JPS6225719A - Copying lens - Google Patents

Abstract

PURPOSE:To obtain high picture quality and to miniaturize a lens by constituting to satisfy specific conditions in a lens system of 4 groups 4 elements arranged symmetrically to an aperture. CONSTITUTION:This lens for copying is constituted of 4 groups 4 elements arranged symetrically to an aperture placed at the center of the lens system. When looked from the subject side, lens components are as follows; The first lens is a biconvex positive lens, the second lens is a biconcave negative lens, the third lens is a biconcave negative lens similar to the second lens, and the fourth lens is a biconvex lens similar t the first lens. These lenses are formed to satisfy the following conditions: I; 0.024<N1-N2<0.063, II; 2.00<R2/R3<2.39, III; 0.30<f1/f<0.42, IV; -0.50<f2/f<-0.30 where N1 is refractive index of the first lens, N2 is refractive index of the second lens, R2 is radius of curvature of image side face of the first lens, R3 is radium of curvature of subject side face of the second lens, f is focal length of the first lens and f2 is focal length of the second lens.

Description

[Detailed description of the invention] purpose of invention (Industrial application field) The present invention relates to a symmetrical copying lens.

(Prior Art) In recent years, with the miniaturization of copying machines, there has been a strong demand for low-cost copying lenses that have a wide angle of view, a full lens length, and a small lens outer diameter.

In order to make lenses more compact and lower in cost, attempts have been made to reduce the number of lens components and to arrange the lens system symmetrically around the aperture. It is well known that distortion can be eliminated if the lens system is arranged symmetrically with respect to the aperture, and this also makes it possible to reduce costs.

Such a symmetrical lens with 4 elements in 4 groups was developed in Japanese Patent Application Laid-open No. 1983-
This can be found in JP-A No. 81316, Japanese Unexamined Patent Publication No. 161823-1980, and the like. However, the former has a slightly bright F value of 5, but
The angle of view is as small as 15° to 18°, which is insufficient to make the copying machine more compact. The latter has an angle of view of 22.6°
Although it is large, the F value is 8, which is dark.

(Problems to be solved by this invention) This invention is a lens system consisting of 4 elements in 4 groups, which is symmetrical around an aperture with an F value of 5.6 and a half angle of view of 18.8 degrees, and is compact and inexpensive. What?
Furthermore, the objective is to obtain a copying lens in which aberrations are sufficiently corrected.

Structure of the invention (means for solving the problem) As shown in FIG. 1, the lens of this invention has the following structure:
The lens system consists of 4 elements in 4 groups arranged symmetrically with respect to the aperture located at the center of the lens system.When looking at each lens component from the object side, the first lens is a biconvex positive lens, and the second lens is a biconcave negative lens. The third lens is a biconcave negative lens that is the same as the second lens, and the fourth lens is a biconvex positive lens that is the same as the first lens.0.024<N, -N2<0.063-・(1 )
2.00 <R2/R3< 2.39... (
2) 0.30 <f1/f< 0.42 ・
・(3)-0,50<f2/f<-0,30...
(4) However, N1: refractive index of the first lens N2: refractive index of the second lens R2: radius of curvature of the image side of the first lens R3: radius of curvature of the object side of the second lens f: focal length of the entire lens system f8: focal length of the first lens f2: focal length of the second lens.

However, symmetrical arrangement with respect to the aperture does not only mean complete symmetry, but also cases where the ratio of form factors, ratio of thickness, and difference in refractive index of lenses corresponding to each other with respect to the aperture are 0, 9<q+/q+'<1 ．． 10.7<tl/
i'< 1.3 IN+-N+' l < o, however, Qi-ii, Nl is the form factor, thickness, refractive index, q, j, t, of the first lens on the object side than the aperture.
1, N1' indicates the shape factor, thickness, and refractive index of the i-th lens on the image side of the aperture, and the shape factor is approximately within the range concavity of Rz I-R21-8, where R is the radius of curvature of the first surface. This is included in the range of symmetry in the lens of the present invention. However, the examples show only completely symmetrical structures.

(Operation) Condition (1) relates to the difference in refractive index between a biconvex lens and a biconcave lens, and is a condition for properly correcting various aberrations over the entire wide angle of view and obtaining well-balanced performance. If the refractive index of the positive lens increases beyond the upper limit, the Petzval sum becomes too small and the astigmatism becomes large, which not only deteriorates the lens performance but also increases the cost of the glass material. If the lower limit is exceeded and the refractive index of the positive lens becomes small, the meridional image plane in the middle of the screen will be overcorrected.

Condition (2) relates to the ratio of the radius of curvature of adjacent surfaces of the positive lens and the negative lens, and is intended to satisfactorily correct comatic aberration, spherical aberration, and astigmatism over a wide angle of view. If the lower limit is exceeded, spherical aberration will be insufficiently corrected, and coma flare will become excessive, making it difficult to correct it in the entire lens system. On the other hand, when the upper limit is exceeded, the astigmatism difference becomes large, making it difficult to obtain well-balanced performance over the entire screen.

Conditions (3) and (4) are conditions for properly correcting field curvature and astigmatism under conditions (1) and (2) and making it possible to widen the angle of view. ) and the lower limit of condition (4), the curvature of field becomes large and it becomes difficult to obtain uniformly good performance over the entire screen. Furthermore, if the lower limit of condition (3) and the upper limit of condition (4) are exceeded, astigmatism becomes large, making it difficult to obtain well-balanced performance over the entire screen. Further, aberration fluctuations due to processing errors in the intervals between the first lens, the second lens, the third lens, and the fourth lens become significant, and processing tolerances must be strictly controlled, leading to increased costs.

(Example) Examples of the present invention will be shown below. The symbols in the table are: R is the radius of curvature of the lens surface, D is the distance between lens surfaces, N is the refractive index of the lens material, ν is the Abbe number of the lens material, F is the F number,
ω indicates the half angle of view.

The focal length f was 100 mm.

Example I F=5.6 ω=18.8°RDN ν 1 2g, 503 4.66 1.63854 5
5.42 -94.761 2.64 3 -41.841 1.13 1.58144
40.74 45.589 1.81 5 ~45.589 1.13 1.58144 4
0.76 41.841 2.64 7 94.761 4.66 1.63854 5
5.48 -28.503 f1/f=0.3483 f,/f=-0.37
35r2/r, =2.2648 N1-N, =0
．． 0571 Example 2 F=5.6 ω=18.8” RD N ν 1 2g, 589 4.69 1.63854 5
5.42 -95.354 2.60 3 -42.133 1.14 1.58144
40.74 45.791 1.82 5 -45.791 1.14 1.58144
40.76 42.133 2.60 7 95.354 4.69 1.63854 5
5.48 -211.589 f,/f=0.3496 f2/f=-0,37
56r, /r, = 2.2632 N1-N2 = 0
．． 0571 Example 3 F=5.6 ω=18.8@RD N ν1 27.
632 4.45 1.61117 55.92
-89.285 2.97 3 -39.458 1.13 1.58144
40.74 49.056 1.81 5 -49.056 1.13 1.58
144 40.76 :(9,4582,9
7 789,2854,451,6111755,98-2
7,632 f1/f=0.3503 f,/f=-0.
3743r2/r, =2.2628 N1-
N, = 0.0297 Effect of the Invention The lens of this invention has a bright F number of 5.6 and a half angle of view of 18.8, as seen in the above embodiment and the aberration diagrams in FIGS. 2 to 4. Although it has a wide angle of view, it is compact and has well-balanced aberration correction across the entire screen. This made it possible to obtain a copying lens that enables high image quality and miniaturization of copying machines.

[Brief explanation of the drawing]

FIG. 1 is a sectional view 2 showing the structure of the copying lens of the present invention.
2 is an aberration curve diagram of Example 1, FIG. 3 is an aberration curve diagram of Example 2, and FIG. 4 is an aberration curve diagram of Example 3. Fig. 1 Fig. 2 Spherical aberration Astigmatism Distortion aberration Fig. 3 Spherical aberration Astigmatism Fig. 4 -4,004,0 -4,004,0 Spherical aberration Astigmatism ω=tsf3 ω=188 -0. 2 0 02 Zhong) Distortion aberration

Claims (1)

[Claims] The lens system consists of four lenses in four groups arranged symmetrically with respect to an aperture located at the center of the lens system, and when looking at each lens component from the object side, the first lens is a biconvex positive lens, the second lens is a biconvex positive lens, and the second lens is a biconvex positive lens. The second lens is a double-concave negative lens, the third lens is a double-concave negative lens that is the same as the second lens, and the fourth lens is a double-convex positive lens that is the same as the first lens.0.024<N_1-N_2<0. 063 2.00<R_2/R_3<2.39 0.30<f_1/f<0.42 -0.50<f_2/f<-0.30 where N_1: refractive index of first lens N_2: second lens Refractive index R_2: Radius of curvature of the image side of the first lens R_3: Radius of curvature of the object side of the second lens f: Focal length of the entire lens system f_1: Focal length of the first lens f_2: Focal length of the second lens A copying lens that satisfies each condition.