JPS6143712A - Lens for copying - Google Patents

Abstract

PURPOSE:To obtain the small-sized copying lens with high performance by using a lens system of completely symmetrical type four-group constitution which has the front group composed of the 1st meniscus lens group having the convex surface on an object field side and the 2nd meniscus single lens group so that a glass block is interposed between the front and rear groups. CONSTITUTION:The front group A and rear group B form the completely symmetrical type four-group constitution about the glass block 5, and the front group A uses the lens system composed of the 1st meniscus cemented lens group 1 having the convex surface on the object field side and the 2nd meniscus single lens group 2 having the convex surface on the object field side. Then, conditions such as radii of curvature of respective lens elements are set so that a spherical aberration is held at a proper value, a wide angle of view and a flat image plane are obtained, and coma flare is removed.

Description

DETAILED DESCRIPTION OF THE INVENTION This invention relates to improvements in fully symmetrical lens systems used primarily for copying purposes.

In general, it is desirable for a copying lens to have good imaging performance for 100% magnification and nearby magnifications, as well as a wide viewing angle in order to make the copying device more compact. There is a demand for a smaller size.

Among the performances, the first order is particularly required.

(1) Distortion aberration must be small since copying accuracy is required.

(2) Since the copy is flat, the image plane is also flat and the astigmatism difference is small.

(3) Coma flare, etc. must be sufficiently removed to improve contrast.

(4) Since the sensitivity of the photoreceptor is also in the short wavelength range, consider the spectral transmittance of the lens constituent materials and avoid using lenses that absorb in the short wavelength range.

This invention satisfies the above-mentioned performance and has an aperture ratio of 1:5.
The objective is to obtain a copying lens with a wide angle of 4 and a field angle of 53@.

Therefore, the copying lens according to the present invention has a completely symmetrical four-group structure in which the front group A and the rear group B sandwich the glass block 5, as shown in FIG. This lens system consists of a meniscus MS lens group 1 cemented with its convex surface facing the object world, and a second meniscus lens group 2 located behind it that is a single lens meniscus with its convex surface facing the object world.

Focal length of the entire system: 1illi2F Radius of curvature of the n-th surface: Rn Distance between the n-th and n+1 surfaces: DnRefractive index between the n-1 and n-th surfaces 2Nn and the n-th surface Interplane hole Q on the mth surface
When i: L, n to m, 1 (1) 0.4L+ to 12 < Rt = I R
121< 0.6L1-, 12(2) 0.6L3~
+o < Ri = I r'+a I < 0.8
L3~10 and (3) 0.6SL 1~12/L3~+o <
R+/R3”Rt2/R10< L+~12/13
~10 [ID4 = Da < 0. O4Fm
1.61 < N2 = N12 < 1.73rV
This satisfies the following condition: 1.68<Ns=N9.

The meanings of each of the above conditions will be explained below.

Condition I indicates a range in which among various aberrations, especially spherical aberration, is kept at an appropriate value.

If R1 = IR121 exceeds the lower limit, spherical aberration will be significantly under-corrected, and if you try to correct this with other parameters, a good balance of aberrations will not be obtained - RI =
The opposite is true if IR121 exceeds the 2 limit.

To correct the spherical aberration that occurs on the 1st and 12th surfaces,
The third surface and the first O surface are optimal within the range of Equation 1(1), and at that time, it is necessary to satisfy the conditions of Equation I(2).

The first lens group 1 preferably changes its power in a state close to bending without changing its power too much, and Rt = l Rt
It is important that the ratio of 21 and R3 = l Rto l is within the range shown in equation (3).

Condition (2) is important for obtaining a flat image surface for the purpose of widening the angle of the lens system. When D4=D8 becomes thicker than the upper limit, astigmatism becomes large and it becomes difficult to maintain a balance between the meridional image surface and the sagittal image surface.In particular, the meridional image surface becomes greatly overcorrected and the astigmatism difference increases. This phenomenon occurs significantly, and also serves to make the lens system more compact.

Condition (2) specifies the essential range for eliminating coma flare and flattening the image surface.

That is, when N2=N12 becomes smaller than the lower limit, the spherical aberration moves in the direction of becoming excessive, and coma flare occurs especially at low image heights, making it impossible to realize a bright lens. On the other hand, if the refractive index is set higher than the upper limit, curvature of the image surface will occur, especially the bulge of the meridional image surface will become large, and the image surface with a large astigmatism difference will become a lens that is not flat, making it impossible to achieve a wide angle. .

Condition (2) is a range for eliminating coma flare, especially at high image heights, thereby creating a clear image with high contrast.

Next, examples according to the present invention will be shown.

Rl r R2...R72 is the radius of curvature of each lens D I r D 2...[)++ is the thickness or air gap N of each lens, N2...N13 is d of each lens or air
Refractive index for line 1. 2... ν13 is the Atsube number of each lens or air RD Nd νd 1.0 0.0 21.8] (i 4.627 1.6584
4 50.956.712+ 3.201
1. (i2004 3G, 317.3g8 2
．． 139 1.0 0.0RD
Nd Sid30.656 1.1
10 1.757 47.945.594
1.110 1.0 0. O
Q 15.256 1.72825
28.5(X) 1.110 1
．． 0 0.0-45.594 1.1
10 1.757 47.9-30.65
6 2.139 1.0 0.
0-17.388 3.201 1.62
004 36.3-56.421 4.627
1.65844 50.9-21.816
1.0 0.0F=1
00.0 FNO,=5.4 Enclosing angle=53@Total length=0.39F Various aberration curves of this example are as shown in FIG.

As shown in FIG. 1(B), it is almost equivalent to arrange a roof prism 6 in place of the glass block 5 in this embodiment, but since it is virtually impossible to use a low image height, The lens was designed with the aim of minimizing curvature of the image plane in the effective image high range, with spherical aberration and astigmatism undercorrected.

In the spherical aberration curve, the solid line is the di line, and the broken line is the F line. In the astigmatism curve, the solid line is the sagittal line, and the broken line is the meridian line.

As this aberration diagram shows, the curvature of the image plane and astigmatism 1-spherical aberration are extremely well balanced, and chromatic aberration and coma aberration are also well corrected, demonstrating the effectiveness of each of the above-mentioned correction means. There is.

According to the lens system in which the Dahabliz 11 is arranged as shown in FIG.
m becomes compact.

Figure 3 shows M-D from the MTF calculation results by dtiA.
The -(u) curve is convenient for examining the best focus position and depth, and it can be seen that an image with high contrast is obtained. In addition, in this curve, u = 5 pieces/m
And so.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a schematic diagram of a lens system according to an embodiment of the present invention.
(A) shows an example of a through type, and (B) shows an example of a roof prism installed. FIG. 2 shows a detailed explanation of this invention, F=100.0F=
5.4 is an aberration curve diagram showing spherical aberration, astigmatism, distortion aberration, and coma aberration diagram. Figure fj53 shows the d-line M T F under the same conditions as Figure 2.
It is a curve diagram of 3f calculation. A...Front group B...Rear group 1...1st
Second lens group 3 for lens group 2...Third lens group 4/Fourth lens details 5...Glass block
6... Roof prism Figure 1 Figure 3 Mol)

Claims (1)

[Claims] It has a completely symmetrical four-group configuration in which the front group and the rear group sandwich a glass block, and the front group includes a meniscus-shaped first lens group joined with a convex surface facing the object world, and It is a lens system consisting of a second lens group of a single lens meniscus with a convex surface facing the object world, and the focal length of the entire system is: F radius of curvature of the n-th surface Rn the n-th surface and the n+1-th surface Distance between surfaces: Dn Refractive index between the n-1th surface and the n-th surface: Nn Distance between the n-th and m-th surfaces: Ln~m When I (1) 0.4L_1_~_1_2< R_1=｜R_
1_2｜<0.6L_1_～_1_2 (2) 0.6L_3_～_1_0<R_3=|R_1_
0 | <0.8L_3_～_1_0 (3) 0.65L_1_～_1_2/L_3_～_1_
0<R_1/R_3=R_1_2/R_1_0<L_1
____1_2/L_3_～_1_0 II D_4=D_8<0.04F III 1.61<N_2=N_1_2<1.73IV 1
．． A copying lens that satisfies the following condition: 68<N_5=N_9.