JP2775964B2 - Zoom lens with simple configuration - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a zoom lens suitable for a photographic camera, a video camera, and the like, and in particular, has three lens groups preceding a lens group having a negative refractive power, These three lens groups are composed of a single lens, and the three lens groups are moved to change the magnification. It is about a lens.

(Prior Art) Conventionally, there are three lens groups, a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a third lens group having a negative refractive power. The present applicant has proposed, for example, Japanese Patent Application Laid-Open No. 63-271214 and Japanese Patent Application Laid-Open No. 64-72114 for a zoom lens in which zooming is performed by moving a group.

This type of zoom lens is relatively widely used as a photographing system for a wide angle of view because it is relatively easy to widen the angle of view.

In this publication, the first, second, and third groups are moved under a certain condition to perform zooming, and the lens configuration of the three lens groups is specified to correct aberration fluctuations accompanying zooming well. 8 to 9 as a whole with a zoom ratio of 2 to 3 times having optical performance
A relatively compact zoom lens, particularly a lens shutter camera, consisting of two lenses has been achieved.

(Problems to be Solved by the Invention) The zoom lenses proposed in the above-mentioned JP-A-63-271214 and JP-A-64-72114 each comprise two or more lenses in each lens group. For example, the chromatic aberration is corrected within each lens unit, and the refractive power of each lens unit is increased to shorten the overall optical length (the distance from the first lens surface to the imaging surface).

The present invention makes use of the refractive power arrangement of the zoom lens previously proposed by the present applicant, further improves the lens configuration of each lens group, particularly aims at ultimate reduction of the number of lenses, and a zoom ratio of 2
With good optical performance over the entire zoom range
It is an object of the present invention to provide a zoom lens having a simple configuration with a number of about 3.6 and particularly suitable for a lens shutter camera.

(Means for Solving the Problems) The zoom lens having a simple configuration according to the present invention includes, in order from the object side, a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a zoom lens 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 perform zooming. The focal length of the i-th group is Fi, When the focal length at the wide-angle end of the entire system is Fw, and the interval between principal points at the wide-angle end of the i-th lens unit and the (i + 1) -th lens unit is Eiw, -2.8 <F1 / Fw <-1.3 (1) 0.11 <E1W /Fw<0.25‥‥‥(2)

(Embodiment) FIGS. 1, 2 and 3 show numerical examples 1 and 2 of the present invention, respectively.
FIG. 4 is a sectional view of a few lenses. In the figure, I is the first negative refractive power.
Group II, the second group with positive refractive power, III the third with negative refractive power
The group and the arrow indicate the moving direction of each lens group when zooming from the wide-angle side to the telephoto side.

When zooming from the wide-angle end to the telephoto end, the zoom lens according to the present embodiment moves all three lens groups independently in the object side direction as shown in each figure. In particular, a predetermined zoom ratio is effectively obtained by greatly changing the distance between the second and third lens units. An aperture stop SP is arranged on the image plane side of the second lens unit, and moves integrally with the second lens unit during zooming.

As shown in FIGS. 1, 2, and 3, the zoom lens according to the present invention is composed of three lens units having, in order from the object side, negative, positive, and negative refractive powers. The first and third units having a negative refractive power are arranged on both sides of the zoom lens so that the refractive power arrangement during zooming has a substantially symmetric lens configuration. The first group employs a high-refractive-index high-dispersion glass, and the second group employs a low-refractive-index low-dispersion glass.

By adopting such a substantially symmetrical lens arrangement and using glass of an appropriate material, it is possible to correct the chromatic aberration in the entire lens system in a well-balanced manner without using a method of correcting chromatic aberration in each lens group as in the related art. I have to.
That is, the three lens groups cancel each other out. The first unit is a meniscus negative first lens having a convex surface facing the object side, and the second unit is a positive second lens having both convex lens surfaces having a strong refractive power on the image surface side. Even if the third lens unit is made up of a meniscus-shaped negative third lens with the convex surface facing the image surface side to reduce the overall length of the lens, various aberrations including chromatic aberration can be repaired in a well-balanced manner over the entire zoom range. And a zoom lens with high optical performance can be obtained.

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

Conditional expression (1) appropriately sets the negative refractive power of the first group,
This is for properly correcting various aberrations.

If the refractive power of the first lens unit becomes too strong beyond the upper limit of conditional expression (1), it becomes difficult to correct various aberrations in a well-balanced manner over the entire zoom range. If the refractive power of the first lens unit is too weak below the lower limit, it becomes difficult to satisfactorily correct axial chromatic aberration on the wide-angle side.

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

If the distance between the principal points of the first and second groups becomes too long beyond the upper limit of conditional expression (2), the effective lens diameter of the first group will increase, and the first group and the second lens will exceed the lower limit. If the distance between the principal points of the two groups is too short, the symmetry of the entire lens system will be lost, and it will be difficult to correct various aberrations in a well-balanced manner.

In addition, in order to favorably correct various aberrations while miniaturizing the entire lens system in the present invention, the i-th lens unit and the (i +
1) When the principal point interval at the telephoto end of the group is EiT, and the refractive index and Abbe number of the material of the lens of the i-th group are Ni and νi, respectively, −1 <F2 / F3 <−0.6 ‥‥‥ (3) It is preferable to satisfy the following condition: ν1 <3ν <2ν ‥‥‥ (6)

Conditional expression (3) is for appropriately setting the ratio between the refractive powers of the second group and the third group to effectively obtain a predetermined zoom ratio.

If the upper limit of conditional expression (3) is exceeded and the refractive power of the third lens unit becomes too weak, the amount of movement of the third lens unit for securing a predetermined zoom ratio increases, and the overall length of the lens increases. If the refractive power of the third lens unit 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 ratio of the amount of change in the principal point distance between the first and second units and the amount of change in the principal point distance between the second and third units during zooming from the wide-angle end to the telephoto end. Is set appropriately, and mainly to satisfactorily correct field curvature.

When the value exceeds the upper limit of conditional expression (4), the field curvature greatly changes in the negative direction when zooming from the wide-angle end to the telephoto end. On the other hand, if the value exceeds the lower limit, the field curvature greatly changes in the positive direction when zooming from the wide-angle end to the telephoto end, which is not good.

Conditional expression (5) is for appropriately setting the refractive index of the material of each lens group and mainly for favorably correcting the image surface characteristics.
Beyond the upper limit, the Petzval sum increases in the positive direction,
On the other hand, if the lower limit is exceeded, the Petzval sum increases in the negative direction, making it difficult to satisfactorily correct astigmatism in any case.

Conditional expression (6) is for appropriately setting the Abbe number of the material of each lens unit and favorably correcting axial 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 order to maintain good optical performance of the entire screen particularly over the entire zoom range in the present invention, an aspherical surface is used for the lens surface on the object side of the first lens unit, and an image surface side lens surface of the second lens unit is used. When an aspheric surface is applied to the lens surface on the object side of the third lens unit, the fourth-order aspherical coefficient of the aspheric surface of the i-th lens unit is Bi, and the diagonal length of the effective screen is Y. ^{B1 · Y 3 <-1 ‥‥ (} 7) -7 <B2 · Y 3 <-0.1 ‥‥ (8) | B3 · Y 3 | <2 ‥‥ (9) made it is better to satisfy the condition.

Conditional expressions (7) and (9) are mainly for favorably correcting field curvature.

If the upper limit of conditional expression (7) or the lower limit of conditional expression (9) is exceeded, it becomes difficult to satisfactorily correct the field curvature. If the lower limit value of the conditional expression (7) or the upper limit value of the conditional expression (9) is exceeded, the aspherical effect becomes too strong, and the field curvature becomes excessively corrected.

If the upper limit of conditional expression (8) is exceeded, the aspherical effect will be too weak, making it difficult to satisfactorily correct spherical aberration. On the other hand, if the value exceeds the lower limit, spherical aberration will be overcorrected, which is not good.

Next, numerical examples of the present invention will be described. In the numerical examples, Ri
Is the radius of curvature of the i-th lens surface in order from the object side, Di is the i-th lens thickness and air spacing from the object side, Ni and νi
Are the refractive index and Abbe number of the glass of the i-th lens in order from the object side.

The aspheric surface has an X-axis in the optical axis direction and H in the direction perpendicular to the optical axis.
R and paraxial radius of curvature, A, B, C, D,
When E is each aspheric coefficient It is represented by the following equation.

Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples.

(Effects of the Invention) According to the present invention, by specifying the refractive powers and the lens configurations of the three lens groups as described above, it is possible to reduce the size of the entire lens system and to achieve a good zooming ratio over the entire zoom range of about 2. A zoom lens having excellent optical performance can be achieved.

[Brief description of the drawings]

FIGS. 1, 2, and 3 are numerical examples 1, 2, and 3, respectively, of the present invention.
3 is a sectional view of a lens, and FIGS. 4, 5, and 6 are various aberration diagrams of Numerical Examples 1, 2, and 3, respectively. In the lens cross-sectional views, I, II, and III indicate the first, second, and third groups, respectively, and arrows indicate the moving direction of each lens group during zooming from the wide-angle end to the telephoto end. B) are aberration diagrams at the wide-angle end and the telephoto end, respectively, d is a d-line, g is a g-line, SC is a sine condition, ΔS is a sagittal image, ΔM is a meridional image plane,
Y is the image height.

Claims (3)

(57) [Claims] 1. A lens system comprising: a first lens unit having a negative refractive power, a second lens unit having a positive refractive power, and a third lens unit having a negative refractive power. Is composed of a single lens and the three lens units are moved to perform zooming. The focal length of the i-th unit is Fi, the focal length at the wide-angle end of the entire system is Fw, and the i-th unit and the ( (i + 1) When the principal point interval at the wide angle end of the group is EiW, −2.8 <F1 / Fw <−1.3 0.11 <E1W / Fw <0.25. 2. The distance between principal points at the telephoto end of the i-th lens unit and the (i + 1) -th lens unit is EiT, and the refractive index and Abbe number of the lens material of the i-th lens unit are Ni and νi, respectively. 2. A simple configuration zoom lens according to claim 1, wherein the following condition is satisfied. 3. An aspherical surface on the object-side lens surface of said group of bases,
An aspheric surface is applied to the lens surface on the image plane side of the second group, and an aspheric surface is applied to the lens surface on the object side of the third group. -15 when the diagonal length was used as a ^{Y <B1 · Y 3 <-1} -7 <B2 · Y 3 <-0.1 | B3 · Y 3 | < claim 2, wherein satisfies the 2 condition: Zoom lens with simple configuration.