JPH09325385A - Focusing plate and method of manufacturing the same - Google Patents

Abstract

(57) Abstract: A focusing screen of a single-lens reflex camera that can give a sufficient amount of light to a photometric sensor and can obtain stable and good photometric characteristics, and a manufacturing method thereof. In a focusing screen 14 formed by forming a plurality of microlenses 14a, a radius of curvature r of the microlenses 14a is set to 16 μm to 32 μm. As a result, the incident light is appropriately diffused and a sufficient amount of straight light is provided. In particular, by forming the surface 14b formed between the adjacent microlenses 14a with a flat surface or a curved surface with a large radius of curvature, the light amount of straight-ahead light is further increased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focusing screen for a single-lens reflex camera and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, in a single-lens reflex camera, a focusing screen having a microlens array surface formed by arranging a large number of microlenses, or a Fresnel lens surface having a microlens array surface on one side and an annular structure on the other side. A reticle is used. In the latter focusing screen, the microlens array surface that diffuses the incident light is used for focusing, and the Fresnel lens surface functions to deflect the imaging light beam outside the optical axis of the taking lens in the optical axis direction. Part of the light that has passed through the reticle enters the photometric sensor that has a light receiving element,
The rest reaches the finder optical system and is observed by the photographer.Therefore, as a focusing screen, when the photographer looks into the finder, the subject image does not have a feeling of roughness, and it has moderate blurring and is easy to focus on. Is required.

However, in a camera having an autofocus function, the subject is automatically focused by half-pressing the release button, so that the photographer does not need to adjust the focus while observing the subject image in the viewfinder. Therefore, it is more important for the photographer to look through the viewfinder and observe the subject image, rather than focusing.
It has a strong meaning to decide the composition and focus target. Further, recent single-lens reflex cameras employ a photometric method called multi-divisional photometry, which selects an optimal photometric area according to various shooting scenes and obtains an appropriate exposure value. For example, FIG. 7 is a diagram showing a division pattern of a light receiving element used for 5-division photometry, and the light receiving element included in each of the five photometric areas a to e outputs a signal corresponding to each area. In a camera equipped with this type of light receiving element, for example, the brightness value of each area, the brightness difference, the maximum brightness value, etc. are stored in the camera.
A comparison calculation is performed by the PU, and a photometric value suitable for the calculation of the proper exposure is selected from the 25 patterns classified in advance and each photometric area. There is a demand for a focusing screen that provides stable and good photometric characteristics to the photometric sensor, rather than making it easier for the observer to focus.

[0004]

However, in the conventional focusing screen, even if it is easy for the observer to focus, it is not possible to give a sufficient amount of light to the photometric sensor, and stable and good photometry is possible. There was a problem that the characteristics could not be obtained.

An object of the present invention is to provide a focusing screen of a single-lens reflex camera which can give a sufficient amount of light to a photometric sensor and can obtain stable and good photometric characteristics, and a manufacturing method thereof.

[0006]

An embodiment of the invention will be described with reference to FIGS. (1) Explaining in association with FIG. 1, the invention of claim 1 is a focusing screen 14 formed by forming a plurality of microlenses 14a.
And the radius of curvature r of the microlens 14a is 16
The above-mentioned object is achieved by setting the thickness to be from 32 μm to 32 μm. (2) The invention of claim 2 is the focusing screen 14 according to claim 1.
In the above, the surface 14b formed between the adjacent microlenses of the plurality of microlenses 14a is constituted by a flat surface or a curved surface having a large radius of curvature. (3) Describing in association with FIG. 3, the invention of claim 3 includes a first step of manufacturing a die by pressing the indenter 1 on the surface of the die base material 5 to form a plurality of indentations, It is applied to a method of manufacturing a focusing screen having a second step of transferring a shape of an indentation formed on the mold to an optical member to form a plurality of microlenses, and a radius of curvature of a tip portion of the indenter 1 is 19 μm.
The above-mentioned object is achieved by setting the thickness to 43 μm.

(1) In the invention of claim 1, the radius of curvature is 16
The microlenses 14a of μm to 32 μm appropriately diffuse the incident light and give a sufficient amount of straight light. (2) In the invention of claim 2, adjacent microlenses 1
The surface 14b formed between 4a increases the light amount of straight light. (3) In the invention of claim 3, the radius of curvature of the tip portion is 19μ.
A microlens having an optimum radius of curvature is formed on a focusing screen manufactured by a mold in which an indentation is formed by an indenter 1 having a diameter of m to 43 μm.

In the meantime, in the section of the means for solving the above-mentioned problems which explains the constitution of the present invention, the drawings of the embodiments of the present invention are used to make the present invention easy to understand, but the present invention However, the present invention is not limited to the embodiment.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 2 is a cross-sectional view of a single-lens reflex camera using a focusing screen according to the present invention, showing mainly the configuration of the parts necessary for explanation. Shooting lens 10
The light flux passing through the main mirror 1 is a half mirror
1 splits the light into two light beams of transmitted light and reflected light. Reference numeral 12 denotes a sub-mirror provided on the back side of the main mirror 11, which reflects the light flux transmitted through the main mirror 11 and guides it to an autofocus sensor 13 having a light receiving element. A focusing plate 14 has a microlens array surface formed on the lower surface side in the figure and a Fresnel lens surface formed on the upper surface side. Reference numeral 15 is a condenser lens, 16 is a pentaprism, and 18 is a finder optical system. The light flux reflected by the main mirror 11 is diffused by the microlens array surface of the focusing screen 14 and then collected by the Fresnel lens surface and the condenser lens 15. Lighted, penta prism 16
Then, the light passes through the finder optical system 18 and enters the eye of an observer looking into the finder. Also, the main mirror 1
A part of the light flux reflected by the beam No. 1 is incident on the photometric sensor 17 arranged near the finder optical system 18, and the photometric sensor 1
Photometry is performed by 7.

FIG. 1 is a view for explaining the focusing screen 14,
(A) is a plan view showing the microlens array surface side,
(B) is an AA sectional view of (a). The focusing screen 1
In FIG. 4, the surface opposite to the microlens array surface is a Fresnel lens surface, but in FIG. 1, the Fresnel lens surface is omitted and shown as a plane. The focusing screen 14 is manufactured by injection molding or compression molding using an optical resin such as acrylic as a material, and a plurality of microlenses 14a having a radius of curvature r as shown in FIG. Are formed. As can be seen from FIG. 1C, the relationship between the radius of curvature r of the microlens 14a and the diffusion characteristic will be described. An optical system with a relatively large radius of curvature r has a small amount of light that travels straight because it has little effect of refraction, while an optical system with a small radius of curvature has a high refractive index when passing through the lens surface, so that the peripheral area is The amount of diffused light that goes toward it increases, and it becomes a dark optical system with a small amount of light that travels straight.

However, the focusing screen 14 is required to have the contradictory characteristics of (a) a large amount of straight-ahead light for easy focusing, and (b) a sufficient amount of light to the light receiving element of the photometric sensor 17. As described above, the conventional focusing screen satisfies the characteristic (a), but does not satisfy the requirement of the characteristic (b). As a result of researching this problem, the present inventor found that both of these contradictory characteristics are satisfied by setting the radius of curvature of the microlens 14a to 16 μm to 32 μm.

Next, a method for manufacturing the focusing screen according to the present invention will be described. The method of manufacturing the focusing screen is an indentation method, that is, an indenter is pressed into the surface of the die base material to form an indentation (concave surface), and the concave surface of the die is transferred to produce a convex surface on the surface of the workpiece, that is, the focusing plate. The processing method for molding the microlens array surface is suitable, and the manufacturing method using the indentation method will be described below. FIG. 3 shows the mold base material 5 of the focusing screen.
FIG. 3 is a schematic view of an apparatus for making impressions as a mold of the microlens array, in which the die base material 5 is placed on the XY stage 6 by a mechanical method or a fixing method such as adhesion. 7X,
7Y is a stage moving motor that drives the XY stage 6, and is controlled by the stage drive circuit 20. 8
X and 8Y are digital micrometers that detect the position of the XY stage 6, and digital micrometers 8X and 8Y.
The movement amount of the XY stage 6 is detected by the stage movement amount detection circuit 21 based on the output of Y.

Reference numeral 2 is a moving coil device fixed to the body 4 of the dent device, and its detailed cross section is shown in FIG.
The indenter 1 having a conical tip is attached to the shaft 31 of the moving coil device 2. The moving coil device 2 includes a shaft 3 to which the indenter 1 is attached.
A motor 3 for rotating 1 is provided. In FIG. 3, 22 is a moving coil drive circuit for driving the shaft of the moving coil device 2 in the vertical direction, 23 is a shaft rotation angle indexing circuit, and 24 is each circuit 2
It is a computer that gives a predetermined instruction to 0, 21, 22, 23.

In FIG. 4, reference numeral 32 denotes a cylindrical permanent magnet provided so as to be externally fitted to the shaft 31, and fixed to the base plate 30c. Reference numeral 33 denotes a coil support frame which is attached to the shaft 31 and is externally inserted to the permanent magnet 32, and the coil 34 is wound in an annular shape. Reference numeral 35 denotes an annular permanent magnet provided so as to be externally fitted to the coil 34, and fixed to the base plate 30a.

39a and 39b are leaf springs, and the leaf spring 3
The base end of 9a is a block 3 fixed to the base plate 30c.
It is fixed to the pressing plate 37a and bolts 7 by means of bolts. The tip of the leaf spring 39a is connected to the shaft 31 by being sandwiched by the pin 38a between the holding plate 36a and the block 36 together with the connecting ring 38 which is integrated with the shaft 31. On the other hand, the base end of the leaf spring 39b is fixed to the block 37 fixed to the base plate 30a by a holding plate 37a and bolts. The tip of the leaf spring 39b is connected to the shaft 31 by being sandwiched between the pressing plate 33a and the support frame 33 together with the connecting ring 38. Therefore, the shaft 31 is elastically supported by the leaf springs 39a and 39b so as to be able to reciprocate on the vertical line, but the shaft 31 itself can rotate. The upper end of the shaft 31 is connected to the indenter rotating motor 3 via a joint 40. Since the joint 40 has rigidity in the rotational (radial) direction and has a flexible structure in the vertical (thrust) direction, the rotation of the motor 3 is transmitted to the shaft 31, but the vertical movement of the shaft 31 does not occur. It is not transmitted to the motor 3.

Next, the operation of the moving coil device 2 will be described with reference to FIG. As shown in FIG.
The lower part is magnetized to the S pole and the upper part is magnetized to the N pole. On the other hand, the permanent magnet 32 is magnetized to the N pole for the lower part and the S pole for the upper part.
In the central axis of the arrow, the direction of the magnetic force lines is vertically downward as indicated by arrow B. Here, when a current is applied so that the magnetic force lines generated in the coil 34 are directed vertically downward as indicated by the arrow B on the central axis of the shaft 31, a vertically downward force is exerted on the coil 34 to move the shaft 31 vertically downward. Driven. On the other hand, when a reverse current is applied to the coil 34, a vertically upward force acts to drive the shaft 31 vertically upward. By controlling the reversal of the polarity of the current by the moving coil drive circuit 22, the indenter 1 can be moved up and down at high speed. This vertical movement cycle is 0.1-50
It can be Hz. Further, the pushing force of the indenter 1 can be changed by changing the applied voltage applied to the coil 14.

As described above, the indenter 1 is driven and the indenter 1 is dented on the die base material 5 placed on the XY stage 6 to continuously form a large number of concave surfaces corresponding to one microlens. Can be formed. The focusing screen 14 is manufactured by pouring an optical resin such as acrylic resin into this mold by injection molding or compression molding. Since the processed surface of the die base material 5 needs to be mirror-finished by metal polishing in advance, a chromium alloy stainless tool steel having small crystal grains and few precipitates is used as a material. Moreover, diamond is suitable for the indenter material.

The tip of the indenter 1 has a vertical angle of 60 degrees or more.
A 120 ° conical shape with a spherical tip (within a diameter of 30 μm) having a spherical shape is used. Especially, for the focusing screen of the present invention, a radius of curvature of 19 to 43 μm is selected and used. The reason will be described below.

When a microlens is manufactured using a mold formed by the above-described dent device, the radius of curvature r of the microlens 14a and the radius of curvature R of the indenter 1 formed by transferring the impression shape. The relationship is expressed by the following equation.

## EQU1 ## r = k.multidot.R (1) Here, k is called a transfer coefficient and is obtained from an experimental value. Therefore, the radius of curvature R of the indenter 1 is determined from the radius of curvature r of the microlens 14a and the transfer coefficient k required for optical design.

FIG. 6 shows the pushing force of the indenter 1 and the die base material 5.
It is a figure explaining the relationship with the curvature radius of the indentation formed in. Pushing force F1, F2, F3 for the die of the indenter 1
When the magnitude relationship of F1 <F2 <F3 is satisfied, the depths H1, H2, and H3 become deeper in proportion to the pushing force, and H1 <H2 <H3. On the other hand, the radius of curvature r1, r2 of the indentation in the region δ required for optical performance,
It was found from an experiment that r3 was r1>r2> r3. That is, the transfer coefficient k in the equation (1) is inversely proportional to the magnitude of the pushing force F of the indenter 1. Therefore, by controlling the pushing force F of the dent device, an indent having a predetermined radius of curvature can be formed on the die base material 5.

If the pushing force is appropriate, it is possible to repeatedly form an indentation having a stable shape with no variation on the die, but this appropriate value varies depending on the performance of the device for pushing the indenter and the die material. The present inventor found through experiments that the transfer coefficient was stable when it was about 0.75 to 0.85. That is, the curvature radius R of the tip of the indenter is r / 0.75 to r / 0.
Manufactured to be 85, the transfer coefficient is 0.75 to 0.8
By controlling the pushing force so as to be 5, it is possible to repeatedly form indentations having a stable shape without variations.
As described above, the optimum value of the curvature radius r of the microlens is 16 to 32 μm, so that the required curvature radius of the indenter tip is 19 to 43 μm.

Here, even if an indenter having a smaller radius of curvature than that of the indenter that exhibits the required performance is used,
When the transfer rate is close to 0.85, that is, when the pushing force is set low, the gap between the microlenses 14a can be increased, and the light amount can be adjusted.

Further, since the tip shape of the indenter 1 actually used is not rotationally symmetrical with respect to the axis of the indenter 1, the indentation shape formed on the die base material 5 is not spherical but distorted. There is. Therefore, since the indentations formed in large numbers have the same directionality of strain, the diffused light has a particular directionality. Therefore, the motor 3 is used to make dents while rotating the indenter 1 by a minute angle to make the directions of the above-mentioned indentations uneven, so that the diffusion by the microlens array surface can be made uniform.

[0024]

As described above, according to the present invention,
The microlens formed on the focusing screen diffuses the incident light moderately and gives a sufficient amount of straight-ahead light, so it can give a sufficient amount of light to the photometric sensor and obtain stable and good photometric characteristics. To be According to the second aspect of the present invention, it is possible to increase the light amount of the straight-ahead light and the photometric characteristics are improved.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a focusing screen according to the present invention,
(A) is a plan view showing the microlens array surface side,
(B) is a sectional view taken along the line AA of (a), and (c) is a view for explaining the action of the microlens array.

FIG. 2 is a sectional view of a single-lens reflex camera.

FIG. 3 is a schematic configuration diagram of a dent device.

4 is a cross-sectional view showing details of the moving coil device 2 of FIG.

FIG. 5 is a diagram for explaining the operation of the moving coil device 2.

FIG. 6 is a diagram illustrating the relationship between the pushing force of an indenter and the radius of curvature of an indentation.

FIG. 7 is a diagram showing a division pattern used for 5-division photometry.

[Explanation of symbols]

 1 indenter 2 moving coil device 5 mold base material 14 focusing plate 14a microlens 14b surface 17 photometric sensor 31 shaft r, R radius of curvature

Claims (3)

[Claims] 1. A focusing screen comprising a plurality of microlenses, wherein the radius of curvature of the microlenses is 16 μm to 32 μm. 2. The focusing screen according to claim 1, wherein a surface formed between adjacent microlenses of the plurality of microlenses is a flat surface or a curved surface having a large radius of curvature. . 3. A first step of manufacturing a die by forming a plurality of indentations by pressing an indenter on the surface of a die base material, and transferring the shape of the indentations formed on the die to an optical member. A method of manufacturing a focusing screen having a second step of forming a plurality of microlenses, wherein the radius of curvature of the tip of the indenter is set to 19 μm to 43 μm.