JPS61140911A - Zoom lens - Google Patents

Abstract

PURPOSE:To correct satisfactorily an aberration by constituting a zoom lens having four lens groups, so that the fourth lens group is stuck to a lens 4B of a positive refractive power, whose refractive index is lower than that of a lens 4A of a negative refractive power, and its convex surface is turned to an image surface side. CONSTITUTION:In case of variable power, an incident height of a velocity of a light of out-of- axis to the fixed fourth lens group is the lowest at the wide angle end, and becomes the highest extending from a middle focal distance to a telephoto end. Accordingly, the fourth lens group is constituted of a cemented lens of a meniscus shape, which has stuck a lens 4A of a negative refractive power and a lens 4B of a positive refractive power consisting of glass whose refractive index is lower than that of the lens 4A, and whose convex surface has been turned to an image surface side. In this way, a meridional image surface of a correction shortage extending from the middle focal distance to the telephoto end is corrected appropriately, and a variation of an astigmatism is reduced as a whole, and a variation of a spherical aberration can also be reduced. In this regard, when leading an aspherical surface into the third lens group, when a focal distance of the third lens group and a focal distance in a telephoto end of the whole system are denoted as f3 and fT, respectively, they are set so as to become 0.12fT<f3<0.35fT, and a variation of an aberration caused by variable power is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a zoom lens, and more particularly to an eye reflex camera, an 8
The present invention relates to a compact zoom lens with a high zoom ratio and high performance, which is suitable for IIll cameras, video cameras, and the like.

In recent years, with the miniaturization of reflex cameras and video cameras, there has been a demand for smaller photographic lenses. In particular, there has been a demand for compact zoom lenses with short overall lens lengths, which tend to have relatively long overall lens lengths.

In order to reduce the total lens length and lens outer diameter of a zoom lens and further improve its optical performance, it is necessary to appropriately set the refractive power and lens shape of each lens group constituting the zoom lens. In general, increasing the refractive power of a lens group shortens the overall length of the lens, but at the same time increases the amount of various surface aberrations that occur.In particular, aberration fluctuations due to zooming become large, making it difficult to properly correct them. As a method for reducing the size of a zoom lens, a method in which a large number of lens groups are moved to change the magnification and at the same time correct aberration fluctuations accompanying the change in magnification is disclosed in, for example, JP-A-57-168209 and JP-A-57-1. 16971
(This was proposed in Publication No. S, etc.) In the same publication, a zoom lens is constructed of four lens groups: 1st, 2nd, 3rd, and 4th lens groups with positive, negative, positive, and positive refractive powers in order from the object side. The four lens groups are moved to change the magnification, and the refractive power is arranged so that the axial light beam emerging from the third lens group becomes parallel light, thereby achieving good aberration correction. However, since the zoom lens disclosed in the same publication adopts a refractive power arrangement such that the axial light beams exiting from the third lens group are approximately parallel, the overall lens length tends to be relatively long. If the axial light beam exiting from the lens group is made into a convergent light beam, the overall length of the lens can be shortened, but aberration fluctuations associated with zooming become large, and it is generally very difficult to properly correct this.

SUMMARY OF THE INVENTION The present invention aims to provide a compact, high-performance zoom lens that has four lens groups and has a high zoom ratio that satisfactorily corrects aberration fluctuations associated with zooming, which has been considered difficult in the past. do.

The main features of the zoom lens for achieving the object of the present invention are, in order from the object side, the first lens group with positive refractive power, the second lens group with negative refractive power, the third lens group with positive refractive power, and the third lens group with positive refractive power. 4 lens groups, the fourth lens group is fixed, the lens group and the fifth lens group are moved toward the object side, and the second lens group is moved toward the object side or the image plane side. In a zoom lens that performs magnification change, the third lens group includes a lens 3M with a concave surface facing toward the image surface side, and a lens 3B with a positive refractive power having at least one aspherical surface on the image surface side of the lens 3A. and the fourth
The lens group has a meniscus shape in which a lens 4A with a negative refractive power and a lens 4B with a positive refractive power made of glass with a refractive index lower than that of the glass of the lens 4A are bonded together, with the convex surface facing the image plane side. It is constructed from a laminated lens.

In this manner, the present invention achieves a high zoom ratio with a small amount of movement by moving the six lens groups. In particular, by specifying the lens configuration of the third lens group that is moved as a result of zooming as described above, aberration fluctuations that occur with zooming are reduced and overall good aberration correction is achieved.

Generally, in such a zoom type, the zoom lens is constructed with only spherical lenses, and in order to correct various aberrations within each lens group, the number of lenses in each lens group must be increased, resulting in a longer overall lens length. There was also a tendency for weight to increase. Also, if the refractive power of the third lens group is strengthened in order to achieve miniaturization, for example, a large amount of spherical aberration and astigmatism will occur within the $3 lens group, making it difficult to correct these various aberrations with other lens groups. It becomes. In particular, if aberration correction is performed using lens groups other than the third lens group in order to reduce aberration fluctuations due to zooming, the refractive power sharing becomes inappropriate, making it difficult to achieve good aberration correction.

One way to eliminate the above aberration fluctuations is to set a diverging lens surface in the third lens group, but since this method uses a diverging lens, it is necessary to add an additional positive lens, making the lens system This will lead to lengthening. Furthermore, it is difficult to satisfactorily correct higher-order aberrations that occur on a strongly diverging surface.

Therefore, in the present invention, the positive refractive power lens of the third lens group is provided with an aspherical surface to eliminate aberration fluctuations due to zooming, and furthermore, to prevent the lens system from becoming long and to achieve a compact zoom lens. There is.

That is, in the present invention, the refractive power of the third lens group is strengthened to shorten the overall lens length, and the fluctuations in spherical aberration and astigmatism that occur at this time are compensated for by providing a strong negative refractive power within the third lens group. This is corrected by a lens 3A having a concave surface.

Furthermore, when the spherical aberration at the wide-angle end and the telephoto end is well corrected by this lens 6A, the spherical aberration becomes overcorrected at the intermediate focal length. Therefore, this overcorrected spherical aberration is corrected by the lens 3B having an aspherical surface.

In this manner, in the present invention, the effect of the negative refractive power of the lens 3A is shared by the lens 5B, thereby weakening the refractive power of the lens 3A and reducing fluctuations in spherical aberration accompanying zooming.

Furthermore, the introduction of an aspherical surface makes it difficult to correct fluctuations in astigmatism. In other words, when the diverging effect is shared by the aspherical surface, the meridional image surface changes from under-corrected to over-corrected at the wide-angle end, but from the intermediate focal length to the telephoto end, the meridional image surface remains under-corrected for the most part. does not change.

Therefore, in the present invention, when changing the magnification, the height of incidence of off-axis light beams on the fixed fourth lens group is lowest at the wide-angle end and highest from the intermediate focal length to the telephoto end, so this characteristic is utilized. The fourth lens group is composed of a lens 4A with a negative refractive power and a lens 4B with a positive refractive power made of glass with a refractive index lower than that of the glass of the lens 4, with the convex surface facing the image plane side. By using a meniscus-shaped bonded lens, the meridional image plane, which is undercorrected from the intermediate focal length to the telephoto end, is appropriately corrected, and fluctuations in astigmatism are reduced overall.

Moreover, by adopting such a configuration, fluctuations in spherical aberration can also be reduced. - As mentioned above, in the present invention, the third. Good aberration correction is achieved by specifying the lens configuration of the fourth lens group, but in particular in the present invention, when introducing an aspherical surface into the third lens group, the focal point of the third lens group When the distance is f3 and the focal length of the gold thread at the telephoto end is /T, 0.12fT<f3<0.35/T (1
) It is preferable to set the condition such that the following conditions are satisfied, since this will further reduce aberration fluctuations due to zooming.

That is, if the lower limit of conditional expression (1) is exceeded and the refractive power of the third lens group becomes too strong, aberration fluctuations due to zooming will increase, and if the upper limit is exceeded, the refractive power of the third lens group becomes weak. This is not preferable because the amount of movement of the third lens group due to zooming increases and the overall length of the lens increases.

Furthermore, in the present invention, in order to perform good aberration correction over the entire screen, the third lens group is composed of three lenses with positive refractive power in order from the object side, and positive and negative refractors with concave surfaces facing the image side. It is preferable to use a double-convex lens having a positive refractive power and an aspherical surface.

With such a lens configuration, it is possible to refract the light rays incident on the third lens group in a nearly aboular aberration state, and it is possible to reduce the amount of spherical aberration generated.

Note that if the lens 3B having an aspherical surface in the third lens group is configured by bonding lenses with positive and negative refractive powers, the degree of freedom in aberration correction will be increased, and fluctuations in chromatic aberration due to zooming will be reduced. Furthermore, it is preferable because the Petzval sum is corrected and good image plane characteristics can be obtained.

Next, the effect of the aspherical surface according to the present invention on aberration correction will be expressed as r
Lens Design Method J Yoshiya Matsui, Kyoritsu Shuppan, will be explained with reference to pages 41 onwards.

Using h as the tracing value of the paraxial ray and paraxial pupil ray on the aspheric surface, the aberration coefficients I, n, and i of the third-order spherical aberration, coma aberration, and astigmatism are as follows: I-IQ+h' ψ 1F-IQ+h'πψ l -door o+h2h2φ. Here, ψ is the aspherical amount defined in the above-mentioned "Lens Design Method J," IO+ "O+ In is the spherical aberration of all threads when each aspherical lens is a spherical surface with paraxial curvature,
These are aberration coefficients for coma aberration and astigmatism.

Here, for example, if the aperture is placed in front of the third lens group, both h and h will be positive.

If an aspherical surface having a negative refractive power effect is arranged in the third-order aberration region in the third lens group, the aspherical amount ψ becomes ψ<0.

Therefore, since h, h)Q, each aberration coefficient of spherical aberration, coma aberration, and astigmatism can be reduced.

Therefore, it is possible to reduce aberration fluctuations due to the positive refractive power of the third lens group during zooming.

In particular, in the present invention, when the aspherical amount ψ is the focal length of the entire system at the wide-angle end as fW, it is set such that it satisfies the following condition: 0<-φ<2 It is preferable to configure.

Here, the lower limit value of conditional expression (2) indicates that the aspherical amount has a negative refractive power effect in the third-order aberration region, and when the upper limit value is exceeded, the astigmatism coefficient at the wide-angle end decreases. is over-corrected and the meridional image plane is over-corrected. Furthermore, the aberration correction performance associated with zooming deteriorates, and spherical aberrations, especially at the telephoto end, become overcorrected, which is undesirable.

Next, in the present invention, in order to achieve good aberration correction over the entire zoom range despite a high zoom ratio, the ts2 lens group is made of a meniscus with negative refractive power that has a convex surface facing the object side in order from the object side. A lens with a negative refractive power that has both concave lens surfaces, a positive refractive power lens that has both convex lens surfaces, and a meniscus lens with a negative refractive power with the convex surface facing the image plane. , when changing the magnification from the wide-angle end to the telephoto end. The third lens group moves toward the object side, and the @2 lens group moves nonlinearly with respect to these movements, keeping the image plane constant. The second lens group is preferably moved toward the object side on the wide-angle side, toward the object side at intermediate focal lengths, and toward the image side on the telephoto side.

In the zoom lens of the present invention, focusing can be performed by extending the first lens group to reduce aberration fluctuations, but focusing may be performed by extending the fourth lens group or all lens groups.

As described above, according to the present invention, in a zoom lens having four lens groups, the third and fourth lens groups are configured as described above, thereby achieving a high-performance yet compact zoom lens. can do.

Next, numerical examples of the present invention will be shown. In the numerical examples, Ri is the radius of curvature of the second lens surface from the object side, Di is the first lens thickness and air gap from the object side,
Hi and ν1 are the refractive index and Abbe number of the glass of the first lens, respectively, in order from the object side.

The shape of the aspherical surface is determined by the amount of displacement at the height H from the optical axis;
The radius of curvature of the reference sphere is 7, and the radius of curvature of the paraxial surface is r1.
Letting the aspheric coefficients be M, B, (3, D, E), it is expressed by the following formula.

Numerical Example 1 F-! 16.0-132. IPNO-1:5.6~4
．． 62taS61.7'~18. <S.

R1-190,0<SD I-2,50N 1-1.
80518 Si1-25.4R2-59,60D 2
-6.40 N 2-165160 ν 2-5
8.6R24=122.38 D24-variable R27=
580.52 D27-5.00 N13-14874
9 Si15-70. IR2B--30,25 R24: Aspherical surface Aspherical coefficient -O B -5,3535X 1 cr' C--93451xlO-9 D --72476x 10'' E-0° Numerical Example 2 F-36,0~152 .FNO-1: 3.tS~4
．． 62P61. f~18.6゜R1-318,08D
I-2,15N 1-180518 ν 1-25.
4R2-67,95D 2-7.00 H2-1<35
160 Shi2-58.6R5--163,95D 3-
0.12R4-44,95D 4-4.20 N 3-
169680 Shi5-35.5R5-11918D 5
-Variable R6-100, 66D 6-1°57 N 4-1.8
8300 Shi4-40.8R7-19,76D 7-5
．． 83 R8--57,65D 8-1.18 N S-188
300shi 5-40.8R9-83, 24D 9-1.7
3 R10-47,94Dlo-4,70N 6-1846
66 Jiro 23.9R11--38,01Dll-0
,88R12--26,70D12-1.03 N 7
-181600 Sheer 46.6113--85.05
D13-variable R14-35, 26D14-3.40
N 8-161800 C8-63.4R15=62
9.24 D15-0.15R16-38,32DI6
-3.40 N 9-1.60311 C9-60.
7117-1684.80 D17-0.15R18-
35,63D18-2.70 N10-151633
C10-64. lR19-35, +51 D19-0.
15R20-22, 31D20-5.54 N11-
1.48749 C11-70. lR21--162
．． 15 D21-7.68 [12-185025shi1
2-23.9R22-14, 89D22-4.86 R23-35, 69D25-3.5 N13-157
309 Shi13-42.6R24--35.33 D2
4-1.0 114-t84666 14-25.9
R25--63,72D25-variable R26-diameter grade D26-variable R27--57,90D27-0.98 N15-1.
83481 Shi15-42.7R2B-279.06
D28-4.90 N16-153172 Shi16-
48.9129--27.90 R25: Aspherical surface Aspherical coefficient B-2,957x10' C--8,998X 10= D--7522X 10='

[Brief explanation of the drawing]

FIGS. 1 and 2 are a cross-section of the lens of Numerical Example 1.2 of the present invention, and FIG. 3. Figure 4 shows numerical examples 1 and 2 of the present invention, respectively.
It is a diagram of various aberrations. In the figure, (4), 03), and (C) are various aberration diagrams at the wide-angle end, intermediate, and telephoto end zoom positions, respectively, and I, l, square, and ■ are the 1. Second. Third. In the fourth lens group, 6M indicates a meridional image plane, and ΔS indicates a sagittal image plane.

Claims (1)

[Claims] (1) In order from the object side, there are four lens groups: a first lens group with positive refractive power, a second lens group with negative refractive power, a third lens group with positive refractive power, and a fourth lens group. It has a lens group, and magnification is changed by fixing the fourth lens group and moving the first lens group and the third lens group toward the object side and the second lens group toward the object side or the image plane side. In zoom lenses,
The third lens group is configured to include a lens 3A having a concave surface facing the image plane side and a lens 3B having a positive refractive power and having at least one aspherical surface on the image plane side of the lens 3A, and the fourth lens The group has a meniscus shape in which a lens 4A with a negative refractive power and a lens 4B with a positive refractive power made of a material having a refractive index lower than that of the material of the lens 4A are bonded together, with the convex surface facing the image plane side. A zoom lens characterized by being constructed from laminated lenses. (2) When the focal length of the third lens group is f_3 and the focal length at the telephoto end of the entire zoom lens system is f_T, the following condition is satisfied: 0.12f_T<f_3<0.35f_T A zoom lens according to claim 1. (3) The third lens group is composed of, in order from the object side, three lenses with positive refractive power, a bonded lens with a concave surface facing the image surface side, and a lens with positive refractive power having an aspherical surface. A zoom lens according to claim 1. (4) The first aspect of the present invention is characterized in that the lens 3B is constructed by bonding lenses with positive and negative refractive powers.
Zoom lens described in section.