JP3064797B2 - Rear focus zoom lens - Google Patents

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 of about 12 and an F number of about 1.8, which is used in a broadcast camera and the like, and has a high zoom ratio.

[0002]

2. Description of the Related Art In recent years, as home video cameras and the like have become smaller and lighter, remarkable progress has been made in miniaturization of zoom lenses for image pickup. Emphasis is placed on simplification.

As one means for achieving these objects, there is known a so-called rear focus type zoom lens which performs focusing by moving a lens group other than the first group on the object side.

In general, a rear focus type zoom lens has a smaller effective diameter of the first lens group than a zoom lens which performs focusing by moving the first lens group, so that the entire lens system can be easily miniaturized, and close-up photographing can be performed. 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 can be performed.

As such a rear focus type zoom lens, for example, JP-A-62-2423 and JP-A-63-247316 disclose a first lens unit having a positive refractive power and a negative refraction in order from the object side. It has four lens groups, a second group of power, a third group of positive refractive power, and a fourth group of positive refractive power. The second group is moved to perform zooming, and the fourth group is moved. In this way, the image plane fluctuation and the focusing due to the magnification change are performed.

In a rear focus zoom lens proposed in Japanese Patent Application Laid-Open Nos. 4-43311 and 4-153615, the fourth lens unit is positioned closer to the image plane at the telephoto end than at the wide-angle end. doing. As a result, the moving distance of the fourth lens group during focusing on the telephoto side is increased, and focusing on an object at a very close distance (tele macro photography) is enabled.

[0007]

Generally, when a rear focus system is employed in a zoom lens, the overall lens system can be reduced in size and quick focusing becomes possible as described above, and further advantages such as close-up photographing can be easily obtained. .

[0008] On the other hand, however, there is a problem in that aberration fluctuation during focusing becomes large, and it becomes very difficult to obtain high optical performance over the entire object distance from an object at infinity to an object at a short distance.

In particular, a zoom lens having a large aperture ratio and a high zoom ratio has a problem that it becomes very difficult to obtain high optical performance over the entire zoom range and over the entire object distance.

Each of the rear focus type zoom lenses described above has a zoom ratio of about 8 times, and the zoom ratio for recent video cameras is not always sufficient.

A rear focus type zoom lens proposed in Japanese Patent Application Laid-Open Nos. 2-55308, 4-26811 and 4-88309 is known as a lens having a front lens diameter and a total lens length. The downsizing of the entire system is not always sufficient.

When the present invention employs a rear focus system to achieve a large aperture ratio and a high zoom ratio, the entire lens system is reduced in size from the wide-angle end to the telephoto end while the size of the entire lens system is reduced. An object of the present invention is to provide a rear focus type zoom lens having excellent optical performance over the entire object distance from an object at infinity to an object at a very close distance.

[0013]

A rear focus type zoom lens according to the present invention comprises, in order from the object side, a first lens unit having a positive refractive power, a second lens unit having a negative refractive power, and a third lens unit having a positive refractive power. And a fourth lens unit of a fourth group having a positive refractive power.
The lens unit is moved to the image plane side to perform zooming from the wide-angle end to the telephoto end, and the image plane fluctuation due to zooming is corrected by moving the fourth unit, and the fourth unit is moved to focus. The third group has at least one positive lens on the object side and a meniscus-shaped negative lens with the concave surface facing the image plane closest to the image plane, and the fourth group has one negative lens and 2 And the focal lengths of the third and fourth groups are f3 and f, respectively.
When 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, which will be described later. FIGS. 5 to 7 show Numerical Examples 1 and 8 to 8. FIG.
11 shows Numerical Example 2, FIGS. 11 to 13 show Numerical Example 3, and FIG.
4 to 16 are graphs showing various aberrations of the 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 indicate intermediate positions, and FIGS. 7, 10, 13 and 16 indicate telephoto ends.

In the drawing, 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 denotes 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 a filter, and IP is an image plane.

In this embodiment, when zooming from the wide-angle end to the telephoto end, the second lens unit is moved to the image plane side as indicated by an arrow, and the image plane fluctuation due to zooming is corrected by projecting the fourth lens unit to the object side. The movement is corrected while having the trajectory.

Also, a rear focus system is employed in which the fourth unit is moved on the optical axis to perform focusing. A solid line curve 4a and a dotted line curve 4b of the fourth lens group shown in the same figure show the image plane fluctuation caused by zooming from the wide-angle end to the telephoto end when focusing on an object at infinity and an object at a short distance, respectively. The movement locus for correction is shown. The first and third units are fixed during zooming and focusing.

In the present embodiment, the fourth lens unit is moved to correct the image plane fluctuation caused by zooming, and the fourth lens unit is moved for focusing. In particular, curve 4 in FIG.
When zooming from the wide-angle end to the telephoto end, as shown in FIGS.
Thus, the space between the third and fourth units is effectively used, and the overall length of the lens is effectively reduced.

In this embodiment, for example, when focusing from an object at infinity to an object at a short distance at the telephoto end, the fourth unit is moved forward as indicated by a straight line 4c in FIG.

Since the zoom lens according to the present invention has a high zoom ratio of 12 times, the amount of movement of the fourth lens unit during zooming is relatively large, and aberration fluctuations due to zooming are also increased. Tend. At the same time, the fourth lens for focusing at the telephoto end is used.
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, aberrations during zooming and focusing are corrected well by specifying the lens configurations of the third and fourth groups as described above. In addition, by disposing a meniscus-shaped negative lens having a strong concave surface on the image surface side closest to the image surface side of the third lens unit, the back focus, which is insufficient due to miniaturization of the lens system, is lengthened. The refractive powers of the third and fourth units are set so as to satisfy the above-mentioned conditional expression (1), and various aberrations are favorably corrected while miniaturizing the entire lens system.

In the zoom lens according to the present invention, if the size of the entire lens system is reduced, the focal length f3 is reduced, and the axial luminous flux emitted from the third lens unit is converged. For this reason, the back focus becomes shorter. In order to solve the problem, the negative meniscus lens in the third lens group becomes important. Further, when the light enters the fourth unit in the convergence system, the incident height greatly changes due to the movement of the fourth unit, so that the aberration fluctuation increases. In order to solve the problem, the lens configuration of the fourth group becomes important.

In consideration of the above points, the present invention provides a third lens group and a fourth lens group.
By setting the lens configuration of the group as described above, various aberrations are favorably corrected while reducing the size of the entire lens system.

Next, the technical meaning of the conditional expression (1) will be described. If the focal length f3 is too long beyond the upper limit value of the conditional expression (1), the back focus becomes too long, and it becomes difficult to reduce the size of the entire lens system. If the focal length f3 is too short below the lower limit, the back focus is too short. If the refractive power of the meniscus-shaped negative lens in the third lens unit is increased to lengthen the focal length, the curvature becomes too small. Occurrence of various aberrations such as spherical aberration and coma increases, and it becomes difficult to satisfactorily correct them.

The rear focus type zoom lens which is the object of the present invention can be achieved by satisfying the above-mentioned conditions. However, it is possible to achieve good optical performance over the entire zoom range while further reducing the size of the entire lens system. In order to obtain the second lens unit, a negative twenty-first meniscus lens having a strong concave surface facing the image surface side in order from the object side, and a negative twenty-second lens having both lens surfaces concave.
It is composed of three single lenses of a lens and a positive twenty-third lens having a convex surface having a higher refractive power directed toward the object side than the image plane side.

In this embodiment, by configuring the second lens unit as described above, the amount of fluctuation of distortion in particular during zooming is reduced. In a conventional general zoom lens, the distortion exceeds -5% at the wide-angle end and is around + 5% at the telephoto end.

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

Also, the position of the front principal point of the second lens unit is set closer to the object side, the distance between the principal points with the first lens unit is shortened, and the first lens unit is moved closer to the stop position. As a result, the height of the off-axis light beam incident on the first group from the optical axis is reduced, the diameter of the first group lens is reduced, and the overall length of the lens is reduced and the size and weight are reduced.

In this embodiment, the negative second lens and the positive twenty-third lens in the second lens unit are constituted by a single lens.
Aberration correction is performed by an air lens formed by both lenses. Thus, various aberrations such as spherical aberration, coma, and axial chromatic aberration are corrected in a well-balanced manner.

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 luminous flux passing through the second group exits the 22nd lens and then enters the 23rd lens is a conventional general bonding. It is higher than with a lens.

For this reason, the effects of various aberrations corrected by the twenty-third lens are too strong. Therefore, the curvature of the object-side lens surface of the twenty-third lens, the curvature of the image-side lens surface of the twenty-first lens, and the curvature of both lens surfaces of the twenty-second lens can be reduced accordingly.

In the present embodiment, various aberrations generated from the second lens unit are thereby reduced, and aberration fluctuations accompanying zooming are corrected well.

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 spacing from the object side, and Ni and νi are the i-th lens surfaces in order from the object side. The refractive index and Abbe number of glass. In the numerical examples, the last two lens surfaces are glass blocks such as a face plate and a filter.

The aspheric surface has an X-axis in the optical axis direction, an H-axis in a direction perpendicular to the optical axis, a positive traveling direction of light, R is a paraxial radius of curvature,
When K, B, C, D, and E are aspheric coefficients, respectively,

[0035]

(Equation 1) It is represented by the following equation. (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 = ∞ Aspheric coefficient 13th 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 2ω = 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 = ∞ Aspheric surface 13th surface 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 coefficient 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 = 8.430 × 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 configuration as described above, it is possible to achieve a high zoom ratio with an F-number of 1.8 and a large aperture ratio and a zoom ratio of 12 while employing the rear focus method. Rear focus with 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 object at infinity to the very close object while miniaturizing the entire lens system A zoom lens of the formula can be achieved.

[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 a sectional view of a lens according to a numerical example 2 of the present invention.

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

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

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

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

FIG. 7 is an aberration diagram at a telephoto end in 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 the numerical example 2 of the present invention.

FIG. 10 is an aberration diagram at a telephoto end in 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 the numerical example 3 of the present invention.

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

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

FIG. 15 is an intermediate aberration diagram of the numerical example 4 of the present invention.

FIG. 16 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 L3 Third lens unit L4 Fourth lens unit SP aperture d d-line g g-line ΔS sagittal image plane ΔM meridional image plane

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G02B 9/00-17/08 G02B 21/02-21/04 G02B 25/00-25/04

Claims (6)

(57) [Claims] 1. A first lens unit having a positive refractive power, a second lens unit having a negative refractive power, a third lens unit having a positive refractive power, and a fourth lens unit having a positive refractive power. The second unit is moved to the image plane side to perform zooming from the wide-angle end to the telephoto end, and the image plane fluctuation due to zooming is corrected by moving the fourth unit. The third group includes at least one positive lens on the object side and a meniscus-shaped negative lens with the concave surface facing the image plane closest to the image plane, and the fourth group includes the fourth group. Has one negative lens and two positive lenses. When the focal lengths of the third and fourth groups are f3 and f4, respectively, the condition 0.73 <f3 / f4 <1.00 is satisfied. Rear focus zoom lens characterized by satisfaction. 2. The second group includes a negative twenty-first meniscus lens having a convex surface facing the object side in order from the object side, a negative second lens having both lens surfaces concave, and an object-side negative lens. 2. The rear focus type zoom lens according to claim 1, comprising three independent lenses of a positive twenty-third lens having a convex surface having a strong positive refractive power. 3. The third lens unit includes, in order from the object side, a positive lens having both lens surfaces convex, a positive lens having a convex surface facing the object side, and a meniscus-shaped negative lens having a concave surface facing the image surface. 3. The rear focus type zoom lens according to claim 2, wherein: 4. The rear focus type zoom lens according to claim 3, wherein said fourth group includes a negative lens, a positive lens, and a positive lens. 5. The rear focus type zoom lens according to claim 3, wherein said fourth group includes a positive lens, a negative lens, and a positive lens. 6. The rear focus type zoom lens according to claim 3, wherein said fourth group includes a positive lens, a positive lens and a negative lens.