JP2000330022A - Zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a compact zoom lens whose variable power ratio is about 3, whose whole length is shortened and which is provided with high optical performance all over a whole variable power range by properly setting the lens constitution of respective lens groups and effectively utilizing an aspherical surface lens as the so-called zoom lens constituted of two groups. SOLUTION: This zoom lens is provided with the 1st lens group L1 having positive refractive power and the 2nd lens group L2 having negative refractive power. Then, a variable power action is executed to a telephoto end from a wide angle end by moving both lens groups to an object side while reducing a gap between them. The group L2 is provided with at least one aspherical surface. Then, when the focal distances of a whole system at the wide angle end and at the telephoto end are defined as (fW) and (fT), that of the group L2 is defined as f2, the lateral magnification of the group L2 at the wide angle end when an object distance is infinite is defined as β2W and that at the telephoto end when the object distance is infinite is defined as β2T, a conditional expression I: 0-31<|f2|/√(fW.fT)<0.36 and a conditional expression II: 2.95<β2T/β2W<3.1 are satisfied.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens, and more particularly to a zoom lens having a zoom ratio of about 3 and a simple lens barrel structure suitable for a still camera such as a lens shutter camera and an electronic still camera. Related to a zoom lens.

[0002]

2. Description of the Related Art Heretofore, as a zoom lens used for a lens shutter camera, a video camera, and the like, a small zoom lens which shortens and simplifies the entire length of the lens has been demanded.

Such a zoom lens has two lens groups, a first group having a positive refractive power and a second group having a negative refractive power, in order from the object side, and the distance between both lens groups is changed. A so-called two-group zoom lens having a relatively short overall lens length has been proposed, for example, in Japanese Patent Application Laid-Open Nos. 7-306361, 8-240771, 10-39212, and the like.

[0004] The present applicant also discloses Japanese Patent Application Laid-Open No. 56-128911.
JP, JP-A-57-201213, JP-A-57-201213
JP-A-170816, JP-A-60-191216, JP-A-62-56917, and the like, in order from the object side, a first group having a positive refractive power and a second group having a negative refractive power.
A small so-called two-unit zoom lens, which includes one lens unit and changes the magnification by changing the distance between the two lens units, has been proposed.

[0005] For example, Japanese Patent Application Laid-Open No. 56-128911
In the publication, the first group is composed of four lenses of positive, negative, positive and positive, and the second group is composed of two lenses of positive and negative, so as to simplify the whole lens system. A zoom lens is proposed.

As another two-group zoom lens, Japanese Patent Laid-Open No.
In Japanese Patent Application Laid-Open No. 3-31224, the first group is composed of four lenses of positive, negative, positive, and positive, and the second group is composed of two lenses of positive and negative, and each lens group has an aspheric surface. A small zoom lens with improved optical performance has been proposed.

Japanese Patent Application Laid-Open No. 4-161914 discloses a first method.
A zoom lens has been proposed in which the group is composed of four lenses, a positive lens, a negative lens, an aspheric lens, and a positive lens, the second group is composed of three lenses, and each lens group has an aspheric surface. I have.

Further, JP-A-62-90611, JP-A-62-113120, and JP-A-3-116110
In Japanese Patent Application Laid-Open Publication No. H11-264, a two-unit zoom lens having a zoom ratio of about 1.5, in which the first unit is composed of four lenses of positive, negative, negative, and positive, is proposed.

[0009]

SUMMARY OF THE INVENTION In the above-described two-unit zoom lens including the first lens unit having the positive refractive power and the second lens unit having the negative refractive power, the size of the entire lens system is reduced. In order to obtain a good optical performance over the entire zoom range, having a zoom ratio of about 3 times, appropriately set the lens configuration of each lens group and provide an aspheric surface of an appropriate shape to each lens group. Use is very effective in correcting aberrations.

However, even if an aspherical surface is used, if the refractive power arrangement and the lens configuration of each lens unit are inappropriate, aberration fluctuations accompanying zooming become large, and it is necessary to obtain high optical performance over the entire zooming range. It becomes difficult.

According to the present invention, in a so-called two-unit zoom lens, by appropriately setting the lens configuration of each lens unit and effectively using an aspherical lens, it is possible to reduce the overall length of the lens at a zoom ratio of about 3. It is an object of the present invention to provide a compact zoom lens having high optical performance over the entire zoom range.

[0012]

The zoom lens according to the present invention has a first lens unit having a positive refractive power and a second lens unit having a negative refractive power in order from the object side. In the zoom lens which performs zooming by changing the focal length, the first lens unit includes a positive eleventh lens and a negative twelfth lens whose both lens surfaces are concave.
A cemented lens in which a positive thirteenth lens whose both lens surfaces are convex and a negative fourteenth lens having a meniscus shape are cemented, a cemented lens surface having a concave surface facing the object side, and a positive fifteenth lens The second lens group includes a positive twenty-first lens and a negative meniscus second lens having a concave surface on the object side, and the second lens group has at least one aspheric surface, and has a wide angle. The focal lengths of the entire system at the end and the telephoto end are fW and fT, the focal length of the second lens unit is f2, and the lateral magnification of the second lens unit at the infinite object distance and the wide-angle end is β2.
W, when the lateral magnification of the second lens group at the telephoto end at infinite object distance is β2T

[0013]

(Equation 2)

It is characterized in that 2.95 <β2T / β2W <3.1３ (2).

[0015]

FIG. 1, FIG. 4, FIG. 7, and FIG. 10 are lens sectional views of Numerical Examples 1 to 4 of the present invention. In the lens sectional views, (A) shows the zoom position at the wide angle end, (B) shows the middle position, and (C) shows the zoom position at the telephoto end.

In the drawing, L1 denotes a first group having a positive refractive power, and L2 denotes a second group having a negative refractive power. While reducing the distance between the two lens groups, both lens groups are moved toward the object side as shown by arrows. The lens is moved to change the magnification from the wide-angle end to the telephoto end. SP denotes an aperture, which is moved integrally with the first lens unit in the present invention. still,
The aperture SP may be moved independently of the first lens unit.

The first lens unit L1 includes a positive meniscus eleventh lens having a convex surface facing the object side, a negative twelfth lens with both lens surfaces concave, and a positive thirteenth lens with both lens surfaces convex. A negative meniscus fourteenth lens having a convex surface facing the surface is cemented, and the cemented lens surface is composed of a cemented lens having a concave surface facing the object side and a positive 15th lens having a convex surface facing the image surface side. ing.

The second lens unit L2 includes a positive twenty-first lens having a convex surface facing the image surface side, and a negative meniscus twenty-second lens having a convex surface facing the image surface side.

The focusing is performed by moving the first group, the second group, or the entire system.

In the present embodiment, the first and second lens units are configured as described above, and conditional expressions (1) and (2) are used.
Is satisfied so as to obtain excellent optical performance over the entire zoom range and a zoom ratio of about 3 while simplifying the lens configuration.

Next, the technical meaning of conditional expressions (1) and (2) will be described. Conditional expression (1) defines the range of the focal length of the second lens unit. If the negative refractive power of the second lens unit exceeds the lower limit and the negative refractive power of the second lens unit becomes strong, the aberration variation during zooming increases. When it becomes difficult to correct in a well-balanced manner over the entire zoom range, and when the negative refractive power of the second lens unit is weakened beyond the upper limit, it becomes difficult to secure the necessary back focus at the wide-angle end. The outer diameters of the lenses of the two groups are also large, which is contrary to compactness.

Conditional expression (2) is for realizing a zoom ratio of about three times.
If the ratio of the lateral magnification of the second lens group to the lateral magnification of the second lens group at the wide-angle end becomes small, it becomes difficult to obtain a predetermined zoom ratio, and the lateral magnification of the second lens group at the telephoto end exceeds the upper limit. And the second at the wide-angle end
When the ratio of the lateral magnification of the group increases, the aberration variation due to the focal length increases, and it becomes difficult to correct the aberration with good balance.

The zoom lens which is the object of the present invention can be achieved by adopting the above-mentioned constitution. In order to obtain a high price performance over the entire screen with less aberration fluctuation over the entire zoom range, the following conditions are required. At least one of them should be satisfied.

(A-1) A stop is provided on the image plane side of the first lens group, and the stop moves integrally with the first lens group during zooming, and the first lens group during focusing. Only on the optical axis.

As described above, by fixing the aperture unit at the time of focusing, quick auto-focusing is enabled, and the lens barrel structure is simplified.

(A-2) The distance from the lens surface closest to the object side at the wide-angle end to the lens surface closest to the image plane is DW, the back focus at the wide-angle end is SKW, and the focal length of the first lens group. Is defined as f1, 0.20 <SKW / DW <0.25 (3) 1.20 <f1 / | f2 | <1.28 (4) 0.22 <f1 / fT < 0.25 ‥‥‥ (5)

Conditional expression (3) defines the ratio of the back focus SKW at the wide-angle end to the length DW from the lens surface closest to the object side at the wide-angle end to the lens surface closest to the image plane. When the back focus is shorter than the value, the outer diameter of the lens of the second group increases, which is not preferable. If the back focus becomes longer than the upper limit, it becomes difficult to satisfactorily correct coma and flare near a wide angle.

Conditional expression (4) defines the ratio of the focal length f1 of the first lens unit to the absolute value of the focal length f2 of the second lens unit. When it becomes stronger, it is a good direction for compactness, but it becomes difficult to correct various aberrations occurring in each lens group in a well-balanced manner.

When the positive refractive power of the first lens unit becomes weaker than the upper limit, the amount of movement of each lens unit for obtaining a predetermined zoom ratio increases, and the lens system increases.

Conditional expression (5) defines the ratio of the focal length f1 of the first lens unit to the focal length fT of the whole lens system at the telephoto end. When the ratio exceeds the lower limit, the positive refractive power of the first lens unit becomes larger. When it becomes stronger, it is a good direction for compactness, but it becomes difficult to correct various aberrations occurring in each lens group in a well-balanced manner. If the positive refractive power of the first unit becomes weaker than the upper limit, the amount of movement of each lens unit for obtaining a predetermined zoom ratio increases, and the lens system increases.

(A-3) When the Abbe number of the material of the twenty-first lens is ν21p and the Abbe number of the material of the twenty-second lens is ν22n, 0.004 <(1 / ν21p) − (1 / ν22n) <0.007 ‥ (6) 37 <ν21p <42 ‥‥‥ (7)

The conditional expressions (6) and (7) are mainly for axial chromatic aberration,
This is for correcting the chromatic aberration of magnification in a well-balanced manner from the wide-angle end to the telephoto end.

Conditional expression (6) defines the difference between the reciprocal of the Abbe number of the glass material of the positive twenty-first lens of the second group and the reciprocal of the Abbe number of the glass material of the negative twenty-second lens. When the difference is smaller than the lower limit, the fluctuation of the axial chromatic aberration at the time of zooming becomes larger, and when the difference is larger than the upper limit, the fluctuation of the axial chromatic aberration becomes smaller, but the fluctuation of the chromatic aberration of magnification becomes larger. Absent.

The conditional expression (7) is the second expression under the conditional expression (6).
The Abbe number of the material of the positive 21st lens of the group is specified. When the Abbe number is smaller than the lower limit and the axial chromatic aberration and the chromatic aberration of magnification at the time of zooming are both reduced,
If the value exceeds the upper limit, a glass material having a low refractive index is selected for the current optical glass, and spherical aberration, coma and the like are undesirably increased.

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 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.

Table 1 shows the relationship between the above-described conditional expressions and various numerical values in the numerical examples. The aspherical shape has an X-axis in the optical axis direction, an H-axis in a direction perpendicular to the optical axis, and a positive traveling direction of light. R is a paraxial radius of curvature, and K, B, C, D, and E are aspherical coefficients, respectively. When

[0037]

(Equation 3)

Is represented by the following equation. "E-0X" means "10- ^X ". (Numerical Example 1) f = 39.2 ~ 116.1 FNo = 1: 4.6 ~ 11.2 2ω = 57.8 ° ~ 21.1 ° r 1 = 14.697 d 1 = 3.01 n 1 = 1.65844 ν 1 = 50.9 r 2 = 79.646 d 2 = 1.34 r 3 = -32.228 d 3 = 1.78 n 2 = 1.83400 ν 2 = 37.2 r 4 = 12.248 d 4 = 0.77 r 5 = 17.775 d 5 = 5.64 n 3 = 1.51742 ν 3 = 52.4 r 6 = -8.584 d 6 = 1.09 n 4 = 1.80400 ν 4 = 46.6 r 7 = -17.909 d 7 = 0.20 r 8 = -233.779 d 8 = 2.92 n 5 = 1.57099 ν 5 = 50.8 r 9 = -13.500 d 9 = 0.75 r1O = 0.000 (aperture) d1O = Variable r11 = -63.948 d11 = 2.82 n 6 = 1.72727 ν 6 = 40.6 r12 = -28.012 (aspherical surface) d12 = 4.90 r13 = -11.059 d13 = 1.50 n 7 = 1.77250 ν 7 = 49.6 r14 = -85.405 Focal length 39.18 69.42 116.11 Variable spacing d 1O 14.05 6.39 2.39 skinf 8.70 33.58 71.99 Aspheric coefficient twelfth surface kbc 5.303122 e + 00 -1.545729 e-05 -3.790888 e-08 de -1.905367 e-09 8.551707 e-12 (Numerical example 2) f = 39.2 ~ 116.1 FNo = 1: 4.6 ~ 11.2 2ω = 57.8 ° ~ 21.1 ° r 1 = 14.025 d 1 = 2.93 n 1 = 1.65844 ν 1 = 50.9 r 2 = 68.037 d 2 = 1.01 r 3 = -34.851 d 3 = 1.69 n 2 = 1.83400 ν 2 = 37.2 r 4 = 12.310 d 4 = 0.70 r 5 = 19.928 d 5 = 4.51 n 3 = 1.51742 ν 3 = 52.4 r 6 = -8.316 d 6 = 0.98 n 4 = 1.80400 ν 4 = 46.6 r 7 = -16.864 d 7 = 1.51 r 8 = -232.200 d 8 = 2.58 n 5 = 1.57099 ν 5 = 50.8 r 9 = -13.271 d 9 = 0.70 r1O = 0.000 ( Aperture) d1O = variable r11 = -77.341 d11 = 2.97 n 6 = 1.72727 ν 6 = 40.6 r12 = -30.512 (aspheric surface) d12 = 4.85 r13 = -10.540 d13 = 1.50 n 7 = 1.77250 ν 7 = 49.6 r14 = -83.789 Focal length 39.18 69.03 116.11 Variable spacing d1O 12.78 5.97 2.35 skinf 9.12 32.74 69.99 Aspheric surface twelfth surface kbc 6.086091 e + 00 -2.868606 e-05 -1.260046 e-07 de -2.311025 e-09 -1.758096 e-12 (Numerical implementation Example 3) f = 39.2 ~ 116.1 FNo = 1: 4.6 ~ 11.2 2ω = 57.8 ° ~ 21.1 ° r 1 = 13.098 d 1 = 3.22 n 1 = 1.60311 ν 1 = 60.6 r 2 = 245.048 d 2 = 0.83 r 3 =- 30.696 d 3 = 1.70 n 2 = 1.83481 ν 2 = 42.7 r 4 = 11.306 d 4 = 1.12 r 5 = 19.000 d 5 = 4.77 n 3 = 1.51742 ν 3 = 52.4 r 6 = -7.829 d 6 = 0.99 n 4 = 1.83481 ν 4 = 42.7 r 7 = -16.479 d 7 = 0.18 r 8 = -126.805 d 8 = 2.71 n 5 = 1.57135 ν 5 = 53.O r 9 = -11.987 d 9 = 0.6 r1O = 0.000 (aperture) d1O = variable r11 = -39.377 (aspheric surface) d11 = 0.05 n 6 = 1.52421 ν 6 = 51.4 r12 = -166.000 d12 = 2.29 n 7 = 1.72342 ν 7 = 38. O r13 = -33.590 d13 = 5.59 r14 = -10.321 d14 = 1.50 n 8 = 1.77250 ν 8 = 49.6 r15 = -39.486 Focal length 39.18 64.82 116.11 Variable spacing d1O 13.26 7.20 3.12 skinf 8.80 29.42 70.66 Aspheric coefficient eleventh surface kbc 5.032013 e + 00 8.153513 e-05 6.232087 e-07 de -1.313629 e-09 2.447293 e-11 (Numerical example 4) f = 39.2 ~ 116.1 FNo = 1: 4.6 ~ 11.2 2ω = 57.8 ° ~ 21.1 ° r 1 = 14.167 d 1 = 2.90 n 1 = 1.65844 ν 1 = 50.9 r 2 = 70.208 d 2 = 1.06 r 3 = -33.348 d 3 = 1.70 n 2 = 1.83400 ν 2 = 37.2 r 4 = 12.287 d 4 = 0.71 r 5 = 18.317 d 5 = 4.90 n 3 = 1.51742 ν 3 = 52.4 r 6 = -8.373 d 6 = 0.98 n 4 = 1.80400 ν 4 = 46.6 r 7 = -16.979 d 7 = 1.09 r 8 = -215.765 d 8 = 2.57 n 5 = 1.57099 ν 5 = 50.8 r 9 = -13.420 d 9 = 0.75 r1O = 0.000 (aperture) d1O = variable r11 = -72.043 d11 = 2.66 n 6 = 1.72727 ν 6 = 40.6 r12 = -30.289 (aspheric) d12 = 4.95 r13 = -10.419 d13 = 1.50 n 7 = 1.77250 ν 7 = 49.6 r14 = -71.626 Focal length 39.18 69.01 116.11 Variable interval d1O 12.73 5.90 2.27 skinf 9.19 32.95 70.46 Aspheric surface twelfth surface kbc 6.058641 e + 00 -2.845032 e-05 -1.051297 e-07 de -2.69112 9 e-09 -2.204888 e-12

[0039]

[Table 1]

[0040]

According to the present invention, in a so-called two-unit zoom lens, by appropriately setting the lens configuration of each lens unit and effectively using an aspherical lens, a zoom ratio of about 3 and a total lens length of It is possible to achieve a compact zoom lens having high optical performance over the entire zoom range in which the zooming is shortened.

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 provided from the object side to provide an appropriate refractive power arrangement and lens configuration. By moving the first lens unit and the diaphragm together and moving only the first lens unit during focusing, it is possible to achieve a compact zoom lens having a good optical performance and a simple configuration with a zoom ratio of about three times. it can.

[Brief description of the drawings]

FIG. 1 is a sectional view of a lens according to a numerical example 1 of the present invention.

FIG. 2 is an aberration diagram at a wide-angle end according to Numerical Embodiment 1 of the present invention.

FIG. 3 is an aberration diagram at a telephoto end in Numerical Example 1 of the present invention;

FIG. 4 is a sectional view of a lens according to a numerical example 2 of the present invention.

FIG. 5 is an aberration diagram at a wide-angle end according to Numerical Example 2 of the present invention.

FIG. 6 is an aberration diagram at a telephoto end in Numerical Example 2 of the present invention.

FIG. 7 is a sectional view of a lens according to a numerical example 3 of the present invention.

FIG. 8 is an aberration diagram at a wide angle end according to Numerical Example 3 of the present invention.

FIG. 9 is an aberration diagram at a telephoto end in Numerical Example 3 of the present invention.

FIG. 10 is a sectional view of a lens according to a numerical example 4 of the present invention.

FIG. 11 is an aberration diagram at a wide angle end according to Numerical Example 4 of the present invention.

FIG. 12 is an aberration diagram at a telephoto end in Numerical Example 4 of the present invention.

[Explanation of symbols]

 L1 First lens unit L2 Second lens unit SP Aperture IP Image plane d d-line g g-line S Sagittal image plane M Meridional

Claims (4)

[Claims] 1. A zoom lens having a first lens unit having a positive refractive power and a second lens unit having a negative refractive power in order from the object side, and performing zooming by changing an interval between the lens units. The first lens unit is configured by joining a positive eleventh lens and a negative twelfth lens with both lens surfaces concave, and a positive thirteenth lens with both lens surfaces convex and a meniscus negative fourteenth lens. A cemented lens having a concave surface facing the object side, and a positive first lens
The second lens group is composed of five positive lenses.
Meniscus negative second lens having a concave surface on the object side with the lens
The second lens group includes at least one lens.
The focal length of the entire system at the wide-angle end and the telephoto end is fW, fT, the focal length of the second lens group is f2,
The lateral magnification of the second lens group at the wide-angle end at an infinite object distance is β
2W, when the lateral magnification of the second lens group at the telephoto end at infinite object distance is β2T. A zoom lens satisfying 2.95 <β2T / β2W <3.1. 2. A stop is provided on the image plane side of the first lens group. The stop moves integrally with the first lens group during zooming, and only focuses on the first lens group during focusing. 2. The zoom lens according to claim 1, wherein the zoom lens is moved on an axis. 3. The distance from the lens surface closest to the object side at the wide-angle end to the lens surface closest to the image plane at the wide-angle end is DW, the back focus at the wide-angle end is SKW, and the focal length of the first lens group is f1. Wherein the following conditional expression is satisfied: 0.20 <SKW / DW <0.25 1.20 <f1 / | f2 | <1.28 0.22 <f1 / fT <0.25 Item 1 or 2
Zoom lens. 4. The Abbe number of the material of the 21st lens is ν
21p, the Abbe number of the material of the 22nd lens is ν22n
Then, 0.004 <(1 / ν21p) − (1 / ν22n) <
4. The zoom lens according to claim 1, wherein the following conditional expression is satisfied: 0.007 37 <ν21p <42.