JP2984501B2 - Zoom lens - Google Patents

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 and a compact and simple structure, and is suitable for a compact lens shutter camera.

[0002]

2. Description of the Related Art In recent years, compact cameras have
The miniaturization and high performance of the lens drive system and the electric system that controls it are progressing. Accordingly, there is a demand for a small lens system and a high zoom ratio in order to obtain an enlarged photographing area. Currently, there are 2 zoom lenses for compact cameras.
Many groups or three-groups have been proposed.
In the group configuration, since the magnification is changed by one group, the size is easily increased at a high magnification. Further, the three-group configuration can obtain a relatively high magnification, but it is difficult to correct fluctuations of various aberrations during zooming.

To solve the above problems, Japanese Patent Application Laid-Open Nos. 3-50516 and 3-8
As proposed in Japanese Patent No. 5508 and the like, 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, a high-magnification four-group zoom lens has a large number of components and a large front lens diameter, so that it has a drawback that it is not suitable for a compact camera.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a high-magnification, compact and high-performance zoom lens with a reduced number of lenses.

[0006]

In order to achieve the above object, the present invention provides, in order from the object side, a first positive lens unit, a second positive lens unit, a third positive lens unit, and a fourth negative lens unit. A lens group, and at the time of zooming, the first, second, and fourth lens groups move on the optical axis in the same direction, and the third lens group moves on the optical axis so as to substantially perform image plane correction. A moving zoom lens, wherein the first lens group is composed of two lenses, a negative lens and a positive lens, and the third lens group is composed of one cemented lens in which a negative lens and a positive lens are cemented. The total lens length of the group is Bd, the focal length of the lens system at the wide-angle end is Fw,
When the Abbe number of the positive lens in the third lens group is νp and the Abbe number of the negative lens in the third lens group is νn,

[0007]

[Outside 3] The zoom lens is configured to satisfy νp−νn> 15.

[0008]

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

Reference numeral 11 denotes a first lens group having a positive refractive power, 12 denotes a second lens group having a positive refractive power, 13 denotes a third lens group having a positive refractive power, and 14 denotes a fourth lens group having a negative refractive power. Are sequentially arranged from the object side. Reference numeral 15 denotes 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 locus from the wide-angle end to the telephoto end of zooming. The lens group 13 moves on the optical axis so as to draw a non-linear locus to compensate for the movement of the image plane.

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

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

[0013]

[Outside 4]

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

The second lens group comprises at least one or more negative lenses and at least one or more positive lenses, thereby satisfactorily correcting chromatic aberration over the entire zoom range. Further, the first object-side first lens in the second lens group
The lens surface has a concave surface facing the object side, and the final lens surface closest to the image surface has a convex surface facing the image surface.

The 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 outgoing coma. In addition, the last lens surface has a positive power, and thus has a role of correcting an excessive correction effect by the last lens surface.

On the other hand, the third lens group is composed of a single cemented lens in which a negative lens and a positive lens are cemented in consideration of compactness and cost. With this configuration, residual chromatic aberration and residual chromatic aberration generated in the second lens group are formed. Spherical aberration is well corrected. It is also effective to introduce an aspherical surface for better optical performance.

If 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. When the power exceeds the upper limit, the power of the first lens surface becomes weaker than the power of the final lens surface. Then, the spherical aberration becomes insufficiently corrected, and the Petzval sum increases positively, so that the image surface tends to be under, and it is difficult to correct this. on the other hand,
If the lower limit is exceeded, overcorrected high-order spherical aberration is likely to occur, which is not good.

In the present invention, the Abbe number of the positive lens constituting the third lens group is νp, and the Abbe number of the negative lens is νp.
Assuming that n, the condition of νp−νn> 15 (3) is satisfied. If the range of conditional expression (3) is exceeded, correction of chromatic aberration in the third lens group will be insufficient, and it will be difficult to obtain good chromatic aberration over the entire zooming range even with the correction action of the other lens groups.

The fourth lens unit 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 a focusing method in the present 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 integrally focused, or the fourth lens group may be moved to the image side.

Next, examples relating to 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 gap in order from the object side, and ni and νi are the i-th lens in order from the object side. Are the refractive index and Abbe number of the glass.

The aspheric coefficients K, A, B, C, D, and E are given by the following equations.

[0026]

[Outside 6] Shall be given by Here, 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 zoom ratio of about 2.8 times and having high optical performance as shown in the aberration diagram, with a small number of lenses.

[Brief description of the drawings]

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

FIG. 2 is a sectional view of a lens according to a first embodiment.

FIG. 3 is a sectional view of a lens according to a second embodiment.

FIG. 4 is a sectional view of a lens according to a third embodiment.

FIG. 5 is a sectional view of a lens according to a third embodiment.

FIG. 6 is a diagram showing various aberrations of Numerical Example 1.

FIG. 7 is a diagram showing various aberrations of Numerical Example 2.

FIG. 8 is a diagram showing various aberrations of Numerical Example 3.

FIG. 9 is a diagram showing various aberrations of Numerical Example 4.

[Explanation of symbols]

 11 First lens group 12 Second lens group 13 Third lens group 14 Fourth lens group C. Curve indicating sine condition ΔS Sagittal image plane ΔM Meridional image plane

(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. (56) References JP-A-3-17609 (JP, A) JP-A-3-50516 (JP, A) JP-A-3-85508 (JP, A) JP-A-3-208004 (JP, A) JP-A-3-241306 (JP, A) JP-A-3-249614 (JP, A) JP-A-4-303809 (JP, A) JP-A-4-338910 (JP, A) JP-A-5-264903 ( JP, A) JP-A-6-118305 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25 / 00-25/04

Claims (4)

(57) [Claims] 1. A first lens unit, a second positive lens unit, a third positive lens unit, and a fourth negative lens unit are arranged in this order from the object side. A zoom lens that moves the second and fourth lens groups in the same direction on the optical axis and the third lens group moves on the optical axis so as to substantially perform image plane correction; The third lens group is composed of one cemented lens in which a negative lens and a positive lens are cemented, and the third lens group is composed of a negative lens and a positive lens.
The total lens length of the lens group is Bd, the focal length of the lens system at the wide-angle end is Fw, the Abbe number of the positive lens of the third lens group is νp, and the Abbe number of the negative lens of the third lens group is vn. When [Outside 1] A zoom lens satisfying νp−νn> 15. 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. The zoom lens according to claim 1, wherein the convex surface is directed to the surface side. 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 is fb, 3. The zoom lens according to claim 2, wherein: 4. The fourth lens group includes a positive meniscus lens having a concave surface facing the object side and a negative lens behind the positive meniscus lens having the concave surface facing the object side.
Zoom lens.