JPH07140390A - Magnifying lens - Google Patents

Abstract

(57) [Summary] [Purpose] To reduce the cost of a zoom lens with a wide-angle four-group configuration. A first lens group having negative refracting power, a second lens group having positive refracting power, a third lens group having negative refracting power, and a fourth lens group having positive refracting power in order from the object side. And has the second lens group from the wide-angle end to the telephoto end,
When the third lens group and the fourth lens group are respectively moved on the optical axis toward the object side for zooming, and the focal lengths of the second lens group and the third lens group are f _II and f _III , respectively | Satisfy the condition of f _II / f _III | <1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable power lens, and is particularly suitable for video cameras, photographic cameras, etc., and has good optical performance over the entire variable power range while having a relatively small number of lenses. Relates to a variable power lens of about 2 times.

[0002]

2. Description of the Related Art Conventionally, as a variable power lens including a wide angle range suitable for a video camera, a photographic camera, etc., a first lens group having a negative refractive power, a second lens group having a positive refractive power, and a negative lens having a negative refractive power are used. A variable power lens including a third lens group and a fourth lens group having a positive refracting power and performing variable power by changing the air space of each lens group is already known, for example, JP-A-58-41.
No. 13, JP-A-5-19170, etc., and such a zoom lens has a zoom ratio of about 3 to 4 times.

Generally, a variable power lens which is preceded by a lens unit having a negative refractive power is suitable for a variable power lens having a variable power range mainly including a wide angle range because the front lens diameter can be made relatively small. In addition, in the variable power lens having the above-mentioned four-group structure, since the number of lens groups is relatively large, high zooming is possible.

Further, in Japanese Patent Laid-Open No. 1-216310, a zoom lens for a video camera has a zoom ratio of about 2 to 3 and the number of lenses in the entire system is 4 to 5 to reduce the cost, the size and the weight. A variable power lens has been proposed.

[0005]

In recent years, the weight and size of video cameras and photographic cameras have been reduced. On the other hand, cost reduction and weight reduction of variable power lenses have also been demanded. However, JP-A-58-4113 and JP-A-5-19 are mentioned above.
The variable power lens proposed in Japanese Patent Laid-Open No. 170, etc., has a relatively large variable power ratio, but has a large number of lenses and is large. Further, the above-mentioned Japanese Patent Laid-Open No. Hei 1 (Kokai) 1 which is intended to reduce cost and weight.
In Japanese Patent Laid-Open No. 216310, although the number of lenses is reduced with a variable power ratio of about 2 to 3, there is a problem that the total optical length of the entire system is large with respect to the image size.

According to the present invention, in a variable power lens of four groups having a predetermined refractive power, by appropriately setting the refractive power and lens configuration of each lens group, a variable power lens having good optical performance over the entire variable power range. It is an object of the present invention to provide a low-cost, small-sized variable magnification lens suitable for a video camera, a photographic camera, etc. having a small number of lenses with a magnification ratio of about 2.

[0007]

According to the present invention, in order from the object side, the first lens unit having a fixed negative refractive power during zooming, the second lens unit having a positive refractive power, and the third lens unit having a negative refractive power are arranged in this order. It has a lens group and a fourth lens group having a positive refractive power, and the second lens group, the third lens group, and the fourth lens group are respectively moved along the optical axis toward the object side from the wide-angle end to the telephoto end, and are changed. It is to be a variable power lens that performs a magnification.

Alternatively, the first lens group having a negative refractive power, the second lens group having a positive refractive power, and 1 in order from the object side.
And a fourth lens group having a positive refractive power, the second lens group from the wide-angle end to the telephoto end.
The lens group, the third lens group, and the fourth lens group are respectively moved on the optical axis toward the object side to perform zooming, and the focal lengths of the second lens group and the third lens group are f _II and f _III , respectively. Then, it is to satisfy the conditional expression | f _II / f _III | <1 (1).

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A variable power lens according to the present invention will be described below with reference to the drawings. In FIG. 1, I is a first lens group having a negative refracting power, II is a second lens group having a positive refracting power, III is a third lens group having a negative refracting power, I
V is a fourth lens group having a positive refractive power.

In this embodiment, by moving the second lens group, the third lens group, and the fourth lens group on the optical axis toward the object side while the first lens group is stationary, the wide-angle end to the telephoto end are moved. Scale. In the present embodiment, a small-sized zoom lens is achieved as a whole with a five-lens structure, a small number of lenses, and satisfying the above conditions.

In particular, the conditional expression (1) is defined by the second lens group and the third lens group.
With respect to the focal length of the lens group, in order to maintain a proper refracting power of the second lens group and the third lens group, it is possible to realize a compact variable power lens with small aberration variation due to variable power despite the small number of lenses. belongs to.

When the upper limit of conditional expression (1) is exceeded and the focal length of the second lens unit becomes larger than the focal length of the third lens unit and the refracting power of the second lens unit weakens, the amount of movement of each unit during zooming is increased. And the total length tends to increase, which is not preferable. Further, in order to obtain high optical performance over the entire zoom range without increasing the refracting power of the second lens group too much,
The lower limit of conditional expression (1) is set to 0.8.

The low-cost, small-sized and lightweight variable magnification lens aimed at by the present invention can be realized by satisfying the above-mentioned requirements, but further corrects various aberrations and is high over the entire variable power range. In order to realize a variable power lens having optical performance, it is desirable to satisfy the following conditions.

The focal lengths of the first lens group and the second lens group are f _I and f _II respectively, the focal length of the entire system at the telephoto end is f _T , and the focal length between the negative lens and the positive lens in the first group is between When the air gap is D and the optical total length of the entire system at the wide-angle end is l, 0.3 <(f _I / f _T ) ² <0.5 ... (2) 0.05 <(f _II / f _T ) ² <0.2 ... (3) 0.03 <D / l <0.12 ... (4).

In particular, when the first lens group is a focusing group, the amount of movement during focusing is appropriate, and
Since it is necessary to reduce aberration fluctuations, the ratio of the focal length of the first lens group to the focal length of the entire system at the telephoto end is defined by conditional expression (2).

If the refractive power of the first lens unit is too strong beyond the lower limit of conditional expression (2), the amount of movement during focusing will be small, and the first lens unit can be miniaturized. The aberration variation becomes large and it becomes difficult to correct with other groups, and if the upper limit is exceeded and the refractive power is too weak, the amount of movement during focusing increases and the size of the first lens group increases, which is preferable. Absent. More preferably, the lower limit value of conditional expression (2) is 0.4 and the upper limit value is 0.47.

Conditional expression (3) relates to the ratio between the focal length of the second lens group and the focal length of the entire system at the telephoto end, and by setting the refractive power of the second lens group appropriately, a predetermined zoom ratio is obtained. It is for suppressing the fluctuation of the aberration during zooming.

When the refracting power of the second lens unit is increased beyond the lower limit of conditional expression (3), the amount of movement at the time of zooming is reduced, but the spherical aberration and the coma are largely varied due to the zooming. At the telephoto end, the amount of aberration increases, which makes it difficult to correct the aberration. Further, when the refractive power of the second lens unit is weakened beyond the upper limit, the amount of movement during zooming increases and the total lens length increases. Not preferable.

Conditional expression (4) relates to the ratio between the air distance between the negative lens and the positive lens in the first lens group and the total lens length, and is mainly for suppressing fluctuations in spherical aberration and coma aberration due to zooming. When the air gap becomes narrower than the lower limit value, the refractive power of the positive lens of the first lens group becomes strong, the fluctuations of spherical aberration and coma aberration generated in the first lens group increase, and the upper limit value becomes If the air space is excessively widened beyond this, the thickness of the first lens group increases, and the total lens length increases, which is not preferable. Further, in order to correct various aberrations and appropriately set the total lens length, the lower limit value of conditional expression (4) is 0.05 and the upper limit value is 0.1.
Is desirable.

Specifically, in order to make up about five lenses, the first lens group is made up of a negative meniscus lens having a convex surface directed toward the object side and a positive meniscus lens having a convex surface directed toward the object side. The lens group is a positive lens whose convex surface faces the object, the third lens group is a negative meniscus lens whose convex surface faces the object side, and the fourth lens group is a biconvex single lens.

Further, in the present invention, the aspherical surface is effectively used to obtain high optical performance. For example, the first
When the lens group is composed of two lenses, a negative meniscus lens and a positive meniscus lens, the positive meniscus lens uses an aspherical surface with a curvature increasing toward the periphery, so that spherical aberration and astigmatism in the entire zoom range can be obtained. Is well balanced, and coma at the wide-angle end can be corrected. Further, by using an aspherical surface having a larger curvature toward the periphery for the positive lens of the second lens group, it is possible to mainly effectively correct spherical aberration. When each of the second to fourth groups is composed of one lens as in the present embodiment, the second to fourth groups are used.
Since it is difficult to select a single group from the group as a focusing group in terms of aberration correction, focusing is performed by multiple groups, or the first group is configured with two or more lenses and focusing is performed by the first group. Is desirable.

Next, numerical examples of the present invention will be shown. In the numerical examples, Ri is the radius of curvature of the i-th lens surface from the object side, Di is the i-th lens thickness and air gap from the object side, and Ni and Vi are the glasses of the i-th lens from the object side, respectively. Is the refractive index and the Abbe number.

In the numerical examples, the aspherical shape is such that the radius of curvature of the lens surface is R, the optical axis direction is the (light traveling direction) is the X axis, the direction perpendicular to the optical axis is the Y axis, and B, C, D, E
When each is an aspherical coefficient,

[0024]

[Outer 1] It is represented by the formula

Table 1 shows the relationship between the numerical examples of the present invention and the conditional expressions (1), (2), (3) and (4).

[0026]

[Outside 2]

[0027]

[Outside 3]

[0028]

[Outside 4]

[0029]

[Table 1]

[0030]

As described above, by setting the refracting power of each group, it is suitable for a video camera, a photographic camera, or the like, which has high optical performance over the entire zoom range and has a small zoom ratio of about 2 lenses. It is possible to realize a low cost, compact and lightweight variable power lens.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view of a zoom lens according to the present invention.

FIG. 2 is a diagram of various types of aberration in Numerical example 1.

FIG. 3 is a diagram of various types of aberration of Numerical example 2.

FIG. 4 is a diagram of various types of aberration of Numerical example 3.

[Explanation of symbols]

 I First lens group II Second lens group III Third lens group IV Fourth lens group SC Sine condition ΔS Sagittal image surface ΔM Meridional image surface d d line g g line

Claims (9)

[Claims] 1. A first lens group having a negative refracting power and fixed during zooming in order from the object side, a second lens group having a positive refracting power, a third lens group having a negative refracting power, and a positive lens group. Having a fourth lens group having a refractive power, and moving the second lens group, the third lens group, and the fourth lens group from the wide-angle end to the telephoto end on the optical axis toward the object side for zooming. A variable power lens featuring. 2. When the focal lengths of the second lens group and the third lens group are f _II and f _III , respectively, | f _II / f _III | <1 is satisfied. Variable magnification lens described. 3. When the focal lengths of the first lens group, the second lens group, and the entire system at the telephoto end are f _I , f _II , and f _T , respectively, 0.3 <(f _I / f _T ) ² The variable power lens according to claim 1, wherein the condition <0.5 0.05 <(f _II / f _T ) ² <0.2 is satisfied. 4. The first lens group has, in order from the object side, a negative meniscus lens convex toward the object side and a positive meniscus lens convex toward the object side, and an air gap between the negative lens and the positive lens is D, at a wide-angle end. 2. The variable power lens according to claim 1, wherein the condition that 0.03 <D / l <0.12 is satisfied, where l is the total optical length of the entire system. 5. The variable power lens according to claim 1 or 4, wherein the first lens group is moved on the optical axis to perform focusing. 6. A first lens element having a negative refractive power in order from the object side.
The second lens group having a lens group, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens group having a positive refractive power, and extending from the wide-angle end to the telephoto end. , The third lens group and the fourth lens group are respectively moved on the optical axis toward the object side for zooming, and the focal lengths of the second lens group and the third lens group are f _II and f _III , respectively. A variable power lens characterized by satisfying a condition of | f _II / f _III | <1. 7. When the focal lengths of the first lens group, the second lens group, and the entire system at the telephoto end are f _I , f _II , and f _T , respectively, 0.3 <(f _I / f _T ) ² 7. The variable power lens according to claim 6, wherein the condition <0.5 0.05 <(f _II / f _T ) ² <0.2 is satisfied. 8. The first lens group has, in order from the object side, a negative meniscus lens convex toward the object side and a positive meniscus lens convex toward the object side, and an air gap between the negative lens and the positive lens is D, at a wide-angle end. 7. The variable power lens according to claim 6, wherein the condition that 0.03 <D / l <0.12 is satisfied, where l is the total optical length of the entire system. 9. The variable power lens according to claim 6, wherein focusing is performed by moving the first lens group on the optical axis.