JPH06148523A - Rear focus type zoom lens - Google Patents

Abstract

PURPOSE:To form a zoom lens system compact, achieve favorable aberration correction for a whole magnification range, and reduce aberration fluctuation in focusing by setting refraction forces for five lens groups, and moving conditions for each lens group in changing a magnification, and moving at least one lens group of the second to the fourth lens group in focusing. CONSTITUTION:A first lens group L1 of a positive refraction force, a second lens group L2 of a negative refraction force, a third lens group L3 of a positive refraction force, a fourth lens group L4 of a negative refraction force, and a fifth lens group L5 of a positive refraction force are provided, and an aperture diaphragm SP is disposed before the third lens group L3. In changing a magnification from a wide angle end to a telephoto end, the second group L2 and the aperture diaphragm SP are moved to an image surface side, and image fluctuation by the change of the magnification is corrected by moving the third group L3 and the fourth group L4. At least one of the second group L2, the third group L3, and the fourth group L4, that is the fourth group L4, for example, is moved along an optical axis for focusing.

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 more particularly to a high zoom ratio with a large zoom ratio of about 10 and an F number of 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 wide angle of view and a short overall lens length.

[0002]

2. Description of the Related Art Recently, with the reduction in size and weight of home video cameras and the like, remarkable progress has been made in the downsizing of zoom lenses for image pickup. Especially, the total lens length is shortened and the front lens diameter is reduced. The effort is focused on simplification.

As one means for achieving these objects, there is known a so-called rear focus type zoom lens in which a lens unit other than the first lens unit on the object side is moved to perform focusing.

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 group having a positive refracting power and a second group having a negative refracting power for zooming are arranged in 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 refractive power and a fourth lens group having a positive refractive power, for correcting the image plane variation due to zooming, the third lens group is moved. Focus.

However, in this zoom lens, it is necessary to secure a moving space for the third lens unit, which tends to increase the total lens length.

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 Japanese Patent Laid-Open No. 63-247316, the first group having a positive refractive power and the second group having a negative refractive power are arranged in this order from the object side.
A lens unit, a third lens unit having a positive refracting power, and a fourth lens unit having a positive refracting power, and moving the second lens unit for zooming, and moving the fourth lens unit for zooming. The image plane is changed and the focus is performed.

Further, in Japanese Patent Laid-Open No. 58-160913, the first group having a positive refractive power, the second group having a negative refractive power, the third group having a positive refractive power, and the positive refractive power are arranged in this order from the object side. Fourth of power
There are four lens groups, and the first group and the second group are moved to perform zooming, and the image plane variation accompanying zooming is moved to 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. 58-129404 and Japanese Patent Laid-Open No. 61-258217, a first group having a positive refractive power, a second group having a negative refractive power, and a second group having a positive refractive power are sequentially arranged from the object side. Three
In a five-group zoom lens consisting of five lens groups, a fourth lens group having a positive refractive power, and a fifth lens group having a negative refractive power, a fifth lens group or a plurality of lens groups including the fifth lens group is moved. Focus.

Japanese Unexamined Patent Publication No. 60-6914 discloses that in the same five-group zoom lens as described above, the position of the focus lens group on the optical axis with respect to an object of a specific finite distance is constant regardless of zooming. I have proposed a zoom lens that has it.

[0012]

Among the rear focus type zoom lenses, the method in which the zooming function is performed by the lens group on the object side of the aperture stop is often used between the front lens and the aperture stop at the focal length at the wide-angle end. Space is required, the entrance pupil position of the entire system tends to be deep, and the diameter of the front lens becomes large.

Further, in Japanese Patent Laid-Open No. 3-158813,
From the object side, a positive first group, a negative second group, a positive third group,
Then, a zoom lens having four positive fourth lens groups, in which the second group and the third group are moved on the optical axis to perform zooming, and the aperture stop is moved integrally with the third group, is suggesting. In this publication, the focus is set to a part of the lenses of the fourth group or the first group.
We are going in groups.

In this zoom system, since the aperture stop is moved integrally with the third lens unit, the mechanism is complicated, and the third lens unit having the aperture stop is located closest to the image plane at the wide-angle end. However, there was a problem that the front lens diameter was increased.

The present invention, while adopting the rear focus system, reduces the front lens diameter to prevent the lens system from becoming large in size when achieving a large aperture ratio, a wide angle of view and a high zoom ratio. At the same time, over the entire zoom range from the wide-angle end to the telephoto end, and over the entire object distance from infinity objects to short-distance objects,
An object of the present invention is to provide a rear focus type zoom lens having good optical performance and a simple structure.

[0016]

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, an aperture stop, and a positive refractive power in order from the object side. It has five lens groups, a third lens group, a fourth lens group having a negative refractive power, and a fifth lens group having a positive refractive power, and moves the second lens group toward the image side to move from the wide-angle end to the telephoto end. The zooming is performed, and the image plane variation due to the zooming is corrected by moving the third group and the fourth group, and at least one lens group of the second group, the third group, and the fourth group is set. The feature is that it is moved along the optical axis to perform focusing.

Particularly in the present invention, the third group has one positive lens and one negative lens, and at least one lens surface is an aspherical surface, and the second group is closer to the object side. It is characterized in that it has two negative lenses and one positive lens in that order with an air gap.

[0018]

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 of the present invention to be described later, and FIGS. 10 to 17 are various aberration diagrams of Numerical Examples 1 to 8 of the present invention to be described later. In the aberration diagram (A)
Shows the wide-angle end and (B) shows the telephoto end.

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 a fourth group having a negative refractive power, and L5 is a fifth group having a positive refractive power. SP is an aperture stop, which is arranged in front of the third lens unit L3. FP is the image plane.

At the time of zooming from the wide-angle end to the telephoto end, the second lens group and the aperture stop SP are moved to the image plane side as indicated by the arrow, and the image plane variation caused by zooming is moved to the third lens group and the fourth lens group. I am correcting it. Also, a rear focus type is adopted in which focusing is performed by moving the fourth lens unit on the optical axis.

The solid curve 4a and the dotted curve 4b of the fourth group shown in the same figure are images at the time of 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 correcting the surface variation is shown. Note that focusing may be performed using at least one lens group of the second, third, and fourth groups. The first and fifth groups are fixed during zooming and focusing.

In this embodiment, the third group and the fourth group are moved to correct the image plane variation due to the magnification change, and the fourth group is moved to perform the focusing. In particular, as shown by the curves 4a and 4b in the figure, when the magnification is changed from the wide-angle end to the telephoto end, it is moved so as to have a convex locus toward the image plane side. As a result, the air of the fourth group and the fifth group is effectively used and the total lens length is effectively shortened.

In this embodiment, for example, when focusing on an object at infinity from a near object at the telephoto end,
As shown by the straight line 4c in the same figure, this is done by moving the fourth group forward.

In the present embodiment, the effective lens diameter of the first lens group is increased by adopting the rear focus method as described above, as compared with the case where the first lens group is extended and focused in the conventional four-group zoom lens. Effectively prevent.

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

Further, by constructing the third lens group to have one positive lens and one negative lens, it is possible to satisfactorily correct various aberrations such as spherical aberration and coma which are mainly caused by zooming. There is.

By constructing the second lens group to have two negative lenses and one positive lens, a zoom lens having a high zoom ratio having good optical performance over the entire zoom range is obtained. .

The rear focus type zoom lens, which is the object of the present invention, can be achieved by satisfying the above various conditions. However, in order to further reduce the size of the entire lens system and achieve a high zoom ratio, It is preferable to satisfy the following conditions in order to reduce the variation in aberration associated with zooming and to obtain high optical performance over the entire zooming range.

When the focal length of the i-th group is fi and the focal length at the wide-angle end of the entire system is fw, 2 <f3 / fw <4 (1) 4 <| f4 / fw | <15. (2) The condition 1 <| f2 / fw | <2 (3) is to be satisfied.

The conditional expression (1) relates to the positive refracting power of the third lens group, and is mainly intended to reduce the total lens length while ensuring a proper back focus. If the positive refractive power of the third lens group becomes too weak beyond the upper limit, the amount of movement of the third lens group and the fourth lens group due to zooming increases, and the entire lens system becomes large.

If the positive refracting power of the third lens group becomes too strong beyond the lower limit, the entire lens system will be downsized, but it will be difficult to obtain a predetermined back focus.

Conditional expression (2) is for satisfactorily correcting the fluctuations of various aberrations associated with the negative refracting power of the fourth lens unit, which are mainly caused by zooming. When the upper limit is exceeded and the negative refractive power of the fourth lens unit becomes too weak, the amount of movement of the fourth lens unit due to zooming increases and the total lens length increases.

If the negative refractive power of the fourth lens unit becomes too strong beyond the lower limit, the angle of incidence of the off-axis light beam on the fifth lens unit becomes too tight, and the fifth lens unit becomes large and various aberrations occur. In particular, it becomes difficult to correct coma.

Conditional expression (3) relates to the negative refracting power of the second lens group, and is mainly for maintaining a good image surface characteristic while reducing the size of the entire lens system. If the negative refractive power of the second lens unit becomes too weak beyond the upper limit, the amount of movement of the second lens unit due to zooming increases and the total lens length increases.

If the negative refracting power of the second lens group becomes too strong beyond the lower limit, the Petzval sum increases in the negative direction, and the field curvature becomes overcorrected, which is not preferable.

In addition to the above, in the present invention, the third group is provided with one positive lens, one negative lens, and at least one aspherical surface on the lens close to the diaphragm surface, and various aberrations, particularly spherical surfaces, are formed. This is preferable for favorably correcting aberrations and coma at the wide-angle end and further reducing the size of the entire lens system.

Further, at this time, if the lens arrangement is such that the positive lens and the negative lens are arranged in this order from the object side, the principal point position of the third lens group can be brought closer to the second lens group side, and the second lens for zooming can be used. The group can be moved to the vicinity of the third group, which is preferable in order to shorten the total lens length.

The second lens group is composed of a negative lens element in order from the object side, and a negative lens element and a positive lens element with a predetermined air gap in between. It is possible to prevent the first and second groups from interfering with each other, and further shorten the distance between the principal points of the first group to widen the angle of view while reducing the front lens diameter and downsizing the entire lens system. It is preferable to achieve

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.

In the numerical examples, the last two lens surfaces are glass materials such as face plates. The aspherical shape is the X axis in the optical axis direction, the H axis in the direction perpendicular to the optical axis, the traveling direction of light is positive, and R ₀ is the paraxial radius of curvature a ₂ , a ₃ , a
_{When 4} and a ₅ are aspherical coefficients respectively

[0041]

[Equation 1] It is expressed by Table 1 shows the relationship with each conditional expression in each numerical example. <Numerical Example 1> f = 1 to 8.07 fno = 1: 2 to 2.8 2 ω = 60.0 ° to 8.2 ° R 1 = 14.958 D 1 = 0.288 N 1 = 1.84666 ν 1 = 23.8 R 2 = 6.587 D 2 = 1.000 N 2 = 1.60311 ν 2 = 60.7 R 3 = -18.206 D 3 = 0.028 R 4 = 4.291 D 4 = 0.576 N 3 = 1.69350 ν 3 = 53.2 R 5 = 9.537 D 5 = Variable R 6 = 23.736 D 6 = 0.153 N 4 = 1.77250 ν 4 = 49.6 R 7 = 1.653 D 7 = 0.746 R 8 = -2.472 D 8 = 0.134 N 5 = 1.60311 ν 5 = 60.7 R 9 = 2.269 D 9 = 0.461 N 6 = 1.84666 ν 6 = 23.8 R10 = 16.851 D10 = Variable R11 = (Aperture) D11 = Variable R12 = 6.280 D12 = 0.615 N 7 = 1.58313 ν 7 = 59.4 R13 = -1.541 D13 = 0.134 N 8 = 1.84666 ν 8 = 23.8 R14 = -2.828 D14 = 0.028 R15 = 3.728 D15 = 0.326 N 9 = 1.51633 ν 9 = 64.2 R16 = -17.975 D16 = Variable R17 = -2.380 D17 = 0.115 N10 = 1.60311 ν10 = 60.7 R18 = 4.319 D18 = 0.287 R19 = -3.442 D19 = 0.307 N11 = 1.72825 ν11 = 28.5 R20 = -1.795 D20 = Variable R21 = 2.215 D21 = 0.153 N12 = 1.84666 ν12 = 23.8 R22 = 1.427 D22 = 0.769 N13 = 1.48749 ν13 = 70.2 R23 = -19.979 D23 = 0.028 R24 = 4.178 D24 = 0.384 N14 = 1.48749 ν14 = 70.2 R25 = -12.773 D25 = 0.288 R26 = ∞ D26 = 0.971 N15 = 1.51633 ν15 = 64.2 R27 = ∞

[0042]

[Table 1] Numerical Example 2 f = 1 to 7.82 fno = 1: 2 to 2.6 2 ω = 60.0 ° to 8.4 ° R 1 = 14.326 D 1 = 0.288 N 1 = 1.84666 ν 1 = 23.8 R 2 = 6.202 D 2 = 1.153 N 2 = 1.60311 ν 2 = 60.7 R 3 = -18.789 D 3 = 0.028 R 4 = 4.257 D 4 = 0.653 N 3 = 1.69680 ν 3 = 55.5 R 5 = 10.710 D 5 = Variable R 6 = 28.031 D 6 = 0.153 N 4 = 1.77250 ν 4 = 49.6 R 7 = 1.514 D 7 = 0.666 R 8 = -2.415 D 8 = 0.134 N 5 = 1.60311 ν 5 = 60.7 R 9 = 2.173 D 9 = 0.461 N 6 = 1.84666 ν 6 = 23.8 R10 = 19.546 D10 = Variable R11 = (Aperture) D11 = Variable R12 = 5.063 D12 = 0.615 N 7 = 1.58313 ν 7 = 59.4 R13 = -1.460 D13 = 0.134 N 8 = 1.84666 ν 8 = 23.8 R14 = -2.559 D14 = 0.028 R15 = 3.079 D15 = 0.326 N 9 = 1.51633 ν 9 = 64.2 R16 = 32.713 D16 = Variable R17 = -2.514 D17 = 0.115 N10 = 1.60311 ν10 = 60.7 R18 = 4.013 D18 = 0.250 R19 = -2.442 D19 = 0.307 N11 = 1.72825 ν11 = 28.5 R20 = -1.679 D20 = Variable R21 = 2.114 D21 = 0.153 N12 = 1.84666 ν12 = 23.8 R22 = 1.418 D22 = 0.673 N13 = 1.48749 ν13 = 70.2 R23 = -11.237 D23 = 0.028 R24 = 2.489 D24 = 0.326 N14 = 1.48749 ν14 = 70.2 R25 = 7.812 D25 = 0.288 R2 6 = ∞ D26 = 0.971 N15 = 1.51633 ν15 = 64.2 R27 = ∞

[0043]

[Table 2] Numerical Example 3 f = 1 to 8.17 fno = 1: 2 to 2.9 2 ω = 66.2 ° to 9.1 ° R 1 = 15.900 D 1 = 0.326 N 1 = 1.84666 ν 1 = 23.8 R 2 = 7.390 D 2 = 1.130 N 2 = 1.60311 ν 2 = 60.7 R 3 = -47.999 D 3 = 0.032 R 4 = 5.802 D 4 = 0.673 N 3 = 1.69350 ν 3 = 53.2 R 5 = 21.220 D 5 = Variable R 6 = 20.381 D 6 = 0.173 N 4 = 1.77250 ν 4 = 49.6 R 7 = 1.970 D 7 = 0.890 R 8 = -3.185 D 8 = 0.152 N 5 = 1.60311 ν 5 = 60.7 R 9 = 2.504 D 9 = 0.521 N 6 = 1.84666 ν 6 = 23.8 R10 = 11.104 D10 = Variable R11 = (Aperture) D11 = Variable R12 = 8.175 D12 = 0.652 N 7 = 1.58313 ν 7 = 59.4 R13 = -1.751 D13 = 0.152 N 8 = 1.84666 ν 8 = 23.8 R14 = -3.447 D14 = 0.032 R15 = 4.474 D15 = 0.434 N 9 = 1.51633 ν 9 = 64.2 R16 = -11.518 D16 = Variable R17 = -2.975 D17 = 0.130 N10 = 1.60311 ν10 = 60.7 R18 = 5.630 D18 = 0.325 R19 = -5.065 D19 = 0.347 N11 = 1.72825 ν11 = 28.5 R20 = -2.322 D20 = Variable R21 = 4.810 D21 = 0.565 N12 = 1.48749 ν12 = 70.2 R22 = -13.141 D22 = 0.032 R23 = 2.262 D23 = 0.173 N13 = 1.84666 ν13 = 23.8 R24 = 1.392 D24 = 0.913 N14 = 1.48749 ν14 = 70.2 R25 = -14.394 D25 = 0.326 R26 = ∞ D26 = 1.097 N15 = 1.51633 ν15 = 64.2 R27 = ∞

[0044]

[Table 3] Numerical Example 4 f = 1 to 9.82 fno = 1: 2 to 2.4 2 ω = 59 ° to 6.6 ° R 1 = 13.336 D 1 = 0.283 N 1 = 1.84666 ν 1 = 23.8 R 2 = 5.695 D 2 = 0.981 N 2 = 1.60311 ν 2 = 60.7 R 3 = -19.711 D 3 = 0.028 R 4 = 4.311 D 4 = 0.547 N 3 = 1.69680 ν 3 = 55.5 R 5 = 11.042 D 5 = Variable R 6 = 20.192 D 6 = 0.150 N 4 = 1.77250 ν 4 = 49.6 R 7 = 1.548 D 7 = 0.718 R 8 = -2.865 D 8 = 0.132 N 5 = 1.69680 ν 5 = 55.5 R 9 = 2.131 D 9 = 0.096 R10 = 2.323 D10 = 0.377 N 6 = 1.84666 ν 6 = 23.8 R11 = 46.566 D11 = variable R12 = (aperture) D12 = variable R13 = 2.663 D13 = 0.603 N 7 = 1.58313 ν 7 = 59.4 R14 = -1.454 D14 = 0.132 N 8 = 1.84666 ν 8 = 23.8 R15 =- 2.216 D15 = Variable R16 = -4.338 D16 = 0.113 N 9 = 1.60311 ν 9 = 60.7 R17 = 3.328 D17 = 0.180 R18 = -2.797 D18 = 0.301 N10 = 1.72825 ν10 = 28.5 R19 = -2.201 D19 = Variable R 20 = 1.983 D20 = 0.150 N11 = 1.84666 ν11 = 23.8 R 21 = 1.343 D21 = 0.754 N12 = 1.48749 ν12 = 70.2 R 22 = -6.058 D22 = 0.028 R 23 = 5.595 D23 = 0.377 N13 = 1.48749 ν13 = 70.2 R 24 = 24.429 D24 = 0.283 R 25 = ∞ D25 = 0.952 N14 = 1.51633 ν14 = 64.2 R 26 = ∞

[0045]

[Table 4] Aspherical surface coefficient R13 k = −2.555 × 10 ⁻¹ a ₂ = −2.
180 × 10 ^-2 a ₃ = 1.810 × 10 ^-4 a ₄ = -1.038 × 1
0 ^-3 a ₅ = 5.087 × 10 ^-4 <Numerical Example 5> f = 1 to 8.06 fno = 1: 2 to 2.7 2 ω = 59 ° to 8.0 ° R 1 = 13.455 D 1 = 0.283 N 1 = 1.84666 ν 1 = 23.8 R 2 = 6.071 D 2 = 0.943 N 2 = 1.60311 ν 2 = 60.7 R 3 = -20.028 D 3 = 0.028 R 4 = 3.997 D 4 = 0.471 N 3 = 1.69680 ν 3 = 55.5 R 5 = 7.399 D 5 = Variable R 6 = 14.169 D 6 = 0.150 N 4 = 1.77250 ν 4 = 49.6 R 7 = 1.598 D 7 = 0.691 R 8 = -3.618 D 8 = 0.132 N 5 = 1.69680 ν 5 = 55.5 R 9 = 2.145 D 9 = 0.096 R10 = 2.341 D10 = 0.377 N 6 = 1.84666 ν 6 = 23.8 R11 = 17.544 D11 = Variable R12 = (Aperture) D12 = Variable R13 = 3.078 D13 = 0.603 N 7 = 1.58313 ν 7 = 59.4 R14 = -1.332 D14 = 0.132 N 8 = 1.84666 ν 8 = 23.8 R15 = -2.091 D15 = Variable R16 = -2.672 D16 = 0.113 N 9 = 1.60311 ν 9 = 60.7 R17 = 5.612 D17 = 0.222 R18 = -3.007 D18 = 0.301 N10 = 1.72825 ν10 = 28.5 R19 = -1.964 D19 = Variable R20 = 1.818 D20 = 0.150 N11 = 1.84666 ν11 = 23.8 R21 = 1.203 D21 = 0.905 N12 = 1.48749 ν12 = 70.2 R22 = -3.810 D22 = 0.283 R23 = ∞ D23 = 0.952 N13 = 1.51633 ν13 = 64.2 R24 = ∞

[0046]

[Table 5] Aspherical coefficients ^{R13 k = 4.035 × 10 -1 a} 2 = -
2.026 × 10 ⁻² a ₃ = 4.201 × 10 ⁻⁴ a ₄ = 1.128 ×
10 ^-3 a ₅ = -2.490 × 10 ^-4 R22 k = 1.429 × 10 ^-1 a ₂ =
5.366 x 10 ^-3 a ₃ = 9.188 x 10 ^-3 a ₄ = -1.448 x
10 ⁻² a ₅ = 1.328 × 10 ⁻⁶ << Numerical Example 6 >> f = 1 to 8.3 fno = 1: 2 to 2.9 2 ω = 59 ° to 7.8 ° R 1 = 13.430 D 1 = 0.283 N 1 = 1.84666 ν 1 = 23.8 R 2 = 5.784 D 2 = 0.981 N 2 = 1.60311 ν 2 = 60.7 R 3 = -16.693 D 3 = 0.028 R 4 = 3.608 D 4 = 0.547 N 3 = 1.69680 ν 3 = 55.5 R 5 = 7.006 D 5 = Variable R 6 = 15.251 D 6 = 0.150 N 4 = 1.77250 ν 4 = 49.6 R 7 = 1.459 D 7 = 0.538 R 8 = -3.725 D 8 = 0.132 N 5 = 1.69680 ν 5 = 55.5 R 9 = 2.011 D 9 = 0.096 R10 = 2.187 D10 = 0.377 N 6 = 1.84666 ν 6 = 23.8 R11 = 9.155 D11 = Variable R12 = (Aperture) D12 = Variable R13 = 2.520 D13 = 0.603 N 7 = 1.58313 ν 7 = 59.4 R14 = -1.512 D14 = 0.132 N 8 = 1.84666 ν 8 = 23.8 R15 = -2.289 D15 = Variable R16 = -6.687 D16 = 0.113 N 9 = 1.60311 ν 9 = 60.7 R17 = 2.475 D17 = 0.200 R18 = -3.310 D18 = 0.301 N10 = 1.72825 ν10 = 28.5 R19 = -2.584 D19 = Variable R20 = 2.106 D20 = 0.150 N11 = 1.84666 ν11 = 23.8 R21 = 1.475 D21 = 0.943 N12 = 1.48749 ν12 = 70.2 R22 = -6.795 D22 = 0.028 R23 = 4.096 D23 = 0.377 N13 = 1.48749 ν13 = 70.2 R24 = 66.287 D24 = 0.283 R25 = D25 = 0.952 N14 = 1.51633 ν14 = 64.2 R26 = ∞

[0047]

[Table 6] Aspherical coefficients ^{R13 k = -2.097 × 10 -1 a} 2 = -
2.351 × 10 ⁻² a ₃ = 1.830 × 10 ⁻³ a ₄ = −5.040 ×
10 ⁻⁴ a ₅ = −2.395 × 10 ⁻³ << Numerical Example 7 >> f = 1 to 7.91 fno = 1: 2 to 2.6 2 ω = 60.0 ° to 8.3 ° R 1 = 15.175 D 1 = 0.288 N 1 = 1.84666 ν 1 = 23.8 R 2 = 6.893 D 2 = 1.038 N 2 = 1.60311 ν 2 = 60.7 R 3 = -23.891 D 3 = 0.028 R 4 = 4.604 D 4 = 0.596 N 3 = 1.69680 ν 3 = 55.5 R 5 = 10.732 D 5 = Variable R 6 = 15.080 D 6 = 0.153 N 4 = 1.77250 ν 4 = 49.6 R 7 = 1.691 D 7 = 0.671 R 8 = -3.850 D 8 = 0.134 N 5 = 1.69680 ν 5 = 55.5 R 9 = 2.114 D 9 = 0.098 R10 = 2.348 D10 = 0.461 N 6 = 1.84666 ν 6 = 23.8 R11 = 14.616 D11 = Variable R12 = (Aperture) D12 = Variable R13 = 5.239 D13 = 0.615 N 7 = 1.58313 ν 7 = 59.4 R14 = -1.587 D14 = 0.134 N 8 = 1.84666 ν 8 = 23.8 R15 = -3.023 D15 = 0.028 R16 = 5.314 D16 = 0.384 N 9 = 1.63854 ν 9 = 55.4 R17 = -11.340 D17 = Variable R18 = -3.363 D18 = 0.115 N10 = 1.60311 ν10 = 60.7 R19 = 3.657 D19 = 0.218 R20 = -3.345 D20 = 0.307 N11 = 1.72825 ν11 = 28.5 R21 = -2.118 D21 = Variable R22 = 2.198 D22 = 0.153 N12 = 1.84666 ν12 = 23.8 R23 = 1.539 D23 = 0.769 N13 = 1.48749 ν13 = 70.2 R24 = -18.419 D24 = 0.02 8 R25 = 4.269 D25 = 0.384 N14 = 1.48749 ν14 = 70.2 R26 = -17.434 D26 = 0.288 R27 = ∞ D27 = 0.971 N15 = 1.51633 ν15 = 64.2 R28 = ∞

[0048]

[Table 7] Numerical Example 8 f = 1 to 8.02 fno = 1: 2 to 2.9 2 ω = 66.2 ° to 9.3 ° R 1 = 16.988 D 1 = 0.326 N 1 = 1.84666 ν 1 = 23.8 R 2 = 7.705 D 2 = 1.260 N 2 = 1.60311 ν 2 = 60.7 R 3 = -30.385 D 3 = 0.032 R 4 = 5.276 D 4 = 0.739 N 3 = 1.69680 ν 3 = 55.5 R 5 = 13.321 D 5 = Variable R 6 = 22.538 D 6 = 0.173 N 4 = 1.77250 ν 4 = 49.6 R 7 = 1.795 D 7 = 0.787 R 8 = -4.560 D 8 = 0.152 N 5 = 1.69680 ν 5 = 55.5 R 9 = 2.368 D 9 = 0.110 R10 = 2.524 D10 = 0.456 N 6 = 1.84666 ν 6 = 23.8 R11 = 16.709 D11 = Variable R12 = (Aperture) D12 = Variable R13 = 12.216 D13 = 0.652 N 7 = 1.58313 ν 7 = 59.4 R14 = -1.620 D14 = 0.152 N 8 = 1.84666 ν 8 = 23.8 R15 =- 2.882 D15 = 0.032 R16 = 8.440 D16 = 0.369 N 9 = 1.63854 ν 9 = 55.4 R17 = -11.101 D17 = Variable R18 = -2.669 D18 = 0.130 N10 = 1.60311 ν10 = 60.7 R19 = 9.481 D19 = 0.246 R20 = -4.913 D20 = 0.347 N11 = 1.72825 ν11 = 28.5 R21 = -2.387 D21 = Variable R22 = 5.464 D22 = 0.565 N12 = 1.48749 ν12 = 70.2 R23 = -5.068 D23 = 0.032 R24 = 2.428 D24 = 0.173 N13 = 1.84666 ν13 = 23.8 R25 = 1.393 D25 = 0.869 N14 = 1.48749 ν14 = 70.2 R 26 = 33.015 D26 = 0.326 R27 = ∞ D27 = 1.097 N15 = 1.51633 ν15 = 64.2 R28 = ∞

[0049]

[Table 8]

[0050]

As described above, according to the present invention, the refractive powers of the five lens groups and the moving conditions of each lens group during zooming are set, and at the time of focusing, the second group, the third group, and the By adopting a lens configuration in which at least one lens group out of the four groups is moved, while achieving miniaturization of the entire lens system and achieving good aberration correction over a variable power ratio of about 10 and the entire variable power range, It is possible to achieve a rear focus type zoom lens having an F number of 2.0 and a large aperture ratio, which has high optical performance with little aberration variation during focusing.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an embodiment showing a paraxial refractive power arrangement of 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 cross-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 a diagram showing various types of aberration in Numerical Example 1 of the present invention.

FIG. 11 is a diagram of various types of aberration in Numerical example 2 of the present invention.

FIG. 12 is a diagram of various types of aberration in Numerical example 3 of the present invention.

FIG. 13 is a diagram of various types of aberration in Numerical example 4 of the present invention.

FIG. 14 is a diagram of various types of aberration of Numerical example 5 of the present invention.

FIG. 15 is a diagram of various types of aberration of Numerical example 6 of the present invention.

FIG. 16 is a diagram of various types of aberration in Numerical example 7 of the present invention.

FIG. 17 is a diagram of various types of aberration of Numerical Example 8 of the present invention.

[Explanation of symbols]

 L1 1st group L2 2nd group L3 3rd group L4 4th group L5 5th group SP Aperture d d line g g line ΔS Sagittal image surface ΔM Meridional image surface

Claims (3)

[Claims] 1. A first group having a positive refractive power, a second group having a negative refractive power, an aperture stop, a third group having a positive refractive power, a fourth group having a negative refractive power, and a positive group in order from the object side. Of the fifth lens group having a refracting power of 5, the second lens group is moved to the image plane side to change the magnification from the wide-angle end to the telephoto end, The third group and the fourth group are moved for correction, and at least one lens group of the second group, the third group, and the fourth group is moved on the optical axis for focusing. Rear focus type zoom lens. 2. The rear focus type zoom lens according to claim 1, wherein the third lens unit has one positive lens and one negative lens, and at least one lens surface is an aspherical surface. lens. 3. The rear focus type zoom lens according to claim 1, wherein the second lens group has two negative lenses and one positive lens, which are arranged in this order from the object side, with an air gap therebetween. lens.