JP3141550B2 - 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 zoom lens suitable for a television camera, a video camera, a photographic camera and the like, and more particularly to a zoom lens by moving a position of an aperture stop on an optical axis under a constant condition with zooming. Aberration fluctuation due to zooming, for example, to suppress fluctuation of lateral chromatic aberration due to the aperture diameter on the telephoto side,
The present invention relates to a zoom lens having high optical performance over the entire zoom range, F1.8, a large aperture ratio of 18.3, and a high zoom ratio.

[0002]

2. Description of the Related Art Conventionally, zoom lenses for television cameras and the like have been required to have a small lens system, a large aperture ratio, and a high zoom ratio in accordance with the miniaturization of television cameras.

In the zoom lens, in order from the object side, a first group having a positive refractive power for focusing (focusing lens group), a second group having a negative refractive power for zooming (variable lens group), Third group of positive or negative refractive power for correcting an image plane that varies with magnification (correction lens group), aperture stop, and fourth group of positive refractive power for imaging (relay lens group) The so-called four-group zoom lens composed of the four lens groups described above is used for not only television cameras but also various other cameras because it is relatively easy to increase the magnification and increase the aperture ratio.

Among the four-group zoom lenses, a large-aperture, high-magnification four-group zoom lens having an aperture ratio of about 1.4 and a zoom ratio of about 12 is disclosed in, for example, JP-A-55-95922 and JP-A-5-95922.
It has been proposed in, for example, JP-A-9-71015.

[0005]

In a four-unit zoom lens, one factor that determines the size of the entire lens system is as follows.
There is a size of the front lens diameter. The size of the front lens diameter is often determined by the open F number at the telephoto end and the off-axis light flux.

It is desirable that the ratio of the off-axis light beam to the on-axis light beam at the telephoto end, that is, the peripheral light amount ratio be large. However, as the peripheral light amount ratio increases, the diameter of the front lens increases. For this reason, the peripheral light amount that does not actually cause a problem is limited to prevent an increase in the diameter of the front lens.

On the telephoto side, if the amount of peripheral light is limited,
Since the lower light beam among the off-axis light beams is restricted, the shift between the center light beam of the aperture stop of the off-axis light beam and the center light beam (principal light beam) of the light beam increases. Then, the point where the principal ray of the off-axis light beam and the optical axis of the central ray of the aperture stop intersect moves to the object side with zooming to the telephoto end. As a result, the fluctuation of the aberration with respect to the off-axis light flux increases.

The zoom lens is responsible for aberration correction by a zooming unit (focusing lens group, zooming lens group, correction lens group) for correcting aberrations that fluctuate with zooming, and aberrations unrelated to zooming. It is divided into a fixed part (relay lens group) for correction.

For example, magnification chromatic aberration, which varies as the magnification changes, mainly occurs from the focusing lens group. This basically since the aperture stop of the zoom lens is arranged behind the magnification unit (image surface side), the position of the entrance pupil is moved rearward had accompanied the zooming to the telephoto end, a focusing lens Come away from the group,
The incident height of the chief ray to the focusing lens group increases. For this reason, the amount of chromatic aberration of magnification depending on the incident height of the principal ray increases. At this time, the chromatic aberration of magnification generated in the focusing lens group is magnified by the variable power unit and enters the relay lens group.

In general, it is very difficult to correct the fluctuating chromatic aberration at this time with a fixed relay lens group, and there is a problem that the optical performance is greatly reduced.

When the aperture diameter of the aperture stop is reduced by the conventional four-group zoom lens, the upper light beam is blocked first, and as a result, the principal ray is displaced downward, and the principal ray passing through the focusing lens group. Incident height becomes higher.

For this reason, on the telephoto side, there is a problem that the chromatic aberration of magnification changes depending on the diameter of the aperture stop.

As a method of correcting chromatic aberration of magnification, it is effective to use anomalous dispersion glass as a lens material. However, this method makes it difficult to correct other aberrations and obtains high optical performance over the entire zoom range. There is a problem that it is difficult.

The present invention relates to a so-called four-group zoom lens,
Various aberrations, such as chromatic aberration of magnification, which fluctuate with the magnification and fluctuate with the aperture diameter of the aperture stop, are well corrected by moving the aperture stop on the optical axis under predetermined conditions with the magnification change, and the entire variation is obtained. It is an object of the present invention to provide a zoom lens having high optical performance over a double range and at all aperture values.

[0015]

A zoom lens according to the present invention comprises, in order from the object side, a first group of positive refractive power for focusing, a second group of negative refractive power for zooming, and an image associated with zooming. In a zoom lens having a third unit having a positive refractive power for correcting a surface variation, an aperture stop, and a fourth unit having a fixed imaging function during zooming,
When the zoom ratio is Z, and when zooming to the telephoto side, the aperture stop
Is fixed at the zoom position equivalent to Z ^1/4 from the wide-angle end.
From the zoom position corresponding to Z ^1/4 to the telephoto end.
Move to the object side, and move to the zoom position equivalent to Z ^1/4 .
Z ^{1/4 based} on the position of the aperture stop
From the zoom position to the zoom position equivalent to Z1 ^{/ 2}
Zoom position corresponding to the moving amount of the aperture stop corresponding to V _b , Z ^1/4
And the amount of movement of the aperture stop to the telephoto end was V _T from
And the condition _Vb ≦ _VT / 5 is satisfied.

[0016]

1A and 1B show a numerical example 1 of the present invention.
3 is a lens cross-sectional view at a wide-angle end and a telephoto end of FIG.

In the drawing, L1 is a first lens unit (focusing lens group) having a positive refractive power for focusing, and L2 is a zoom lens which moves monotonously to the image plane side when zooming from the wide-angle end to the telephoto end. A second lens unit (magnification unit) having a negative refractive power, L3 is a positive lens which moves non-linearly to the object side from the wide-angle end to the telephoto end in order to maintain an image plane that fluctuates with magnification at a fixed position. Third group of refractive power (correction lens group),
L4 is a fourth group (relay lens group) having a positive refractive power that performs a fixed image-forming action, and SP is an aperture stop, which is arranged between the third and fourth groups. Moving under certain conditions. An arrow SPa indicates a moving trajectory that moves as the magnification of the aperture stop SP changes from the wide-angle end to the telephoto end.

G is a glass block such as a color separation prism and a filter. The first unit L1, the second unit L2, and the third unit L3 constitute a variable power system.

FIG. 2 is an explanatory view showing a state in which the aperture stop SP moves with zooming in this embodiment. In the figure, the horizontal axis indicates the zoom position, and the vertical axis indicates the amount of movement. In the figure, the movement to the object side is shown as positive.

In Numerical Example 1 described later, the focal length is 12.
The zoom ratio Z = 18.3 at the range of 5 to 228.95, and the maximum movement amount V _T = 25 for zooming the aperture stop from the wide-angle end to the telephoto end
It is.

In this embodiment, as shown in FIGS. 1 and 2, the aperture stop is fixed from the wide-angle end to a predetermined zoom position.
When zooming from a predetermined zoom position to the telephoto end, the zoom lens is moved forward (object side). The aperture stop is located near the intersection of the central ray of the light beam with the optical axis.

[0022] Specifically, upon zooming to the telephoto end from the wide angle end, the third group so as to correspond to move toward the object side, using a space formed at that time, considerable angle end to Z ^1/4 Do
Fixed up to zoom position (f = 26) , equivalent to Z ^1/4
The aperture stop is moved to the object side from the zoom position (f = 26) to the telephoto end.

At this time , the zoom position (f) corresponding to Z ^1/4
= 26) to the zoom position corresponding to Z ^1/2 (f = 54)
Up to this point, the moving amount _Vb is moved less than the total moving amount V _T (25) so that V _b ≦ V _T / 5. And are curved manner is greatly moved zoom position corresponding to Z ^1/2 from (f = 54) to the telephoto end (zoom ratio Z, f = 228.95).

Finally, the aperture stop SP is located closer to the object side at the telephoto end than at the wide-angle end. Thus, when the aperture stop is stopped down, the lower beam among the off-axis beams is blocked, and the height of the principal ray passing through the focusing lens unit from the optical axis is reduced so that the magnification from the focusing lens unit is reduced. The amount of occurrence of chromatic aberration is reduced.

In this embodiment, with such a configuration, variation in aberration when the aperture stop is stopped down is reduced, and especially, variation in chromatic aberration of magnification is reduced. For example, a registration error when used in a television camera or the like is reduced. High optical performance is obtained over the entire zoom range.

In the zoom lens according to the present embodiment, in order to secure a space for moving the aperture stop toward the object side at the time of zooming from a predetermined zoom position to the telephoto end, the zoom lens must be zoomed from the wide-angle end to the telephoto end. As described above, the refractive power of each lens group is set so as to be a zoom type in which the three groups move forward.

3 and 4 are aberration diagrams of the numerical example 1 when the F-number at the telephoto end is F2.2 (open) and F5.6.

In the zoom lens according to the present embodiment, since the aperture stop is moved so that the center of the stop and the principal ray substantially coincide with each other, the chromatic aberration of magnification is favorably corrected both at the time of opening and at F5.6 regardless of the stop diameter. Have been.

In the present invention, when the aperture stop is moved forward with zooming, the incident height of the light beam for determining the F-number and the off-axis light beam to each lens group changes, so that the stop diameter is changed accordingly. Is good. The change in the aperture diameter at this time is preferably performed using, for example, an auto iris mechanism.

In order to reduce the fluctuation of the exit pupil when the aperture stop is moved forward, the position of the exit pupil of the zoom lens is set in the minus direction (front) at the wide-angle end and in the plus direction (rear) at the telephoto end. It is composed of a telecentric system as follows. This reduces the amount of color shading when used in, for example, a television camera.

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. R46, R4
Reference numeral 7 denotes a glass block such as a color separation prism and a color filter.

Numerical Example 1 F = 12.5 to 228.95 FNO = 1: 2.2 to 5.6 2ω = 65.2 to 4.0 R 1 = 2455.41 D 1 = 5.40 N 1 = 1.69979 ν 1 = 55.5 R 2 = 271.91 D 2 = 28.94 R 3 = -267.58 D 3 = 3.00 N 2 = 1.69979 ν 2 = 55.5 R 4 = -2503.19 D 4 = 1.98 R 5 = 9738.25 D 5 = 3.00 N 3 = 1.64254 ν 3 = 60.1 R 6 = 224.83 D 6 = 14.59 N 4 = 1.76168 ν 4 = 27.5 R 7 = 1879.70 D 7 = 1.84 R 8 = 1282.45 D 8 = 13.52 N 5 = 1.62287 ν 5 = 60.3 R 9 = -242.57 D 9 = 0.30 R10 = 1074.61 D10 = 4.50 N 6 = 1.81265 ν 6 = 25.4 R11 = 150.07 D11 = 20.80 N 7 = 1.48915 ν 7 = 70.2 R12 = -401.90 D12 = 0.30 R13 = 160.26 D13 = 16.10 N 8 = 1.48915 ν 8 = 70.2 R14 = 45982.92 D14 = 0.30 R15 = 148.13 D15 = 12.92 N 9 = 1.62287 ν 9 = 60.3 R16 = 512.54 D16 = Variable R17 = 95.44 D17 = 2.40 N 10 = 1.77621 ν 10 = 49.6 R18 = 42.25 D18 = 9.16 R19 = -1689.53 D19 = 2.20 N 11 = 1.77621 ν 11 = 49.6 R20 = 84.69 D20 = 11.71 R21 = -46.36 D21 = 2.20 N 12 = 1.77621 ν 12 = 49.6 R22 = 779.13 D22 = 5.58 N 13 = 1.93306 ν 13 = 21.3 R23 = -92.60 D23 = Variable R24 = 1110.01 D24 = 8.90 N 14 = 1.48915 ν 14 = 70.2 R25 = -82.86 D25 = 0.30 R26 = 325. 37 D26 = 12.18 N 15 = 1.64254 ν 15 = 60.1 R27 = -71.86 D27 = 2.40 N 16 = 1.81265 ν 16 = 25.4 R28 = -222.32 D28 = 0.30 R29 = 84.97 D29 = 9.95 N 17 = 1.48915 ν 17 = 70.2 R30 = -1089.44 D30 = Variable R31 = (Aperture) D31 = Variable R32 = -47.08 D32 = 1.40 N 18 = 1.62032 ν 18 = 63.4 R33 = 39.65 D33 = 5.94 N 19 = 1.81265 ν 19 = 25.4 R34 = 65.31 D34 = 9.57 R35 = -38.40 D35 = 1.50 N 20 = 1.64254 ν 20 = 60.1 R36 = -1105.33 D36 = 9.77 N 21 = 1.69417 ν 21 = 31.1 R37 = -38.03 D37 = 13.00 R38 = 73.63 D38 = 12.37 N 22 = 1.49845 ν 22 = 81.6 R39 = -88.22 D39 = 0.20 R40 = -3325.75 D40 = 2.00 N 23 = 1.85501 ν 23 = 23.9 R41 = 56.24 D41 = 2.72 R42 = 105.85 D42 = 8.04 N 24 = 1.45720 ν 24 = 90.3 R43 = -70.51 D43 = 1.10 R44 = 50.76 D44 = 8.23 N 25 = 1.43985 ν 25 = 95.0 R45 = -3158.30 D45 = 8.30 R46 = ∞ D46 = 69.20 N 26 = 1.51825 ν 26 = 64.2 R47 =

[0033]

[Table 1]

[0034]

As described above, according to the present invention, in the so-called four-unit zoom lens, various aberrations that fluctuate with zooming and fluctuate depending on the aperture diameter of the aperture stop, for example, fluctuations in chromatic aberration of magnification are changed by changing the aperture stop. It is possible to achieve a zoom lens having high optical performance over the entire zoom range and at all aperture values by performing good correction by moving on the optical axis under predetermined conditions with magnification.

[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 an explanatory diagram showing a moving state of an aperture stop according to the present invention.

FIG. 3 is a lateral aberration diagram of F2.2 in Numerical Example 1 of the present invention.

FIG. 4 is a longitudinal aberration diagram of F2.2 in Numerical Example 1 of the present invention.

FIG. 5 is a lateral aberration diagram of F5.6 in Numerical Example 1 of the present invention.

FIG. 6 is a longitudinal aberration diagram of F5.6 according to Numerical Embodiment 1 of the present invention.

[Explanation of symbols]

 L1 First unit L2 Second unit L3 Third unit L4 Fourth unit SP Aperture stop d d-line g g-line S Sagittal image plane M Meridional image plane Y Image height

Claims (2)

(57) [Claims] 1. A first lens unit having a positive refractive power for focusing, a second lens unit having a negative refractive power for zooming, and a positive lens having a positive refractive power for correcting an image plane variation caused by zooming in order from the object side. A zoom lens having a third group, an aperture stop, and a fourth group having a fixed image forming function during zooming, wherein the zoom ratio is Z, and when zooming to the telephoto side, the aperture stop is set.
Is fixed at the zoom position equivalent to Z ^1/4 from the wide-angle end.
From the zoom position corresponding to Z ^1/4 to the telephoto end.
And moves to the object side, and the position of the aperture stop at a zoom position corresponding to Z ^1/4
Based on the location, Z ^1/2 from the zoom position corresponding to Z ^1/4
The amount of movement of the aperture stop up to the zoom position corresponding to
_b , the opening from the zoom position corresponding to Z ^1/4 to the telephoto end.
When the amount of movement of the mouth aperture was V _T, the zoom lens satisfies the V _b ≦ V _T / 5 following condition. Wherein said zoom lens becomes negative direction at the wide-angle end position of the exit pupil, zoom according to claim 1, characterized in that it is constituted by a telecentric system such that the positive direction at the telephoto end lens.