JPH07234361A - Small-sized zoom lens - Google Patents

Abstract

PURPOSE:To obtain the small-sized zoom lens which is shortened in overall lens length while having a power variation ratio of about 2 and a wide field angle, and also has high optical performance over the entire power variation range by composing the zoom lens of two groups and specifying the lens constitution of the respective lens groups. CONSTITUTION:The zoom lens has the 1st group L1 with positive refracting power and the 2nd group L2 with negative refracting power in order from the object side and the interval between both the lens groups L1 and L2 is varied to vary the power. For the purpose, the 1st group L1 has four lenses which are a positive lens 11, a negative lens 12, a positive lens 13, and a positive lens 14, and the 2nd group L2 has two lenses which are a positive lens 21 and a negative lens 22. Then the conditions shown by the expressions are satisfied, where f1 is the focal length of the 1st group L1, fw the focal length of the whole system at the wide-angle end, DL11 the air gap between the lenses 11 and 12, DL21 the air gap between the lenses 21 and 22, and N, 2i the refractive indexes of the materials of the lenses 2i.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact zoom lens composed of two lens groups suitable for a lens shutter camera, a video camera, etc., and in particular, by properly setting the lens configuration of each lens group, aberration correction is possible. The present invention relates to a compact zoom lens having a wide angle of view and a zoom ratio of about 2, which is favorably performed and the overall lens length (distance from the first lens surface to the image surface) is shortened.

[0002]

2. Description of the Related Art Recently, with the downsizing of lens shutter cameras, video cameras, etc., there has been a demand for a compact zoom lens having a short overall lens length.

The applicant of the present invention has previously filed Japanese Patent Application Laid-Open No. 56-128911.
JP-A-57-201213 and JP-A-60-
-170816, JP-A-60-191216, JP-A-62-56917, etc., a first lens group having a positive refractive power and a second lens group having a negative refractive power are arranged in order from the object side.
We have proposed a so-called two-group zoom lens that is composed of one lens group and that varies the magnification by changing the distance between both lens groups.

In this publication, a positive / negative refractive power arrangement is adopted in order from the object side to provide a two-group zoom lens having high optical performance with a relatively short back focus and a shortened overall lens length. Has achieved.

Of these, in Japanese Patent Laid-Open No. 56-128911, a small zoom in which the first group is composed of four lenses, positive, negative, positive and positive, and the second group is composed of two lenses, positive and negative. I am proposing a lens.

In addition to these, Japanese Patent Laid-Open Nos. 62-284319, 62-256915, and 64-5.
No. 2111, JP-A-1-193807, etc., the first lens unit has a positive refractive power and the second lens unit has a negative refractive power, and both lens units are moved forward while changing the distance between the two lens units. There is disclosed a two-group zoom lens in which zooming is performed by doing so.

In addition to this, as a second group zoom lens, Japanese Patent Laid-Open No.
2-90611, JP-A-62-113120, and JP-A-3-116110, the first group is positive,
A two-group zoom lens composed of four lenses of negative, negative, and positive and having a zoom ratio of about 1.5 is disclosed.

[0008]

In the above-described two-group zoom lens composed of two lens groups, the first lens group having a positive refractive power and the second lens group having a negative refractive power, the overall lens system is downsized. In order to obtain good optical performance over the entire zoom range while having a zoom ratio of about 2 ×, it is necessary to set the lens configuration of each lens group appropriately.

For example, Japanese Patent Laid-Open No. 3-127008, 2
In the group zoom lens, the number of lenses is reduced to reduce the size of the entire lens system, but since a lot of aspherical surfaces are used, the assembly accuracy is severe and the optical performance is greatly degraded due to decentering. There is a point.

Generally, if the refractive powers of both the first and second groups are strengthened, the amount of movement of each lens group during zooming is reduced, and the total lens length can be shortened.

However, if the refracting power of each lens group is simply increased, the aberration variation due to zooming becomes large, and it becomes difficult to satisfactorily correct this.

According to the present invention, in a so-called two-group zoom lens, by appropriately setting the lens configuration of each lens group, it is possible to shorten the total lens length while having a wide angle of view especially at a zoom ratio of about 2. Another object of the present invention is to provide a compact zoom lens having high optical performance over the entire zoom range.

[0013]

A small zoom lens system according to the present invention comprises (1-1) two lens groups, a first lens group having a positive refractive power and a second lens group having a negative refractive power, in order from the object side. In a small-sized zoom lens having a variable magnification by changing the distance between both lens groups, the first group includes a positive eleventh lens, a negative twelfth lens, a positive thirteenth lens and a positive fourteenth lens. It has four lenses, the second group has two lenses, a positive 21st lens and a negative 22nd lens, the focal length of the first group is f1, and the focal length of the entire system at the wide-angle end is fw, 11th lens and 1st
The air gap between the two lenses is DL11, and the 21st and 22nd lenses are
When the air distance of the lens is DL21 and the refractive index of the material of the 2i-th lens is N, 2i 0.685 <f1 / fw <0.855 (1a) 0 ≦ DL11 / fw <0.095. (2a) 0.115 <DL21 / fw <0.155 (3a) 1.48 <N, 21 <1.71 (4a) 1.65 <N, 22 <1.84 The feature is that the condition (5a) is satisfied.

In particular, the focal length of the entire system at the telephoto end is f
When T is set, 0.385 <f1 / fT <0.495 (6a) is satisfied, and when the focal length of the eleventh lens is f11, 0.75 <f11 / fw <1 .83 (7a) is satisfied.

(1-2) It has two lens groups, a first lens group having a positive refractive power and a second lens group having a negative refractive power, in order from the object side, and performs zooming by changing the distance between both lens groups. In a compact zoom lens, the first group has four lenses, namely, a positive eleventh lens, a negative twelfth lens, a positive thirteenth lens and a positive fourteenth lens, and the second group has a positive first lens. It has two lenses, a 21st lens and a negative 22nd lens, the focal length of the first group is f1, the focal length of the 11th lens is f11, and the focal lengths of the entire system at the wide-angle end and the telephoto end are fw, respectively. fT, 21st
When the air distance between the lens and the 22nd lens is DL21 and the refractive index of the material of the 2i-th lens is N, 2i 0.685 <f1 / fw <0.855 (1b) 0.385 <f1 / fT <0.495 (2b) 0.75 <f11 / fw <1.83 (3b) 0.1 <DL21 / fw <0.166 (4b) 1.48 <N, 21 <1.71 (5b) 1.65 <N, 22 <1.84 (6b) are satisfied.

In particular, when the air distance between the eleventh lens and the twelfth lens is DL11, the condition 0 ≦ DL11 / fw <0.095 (7b) is satisfied.

[0017]

1 to 4 are sectional views of lenses at wide-angle ends according to Numerical Embodiments 1 to 4 of the present invention.

In the figure, L1 is a first lens unit having a positive refractive power, and L2 is a second lens unit having a negative refractive power. Both lens units are moved toward the object side as indicated by arrows while reducing the distance between both lens units. It is moved to zoom from the wide-angle end to the telephoto end.

SP is a stop, which is arranged on the image plane side of the first lens unit in the present invention, and moves integrally with the first lens unit upon zooming. IP is the image plane.

In this embodiment, by adopting such a zoom system and the lens structure as described above, the total length of the lens can be shortened, in particular, the wide angle of view at the wide-angle end and the total length of the lens can be shortened. With a magnification ratio of about 2, aberration fluctuations due to zooming are corrected well, and high optical performance is obtained over the entire zoom range.

Next, the features of the lens structure of the two-group zoom lens according to the present invention will be described.

The first aspect of the two-group zoom lens of the present invention
Since the image forming performance of the group is enlarged while being corrected by the second group, the first group is desired to have a lens configuration capable of excellently correcting aberrations. Therefore, the first lens group has a basic structure of a triplet lens composed of three lenses, positive, negative and positive lenses, which are capable of excellent aberration correction as a single focus lens. Then, the third lens of the triplet lens is divided into two lenses, positive and positive, to form a total of four lens configurations of positive, negative, positive and positive lenses capable of good aberration correction.

In particular, a positive meniscus eleventh lens having a convex surface directed toward the object side, a negative twelfth lens having both concave lens surfaces, a positive thirteenth lens, and a positive fourteenth lens having both convex lens surfaces. By using four lenses, mainly spherical aberration, coma aberration, chromatic aberration, and the like are favorably corrected, and the assembling accuracy in lens assembling is relaxed.

Further, in the two-group zoom lens, the second lens group is located closer to the image plane, so that the lens outer diameter becomes larger. For this reason, if the second lens group is configured with a large number of lenses, the size of the lens system will be increased.

Therefore, in the present invention, it is constituted by two lenses having a predetermined shape. In particular, by constructing from two lenses, a meniscus-shaped positive 21st lens with the convex surface facing the image side and a meniscus-shaped negative 22nd lens with the convex surface facing the image surface side Off-axis aberrations such as mold distortion are well corrected.

In the compact zoom lens according to the present invention, the first lens unit having a positive refractive power and the second lens unit having a negative refractive power are arranged in order from the object side.
In a small-sized zoom lens having two lens groups and performing zooming by changing the distance between both lens groups, the first lens group is a positive first lens group.
It has four lenses, namely, a first lens, a negative twelfth lens, a positive thirteenth lens, and a positive fourteenth lens, and the second group has two lenses, a positive twenty-first lens and a negative twenty-second lens. The basic configuration is the lens configuration.

In the lens construction of the basic construction, one satisfying the above-mentioned conditional expressions (1a) to (5a) is defined as the first invention, and in order to further improve the optical performance, the conditional expression (6)
A) and (7a) are satisfied. In addition, in the lens configuration of the basic configuration, the above conditional expressions (1b) to (6)
The second invention satisfies the condition (b), and the conditional expression (7b) is satisfied in order to further improve the optical performance.

Next, the technical meanings of the conditional expressions according to the first and second inventions will be described. Conditional expression (1a),
(1b) relates to the refracting power of the first group, and the conditional expression (1a),
If the refractive power of the first group becomes too weak (the focal length is too long) beyond the upper limit of (1b), the movement amount of the first group at the time of zooming becomes large and the lens system becomes large. On the other hand, when the value goes below the lower limit, the refractive power of the first lens unit becomes too strong, and the amount of image shift with respect to the positional shift becomes large, so that a highly accurate lens holding mechanism is required and the holding mechanism becomes complicated, which is not preferable.

The conditional expressions (2a) and (7b) relate to the lens interval between the positive 11th lens and the negative 12th lens. If the upper limit of conditional expressions (2a) and (7b) is exceeded, the first
It becomes difficult to place the principal point position of the lens unit on the second lens unit side, and it becomes impossible to increase the focal length at the telephoto end. As a result, a sufficient zoom ratio cannot be obtained. The lower limit value corresponds to the case where the eleventh lens and the twelfth lens are cemented.

The conditional expressions (3a) and (4b) relate to the lens spacing between the 21st lens and the 22nd lens in the second lens group. If the upper limit of conditional expression (4b) is exceeded, it will be difficult to place the principal point position of the second lens unit near the first lens unit, and it will not be possible to increase the focal length at the telephoto end, resulting in sufficient zooming. The ratio cannot be obtained. More preferably, the conditional expression (3
It is better not to exceed the upper limit of a). When the value goes below the lower limit of the conditional expression (4b), the fluctuation of spherical aberration at the time of zooming at a high zoom ratio increases, which is not preferable. More preferably, the lower limit of conditional expression (3a) should not be exceeded.

Conditional expressions (4b) and (5b) are related to the refractive index of the material of the positive 21st lens, and if the refractive index exceeds the upper limit and becomes too high, the image plane becomes excessive on the telephoto side.
If the lower limit is exceeded and the refractive index becomes too low, the image surface will become underexposed on the wide angle side, which is not preferable.

The conditional expressions (5a) and (6b) relate to the refractive index of the material of the negative 22nd lens. If the upper limit is exceeded, the material cost of the lens material will increase significantly if the refractive index becomes too high, and the wide angle The image surface is under side. On the other hand, if the value goes below the lower limit, distortion becomes large on the wide angle side, which is not good.

Conditional expressions (6a) and (2b) relate to the ratio of the focal length at the telephoto end of the entire lens system to the first lens group. If the upper limit is exceeded, the amount of movement of the first lens group during zooming becomes large. The system becomes large. If the value goes below the lower limit, the displacement of the image with respect to the displacement of the first group becomes large, and a highly accurate lens holding mechanism is required, and the holding mechanism becomes complicated.

Conditional expressions (7a) and (3b) relate to the positive focal length of the eleventh lens, and if the refracting power is weakened beyond the upper limit value, the negative refracting power of the negative twelfth lens is also corrected in order to satisfactorily correct spherical aberration. Need to weaken.

As a result, the positive distortion becomes large on the wide angle side, and it becomes difficult to satisfactorily correct coma. On the other hand, when the value goes below the lower limit, the positive refracting power of the eleventh lens becomes strong, it becomes difficult to position the principal point position of the first lens unit on the second lens unit side, and a sufficient zoom ratio cannot be obtained.

In order to further reduce the aberration variation due to zooming and to have a high optical performance over the entire zoom range and to shorten the total lens length, the conditional expressions according to the first invention and the second invention are given as follows. It is better to set it as follows.

First, the conditional expressions (1a) to (7) according to the first invention.
a), 0.728 <f1 / fw <0.813 0.024 <DL11 / fw <0.072 0.125 <D21 / fw <0.147 1.53 <N, 21 <1.66 1. It is preferable that 70 <N, 22 <1.81 0.405 <f1 / fT <0.445 0.85 <f11 / fw <1.45.

Conditional expressions (1b) to (7b) according to the second invention.
0.728 <f1 / fw <0.813 0.405 <f1 / fT <0.445 0.85 <f11 / fw <1.45 0.115 <D21 / fw <0.155 1.53 < It is preferable that N, 21 <1.66 1.70 <N, 22 <1.81 0.024 <DL11 / fw <0.072.

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 in order from the object side, Di is the i-th lens thickness and air gap from the object side, and Ni and νi are respectively from the object side of the i-th lens. The refractive index of glass and the Abbe number. Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples.

Numerical Example 1 f = 36.10 to 67.9 fno = 1: 4.31 to 8.10 2ω = 61.9 ° to 35.4 ° R 1 = 14.06 D 1 = 2.20 N 1 = 1.57501 ν 1 = 41.5 R 2 = 46.68 D 2 = 1.18 R 3 = -21.33 D 3 = 0.80 N 2 = 1.83400 ν 2 = 37.2 R 4 = 21.33 D 4 = 2.29 R 5 = 45.12 D 5 = 4.01 N 3 = 1.48749 ν 3 = 70.2 R 6 = -18.27 D 6 = 0.15 R 7 = 56.47 D 7 = 2.50 N 4 = 1.60311 ν 4 = 60.7 R 8 = -25.23 D 8 = 1.20 R 9 = (Aperture) D 9 variable R10 = -27.97 D10 = 2.50 N 5 = 1.60342 ν 5 = 38.0 R11 = -17.61 D11 = 4.79 R12 = -14.06 D12 = 1.30 N 6 = 1.78590 ν 6 = 44.2 R13 = -85.01

[0041]

[Table 1] <Numerical Example 2> f = 36.09 to 67.9 fno = 1: 4.31 to 8.11 2 ω = 61.9 ° to 35.3 ° R 1 = 14.98 D 1 = 2.00 N 1 = 1.53172 ν 1 = 48.9 R 2 = 69.43 D 2 = 1.23 R 3 = -18.81 D 3 = 0.80 N 2 = 1.80610 ν 2 = 41.0 R 4 = 26.94 D 4 = 3.16 R 5 = 147.89 D 5 = 2.49 N 3 = 1.48749 ν 3 = 70.2 R 6 = -14.85 D 6 = 0.15 R 7 = 33.07 D 7 = 3.02 N 4 = 1.48749 ν 4 = 70.2 R 8 = -28.68 D 8 = 1.20 R 9 = (Aperture) D 9 Variable R10 = -27.07 D10 = 2.30 N 5 = 1.63980 ν 5 = 34.5 R11 = -17.32 D11 = 4.59 R12 = -13.95 D12 = 1.30 N 6 = 1.79952 ν 6 = 42.2 R13 = -78.84

[0042]

[Table 2] Numerical Example 3 f = 36.09 to 67.9 fno = 1: 4.31 to 8.11 2 ω = 61.9 ° to 35.4 ° R 1 = 18.29 D 1 = 2.00 N 1 = 1.74077 ν 1 = 27.8 R 2 = 46.79 D 2 = 1.18 R 3 = -18.12 D 3 = 2.80 N 2 = 1.84666 ν 2 = 23.8 R 4 = 41.99 D 4 = 0.71 R 5 = -52.69 D 5 = 4.23 N 3 = 1.54814 ν 3 = 45.8 R 6 = -15.19 D 6 = 0.15 R 7 = 30.53 D 7 = 1.96 N 4 = 1.57501 ν 4 = 41.5 R 8 = -28.53 D 8 = 1.20 R 9 = (Aperture) D 9 Variable R10 = -27.44 D10 = 2.30 N 5 = 1.54814 ν 5 = 45.8 R11 = -17.57 D11 = 5.26 R12 = -14.50 D12 = 1.30 N 6 = 1.78590 ν 6 = 44.2 R13 = -88.74

[0043]

[Table 3] Numerical Example 4 f = 36.09 to 67.9 fno = 1: 4.31 to 8.11 2 ω = 61.9 ° to 35.4 ° R 1 = 14.35 D 1 = 2.00 N 1 = 1.58144 ν 1 = 40.8 R 2 = 37.91 D 2 = 1.25 R 3 = -19.60 D 3 = 1.04 N 2 = 1.83400 ν 2 = 37.2 R 4 = 24.47 D 4 = 1.45 R 5 = 60.68 D 5 = 4.70 N 3 = 1.48749 ν 3 = 70.2 R 6 = -16.72 D 6 = 0.15 R 7 = 38.33 D 7 = 2.50 N 4 = 1.56384 ν 4 = 60.7 R 8 = -25.72 D 8 = 1.20 R 9 = (Aperture) D 9 Variable R10 = -26.16 D10 = 2.30 N 5 = 1.57501 ν 5 = 41.5 R11 = -17.22 D11 = 5.13 R12 = -13.97 D12 = 1.30 N 6 = 1.75700 ν 6 = 47.8 R13 = -87.92

[0044]

[Table 4]

[0045]

[Table 5]

[0046]

According to the present invention, the total lens length can be shortened by setting the lens configuration of each lens group of the zoom lens that performs zooming by moving two lens groups having a predetermined refractive power. It is possible to achieve a small-sized zoom lens having a simple configuration, which has high optical performance over the entire zooming range with a zooming ratio of about 2.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view of Numerical Example 1 of the present invention.

FIG. 2 is a lens cross-sectional view of Numerical Example 2 of the present invention.

FIG. 3 is a lens cross-sectional view of Numerical Example 3 of the present invention.

FIG. 4 is a lens cross-sectional view of Numerical Example 4 of the present invention.

FIG. 5 is an aberration diagram at the wide-angle end according to Numerical Example 1 of the present invention.

FIG. 6 is an intermediate aberration diagram of Numerical example 1 of the present invention.

FIG. 7 is an aberration diagram at a telephoto end according to Numerical Example 1 of the present invention.

FIG. 8 is an aberration diagram at a wide-angle end according to Numerical Example 2 of the present invention.

FIG. 9 is an intermediate aberration diagram of Numerical example 2 of the present invention.

FIG. 10 is an aberration diagram at a telephoto end according to Numerical Example 2 of the present invention.

FIG. 11 is an aberration diagram at a wide-angle end according to Numerical Example 3 of the present invention.

FIG. 12 is an intermediate aberration diagram of Numerical Example 3 of the present invention.

FIG. 13 is an aberration diagram at a telephoto end according to Numerical Example 3 of the present invention.

FIG. 14 is an aberration diagram at the wide-angle end according to Numerical Example 4 of the present invention.

FIG. 15 is an intermediate aberration diagram of Numerical Example 4 of the present invention.

FIG. 16 is an aberration diagram at a telephoto end according to Numerical Example 4 of the present invention.

[Explanation of symbols]

 L1 1st group L2 2nd group SP aperture IP image plane d d line g g line S sagittal image plane M meridional image plane

Claims (5)

[Claims] 1. A compact zoom lens system having two lens units, a first lens unit having a positive refractive power and a second lens unit having a negative refractive power, which are arranged in order from the object side, and performing zooming by changing the distance between both lens units. In the lens, the first group is a positive eleventh lens, a negative twelfth lens,
It has four lenses, a positive thirteenth lens and a positive fourteenth lens, the second group has two lenses, a positive twenty-first lens and a negative twenty-second lens, and a focal length of the first group. F
1, the focal length of the entire system at the wide-angle end is fw, the air gap between the eleventh lens and the twelfth lens is DL11, the air gap between the twenty-first lens and the twenty-second lens is DL21, the refractive index of the material of the second i lens is N, 2i 0.685 <f1 / fw <0.855 0 ≦ DL11 / fw <0.095 0.115 <DL21 / fw <0.155 1.48 <N, 21 <1.71 1.65 < A compact zoom lens characterized by satisfying the condition of N, 22 <1.84. 2. The compact zoom lens according to claim 1, wherein the condition of 0.385 <f1 / fT <0.495 is satisfied when the focal length of the entire system at the telephoto end is fT. 3. The compact zoom lens according to claim 1, wherein the condition of 0.75 <f11 / fw <1.83 is satisfied when the focal length of the eleventh lens is f11. 4. A compact zoom having two lens groups, a first lens group having a positive refractive power and a second lens group having a negative refractive power, in order from the object side, and varying the distance between both lens groups to perform zooming. In the lens, the first group is a positive eleventh lens, a negative twelfth lens,
It has four lenses, a positive thirteenth lens and a positive fourteenth lens, the second group has two lenses, a positive twenty-first lens and a negative twenty-second lens, and a focal length of the first group. F
1, the focal length of the 11th lens is f11, the focal lengths of the entire system at the wide-angle end and the telephoto end are fw and fT, the air gap between the 21st and 22nd lenses is DL21, and the refractive index of the material of the 2ith lens is N, 2i 0.685 <f1 / fw <0.855 0.385 <f1 / fT <0.495 0.75 <f11 / fw <1.83 0.1 <DL21 / fw <0.166 A small zoom lens characterized by satisfying the conditions of 1.48 <N, 21 <1.71 1.65 <N, 22 <1.84. 5. The compact zoom lens according to claim 4, wherein a condition of 0 ≦ DL11 / fw <0.095 is satisfied when an air gap between the eleventh lens and the twelfth lens is DL11.