JPH01123210A - Variable power optical system for copying - Google Patents

Abstract

PURPOSE:To obtain good performance in a wide variable power range by specifying the moving method of a zoom lens system consisting of 3 groups; negative, positive and negative. CONSTITUTION:The spacing between the 1st and 2nd lens groups and the spacing between the 2nd and 3rd lens groups are asymmetrically changed. For example, the 1st, 3rd lens groups I, III having symmetrically negative powers are disposed on both sides of the 2nd lens group II having a positive power at the time of unmagnification. The spacings between the 1st and 2nd lens groups and the 2nd and 3rd lens groups are asymmetrically changed and the powers are varied by moving the entire part while the specified object plane and imaging plane are maintained at the time of varying the powers. The good performance is thereby obtd. in a variable power region and a wide variable power of about 0.5X-2.0X.

Description

Detailed Description of the Invention: a. Technical Field The present invention relates to a variable magnification (zoom) for copying, which is used in the optical system of a copying machine, and is capable of continuously changing the magnification while keeping the distance between the object plane and the image plane constant. It is related to optical systems.

b. Prior Art and its Problems In recent years, copying machines that can continuously change magnification from reduction to enlargement are becoming increasingly popular. In addition to the conventional method using fixed-focus lenses, variable-focus (zoom) lenses are used as optical systems for such variable-magnification copying machines because the mechanism for variable-magnification is relatively simple. A method has been proposed.

For example, a variable magnification (zoom) lens for copying consisting of three lens groups was filed in a patent application filed in 1983 by the same applicant.
This invention has been proposed in Japanese Patent Application No. 12789-12789 and Japanese Patent Application No. 12790-1988 (hereinafter referred to as earlier inventions).

These zoom lenses consist of three lens groups: negative, positive, and negative. The second lens group and the second lens group. Third
The focal length is made variable by changing the spacing between the lens groups, but the configuration is basically symmetrical even when changing magnification, so the brightness is FN, 1 near class, and the variable magnification range is 0.64X to 1.42.
The limit was about X.

However, recently, 0.5X to 2.0X exceeds this limit.
In order to perform wide-range variable magnification optical systems such as 0x and color separation in special color copying machines, lenses with large aperture ratios such as F, OL:4 class are also required.

However, 0.5X~2. In order to meet the demands for a wide-range variable magnification optical system such as OX and a large aperture ratio of FNOI: 4 class, if you use the zoom lens of the previous invention and expand the variable magnification range or make the FNO brighter, you can increase the magnification from 1x to As the magnification range increases, due to the symmetrical configuration,
There is a problem that off-axis coma aberration worsens and the occurrence of coma flare reduces the contrast at low frequencies of about 5 lines/m to 10 lines/m, which is important for copying machine optical systems, and there is still room for improvement. there were.

C0 Purpose The present invention was made to solve the above-mentioned problems,
By improving the movement method of the zoom lens system consisting of three groups, negative, positive, and negative, as in the previous invention,
It is possible to obtain good performance in a wide variable power range from x to 2.0x, and even when compatible with lenses with large aperture ratios of the FNOl:4 class, it is possible to obtain good performance in a wide variable power range. The object of the present invention is to provide a variable magnification optical system for copying.

d0 Structure of the Invention The variable magnification optical system for copying of the present invention comprises, in order from the object side, a first lens group consisting of at least one lens and having a negative focal length as a whole, and a first lens group consisting of at least three lenses as a whole. The first lens group is composed of a second lens group having a positive focal length, and a third lens group consisting of at least one lens and having a negative focal length as a whole. A variable magnification optical system for copying that changes the distance between the second lens group and the second and third lens groups and moves the entire system to change the magnification while keeping the distance between the object plane and the image forming plane constant. , the distance between the 1st lens group and the 2nd lens group is 1°. It is characterized in that the interval between the third lens groups is changed asymmetrically.

The present invention achieves its object by having a structure having such characteristics, but in such a variable magnification optical system for copying, the imaging magnification is M, the 1st . The second lens group spacing is dl
, I [I 2nd. Let the third lens group spacing be dll, ff+, and the amount of change in each group spacing when M becomes minute is ΔdI−
When 11wΔdπ0m, it is desirable to satisfy the following condition (1).

(1) When M>1.0× Δci,,,<Δd I[
When ellM<1.0× Δdr, r>Δdff,
ff+Furthermore, in the variable magnification optical system for copying, the second lens group has a symmetrical configuration with respect to the lens or aperture located at the center, and the second lens group has a symmetrical configuration with respect to the lens or aperture located at the center. The third lens group is characterized in that it is configured symmetrically with respect to the second lens group.In addition, in the above-mentioned variable magnification optical system for copying, when the magnification is equal to the first lens group, the third lens group is configured symmetrically with respect to the second lens group. The distance between the second lens group and the second lens group. The intervals between the third lens groups are made equal, and the optical system is symmetrical as a whole. The distance between the second lens group and the second lens group. It is characterized in that the interval between the third lens groups is changed asymmetrically.

00 action The present invention will be described below with reference to the accompanying drawings.

FIG. 1 schematically shows the configuration of the present invention. At the same magnification (M=1.OX), the first lens group with negative power is placed symmetrically on both sides of the second lens group (If) with positive power.
．． A third lens group (1, III) is arranged. When changing magnification (
M>1. ox, M<1. For Ox).

As shown by the solid line in FIG. The second lens group and the second lens group. The distance between the third lens group is changed asymmetrically, and the entire lens group is moved to change the magnification while keeping the object plane and the imaging plane constant. It shows the movement method of each group when changing the magnification of the zoom lens.

As shown in FIG. 1, in the three-group zoom lens of the previous invention, the first lens group and the second lens group are different from each other. The third lens group moved in a nearly symmetrical manner.

In the present invention, by actively adopting an asymmetrical movement method when changing the magnification, it is possible to change the magnification over a wide range and even with a lens having a large aperture ratio, as shown in the examples and attached aberration diagrams. It has been achieved that the performance is good enough to be used.

Even with a 3-group zoom lens like the previous invention, which has a nearly symmetrical configuration when changing magnification, good performance can be obtained at the same magnification and nearby magnifications. When the area is expanded or the aperture ratio is made brighter, due to the symmetrical configuration, strong comatic aberration occurs as the magnification deviates from 1:1, which is important for copying machines at 5 to 10 lines/m. The contrast at frequencies as low as /I is reduced. Therefore, in the present invention.

When changing the magnification, the first. The distance between the second lens group and the second lens group. By changing the amount of change in the distance between the third lens groups, the asymmetric configuration minimizes the occurrence of coma aberration, reduces the decrease in contrast, and makes it possible to obtain good performance at any magnification.

Condition (1) is a condition for properly correcting coma aberration that occurs during zooming. From actual size to enlargement, the first
．． The second lens interval is set to the second lens interval. The distance between the first and second lenses is smaller than the third lens interval, and from 1 to 1:1 magnification to reduction. The second lens interval is set to the second lens interval. By making the interval larger than the third lens interval,
This makes it possible to efficiently correct coma aberration during zooming and obtain good performance. Furthermore, from magnification to demagnification, the distance from the object plane to the lens surface must be greater on the magnification side than when using a symmetrical lens configuration.

Furthermore, when reducing the size, it is possible to increase the distance from the lens surface to the imaging plane, which is advantageous in terms of space.

f. Example Below, numerical data of Examples of the present invention are shown.

However, FNO is the aperture ratio F, fkl is the focal length of the entire system at equal magnification, ω is the half angle of view, r is the radius of curvature of each lens surface,
d is lens thickness or air gap, n is d-1i of each lens
The refractive index of ne and ν are the Abbe numbers of each lens.

In addition, since there is an advantage that the optical system can be manufactured at low cost, in the embodiment of the present invention, at 1 equal magnification (1, OX),
Although the lens configuration is shown to be completely symmetrical with respect to the lens or diaphragm placed in the center, the present invention can be applied even if some asymmetry is imparted to the radius of curvature, lens thickness, air spacing, etc. Of course, the same purpose can be achieved.

[Example 1] F~, = 1: 6.7 f, = 198.1
0ω=20.8°~15.7@~16.1″ plane Nα
r d n ya 1 -85
．． 092 2.55 1.51633 64.1
2 -224.225 3.00 3 66.788 7.98 1.67790
55.34 -119.063 8.52 5 -56.817 3.00 1.60342
38.06 56.817 8.52 7 119.063 7.98 1.67790
55.38 -66.788 3.00 9 224.225 2.55 1.51633
64.110 85.092 [Example 2] FNO=1:4 f M=281.50
ω=15.0″~12.46~12.5g surface Ha
r d nl -136,6524,
001,5163364,12-294,9074,0
0 37g, 389 20.28 1.61800 6
3.44 -195.727 3.55 5 -183.798 3.05 1.53172
48.96 59.400 8.54 7 136.110 6.35 1.67790
55.38 704.000 11.24 9 -704.000 6.35 1.67790
55.310-136.110 8.54 11 -59.400 3.05 1.53172
48.912 183.798 3.55 13 195.727 20.28 1.61800
63.414 -78.389 4.00 15 294.907 4.00 1.51633
64.116 136.652 g, Effect As mentioned above, according to the present invention, up to now, in a zoom lens consisting of three groups, the weight is 0.64 in the variable power range.
The limit was about X to 1.42X, or the FNol near class was the limit in terms of aperture ratio.

By changing the movement method of each lens group, O, S
X~2. Good performance can be obtained even at a wide magnification of about 0x, and the brightness can be handled up to FNol: 4 class, so that the object of the present invention can be fully achieved.

[Brief explanation of the drawing]

FIG. 1 is a diagram schematically showing the configuration of the present invention. 2 is a cross-sectional view of the lens of Example 1, and FIGS. 3, 4, and 5 are lens cross-sectional views of Example 1 with a magnification of 1. OX, 2. OX, 0
．． It is a diagram of various aberrations at 5×. FIG. 6 is a cross-sectional view of the lens of Example 2, and FIGS. 7, 8, and 9 are lens cross-sectional views of Example 2 with a magnification of 1. OX, 1.54X. It is an aberration diagram at 0.64X. Figure 1 Figure 2 Figure 3 Blue Figure 4 Figure 5 B Tsuru Blue Figure 7 Figure 7 BI Threat Figure 8 Figure 9 Sine condition

Claims (1)

[Claims] 1. In order from the object side, a first lens group consisting of at least one lens and having an overall negative focal length, and a second lens group consisting of at least three lenses and having an overall positive focal length. It is composed of a lens group and a third lens group consisting of at least one lens and having a negative focal length as a whole, and the distance between the first and second lens groups and the distance between the second and third lens groups are changed, In a variable magnification optical system for copying that moves the entire system to change the magnification while keeping the distance between the object plane and the image plane constant, the distance between the first and second lens groups and the distance between the second and third lens groups are asymmetric. A variable magnification optical system for copying, which is characterized by changing the magnification. 2. In the variable magnification optical system for copying as set forth in claim 1, the imaging magnification is M, the distance between the first and second lens groups is d_I_・_II, and the distance between the second and third lens groups is d_II_
- A variable magnification optical system for copying, characterized in that it satisfies the following conditions, where _III and the amount of change in each group spacing when M changes by a minute amount are Δd_I _·_II and Δd_II_·_III. When M>1.0×, Δd_ I ＿・＿II＜Δd＿II＿・
If _IIIM<1.0×, Δd_ I ＿・＿II>Δd_I
I_・_III3 The variable magnification optical system for copying according to claim 1, wherein the second lens group has a symmetrical configuration with respect to a lens located at the center or an aperture. . 4. The variable magnification optical system for copying according to claim 1, wherein the first and third lens groups are configured symmetrically with respect to the second lens group. 5. In the variable magnification optical system for copying according to any one of claims 1 to 4, when the magnification is the same, the distance between the first and second lens groups and the distance between the second and third lens groups are equal. A variable magnification optical system for copying, characterized in that the optical system is symmetrical as a whole, and the distance between the first and second lens groups and the distance between the second and third lens groups are changed asymmetrically during zooming.