JPS61284719A - Zoom lens having variable refracting power lens - Google Patents

Abstract

PURPOSE:To perform focusing while reducing aberrational variation over an object distance by extending a zoom lens wherein a lens group with negative refracting power precedes while decreasing the refracting power of the 1st lens group. CONSTITUTION:The 1st lens group I has negative refracting power and the 2nd lens group II has positive refracting power. when the focus is adjusted from an infinite distance body to a short-distance body, the 1st lens group I is moved out and the refracting power of at least one lens surface in the 1st lens group so as to decrease the negative refracting power of the 1st lens group I on the whole, reducing the aberrational variation. The 2nd lens with negative refracting power from the object side of the 1st lens group I is made of an optical elastic body such as silicone rubber and the object-side and image- side lens surfaces are varied in refracting power.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a zoom lens having a variable refractive power lens suitable for photographic cameras, video cameras, etc., and particularly for focusing from an object at infinity to a close object. The present invention relates to a zoom lens having a high-performance variable refractive power lens that is designed to reduce aberration fluctuations during image processing.

(Prior art) Conventionally, there are two lens groups, a first lens group with a negative refractive power and a second lens group with a positive refractive power, in order from the object side, and both lens groups are moved to change the magnification in five positions. Various 1112p zoom lenses have been proposed as effective zoom lenses for wide angles of view. In this two-group zoom lens, focusing is performed by extending the first lens group.

In general, with a two-group zoom lens, when focusing from an object at infinity to a near-distance object, the first lens group with negative refractive power is extended, so there is a difference in ball recovery, especially from the intermediate zoom position to the telephoto end zoom position. This results in overcorrection, and relatively large aberration fluctuations occur depending on the object distance. Therefore, @-Kokai No. 55-36833 proposes a so-called floating method in which the first lens group is divided into two lens groups, a front group and a rear group, and both groups are moved out while changing the distance between the two groups during focusing. We are proposing a two-group zoom lens that aims to reduce fluctuations in aberrations by taking the following measures. However, with this method, it is difficult to sufficiently reduce fluctuations in aberrations, and the mechanism on the lens barrel tends to be complicated, requiring a higher assembly volume.

Another method for reducing aberration fluctuations during focusing in a 2# zoom lens is to weaken the refractive power of the entire first lens group in advance, but this method does not allow the lens to extend during focusing. The disadvantage is that the amount increases and the entire lens system becomes large.

(Problems to be Solved by the Invention) An object of the present invention is to provide a zoom lens having a variable refractive power lens suitable for photographic cameras, video cameras, etc., which reduces aberration fluctuations during focusing over the entire object distance. shall be.

A further object of the present invention is to provide an effective method for utilizing a zoom lens in which aberration fluctuations during focusing are reduced by changing the shape of the lens surface.

(Means for solving the problem) It has at least two lens groups, a first lens group with negative refractive power and a second lens group with positive refractive power, in order from the object side, and the distance between both lens groups is changed. When changing the magnification and focusing from an object at infinity to an object at close distance, the first lens group is extended and the refractive power of at least one lens surface of the first lens group is changed to the negative refractive power of the first lens group. Change it so that it weakens overall and the next thing will happen.

The features of this pond water invention are described in the Examples.

(Example) FIG. 1 is a sectional view of a lens according to a numerical example of the present invention. In the figure, ■ is the first lens group with negative refractive power, and ■ is the second lens group with positive refractive power.

In this embodiment, when the first lens group I is extended when focusing from an object at infinity to an object at a short distance, at least one lens in the first lens group The refractive power of each lens surface is changed to reduce aberration fluctuations.

In this example, the second lens with negative refractive power from the object side of the first lens group is made of an optical elastic material such as silicone rubber, and the refractive powers of the lens surfaces on the object side and image side are changed. I'm letting you do it.

In this embodiment, the lens surface of the lens having positive refractive power may be changed to become stronger in the positive direction, thereby weakening the negative refractive power of the entire first lens group.

Next, the effectiveness of focusing in this example will be explained using a paraxial power arrangement. When focusing on a finite-distance object with a two-group zoom lens preceded by a lens group with negative refractive power, the image point position of the first lens group of the finite-distance object is the same as the image point position of the first lens group of the infinite object. should match.

For the sake of simplicity, it is assumed that only the refractive power is changed without extending the first lens group during focusing.

Object distance t-elN If the image point position is 3' and the focal length of the first lens group 'ef, then 1/s' -17s + 1// is obtained. Next, if the focal length of the first lens group is t fl when the object is at infinity, then the image point position j2
becomes S knee f1o, . Also, assuming that there is one finite distance object and the focal length of the first lens group is 1-/length, it becomes 1/7□--1/&yfg+1/7 length. From this, (f bribe-f□-)/Cf1~・f bribe)-8 exists.

For finite distance objects, t+existence<O (f□existence−
11-)//1- “f□Yes<.

becomes. When focusing on a finite distance object, it is sufficient to change the refractive power of the first lens group so that 1□<fl-. This corresponds to changing the negative focal length of the first lens group in the direction of increasing it, that is, changing the negative refractive power of the first lens group so as to weaken it. When such a change is made, spherical aberration tends to be undercorrected in many cases.

When focusing on a finite distance object by extending the first lens group in a two-group zoom lens preceded by a lens group with negative refractive power, spherical aberration tends to be overcorrected as described above.

However, if the negative refractive power of the first lens group is weakened as in this embodiment, spherical aberration tends to be undercorrected. As a result, as in this example, if the first lens group is extended and the refractive power of at least one lens surface in the first lens group is changed to weaken the negative refractive power of the first lens group, spherical aberration can be reduced. They cancel each other out, making it possible to maintain an overall balanced aberration. Further, the amount of extension of the first lens group P is smaller than that in the case where the first lens group is simply extended without weakening its refractive power, and the amount of aberration fluctuation due to focusing can be reduced. Furthermore, since the amount of extension of the first lens group is small, it is easy to secure an off-axis light beam, prevent the diameter of the front lens from increasing, and easily achieve miniaturization of the entire lens system.

In comparison, for example, a zoom lens has a first lens group with positive refractive power and a second lens group with negative refractive power, which changes the magnification by changing the distance between both lens groups, and focuses on an object at a finite distance. If the refractive power of the first lens group for distortion removal is made stronger, that is, the refractive power of the lens surface in the first lens group is changed so that the negative refractive power is weakened, spherical aberration tends to be undercorrected. becomes. Furthermore, in this zoom lens, when the first lens group having the refractive power for removing distortion during focusing is extended, spherical aberration is often undercorrected.

Therefore, in a zoom lens in which a lens group with positive refractive power precedes the lens group, if the refractive power of the first lens group is strengthened and extended, the spherical aberration will be promoted in the direction of insufficient correction, which will cause the overall optical performance to deteriorate, which is undesirable.

On the other hand, the focusing method of the present invention in which the negative refractive power of the first lens group is weakened and extended in a zoom lens in which a lens group with a negative refractive power is in front cancels out aberration fluctuations. It has the advantage that high-performance imaging performance can be easily obtained.

In this embodiment, the refractive power of the lens surface may be varied by using a liquid lens and changing the water pressure of the liquid to change the radius of curvature of the lens surface.As shown in FIG. 5, a transparent elastic material such as silicone rubber may be used. The curvature radius of the lens surface may be changed by molding into a lens shape and applying pressure to the outer edge. That is, in FIG. 5, 11 is a cylindrical container having circular openings 12 and 12'; 1 is a silicone rubber, and 14 is a movable part for pressurizing the silicone rubber.

Prisoner No. 51 was released without applying any pressure.

Figure 5 03) shows a state in which pressure is applied to the silicone rubber 13 through the 14-karat gold movable part, and in this case, a portion of the silicone rubber is A convex shape protrudes from the opening. FIG. 5 (0 shows a state in which negative pressure is applied to the silicone rubber through the movable part 14t; in this case, the silicone rubber has a concave lens shape at the opening.

In this way, by changing the magnitude of the external force applied to the movable part of the container and the size of the opening, the radius of curvature of the lens surface, the lens thickness, and other shapes can be easily varied.

Note that the movable portion 14 and the silicone rubber 13 may be bonded together using an adhesive or the like, if necessary.

There are many possible ways to apply pressure to the silicone rubber 13 by driving the movable part 14. Simple methods include cutting a screw in the container and screwing the movable part into it, or using an electromagnet. The movable part may be controlled by using the same.

Next, numerical examples of the present invention will be shown. R in the numerical implementation sequence
1 is the radius of curvature of the i-th lens surface in order from the object side, D
i is the first lens thickness and air distance from the object side, Nt
and νi are the refractive index and Abbe number of the glass of the i-th lens in order from the object side, respectively.

Numerical implementation sequence F=36-68. OFNO-1:4 2ω-61σ
-35,3@R1= 5170 D 1
- & 10 N 1-L 69680 v
1-55. SR>'2168 D2
-5.90R3-- Company D 3-3.00 N 2-1
．． 40590 Shi2-5λ0R4-2a14W D4
-470 R5--21L 36 D 5-λ00 N 3
-1.69680 Shi3-5L 5R6--275L
41 D 6-0.60R7-342307-
2,50N 4-L 80518y 4=2
&4R&-67,5908-variable R9-45,08D 9=160 N S-L
49831y 5-6Fh, 0RIO--109
,48Diσ-0,50R11 voices 29.15
Dll-4,26N6-L51009 Jiro 6λ
7R12-66, 84D12-2.90 R13-D13-0.50R1
4-2Z 01 D14-3.30 N? −
1,51009y 7→17R15-70,99D15
-116 R16--To 18 72 D16- SL 6
6 N 8=L80518 y 8P2S,
4R17-IQ, 84 D1? -5, Chrysanthemum R1
8-9λ95 01B-3L00 N 9
-L 61659 $19=3&6R19--3
4L99 01G-allR2G-- Fig. 2 shows an aberration diagram of an object at infinity in the numerical implementation sequence.

In the numerical embodiment, the second 1-2 lens of the first lens group having a negative refractive power is made of silicone rubber made of an optically elastic material having a variable refractive power, a liquid lens, or the like. Then, while extending the first lens group, the radius of curvature of the lens surface on the image side of the first and second lenses is changed from 12 & 14 to z9.0 so that the negative refractive power is weakened. Focusing on a finite distance object. At this time, the focal length f□2 of the first and second lenses changes from -50 to 15 and 14.

An aberration diagram at this time is shown in FIG.

Weakening the negative refractive power of at least one lens surface in the first lens group in this way corresponds to weakening the negative refractive power of the entire first lens group, and this also means that the negative refractive power of at least one lens surface in the first lens group is weakened. It has the same effect as pumping out. This reduces the amount of extension of the first lens group and reduces aberration fluctuations during focusing.

In this embodiment, in order to further reduce fluctuations in aberrations during focusing, it is preferable to change the refractive powers of a plurality of lens surfaces. For example, if the radius of curvature of the object-side lens surface of the first and second lenses is changed from infinity to 200 in the above-mentioned state, it is possible to focus on an object at a finite distance of about -34c1n. At this time, the focal lengths of the first and second lenses are -57.24. An aberration diagram at this time is shown in FIG.

Changing the refractive powers of a plurality of lens surfaces in this way has the advantage of reducing aberration fluctuations, particularly off-axis sesame aberration fluctuations.

In this embodiment, the refractive powers of a plurality of lens surfaces having positive and negative refractive powers in the first lens group may be changed, and thereby the overall aberration can be reduced.

Further, in this embodiment, the first lens group may be fixed and only the refractive power may be changed if a slight variation in aberration can be tolerated during focusing.

In this embodiment, a third lens group having a positive or negative refractive power that is fixed or movable during zooming may be arranged behind the second lens group.

In the present invention, any zoom lens can be used as long as it has a plurality of lens groups preceded by a lens group with negative refractive power, and focuses by extending the lens group with negative refractive power. It can also be applied to lenses.

(Effects of the Invention) According to the present invention, aberration fluctuations can be suppressed over the entire object distance by moving a lens group with a negative refractive power toward the preceding zoom lens while weakening the negative refractive power of the first lens group. It is possible to achieve a zoom lens having a variable refractive power lens that can be focused with less sharpness.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a lens according to a numerical example of the present invention, FIG.
Figures 3 and 4 are objects at infinity, approximately 573 degrees from the image plane, respectively.
This is an aberration diagram for an object at a finite distance of about 34 ar1 from the a-plane. FIG. 5 is an explanatory diagram of an embodiment in which the refractive power of the lens surface is changed in the present invention. In the aberration diagram, @, and Ω are the aberration diagrams at the wide-angle end, middle, and telephoto end, respectively.
Ru. In the figure, ΔS is the sagittal image plane, 6M is the meridional image plane,
d is the d-line, g is the g-line, and y/ is the image height.

Claims (1)

[Claims] It has at least two lens groups, a first lens group with a negative refractive power and a second lens group with a positive refractive power, in order from the object side, and the distance between both lens groups is changed to change the magnification. When focusing on a distance object, the first lens group is extended and the refractive power of at least one lens surface of the first lens group is changed so that the negative refractive power of the first lens group is weakened as a whole. A zoom lens having a variable refractive power lens.