JPS61149914A - Image readout lens - Google Patents

Abstract

PURPOSE:To obtain a wide-angle, bright lens which has high resolution by composing the lens of six lens groups of a positive and a negative meniscus lens and a cemented lens of a biconcave lens and a biconvex lens and satisfying specific conditions. CONSTITUTION:The lens consists of the 1st group and the 2nd group of a positive meniscus lens, the 3rd group of a negative meniscus lens, the 4th group of a negative meniscus lens having a concave surface on an enlargement side, the 5th group of the cemented lens of the biconcave lens and biconvex lens, and the 6th group of at least one positive meniscus lens from the enlargement side. Then, the meniscus lens of the 6th group is introduced for a Xenotar type to compensate a positive-directional spherical aberration generated by the 4th group in a negative direction and also remove sagital flare, and the 2nd and the 3rd groups are separated to facilitate the compensation of a coma aberration and field curvature. Further, various conditions shown by inequalities I-IV are satisfied to improve image performance more.

Description

[Detailed description of the invention] B Industrial application field The present invention relates to a lens with a wide angle of view and brightness (high resolution).

For example, the image reading lens has a resolution of 400 dots per document surface.
A resolution of about 1/2 inch is required, and due to the size of the device and the number of grooves in the CCD image sensor,
Specifications are required, such as a reduced projection of about /15 and an angle of view of about 40 degrees. In a reduction projection type image scanner, image information on the document surface is captured by CC using a projection lens system.
Dr. (The image information is digitized by reducing the projection onto which light receiving element. For this reason, the projection lens must have high contrast in the frequency range below the spatial frequency corresponding to the pixel density of the light receiving element. Since the width of one pixel dot of the device is about 7 μm, the projected image needs to have a resolution of 72 lines/mm (having high contrast at a spatial frequency of 72 lines/mm or less).The present invention aims to provide a high-resolution, wide-angle, and bright lens that meets these demands.

Conventional technology Gauss dive and Kusetsuta types are known as basic types of lenses with wide angles of view and brightness. The Gaussian type does not have much difficulty in terms of brightness, but as the angle of view C2w) increases to about 40 degrees, the screen around the image tilts significantly, and is inferior to the Kusetsuta type in terms of wide angle of view. With the Kusetsuta type, there is less image distortion, but in a wide field of view, part of the luminous flux is eclipsed by the lens periphery, reducing the aperture efficiency of the diaphragm. The brightness is low, and even those called FNO2 and 8 are actually FN.
O, must be considered to be about 5. Also, there is a weakness in that sagittal flare increases when FN) is lowered. As described above, each type has its advantages and disadvantages, and none of them can meet current demands.

Special Publication No. 47-1801 as a lens with high angle of view and high resolution.
There is a 4th disclosure. This can be seen as the introduction of a characteristic meniscus lens of the Gaussian type and the Kusetsuta type to compensate for the shortcomings of each lens and take advantage of their characteristics, but although the angle of view is sufficient at 2-250, it is not bright enough. The value of FNO is about 5, which is still far from sufficient.

C. Problems to be solved by the invention The present invention goes beyond the conventional examples mentioned above, and
The objective is to provide a lens that is superior in brightness to that disclosed in No. 18014.

2. Means for Solving Problems The present invention provides, from the magnification side, a first group consisting of a positive meniscus lens, a second group consisting of a positive meniscus lens, a third group consisting of a negative meniscus lens, and a concave surface facing the magnification side. The projection lens was composed of a fourth group consisting of a negative meniscus lens, a fifth group consisting of a combination of a biconcave lens and a biconvex lens, and a sixth group consisting of at least one positive meniscus lens.

By introducing a meniscus lens in the 6th group to the 4th group, the positive spherical aberration generated in the 4th group is corrected in the negative direction, sagittal flare is removed, and the 2nd group By separating the lens from the third group, it is easy to correct coma aberration and curvature of the field.

Example FIG. 1 shows one embodiment. The table below shows each numerical value.

Total system focal length: 40.0 1 17.35 FIG. 2 shows another embodiment. In this embodiment, the sixth group consists of two positive meniscus lenses.

The figures are shown in the table below.

Total system focal length 40.0 Radius of curvature Axis spacing Refractive index Atsube number d L L6.81 3.3 1.7495 50.00
34 25.9 to 0.44 5 31.95 1.5 1.8052 25.43
78 -16.03 0.18 13 -28.10 1.0 13 The table below shows still other examples. The lens configuration is similar to that shown in FIG. 2, with the sixth group consisting of two meniscus lenses.

Total system focal length 40.0 Radius of curvature Axis spacing Refractive index Ambe number d 6 7.30 9.46 7-9.97 1.5 1.8052 25.43
78 -14.73 0.18 9-134.74 1.5 1.7500 25.14
910 28.18 4・, 5 11; 70 U 39.23
1011 -56.40 0・1 111
2-120.40 3.0 1.7234 37.88 12
13 -41.50 0.5 131
4-130.58 45 1.7495 35.17 1
4is -2406 SUMT: 35.2 Figure 3 shows the performance of the first example lens, where A is the spherical aberration, the solid line d is the aberration at the d-line, the dashed line is the aberration at the g-line, and the dashed-double line is the aberration at the g-line. Aberrations at the C-line are shown. Figure B shows astigmatism, the solid line shows sagittal aberration, and the dotted line shows tangential aberration. C in the figure shows distortion. FIG. 4 shows the performance of the second embodiment, and FIG. 5 shows the performance of the third embodiment, A and B, respectively.

C has the same content as A, B, and C in FIG.

Taking the above examples together, it has been found that in terms of image performance, it is desirable for the lens configuration shown in the section of means for solving the above-mentioned problems to further satisfy the following quantitative conditions.

1.1) f<fa<2. Of tll-1,3
f < f 4 <-0,9f [210,5f
<f6<1. Of t31 f: Focal length of the entire system fa: 1st. 2. Combined focal length of the 3rd group f4: Focal length of the 4th group f6: Focal length of the 6th group R9: Radius of curvature of the enlarged side surface of the 5th group (see Figures 1 and 2) R11: Reduction of the 5th group The radius of curvature of the side surface (see Figures 1 and 2) The meaning of the fi1 equation above is that if fa exceeds the upper limit of the open equation, the spherical aberration will be overcorrected by 1 degree in the positive direction, and if fa exceeds the lower limit, the Petzval sum will become 4. 5. The 6th group cannot fully compensate in the negative direction.

In the above equation (2), if f4 exceeds the upper limit, spherical aberration will be overcorrected in the positive direction, and the occurrence of inner coma will increase. If f4 exceeds the lower limit, outer coma and distortion will increase.

In the above equation (3), when f6 exceeds the upper limit, the astigmatic difference increases, and when f6 exceeds the lower limit, the inner coma aberration increases, resulting in a decrease in contrast.

If the condition of the above equation (4) is not met, the inner coma becomes noticeable and the contrast decreases.

G Effect According to the present invention 1, the angle of view is 2 (t/: FNO at about 40).
.

A lens with a wide angle of view of 2.8 to 3.5, brightness, and excellent resolution and contrast can be achieved.

[Brief explanation of drawings]

FIG. 1 is a block diagram of the first example lens of the present invention, and FIG. 2 is a configuration diagram of the second example lens of the present invention. The configuration diagram of the lens of the third embodiment, FIG. 3 is a diagram showing the performance of the lens of the first embodiment, where A is the spherical aberration,
B indicates astigmatism, and C indicates distortion. Figure 4 shows the performance of the second practical example lens, where A is spherical aberration, B is astigmatism, and C is distortion. Figure 5 is the performance of the third example lens, where A is spherical aberration, B is indicates astigmatism, and C indicates distortion. Agent: Hiroshi Mai, patent attorney Valve tube Figure 1 Figure 2

Claims (1)

[Claims] From the magnifying side: a first group consisting of a positive meniscus lens, a second group consisting of a positive meniscus lens, a third group consisting of a negative meniscus lens, and a negative meniscus with a concave surface facing the magnifying side. Consisting of a fourth group consisting of a lens, a fifth group consisting of a cemented biconcave lens and a biconvex lens, and a sixth group consisting of at least one positive meniscus lens,
The focal length of the entire system is f, the combined focal length of the first, second, and third groups is fa, the focal length of the fourth group is f4, the focal length of the sixth group is f6, and the enlarged side surface of the fifth group. When the radius of curvature of is R9 and the radius of curvature of the reduction side surface of the fifth group is R11, the following conditional expression 1.0f<fa<2.0f...
・(1)-1.3f<f4<-0.9f・・・・・・・
......(2) 0.5f<f6<1.0f...
・・・・・・・・・(3)(R9-R11)/(R9+
R11) An image reading lens that satisfies (4).