JPS589401B2 - Zoom lens at finite distance - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a continuous variable magnification lens used mainly as a copying lens, a photolithography lens, a relay lens in an optical system, etc. when the imaging magnification is close to 1x. It is.

Due to the nature of copying and plate making, the subject area and imaging area are often quite large, and the lens system used for this process also has a wide range of focal lengths due to the focal length of the angle of view.
It is normal for the outer diameter and overall length to be relatively large.

Therefore, considering the ease of connection with the device and the manufacturability of the lens, it is desirable that the lens system be as small as possible.

Furthermore, in copying and plate making, etc., the slightest image distortion is not allowed due to the purpose, and the lenses used for this purpose have much stricter distortion aberration than general photographic lenses, preferably 0%. They are constrained to have to be restrained.

For this reason, in general, a symmetrical lens that has the same magnification and theoretically does not generate distortion is often used as a lens for copying and plate making.

In this case, in order to change the magnification using a fixed focal length lens system where the focal length does not change, the object plane, image plane,
It is well known that at least two of the three parts of the lens system must be moved, or that two of the three parts of the lens system, the subject plane, the image plane, and the lens system must be moved when changing the magnification. This is extremely disadvantageous in terms of work, and even if it were possible to move either the object plane or the image plane along with the movement of the lens system by some kind of interlocking mechanism, it would not be a good idea because the apparatus would become complicated or too large.

In any case, in this force method, it is inevitable in principle that the mutual yoke distance from the object plane to the image plane is at its minimum when the magnification is the same, and that it changes in the direction of increasing as the magnification changes.

Furthermore, even if a symmetrical lens is used and the distortion is set to 0% at 1x, distortion will occur if the magnification is changed, and if the magnification is further changed, the distortion will not only increase, but also change in other aberrations. It is difficult to do anything about this, which causes deterioration of image performance, as long as a lens with a fixed focal length is used, even if it is symmetrical.

In addition to the power method, which fixes the object plane and the image plane and changes magnification using only lenses, it is also known that there is a method in which an attachment lens corresponding to each magnification is added to change the focal length.

However, this method has no advantage in correcting distortion aberration, and the magnification obtained by this method is only a single magnification determined by the combined focal length of the attached attachment lens and the main lens, and is continuously variable. Of course, this is not possible, but in order to obtain multiple magnification changes, it is a complicated mechanism that requires adding and removing different attachment lenses as many times as the entire lens system moves. is required.

Even with this method, if the magnification is to be greatly changed, it is necessary to add an attachment lens with strong power, which leads to further increase in distortion and deterioration of other aberrations.

The present invention relates to a continuous variable magnification lens system that improves the above-mentioned drawbacks that occur when using a fixed focal length lens or when using an attachment lens. lens group,
It is composed of four groups: a first moving lens group, a second moving lens group, and a second fixed lens group.The aperture is located at the center of the entire lens system between the first moving lens group and the second moving lens group. The first fixed lens group and the second fixed lens group have the same lens element and are arranged facing the aforementioned aperture, and similarly, the first moving lens group and the second moving lens group are also the same. In an optical system in which each lens element is arranged facing the aperture mentioned above, the first moving lens group and the second moving lens group are respectively moved in conjunction with the movement of the entire lens thread to change the magnification. By giving an asymmetrical movement to the aperture, the yoke distance is always kept constant during zooming.
The purpose is to prevent distortion from occurring at all, and to also correct focal plane fluctuations due to changes in image curvature.

Another feature is that the lens system as a whole can be miniaturized by appropriately distributing the power between each group and the elements within each group.

The details of each will be explained below.

For a variable magnification lens system that maintains a constant co-yoke distance, it is sufficient to move at least two of the constituent lens groups, and in order to change the magnification including the 1x magnification position, the lens system must be set at 1x magnification. It is desirable to have a symmetrical structure in which the distortion aberration is theoretically 0%.

It is also good to have a force that maintains the symmetry of each lens element with respect to the aperture when changing the magnification.

In other words, each group is arranged at symmetrical positions so as to maintain a constant co-yoke distance in conjunction with the movement of the entire lens system to change the magnification, and to avoid extremely destroying the symmetry of the entire lens system. A force that moves almost symmetrically with respect to the aperture is advantageous in suppressing the occurrence of distortion.

Also, whether such a lens system can be made compact depends on how the power is distributed between each lens group, but if the angle of view is constant, it is not possible to make a lens system with a fixed focal length. In comparison, it can be noted that the power of the variable magnification lens system has a large degree of freedom in selecting the degree of miniaturization through power distribution.

In other words, in a variable magnification lens system, if the power of the movable lens group is weakened, the structure of the lens element becomes simpler, but the distance it moves becomes larger, which increases the overall length and diameter of the lens system. If it is made stronger, a compact lens system with a small travel distance and therefore a small diameter will be obtained.

However, if the power of the lens group is made too strong, aberration fluctuations during zooming will increase, making it impossible to realize a lens system with practical brightness and angle of view.

Therefore, in the lens system of the present invention, the power of each group is carefully distributed so that the entire system does not exceed a certain size, and the power is divided among three elements within each group. This is the result of removing various aberrations.

Furthermore, in the lens system of the present invention, the fixed lens group is placed outside the movable lens group, which facilitates the structure of the lens barrel and the maintenance of the product, and the lens elements in the fixed group are completely common. In addition, the lens elements within the movable group can also be made completely common, making it economical to manufacture.

FIG. 1 is a block diagram showing the configuration of a lens system according to the present invention.

In Figure 1f, the A and D groups are fixed lens groups that are each composed of the same lens elements and are arranged symmetrically with respect to the aperture located at the center of the entire lens system, and the B and C groups are each composed of the same lens elements. A movable lens group composed of lens elements and arranged symmetrically to the aperture mentioned above, fm is the focal length of the fixed lens group (A group, D group), fV is the focal length of the movable lens group (B group, C group), t1 is the axial distance between groups A and B, and t2 is the distance between groups B and C.
The axial spacing between groups, t3, is the axial spacing between groups C and D;
Let DL be the amount of movement of the entire lens system to perform magnification change, and DL, t1, t2, and t3 when changing the magnification from the standard magnification 1x to an arbitrary magnification ma while keeping the co-yoke distance fixed are DLa, respectively.
, t1a, t2a, t3a, t4a, t3a
is a value that is determined dependently by giving DLa, and t2a is a value that is determined dependently on t1a and t3a.

In other words, when the magnification is changed from the standard magnification to the magnification ma, if DLa is changed sequentially as a parameter, the values of L1a and t3a will change, and by changing DLa, t
It can be seen that there are an infinite number of values as solutions for 1a and t3a.

Here, if DLa is selected appropriately, it is possible to solve t1a=t3a and move the first moving lens group and the second moving lens group completely symmetrically with respect to the aperture, but in this case, the distortion can be reduced to 0%. Distortion occurs only at 1x magnification, and as the magnification changes, distortion occurs, and the degree of distortion increases as the magnification change range becomes wider.

Therefore, solving tla = t3a is limited to 1x, and at other magnifications, t1 slightly breaks the symmetry.
It is better to make an asymmetrical movement in a state where a≠t3a.

In the present invention, a lens system is configured such that the distortion aberration is always 0% at any magnification, which is obtained by performing an appropriate convergence calculation from among the countless solutions mentioned above and only calculating the magnification by 1. be.

FIG. 2 shows the lens system of Example 1 according to the present invention with a magnification of 0.5.
This figure shows the relationship between t1a/t3a and distortion when DLa is changed in the magnification, and from the figure, t1a/t3
a=1.0, that is, when the movable lens group is moved symmetrically with respect to the aperture, the distortion that was 0.3% is t1a/t3a20
．． It can be seen that by moving it asymmetrically to 84, it becomes 0%.

Similarly, FIG. 3 shows when the lens system of Example 1 is magnified,
The relationship between t1a/t3a at which the distortion aberration at each magnification is 0% is shown by plotting the logarithm (logβ) of the magnification on the horizontal axis.

From this figure, it can be seen that at any magnification, the distortion can be reduced to 0% by selecting t1a/t3a.

In addition, as a matter that must be practically taken into account in a variable power lens, there is the problem of variation in the amount of field curvature that occurs during variable power.

Since the image plane must be flat when photographing flat objects with no depth, such as copying or plate making, it is desirable to fix the center of the total depth of focus within the entire field of view as the image plane. In general, the center of the focal depth is located at a distance from the so-called Gaussian image plane and changes with the magnification, and even in a variable magnification optical system, the amount of distance usually differs depending on the magnification. be.

For this reason, even if you try to keep the common distance from the subject plane to the image plane constant, when you change the magnification, the depth of focus commonly obtained at each magnification in the same space will be within a very narrow range. In severe cases, defocus usually occurs.

In order to avoid this disadvantage, the most effective method is to perform some kind of correction so that the center of the depth of focus always stays at the same spatial position on the image plane during zooming.

There are several ways to perform this kind of correction, but if there is one that works effectively for both distortion aberration correction and image plane correction, consider moving other lens elements for image plane correction. You don't have to worry about the lens mechanism, assembly,
This is extremely advantageous in terms of manufacturing since adjustment can be simplified.

Therefore, in the present invention, we focus on reversing the movement of the second moving group to keep the Gaussian image plane stationary during zooming,
Compensation was performed by slightly moving the value of t3a described above in the direction of canceling the positional shift of the center of the depth of focus due to the change in the field curvature.

In other words, a feature of the present invention is that the seemingly simple movement of the second moving group is simultaneously responsible for correction of distortion fluctuations and correction of image plane fluctuations in addition to zooming as its main function.

Hereinafter, embodiments according to the present invention will be described. The radius of curvature of each lens, the 10-axis spacing, the refractive index of the glass for the d-line, and the Abbe number are sequentially determined from R1 to R2, d1 to d19, N
1 to N12, and ν1 to ν12.

Example 1 (Best side) Example 2 (Best side) In addition, in FIGS. 5 to 9, 8 is used for each magnification of 8 in Example 1.
It shows the compensation iE state of spherical aberration, astigmatism, and distortion aberration, and the magnification is 0. Despite the wide zooming range from 5X to 2X, it was found that the distortion aberration was kept at 0% with little variation in other aberrations, and the zoom lens according to the present invention has extremely high zooming ability at a finite reciprocal distance. It can be said that it is a good lens.

[Brief explanation of drawings]

Fig. 1 is a block diagram showing the configuration of a zoom lens with a finite co-yoke distance of 3 according to the present invention, Fig. 2 c is a relational diagram showing the relationship between the movement of the movable lens group and the amount of distortion, and Fig. 3 is a diagram showing the relationship between each magnification. FIG. 4 is a cross-sectional view showing the lens configuration of Example 1 according to the present invention, and FIGS. FIG. 4 is an aberration diagram at each magnification of Example 1. FIG.

Claims (1)

[Claims] 1. Regarding the diaphragm located at the center of all lens threads,
The first fixed lens group and the first moving lens group are arranged in order from the subject side so that the first and second movable lens groups having the same lens element and the first and second fixed lens groups are opposed to each other. , an aperture, a second movable lens group, and a second fixed lens group are disposed, and the first movable lens group and the second movable lens group are mutually moved with respect to the aperture in conjunction with the movement of the entire lens system for changing the magnification. The radius of curvature, the axial spacing, the refractive index of the glass for the d-line, and the Atsube number of each lens constituting the lens group are sequentially adjusted using a zoom lens that is moved asymmetrically at a finite co-yoke distance. A zoom lens with a finite reciprocal distance characterized by having the following configuration, where R1 to R20, d1 to d19, N1 to N12, and v0 to V12. However, for the husbands with axial spacing d5, d10, d10, and d15, when the magnification is -20, the values are 17.21, 3.65,
6.8 0, 1 4,0 9, when the magnification is -1.4, 1. 1.9 2 , 8.97 , 1 0.28
, 10, 61, when the magnification is -1.0, 10.0,
10.89, 10.98, 9.9 1, 10.73, 10.16, 9.11, 1 when the magnification is -0.7
1.78, 1 4.2 5 when the magnification is -0.5,
6.6 4,4.0 1, 1. 6.8 8.