JPH07110447A - Zoom lens - Google Patents

Abstract

PURPOSE:To provide the 5-group zoom lens having a prescribed back focus and high optical performance over the entire variable power range by setting the lens constitution of the respective lens groups at specific values. CONSTITUTION:This zoom lens consists of the first group L1 having a positive refracting power for focusing, a second group L2 having a negative refracting power for variable power, the third group L3 having a negative refracting power for correcting the image plane fluctuating with the variable power, the fourth group L4 having a fixed imaging function and positive refracting power and the fifth group L5 having a fixed imaging function and a positive refracting power. The lens constitution, the refracting powers of the respective lens groups, etc., are set like the following condition equations. These equations are 1.1<Bf/f5<1.8, >>f3/f4>1.0, >>f5/f4>0.63, 0.19<>>fw/f3>0.26. In these equations, the air equiv. length from the final lens face to the image plane is shown by Bf, the focal length of the (i) group is shown by fi and the focal length of the entire system at the wide angle end is shown by fw.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens, and particularly, it has an F number of about 2.4 and a zoom ratio of about 3 and has good optical performance over the entire zoom range and has a relatively long back focus. The present invention relates to a zoom lens suitable for a photographic camera, a video camera, a broadcast camera and the like.

[0002]

2. Description of the Related Art Conventionally, a zoom lens having a predetermined back focus and high optical performance over the entire zoom range has been required for a photographic camera, a video camera and the like.

For example, in a zoom lens used in a multi-plate type video camera for a broadcasting station, a thick optical member such as a color filter or a color separation prism is arranged on the image side. And long back focus is required.

Further, in recent zoom lenses for video cameras, high resolution is required over the entire screen as the number of pixels of an image pickup device such as a CCD is increased, for example, from 250,000 pixels to 330,000 pixels.

Generally, as a zoom lens having a relatively long back focus, a predetermined zoom ratio, and relatively high optical performance over the entire screen, a positive refractive power for focusing is sequentially provided from the object side. , A second group of negative refracting power for zooming, a third group of positive or negative refracting power for correcting an image plane fluctuated by zooming, and a positive refracting power for imaging. There is a so-called five-group zoom lens having five lens groups, a fourth group and a fifth group having a positive refractive power for image formation.

For example, such a 5-group zoom lens has been proposed in Japanese Patent Laid-Open Nos. 2-208618 and 2-208620.

[0007]

Generally, in a 5-group zoom lens, a lens system is constructed in order to obtain a high optical performance while having a predetermined back focus and a variable power ratio, and further to downsize the entire lens system. It is important to properly set the optical constants of each lens group.

For example, if the refractive power of each lens unit is strengthened or the number of lenses is increased in order to achieve high performance, the entire lens system becomes large, and spherical aberration at the center of the screen, coma aberration at the periphery of the screen, and sagittal halo. A lot of high-order aberrations such as aberrations occur, and the variation of aberrations at the time of zooming also becomes large, which makes it difficult to obtain high optical performance.

According to the present invention, in a so-called five-group zoom lens, by appropriately setting the lens configuration and refractive power of each lens group, the aperture ratio is as bright as F / 2.4 and the zoom ratio is about 3 It is an object of the present invention to provide a zoom lens having a long back focus, which has a high optical performance over the entire zoom range.

[0010]

A 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 having a zooming function, and an image plane which varies with zooming. A third lens unit having a negative refractive power, a fourth lens unit having a positive refractive power, and a fifth lens unit having a positive refractive power,
The group consists of a negative 21st lens with a concave surface having a strong refractive power facing the image side, a negative 22nd lens with a concave surface on both lens surfaces, and a positive 23rd lens with a convex surface having a strong refractive power facing the object side. The twenty-second lens and the twenty-third lens are independent or cemented, and the air conversion length from the final lens surface to the image plane is B
f, where the focal length of the i-th group is fi and the focal length of the entire system at the wide-angle end is fw 1.1 <Bf / f5 <1.8 ... (1) | f3 / f4 | <1 ..... (2) | f5 / f4 | <0.63 ... (3) 0.19 <| fw / f3 | <0.26 ... (4) Satisfies the condition It is characterized by that.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1 to 4 are numerical examples 1 of the present invention which will be described later.
4 to 4 are lens sectional views, FIGS. 5 to 7 are aberration diagrams at wide-angle end, middle, and telephoto end zoom positions of Numerical Embodiment 1 of the present invention, and FIGS. 8 to 10 are wide-angle lenses of Numerical Embodiment 2 of the present invention. Aberration diagrams at the zoom positions at the end, the middle, and the telephoto end, FIGS.
3 is an aberration diagram at the wide-angle end, middle, and telephoto end zoom positions of Numerical Embodiment 3 of the present invention, and FIGS. 14 to 16 are aberrations at the wide-angle end, middle, and telephoto end zoom positions of Numerical Embodiment 4 of the present invention. It is a figure.

In the lens sectional view, L1 is a first lens unit having a positive refractive power for focusing, L2 is a second lens unit having a negative refractive power for zooming,
L3 is a third group of negative refracting power for correcting an image plane that varies with zooming, L4 is a fourth group of positive refracting power having a fixed image forming function, and L5 is a fixed image forming function. A fifth lens unit SP having a positive refractive power, SP, is a fixed diaphragm and is arranged between the third lens unit L3 and the fourth lens unit L4 or in the fourth lens unit. G is a glass block such as a filter or a face plate. IP
Is the image plane.

In the present embodiment, in the zoom type composed of such five lens groups, the lens structure of the second lens group and the refracting power of each lens group are set as in conditional expressions (1) to (4). It has a predetermined back focus, reduces aberration fluctuations associated with zooming, and obtains good optical performance over the entire zoom range.

For example, spherical aberration, coma aberration, chromatic aberration, and the like in a variable power system are corrected in a well-balanced manner while shortening the total lens length.

The air-converted length Bf from the final lens surface to the image surface is the value converted into the air-converted length excluding the glass block G such as a color filter or color separation prism provided on the image surface side of the optical system, so-called back focus. That is.

Next, the technical meaning of the conditional expressions (1) to (4) will be described.

Conditional expression (1) is the back focus length B.
This is for easily improving the performance when the ratio between f and the focal length of the fifth lens unit is appropriately set and applied to, for example, a zoom lens for a multi-plate video camera.

If the lower limit of conditional expression (1) is exceeded, it will be difficult to obtain the necessary back focus, and if the upper limit is exceeded, the power of the fifth lens unit will become too strong, and spherical aberration and field curvature will deteriorate. It's not good because it comes.

Conditional expression (2) has a good telecentricity when the ratio of the focal lengths of the third lens unit and the fourth lens unit is appropriately set and is mainly used for a zoom lens for a multi-plate video camera. Moreover, it is for giving a long back focus. If the upper limit of conditional expression (2) is exceeded, it will be difficult to obtain a back focus of the required length while maintaining optical performance, and field curvature will deteriorate, which is not preferable.

Conditional expression (3) sets the ratio of the focal lengths of the fourth lens unit and the fifth lens unit appropriately, and mainly makes the divergent light flux from the fourth lens unit substantially parallel light, and has good telecentricity in the fifth lens unit. And has a long back focus. If the upper limit of conditional expression (3) is exceeded, spherical aberration and field curvature will deteriorate and it will become difficult to obtain the necessary back focus.

Conditional expression (4) appropriately sets the ratio of the focal length of the third lens unit to the focal length at the wide-angle end of the entire system, and satisfactorily corrects chromatic aberration and field curvature mainly associated with zooming. It is for the purpose. The refractive powers of the third, fourth, and fifth groups are conditional expressions (1) to
When set in the range of (3), if the third group is not within the range of the conditional expression (4), the movement locus of each lens group during zooming exceeds the range in which various aberrations can be properly corrected. .

Specifically, if the lower limit of conditional expression (5) is exceeded, the variation of chromatic aberration will increase, and if it exceeds the upper limit, the variation of curvature of field accompanying zooming will become large, and further, in the entire zooming range. The Petzval sum increases, and the curvature of field deteriorates over the entire zoom range.

In this embodiment, a cemented lens in which a negative meniscus eleventh lens element having a convex surface facing the object side in the first lens group and a twelfth lens element having convex lens surfaces on both sides is cemented, and a convex surface element on the object side is provided. It is composed of a positive meniscus thirteenth lens aimed at, and satisfactorily corrects aberration fluctuations at the time of focusing.

In the present embodiment, the third lens unit is composed of a single negative lens to reduce the size of the entire lens system.

The fourth group is composed of two lenses of a positive lens and a negative lens, or three lenses of two positive lenses and a negative lens, or two lenses of a positive lens, a negative lens and a positive lens, and a fifth lens. High optical power over the entire zoom range by composing the lens unit with a positive meniscus lens with convex surface facing the image side, a negative meniscus lens with convex surface facing the object side, and four positive lenses Has gained performance.

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 spatial interval 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 final three lens surfaces are glass plates such as a face plate, a filter and a color separation prism.

Table 1 shows the relationship between the above-mentioned conditional expressions and various numerical values in the numerical examples.

Numerical Example 1 F = 1 fno = 1: 2.4 2ω = 53.1 R 1 = 23.069 D 1 = 0.211 N 1 = 1.84666 ν 1 = 23.8 R 2 = 5.105 D 2 = 1.055 N 2 = 1.60342 ν 2 = 38.0 R 3 = -21.059 D 3 = 0.023 R 4 = 5.145 D 4 = 0.694 N 3 = 1.75500 ν 3 = 52.3 R 5 = 34.487 D 5 = Variable R 6 = -503.866 D 6 = 0.117 N 4 = 1.77250 ν 4 = 49.6 R 7 = 1.764 D 7 = 0.476 R 8 = -3.521 D 8 = 0.117 N 5 = 1.69680 ν 5 = 55.5 R 9 = 3.487 D 9 = 0.141 R10 = 3.311 D10 = 0.385 N 6 = 1.84666 ν 6 = 23.8 R11 = -12.274 D11 = Variable R12 = -5.527 D12 = 0.211 N 7 = 1.69680 ν 7 = 55.5 R13 = 9.111 D13 = Variable R14 = (Aperture) D14 = 0.182 R15 = 22.764 D15 = 0.176 N 8 = 1.69895 ν 8 = 30.1 R16 = -3.146 D16 = 0.321 R17 = -1.591 D17 = 0.223 N 9 = 1.60311 ν 9 = 60.7 R18 = -5.854 D18 = 1.585 R19 = -8.921 D19 = 0.341 N10 = 1.51823 ν10 = 59.0 R20 = -2.391 D20 = 0.023 R21 = 23.740 D21 = 0.117 N11 = 1.80518 ν11 = 25.4 R22 = 2.035 D22 = 0.518 N12 = 1.62374 ν12 = 47.1 R23 = -9.892 D23 = 0.035 R24 = 2.965 D24 = 0.412 N13 = 1.5174 2 ν13 = 52.4 R25 = -10.565 D25 = 0.941 R26 = ∞ D26 = 3.296 N14 = 1.60342 ν14 = 38.0 R27 = ∞ D27 = 0.894 N15 = 1.51633 ν15 = 64.2 R28 = ∞

[0030]

[Table 1] <Numerical Example 2> F = 1 fno = 1: 2.4 2ω = 53.1 R 1 = 9.509 D 1 = 0.159 N 1 = 1.80518 ν 1 = 25.4 R 2 = 3.906 D 2 = 1.032 N 2 = 1.60311 ν 2 = 60.7 R 3 = -21.157 D 3 = 0.023 R 4 = 3.059 D 4 = 0.647 N 3 = 1.69680 ν 3 = 55.5 R 5 = 13.036 D 5 = Variable R 6 = 0.000 D 6 = 0.117 N 4 = 1.78590 ν 4 = 44.2 R 7 = 1.301 D 7 = 0.439 R 8 = -1.832 D 8 = 0.117 N 5 = 1.69680 ν 5 = 55.5 R 9 = 1.254 D 9 = 0.411 N 6 = 1.76182 ν 6 = 26.5 R10 = -7.248 D10 = variable R11 = -100.924 D11 = 0.117 N 7 = 1.84666 ν 7 = 23.8 R12 = 3.693 D12 = Variable R13 = -19.169 D13 = 0.235 N 8 = 1.48749 ν 8 = 70.2 R14 = -2.467 D14 = 0.176 R15 = (Aperture) D15 = 0.305 R16 = 6.329 D16 = 0.470 N 9 = 1.69895 ν 9 = 30.1 R17 = -0.930 D17 = 0.117 N10 = 1.77250 ν10 = 49.6 R18 = 5.027 D18 = 1.890 R19 = -21.339 D19 = 0.352 N11 = 1.51633 ν11 = 64.2 R20 = -2.546 D20 = 0.023 R21 = 87.299 D21 = 0.117 N12 = 1.84666 ν12 = 23.8 R22 = 3.237 D22 = 0.588 N13 = 1.51633 ν13 = 64.2 R23 = -4.972 D23 = 0.023 R24 = 4.166 D24 = 0.470 N14 = 1.51633 ν14 = 64.2 R25 = -6.264 D25 = 0.941 R26 = ∞ D26 = 3.294 N15 = 1.60342 ν15 = 38.0 R27 = ∞ D27 = 0.894 N16 = 1.51633 ν16 = 64.2 R28 = ∞

[0031]

[Table 2] Numerical Example 3 F = 1 fno = 1: 2.4 2ω = 53.1 R 1 = 10.279 D 1 = 0.159 N 1 = 1.80518 ν 1 = 25.4 R 2 = 3.761 D 2 = 0.882 N 2 = 1.60311 ν 2 = 60.7 R 3 = -12.315 D 3 = 0.023 R 4 = 3.122 D 4 = 0.470 N 3 = 1.69680 ν 3 = 55.5 R 5 = 11.301 D 5 = Variable R 6 = 11.458 D 6 = 0.117 N 4 = 1.77250 ν 4 = 49.6 R 7 = 1.264 D 7 = 0.411 R 8 = -1.759 D 8 = 0.117 N 5 = 1.69680 ν 5 = 55.5 R 9 = 1.754 D 9 = 0.294 N 6 = 1.84666 ν 6 = 23.8 R10 = -19.221 D10 = variable R11 = -1.952 D11 = 0.117 N 7 = 1.69680 ν 7 = 55.5 R12 = -5.992 D12 = Variable R13 = -20.778 D13 = 0.235 N 8 = 1.74400 ν 8 = 44.8 R14 = -2.095 D14 = 0.117 R15 = (Aperture) D15 = 0.305 R16 = 5.526 D16 = 0.352 N 9 = 1.62374 ν 9 = 47.1 R17 = -0.956 D17 = 0.117 N10 = 1.77250 ν10 = 49.6 R18 = 7.664 D18 = 1.670 R19 = -14.044 D19 = 0.352 N11 = 1.51742 ν11 = 52.4 R20 = -2.174 D20 = 0.023 R21 = 17.598 D21 = 0.117 N12 = 1.80518 ν12 = 25.4 R22 = 2.479 D22 = 0.588 N13 = 1.51633 ν13 = 64.2 R23 = -4.731 D23 = 0.023 R24 = 2.653 D24 = 0.411 N1 4 = 1.51633 ν14 = 64.2 R25 = -28.301 D25 = 0.611 R26 = ∞ D26 = 2.140 N15 = 1.60342 ν15 = 38.0 R27 = ∞ D27 = 0.580 N16 = 1.51633 ν16 = 64.2 R28 = ∞

[0032]

[Table 3] Numerical Example 4 F = 1 fno = 1: 2.4 2ω = 52.5 R 1 = 15.538 D 1 = 0.220 N 1 = 1.80518 ν 1 = 25.4 R 2 = 6.768 D 2 = 0.825 N 2 = 1.60311 ν 2 = 60.7 R 3 = -23.305 D 3 = 0.023 R 4 = 4.226 D 4 = 0.569 N 3 = 1.64000 ν 3 = 60.1 R 5 = 11.312 D 5 = Variable R 6 = 18.341 D 6 = 0.116 N 4 = 1.77250 ν 4 = 49.6 R 7 = 1.703 D 7 = 0.776 R 8 = -2.357 D 8 = 0.116 N 5 = 1.69680 ν 5 = 55.5 R 9 = 2.181 D 9 = 0.337 N 6 = 1.84666 ν 6 = 23.9 R10 = -15.258 D10 = variable R11 = -3.688 D11 = 0.127 N 7 = 1.74400 ν 7 = 44.8 R12 = 908.365 D12 = Variable R13 = 336.078 D13 = 0.244 N 8 = 1.60311 ν 8 = 60.7 R14 = -2.496 D14 = 0.127 R15 = (Aperture) D15 = 0.364 R16 = 7.582 D16 = 0.337 N 9 = 1.60342 ν 9 = 38.0 R17 = -1.546 D17 = 0.104 N10 = 1.83481 ν10 = 42.7 R18 = 13.680 D18 = 1.238 R19 = 9.136 D19 = 0.232 N11 = 1.51633 ν11 = 64.2 R20 = 16.439 D20 = 2.470 R21 =- 5.819 D21 = 0.267 N12 = 1.51742 ν12 = 52.4 R22 = -3.311 D22 = 0.022 R23 = 11.900 D23 = 0.116 N13 = 1.80518 ν13 = 25.4 R24 = 3.550 D24 = 0.476 N 14 = 1.51633 ν14 = 64.2 R25 = -5.404 D25 = 0.023 R26 = 3.893 D26 = 0.371 N15 = 1.48749 ν15 = 70.2 R27 = -12.232 D27 = 0.929 R28 = ∞ D28 = 3.254 N16 = 1.60342 ν16 = 38.0 R29 = ∞ D29 = 0.883 N17 = 1.51633 ν17 = 64.2 R30 = ∞

[0033]

[Table 4]

[0034]

As described above, according to the present invention, in a so-called five-group zoom lens, by appropriately setting the lens configuration of each lens group, a predetermined back focus is obtained and the zoom range is high over the entire zoom range. It is possible to achieve a zoom lens having an F number of 2.4 and a zoom ratio of about 3 which has optical performance.

[Brief description of drawings]

FIG. 1 is a lens cross-sectional view at a wide-angle end according to Numerical Example 1 of the present invention.

FIG. 2 is a lens cross-sectional view at a wide-angle end according to Numerical Example 2 of the present invention.

FIG. 3 is a lens cross-sectional view at a wide-angle end according to Numerical Example 3 of the present invention.

FIG. 4 is a lens cross-sectional view at a wide-angle end according to 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 L5 5th group SP Aperture IP Image plane G Glass block ΔS Sagittal image plane ΔM Meridional image plane

Claims (1)

[Claims] 1. A first group having a positive refracting power, a second group having a negative refracting power having a variable power function, and a third group having a negative refracting power for correcting an image plane fluctuating due to zooming, in order from the object side. , A fourth lens unit having a positive refractive power, and a fifth lens unit having a positive refractive power, and the second lens unit is a negative twenty-first lens unit having a concave surface having a strong refractive power facing the image side. , A negative 22nd lens element with both concave lens surfaces,
And a positive 23rd lens with a convex surface having a strong refractive power facing the object side. The 22nd lens and the 23rd lens are independent or cemented, and the air-converted length from the final lens surface to the image surface is calculated. Bf, where the focal length of the i-th group is fi and the focal length of the entire system at the wide-angle end is fw 1.1 <Bf / f5 <1.8 | f3 / f4 | <1.0 | f5 / f4 | <0.63 0.19 <| fw / f3 | <0.26 The zoom lens characterized by satisfying the conditions.