JP2548926B2 - Variable magnification lens for copying - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION a. Technical Field The present invention is applicable to an optical system of a copying machine, such as F _NO 1: 7.
The present invention relates to a variable magnification (zoom) lens for copying of a three-group type having a certain brightness and capable of hugging up to a half angle of view of about 20 ° and having a constant object-image distance.

b. Prior art and its problems In recent years, as the downsizing and cost reduction of copying machines have been increasingly required, downsizing and cost reduction of copying lenses are also desired. Also, similar needs are increasing for copiers that can be enlarged and reduced, and variable magnification (zoom) lenses for enlargement and reduction.

As the copying lens, a lens composed of three lens groups is disclosed in, for example, JP-A-57-67909 and JP-A-60-12141.
The inventions of Japanese Patent No. 4 are known, but these are expensive because of the large number of constituent sheets of 8 to 10, and recent miniaturization of copying machines,
There is a problem that it cannot fully meet the demand for lower prices.

Therefore, to further downsize and lower the price,
The invention of JP-A-61-140912 has been proposed. However, this is a 7-group, 7-element configuration with a half angle of view of 25.
It was a wide-angle type that included up to around °. Therefore, the number of components is still large for a copying machine with a half angle of view of about 20 °,
It was hard to say that sufficient price reduction was achieved, and there was room for improvement.

c. Objective The present invention has been made to solve the above problems, and further improves the invention of the above-mentioned JP-A-61-140912 to reduce the number of constituent elements to simplify the lens configuration and reduce the size. While satisfying both cost reduction and price reduction, 0.
It is an object of the present invention to provide a variable magnification lens for copying, which has a large variable magnification of 6 to 1.4 × and good performance.

d. Structure of the Invention In order to achieve the above-mentioned object, the variable magnification lens for copying of the present invention comprises, in order from the object side, a first lens group having a negative focal length and a second lens group having a positive focal length. It is composed of a lens group and a third lens group having a negative focal length, and changes the distance between the first and second lens groups and the distance between the second and third lens groups, and moves the entire system to connect with the object plane. In a variable power lens for copying, which performs variable power while keeping the distance of the image surface constant, the first lens group is composed of one negative meniscus lens (first lens) with the concave surface facing the object side, and the second lens group is It consists of 4 elements in 4 groups, a positive second lens, a negative third lens, a negative fourth lens, and a positive fifth lens from the object side. The third lens group is a single element with a concave surface facing the image formation side. It consists of a negative meniscus lens (6th lens) of, and is composed of 6 lenses in 6 groups as a whole system. 0.3 <satisfying the condition of f _II / f _M <0.9 and is characterized in.

Further, in the present invention configured as described above, in order to keep the performance further favorable, in the negative meniscus lens (first and sixth lenses) of the first and third lens groups, (2) 0.1 <R ₁ / f ₁ <0.45 0.1 <-r ₁₂ / f ₆ <0.45 It is desirable that the condition of is satisfied, and the second lens group (second,
For the 3rd, 4th and 5th lenses) (6) 0.2 <f ₂ / f _II <1.0 0.2 <f ₅ / f _II <1.0 (8) It is desirable to satisfy the condition of 0.3 <r ₅ / r ₄ <0.9 0.3 <r ₈ / r ₉ <0.9.

 Here, the signs of the above conditional expressions are determined as follows.

f _M : Focal length of entire lens system at equal magnification f _II : Focal length of second lens group f _i : Focal length of _i- th lens n _i : d-line refractive index of _i- th lens ν _i : i-th lens Abbe number r _i : radius of curvature of the i-th surface from the object side In addition, according to the present invention, in the variable magnification lens for copying configured as described above, the first lens, the sixth lens, and the The second lens and the fifth lens, and the third lens and the fourth lens have the same shape and are symmetrical.

e. Operation The most characteristic feature of the present invention is that the conventional variable magnification lens for copying, which is composed of three groups of this type, has the second lens group composed of 5 to 8 elements. Then, the second lens group is achieved by a simple structure of 4 elements in 4 groups.

 Hereinafter, each of the above conditions will be described.

The condition (1) relates to the ratio between the focal length of the second lens group and the focal length of the entire system. In this type of variable magnification lens for copying consisting of three groups, the second lens group mainly plays the role of image formation, and the first lens group and the third lens group are the first and second lens groups during zooming. By changing the distance and the distance between the second lens group and the third lens group, the focal length of the entire system is changed and the distance between the object plane and the image plane is kept constant. If the upper limit of condition (1) is exceeded, the power of the second lens group becomes loose, which is advantageous in terms of aberration correction within the second lens group, but the first lens group and the third lens group associated with zooming. The amount of movement is large, which is not preferable in terms of downsizing. On the other hand, when the value goes below the lower limit, the power of the second lens group becomes large, so that the movement amount of the first lens group and the third lens group due to zooming can be made small, but it is good in the second lens group. In addition, it becomes difficult to suppress the aberration to a small value, and the sensitivity of each lens group becomes large, which makes it difficult to maintain good performance in manufacturing.

Conditions (2) and (3) relate to the negative meniscus lens of the first lens group and the third lens group. Since the first lens group and the third lens group are both composed of one single lens, it is difficult for the first and third lens groups to largely correct the residual aberration of the second lens group. . Therefore, the conditions (2) and (3) change the focal length of the entire system during zooming without deteriorating the various aberrations that are well corrected in the second lens group, and keep the object plane and the imaging plane constant. It is a condition that makes it possible to keep

The condition (2) relates to the radius of curvature of the negative meniscus lens on the object side and the image forming side of the first lens group and the third lens group, respectively. By keeping the radius of curvature of the concave surface of the two negative meniscus lenses within the condition (2), aberration fluctuations during zooming can be kept small without deteriorating well-corrected aberrations in the first lens group. It will be possible. If the upper limit or the lower limit of this condition (2) is exceeded, astigmatism will be particularly aggravated, and aberration fluctuation during zooming will be large, such being undesirable.

The condition (3) relates to the chromatic aberration of the first lens group and the third lens group. In the present invention, the first and third lens groups are single-lens constituent single lenses, and it is impossible to perform chromatic aberration correction within the first and third lens groups. Therefore, it is necessary to avoid the occurrence of chromatic aberration in the first and third lens groups as much as possible,
By setting within the condition (3), it is possible to keep the chromatic aberration well corrected in the second lens group favorable without being deteriorated by zooming.

As described above, since the first lens group and the third lens group are composed of a single-lens single lens, it is difficult to correct aberrations.
Therefore, it is desirable that the performance and the like at the time of zooming be sufficiently well corrected in the second lens group. Conditions (4)-(6)
Is a condition for properly distributing the power of each lens in the second lens group and correcting various aberrations such as image flatness and chromatic aberration, which are important as a copying lens, in a well-balanced manner.

The condition (4) relates to the Petzval sum in the second lens group, and the Petzval sum is satisfactorily corrected in the second lens group in order to obtain the flatness of the image surface at a wide angle of view, which is important for the copying lens. It is a condition for doing. If the upper limit of condition (4) is exceeded, the Petzval sum will be too large, and it will be difficult to obtain a flat image surface. On the other hand, if the lower limit is exceeded, the power of each lens will increase, resulting in spherical aberration and coma. It becomes difficult to satisfactorily correct various aberrations such as.

The condition (5) is a condition for correcting chromatic aberration in the second lens group. Since the first and third lens groups have a single lens structure, it is necessary to sufficiently correct the chromatic aberration generated in the second lens group in order to sufficiently reduce the variation in chromatic aberration due to zooming. If the upper limit or the lower limit is exceeded in condition (5), the chromatic aberration generated in the second lens group becomes excessive, and the chromatic aberration fluctuation associated with zooming increases, which is not preferable.

The condition (6) relates to the powers of the two positive lenses in the second lens group. In condition (6),
If the upper limit or the lower limit is exceeded, it becomes difficult to favorably correct spherical aberration, coma, and astigmatism in the second lens group.

The condition (7) relates to the difference in refractive index between the positive lens and the negative lens in the second lens group. By suppressing the difference in refractive index between the positive lens and the negative lens within this condition (7), it becomes possible to obtain a flat image surface and a wide image circle which are important as a good copying lens.

The condition (8) relates to the ratio of the radiuses of curvature of the positive lens and the negative lens in the second lens group which are adjacent to each other. By controlling the ratio of the radii of curvature within this condition (8), spherical aberration, coma and astigmatism can be corrected in a well-balanced manner. If the upper limit of the condition (8) is exceeded, it becomes difficult to satisfactorily correct coma and astigmatism. On the other hand, if the value goes below the lower limit, spherical aberration is undercorrected, which is not preferable.

As described above, the lens configuration of the present invention is a 6-group 6-element configuration, but the first lens and the sixth lens, the second lens and the fifth lens, the third lens and the fourth lens are respectively arranged from the object side. By adopting the symmetrical shape with the same shape, it is possible to form the lens system with substantially three kinds of lenses, so that it is possible to provide a cost-effective lens system.

f. Examples Numerical data of Examples of the present invention are shown below. However, F _NO is the aperture ratio, f _M is the focal length of the entire system at the same magnification,
ω is the half angle of view, r is the radius of curvature of each lens surface, d is the lens thickness or lens spacing, n is the d-line refractive index of each lens, and ν
Is the Abbe number of each lens.

The numerical value of the conditional expression relating to the focal length is calculated based on e-line.

[Example 1] (1) f _II / f _M = 0.458 (2) f ₁ / f ₁ = -r ₁₂ / f ₆ = 0.324 _{(6) f 2 / f II} = f 5 / f II = 0.727 (8) r ₅ / f ₄ = r ₈ / r ₃ = 0.626 [Example 2] (1) f _II / f _M = 0.527 (2) r ₁ / f ₁ = -r ₁₂ / f ₆ = 0.309 _{(6) f 2 / f II} = f 5 / f II = 0.623 (8) r ₅ / r ₄ = r ₈ / r ₉ = 0.492 [Example 3] (1) f _II / f _M = 0.643 (2) r ₁ / f ₁ = -r ₁₂ / f ₆ = 0.228 _{(6) f 2 / f II} = f 5 / f II = 0.506 (8) r ₅ / r ₄ = r ₈ / r ₉ = 0.505 [Example 4] (1) f _II / f _M = 0.615 (2) r ₁ / f ₁ = -r ₁₂ / f ₆ = 0.246 (6) f ₂ / f _II = f ₅ / f _II = 0.485 (8) r ₅ / r ₄ = r ₈ / r ₉ = 0.615 [Example 5] (1) f _II / f _M = 0.704 (2) r ₁ / f ₁ = -r ₁₂ / f ₆ = 0.197 _{(6) f 2 / f II} = 0.394, f 5 / f II = 0.395 (8) r ₅ / r ₄ = 0.606, r ₈ / r ₉ = 0.628 [Example 6] (1) f _II / f _M = 0.420 (2) r ₁ / f ₁ = -r ₁₂ / f ₆ = 0.347 (6) f ₂ / f _II = 0.772, f ₅ / f _II = 0.741 (8) r ₅ / r ₄ = 0.570, r ₈ / r ₉ = 0.570 g. Effect As described above, according to the present invention, at least 7 groups have been used in the past.
The variable magnification lens for copying, which consisted of one lens,
This is achieved with a lens configuration of 6 lenses in a group, is very simple, has a great effect on size reduction and cost reduction, and the object of the present invention can be sufficiently achieved.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1,5,9,13,17,21 show the first, second, third, fourth, fifth, and third embodiments of the present invention in order.
6 is a lens cross-sectional view of FIG. 2,6,10,14,18,22, the embodiment of the present invention, 1, 2, 3, 4,
Aberration diagrams of 5 and 6 at 1.0 × magnification. Figures 3,7,11,15,19,23 are, in order, Examples 1, 2, 3, 4, of the present invention.
Aberration diagrams at magnifications of 1.42 × for 5 and 6. Figures 4,8,12,16,20,24 are, in order, Examples 1, 2, 3, 4, of the present invention.
Aberration diagrams at magnifications of 0.64 × for 5 and 6.

Claims (5)

(57) [Claims] 1. A first lens unit having a negative focal length in order from the object side.
It is composed of a lens group, a second lens group having a positive focal length, and a third lens group having a negative focal length, and changes the first and second lens group intervals and the second and third lens group intervals. In the variable magnification lens for copying, in which the entire system is moved and the distance between the object plane and the image plane is kept constant, the first lens group is a negative meniscus lens with a concave surface facing the object side. (First lens), the second lens group is composed of a second lens element positive from the object side, a third negative lens element, a fourth negative lens element, and a fifth positive lens element. The group consists of one negative meniscus lens (sixth lens) with the concave surface facing the image side, and is composed of 6 lenses in 6 groups as a whole system. The focal length at the same magnification of the whole lens system is f _M , When the focal length of the second lens group is f _II , the following condition (1) must be satisfied. Variable magnification lens for copying. (1) 0.3 <f _II / f _M <0.9 2. The variable magnification lens for copying according to claim ₁ , wherein the focal length of the negative meniscus lens (first lens) of the first lens group is f ₁ , and the radius of curvature of the object-side surface is
When r ₁ and Abbe number are ν ₁ , the focal length of the negative meniscus lens (sixth lens) of the third lens group is f ₆ , the radius of curvature of the image-side surface is r ₁₂ , and the Abbe number is ν _6. A variable power lens for copying, characterized in that the following conditions (2) and (3) are satisfied. (2) 0.1 <r ₁ / f ₁ <0.45 0.1 <−r ₁₂ / f ₆ <0.45 3. The variable magnification lens for copying according to claim 1, wherein four lenses (second, third, and second lenses in the second lens group are included.
(4,5 lenses) have focal lengths of f ₂ , f ₃ , f ₄ , f ₅ , d-line refractive indices of n ₂ , n ₃ , n ₄ , n ₅ , and Abbe numbers of ν ₂ , ν ₃ ,
A variable magnification lens for copying, characterized in that ν ₄ , ν ₅ , and the focal length of the second lens group are f _II, and the following conditions (4) to (6) are satisfied. (6) 0.2 <f ₂ / f _II <1.0 0.2 <f ₅ / f _II <1.0 4. The variable magnification lens for copying according to claim 3, wherein the d-line refractive index of the second, third, fourth and fifth lenses is n.
₂ , n ₃ , n ₄ , n ₅ , each of the image-side surface of the second lens, the object-side surface of the third lens, the image-side surface of the fourth lens, and the object-side surface of the fifth lens A variable magnification lens for copying, characterized in that the following conditions (7) and (8) are satisfied when the curvature radii of are r ₄ , r ₅ , r ₈ , and r ₉ . (8) 0.3 <r ₅ / r ₄ <0.9 0.3 <r ₈ / r ₉ <0.9 5. The variable magnification lens for copying according to claim 1, wherein the first lens and the sixth lens are from the object side, the second lens and the fifth lens are from the object side. A variable magnification lens for copying, wherein the third lens and the fourth lens have the same shape and are symmetrical.