JPS62211611A - Zoom lens - Google Patents

Abstract

PURPOSE:To improve the image formation performance by correcting an aberration of each group, and also, to make the titled compact, by constituting said lens of tow groups consisting of the first group negative lenses and the second group positive lenses containing a diaphragm, and providing an aspherical surface on at least one surface of the lenses for constituting the second group lenses. CONSTITUTION:The first group lenses consist of a negative meniscus lens having a convex surface to an object side, a gentle negative meniscus lens having a concave surface to the object side, and positive meniscus lens having a convex surface to the object side, in order from the object side, and by this constitution, the generation quantity of various aberration can be decreased by strengthening a refracting power of the first group lenses. The second group lenses consist of two pieces of positive lenses, a biconcave lens, and a positive lens, and a diaphragm is placed between two pieces of positive lenses. Also, an aspherical surface 14 is provided on the surface of an image side from the diaphragm. This aspherical surface 14 is provided so that in case of the positive lens, it becomes a direction for weakening a positive refracting power as it is separated from the optical axis. Also, as the diaphragm and the aspherical surface are separated, the flatness of the best image surface and the correction of various aberrations coexist easily.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a compact zoom lens used in single-lens 7-lens cameras and the like.

[Conventional technology]

Conventionally, a zoom lens that covers a wide-angle range consists of, in order from the object side, an 1I lens group with negative refractive power and an 1I 2 group lens with positive refractive power, and by changing the spacing between both lens groups, the entire system can be adjusted. A device in which 7-ocusing was performed by changing the focal length and moving only the first lens group was developed in 1977-207.
] No. 3, JP-A-59-142515, etc. In order to make such a zoom lens even more compact, an effective means is to increase the refractive power of each lens group. In addition, in order to simplify the problem of lens movement when trying to focus at close range in the entire range from the wide-angle end to the telephoto end, it is necessary to I need to become stronger.

However, if the refractive power of each group is increased, various aberrations will worsen over the entire axial and off-axis areas, and aberration fluctuations will also become thicker as the focal length changes.

On the other hand, JP-A-58-111013, JP-A-60
-120331 etc., I! In order to correct comatic aberration on the telephoto side and astigmatism on the wide-angle side, a meniscus lens with weak refractive power fixed to the image plane is provided on the image side of the above two lens groups.

[Problem to be Solved by the Invention J] In the configuration in which the above-mentioned meniscus lens is added, the number of lenses increases, which is contradictory to making the zoom lens more compact. In order to avoid this, if the wall thickness of each lens is made thinner, the fine wall thickness becomes significantly smaller, which causes problems in manufacturing.

Alternatively, since the wall thickness is limited to a certain extent, there is no margin for correcting aberrations, which causes problems such as a shift between the best image plane at the center of °C and the best image plane at the periphery of the screen, especially at intermediate focal lengths.

The present invention provides a compact zoom lens that maintains a two-group configuration, effectively corrects aberrations caused by increasing the refractive power of each group, and achieves good convergence performance from the wide-angle end to the telephoto end. Furthermore, the present invention realizes short photographing at close range by 7 focusing by moving only one lens group.

[Means and effects for solving the problems] The present invention has the following features:
Consisting of, in order from the object side, a first group lens having a negative refractive power and a second group lens including a diaphragm and having a positive refractive power,
This zoom lens is characterized in that the focal length of the entire system is changed by changing the distance between both groups, and that at least one surface of the lens constituting the second lens group is provided with an aspherical surface.

If the refractive power of the first group lens is strengthened in order to make the entire system more compact, the amount of aberration generated in the first group lens will increase, and the aberrations of the entire system including the second group lens will also increase on-axis and off-axis. The aberrations are worsened over the entire screen, and the aberration fluctuations due to changes in focal length are also large. It is effective to provide an aspherical surface.In a lens whose object side is closer to the aperture, eccentricity has a relatively large effect on the stiffness performance, and if an aspherical surface is provided, the effect of eccentricity will be even greater. It is preferable to provide the lens on the second surface rather than on the diaphragm from the perspective of assembling the lens system. Also, the farther the diaphragm and the aspherical surface are, the easier it is to achieve both the flatness of the best ff1ffilF and the correction of various aberrations.

The above-mentioned aspherical surface preferably has a shape in which the positive refractive power of a positive lens becomes weaker (or the negative refractive power of a negative lens becomes stronger) as it moves away from the optical axis. This is because when the refractive power of the second group lens is increased, in a spherical lens, it moves away from the optical axis (the refractive power becomes stronger), and this is a major cause of various aberrations.

In order to realize a more compact optical system, it is desirable to satisfy the following equation. where fl is the focal length of the first lens group, flI is the focal length of the second lens group,
fW is the focal length of the entire system at the wide-angle end, and fT is the focal length of the entire system at the telephoto end.

1.2< Ifx l/fw<2.5 (])0
, z<1ftN/fr<2.0 (2) If the lower limit of formula (1) is exceeded, the amount of aberration generated in the first lens group increases, and it cannot be corrected with a small number of elements, making it more compact and simple. The purpose of configuration cannot be achieved. (]
) If the upper limit of the equation is exceeded, the amount of extension of the first lens group in 7-ocusing becomes too large (and therefore, achieving a short close-up distance with a small filter diameter at the wide-angle end cannot be achieved with 7o-cushion by extending only the first lens). If the lower limit of equation (2) is exceeded, it becomes difficult to obtain the necessary amount of back 7 orcus at the wide-angle end. (2)
) If the upper limit of the formula is exceeded, the effect of compaction becomes weak (becomes).

Furthermore, the first lens group consists of, in order from the object side, a negative meniscus lens with a gentle curvature on the object side, a negative lens, and a positive meniscus lens with a gentle curvature on the image side. This makes it possible to strengthen the refractive power of the X-lens group while reducing the amount of various aberrations (and to position the rear principal point of the first lens group on the image side. At the wide-angle end, the small filter 4 It is advantageous to achieve a short shooting distance with 7-ocusing by extending only one lens.Furthermore, it is desirable for the first lens group to satisfy the condition of "C" or less.However, fs, ft.

fs are the focal lengths of the ]th, second, and third lenses from the image side, Vl, V2 . Vs is the number of 7 lenses of the first, second, and third lenses from the image side, R
s is the radius of curvature of the first lens group closest to the image side.

-0,001(1/(ft・Vt) +1/(fm・Vt)
z)+1/ (fm・Vs)(0,001(31 0,3(Rs/fw) (2(41) If the condition of equation (3) is removed, the chromatic aberration generated in the first lens group becomes thick (becomes the second The lens group cannot fully compensate.

If the upper limit of equation (4) is exceeded, the principal point of the first lens group will be located too close to the object side, making it difficult to achieve a short shooting distance at the wide-angle end by using a small filter diameter and focusing by extending only the first lens. I feel nervous. If the lower limit of equation (4) is exceeded, the spherical aberration generated in the first lens group becomes large (and cannot be completely corrected by the second lens group).

Furthermore, the configuration of the second lens group includes an aperture, and in front of the aperture there are at least a few positive lenses.

It is desirable that there be at least one negative lens behind the diaphragm and that the following conditions be satisfied.

However, Ry is the radius of curvature of the second lens group closest to the object side, and NR is the average refractive index of the negative component of the second lens group.

0.5 (Ry / fw (3 (5) This will result in over-correction. If the condition of equation (6) is removed, the curvature of the negative lens will become steeper, making it difficult to correct coma aberration, which is not preferable.

〔Example〕

In the embodiments of the present invention described below, as shown in FIG. 1, the 1f# lens is a negative meniscus lens having a convex surface on the object side in order from the object side, and a gentle negative meniscus lens having a concave surface on the object side.

It consists of a positive meniscus lens with a convex surface on the object side, the second lens group consists of two positive lenses, a biconcave lens, and a positive lens, and the aperture is arranged between the two positive lenses.

In addition, the aspheric surface used in the examples is expressed by a general formula when the origin is the intersection of the reference sphere with the radius of curvature R and the optical axis, the X axis is in the optical axis direction, and the h axis is in the plane perpendicular to the optical axis. It is something that can be done.

Dark side 1 ft36~67 F/3.6~4.6RD
N V l 45.0271 1.8500 1.6935
53.232 19.5120 8.6604 3 -72.1371 1.5552 1.6935
53.234-1514850 0jO00 525,129] 2.05] 1.805] 8
25.436 31.8344 Dr(”P&)
? 25.4292 3.6733 1.6170
0 62.798 -]]6.3459 1'j57
4 (final) 1.0316 9 25.5533 6.0263 1.79
952 42.2410 79.5813 0
．． 840711 -62.6903 1.0000
1.80518 25.4312 20.6
017 5.349013 -335.3818 2
．． 2000 1.63980 34.4834 -
29.92] 1 (Aspherical surface) B=0.1] 356X10
C co-0,55260 mowing 0-7E=0.92405
X10″F=O,]9822X10-”DI
f 28.758 36 12.067 50 0.644 67 Aoi” 11 upper ft36~fi7 F/3.6~4.6RD
N Vl 44.
3797 1.8500 1.69350 53
．． 232 19.4616 8.66503
-73.3658 1.5552 1.69350
53.234 -163.2002 0.100
05 25.4070 2.0720 1.8
0518 25.436 32.5516 1
．． s(possible'i)7 25.355] 3.6
574 1.6] 700 62.798 -12
4.0621 0.914] (End Li) 1.03
16 9 23.1906 5.2711 1.80
440 39.5830 103.2476 0
．． 647511 -89.4594 1.0OGG
1.80518 25.4312 18.
1614 5.932313 -107.4587
2.2000 1.64769 33.8034
-29.992] pitch surface) B=-0,13463 cut 0-' C= 0.9267
4 cutting 0-7g=-0,]]949X]OF'=0.33
935X] 0G = -0,65893 .8500 1
．． 69350 53.232 20.1225
8.66053 -66.1768 1.5
552 1.69350 53.234 -13
9.1098 0゜】0005 27.122
5 2.0876 1.8Q518 25.43
6 35.9362 D, (variable)?
25.2200 3.6930 1.61700
62.798 -116.575] 1.46
24 (Kizorin 1.0316 9 24.7792 6.2645 1.7
9952 42.2410 65.3309
0.995211 -5(1,55]2 1.
0473 1.8051B 25.4312
193386 4.5]0133 -308.
9816 2-2000 1.63980 3
4.4814 -24.856] (aspherical surface) B = 0.79782 cut OC = -0,507] 7X]
O-'[i:=0.32022X10 F=0.1
5382X10-”G=0.97499X10””’ D! f 29.181 36 12.237 50 0.66 67 Retraction” 1-1 f=36~67 F/34~4.6RD
N V l 43.6086 1.9300 1.69
680 55.522 19.7013 8
．． 93703 -68.1836 1.6300
1.69350 53.234 -137.192
1 0.10QO525,074B 1.9951
1.8051B 23.436 30.9
516 0+(variable) 7 27.8865 3
．． 6062 1.61700 62.798 -1
26.1057 1.4101 (aperture) 0.
2000 9 22.9621 6.4321 1.79
952 42.2410 88.4488
0.587611 -130.1234 1.000
0 1.805] 8 25.4512 18.
2358 6.41)0813 -350.0000
2.4800 1.63980 34.481
4 -36.3823(Aspherical B=O,]0]63X]OC=-0,22463X]0
″″7E=0.55849X10-' F=(11
6355X10”””Os f 28.495 36 11.959 50 0.661 67 In each example, R is the radius of curvature of the lens box.

D is the distance between lens cases, and N is the refractive index of each lens.

(2) is the Abbe number of each lens, B, C, W, F, and a are aspherical coefficients, f is the focal length of the entire system, and F/ is the F number.

Also, the aberration of actual opening 1! J is shown in FX2 diagram and s3 diagram, and the aberration of Example 2 is Ka41. In Figure 5, the aberration of Eitaki Example 3 is 6th.
7, and the aberrations of actual opening 1 are shown in FIG. 48 and FIG. 9, respectively. From these figures, each actual m column is at the wide-angle end.

It is understood that the aberrations are sufficiently well corrected at any telephoto end, but in particular, the aberration correction effect of the aspherical surface will be shown with a table of Zygmen's coefficients for Example.

Ku nu wa wa ku wa wa wa wa wa wa wa. . . -9°, -;II
-″″″I M M-Ikkōichi m Q
x to ω■low■啼43m
1"l F'l M M ++"""δ In the above table, J
4 is the Seidel coefficient due to the spherical surface of the 14th surface, and the 14th bone is the Didel coefficient due to the aspherical button. It is clear from the table that the Seidel coefficient due to the aspheric surface makes a large contribution to reducing the sum of spherical aberration, coma aberration, and astigmatism at each focal length. In this way, the first group lens,
Introducing an aspherical surface is extremely effective in correcting the deterioration of aberrations caused by increasing the refractive power of the group lens.

In addition to glass cutting, the aspherical surface can be manufactured at ℃ using various methods such as plastic additive molding, replica molding, and glass molding.

〔Effect of the invention〕

According to the present invention, it is possible to obtain a zoom lens that is compact and has various aberrations well corrected.

[Brief explanation of drawings]

@ Figure 1 is a sectional view showing the lens arrangement of an embodiment of the present invention, and Figures 2 to 9 are aberration curve diagrams of each embodiment of the present invention. 1st diagram fIJ collection 21st ball I collection slope non-j! , JJXjl No. 31 Distortion aberration ) 7 Tori rough 15 (f proverb 36) Distortion aberration Comatic aberration (f wealth 67) Spherical convergence Astigmatism No. 4 Sphere mQdL O 龜 convergence slope No. 5 1NxJ1 Coma convergence j1 Figure ke shit 36) Distortion convergence Core 4WJL diagram (f-67) Vapor plane IJIC Yasha Aberration No. 61 Man convergence Astigmatism No. 7 Distortion aberration Coma aberration threshold (f-36) Slight convergence Coma aberration diagram Tomi 67) Spherical convergence Shaki convergence No. 8 1ft aberration Shamaru convergence No. 9 Distortion aberration Comatic aberration rXJ (f-36) Distortion 6113 (slope Coma 01 diagram
Tree procedural amendment June 3, 1986

Claims (2)

[Claims] (1) In order from the object side, it consists of a first group lens having a negative refractive power and a second group lens including an aperture and having a positive refractive power, and the distance between the first group lens and the second group lens is changed. 1. A zoom lens in which the focal length of the entire system is changed by changing the focal length of the entire system, characterized in that at least one surface of the lens constituting the second lens group is provided with an aspherical surface. (2) The zoom lens according to claim 1, wherein the aspherical surface is provided on a surface closer to the image side than the aperture.