JPH03291613A - Optical lens for copying - Google Patents

Abstract

PURPOSE:To obtain the optical lens for copying which is compact in spite of a bright lens, whose various aberrations are corrected satisfactorily and whose high variable magnification rate can be obtained by specifying a ratio of focal distances of a first and a second meniscus lenses and a ratio of focal distances f5 of a sixth and a fifth meniscus lenses. CONSTITUTION:The optical lens is constituted of six groups and six pieces, lenses L1 - L3 of a front group and lenses L4 - L6 of a rear group are placed symmetrically or roughly symmetrically against a diaphragm S, and concave faces of each lens are all turned in the direction of the diaphragm S. Also, a ratio f1/f2 of a focal distance f1 of a first meniscus lens L1 and a focal distance f2 of a second meniscus lens L2 and a ratio f6/f5 of a focal distance f6 of a sixth meniscus lens L6 and a focal distance f5 of a fifth meniscus lens L5 are determined so as to be within a range of an expression I and an expression II, respectively. In such a way, various aberrations are corrected satisfactorily, a high variable magnification rate is attained, and also, the optical lens can be made small in size and compact.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a copying optical lens used in copying machines and the like.

2. Description of the Related Art Conventional copying machines generally have a same magnification and a slow copying speed, have dark lenses, and often use fixed-focus lenses. On the other hand, in recent years, with the diversification of needs for copying machines, there has been a demand for machines with high copying speeds and machines with enlargement and reduction functions, and their magnification ratios have also become higher.

To change the copying magnification, there are two methods: using a fixed focus lens to change the object-to-image distance by moving a mirror, etc., and using a zoom lens to continuously change the focal length. .

Problems to be Solved by the Invention Although the method using a fixed focus lens has the advantage of a relatively simple structure, it has the problem of limited magnification ratio, but this method is not so disadvantageous when used in a copying machine. It's not a condition. On the other hand, the method using a zoom lens has the advantage of being able to change the magnification ratio arbitrarily, but on the other hand, the number of lenses is large, the lens diameter is also large, the lens is dark, and a cam mechanism for zooming is required, making it smaller and more compact. However, there is a problem in that the entire copying machine becomes larger.

Therefore, the present invention uses a method of changing the object-image distance using a fixed focal length lens, and although the number of lenses is small and the lens is bright, it is compact and allows for a high variable magnification ratio with various aberrations well corrected. The purpose of the present invention is to provide an optical lens for copying.

Means for Solving the Problems In order to achieve the above objects, the present invention provides a first meniscus lens having a positive refractive power and a second meniscus lens having a negative refractive power arranged in order from the object side. A third meniscus lens having a positive refractive power, an aperture, a fourth meniscus lens having a positive refractive power arranged symmetrically or almost symmetrically with respect to the aperture, and a fifth meniscus lens having a negative refractive power. and a sixth meniscus lens having positive refractive power, each lens surface is arranged so that the concave side faces the aperture, and the focal length ratio of the first meniscus lens to the second meniscus lens is f1/f2 and the sixth meniscus lens has a positive refractive power. Focal length ratio f6 between the meniscus lens and the fifth meniscus lens
/f5 satisfies the following: 1.0<fl/f2 -1,2 1,0<f6/f5<-1,2.

Effect of the Invention The present invention has the above-mentioned structure of 6 elements in 6 groups, so that although the lens is bright, the overall length of the lens is short and the diameter of the lens is also small, making it possible to realize a small and compact optical lens for copying.

In addition, the present invention has a structure of 6 elements in 6 groups without bonded lenses, which increases the degree of freedom in design, effectively corrects spherical aberration and comatic aberration, and arranges the lenses symmetrically or almost symmetrically with respect to the aperture. This makes it possible to satisfactorily correct astigmatism and distortion that occur off-axis.

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 shows a lens configuration in an embodiment of the present invention,
A first meniscus lens L1 having a positive refractive power, a second meniscus lens L2 having a negative refractive power, a third meniscus lens L3 having a positive refractive power, and a diaphragm S1 having a positive refractive power are arranged in order from the object side to the image side. A fourth meniscus lens L4 having a refractive power, a fifth meniscus lens L5 having a negative refractive power, and a sixth meniscus lens L6 having a positive refractive power.
It is composed of 6 elements in 6 groups. Front group lens Ll,
L2. L3 and rear group lens L4. L5 and L6 are arranged symmetrically or almost symmetrically with respect to the aperture S, and the concave surfaces of each lens are all directed toward the aperture S. Also,
The ratio f1/f2 between the focal length 11fl of the first meniscus lens L1 and the focal length f2 of the second meniscus lens L2, and the ratio f6 between the focal length f6 of the sixth meniscus lens L6 and the focal length f5 of the fifth meniscus lens L5. /f5 is determined to be within the following ranges.

1.0<fl/f2<-1,2 -1,0<f6/f5<-1,2 Example 1 Table 1 shows specific numerical values for each lens in the first example of the present invention. There is. This table shows the focal length f of the entire system as 10
The image is normalized to 0 mm, F is the F number, and Yl is the image height at the same magnification. In addition, R1 is the radius of curvature of the i-th lens surface (III
+), Di is the thickness of the i-th lens and the air gap (distance) in order from the object side, and ni and νi are the refractive index and Abbe number of the glass of the i-th lens, respectively, in order from the object side. R
1-R13 and D1 to D12 correspond to those shown in FIG.

Table 1 f=100. F=8. Y'=81 (image height at same magnification)
As is clear from FIG. 1 and Table 1, in Example 1, the front group lenses LL, L2. L3 and rear group lens L4. L5. L6 is arranged completely symmetrically with respect to the aperture S. In this way, by arranging the front and rear lenses symmetrically with respect to the aperture S, distortion can be eliminated. Furthermore, since the concave surface of each lens is directed toward the aperture S side, astigmatism can be reduced. Furthermore, since the lens is configured with 6 elements in 6 groups, spherical aberration and comatic aberration can be reduced. Also, since the F number is smaller than before, the lens is brighter and has higher resolution, and by narrowing down the aperture S, the depth of focus can be increased.

FIG. 2 shows the aberration characteristics of the copying optical lens in Example 1 at the same magnification (IXI), and FIG. 3 shows the aberration characteristics at the time of reduction (×0.
5), FIG. 4 shows the aberration characteristics at the time of magnification (×2).

Note that ΔM indicates a meridional image plane, and ΔS indicates a sagittal image plane.

As is clear from these figures, the copying optical lens in Example 1 has a slightly worse spherical aberration for the d-line during magnification (x2), but this is very important for the focal length f=100+
There is only 12% aberration with respect to nm, which is completely satisfactory.

Example 2 Table 2 shows a second example of the present invention, and the meaning of each symbol is the same as in Table 1. In this second embodiment as well, the front group lenses LL, L2 . L3 and rear group lens L4. L5
．． L6 is arranged completely symmetrically with respect to the aperture S.

In this Example 2, the F number is smaller and the lens is brighter than in Example 1, but the overall length of the lens is slightly longer, but as shown in FIGS. Aberrations are well corrected as in Example 1.

Table 2 f=100. F=6.3. Y'=77 (image height at same magnification) Effects of the invention As described above, the copying optical lens according to the present invention has a structure of 6 elements in 6 groups, which increases the degree of freedom in design, and each lens has a concave surface with respect to the aperture. By arranging the lens so that the side faces the aperture and symmetrically or almost symmetrically with respect to the aperture, various aberrations can be well corrected.Also, although the lens is bright, the lens diameter is small and the overall lens length is short. Furthermore, despite being a fixed focal length lens, it achieves a high variable magnification, making it possible to realize a small, compact, and high-performance copying optical lens, which has great practical effects.

[Brief explanation of drawings]

FIG. 1 is a lens configuration diagram in an embodiment of the present invention, and FIGS. 2, 3, and 4 are various aberration diagrams at equal magnification, reduction, and enlargement, respectively, in the first embodiment of the present invention. FIG. 5, FIG. 6, and FIG. 7 are various aberration diagrams at the time of equal magnification, reduction, and enlargement, respectively, in the second embodiment of the present invention. Ll...first meniscus lens, L2...second meniscus lens, L3...third meniscus lens, S.
...Crest, L4...4th meniscus lens, L5...
・5th meniscus lens, L6... 6th meniscus lens, R... radius of curvature, D... spacing, thickness, n...
・Refractive index, ν...Atsube number, f...focal length, F・
...F number, Yo... Image height at 1:1 magnification.

Claims (1)

[Claims] A first meniscus lens having a positive refractive power, a second meniscus lens having a negative refractive power, and a third meniscus lens having a positive refractive power arranged in order from the object side,
an aperture, a fourth meniscus lens having a positive refractive power arranged symmetrically or almost symmetrically with respect to the aperture, a fifth meniscus lens having a negative refractive power, and a sixth meniscus lens having a positive refractive power. Each lens surface is arranged so that the concave side faces the aperture, and the ratio of the focal length f1 of the first meniscus lens to the focal length f2 of the second meniscus lens and the focal length of the sixth meniscus lens The ratio of f6 to the focal length f5 of the fifth meniscus lens satisfies -1.0<f1/f2<-1.2 -1.0<f6/f5<-1.2. Optical lens for copying.