JPH07253543A - Rear focus type zoom lens - Google Patents

Abstract

PURPOSE:To obtain excellent optical performance over a whole variable power range from the wide-angle end to the telescopic end and over all distances of an object from an object at infinity to the closest object while miniaturizing the whole lens by performing compensation due to power variation and focusing by moving a fourth group. CONSTITUTION:This zoom lens comprised of four lens groups of a first lens group L1l having a positive refractive power, a second lens group L2 having a negative refractive power, a third lens group L3 having a positive refractive power and a fourth lens group L4 having a positive refractive power in order from the object side. Power variation from a wide-angle end to a telescopic end is performed by moving the second group L2 to the image plane side, the fluctuation of the image plane due to the power variation is compensated by moving the fourth group L4 and focusing is performed by moving the fourth group L4. The third group L3 comprised of a positive lens on the object side and a meniscus-like negative lens, whose concave surface confronts the image-plane side, on the closest side of the image plane and the fourth group L4 comprised of a negative lens and two positive lenses. By representing focal length of the third group L3 and the fourth group L4 by f3, f4, respectively, the condition: 0.73<f3<f4<1.00 is satisfied.

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 photographic camera, a video camera,
Further, the present invention relates to a rear focus type zoom lens having a large aperture ratio with a variable power ratio of 12, an F number of about 1.8, and a high variable power ratio, which is used in broadcast cameras and the like.

[0002]

2. Description of the Related Art Recently, as home video cameras have become smaller and lighter, remarkable progress has been made in the miniaturization of zoom lenses for image pickup. Especially, the total lens length and front lens diameter have been 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 for 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. In particular, since extremely close-up photography is facilitated and 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 JP-A-62-24213 and JP-A-63-247316, a first group having a positive refractive power and a negative refractive power are arranged in order from the object side. It has four lens groups, a second lens group of power, a third lens group of positive refractive power, and a fourth lens group of positive refractive power, and moves the second lens group to perform zooming and move the fourth lens group. Then, the image plane variation and the focus due to the magnification change are performed.

In the rear focus type zoom lens proposed in JP-A-4-43311 and JP-A-4-153615, the fourth lens unit is located closer to the image plane side at the telephoto end than at the wide-angle end. is doing. As a result, the moving distance during focusing of the fourth lens unit on the telephoto side is increased, and it is possible to focus on a super close-range (tele-macro shooting) object.

[0007]

Generally, when a rear focus system is adopted in a zoom lens, the entire lens system is downsized as described above, quick focusing is possible, and further close-up photography is facilitated. .

On the other hand, however, the aberration variation at the time of focusing becomes large, and it becomes very difficult to obtain high optical performance over the entire object distance from an object at infinity to a near object.

Particularly in 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.

The zoom ratios of the rear focus type zoom lenses described above are about 8 times, and the zoom ratios have not always been sufficient for recent zoom lenses for video cameras.

Further, the rear focus type zoom lens proposed in JP-A-2-55308, JP-A-4-26811, and JP-A-4-88309 is a lens having a front lens diameter, a total lens length, and the like. The downsizing of the entire system is not always sufficient.

The present invention adopts the rear focus method, and at the time of achieving a large aperture ratio and a high zoom ratio, downsizing the entire lens system while over 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 over the entire object distance from an infinitely distant object to a super close object.

[0013]

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. , And a fourth lens group of a fourth lens group having a positive refractive power,
The lens unit is moved to the image plane side to change the magnification from the wide-angle end to the telephoto end, and the image plane variation due to the magnification change is corrected by moving the fourth unit and moving the fourth unit. The third group has at least one positive lens on the object side and a meniscus-shaped negative lens having a concave surface closest to the image surface on the image side, and the fourth group includes one negative lens and two negative lenses. Two positive lenses, and the focal lengths of the third group and the fourth group are f3 and f, respectively.
When it is set to 4, 0.73 <f3 / f4 <1.00 (1) is satisfied.

[0014]

1 to 4 are sectional views of a rear focus type zoom lens according to the present invention at the wide-angle end in Numerical Examples 1 to 4 to be described later, and FIGS. 5 to 7 are Numerical Example 1 and FIG. Figure 10
Is a numerical example 2, FIGS. 11 to 13 are numerical examples 3, FIG.
4 to 16 are various aberration diagrams of Numerical Example 4. In the aberration diagrams, FIGS. 5, 8, 11 and 14 are at the wide angle end, and FIGS.
Reference numerals 2 and 15 are intermediate, and FIGS. 7, 10, 13 and 16 are telephoto ends.

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 positive refractive power. . SP is an aperture stop, which is arranged in front of the third lens unit L3. G is a glass block such as a face plate or filter, and IP is an image plane.

In this embodiment, the second lens unit is moved to the image plane side as indicated by the arrow when the magnification is changed from the wide-angle end to the telephoto end, and the fourth lens unit is convex toward the object side due to the image plane variation due to the magnification change. It is corrected by moving while having the locus of.

Further, a rear focus type in which focusing is performed by moving the fourth lens unit on the optical axis 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 shown in 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 this embodiment, for example, when focusing from an object at infinity to a near object at the telephoto end, the fourth lens unit is moved forward as indicated by a straight line 4c in the figure.

Since the zoom lens of the present invention has a high zoom ratio of 12 times, the moving amount of the fourth lens unit due to zooming becomes relatively large, and the variation of aberration due to zooming also increases. Tend. At the same time, the fourth lens for focusing at the telephoto end
The amount of movement of the group also increases, and it becomes difficult to correct aberration fluctuations due to focusing from an object at infinity to a close object.

Therefore, in the present invention, by specifying the lens configurations of the third group and the fourth group as described above, aberration fluctuations during zooming and focusing are satisfactorily corrected. Further, by disposing a meniscus-shaped negative lens with a strong concave surface facing the image surface side closest to the image surface in the third lens group, the back focus, which is insufficient due to the size reduction of the lens system, is lengthened. Then, the refracting powers of the third and fourth groups are set so as to satisfy the above-mentioned conditional expression (1), and the various aberrations are corrected well while the overall size of the lens system is reduced.

In the zoom lens according to the present invention, if the miniaturization of the entire lens system is pursued, the focal length f3 becomes short, and the axial light flux emerging from the third lens group becomes a convergent system. Therefore, the back focus becomes shorter. In order to solve the problem, the meniscus-shaped negative lens in the third lens group becomes important. Further, when the light beam enters the fourth lens unit in the convergent system, the aberration height increases due to a large change in the incident height due to the movement of the fourth lens unit. In order to solve the problem, the lens structure of the fourth group becomes important.

In consideration of the above points, the present invention provides the third group and the fourth group.
By setting the lens configuration of the group as described above, various aberrations are satisfactorily corrected while aiming at downsizing of the entire lens system.

Next, the technical meaning of the conditional expression (1) will be described. If the focal length f3 becomes too long beyond the upper limit of the conditional expression (1), the back focus becomes too long and it becomes difficult to downsize the entire lens system. If the focal length f3 becomes too short beyond the lower limit, the back focus becomes too short. If the refractive power of the meniscus negative lens in the third lens group is increased to make it longer, the curvature becomes too small. The occurrence of various aberrations such as spherical aberration and coma becomes large, and it becomes difficult to satisfactorily correct these aberrations.

The rear focus type zoom lens, which is the object of the present invention, can be achieved by satisfying the above-mentioned various conditions. Further, the overall lens system can be downsized and good optical performance can be obtained over the entire zoom range. To obtain, the second lens unit has a negative meniscus 21st lens with a strong concave surface facing the image surface side in order from the object side, and a negative 22nd lens element with both lens surfaces concave.
The third lens element is a lens and a positive 23rd lens having a convex surface having a stronger refractive power toward the object side than the image side.

In the present embodiment, the second group is configured as described above, so that the amount of fluctuation of the distortion aberration is particularly reduced during zooming. In a conventional general zoom lens, the distortion aberration exceeds -5% at the wide-angle end and around + 5% at the telephoto end.

On the other hand, in this embodiment, the distortion aberration is less than -5% at the wide-angle end and is drastically reduced to + 3% or less at the telephoto end.

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

In the present embodiment, the negative 22nd lens and the positive 23rd lens in the second lens group are composed of a single lens,
Aberration correction is performed by an air lens formed by both lenses. As a result, various aberrations such as spherical aberration, coma and axial chromatic aberration are corrected in good balance.

In this embodiment, the 22nd lens and the 2nd lens
Since the three lenses are composed of a single lens, the height from the optical axis when the on-axis light flux passing through the second lens group enters the 23rd lens after exiting the 22nd lens, the conventional general bonding It will be higher than when using a lens.

Therefore, the effects of various aberrations corrected by the 23rd lens become too strong. Therefore, the curvature of the object-side lens surface of the 23rd lens, the curvature of the image-side lens surface of the 21st lens, and the curvatures of both lens surfaces of the 22nd lens can be reduced accordingly.

In this embodiment, various aberrations generated from the second lens group are thereby reduced, and aberration fluctuations associated with zooming are corrected well.

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 in the i-th lens. The refractive index of glass and the Abbe number. In the numerical examples, the last two lens surfaces are glass blocks such as face plates and filters.

The aspherical shape has an X axis in the optical axis direction, an H axis in a direction perpendicular to the optical axis, a positive light traveling direction, and R as a paraxial radius of curvature,
When K, B, C, D and E are aspherical coefficients,

[0035]

[Equation 1] It is expressed by (Numerical Example 1) F = 1 to 12.01 fNO = 1: 1.8 to 2.6 2ω = 64.3 ° to 6.0 ° R 1 = 9.584 D 1 = 0.255 N 1 = 1.84666 ν 1 = 23.8 R 2 = 4.918 D 2 = 1.139 N 2 = 1.60311 ν 2 = 60.7 R 3 = -43.318 D 3 = 0.039 R 4 = 4.096 D 4 = 0.599 N 3 = 1.71300 ν 3 = 53.8 R 5 = 10.014 D 5 = variable R 6 = 6.188 D 6 = 0.117 N 4 = 1.88300 ν 4 = 40.8 R 7 = 1.209 D 7 = 0.520 R 8 = -2.220 D 8 = 0.117 N 5 = 1.77250 ν 5 = 49.6 R 9 = 2.220 D 9 = 0.150 R10 = 2.646 D10 = 0.353 N 6 = 1.84666 ν 6 = 23.8 R11 = -11.640 D11 = Variable R12 = (Aperture) D12 = 0.216 R13 = 2.915 D13 = 0.613 N 7 = 1.58313 ν 7 = 59.4 R14 = -8.355 D14 = 0.029 R15 = 2.695 D15 = 0.458 N 8 = 1.63854 ν 8 = 55.4 R16 = -24.147 D16 = 0.123 R17 = 6.138 D17 = 0.137 N 9 = 1.72825 ν 9 = 28.5 R18 = 1.714 D18 = Variable R19 = 2.550 D19 = 0.117 N10 = 1.80518 ν10 = 25.4 R20 = 1.424 D20 = 0.530 N11 = 1.51633 ν11 = 64.2 R21 = -14.796 D21 = 0.029 R22 = 5.917 D22 = 0.235 N12 = 1.51633 ν12 = 64.2 R23 = -31.294 D23 = 0.589 R24 = ∞ D24 = 0.982 N13 = 1.51633 ν13 = 64.2 R25 = ∞ Aspherical surface No. 13 Surface R = 2.915 K = 1.432 B = -2.274 × 10 ^-2 C = -2.665 × 10 ^-3 D = -2.484 × 10 ^-4 E = 1.433 × 10 ^-4

[0036]

[Table 1] (Numerical Example 2) F = 1 to 12.00 fNO = 1: 1.8 to 2.5 2 ω = 64.3 ° to 6.0 ° R 1 = 9.495 D 1 = 0.255 N 1 = 1.84666 ν 1 = 23.8 R 2 = 4.990 D 2 = 1.139 N 2 = 1.60311 ν 2 = 60.7 R 3 = -47.337 D 3 = 0.039 R 4 = 4.064 D 4 = 0.599 N 3 = 1.71300 ν 3 = 53.8 R 5 = 9.696 D 5 = variable R 6 = 6.607 D 6 = 0.117 N 4 = 1.88300 ν 4 = 40.8 R 7 = 1.230 D 7 = 0.520 R 8 = -2.298 D 8 = 0.117 N 5 = 1.77250 ν 5 = 49.6 R 9 = 2.298 D 9 = 0.150 R10 = 2.731 D10 = 0.353 N 6 = 1.84666 ν 6 = 23.8 R11 = -13.327 D11 = Variable R12 = (Aperture) D12 = 0.216 R13 = 2.709 D13 = 0.637 N 7 = 1.58313 ν 7 = 59.4 R14 = -8.485 D14 = 0.029 R15 = 2.208 D15 = 0.505 N 8 = 1.63854 ν 8 = 55.4 R16 = 159.833 D16 = 0.123 R17 = 5.431 D17 = 0.137 N 9 = 1.74077 ν 9 = 27.8 R18 = 1.390 D18 = Variable R19 = 3.333 D19 = 0.451 N10 = 1.51633 ν10 = 64.2 R20 = -2.532 D20 = 0.117 N11 = 1.84666 ν11 = 23.8 R21 = -4.570 D21 = 0.029 R22 = 4.439 D22 = 0.235 N12 = 1.51633 ν12 = 64.2 R23 = 15.125 D23 = 0.589 R24 = ∞ D24 = 0.982 N13 = 1.51633 ν13 = 64.2 R25 = ∞ Aspherical surface No. 13 R = 2.709 K = 1.185 B = -2.269 × 10 ^-2 C = -3.263 × 10 ^-3 D = 1.873 × 10 ^-4 E = -1.852 × 10 ^-4

[0037]

[Table 2] (Numerical Example 3) F = 1 to 12.00 fNO = 1: 1.8 to 2.5 2ω = 64.3 ° to 6.0 ° R 1 = 9.585 D 1 = 0.255 N 1 = 1.84666 ν 1 = 23.8 R 2 = 5.063 D 2 = 1.139 N 2 = 1.60311 ν 2 = 60.7 R 3 = -43.248 D 3 = 0.039 R 4 = 4.105 D 4 = 0.599 N 3 = 1.71300 ν 3 = 53.8 R 5 = 9.849 D 5 = variable R 6 = 7.587 D 6 = 0.117 N 4 = 1.88300 ν 4 = 40.8 R 7 = 1.244 D 7 = 0.520 R 8 = -2.307 D 8 = 0.117 N 5 = 1.77250 ν 5 = 49.6 R 9 = 2.307 D 9 = 0.150 R10 = 2.770 D10 = 0.353 N 6 = 1.84666 ν 6 = 23.8 R11 = -11.822 D11 = Variable R12 = (Aperture) D12 = 0.216 R13 = 3.405 D13 = 0.520 N 7 = 1.58313 ν 7 = 59.4 R14 = -10.290 D14 = 0.029 R15 = 2.513 D15 = 0.601 N 8 = 1.63854 ν 8 = 55.4 R16 = -5.548 D16 = 0.123 R17 = 7.406 D17 = 0.137 N 9 = 1.76182 ν 9 = 26.5 R18 = 1.539 D18 = Variable R19 = 7.393 D19 = 0.255 N10 = 1.51633 ν10 = 64.2 R20 = -10.413 D20 = 0.029 R21 = 3.628 D21 = 0.117 N11 = 1.80518 ν11 = 25.4 R22 = 2.447 D22 = 0.392 N12 = 1.51633 ν12 = 64.2 R23 = -12.050 D23 = 0.589 R24 = ∞ D24 = 0.982 N13 = 1.51633 ν13 = 64.2 R25 = ∞ Aspheric surface No. 13 Surface R = 3.405 K = 2.650 B = -3.054 × 10 ^-2 C = -4.716 × 10 ^-3 D = -1.599 × 10 ^-3 E = 8.4 30 × 10 ^-4

[0038]

[Table 3] (Numerical Example 4) F = 1 to 11.99 fNO = 1: 1.8 to 2.5 2ω = 64.3 ° to 6.0 ° R 1 = 9.634 D 1 = 0.255 N 1 = 1.84666 ν 1 = 23.8 R 2 = 4.960 D 2 = 1.139 N 2 = 1.60311 ν 2 = 60.7 R 3 = -41.062 D 3 = 0.039 R 4 = 4.101 D 4 = 0.599 N 3 = 1.71300 ν 3 = 53.8 R 5 = 9.967 D 5 = variable R 6 = 6.071 D 6 = 0.117 N 4 = 1.88300 ν 4 = 40.8 R 7 = 1.190 D 7 = 0.520 R 8 = -2.236 D 8 = 0.117 N 5 = 1.77250 ν 5 = 49.6 R 9 = 2.236 D 9 = 0.150 R10 = 2.666 D10 = 0.353 N 6 = 1.84666 ν 6 = 23.8 R11 = -11.097 D11 = Variable R12 = (Aperture) D12 = 0.216 R13 = 3.563 D13 = 0.512 N 7 = 1.58313 ν 7 = 59.4 R14 = -8.772 D14 = 0.029 R15 = 2.323 D15 = 0.548 N 8 = 1.63854 ν 8 = 55.4 R16 = -9.751 D16 = 0.123 R17 = 7.535 D17 = 0.137 N 9 = 1.76182 ν 9 = 26.5 R18 = 1.626 D18 = Variable R19 = 3.356 D19 = 0.196 N10 = 1.51742 ν10 = 52.4 R20 = 9.402 D20 = 0.196 R21 = 6.363 D21 = 0.550 N11 = 1.51742 ν11 = 52.4 R22 = -1.370 D22 = 0.117 N12 = 1.80518 ν12 = 25.4 R23 = -2.593 D23 = 0.589 R24 = ∞ D24 = 0.982 N13 = 1.51633 ν13 = 64.2 R25 = ∞ Aspheric coefficient No. 13 Surface R = 3.563 K = 2.468 B = -2.405 × 10 ^-2 C = -1.233 × 10 ^-4 D =- 1.272 × 10 ^-3 E = -2.165 × 10 ^-4

[0039]

[Table 4]

[0040]

According to the present invention, by setting the lens structure as described above, while adopting the rear focus system, the F number is 1.8 and the large aperture ratio is achieved, and the zoom ratio is 12 and the high zoom ratio is achieved. The rear focus has good optical performance over the entire zoom range from the wide-angle end to the telephoto end, and over the entire object distance from the infinity object to the ultra close object while reducing the overall size of the lens system. Formula zoom lens can be achieved.

[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 L3 3rd group L4 4th group SP Aperture d d line g g line ΔS Sagittal image surface ΔM Meridional image surface

Claims (2)

[Claims] 1. Four lens groups, in order from the object side, a first group having a positive refractive power, a second group having a negative refractive power, a third group having a positive refractive power, and a fourth group having a positive refractive power. And moving the second lens group toward the image plane side to perform zooming from the wide-angle end to the telephoto end, and moving the fourth lens group to correct the image plane variation due to zooming and The third group includes at least one positive lens on the object side and a meniscus-shaped negative lens with a concave surface facing the image side closest to the image side, and the fourth group Has one negative lens and two positive lenses. When the focal lengths of the third group and the fourth group are f3 and f4, 0.73 <f3 / f4 <1.00 A rear-focus type zoom lens characterized by satisfaction. 2. The second lens unit is a negative meniscus lens having a convex surface directed toward the object side in order from the object side, a negative second lens having both concave lens surfaces, and a lens element facing the object side as compared to the image side. The rear-focus type zoom lens according to claim 1, wherein the rear-focus type zoom lens comprises three independent lenses of a positive 23rd lens having a convex surface having a strong positive refractive power.