JPS599622A - Optical resolving system - Google Patents

Abstract

PURPOSE:To vary resolving power continuously without varying an aperture diameter and changing lenses by providing the 2nd adjusting mechanism which operates associatively with the 1st adjusting mechanism which varies the distance between an original surface and an objective. CONSTITUTION:The objective 3 is mounted on the 1st lens barrel 6 which is rotated to vary the distance (a) between the original surface 1 and objective 3. Simultaneously, a projection 12 moves relatively along a spiral groove 8, but the 2nd lens barrel 11 does not rotate because a key groove 14 operates as a rotation stopper, so the lens barrel 11 moves forth and back according to the pitch of the spiral groove 8 to move an aperture 4 and a photodetector 5 fixed to the rear part of the lens barrel 11 together with the lens barrel 11. Namely, the distance (a) between the original surface and objective 3 is varied, and consequently the distance (b) between the objective 3 and aperture 4 for extracting a fine area in the original surface 1 placed on the image forming surface of the objective 2 is varied nonlinearly and assiciatively with said variation.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a resolving optical system for image scanning used in facsimiles, electronic plate making scanners, and the like.

Conventionally, devices such as drum-rotating scanners that scan the document surface in a point-by-point manner, and microdensitometers that measure the density by making small movements on the film surface, basically perform a scan as shown in Figure 1. A resolving optical system is used.
In the figure, light reflected (or transmitted) from a pixel dot 2 on a document surface 1 illuminated by spot light forms an image of the pixel dot 2 on an aperture 4 by an objective lens 3.

The aperture 4 has a small hole in its center, and light passing through the small hole is received by a photodetector 5 and converted into an electrical signal. It is well known that the resolution of such a resolving optical system is determined by the image magnification determined by the positional relationship between the objective lens 3 and the aperture 4 and the aperture d diameter of the aperture 4. Therefore, when it is desired to change the resolution, it is necessary to change the aperture diameter while changing the image magnification. In the above-mentioned plate-making scanners and microdensitometers, the resolution is generally changed by changing the aperture size; for example, by switching or replacing several types of apertures with different aperture diameters, or by changing the aperture diameter slightly. Methods have been used, such as using a variable aperture that can be adjusted by a mechanism. These methods can be realized by incorporating a mechanism having such a function at the position of the aperture 4 in FIG. 1.

However, since it is mechanically complex and requires high precision, it tends to be expensive. Furthermore, when the aperture diameter is changed, the light weight changes significantly depending on the square ratio of the aperture diameter, so there is a drawback that the sensitivity adjustment range of the detection system must be widened.

Alternatively, instead of changing the aperture diameter, there is a method of exchanging objective lenses 3 with different focal lengths, but this is not a good idea because the exchange is laborious and the focus adjustment is complicated.

An object of the present invention is to improve the above-mentioned problems and to realize a resolving optical system in which the resolution can be continuously varied without changing the aperture diameter or lens.

That is, an object of the present invention is to provide a resolving optical system having a simple and practical focus adjustment mechanism that can continuously vary the image magnification instead of the aperture diameter without blurring the focus.

The principle structure of the present invention will be explained below, and the details will be described based on specific examples.

Once the focus is adjusted in the resolving optical system shown in FIG. 1, the distance a from the document surface 1 to the objective lens 3 and the distance from the objective lens 3 to the aperture 4 are fixed. Here, the focal length of the objective lens 3 is f,! : There is the following well-known relationship between a, b and image magnification m.

Equation (1) is obtained, and if the distance from the document surface 1 to the aperture 4 is C, then 2 c = a + b = -(4) - f.

FIG. 2 (- and (B) are equations (2) and (3),
This is a graph of equation (4) versus distance a.

According to Figure 2 (B), as a increases under the conditions of a) f, b becomes a monotonically decreasing function that asymptotes to b = f, and according to Figure 2 (5), m asymptotes to m = O. Although it is a monotonically decreasing function, it is non-linear as shown in the figure. Also a
When = 2 f, a=b, m=1, and 2 f :>
The image is enlarged in the range of a > f, and the image is reduced in the range of a) 2 f. However, the distance C from the document surface to the aperture, which is the imaging plane, is the minimum value c at a = 2f from Fig. 2 (B).
= 4 Take f. Therefore, the aperture plane is a=
It should be noted that it is always located behind c=4f with -2f as the boundary.

If you pay attention to the above characteristics, for example, if you change a and make an adjustment so that b or C moves along the curve shown in Figure 2 in conjunction with a, the image magnification m will change as a increases or decreases in a. It is clear that it can be monotonically increased or decreased. The principle of the present invention is to slightly move b or C with respect to a in a nonlinear manner while satisfying the imaging conditions shown in FIG. 2, and to continuously vary m, that is, the resolution.

FIGS. 3(A) and 3(B) are a cross-sectional side view and a perspective view showing a specific embodiment of the resolving optical system according to the present invention,
The same parts in the figure as in FIG. 1 are given the same reference numerals.

The objective lens 3 connects the image of the pixel dot 2 on the document surface 1 to the aperture 4, and the light passing through the aperture 4 is transmitted to the photodetector 5.
is converted into an electrical signal by Although this example illustrates the case of monochromatic separation, if the document is in color, a color separation filter and a photodetector corresponding to each color component may be arranged behind the aperture 4. The objective lens 3 is mounted on a first lens barrel 6, and the lens barrel 6 has a moving threaded portion 7 with a constant pin on the front barrel. Spiral grooves 8 are carved at irregular intervals in the rear cylinder part. The lens barrel 6 is inserted and held in a fixed bracket 9 having the same screw pitch as the movable screw portion 7, and by rotating the ring portion 1o, the entire lens barrel 6 rotates and moves forward or backward in a direction perpendicular to the document surface. That is, the distance a between the pixel point 2 and the objective lens 3 changes in proportion to the rotation angle of the lens barrel 6. On the other hand, the spiral groove 80 portion of the lens barrel 6 is inserted into the second lens barrel 11 and processed so that the protrusion 12 on the inner wall of the lens barrel 11 fits into the spiral groove 8. A slide key part 13 protrudes in the axial direction from the lower part of the second lens barrel 11, and is fitted so as to slide smoothly back and forth along a key groove 14. Therefore, when the first lens barrel 6 is rotated, the protrusion 1
2 moves relatively along the spiral groove 8, but the second
Since the lens barrel 11 does not rotate because the key groove 14 serves as a rotation stopper, the lens barrel 11 moves back and forth according to the pinch of the spiral groove 8.

The aperture 4 and the photodetector 5 are fixed to the rear of the lens barrel 11 and move together with the lens barrel 11. As shown in the figure, the pitch of the spiral groove 8 changes continuously from fine to coarse with non-linearity, and when the lens barrel 6 rotates in a direction that brings the lens barrel 6 closer to the document surface 1, the lens barrel 11 moves closer to the lens barrel 6. Conversely, when the lens barrel 6 is rotated in a direction away from the document surface, the lens barrel 11 moves forward relative to the lens barrel 6. That is, in response to rotation in the direction of decreasing a in FIG. 2, the protrusion 12 moves in a direction in which the pitch of the spiral groove 8 becomes coarser; 12 moves in the direction in which the pitch of the spiral grooves 8 becomes denser. There, the spiral groove 8 that seals the rotation
By processing the nonlinear pitch so that the progression of the curve matches the curve shown in FIG. 2(B), it is possible to interlock and vary b relative to a while satisfying the imaging condition.

- As an example, in Fig. 2, the range of change of a is 15f to 3
．． on the other hand, b changes in the range of 3.0f to 15f, but C changes to 0.5 between 4.5f and 4of.
It changes by f, and the image magnification m has a four-fold change range of 2.0 to %. This numerical example is a very practical value, and since the change in the distance C from the document surface 1 to the four apertures is small, movement of the lens barrel 11 does not pose a problem in manufacturing the apparatus.

However, in the present invention, the aperture diameter of the aperture 4 is constant, and the amount of detected light depends on the light flux that reaches within the solid angle expected by the aperture diameter of the objective lens 3 with respect to a change in a. The solid angle is a
The one-sided magnification m also decreases with increasing a. On the other hand, when the surface magnification m becomes smaller, the pixel area of the original image 1fi1 that is focused within a certain aperture diameter increases, and as a increases, the pixel area becomes proportional to the pixel area. The amount of reflected light increases. In other words, the above-mentioned change in the solid angle and change in the area of the picture element to be picked up have an inverse relationship with respect to the change in a, and as a result, there is no effect of offsetting the change in the amount of light passing through the aperture 4. ,
It has a characteristic of suppressing changes in light amount with respect to changes in image magnification m. Therefore, compared to the conventional method of changing the image magnification by changing the aperture diameter, the present invention has the advantage that the adjustment range of the sensitivity level of the detection light can be narrowed.

In the embodiment shown in FIG. 3, the case where the distance a is changed by a constant bias and the distance is changed by a non-linear variable pinch is exemplified.
It goes without saying that this may be reversed and that a has a variable pitch and b a constant pitch.Also, it goes without saying that even if both have variable pitches, the objective can be achieved.

As described above, the present invention provides a distance a between the document surface and the objective lens.
a first adjustment mechanism that changes the distance between the aperture plate and the objective lens; and a second adjustment mechanism that changes the distance between the aperture plate and the objective lens in conjunction with the first adjustment mechanism. It provides a resolving optical system with variable magnification that changes non-linearly, allowing the resolution to be arbitrarily selected by continuously changing the image magnification, and the focal plane being automatically adjusted at all times. It also has excellent operability. Furthermore, as shown in the examples, it is mechanically simple and suitable for downsizing and economy. Further, even when the magnification is changed, there is little change in the level of the detection light meter, and practical effects such as easy sensitivity adjustment of the detection circuit system can be obtained.

[Brief explanation of drawings]

Fig. 1 is a cross-sectional view showing an example of a conventional resolving optical system, Figs. 2 (A) and (B) are graphs showing the imaging characteristics of a lens that does not provide a detailed explanation of the present invention, and Fig. 3 (A ), (B
) are a cross-sectional side view and a perspective view showing an embodiment of a resolving optical system according to the present invention. 1... Original surface, 2... Pixel point, 3... Objective lens, 4... Aperture, 5-... Photodetector, 6
．． 11... - Lens barrel, completed -... Moving screw, 8...
・Spiral groove, 9... Fixed bracket, 10...
Ring, 12...Protrusion, 13...Stride key, 14...Keyway. Name of agent: Patent attorney Toshio Nakao and 1 other person
1(2) a- α.

Claims (2)

[Claims] (1) First step to change the distance a between the document surface and the objective lens
an adjustment mechanism, an aperture plate placed on the imaging plane of the objective lens for extracting a minute area on the document surface, and an aperture plate that adjusts the distance between the aperture plate and the objective lens in conjunction with the first adjustment mechanism 1. A resolving optical system comprising: a second adjustment mechanism that moves along the optical axis so as to change the distance a non-linearly. (2) The resolving optical system according to claim 1, wherein at least one of the first or second adjustment mechanism is a feed screw mechanism whose pitch is continuously variable.