JPS629310A - Copying lens - Google Patents

Abstract

PURPOSE:To simplify the constitution of a copying lens, to use a material having a low refractive index, and to reduce the cost by employing four-group, four- element constitution which is completely symmetrical about a diaphragm in the center of the lens system and setting specific conditional inequalities among radii of curvatures and focal lengths. CONSTITUTION:The constitution is completely symmetrical about the diaphragm in the center of the lens system and the 1st and the 4th positive biconvex lenses and the 2nd and the 3rd negative biconcave lenses are provided. Four conditional inequalities are set among radii R of curvature, focal lengths (f), and Abbe numbers nu. The inequality I is for compensating coma aberration, spherical aberration, and astigmatism over a wide view angle range, inequalities II and III are for compensating curvature of field and astigmatism and relieving the work tolerance of gaps between the 1st and the 2nd lenses and the 3rd and the 4th lenses, and the inequality IV is for compensating chromatic aberration and astigmatism. Therefore, various aberrations are compensated excellently over a wide view angle range by the simple constitution by using an inexpensive glass material.

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Field of Application) This invention relates to a copying lens having a completely symmetrical arrangement around an aperture.

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

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 completely symmetrically around the aperture. It is well known that distortion can be eliminated if the lens system is arranged completely symmetrically with respect to the aperture. In addition, the number of types of lenses that make up a lens system is halved, the number of lens manufacturing steps is also reduced, and there is no risk of incorrect assembly of lenses during assembly, which would occur if the aperture is asymmetric. It can be much cheaper than other things.

Among these types of lenses, perfectly symmetrical lenses with four elements in four groups, which have the most Western-style construction, are known as Japanese Patent Laid-Open Nos. 55-81316 and 1982-161823.

However, the former has a slightly bright F1 direct focus of 5, but the angle of view is 15 ~
18, which is not sufficient for downsizing copying machines. The latter has a large angle of view of 22.6, but it uses expensive glass material with a relatively high refractive index for the biconvex positive lens, so it is difficult to say that it satisfies the demand for cost reduction. .

(Problems to be Solved by the Invention) In order to downsize copying machines, this invention aims to obtain a copying lens with sufficient aberration correction by reducing the overall lens length and lens casing while widening the angle of view. That is. Furthermore, it has a Western-style construction with four elements in four groups that are completely symmetrical around the aperture, and is intended to reduce costs by using inexpensive glass materials with a relatively low refractive index.

(Means for Solving the Problems) The copying lens of the present invention has a four-element structure in four groups that is completely symmetrical about the aperture located at the center of the lens system, and each lens component is arranged from the object side. The first lens is a biconvex positive lens, the second lens is a biconcave negative lens, and the third lens is a biconcave negative lens.
The fourth lens is a double-concave negative lens that is the same as the first lens, and the fourth lens is a double-convex positive lens that is the same as the first lens.1.10<R2^ (1,53...(1)
0.23 <f1/f <0.37
・・・・・・ (2) −0,41<f2/f
(-0, 23... (3) ν2 (
49,0... (4) However, R2: Radius of curvature f of the ward side of the first lens and the object side of the fourth lens R5: Radius of curvature f of the object side of the second lens and the image side of the third lens : Synthetic focal length of the entire system fl : Focal length of the first and fourth lenses f2 : Focal lengths of the second and third lenses Shear : The conditions of the Abbe numbers of the second and third lenses are satisfied.

(Function) Article ff (1) C. Specifies the ratio of the radius of curvature of the adjacent surfaces of the first lens and the second lens (the fourth lens and the third lens), and prevents sikoma aberration, spherical aberration, and aberration over a wide angle of view. This is for correcting point aberrations well. If this ratio exceeds the lower limit of condition (1) due to shortening or lengthening of the lens, spherical aberration will be undercorrected, coma flare will be excessive, and correction will become difficult for the lens system as a whole. . Conversely, if the upper limit is exceeded, the astigmatism difference becomes large, making it difficult to obtain well-balanced performance over the entire screen, and it becomes difficult to set the song conditions and correct this to create a wide-angle lens. Become.

The lines f'l'' (2) and (3) are related to the focal length of each component lens, and assuming the line Ft' (1), the f8! surface curvature,
This is a condition for satisfactorily correcting astigmatism and making it possible to widen the angle of view. If the upper limit of condition (2) and the lower limit of condition (3) are exceeded, the curvature of field becomes large, making it difficult to obtain uniformly good performance over all angles of view. On the other hand, if the lower limit of condition (2) and the upper limit of condition (3) are exceeded, the astigmatism difference becomes large, making it difficult to obtain good performance with good lance over the entire field of view, and making it difficult to widen the field of view @VC. . Furthermore, aberration fluctuations due to machining errors in the distances between the first and second lenses and between the third and fourth lenses become significantly large, requiring strict control of machining tolerances, resulting in higher manufacturing costs. Become.

Condition (4) is a condition related to correction of astigmatism as well as correction of chromatic aberration. If the upper limit is exceeded, f2/f must be increased to correct chromatic aberration.
This will result in exceeding the upper limit of the amount.

As mentioned above, this makes it difficult to widen the angle of view, tightens processing tolerances, and increases manufacturing costs.

Also, article f! In addition to l-(4), it is desirable that the ridges of the first lens (fourth lens) be 1ft60 or less.

If ν1 exceeds this value, f+71 becomes small due to chromatic aberration correction, exceeding the lower limit of (2) and producing the above-mentioned result.0 (Sister Example) An embodiment f of the present invention will be shown below.

Actual sister example 1 f = 100 F7 ω = 22.6RDN ν f1/f = 0.287 f2/f = -0,304 R2/R, = 1.37 Example 2 f = 100 F7 ω = 22°6 RDN ν 1 31.410 6.67 1.65100
56.22 -52303 0.74 3 -38.947 1.18 1.54814
45B4 34.897 4.44 5 -34.897 1.18 1.54814
45B6 38.947 0.74 7 52303 6.67 1.65100
5628 -31.410 fl, #=0.311 f27 f= -0,334 R2/R,= 1.34 Example 3 f=100 F7 ω=22.6°RDN
ν 1 27.989 539 1.62280
57.02 -55.195 1.00 3 -37.716 1.18 1.54814
45.84 34.469 2.78 5 -34.469 1.18 1.54814
45.86 37.716 1.00 7 55.195 539 1.62280
57.08 -27.989 fl /f -0,306 f2/ f = -0,327 Field/R3=1.46 Example 4 7=100 F7 ω=22.6 f1/f =0.295 f2/ f = -0,314 R7/mo = 143 Example 5 f = 100 F7 ω = 22.6° RDN ν 1 29.119 6.99 1.62280
57.02 -44.426 0.66 3 -34.125 1.18 154814
45.84 3:3814 2.16 5 -33J314 1.18 1.54814
45.86 34.125 066 7 44.426 6.99 1.62280
57.08 -29.119 f1/f =0.293 f2/f =-0,308 R2/R5=1.30 Example 6 f=100 1”8 ω=22.6 RDN ν f1/f =0 .318 f2/f =-0,340 R2/f%=1.50 Example 7 f=100 F8 ω=22.6°RDN
ν f1/f=0.295 f2/f =-0,312 R,=1.31 Example 8 f=100 F8 ω=22.6°RDN ν 1 29.719 6.43 1.63854
55.42 -47.432 0.64 3 -35J343 1.18 1.54814
45.84 33.461 308 5 -33.461 1.18 1.54814
45.8f1/f=0.296 f2/f =-0,314 R2/R3=1.32 Example 9 f=100 F3 ω=22.6°RD
N ν f1/f=0.297 '2/f =-0,315 R2/R3=1.32 Example 10 f=100 F8 ω=22.1 RDN ν 1 28.805 624 1.63854
55.4 '2 -47.011 0.64 3 -35.748 1.15 1.54814
45134 3], 753 2-t>15
-31.753 1.15 1.54814
45.8f1 /f =0.297 f2/f = -0,313 R2/Akira = 1.32 Example 11 f=100 F7 ω=22.1'l D
N ν f1/f = 0.308 f2/f = -0,339 埒/R3 = 1.35 Example 12 f=100 F5.6 ω=18.8°RDN
ν f1/f=0.291 f2/f =-0,30g R2/Rs=1.499 Example 13 f=100 F5.6 ω=18.8°f1/
f=0,293 '2/f =-0,311 R2/R5=1.506 Example 14 °f=100 F6.3 ω=19.3RDN
ν f1/f=0.288 f2/f=-0,306 R2/R3=1.471 Example 15, f=100 F6.5 ω=205°RDN
ν'1/f =027'2/f =-0,29 R2/R3=1.39 Example 16 f=100 F6.3 +, 1=20.6°f
1/f = 0.25 f2/f = -0,26 Asahi + [i21 Effects of the Invention As shown in the structure and aberration curve diagram, the copying lens of the present invention uses a low-cost glass material and has the following advantages: With this configuration, we were able to obtain a copying lens that does not have strict processing tolerances and has aberrations well corrected over a wide angle of view.

[Brief explanation of drawings]

Figure 1, Figure 3, Figure 5, Figure 7, Figure 9 (2), Figure 11
Fig. 13, Fig. 15, Fig. 17, Fig. 19, Fig. 21
Fig. 23, Fig. 25, Fig. 27, Fig. 29, Fig. 31
The figures show Examples 1, 2, 3, 4, 5, 6, 7, and 8, respectively.
9.10, 11.12.13.14.15.16 cross section, Figure 2, Figure 4,! Figure 6, Figure 8, Figure 10, Figure 1
Figure 2, Figure 14, Figure 16, Figure 18, Figure 20, Figure 2
Figure 2, Figure 24, Figure 26, Figure 28, Figure 30, Figure 3
FIG. 2 is aberration curve diagrams of 16 to 16 layers, respectively. Patent applicant: Roku Konishi Photo Industry Co., Ltd. Tsujiomi 3
Figure F7 ω-value 22.6
ω=226 Spherical aberration Jl single point stop φ difference in number of curves F7 ω=22
6 ω=22. fi spherical aberration
Astigmatism Distortion No. 5 [
! 2+F7U=22. fi
U=22. fi drive 9 Figure 7F7 tAJ=22. h
ω=22. fi jiko ++li&
T F7 bJ=22. fi
t, J=22. Fi spherical aberration astigmatism
Distortion L15? Difference F8 ~=
22. fi ω=22.6 Spherical aberration Astigmatism Distortion aberration 13th
Figure F8 ω=22. fi
ω=22. fi Spherical aberration Astigmatism Distortion; Lu 15 Figure F8 ω-22, h t,
J-=22.6° Spherical aberration Astigmatism
Distortion collection * 17 Figure F8 ta) = 22,6
ω=22.6 spherical aberration
Astigmatism Distortion Aberration No. 19 Figure F8 1. J=22.1
=22.1 Spherical aberration Astigmatism Distortion etc. Fig. 21 Fig. 22 Fig. 25 Fig. 23 Fig. 24 Fig. 27 Fig. 26 Spherical aberration Astigmatism Distortion aberration F
6.3 ω=19.3
ω=19.3 Spherical aberration Astigmatism
φ curvature aberration Fig. 29 Fig. 30 Body tube aberration Astigmatism I fi curvature aberration Fig. 31 @ Fig. 32

Claims (1)

[Claims] The lens system is composed of four lenses in four groups that are completely symmetrical around an aperture located at the center of the lens system, and each lens component is arranged in order as viewed from the object side: the first lens is a biconvex positive lens, and the second lens is a biconvex positive lens. The 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. 1.10<R_2/R_3<1.53 0 .23<f_1/f<0.37 -0.41<f_2/f<-0.23 ν_2<49.0 However, R_2: radius of curvature of the image side of the first lens, object side of the fourth lens R_3: radius of curvature of the object side of the fourth lens Radius of curvature f of the object side of the second lens and image side of the third lens: Synthetic focal length of the entire system f_1: Focal length of the first and fourth lenses f_2: Focal length of the second and third lenses ν_2: Second, A copying lens characterized by satisfying the condition of Atsube's number of the third lens.