7 is an explanatory view showing a mask original plate of a focusing plate of the present invention, and FIG. 8 is a mat of a focusing plate made by the mask original plate of FIG. FIG. 9 shows a contour map showing the undulations of the surface, FIG. 9 shows an explanatory view of a diffraction image by the periodic grating of the focusing screen of the present invention, and FIG. 10 shows a diffraction intensity distribution of the diffraction image shown in FIG. The explanatory view showing is shown. 11 to 15 are explanatory views for explaining the structure and manufacturing method of a conventional focusing screen.

Claims (6)

(57) [Claims] 1. A microlens-shaped curved surface having substantially the same shape is 2
In the diffuser plate arranged in a dimension, the average pitch P of the microlenses is 8 μ <P <30 μ.
And the center coordinates (X, Y) of the microlens are determined by the average pitch P and the set of integers (I, J), and the next periodic lattice point (X ′, Y ′) , The predetermined distance range is limited to a range of width K × P centered on the periodic lattice point using a constant K of 0.1 <K <0.4. A focusing screen characterized by that. 2. The range according to claim 1, wherein the predetermined distance range is limited to a range of width K × P around a periodic lattice point using a constant of 0.2 <K <0.3. ) The focusing screen described in the above item. 3. The focusing screen according to claim 1, wherein the variation within the predetermined distance range is random with respect to the set of integers (I, J). 4. A mask original plate having a distribution of light and shade with a periodic structure having a pitch P ₀ and varying within a predetermined distance range,
A method of manufacturing a focusing screen, wherein unevenness having an average pitch of 8μ to 30μ is formed on the photosensitive material by exposing the photosensitive material close to the photosensitive material or by reducing projection exposure. The structure of the light and shade distribution is as follows: (a) The central locus (X, Y) of the concentration (or light part) is determined by the set of integers (I, J) at the next periodic lattice point (X '(I, J) ,
Y '(I, J)) However, I = 1,2, ... I _M ; J = 1,2, ... J _M are formed with a variation within a predetermined distance range. (B) The predetermined distance range is 0.1 The range is K × P in width using a constant K such that <K <0.5, and (c) the density distribution structure of the mask original plate by periodically repeating the I _M × J _M basic lattices a plurality of times. A method of manufacturing a focusing screen, which comprises: 5. The range according to claim 3, wherein the predetermined distance range is limited to a range of width K × P around a periodic lattice point using a constant of 0.2 <K <0.3. ) A method of manufacturing a focusing screen according to the above item. 6. The method of manufacturing a focusing screen according to claim 4, wherein the variation within the predetermined distance range is random with respect to the set of integers (I, J).