JPH075359A - Zoom lens for definite distance - Google Patents

Abstract

PURPOSE:To obtain a zoom lens for definite distance capable of excellently compensating magnification chromatic aberration over a wide range without versatile use of a glass material having abnormal dispersability by making a lens on the most objective side of a first group a joined lens of a positive refractive power. CONSTITUTION:This lens has a first group of a negative refractive power and a second group of a positive refractive power in order from an enlarging side and the spacing between the first group and the second group is changed by varying the power. In this case, by making a first lens a joined lens having a positive refractive power and subjecting to an achromatic processing in the joined lens, the magnification chromatic aberration is excellently compensated over the whole zooming area. Also, by making the enlarging side of the joined surface of the joined lens a concave surface, the compensation of off-axis light beam is facilitated. Namely, since an incident angle to recessed surface on the enlarging side becomes larger than that of a convexed surface for an off-axis light beam, the compensation of the off-axis light beam is easily performed. Since the joined surface has a negative refractive power, the compensating effect of the magnification chromatic aberration is enhanced as it goes farther to off-axis.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a finite distance zoom lens, and more particularly, to a finite distance zoom lens that requires high performance, such as a zoom lens for stretching a photographic film.

[0002]

2. Description of the Related Art Generally, the image forming performance required for a lens used for stretching, reducing or copying a photographic film is very severe. In particular, in order to prevent deterioration of image quality due to color bleeding, axial chromatic aberration and lateral chromatic aberration must be suppressed as much as possible. However, in the zoom lens for enlargement, which has been widely used in recent years because the image magnification can be continuously changed, it is very difficult to suppress the occurrence of lateral chromatic aberration to be small over the entire zoom range.

In Japanese Patent Laid-Open No. 59-198416, a zoom lens having a first group having a positive refractive power and a second group having a negative refractive power has an anomalous dispersion property in the negative lens of the second group. A means of using a glass material to reduce the generation amount of the secondary spectrum of the chromatic aberration of magnification is shown. However, the zoom type in which the first lens unit has a positive refractive power has a large variation in lateral chromatic aberration due to zooming, and even if the secondary spectrum is reduced by using a glass material having anomalous dispersion, a zoom lens having a large zoom ratio is provided. However, it was difficult to sufficiently reduce the amount of chromatic aberration of magnification. In addition, when a negative lens material with anomalous dispersion is used, the secondary spectrum of axial chromatic aberration increases, so in order to cancel it, glass materials with anomalous dispersion must be used for the positive lenses of other groups. I won't. In general, a glass material having anomalous dispersion is not only expensive, but also has a low refractive index, which leads to an increase in the number of lens components, which easily leads to further cost increase and size increase.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a zoom lens for a finite distance, which can favorably correct lateral chromatic aberration over the entire zoom range without using a glass material having anomalous dispersion. is there.

[0005]

In order to achieve the above object, in the present invention, a first refracting power having a negative refracting power is provided in order from the enlargement side.
In a finite distance zoom lens that has a lens unit and a second lens unit having a positive refractive power, and the distance between the first lens unit and the second lens unit changes during zooming, the lens closest to the object side in the first lens unit is The cemented lens has a positive refractive power.

Further, the cemented surface of the cemented lens is concave on the magnifying side and has a negative refractive power.

[0007]

With the above arrangement, the zoom lens for finite distance of the present invention satisfactorily corrects lateral chromatic aberration over the entire zoom range without using many glass materials having anomalous dispersion.

[0008]

EXAMPLES Examples of the present invention will be described in detail below.

Generally, a zoom lens having a first group having a negative refracting power and a second group having a positive refracting power in order from the magnifying side is a first lens group having a positive refracting power and a negative refracting power. It is known that the variation of the lateral chromatic aberration due to zooming is smaller than that of the zoom lens having the second group having. This is because, in the latter case, the positive refractive power of the first group causes the angle of the off-axis chief ray incident on the second group having a strong negative refractive power to change greatly due to zooming, whereas in the former case, This is because the angle of the off-axis chief ray incident on the second group having a refractive power does not change significantly due to zooming.

On the other hand, a disadvantage of the zoom lens in which the first lens unit has a negative refractive power is that a large negative distortion occurs on the wide angle side. In order to correct this negative distortion, the lens closest to the object in the first group (hereinafter referred to as the first lens)
There is no effective measure other than using as a positive lens. However, if the first lens is a positive lens, the off-axis chief ray on the wide-angle side passes through a very large diameter of the first lens, so that a large chromatic aberration of magnification occurs here, and it is very difficult to correct it. Become. Even if an extremely low-dispersion glass is used for the first lens, such a glass generally has an anomalous dispersion property called Lange, which conversely increases the secondary spectrum of the chromatic aberration of magnification, and as a result, the magnification. It becomes impossible to satisfactorily correct chromatic aberration.

Therefore, in the present invention, the first lens is used as a cemented lens having a positive refracting power, and achromaticity is performed in the cemented lens, whereby lateral chromatic aberration is satisfactorily corrected in the entire zoom range.

Furthermore, by making the enlargement side of the cemented surface of this cemented lens a concave surface, it is easy to correct the off-axis light flux. In other words, for the off-axis light beam, the incident angle with respect to the surface is larger when the enlargement side is the convex surface than when it is the convex surface.

Further, since the cemented surface has a negative refracting power, in the zoom lens composed of the first group having a negative refracting power and the second group having a positive refracting power as in the present invention, The effect of correcting the lateral chromatic aberration is increased as it goes outward.

Specific numerical examples of the finite distance zoom lens according to the present invention will be shown below. In each example,
With zooming from the tele side to the wide side, the first group moves along a convex trajectory toward the reduction side, and the second group moves toward the reduction side. In each embodiment, ri (i = 1, 2, 3, ...) Is the radius of curvature of the i-th surface counted from the expansion side, and di (i = 1,
(2, 3, ...) is the i-th axial upper surface distance counted from the expansion side,
Ni (i = 1,2,3, ...) and νi (i = 1,2,3, ...) are the d-line (λ = 587.6) of the i-th lens counted from the magnification side, respectively.
The refractive index and Abbe number with respect to (nm) are shown.

<Example 1> Magnification factor = -0.333 to -0.200 to -0.143 to -0.111 Effective FNO. = 11.48 to 8.08 to 6.49 to -5.50 Radius of curvature, axial upper surface spacing Refractive index Abbe number r 1 73.493 d 1 12.000 N 1 1.69680 ν 1 56.47 r 2 -232.348 d 2 4.000 N 2 1.80518 ν 2 25.43 r 3 -3285.907 d 3 1.000 r 4 232.001 d 4 4.000 N 3 1.51680 ν 3 64.20 r 5 37.375 d 5 11.000 r 6 -163.766 d 6 4.000 N 4 1.62041 ν 4 60.29 r 7 37.795 d 7 7.000 r 8 45.175 d 8 6.000 N 5 1.65 446 ν 5 33.86 r 9 146.517 d 9 4.000 ~ 26.372 ~ 51.373 ~ 78.960 r10 39.543 d10 5.000 N 6 1.49310 ν 6 83.58 r11 -39 0.500 r12 39.956 d12 4.000 N 7 1.49310 ν 7 83.58 r13 138.178 d13 5.000 r14 -107.439 d14 7.000 N 8 1.61950 ν 8 43.14 r15 29.553 d15 4.000 r16 69.000 d N10 1.61800 ν10 63.39 r19 -65.370 d19 2.000 <Example 2> Multiplier = -0.333 ~ -0.200 ~ -0.143 ~ -0.111 Effective FNO. = 11.53 ~ 8.13 ~ 6.53 ~ -5.50 Curvature radius Axial surface spacing Refractive index Abbe number r 1 73.490 d 2 12.000 N 1 1.69680 ν 1 56.47 r 2 -203.484 d 3 4.000 N 2 1.80518 ν 2 25.43 r 3 -1228.833 d 4 1.000 r 4 253.342 d 5 4.000 N 3 1.51680 v 3 64.20 r 5 37.471 d 6 11.000 r 6 -157.062 d 7 4.000 N 4 1.62041 v 4 60.29 r 7 36.857 d 8 7.000 r 8 44.479 d 9 6.000 N 5 1.65446 ν 5 33.86 r 9 148.265 d10 4.000 ~ 26.443 ~ 51.532 ~ 79.227 r10 42.047 d11 5.000 N 6 1.49310 ν 6 83.58 r11 -463.699 d12 0.500 r12 40.357 d13 4.000 r7 1.25.7 r. 8 1.65100 ν 8 39.55 r15 30.215 d16 4.000 r16 73.715 d17 4.000 N 9 1.51728 ν 9 69.43 r17 -334.460 d18 5.000 r18 -249.119 d19 3.000 N10 1.61800 ν10 63.39 r19 -58.686 d20 2.33 <Example->3> 0.200 to -0.143 to -0.111 Effective FNO. = 11.91 to 8.22 to 6.54 to -5.50 Radius of curvature On-axis Surface spacing Refractive index Abbe number r 1 123.509 d 1 12.000 N 1 1.69680 ν 1 56.47 r 2 -313.719 d 2 4.000 N 2 1.83350 ν 2 21.00 r 3 986.670 d 3 1.000 r 4 110.650 d 4 4.000 N 3 1.51680 ν 3 64.20 r 5 40.041 d 5 11.000 r 6 -206.433 d 6 4.000 N 4 1.62041 ν 4 60.29 r 7 43.125 d 7 7.000 r 8 50.389 d 8 6.000 N 5 1.68 300 ν 5 31.52 r 9 204.731 d 9 4.000 ~ 30.494 ~ 60.324 ~ 93.957 r10 37.455 d10 5.000 N 6 1.49310 ν 6 83.58 r11 -149.068 d11 0.500 r12 36.785 d12 4.000 N 7 1.49520 ν 7 79.74 r13 340.710 d13 5.000 r14 -80.371 d14 7.000 N 8 1.61950 4.ν 8 43.14 r15 25.229 1616. 9 79.74 r17 -1563.942 d17 5.000 r18 -85.695 d18 3.000 N10 1.61800 ν10 63.39 r19 -45.087 d19 81.452 〜 38.412 〜 18.028 〜 5.999 r20 INF d20 3.000 N11 1.51680 ν11 64.20 r21 258.400 In each case It is a × to 1/9 × 3x zoom lens. In the third embodiment, a lens having a fixed negative refractive power is further arranged on the reduction side of the second group during zooming to reduce the movement amount of the first group and the second group. Thus, it is easy to dispose a fixed or movable lens component having a relatively weak refractive power with a simple structure between the reduction side of the entire system and between the lens groups, and this is included in the spirit of the present invention.

[0016]

According to the structure of the present invention, it is possible to obtain a zoom lens for a finite distance capable of favorably correcting lateral chromatic aberration over the entire zoom range without using a glass material having anomalous dispersion.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a lens corresponding to Example 1 of the present invention.

FIG. 2 is a configuration diagram of a lens corresponding to Example 2 of the present invention.

FIG. 3 is a configuration diagram of a lens corresponding to Example 3 of the present invention.

FIG. 4 is an aberration diagram of a lens corresponding to Example 1 of the present invention.

FIG. 5 is an aberration (chromatic aberration of magnification) diagram of a lens corresponding to Example 1 of the present invention.

FIG. 6 is an aberration diagram of a lens corresponding to Example 2 of the present invention.

FIG. 7 is an aberration (chromatic aberration of magnification) diagram of a lens corresponding to Example 2 of the invention.

FIG. 8 is an aberration diagram of a lens corresponding to Example 3 of the present invention.

FIG. 9 is an aberration (chromatic aberration of magnification) diagram of a lens corresponding to Example 3 of the present invention.

Claims (2)

[Claims] 1. A first group having a negative refracting power and a second group having a positive refracting power are arranged in this order from the enlargement side, and the first group is used for zooming.
A zoom lens for a finite distance, wherein the lens closest to the object side in the first group is a cemented lens having a positive refractive power, in a zoom lens for a finite distance in which the distance between the group and the second group changes. 2. The zoom lens for a finite distance according to claim 1, wherein the cemented surface of the cemented lens is concave on the enlargement side and has a negative refracting power.