JPH06214157A - Zoom lens - Google Patents

Abstract

PURPOSE:To provide a high variable power and high-performance zoom lens in spite of short entire length. CONSTITUTION:A first lens group 11 having positive refracting power, a second lens group 12 having positive refracting power, a third lens group 13 having positive refracting power, and a fourth lens group 14 having negative refracting power are arranged in that order; and in the case of performing variable power, the first, the second, the third, and the fourth lens groups 11-14 are moved on an optical axis and in the same direction, and also the third lens group is moved on the optical axis 50 so that image surface correction is substantially performed, and 1.3>Bd/Fw>0 is satisfied in the case the lens entire length of the first lens group 11 is Bd and the focal distance of a lens system on a wide-angle end is Fw.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens having a high zoom ratio, a compact size and a simple structure, and is suitable for a compact lens shutter camera.

[0002]

2. Description of the Related Art In recent years, compact cameras have
Lens drive systems and electric systems that control them are becoming smaller and more sophisticated. Along with this, there is a demand for a lens system that is also small and has a high zoom ratio in order to obtain an enlarged photographing area. Currently 2 as a zoom lens for compact cameras
Many group configurations or three-group configurations have been proposed, but 2
As for the group configuration, since the magnification is changed by one group, it is easy to increase the size at high magnification. In addition, although the three-group configuration can obtain a relatively high zoom ratio, it becomes difficult to correct variations of various aberrations during zooming.

As a solution to the above-mentioned problems, for example, Japanese Patent Laid-Open Nos. 3-50516 and 3-8.
As proposed in Japanese Patent No. 5508, there is a four-group zoom lens in which the first lens group is positive, the second lens group is positive, the third lens group is positive, and the fourth lens group is negative.

However, the high-magnification four-group zoom lens has a large number of lenses and tends to have a large front lens diameter, so that it cannot be said to be suitable for a compact camera.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a zoom lens system having a high zoom ratio, a compact size and a high performance while suppressing the number of lens components.

[0006]

According to the present invention, a first lens group having a positive refractive power, a second lens group having a positive refractive power, a third lens group having a positive refractive power, and a fourth lens group having a negative refractive power are provided. Put the lens groups in order,
Upon zooming, the first, second, and fourth lens groups are moved in the same direction on the optical axis, and the third lens group is moved on the optical axis so as to substantially perform image plane correction. When the total lens length is Bd and the focal length of the lens system at the wide-angle end is Fw,

[0007]

[Outside 3] The zoom lens is constructed so as to satisfy the conditional expression of.

[0008]

1 shows the basic arrangement of an embodiment of the invention in a thin-walled system.

Reference numeral 11 is a first lens group having a positive refractive power, 12 is a second lens group having a positive refractive power, 13 is a third lens group having a positive refractive power, and 14 is a fourth lens group having a negative refractive power. Are sequentially arranged from the object side. Reference numeral 15 indicates an image plane.

The first lens group 11, the second lens group 12, and the fourth lens group 14 move on the optical axis so as to draw a non-integral linear trajectory from the wide-angle end to the telephoto end of zooming, and the third lens group The lens group 13 moves on the optical axis so as to draw a non-linear locus in order to compensate the movement of the image plane.

2 to 5 each show a zoom lens composed of a thick-walled system, and lens data will be described later. Reference numerals 11 to 14 denote the same lens group as in FIG. 1, and S denotes a diaphragm which moves integrally with the second lens group.

As described above, in the first lens group 11, the total lens length is Bd, and the focal length of the lens system on the wide angle side is Fw.
Then, the following expression is satisfied.

[0013]

[Outside 4]

This condition relates to the reduction of the total lens length and the diameter of the front lens of the lens. The lower limit of the conditional expression is to have a finite thickness. On the other hand, if the upper limit is exceeded, the total length of the first lens group becomes too long, which leads to an increase in the overall length of the lens system. When the one lens unit is arranged closer to the image plane, the position of the entrance pupil moves toward the image plane, and it becomes difficult to achieve a compact lens system with an increase in the diameter of the front lens.

Further, the second lens group is composed of at least one negative lens and at least one positive lens, so that chromatic aberration is well corrected over the entire zoom range. Further, the first object side closest to the object in the second lens group.
The lens surface is configured so that the concave surface faces the object side, and the final lens surface closest to the image surface faces the convex surface toward the image surface side.

This first lens surface is a surface having a strong negative power and has a function of increasing the Petzval sum to a negative value and correcting spherical aberration and outward coma. Further, since the final lens surface has a positive power, it has a role of correcting an excessive correction action by the final lens surface.

On the other hand, it is preferable that at least one negative lens and at least one positive lens are arranged in the third lens group. With this configuration, the residual chromatic aberration and spherical aberration generated in the second lens group are satisfactorily corrected. ing. In the present embodiment, the number of negative and positive lenses is small and the cemented structure is used in consideration of the compactness of the lens system and the cost. However, the number of constituent members may be increased for better optical performance. However, it is effective to introduce an aspherical surface, and it can be used in general.

When the focal length of the first lens surface of the second lens group is fa and the focal length of the final lens surface is fb, it is convenient to satisfy the following conditional expression.

[0019]

[Outside 5]

Conditional expression (2) represents the ratio of the power of the final lens surface to the first lens surface, and when the upper limit is exceeded, the power of the first lens surface becomes weaker than the power of the final lens surface. Then, the spherical aberration is undercorrected, and the Petzval sum increases positively, so that the image surface tends to be under-corrected and it becomes difficult to correct it. on the other hand,
If the lower limit is exceeded, overcorrected high-order spherical aberration is likely to occur, which is not good.

If the average Abbe number of the positive lenses in the third lens group is vp and the average Abbe number of the negative lenses is vn, it is desirable to satisfy the condition of vp-vn> 15 (3). If the range of conditional expression (3) is exceeded, correction of chromatic aberration in the third lens group will be insufficient,
It is difficult to obtain good chromatic aberration over the entire zooming range even if the correction action of other lens groups is used. In the embodiment, the third lens group is composed of one lens for each of positive and negative, but in consideration of the case where a plurality of positive lenses and negative lenses are included, the expression is called the average of Abbe numbers.

The fourth lens group is composed of a positive meniscus lens having a concave surface facing the object side and two negative lenses having a concave surface facing the object side.

As the focusing method in this embodiment, the second lens group 12 and the third lens group 13 are integrally moved to the object side to focus on a short-distance object. The lens group may be focused integrally, or the fourth lens group may be moved to the image side.

Next, examples of the present invention will be shown. 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 gap in order from the object side, and ni and vi are the i-th lens in order from the object side, respectively. Is the refractive index and Abbe number of the glass.

The aspherical coefficients K, A, B, C, D and E are given by

[0026]

[Outside 6] Shall be given in. However, X is the amount of displacement from the lens vertex in the optical axis direction, h is the distance from the optical axis, and R is the radius of curvature.

[0027]

[Outside 7]

[0028]

[Outside 8]

[0029]

[Outside 9]

[0030]

[Outside 10]

[0031]

[Table 1]

[0032]

According to the present invention described above, it is possible to achieve a compact zoom lens having a variable magnification ratio of about 2.8 and a high optical performance as shown in the aberration diagram with a small number of lenses.

[Brief description of drawings]

FIG. 1 is a diagram of a thin-walled system according to an embodiment of the present invention.

FIG. 2 is a lens cross-sectional view of Example 1.

FIG. 3 is a lens cross-sectional view of Example 2.

FIG. 4 is a lens cross-sectional view of Example 3.

FIG. 5 is a lens cross-sectional view of Example 3.

FIG. 6 is a diagram of various types of aberration in Numerical example 1.

FIG. 7 is a diagram of various types of aberration in Numerical example 2.

FIG. 8 is a diagram showing various types of aberration in Numerical Example 3.

FIG. 9 is a diagram of various types of aberration in Numerical example 4.

[Explanation of symbols]

 11 1st lens group 12 2nd lens group 13 3rd lens group 14 4th lens group S.I. C. Curve showing sine condition ΔS Sagittal image plane ΔM Meridional image plane

Front Page Continuation (72) Inventor Makoto Misaka 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Takeshi Koyama 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (6)

[Claims] 1. A first lens group having a positive refractive power, a second lens group having a positive refractive power, a third lens group having a positive refractive power, and a fourth lens group having a negative refractive power are arranged in order, and At the time of magnification, the first, second, and fourth lens groups are moved in the same direction on the optical axis, and the third lens group is moved on the optical axis so as to substantially perform image plane correction, and the lens of the first lens group is moved. When the total length is Bd and the focal length of the lens system at the wide angle end is Fw, A zoom lens that satisfies the conditional expression of. 2. The second lens group includes at least one negative lens and at least one positive lens, the first lens surface of the second lens group has a concave surface facing the object side, and the final lens surface has an image surface. The convex surface is directed to the side.
Zoom lens. 3. When the focal length of the first lens surface of the second lens group is fa and the focal length of the final lens surface of the second lens group is fb, The zoom lens according to claim 3, wherein the conditional expression is satisfied. 4. The zoom lens according to claim 1, wherein the third lens group includes at least one negative lens and at least one positive lens. 5. If the average Abbe number of the positive lenses in the third lens group is vp and the average Abbe number of the negative lenses is vn, then vp-vn> 15 is satisfied. Zoom lens. 6. The fourth lens group includes a positive meniscus lens having a concave surface facing the third group, and a negative lens having a concave surface facing the third group behind the positive meniscus lens. Zoom lens.