JPH06337353A - Rear-focus system zoom lens - Google Patents

Abstract

PURPOSE:To obtain a rear-focus system zoom lens provided with four lens groups as a whole, a high power variation range up to power variation ratio of 8-10 and good optical performance over the whole power variation range and also over the whole object distance. CONSTITUTION:The zoom lens is provided with four lens groups; a 1st group L1 having a positive refractive power, a 2nd group L2 having a negative refractive power, a 3rd group L3 having a positive refractive power and a 4th group L4 having a positive refractive power in this order from the object side, and the 2nd group L2 is moved to an image field side so as to vary the power from a wide angle end to a telephoto end, and the image field fluctuation following the power variation is corrected by moving the 4th group L4, and also, the focusing is performed by moving the 4th group L4, and provided that Fi denotes the focal distance of the (i) group, the following condition is satisfied; 3.5 < F3/F4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear focus type zoom lens, and particularly to a large zoom ratio of 8 to 10 and an F number of 1.6 to 2 used for photographic cameras, video cameras, broadcast cameras and the like. The present invention relates to a rear focus type zoom lens having a long aperture ratio and a high zoom ratio and a long back focus.

[0002]

2. Description of the Related Art Conventionally, various zoom lenses for photographic cameras, video cameras, etc. have been proposed which employ a so-called rear focus type in which focusing is performed by moving a lens unit other than the first lens unit on the object side. ing.

Generally, in a rear focus type zoom lens, the effective diameter of the first lens group is smaller than that of a zoom lens in which the first lens group is moved to perform focusing, which facilitates downsizing of the entire lens system and close-up photography. Especially, it is easy to perform extremely close-up photography, and since the relatively small and lightweight lens group is moved, the driving force of the lens group is small and quick focusing is possible.

As such a rear focus type zoom lens, for example, in Japanese Patent Laid-Open No. 63-44614, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power for zooming, and a zooming lens are arranged in this order from the object side. In a so-called four-group zoom lens composed of four lens groups, a third lens group having a negative refracting power and a fourth lens group having a positive refracting power for correcting an image plane variation caused by doubling, the third lens group is moved. I'm focusing. However, this zoom lens tends to increase the total lens length because it is necessary to secure a moving space for the third lens group.

In Japanese Patent Laid-Open No. 58-136012, the variable power portion is composed of three or more lens groups, and some of these lens groups are moved for focusing.

In JP-A-63-247316 and JP-A-62-24213, the first group having a positive refractive power, the second group having a negative refractive power, and the third group having a positive refractive power are sequentially arranged from the object side. group,
Further, it has four lens groups of the fourth group having a positive refractive power, and the second group is moved to perform zooming, and the fourth group is moved to perform image plane variation and focusing due to zooming. .

In Japanese Patent Laid-Open No. 58-160913, the first group having a positive refractive power, the second group having a negative refractive power, are arranged in this order from the object side.
The third lens unit has a positive refracting power and the fourth lens unit has a positive refracting power, and the first lens unit and the second lens unit are moved to perform zooming, and the image plane changes due to zooming. Is performed by moving the fourth group. Then, one or two or more lens groups of these lens groups are moved to perform focusing.

In Japanese Patent Laid-Open No. 63-278013, the first group having a positive refractive power, the second group having a negative refractive power, the third group having a negative refractive power, and the third group having a positive refractive power are arranged in this order from the object side. 4 of the 4th group
It has one lens group, and the second group is moved to perform zooming.
The image plane variation due to zooming is corrected by moving the fourth lens group and focusing is performed.

[0009]

Generally, when a rear focus system is adopted in a zoom lens, the entire lens system is downsized and quick focusing becomes possible.

On the other hand, however, the aberration variation during focusing becomes large, and it becomes very difficult to obtain high optical performance while miniaturizing the entire lens system over the entire object distance from an infinite object to a short-distance object. The problem arises. In particular, with a zoom lens having a large aperture ratio and a high zoom ratio, it becomes very difficult to obtain high optical performance over the entire zoom range and over the entire object distance.

At present, a single plate type is used in many things as an image pickup means of a consumer video camera. In this case, the back focus of the single-plate type zoom lens is relatively short because it is not necessary to use the color separation prism or the like used in the multi-plate type zoom lens mainly used for business.

In the case of the multi-plate type, a color separation prism or the like is arranged behind the taking lens (zoom lens). For this reason, the multi-lens type zoom lens requires a relatively long back focus as compared with the single-lens type consumer video camera zoom lens.

The present invention adopts the rear focus system, achieves a large aperture ratio and a high zoom ratio, and at the same time miniaturizes the entire lens system, and covers the entire zoom range from the wide-angle end to the telephoto end. An object of the present invention is to provide a rear focus type zoom lens having good optical performance and a predetermined back focus over the entire object distance from an object at infinity to an object at a short distance.

[0014]

A rear focus type zoom lens according to the present invention comprises a first group having a positive refractive power, a second group having a negative refractive power, and a third group having a positive refractive power in order from the object side. Then, it has four lens units of the fourth lens unit having a positive refractive power, and moves the second lens unit to the image plane side to perform zooming from the wide-angle end to the telephoto end, thereby changing the image plane due to zooming. The fourth group is moved for correction, and the fourth group is moved for focusing,
It is characterized in that the condition of 3.5 <F3 / F4 (1) is satisfied when the focal length of the group is Fi.

[0015]

FIG. 1 is a schematic view of an embodiment showing a paraxial refractive power arrangement of a rear focus type zoom lens according to the present invention. 2 to 9 are lens cross-sectional views of Numerical Examples 1 to 8 described later. 10 to 25 are numerical examples 1 to 1 of the present invention.
FIG. 8 is an aberration diagram of No. 8.

In the figure, L1 is a first group having a positive refractive power, L2 is a second group having a negative refractive power, L3 is a third group having a positive refractive power, and L4.
Is the fourth group of positive refractive power. SP is an aperture stop,
It is arranged in front of the third unit L3. G is a glass block such as a color separation prism or filter, and IP is an image plane.

During zooming from the wide-angle end to the telephoto end, the second lens unit is moved to the image surface side as indicated by the arrow, and the image surface variation due to zooming is moved by moving the fourth lens unit.

Further, a rear focus type in which the fourth lens unit is moved on the optical axis for focusing is adopted. The solid curve 4a and the dotted curve 4b of the fourth group shown in the same figure represent image plane fluctuations due to zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and a near object, respectively. The movement locus for correction is shown. The first and third groups are fixed during zooming and focusing.

In the present embodiment, the fourth lens unit is moved to correct the image plane variation due to zooming, and the fourth lens unit is moved to perform focusing. Curve 4 in the figure
As indicated by a and 4b, the zoom lens is moved so as to have a convex locus toward the object side during zooming from the wide-angle end to the telephoto end.
As a result, the space between the third group and the fourth group is effectively used, and the total lens length is effectively shortened.

In the present embodiment, for example, when focusing on an object at infinity from a near object at the telephoto end, the fourth group is moved forward as shown by a straight line 4c in the figure.

In the present embodiment, the rear focus system as described above is adopted as compared with the case where the first group is extended to perform the focusing in the conventional four-group zoom lens, and the effective lens diameter of the first group is increased. To prevent it.

By arranging the aperture stop immediately before the third lens unit, the aberration variation due to the movable lens unit is reduced, and by shortening the distance between the lens units in front of the aperture stop, the diameter of the front lens is reduced. Is easily achieved.

By specifying the refracting power and the like of each lens group as described above, it is possible to reduce the size of the entire lens system, ensure a predetermined back focus, and improve the entire object range and the entire object distance. We have obtained a high zoom ratio zoom lens with optical performance.

Next, the technical meanings of the above conditional expressions will be described.

Conditional expression (1) relates to the ratio of the focal lengths of the third lens unit and the fourth lens unit, and the back focus is sufficiently long to achieve good optical performance while achieving a compact lens system after the diaphragm. It is for maintaining.

When the lower limit of conditional expression (1) is exceeded and the focal length of the third lens unit becomes short, it becomes difficult to correct fluctuations in spherical aberration due to zooming or during focusing. Further, it becomes difficult to secure a sufficient back focus, and the amount of movement of the fourth lens unit becomes large, which causes a large amount of variation in aberration during zooming and focusing.

In the present invention, the following conditions should be satisfied in order to obtain good optical performance over the entire zoom range and the entire object distance while further downsizing the entire lens system.

(2-1) When the focal length of the entire system at the wide-angle end is Fw and the back focus at the wide-angle end is bfw: 3 <bfw / Fw <5 (2) -0.8 <Fw / F2 <−0.4 (3) 5 <F1 / Fw <12 (4)

Conditional expression (2) relates to the ratio of the back focus bfw to the focal length Fw at the wide-angle end.
If the back focus becomes shorter than the lower limit of conditional expression (2), it becomes impossible to arrange a color separation prism or the like, or the telecentric system will be displaced, and the angle of the light beam incident on the color separation prism will be tight, and Not good because shading occurs.

On the contrary, if the back focus exceeds the upper limit and becomes too long, the effective diameter of the fourth lens unit becomes large and the lens system becomes heavy, which causes a problem that smooth focusing cannot be performed.

Conditional expression (3) relates to the ratio between the focal length at the wide-angle end and the focal length of the second lens unit. If the focal length of the second lens unit becomes too short beyond the upper limit of conditional expression (3), the Petzval sum will increase in the under direction, making it difficult to correct various aberrations such as image plane tilt.

On the other hand, if the focal length of the second lens unit becomes too long beyond the lower limit, the amount of movement of the second lens unit due to zooming increases and the front lens diameter becomes too large.

Conditional expression (4) is an expression relating to the object point, that is, the magnification, with respect to the second group. In order to set the entire lens system small, it is preferable that the second lens group has the same magnification during zooming. If the same magnification is sandwiched, the locus of zooming of the fourth lens group becomes a substantially reciprocating movement, and it becomes possible to achieve high magnification variation with the most effective space efficiency.

Specifically, when the upper limit of conditional expression (4) is exceeded, the object point with respect to the second lens unit becomes far, and the image forming magnification of the second lens unit becomes low, effectively reducing the size of the lens system. Becomes difficult.

Further, the distance between the first group and the second group becomes large, which makes it difficult to achieve miniaturization of the lens system. On the other hand, when the value goes below the lower limit, the magnification of the second lens group becomes large, and it becomes difficult to achieve high magnification.

(2-2) The second lens unit is provided with a negative 21st lens element having a concave surface having a stronger refractive power toward the image side than the object side in order from the object side; The lens is composed of three single lenses, that is, a positive 23rd lens with a convex surface having a stronger refractive power facing the object side than the image side.

As a result, the position of the front principal point of the second group is set closer to the object side, and the principal point interval with the first group is shortened. As a result, the height of the off-axis light beam entering the first group from the optical axis is lowered, and the lens diameter of the first group is reduced.

(2-3) In order from the object side, the first group is composed of three lenses, namely, a negative eleventh lens, a positive twelfth lens and a positive thirteenth lens, and the second group is a negative twenty-first lens.
Lens, negative 22nd lens and positive 23rd lens 3
The third lens group includes two lenses, namely, a positive 31a lens and a negative 32a lens, or a negative 31b lens and a positive 32b lens, and the fourth lens group includes a positive 41a lens. , Negative 42a lens and positive fourth
Three lenses of 3a lens or positive 41b lens, negative 42b lens, positive 43b lens and positive 4th lens
It is to be composed of four 4b lenses.

As a result, high optical performance is obtained over the entire zoom range and over the entire screen.

(2-4) The radius of curvature of the image side lens surface of the twenty-first lens in the second group is R _{21, R} , and the radius of curvature of the object side lens surface of the 22nd lens is R _{22, F} , When the focal length of the entire system at the telephoto end is FT and the combined focal length of the first to third groups at the telephoto end is FT _1,3

[0041]

[Equation 1] To satisfy the condition.

The conditional expression (5) relates to the air lens and the focal length of the second lens group. When the value goes below the lower limit, the distortion at the wide-angle end tends to be a barrel type.

On the other hand, when the value exceeds the upper limit, the distortion at the telephoto end tends to be a pincushion type.

Conditional expression (6) relates to the axial light flux emitted from the third lens group at the telephoto end. When the value goes below the lower limit, the divergence of the axial light flux emitted from the third lens group becomes strong and the lens diameter of the fourth lens group becomes large. Further, there arises a problem that the variation of spherical aberration due to focusing becomes large.

On the other hand, when the value exceeds the upper limit, the convergence of the axial light flux emitted from the third lens group becomes strong, and there arises a problem that a sufficient back focus and an exit pupil cannot be obtained.

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. The last three lens surfaces in the numerical examples are glass blocks such as color separation prisms and filters. Table 1 shows the relationship between the above-mentioned 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 the direction perpendicular to the optical axis, a light traveling direction is positive, R is a paraxial radius of curvature, and A, B, C, D, and E are aspherical shapes, respectively. When using spherical coefficient

[0048]

[Equation 2] It is expressed by the formula. Further, "e-0X" means "10 ^-X ".

Numerical Example 1 f = 1 to 8.0 Fno = 1: 1.65 2ω = 56.4 ° to 7.3 ° R 1 = 9.760 D 1 = 0.305 N 1 = 1.80518 ν 1 = 25.4 R 2 = 5.255 D 2 = 0.915 N 2 = 1.60311 ν 2 = 60.7 R 3 = 57.424 D 3 = 0.033 R 4 = 5.401 D 4 = 0.559 N 3 = 1.69680 ν 3 = 55.5 R 5 = 14.080 D 5 = Variable R 6 = 6.644 D 6 = 0.152 N 4 = 1.88300 ν 4 = 40.8 R 7 = 1.421 D 7 = 0.593 R 8 = -7.409 D 8 = 0.135 N 5 = 1.69680 ν 5 = 55.5 R 9 = 3.188 D 9 = 0.169 R10 = 2.673 D10 = 0.423 N 6 = 1.84666 ν 6 = 23.8 R11 = 19.594 D11 = Variable R12 = (Aperture) D12 0.254 R13 = 16.349 D13 = 0.152 N 7 = 1.80400 ν 7 = 46.6 R14 = 1.863 D14 = 0.644 N 8 = 1.60342 ν 8 = 38.0 R15 = -5.937 D15 = Variable R16 = -90.332 D16 = 0.423 N 9 = 1.48749 ν 9 = 70.2 R17 = -4.286 D17 = 0.025 R18 = 8.585 D18 = 0.169 N10 = 1.80518 ν10 = 25.4 R19 = 2.706 D19 = 0.576 N11 = 1.48749 ν11 = 70.2 R20 =- 19.124 D20 = 0.025 R21 = 3.892 D21 = 0.542 N12 = 1.48749 ν12 = 70.2 R22 = -5.134 D22 = 0.678 R23 = ∞ D23 = 0.423 N13 = 1.51633 ν13 = 64.2 R24 = ∞ D24 = 3.389 N14 = 1.60342 ν14 = 38.0 R25 = ∞

[0050]

[Table 1] <Numerical Example 2> f = 1 to 12.65 Fno = 1: 1.65 to 22 ω = 60.0 ° to 5.2
° R 1 = 15.833 D 1 = 0.346 N 1 = 1.80518 ν 1 = 25.4 R 2 = 6.746 D 2 = 1.500 N 2 = 1.60311 ν 2 = 60.7 R 3 = -38.377 D 3 = 0.038 R 4 = 6.039 D 4 = 0.730 N 3 = 1.69680 ν 3 = 55.5 R 5 = 15.975 D 5 = Variable R 6 = 7.024 D 6 = 0.173 N 4 = 1.88300 ν 4 = 40.8 R 7 = 1.692 D 7 = 0.786 R 8 = -3.073 D 8 = 0.153 N 5 = 1.69680 ν 5 = 55.5 R 9 = 2.791 D 9 = 0.192 R10 = 3.248 D10 = 0.423 N 6 = 1.84666 ν 6 = 23.8 R11 = -36.211 D11 = Variable R12 = (Aperture) D12 0.288 R13 = 7.387 D13 = 0.807 N 7 = 1.62588 ν 7 = 35.7 R14 = -2.053 D14 = 0.173 N 8 = 1.77250 ν 8 = 49.6 R15 = -13.939 D15 = Variable R16 = 84.254 D16 = 0.480 N 9 = 1.51633 ν 9 = 64.2 R17 = -4.349 D17 = 0.028 R18 = 8.629 D18 = 0.192 N10 = 1.80518 ν10 = 25.4 R19 = 2.482 D19 = 0.769 N11 = 1.48749 ν11 = 70.2 R20 = -22.864 D20 = 0.028 R21 = 2.808 D21 = 0.538 N12 = 1.48749 ν12 = 70.2 R22 = 47.595 D22 = 0.769 R23 = ∞ D23 = 0.480 N13 = 1.51633 ν13 = 64.2 R24 = ∞ D24 = 3.461 N14 = 1.60342 ν14 = 38.0 R25 = ∞

[0051]

[Table 2] <Numerical Example 3> f = 1 to 10.0 Fno = 1: 1.65 to 1.85 2ω = 56.4 ° to
6.1 ° R 1 = 13.935 D 1 = 0.321 N 1 = 1.80518 ν 1 = 25.4 R 2 = 6.199 D 2 = 1.160 N 2 = 1.60311 ν 2 = 60.7 R 3 = -46.242 D 3 = 0.035 R 4 = 6.062 D 4 = 0.642 N 3 = 1.69680 ν 3 = 55.5 R 5 = 18.709 D 5 = Variable R 6 = 5.215 D 6 = 0.142 N 4 = 1.88 300 ν 4 = 40.8 R 7 = 1.640 D 7 = 0.653 R 8 = -2.610 D 8 = 0.142 N 5 = 1.69680 ν 5 = 55.5 R 9 = 2.588 D 9 = 0.178 R10 = 3.060 D10 = 0.392 N 6 = 1.84666 ν 6 = 23.8 R11 = -19.876 D11 = Variable R12 = (Aperture) D12 0.267 R13 = 8.618 D13 = 0.714 N 7 = 1.60342 ν 7 = 38.0 R14 = -1.616 D14 = 0.142 N 8 = 1.77250 ν 8 = 49.6 R15 = -19.460 D15 = Variable R16 = -104.168 D16 = 0.446 N 9 = 1.51633 ν 9 = 64.2 R17 = -4.034 D17 = 0.026 R18 = 8.573 D18 = 0.178 N10 = 1.84666 ν10 = 23.8 R19 = 2.919 D19 = 0.714 N11 = 1.48749 ν11 = 70.2 R20 = -11.679 D20 = 0.026 R21 = 3.431 D21 = 0.500 N12 = 1.51633 ν12 = 64.2 R22 = -22.410 D22 = 0.714 R23 = ∞ D23 = 0.446 N13 = 1.51633 ν13 = 64.2 R24 = ∞ D24 = 3.571 N14 = 1.60342 ν14 = 38.0 R25 = ∞

[0052]

[Table 3] <Numerical Example 4> f = 1 to 10.0 Fno = 1: 1.65 to 1.85 2ω = 56.4 ° to
7.3 ° R 1 = 10.876 D 1 = 0.321 N 1 = 1.80518 ν 1 = 25.4 R 2 = 5.631 D 2 = 1.160 N 2 = 1.60311 ν 2 = 60.7 R 3 = -32.694 D 3 = 0.035 R 4 = 6.601 D 4 = 0.571 N 3 = 1.69680 ν 3 = 55.5 R 5 = 15.120 D 5 = Variable R 6 = 6.050 D 6 = 0.142 N 4 = 1.88 300 ν 4 = 40.8 R 7 = 1.679 D 7 = 0.703 R 8 = -2.707 D 8 = 0.142 N 5 = 1.69680 ν 5 = 55.5 R 9 = 2.918 D 9 = 0.178 R10 = 3.235 D10 = 0.392 N 6 = 1.84666 ν 6 = 23.8 R11 = -23.215 D11 = Variable R12 = (Aperture) D12 0.267 R13 = 112.150 D13 = 0.714 N 7 = 1.60342 ν 7 = 38.0 R14 = -1.888 D14 = 0.142 N 8 = 1.80400 ν 8 = 46.6 R15 = -6.647 D15 = Variable R16 = 3.724 D16 = 0.642 N 9 = 1.48749 ν 9 = 70.2 R17 = -7.678 D17 = 0.026 R18 = 5.683 D18 = 0.178 N10 = 1.84666 ν10 = 23.8 R19 = 2.652 D19 = 0.821 N11 = 1.48749 ν11 = 70.2 R20 = -4.896 D20 = 0.714 R21 = ∞ D21 = 0.446 N12 = 1.51633 ν12 = 64.2 R22 = ∞ D22 = 3.571 N13 = 1.60342 ν13 = 38.0 R23 = ∞

[0053]

[Table 4] <Numerical value example 5> f = 1 to 10.0 Fno = 1: 1.65 to 1.8 2 ω = 56.4 ° to
7.3 ° R 1 = 9.706 D 1 = 0.321 N 1 = 1.80518 ν 1 = 25.4 R 2 = 5.409 D 2 = 1.160 N 2 = 1.51633 ν 2 = 64.2 R 3 = 1713.793 D 3 = 0.035 R 4 = 6.342 D 4 = 0.625 N 3 = 1.69680 ν 3 = 55.5 R 5 = 31.759 D 5 = Variable R 6 = 4.624 D 6 = 0.142 N 4 = 1.88 300 ν 4 = 40.8 R 7 = 1.649 D 7 = 0.722 R 8 = -2.569 D 8 = 0.142 N 5 = 1.69680 ν 5 = 55.5 R 9 = 2.896 D 9 = 0.178 R10 = 3.254 D10 = 0.392 N 6 = 1.84666 ν 6 = 23.8 R11 = -34.333 D11 = Variable R12 = (Aperture) D12 0.267 R13 = 121.593 D13 = 0.714 N 7 = 1.61293 ν 7 = 37.0 R14 = -1.968 D14 = 0.142 N 8 = 1.77250 ν 8 = 49.6 R15 = -6.912 D15 = Variable R16 = 3.821 D16 = 0.642 N 9 = 1.51633 ν 9 = 64.2 R17 = -5.790 D17 = 0.026 R18 = 5.124 D18 = 0.178 N10 = 1.84666 ν10 = 23.8 R19 = 2.187 D19 = 0.535 R20 = 2.335 D20 = 0.821 N11 = 1.48749 ν11 = 70.2 R21 = -4.801 D21 = 0.714 R22 = ∞ D22 = 0.446 N12 = 1.51633 ν12 = 64.2 R23 = ∞ D23 = 3.571 N13 = 1.60342 ν13 = 38.0 R24 = ∞

[0054]

[Table 5] <Numerical Example 6> f = 1 to 10.0 Fno = 1: 1.65 to 1.95 2ω = 56.4 ° to 7.
3 ° R 1 = 12.257 D 1 = 0.285 N 1 = 1.80518 ν 1 = 25.4 R 2 = 5.953 D 2 = 0.267 R 3 = 7.776 D 3 = 0.803 N 2 = 1.49700 ν 2 = 81.6 R 4 = -246.325 D 4 = 0.035 R 5 = 5.666 D 5 = 0.928 N 3 = 1.69680 ν 3 = 55.5 R 6 = 226.941 D 6 = Variable R 7 = 5.144 D 7 = 0.142 N 4 = 1. 88300 ν 4 = 40.8 R 8 = 1.664 D 8 = 0.667 R 9 = -2.600 D 9 = 0.142 N 5 = 1.69680 ν 5 = 55.5 R10 = 2.617 D10 = 0.178 R11 = 3.115 D11 = 0.392 N 6 = 1.84666 ν 6 = 23.8 R12 = -21.490 D12 = Variable R13 = (Aperture) D13 = 0.267 R14 = 8.690 D14 = 0.714 N 7 = 1.61293 ν 7 = 37.0 R15 = -1.618 D15 = 0.142 N 8 = 1.77250 ν 8 = 49.6 R16 = -17.470 D16 = Variable R17 = -80.048 D17 = 0.446 N 9 = 1.48749 ν 9 = 70.2 R18 = -4.119 D18 = 0.026 R19 = 8.509 D19 = 0.178 N10 = 1.84666 ν10 = 23.8 R20 = 2.945 D20 = 0.714 N11 = 1.48749 ν11 = 70.2 R21 = -11.983 D21 = 0.026 R22 = 3.435 D22 = 0.500 N12 = 1.51633 ν12 = 64.2 R23 = -25.034 D23 = 0.714 R24 = ∞ D24 = 0.446 N13 = 1.51633 ν13 = 64.2 R25 = ∞ D25 = 3.571 N14 = 1.60342 ν14 = 38.0 R26 = ∞

[0055]

[Table 6] <Numerical Example 7> f = 1 to 10.0 Fno = 1: 1.65 to 1.96 2ω = 56.4 ° to 7.
3 ° R 1 = 12.989 D 1 = 0.285 N 1 = 1.80518 ν 1 = 25.4 R 2 = 6.175 D 2 = 0.257 R 3 = 7.871 D 3 = 0.803 N 2 = 1.49700 ν 2 = 81.6 R 4 = -80.049 D 4 = 0.089 R 5 = 5.647 D 5 = 0.857 N 3 = 1.69680 ν 3 = 55.5 R 6 = 85.989 D 6 = Variable R 7 = 4.788 D 7 = 0.142 N 4 = 1. 88300 ν 4 = 40.8 R 8 = 1.628 D 8 = 0.691 R 9 = -2.589 D 9 = 0.142 N 5 = 1.69680 ν 5 = 55.5 R10 = 2.635 D10 = 0.178 R11 = 3.131 D11 = 0.357 N 6 = 1.84666 ν 6 = 23.8 R12 = -21.153 D12 = Variable R13 = (Aperture) D13 = 0.267 R14 = 8.729 D14 = 0.678 N 7 = 1.61293 ν 7 = 37.0 R15 = -1.896 D15 = 0.046 R16 = -1.765 D16 = 0.142 N 8 = 1.77250 ν 8 = 49.6 R17 = -12.326 D17 = Variable R18 = -28.412 D18 = 0.464 N 9 = 1.48749 ν 9 = 70.2 R19 = -4.142 D19 = 0.026 R20 = 8.004 D20 = 0.160 N10 = 1.84666 ν10 = 23.8 R21 = 2.872 D21 = 0.678 N11 = 1.48749 ν11 = 70.2 R22 = -12.333 D22 = 0.026 R23 = 3.713 D23 = 0.535 N12 = 1.51633 ν12 = 64.2 R24 = -11.186 D24 = 0.714 R25 = ∞ D25 = 0.446 N13 = 1.51633 ν13 = 64.2 R26 = ∞ D26 = 3.571 N14 = 1.60342 ν14 = 38.0 R27 = ∞

[0056]

[Table 7] <Numerical Example 8> f = 1 to 8.0 Fno = 1: 1.65 to 22 ω = 53.1 ° to 7.
2 ° R 1 = 14.585 D 1 = 0.300 N 1 = 1.80518 ν 1 = 25.4 R 2 = 4.950 D 2 = 1.000 N 2 = 1.60311 ν 2 = 60.7 R 3 = -12.965 D 3 = 0.033 R 4 = 3.950 D 4 = 0.500 N 3 = 1.69680 ν 3 = 55.5 R 5 = 9.147 D 5 = Variable R 6 = 7.777 D 6 = 0.150 N 4 = 1.88 300 ν 4 = 40.8 R 7 = 1.459 D 7 = 0.538 R 8 = -1.730 D 8 = 0.133 N 5 = 1.69680 ν 5 = 55.5 R 9 = 2.114 D 9 = 0.383 N 6 = 1.84666 ν 6 = 23.8 R10 = -8.785 D10 = Variable R11 = (Aperture) D11 = 0.250 R12 = 7.249 D12 = 0.666 N 7 = 1.62588 ν 7 = 35.7 R13 = -1.513 D13 = 0.150 N 8 = 1.77250 ν 8 = 49.6 R14 = -8.358 D14 = Variable R15 = -107.336 D15 = 0.416 N 9 = 1.51633 ν 9 = 64.2 R16 = -3.600 D16 = 0.025 R17 = 7.512 D17 = 0.166 N10 = 1.80518 ν10 = 25.4 R18 = 2.098 D18 = 0.666 N11 = 1.48749 ν11 = 70.2 R19 = -12.762 D19 = 0.025 R20 = 3.046 D20 = 0.550 N12 = 1.48749 ν12 = 70.2 R21 = -7.730 D21 = 0.666 R22 = ∞ D22 = 0.416 N13 = 1.51633 ν13 = 64.2 R23 = ∞ D23 = 3.000 N14 = 1.60342 ν14 = 38.0 R24 = ∞

[0057]

[Table 8]

[0058]

As described above, according to the present invention, by adopting the lens structure which is composed of four lens groups as a whole, the refractive power of each lens group is set, and the fourth lens group is moved during focusing. Achieves good aberration correction over the entire zoom range while reducing the overall size of the lens system, and achieves a rear-focus type zoom lens with a large aperture ratio and long back focal length with little aberration fluctuation during focusing. can do.

[Brief description of drawings]

FIG. 1 is an explanatory view of a paraxial refractive power arrangement according to the present invention.

FIG. 2 is a lens cross-sectional view of Numerical Example 1 of the present invention.

FIG. 3 is a lens cross-sectional view of Numerical Example 2 of the present invention.

FIG. 4 is a lens sectional view of Numerical Example 3 of the present invention.

FIG. 5 is a lens cross-sectional view of Numerical Example 4 of the present invention.

FIG. 6 is a lens cross-sectional view of Numerical Example 5 of the present invention.

FIG. 7 is a lens cross-sectional view of Numerical Example 6 of the present invention.

FIG. 8 is a lens cross-sectional view of Numerical Example 7 of the present invention.

FIG. 9 is a lens cross-sectional view of Numerical Example 8 of the present invention.

FIG. 10 is an aberration diagram at the wide-angle end according to Numerical Example 1 of the present invention.

FIG. 11 is an aberration diagram at a telephoto end according to Numerical Example 1 of the present invention.

FIG. 12 is an aberration diagram at a wide-angle end according to Numerical Example 2 of the present invention.

FIG. 13 is an aberration diagram at a telephoto end according to Numerical Example 2 of the present invention.

FIG. 14 is an aberration diagram at a wide-angle end according to Numerical Example 3 of the present invention.

FIG. 15 is an aberration diagram at a telephoto end according to Numerical Example 3 of the present invention.

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

FIG. 17 is an aberration diagram at a telephoto end according to Numerical Example 4 of the present invention.

FIG. 18 is an aberration diagram at a wide-angle end according to Numerical Example 5 of the present invention.

FIG. 19 is an aberration diagram at a telephoto end according to Numerical Example 5 of the present invention.

FIG. 20 is an aberration diagram at a wide-angle end according to Numerical Example 6 of the present invention.

FIG. 21 is an aberration diagram at a telephoto end according to Numerical Example 6 of the present invention.

FIG. 22 is an aberration diagram at a wide-angle end according to Numerical Example 7 of the present invention.

FIG. 23 is an aberration diagram at a telephoto end according to Numerical Example 7 of the present invention.

FIG. 24 is an aberration diagram at a wide-angle end according to Numerical Example 8 of the present invention.

FIG. 25 is an aberration diagram at a telephoto end according to Numerical Example 8 of the present invention.

[Explanation of symbols]

 L1 1st group L2 2nd group L3 3rd group L4 4th group SP Aperture IP Image plane d d line g g line ΔS Sagittal image plane ΔM Meridional image plane

Claims (5)

[Claims] 1. A four-lens group consisting of a first lens group having a positive refractive power, a second lens group having a negative refractive power, a third lens group having a positive refractive power, and a fourth lens group having a positive refractive power in order from the object side. The second lens unit is moved to the image surface side to perform zooming from the wide-angle end to the telephoto end, and the image surface fluctuation associated with zooming is corrected by moving the fourth lens unit. The rear-focus type zoom lens is characterized by satisfying a condition of 3.5 <F3 / F4 when the focal length of the i-th group is Fi by moving. 2. The second lens unit includes, in order from the object side, a negative 21st lens having a concave surface having a stronger refractive power toward the image surface side than the object side, a negative 22nd lens having concave lens surfaces on both sides, and A positive second lens with a convex surface having a stronger refractive power facing the object side than the image side.
2. The rear focus type zoom lens according to claim 1, wherein the rear focus type zoom lens comprises three single lenses of three lenses. 3. The negative first lens unit is arranged in order from the object side.
Lens, positive 12th lens and positive 13th lens 3
Two lenses, the second group is the negative 21st lens,
The third lens unit is composed of three lenses, a negative 22nd lens and a positive 23rd lens, and the third lens group is a positive 31a lens and a negative 32a lens or a negative 31b lens and a positive 32b lens. And the fourth group is the positive 41st
a lens, a negative 42a lens and a positive 43a lens, or a positive 41b lens, a negative 42nd lens
2. The rear focus type zoom lens according to claim 1, wherein the rear focus type zoom lens is composed of four lenses of a b lens, a positive 43b lens and a positive 44b lens. 4. The rear focus type zoom lens according to claim 2, wherein an aperture stop is arranged on the object side of the third group. 5. The focal length of the entire system at the wide-angle end is Fw,
5. When the back focus at the wide-angle end is bfw, the condition 3 <bfw / Fw <5--0.8 <Fw / F2 <-0.45 <F1 / Fw <12 is satisfied. Rear focus type zoom lens.