JPS6095416A - Wide-angle lens - Google Patents

Abstract

PURPOSE:To compensate the coma aberration and distortion aberration of a wide-angle lens used for facsimile, OCR, etc., and improve image-forming performance over the entire image plane by composing the lens of six elements in five groups and satisfying specific conditions. CONSTITUTION:The lens system consists of the 1st negative meniscus lens having a convex surface on a subject side, the 2nd positive lens having a large-curvature convex surface on the subject side, the 3rd negative lens having a large- curvature concave surface on the image side, the cemented lens of the 4th negative lens and the 5th positive lens, and the 6th meniscus lens having a concave surface on the image side, and meets requirements shown by inequalities I -VI. Consequently, the coma aberration and distortion aberration with a 1:2.8 aperture ratio, an about 30 deg. half view angle, and an almost 100% aperture rate are compensated small to obtain the wide-angle lens for facsimile, OCR, etc., which has the image-forming performance improved over the entire image plane.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a wide-angle lens, and more specifically, an aperture ratio of 1:2, 8. Facsimile and OCR with half angle of view of approximately 30°, aperture efficiency close to 100%, and aberrations for close objects, especially distortion, well corrected to approximately 1% or less.
This relates to wide-angle lenses used for etc.

Ordinary wide-angle lenses are designed to be used in cameras that use photosensitive materials It (films, dry plates, etc.), so their aperture efficiency is generally about 60% at most when wide-open. However, lenses used for facsimile, OCR, etc. need to have as much light as possible at the periphery of the screen, so an aperture efficiency of nearly 100% is required. The luminous flux becomes larger, making it more difficult to correct coma aberration. Further, there is a lens of this type, for example, Japanese Patent Laid-Open No. 54-49132, but its distortion is about 2%, which is not yet sufficiently corrected.

The present invention has an aperture ratio of 1:2.8. A facsimile machine having a half angle of view of about 30° and an aperture efficiency of nearly 100%, which satisfactorily corrects the coma aberration, and also satisfactorily corrects distortion aberration to about 1% or less, and has good imaging performance over the entire screen.

The purpose is to provide a wide-angle lens used for OCR, etc.

First, the lens configuration of the present invention will be explained. In order from the object side, the first lens is a negative meniscus lens, the second lens is a positive lens, the third lens is a negative lens, the fourth lens is a negative lens, and the third lens is a positive lens. In a lens consisting of 6 elements in 5 groups, consisting of a cemented lens with a 5th lens and a 6th lens which is a meniscus lens, the convex surface of the 2nd lens faces the object side, the convex surface of the 2nd lens faces the object side, and the 6th lens is a meniscus lens. This wide-angle lens is characterized in that the third lens has a concave surface with a strong curvature facing the image side, and the sixth lens has a concave surface facing the image side, and is configured to satisfy the following conditions.

(1) L3f<l f + 1<1.9f, f t
<0(2) 0.32 f (r 2 <0.40
f(3) 0.59 f < r 3 < 0.8Of(
4) 0.60 f < r, o < 0.75 fl
, 80< r 1t / d 1o <3.05 (5)
0.38 f < d 3~5 (0,57 f(6)
n 2 1 n 3 >1-. 6545〉(Y2+ν3
) /2 >28 However, f is the focal length of the entire system, fl
is the focal length of the lens, rl is the radius of curvature of the first surface from the object side, dlo is the thickness of the sixth lens, and d3 to 5 are from the object side surface of the second lens to the image side surface of the third lens. 3- interval, n2yn3 is the refractive index of the second lens and the third lens, respectively. C3 is the second lens.

This is the Atsube number of the third lens.

Next, each of the above conditional expressions will be explained.

Condition (1) is an expression regarding the power of the first lens, and represents the range in which a wide angle of view can be achieved.

Therefore, when the lower limit is exceeded and the negative power becomes stronger, the second
If a large amount of inward coma flare occurs on the surface, and if the upper limit value is exceeded and the negative power becomes weak, outward coma flare will occur, and the wide angle of view, which is the objective of the present application, cannot be achieved.

In order to secure the amount of peripheral light aimed at by the present invention, it is advantageous to downsize the entire device, and the above conditions are indispensable for this purpose as well.

Also, in connection with this, it is naturally desirable that the Atsbe number of the first run be large, and in the embodiment, 60 or more is used.

Condition (2) relates to the image-side surface r2 of the lens, and in order to widen the angle of view under condition (1), the radius of curvature of the second surface of the negative meniscus lens must of course bear negative degrees. However, if the radius of curvature is too small, comatic aberration will occur significantly, and on the other hand, it will be difficult to correct the angle. Therefore, if the radius of curvature of r2 becomes small beyond the lower limit, it becomes difficult to correct positive spherical aberration and coma flare of the principal ray, and conversely, if it becomes large beyond the upper limit, correction of negative spherical aberration becomes insufficient. Therefore, it becomes impossible to correct coma flare, and the imaging performance becomes unsatisfactory.

Condition (3) regulates the object-side surface r3 of the second lens, and indicates the range in which 1-spherical aberration and comatic aberration can be corrected.If the radius of curvature of r3 increases beyond the upper limit, the positive Correction of spherical aberration becomes insufficient, and coma flare also occurs. Conversely, if the radius of curvature becomes small beyond the lower limit, the spherical aberration will be insufficiently corrected, which is inappropriate.

That is, in this lens, most of the positive spherical aberration occurs at the third and ninth surfaces. It is desirable to share the burden, but if the third surface does not bear the burden of correcting the negative spherical aberration generated at the second surface, the residual will have a large adverse effect, so the above conditions are appropriate.

The condition (4) restricts the shape of the sixth lens, which is an advantageous lens that can correct astigmatism and distortion with little influence on spherical aberration. Therefore, conditional expression 0.
60 f < r s o < 0.75 When the radius of curvature increases beyond the 1st limit of f, the Petzval sum increases and the meridional image plane in particular becomes overcorrected, making it difficult to correct astigmatism. On the other hand, if the radius of curvature becomes smaller than the lower limit, astigmatism will be insufficiently corrected, making it impossible to balance the imaging surface at the periphery, and at the same time, negative distortion, which tends to occur with wide-angle lenses, will increase, resulting in disadvantages. Become.

In addition, conditional expression 1.80< r 1s / d 1o
If it becomes smaller than the lower limit of <3.05, that is, d,
. When it becomes thick, the image plane becomes under-corrected, the astigmatism difference becomes large, and the image plane becomes unbalanced. on the other hand,
When rll becomes small, the image plane is overcorrected and correction becomes difficult. On the other hand, when the upper limit is exceeded, that is, when dlO becomes thinner and rll becomes larger, the image plane becomes overcorrected and becomes difficult to correct, and the negative distortion becomes large, and the object of the present invention is become unattainable.

The condition (5) is the thickness of the second lens, the thickness of the third lens, and the thickness of the second lens. The distance between the third lenses is regulated, which is very advantageous for correcting field curvature. Therefore, if it becomes smaller than the lower limit, the image plane will be under-corrected, and conversely, if it becomes larger than the upper limit, the image plane will be over-corrected, and in both cases it will be very difficult to balance the image plane. .

Condition (6) corrects the chromatic aberration caused by the condition (1), and satisfactorily corrects the chromatic aberration in the front group (1st to 3rd lenses) in correspondence with the rear group (4th to 6th lenses). At the same time, it is necessary to increase the refractive index in order to prevent the occurrence of coma aberration.

That is, in order to reduce the burden on the fourth surface in relation to the radius of curvature of r3, which is limited by the condition (3), n2 should be 1.65.
If the above is necessary and n2 is smaller than 1.65, the fourth surface will have a small negative radius of curvature, and the fifth surface will have a small negative radius of curvature.
It may become difficult to maintain the aberration balance after the surface. The same is true for n3; it is necessary not to reduce the radius of curvature of the sixth surface while maintaining the refractive power of the fifth surface, and n3>1.65 is an essential condition. Condition 45 regarding Atsube number (Sh2+Sh3)/2>28 depends on condition (1),
In a wide-angle lens like this lens, which is also compact, the second. Quite extreme with the third lens,
It is desirable that chromatic aberration be under-corrected in the second lens and over-corrected in the third lens. As a result, as mentioned above, it is necessary to make a certain amount of correction in the front group in correspondence with the rear group, and these conditions indicate this appropriate range.

Examples of the present invention will be shown below. Here, f is the focal length of the entire system, rlyr2...rll is the radius of curvature of each lens surface, d+, d2...dlO is the wall thickness and air gap of each lens, nl+n2... ...ne is the refractive index of each lens, '1'l+v2... Shiro is the Abbe number of each lens.

8- [Example 11 FNo 1:2.8 f = 1.0rl
O,681dt O,051ntl,58913 C161. Or2 0.381 dt0.245 r3 0.760 d3 0.286 n21.834
00 v237.2r4 13.214 da O,0
36r5 5.811 d50.176 n31.80
518 y325.4r60.829 d60.075 r7 3.087 d7 0.036 nA 1.76
182 v4 26.6rB 1.440 do O,
161n51.77250 vs49.7r9 0.5
61 d90.011 r1o O,697dt o O,325ne 1.5
8913 we 61. Orl 1 0.687 (1) f ,=-1,6f (2) r 2 =0.38f (3) r 3 =0.76f (4) rl(1=0.70f rt t/dso=2.
11(5) d3~5=0.50f (6) n 2 = 1.83400 n 3 = 1.8
0518 (Si2+Si3)/2=31.3 [Example 21 FNo. 1:2.8 f=1. Ort.
O,725dt O,046n+1.51633 164.1r2 0.362 dl0.293 r3 0.675 dB0.333 n21.8340
0 shi237.2rA 2.753 da O,011 r5 -1.557 ds O,104n3 1.80
51B! 3 25.4r5 0.711 ds O,
061 r7 -2.050 dt0.036 nl 1.75
520 ν4 27.5r9 5.080 do O,
107nsl, 77250 v540.1r9 0.5
17 de O, 01g rs o O, 668dt o O, 286ne 1.
51633 we 64.1r□, 0.751 (1) f t = 1.5f (2) r 2 =0.36f (3) r 3 =0.68f (4) r1o=0.67f rtt/d+o=2 .62
(5) d3~6=0.45f (6) n 2 =1.83400 n 3 =1. '
80518 (C2+C3)/2=31.3 [Example 31 F*o 1: 2.8 f =1. Or
l 0.765 dl 0.046 ntl, 5163
3 y+64.1r2 0.391 dl0.251 r3 0.778 d3 0.215 n21.834
00 v237.2r4 6.043 d40.036 r5-5.3B5 ds O,305n31.8051
8 ν325.4r8 0.869 ds O,075 r7 -9.149 d7 0.036 nl 1.7
6182 '11426.6re 1.267 do
0.16I nsl, 77250 v549.7r9
0.598 di+ 0.011rt o O,664
dt o O,339ne 1.51633 we 6
4.1rx s O, 63g (1) f 1 = -1,6f (2) r 2 = 0.39f (3) r 3 = 0.78f (4) rl O = 0.66f rls /d1o =
1.88(5) d3-5 =0.55f (6) n2 =1.83400 n3 =1.8
0518 (Sh2+Sh3)/2=31.3 11- [Example 4] Fyo1: 2.8 f=1.
,Orl o,eeo dt O,067ntl,58
913 vt61. .

r2 0.354 d2 0.201 r30.618 dB0.197 r+21.8340
0 9237.2r4 9.812 da O,036 r5 -6.484 ds O,179n3 1.80
518 93 25.4re O,690da O,0
75 r7 -4.079 d7 0.036 nl 1.6
9895 v430.1re O,826de O,1
75n61.69350 vs50.8r9 -0.5
16 dB0.011 rl OO,692dx o 0,326ne 1.5
8913 9fi 61. Orl 1 0.670 (1) f s =-1,4f (2) r 2 =0.35f (3) r a =0.62f (4) rl B =0.69f rl t /dt
o = 1.95 (5) d3~s = 0.41f (6) n 2 = 1.83400 n 3 = 1.8
0518 (Si2+Si3)/2=31.3 12- [Example 51 FNO1: 2.8 f=1.0rx O
,555dt O,126nl 1.58913 vs
61,0r20.337 dl0.180 r30.608 dB0.218 n21.65844
y250.9ra 2.473 d40.036 rs 5.318 ds O,179n31.6727
0 v332.1re O,746ds O,075 r7 -2.124 d7 0.036 nl 1.7
6182 v4 26.6re 1.133 dB 0
．． 156 n51.77250 v549.7r90.
531 di+ 0.011 rt o O, 648 dt o O, 286 n5 1.
58913 9B 61. Or+ 10.638 (L) f s =1.8f (2) r 2 ”0.34 f (3) r 3 =0.61f (4) rl o=0.65f r14/dto=2.9
2(5) d3~5=0.40f (6) n 2 = 1.65844 n 3 = 1.6
7270 (Sh2+Sh3)/2=41.5

[Brief explanation of the drawing]

FIG. 1, FIG. 3, FIG. 5, FIG. 7, and FIG. 9 show examples 1, 2, and 3 of the present invention, respectively. /I, 5 lens sectional views, FIG. 2, FIG. 4, FIG. 6, FIG. 8, and FIG. 10 are aberration diagrams of Examples 1, 2, 3, and 4°5 of the present invention, respectively. 15-

Claims (1)

[Claims] In order from the object side, a negative meniscus lens, a positive second lens, a negative third lens, a negative fourth lens, and a positive fifth lens. 5 groups 6 consisting of a cemented lens and a 6th lens which is a meniscus lens
In the lens, the convex surface of the first lens faces the object side, the second lens faces the convex surface with a strong curvature towards the object side, the third lens faces the concave surface with a strong curvature towards the image side, and the sixth lens faces the image side. A wide-angle lens arranged with a concave surface facing and configured to satisfy each of the following conditions. (1) 1.3f< I f II <1.9f , f
s<. (2) 0.321 < r 2 < 0.4Of(3)
0.59 f < r 3 < 0.80 f(4) 0
．． 6Of < r s o < 0.75 fl, 80 <
r, s/d 1o <3.05(5) 0.3
8 f < d 3 NS < 0.57 f(6) n
2 # n 3 > 1.6545〉 (Shi 2 + Ya 3) /
2>28 However, f is the focal length of the entire system, fl is the focal length of the first lens, rl is the radius of curvature of the first surface from the object side, and atO is the sixth lens.
The thickness of the lens, d3-5 is the distance from the object side surface of the second lens to the image side surface of the third lens, n2yn3 is the refractive index of the second lens and the third lens, v2. ν3 is the second lens. This is the Atsube number of the third lens.