JPH03260611A - Zoom lens with simple configuration - Google Patents

Abstract

PURPOSE:To obtain a compact zoom lens having effective performance in the whole variable power range with about 2 variable power by constituting the lens system three lenses in the three groups and satisfying specific conditions. CONSTITUTION:The lens system is constituted three lens groups, i.e. a 1st group I having negative refractive power, a 2nd group II having positive refractive power and a 3rd group III having negative refractive power successively arranged from the object side. Each of the three lens groups is constituted of a single lens and the power of the whole system is varied by moving the three lenses. When it is defined that the focal distance of the 1st group I is F1, the focal distance of the whole system on the wide angle end is Fw and the main point interval between the i-th group and the (i+1)th group on the wide angle end is Eiw, the conditions of -2.8<F1/Fw<-1.3 and 0.11<E1w/Fw<0.25 are satisfied.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a zoom lens suitable for photographic cameras, video cameras, etc.
These three lens groups are composed of a single lens, and the three lens groups are moved to change the magnification.The lens has an F number of about 3.6 and a variable magnification ratio of about 2. The present invention relates to a compact zoom lens with a simple structure having a short length and good optical performance.

(Prior art) Conventionally, the lens has three lens groups in order from the object side: a first group with negative refractive power, a second group with positive refractive power, and a third group with negative refractive power. The present applicant has developed a zoom lens that changes magnification by moving the lens group, for example, in Japanese Patent Application Laid-Open No. 63-27.
This method has been proposed in Japanese Patent Application Laid-open No. 1214, Japanese Patent Application Laid-Open No. 64-72114, etc.

This type of zoom lens is relatively easy to widen, so it is often used as a wide-angle photography system.

The bulletin is No. 1. Second. Variable power ratio 2 with high optical performance that performs zooming by moving the third group under a certain condition F and also satisfactorily corrects aberration fluctuations due to zooming by specifying the lens configuration of the three lens groups. ~3x overall 8~
A relatively compact zoom lens consisting of nine lenses, particularly suitable for lens-shutter cameras, has been achieved.

(Problems to be solved by the present invention)
The zoom lens proposed in Publication No. 72114 has each lens group composed of two or more lenses, and for example, corrects chromatic aberration within each lens group and strengthens the refractive power of each lens group to increase the total optical length (first lens surface). Distance 11i from to the imaging plane
).

The present invention utilizes the refractive power arrangement of the zoom lens previously proposed by the applicant, further improves the lens configuration of each lens group,
In particular, to provide a zoom lens with a simple structure suitable for a lens shutter camera, with an F number of about 3.6, which aims to ultimately reduce the number of lenses, and has good optical performance over the entire zoom range with a variable power ratio of about 2. With the goal.

(Means for Solving the Problems) A zoom lens of the present invention having a simple configuration includes, in order from the object side, a first group having a negative refractive power, a second group having a positive refractive power, and a second group having a negative refractive power. It has three lens groups of three groups, each of these three lens groups is composed of a single lens, and the three lens groups are moved to change the magnification, and the focal length of the third group is set to Fi. , when the focal length of the entire system at the wide-angle end is Fw, and the distance between the principal points of the third group and the (i+1) group at the wide-angle end is EiW, -2,8< Fl/Fw <-1,3... ...
(1) 0.11<E1W/Fw<0.25...
・(2) It is characterized by satisfying the following conditions.

(Example) Figures 1, 2, and 3 are numerical example 1 of the present invention,
2.3 is a sectional view of the lens. In the figure, the 1st group has a negative refractive power, ■ the 2nd group has a positive refractive power, and ■ the 3rd group has a negative refractive power.
Groups and arrows indicate the direction of movement of each lens group when changing magnification from the wide-angle side to the telephoto side.

In the zoom lens according to this embodiment, when changing the magnification from the wide-angle end to the telephoto end, all three lens groups are independently moved in the object side direction, as shown in each figure.

In particular, a predetermined variable power ratio is effectively obtained by greatly changing the distance between the second and third groups. Incidentally, the sp is stopped and placed on the image plane side of the second group, and moves integrally with the second group during zooming.

The zoom lens of the present invention is the first one. Second. As shown in Figure 3, it consists of three lens groups with negative refractive power, negative refractive power, positive refractive power, and negative refractive power in order from the object side, that is, a first group with negative refractive power is placed on both sides of the second group with positive refractive power. The third lens group is arranged to have a variable magnification medium refractive power arrangement or a substantially symmetrical lens structure. In addition, high refractive index, high dispersion glass is used for the first group, and low refractive index, low dispersion glass is used for the second group.

By arranging the lenses in such a nearly symmetrical manner and using glass made of an appropriate material, chromatic aberrations can be corrected within each lens group in a well-balanced manner as in the conventional method. That's what I do.

In other words, the aberrations of the three lens groups cancel each other out.

In addition, the first group is a meniscus-shaped negative lens with a convex surface facing the object side, the second group is a positive second lens whose lens surface on the image side has a strong refractive index, and both lens surfaces are convex. Even if the lens group is composed of a meniscus-shaped negative third lens with a convex surface facing the image plane and the overall lens length is shortened, it is not possible to correct various aberrations including chromatic aberration in a well-balanced manner over the entire zoom range. This makes it possible to obtain a zoom lens with high optical performance.

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

Conditional expression (1) is used to appropriately set the negative refractive power of the first group and to satisfactorily correct various aberrations.

If the refractive power of the first group becomes too strong exceeding the upper limit of conditional expression (1), it becomes difficult to correct various aberrations in a well-balanced manner over the entire zoom range. Also, if the lower limit is exceeded and the refractive power of the first group becomes too weak, is it possible to properly correct longitudinal chromatic aberration on the wide-angle side?

It's getting worse.

Conditional expression (2) is used to appropriately set the distance between the principal points of the first group and the second group at the wide-angle end, and to correct various aberrations in a well-balanced manner while reducing the size of the entire lens system.

If the upper limit of conditional expression (2) is exceeded and the distance between the principal points of the first group and the second group becomes too long, the effective lens diameter of the first group increases; If the distance between the principal points and the second group becomes too short, the symmetry of the entire lens system will deteriorate, making it difficult to correct various aberrations in a well-balanced manner.

In addition, in the present invention, in order to satisfactorily correct various aberrations while downsizing the entire lens system, the first group and the (i+1)
When EiT is the distance between the principal points at the telephoto end of the group, and the refractive index and Abbe number of the lens material of the first group are Ni and νi, respectively, 1< F2/F3 <-0, 6 ( 3)
・・・・・・(4) ・・・・・・(5) υ 1〈 ν3 〈ν2 ・・・・
It is good to satisfy the condition (6).

Conditional expression (3) is used to appropriately set the ratio of the refractive powers of the second group and the third group to effectively obtain a predetermined variable power ratio.

If the upper limit of conditional expression (3) is exceeded and the refractive power of the third group becomes too weak, the amount of movement of the third group to ensure a predetermined variable power ratio increases, and the overall length of the lens becomes longer. Furthermore, if the refractive power of the third group becomes too strong beyond the lower limit, it becomes difficult to satisfactorily correct off-axis aberrations such as field curvature.

Conditional expression (4) is the first variable in zooming from the wide-angle end to the telephoto end.
The ratio of the amount of change in the distance between the principal points between the second group and the second group and the amount of change in the distance between the principal points between the second group and the third group is set appropriately, and the main purpose is to properly correct field curvature. It is something.

If the upper limit of conditional expression (4) is exceeded, the curvature of field will vary greatly in the negative direction when changing the magnification from the wide-angle end to the telephoto end. On the other hand, if the lower limit is exceeded, the curvature of field will change significantly in the positive direction when changing the magnification from the wide-angle end to the telephoto end, which is not good.

Conditional expression (5) is used to appropriately set the refractive index of the material of each lens group and mainly to satisfactorily correct the image plane characteristics. When the upper limit is exceeded, the Petzval sum increases in the positive direction, and when the lower limit is exceeded, the Petzval sum increases in the negative direction, and in either case, it becomes difficult to correct astigmatism well. come.

Conditional expression (6) is used to appropriately set the Abbe number of the material of each lens group and to satisfactorily correct longitudinal chromatic aberration and lateral chromatic aberration over the entire zoom range.

If conditional expression (6) is not satisfied, it becomes difficult to correct these chromatic aberrations in a well-balanced manner over the entire zoom range.

In addition, in the present invention, in order to maintain good optical performance of the entire screen over the entire magnification range, (3) the lens surface on the object side of the first group has an aspherical surface; an aspherical surface is applied to the lens surface of the third group, an aspherical surface is applied to the object side lens surface of the third group, an aspherical surface is applied to the first group, the aspherical coefficient of the i-th group is Bi, and the diagonal length of the effective screen is Y. When 15< Bl-Y3 <-1...(7)-7<
82・Y3 <-0, 1...(8) R3・Y31
<2 It is good if the condition (9) is satisfied.

Conditional expressions (7) and (9) are mainly used to satisfactorily correct field curvature.

If the upper limit of conditional expression (a) or the lower limit of conditional expression (9) is exceeded, it becomes difficult to satisfactorily correct field curvature. Furthermore, if the lower limit of conditional expression (7>) or the upper limit of conditional expression (9) is exceeded, the aspherical effect tends to become strong and the curvature of field becomes overcorrected, which is not good.

If the upper limit of conditional expression (8) is exceeded, the aspherical effect becomes too weak, making it difficult to properly correct spherical aberration. Moreover, if the lower limit is exceeded, spherical aberration or overcorrection will occur, which is not good.

Next, numerical examples of the present invention will be shown. In numerical examples R
i is the radius of curvature of the first lens surface from the object side, D
i is the first lens thickness and air gap from the object side, Ni
and νi are the refractive index and Abbe number of the first lens, respectively, in order from the object side.

The aspherical shape has an X axis in the optical axis direction, an H axis in a direction perpendicular to the optical axis,
The traveling direction of light is positive, R is the paraxial curvature ↑ diameter, A, B, C,
When D and E are each aspherical coefficients, it is expressed by the formula +DH8+El''.

Furthermore, Table 1 shows the relationship between each of the above-mentioned conditional expressions and the word values in the numerical examples.

Numerical Example I F-36,2 ~ 67.7 RI-33,42 R2-20,:II R3-238,3] 8 4- -11.57 R5- (aperture) R6--15,98 R7- -79,26 FNo=I:3.6 2ω-61,7°~7
~354°N I・1.80518 v l-25,41-
1,6 2・Variable 3・3.0 4- 1.0 5・Variable 6-1.7 2-1.49831 ν? 65.03-1.729
+6 ν 3-54.7 Numerical Example 2 F-36,2 ~ 67.7 R1-38,28 R2 voice 2301 R3-229,45 R4--11,58 85-(aperture) R6--16,06 87-195,68 FNoi: 3.5 ~7 1~1,61 2-Variable 3- 3.08 4-103 5-Variable 6- 1.7O 2ω・6170 ~3540 1=], 9+348 υ l-32 ,42-1,49
700ν 2-8+, 63-1.61800ν
3-6: 1.4 Aspheric coefficient R1: R4: R6: 5.08X 10-' 9.39X 10-8 3.53X 1O-8 B~-1,07X 10-' D--1,57x 1O -8 B--1,5]x 1O-5 B--2,I2x 10-6 Aspheric coefficient 1 4 6 A -OB--9,34x 1O-5G--4,35
xiO-' D--1,31xlO-8A-08--
1,05X 10-' C--3,97X 1O-8 A -OB--1,68X 10-'C~ -5,6
4X 10-8 Numerical Example 3 F-35,2 ~ 67.8 RI= 26.38 R2-18,8] R3-95,75 1 (4--11,33 R5・ (Aperture) R6--13 ,59 R7-179,43 FNol: 3.6 ~ 7 1- 1.60 2・Variable 3 ~ 3.30 4 ~ 1.04 5・Variable 6- 1.70 2ω ~ 61.7° ~ 35,4 °N ]i, 87800 v l-38,1N
2J, 43387 v 2-95.1N 3-1
．． 49700 v 3-81.6 Table-1 Aspheric coefficient R1: 4 6 A ・ OB--8,22x 10"C--4,56xlO-' D--1, ]5xlO-
8^ -OB--], 52X 10"" C ~ -5,07X lo-8 A -OB--3,8]x IQ-6C--8, +2
X 10-8 D・ 1.98X 1O-9E=
-2,53X 1O-12 (Effect of the invention) According to the invention, the refractive power of the three lens groups as described above
By specifying the lens configuration, it is possible to achieve a Zoom 18 lens that has a compact lens system and has good optical performance over the entire zoom range with a zoom ratio of about 2.

[Brief explanation of drawings]

Figures 1, 2, and 3 are numerical examples of the present invention! ,
2.3 is a sectional view of the lens, and FIGS. 4, 5, and 6 are various aberration diagrams of numerical example 1.2.3 of the present invention, respectively. ■ in the cross-sectional view of the lens. n and m are the first group, second group, and third group in order, the arrows are the movement directions of each lens group during zooming from the wide-angle end to the telephoto end, and (A) and (B) in the aberration diagram are the respective directions at the wide-angle end. , aberration diagram at the telephoto end, d is d-line, g is g-line, S, C is sine condition,
ΔS is a sagittal image plane, ΔM is a meridional image plane, and Y is an image height. (A) Figure 2 (A) Figure (A) Figure (B)

Claims (3)

[Claims] (1) It has three lens groups in order from the object side: a first group with negative refractive power, a second group with positive refractive power, and a third group with negative refractive power, and each of these three lens groups It is composed of a single lens, and the three lens groups are moved to change the magnification. The focal length of the i-th group is Fi, the focal length of the entire system at the wide-angle end is Fw, and the i-th group and the (i+1 ) A simple method characterized by satisfying the following conditions: -2.8<F1/Fw<-1.3 0.11<E1W/Fw<0.25, where EiW is the principal point interval at the wide-angle end of the group. Composition zoom lens. (2) Let EiT be the principal point interval at the telephoto end of the i-th group and the (i+1)-th group, and let Ni and νi be the refractive index and Abbe number of the lens material of the i-th group, respectively. -1<F2/ F3<
-0.6 -0.3<(E1W-E1T)/(E2W-E2T)<
0.20.16<(N1+N3)/2-N2<0.45
2. The simply constructed zoom lens according to claim 1, wherein the zoom lens satisfies the following condition: ν1<ν3<ν2. (3) an aspherical surface is applied to the object-side lens surface of the first group, an aspherical surface is applied to the image-side lens surface of the second group, and an aspherical surface is applied to the object-side lens surface of the third group; When the fourth-order aspheric coefficient of the aspheric surface of the i-th group is Bi, and the diagonal length of the effective screen is Y, -15<B1・Y^3<-1 -7<B2・Y^3<-0.1 3. A zoom lens having a simple configuration according to claim 2, wherein the zoom lens satisfies the following condition: |B3·Y^3|<2.