JPS59109018A - Photographic lens - Google Patents

Abstract

PURPOSE:To obtain a lens for a compact camera with a reduced astigmatic difference and a corrected positive distortion in a lens system of five groups and five elements consisting of a positive meniscus lens, a biconcave lens, a positive lens, a biconvex lens and a negative meniscus lens by satisfying a specified condition. CONSTITUTION:In a lens system of five groups and five elements constitution having a positive meniscus lens, a biconcave lens, a positive lens, a biconvex lens and a negative meniscus lens in order from an object side, a condition of 0.15f<d7<0.4f is satisfied where (f) is a focal length of the whole system and d7 is a thickness of the lens of fourth group. When the lower limit of this condition is exceeded, the correcting action of the convex lens becomes weak, and the astigmatic difference and the distortion cannot be corrected. When the upper limit is exceeded, the lens system becomes large and becomes unsuitable for a compact camera. By satisfying this condition, a lens for a compact camera small in astigmatic difference and corrected for positive distortion can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a lens for a compact camera with an angle of view of 70° or more + F/3.5.

Hitherto, various types of lens systems in addition to the tether type have been known for use in compact cameras, but the angle of view was about 60° to 65° at most.

Generally, when attempting to further increase the angle of view, problems arise from astigmatism and distortion. Therefore, even if the field curvature can be corrected by appropriately selecting the Petzuba lens, the astigmatism difference will still be affected. Due to the nature of lenses for compact cameras, it is not desirable for them to be too expensive, so it is not desirable to complicate the lens configuration to correct astigmatism. Further, even if the structure is allowed to be made more complex, the overall length of a lens for a compact camera cannot be increased, and the lens must be arranged within a limited space, so it is practically impossible to make the structure more complicated. Therefore, it has been difficult to correct astigmatism in compact camera lenses.

In recent years, in order to shorten the overall length of the lens, lenses with a relatively simple structure have been known that employ a so-called telephoto type in which the front group has a convex ridge group and the group has a concave ridge. For example, special public service in 1984-50
This is the lens described in Japanese Patent No. 248.

However, in such a lens system, since a lens with strong positive power is arranged in the front group, positive distortion occurs in this lens. Also, since a negative meniscus lens with a convex surface facing the image plane is placed on the image side of the diaphragm, the angle of view becomes larger and when the chief ray enters the meniscus lens of the shell, As the angle increases, positive distortion occurs in this lens. It is difficult to correct these fixed distortion aberrations.

The present invention employs the above-mentioned telephoto type, places a thick convex lens behind the aperture, and makes the thickness of this lens appropriate, thereby reducing astigmatism and at the same time correcting positive distortion. The objective is to provide a compact camera lens with an unprecedentedly wide angle of view exceeding 70 degrees.

The thick convex lens placed behind the diaphragm described above is considered to be a combination of two thin plano-convex lenses and a plane-parallel plate, and changes in aberrations when a plane-parallel plate is placed behind the diaphragm will be studied.

Generally, when a converging light beam passes through a parallel plane plate, a positive field curvature occurs, and the amount thereof is expressed by the following equation.

Here, d is the thickness of the plane-parallel plate, n is the refractive index of the plane-parallel plate, i is the angle of incidence, and l/ is the angle of refraction.

As mentioned above, since a positive astigmatism difference is generated by the parallel plane plate, the astigmatism difference can be reduced by setting the thickness to an appropriate value.

Distortion aberration occurs in the parallel plane plate, and its amount can be expressed by the following equation.

Since tani<O in the above equation, Δy'<0, and negative distortion occurs. Therefore, the positive power of the front group and the positive distortion generated in the final lens can be corrected by the parallel plane plate.

For the above reasons, astigmatism and distortion can be corrected by placing a thick lens behind the diaphragm and adjusting the thickness to an appropriate value.

From the above, the lens system of the present invention includes a first lens group that is a positive meniscus lens with a convex surface facing the object side, a second group lens that is a biconcave lens, a third group lens that is a positive lens, and a lens that is a biconvex lens. The lens system was made up of 5 lenses in 5 groups, consisting of a #4 lens and a 5th lens group which was a negative meniscus lens with its convex surface facing the image side. By setting the thickness d7 of the fourth lens group disposed next to the diaphragm within the range shown in condition (1) below, the astigmatism and distortion described above can be well corrected.

(1) 0.15f<d7<0.4f, where f is the focal length of the entire system.

If the lower limit of this condition (1) is exceeded, the correcting effect of the convex lens is lost, and astigmatism and positive distortion cannot be corrected. If the upper limit is exceeded, the lens system becomes too large and becomes unsuitable for compact camera lenses.

Although the photographic lens having the above-mentioned structure is not able to achieve the object of the present invention, an even better photographic lens can be obtained by further making the following description.

In order to reduce the field curvature, it is necessary to reduce the Petzval sum l]. However, if the Petzval sum is too small, when correcting the astigmatic difference using the convex lens (fourth group lens), if the astigmatism difference is well corrected near the maximum angle of view, the astigmatism difference will increase at intermediate angles of view. Put it away.

In order to set the Petzval sum to an appropriate value in consideration of the above points, it is desirable that the refractive index n2 of the second group lens satisfies the following condition (2).

(2) 1.7 < n2 < 1.82 If the lower limit of condition (2) is exceeded, the Petzval sum/lo becomes too small and the astigmatism difference cannot be corrected at an intermediate angle of view. If the upper limit is exceeded, the Petzval sum becomes too sharp and the field curvature increases.

In order to further suppress the occurrence of positive distortion and obtain a lens system with better performance, it is desirable to select the focal length f5 of the fifth group lens so as to satisfy the following condition (B).

(8) 0.4f 1f51 < 0.
6f, f5 <O If the lower limit of condition (8) is exceeded, positive distortion increases. Moreover, if the upper limit is exceeded, the total length becomes too long, making it unsuitable for use as a compact camera lens.

Next, examples of the photographic lens of the present invention described above will be shown.

Example 1 r, =36.9278 d, =10.6219 n1=1.88300
ci1=40.76r2=71.8243 d2=4.9584 r3--251.7459 d=3.4445 n=1,80518
ν2=25.432 r4=35.6209 d4=2.5517 r5=42.5414 d5=9.3616 n3=1.72000 1/3
=41.98r6--1096.6423 d6=6.9452 r7=95.5925 d7=22.8878 n4=1.59270 ν
4=35.29r8 51.5733 d8=6.3414 r9=-29,3375 d -3,4448n5-1.62606 5-3
9.21rlo) 177.0669 f = 100, f5 = -55,675 Example 2 r1 = 37.2084 d1 = 10.618I n, = 1.88300
ν1=40.76 'r2 =69.9787 d2=4.9411 r3=-221,5758 d=3.4433 n=1,76182
C2=26.553
2r4=35.9272 d4=2.5508 r5=42.3315 d=9.3582 n=1.71700 1
/3=47.943 r6--2207.6200 d6=6.905.7 r7=92.4645 d=23.1448 n44.59270 ν
4=35.29r8-51.0854 d8=5.9603 r9・=-29,4121 d9=3.6096 n5=1.66998
J15=39.32r1o=-154,9387 f=100, f5=-54°819 Example 3 r, =37. '7611 d, -11,6679n1=1.88300 V,
=40.76r2=73.0205 d2=4.6672 r3=-244,9971 d3=3.4483 n2=1.80518 v2
=25.43r4=37.4424 d4=2.5545 r5=44.3299 d5=9.3717 n3=1.72000 ν3
=41.98r6--656.8615 d6=7.6324 r7=99.1495 d7=20.3054 n4=1.59739 C-34,48r8=-46,F65Fd8=5.4097 r,C29 .4558 d, = 7.5910 n5 = 1.62831
ν5=37.95r 1o--282,7250 f=100 f5=-52,946 Example 4 r1=37.1666 d1=n, 6679n+=1. H3oo P+”4G
-76r2=70.7724 d2=4.6672 r3=-314,4423 d3=3.4483 n2=1°80518 1'2
=25.43r4-♀6.3377 d4=2.5545 r5=43.7507 ds -9,3717n3-1.72000 'a
”'41.-.

r6=-732,0967 d6=7.6324 r7=ioi, 5236 d7=22.7588 n4=1.59270 2
=35.29r8=-51,8227 d8=5.4097 r9--30.4738 d9-=6,8967 n5==1.62606
1'5=39.211-, o=-225,3586 f=100, f5--57,064 Example 5 r, =38.0501 d=1.1.6679 n=1.
．． 88300 v, = 4 (in 76J n2 2 70.2468 d 2 ""4, 6672 r, -215,0498 d = 3.4483 n = 1.8051.8
v2=25.432]-4=41.1290 d4=2.5545 n5244.6558 d=9.3717 n=1.72000
C3=43.703 r6=-1355,6606 d6-5°8781 n7292.5723 d7=2'2,5159 n4==1.5927
0 z =35.29r8--50.0412 d8=5.4097 r9--28.1250 d =6.9005 n =1. ．． 62606
115=39.215 r, oney 172.7446 f=100, f5--54,665 Example 6 r, =37.5812 d =11.6238 n1=1.88300
v1=40.76n2272.9450 d2=4.6496 r3--228.4699 d3-3.4352 n2221.80518 Shear 25.43r4=36.4531 d4=2.5448 r5242.1673 d= 9.3363 n3=1.72000 1'
3=4],,98r6;-t816.9711 d6=7.6036 n7296.4188 d=20,2247 n=1,63980
ν4=34.484 r8-47.0295 d8=5.3892 r9--29.4885 d=7,5593 n5=1.72342
ν5 = 37.95r,. =-215,6929 f=100, f5--48,037 Example 7 r, =37.2670 d, =1.0.6334 n, =1.84100
ν1=43.23r2-71.1567 d2=4.9483 r3-211. , 9667 d3=3.44.83 n2=1.71736 ν
2=29.51r, -=35.1359 d4=2.5545 n5242.5678 d5=9.3717 113=1.71700 ν3
=47.94r6-=-5122,0812 d6=6.9156 n72103.8046 d, =23.1784 n4=1.59880
ν4=40.00rB 49,0515 d8=5.9690 r9--29.9591 d9=3.6149 n5=1.66390
v5=39.32r1o --152,3278 f=100, f5 knee 56,844
However, rl, r2+...l rlo is the radius of curvature of each lens surface, d1+d2+..., d is the wall thickness and air spacing of each lens, n, , n,, ,..., n5 is the radius of curvature of each lens surface. Refractive index, C1. C2. ..., ν5 is the Atsube number of each lens.

As is clear from the above description and examples, the photographic lens of the present invention has a convex object side and a concave image '1lIII.
It is a compact lens system, and by arranging a thick convex lens behind the diaphragm, it has a wide angle and various aberrations such as astigmatism and distortion are well corrected.

In addition, in the lens system of Example 1, what corresponds to the thick parallel plane plate was replaced with air to create a configuration as shown in Fig. 9. The aberration situation of the lens system according to the data below is as shown in Fig. 10. .

r, =36.9278 d =10.6219 n, =1.88300
ν, =40.76r2=71.8243 d2=4.9584 r3--251.7459 d3=3.4445 n2=1.80518 v2
=25.43r4=35.6209 d4=2.5517 r5=42.5414 d5=9.3616 n3=1.72000 1/3
=41.98r6=-1096,6423 d6=6.9452 r, =95.5924 d7-=1.4439 n4 =1.59270
2 = 35.291-7/:o.

d 7t ””12.5573 r8/= ■ d8'-1・4439n4'=1.59270shi41-
35,29r8--51.5733 a8=6.3414 r9--29.3375 d=3,4448 n=1.62606
L'5=39.215 r, o--177,0669 The aberration situation of the above lens system is compared to the aberration situation of Example 1 (second
As is clear from comparison with Figure 1, various aberrations, especially astigmatism and distortion, have deteriorated significantly.

From this, it is clear that the effects of the present invention, especially the effects of the thick lens placed after the diaphragm, are remarkable.

[Brief explanation of the drawing]

Figure 1 is a sectional view of the photographic lens of the present invention, Figures 2 to 8 are aberration curve diagrams of Examples 1 to 7 of the invention, respectively, and Figure 9 is a thick lens of the lens system of Example 1. FIG. 10 is a cross-sectional view of the lens in which air is replaced with air, and its aberration curve is shown in FIG. Spherical aberration Astigmatism Figure 6 Distortion Aberration Spherical aberration Astigmatism Distortion aberration Comatic aberration

Claims (1)

[Claims] A first # lens of a positive meniscus lens wrapped around a convex surface r object 11I11, a second lens #2 of a biconcave lens, a third group lens of a positive lens, and a fourth group lens of a biconvex lens;
A photographic lens having a lens system consisting of five elements in five groups, including a fifth group lens which is a negative meniscus lens with a convex surface facing It 4111, and which satisfies the following conditions. 0.1'5f < d7 < 0.4f where f is the focal length of the entire system, and d7 is the thickness of the fourth group lens.