JPS61248015A - Variable focal distance lens - Google Patents

Abstract

PURPOSE:To compensate aberration effectively and to reduce the number of constitutional lenses by using a refractive index distribution type lens for the 1st lens group. CONSTITUTION:The 1st negative lens group A and 2nd positive lens group B are arranged successively from the object side and the magnification is varied while contracting a distance between the 1st lens group A and the 2nd lens group B as shown by arrows from a wide angle end to a telescopic end. The 1st negative lens group A consists of negative meniscus lenses having curved surfaces R1, R2 and arranged successively from the object side so that their convex surfaces are turned to the object side and radial and refractive index distribution type lenses having curved surfaces R3, R4 respectively and positive transfer power and all lenses constituting the 2nd positive lens group B have uniform media. The refractive index distribution type lens has the distribution of refractive indexes which reduces the change of refractive indexes near an optical axis and reduces the refractive index suddenly at a peripheral part, so that the generation of a barrel type curve aberration at the wide angle end can be compensated to a small value.

Description

Detailed Description of the Invention (1) Technical Field The present invention relates to a variable focal length lens, particularly a variable focal length lens, which is composed of a plurality of lens groups, and in order from the object side, a first lens group, a negative lens group, @
The present invention relates to a variable focal length lens in which two lens groups are composed of positive lens groups, and magnification is changed by changing the distance between the first lens group and the second lens group.

(2) Prior Art In general, in a variable focal length lens, in addition to correcting aberrations in the reference state, aberration fluctuations during zooming must be corrected to be as small as possible. Therefore, the spherical aberration, coma aberration, and astigmatism of each lens group must be individually corrected in each lens group, and each lens group is usually composed of several lenses.

In recent years, there has been an increasing demand for variable focal length lenses to be more compact and to have a high variable power ratio. In order to make a variable focal length lens compact, which consists of a positive lens group and performs magnification by changing the distance between the first and second lens groups, paraxially it is necessary to Either the power can be increased or the distance between the principal points between each lens group can be reduced. On the other hand, in order to increase the magnification ratio of a variable focal length lens, paraxially it is sufficient to increase the power ξ of each lens group or to increase the moving distance of the variable focal length lens group. In this way, from a paraxial point of view, it is sufficient to increase the power of each lens group in order to make the variable focal length lens of the above type compact and increase the variable power ratio, but in actual lens systems, it is sufficient to increase the power of each lens group. Therefore, a large number of lenses are required to minimize the occurrence of aberrations while increasing the power of the lens group. Also, if the power per lens is strong, the curvature becomes tight, and the center lens thickness of a convex lens when the required flange thickness is taken, or the air gap where the concave surface contacts when taking the marginal distance from the adjacent lens becomes large. is necessary. In this case, the total length of the lens group increases, and the distance between the principal points must be increased, and as a result, it becomes impossible to shorten the total optical length of the entire system. Furthermore, as the length of the lens group increases, the movement space of the variable power lens group becomes smaller, making it impossible to achieve a high variable power ratio.

The above-mentioned zoom type is a zoom type mainly used for wide-angle zoom lenses, and the effective diameter of the front lens required for off-axis light beams is extremely large. Therefore, if the thickness of the first lens group becomes large, the effective diameter of the front element required for off-axis light flux cannot be made compact, and due to this vicious cycle, ordinary homogeneous medium lens systems cannot be used. There were limits to miniaturization and high magnification.

Also, it consists of a plurality of lens groups, and in order from the object side, the first negative lens group,! In a two-group type variable focal length lens that is composed of two positive lens groups and changes magnification by decreasing the distance between the first negative lens group and the second positive lens group from the wide-angle end to the telephoto end, the first negative lens group By increasing the power of the second positive lens group and by decreasing the distance between the principal points between the first negative lens group and the second positive lens group, it is possible to reduce the total optical length of the entire system. If the power of the first negative lens group is increased, the number of lenses required to correct the aberrations of the first negative lens group will increase, and the total length of this lens group will become longer. Therefore, the first negative lens group and the second
The distance between the principal points between the positive lens groups cannot be made much smaller υ
, it was not possible to reduce the total optical length of the entire system.

(3) Summary of the Invention An object of the present invention is to eliminate the above-mentioned conventional drawbacks and provide a compact, high-performance, high-magnification variable focal length lens. A further object of the present invention is to provide a variable focal length lens that is easy to assemble and adjust.

In order to achieve the above object, the variable focal length lens according to the present invention consists of a plurality of lens groups, and the first lens is arranged in order from the object side.
In a variable focal length lens that includes a negative lens group as a lens group and a positive lens group as a second lens group, and performs magnification by changing the distance between the first lens group and the second lens group, at least It is characterized by having at least one gradient index lens in the first lens group.

The refractive index distribution of the gradient index lens includes a distribution in which the refractive index changes in the radial direction from the optical axis of the lens (hereinafter referred to as radial type), a distribution in which the refractive index changes in the optical axis direction of the lens ( There are also lenses that have both radial type and axial type distributions (hereinafter referred to as axial type). Further, among the radial type lenses, those having a distribution in which the refractive index decreases in the radial direction from the optical axis are classified as lenses having positive transfer power, and those having a distribution in which the refractive index increases in the radial direction from the optical axis. A lens having a negative transfer power will be described below as a lens having a negative transfer power.

As mentioned above, the present variable focal length lens can effectively correct aberrations by using at least one gradient index lens in at least the first lens group, and can achieve a reduction in the number of constituent lenses. Further effects can be obtained by designing lenses using the gradient index lens in lens groups other than the first lens group. Further, the shape of the refractive index distribution type lens may be any shape, and by controlling the curvature, focal length, and refractive index distribution shape, it can be made into a lens with various performances, and can be placed at any position in each lens group. Various types of lens systems can be obtained by arranging them.

Hereinafter, the present invention will be explained in detail using Examples.

(4) Embodiment FIGS. 1 and 2 are cross-sectional views and aberration diagrams showing a configuration example of a variable focal length lens according to the present invention. In the figures, Rt (t=L
2+ 3+...) is the i-th surface counting from the object side, and Di (i=1.2.3......) is the distance between the i+1-th surface counting from the object side. The axial air spacing or the axial wall thickness is indicated by A indicating the first lens group and B indicating the second lens group. The arrows in the figure represent the approximate movement locus of the movable lens group.

Also, in the aberration diagram, the focal length f is 100 yen, 138.9 m+.

The figure shows spherical aberration, astigmatism, and distortion in the case of 188.4 m, where t is the spherical aberration for the f-line, d is the spherical aberration for the d-line, S is the astigmatism on the sagittal plane, and M is the spherical aberration for the d-line. refers to astigmatism on the meridional surface.

Tables 1-1 to 1-3 below show lens data of this variable focal length lens and coefficients representing the refractive index distribution of the gradient index lens used. In Table 1-1, f is the focal length,
FNO is the F number, 2W is the angle of view, and R1 (1=1.2.
3. ...) indicates the radius of curvature of the i-th surface counted from the object side, and is positive when it is convex toward the object side and negative when it is concave. Also, Di (1=1゜2.3...)
is the axial air gap or axial wall thickness between the i-th and i+1-th surfaces counting from the object side, Ni, Vi (i
=1.2.3p-...) respectively indicate the refractive index and Atsube number of the i-th lens counting from the object side. Furthermore, N1 (h)
represents the refractive index distribution of the radial type gradient index lens positioned first from the object side, and this distribution can be expressed by the following equation (1).

N i (h) ” No +N+h Snow +N Goose
4+Nah4+Nah-tenNeh”+・・・・・・ (
1) Here, h is the distance in the radial direction from the optical axis, N.

is the refractive index on the axis, Nr, Nr Ns e...
... is the refractive index distribution coefficient. Therefore, Table 1-3
represents the refractive index distribution of each gradient index lens for the 2-line and the d-line. Table 1-2 shows each focal length and the axial air distance between each lens group during zooming.

The present variable focal length lens will be described in detail below.

This variable focal length lens consists of a first negative lens group A and a second positive lens group B in order from the object side.From the wide-angle end to the telephoto end, the first negative lens group A and the second positive lens group This is to change the magnification while reducing the distance between the lens group B and the lens group B. The first negative lens group A includes, in order from the object side, a curved surface R1,
The second positive lens group B consists of a negative meniscus lens convex to the object side consisting of R2, and a radial type gradient index lens having a positive transfer power formed by curved surfaces R3 and a4, and all lenses constituting the second positive lens group B are It is a homogeneous medium lens.

The gradient index lens described above has a refractive index distribution in which the change in refractive index is small near the optical axis, and the refractive index decreases rapidly at the outer periphery, and the coefficient tooth of the refractive index distribution N(h) is Nr<', 0, the occurrence of barrel-shaped distortion at the wide-angle end can be corrected to a small value.

Also, at the telephoto end, the spherical aberration that occurs largely in one direction on the second surface R2 of the negative meniscus lens closest to the object in the first negative lens group A can be avoided by the light ray traveling inside the gradient index lens. The undertone is corrected in one direction. Furthermore, coma aberration at the telephoto end is corrected in one direction while the light ray travels inside the lens.For this reason, the first negative lens group, which normally consists of three to four lenses, is composed of two lenses. However, we were able to achieve a zoom lens in which various aberrations were well corrected at all focal lengths.

Furthermore, the effect of the gradient index lens in this variable focal length lens will be explained in detail.

As mentioned above, the first negative lens group A has a large diameter and a large weight.
The number of constituent elements can be reduced, the weight and size can be reduced, and the total optical length of the entire system can be shortened accordingly. In addition, the effective diameter of the front lens required for off-axis light flux is small, making it unnecessary, and the lens outer diameter and filter diameter also become smaller. Furthermore, regarding aberration correction, we suppressed the occurrence of barrel-shaped distortion at the wide-angle end, and the occurrence of spherical aberration and coma aberration at the telephoto end.
=62° to 35.4° FIGS. 3 and 4 are cross-sectional views and aberration diagrams showing another example of the configuration of the variable focal length lens according to the present invention. The symbols and arrows in the figure have the same meanings as in the previous example, C is the third lens group, D is the fourth lens group, and the aberration diagrams are for focal lengths f of 100 mm, 171 m, and 287 mm. It shows what is happening. In addition, Tables 2-1 to 2 below
-3 indicates the lens data of this variable focal length lens and the coefficient representing the refractive index distribution of the gradient index lens used, and the format of the description and the symbols in the table are the same as in the previous example.

The present variable focal length lens will be described in detail below.

This variable focal length lens is composed of, in order from the object side, a first negative lens group A, a second positive lens group B, a third negative lens group C, and a fourth positive lens group. The distance between the first negative lens group A and the second positive lens group B,
Then, the distance between the third negative lens group C and the fourth positive lens group is reduced, and the distance between the second positive lens group B and the third negative lens group C is expanded to perform zooming. First negative lens group A
(d) A radial type gradient index meniscus lens having a positive transfer power generated from curved surfaces R1 and R2 is provided closest to the object side.

In a wide-angle variable focal length lens such as this variable focal length lens where the first lens group is a negative lens group, barrel-deaf distortion occurs in the first negative lens group at the wide-angle end, making it difficult to correct aberrations. It became. However, in this variable focal length lens, the negative meniscus lens closest to the object in the first negative lens group A has a refractive index at the outer periphery that is smaller than the refractive index near the optical axis in the direction perpendicular to the optical axis. refractive index distribution,
That is, a radial type gradient index lens having positive transfer power is used to reduce the occurrence of barrel distortion in the first negative lens group at the wide-angle end.

On the other hand, in the negative meniscus lens of the first negative lens group and the second WR2 of the x-direction lens, spherical aberration usually occurs largely in one direction, but since it has the above refractive index distribution, the negative meniscus lens On the concave surface of the second surface R2, the refractive index decreases from the optical axis toward the outer periphery, and the occurrence of spherical aberration in one direction becomes smaller.

Also, with such a refractive index distribution, when a ray of light travels inside the negative meniscus lens of the first negative lens group A, spherical aberration and coma aberration occur at the second surface of the negative meniscus lens. On the contrary, the undertone occurs in one direction and has the effect of correcting it.

Therefore, it was possible to achieve a variable focal length lens in which various aberrations were well corrected at all focal lengths.

Furthermore, to describe the effect of the gradient index lens in this variable focal length lens, the first negative lens group of this type of variable focal length lens usually consists of four or more lenses, but it has three lenses. Since it can be configured with a small number of lenses, it is possible to achieve weight reduction and compactness, and the length of the first negative lens group is reduced, making it possible to shorten the total optical length of the entire system.

Furthermore, the occurrence of barrel distortion at the wide-angle end can be suppressed, and spherical aberration and coma aberration at the telephoto end can also be favorably corrected.

The above-mentioned effects can be particularly achieved by setting the coefficient teeth of the refractive index distribution N (h) of the gradient index lens to be Nt < 0.

Table 2-1 f-100~287m FNO=4.0 2w
=73.6" to 29.3° FIGS. 5 and 6 are cross-sectional views and aberration diagrams showing another configuration example of the variable focal length lens according to the present invention. Symbols and arrows in the figures indicate the above-mentioned It has the same meaning as the example, and the aberration diagram shows focal length f of 100 m and 170 m.
-8g, 286m is shown. or,
Tables 3-1 to 3-3 below show the lens data of this variable focal length lens and the coefficients representing the refractive index distribution of the gradient index lens used, and the formats and symbols in the tables are as follows: This is the same as in the previous embodiment.

Here, N1(x) represents the refractive index distribution of the axial type gradient index lens positioned first from the object side, and this distribution can be expressed by the following equation (2).

N i (x)=Ne +N+ x +N+Nl
xj ten N4 x' + ・= = (2) Here, X is the distance from the object side apex to the optical axis, N is the refractive index at the object side apex, N++ Nt, Na,...・
... is the refractive index distribution coefficient.

The present variable focal length lens will be described in detail below.

This variable focal length lens consists of, in order from the object side, a first negative lens group A, a second positive lens group B, a third negative lens group C, and a fourth positive lens. The distance between the first negative lens group and the second positive lens group B and the distance between the third negative lens group C and the fourth positive lens group are reduced as shown in FIG. The distance between the lens group C and the lens group C is increased to perform magnification change. The first negative lens group A includes a radial type gradient index meniscus lens having positive transfer power from curved surfaces R1 and R2 on the object side, and curved surfaces R3 and R on the image side of the gradient index lens.
It is equipped with an axial type gradient index lens whose refractive index increases along the optical axis from the object side to the image side.

In a wide-angle variable focal length lens such as this variable focal length lens where the first lens group is a negative lens group, the first lens group is
Barrel-shaped distortion aberration was large in the negative lens group, which was a bottleneck in aberration correction9.

In this variable focal length lens, the negative meniscus lens closest to the object in the first negative lens group A has a refractive index in the outer peripheral part that is smaller than the refractive index near the optical axis in the direction perpendicular to the optical axis. A radial type lens with a refractive index distribution, that is, a positive transfer power, is used to reduce the occurrence of barrel-shaped distortion in the first negative lens group at the wide-angle end. There is.

On the other hand, on the second surface R2 of the negative meniscus lens closest to the object side of the first negative lens group A, spherical aberration usually occurs largely in one direction, but if it has the above refractive index distribution,
On the concave surface of the second surface R2 of the negative meniscus lens, the refractive index decreases from the optical axis toward the outer periphery, so that the occurrence of spherical aberration in one direction becomes smaller.

Also, with such a refractive index distribution, spherical aberration and comatic aberration occur at the second surface R2 of the negative meniscus lens while a light ray travels inside the negative meniscus lens in the first negative lens group. On the other hand, under is generated in one direction and has the effect of correcting it. Similarly, the above aberration correction effect is particularly effective when the refractive index distribution N
This was achieved by setting the coefficient tooth of (h) to be Nt<O.

On the other hand, the lens consisting of the image-side curved surfaces R3 and R4 of the first negative lens group has a refractive index distribution such that the refractive index increases from the object side to the image side in the optical axis direction. It has the effect of over-correcting spherical aberration in one direction, which is over-corrected by the negative meniscus lens in the lens group.

Therefore, it was possible to achieve a variable focal length lens in which various aberrations were well corrected at all focal lengths.

, Pa″-bow 2, j Table 3-1 f=100~286+m FNO=4
2w=75.4° to 28.6 In each of the above configuration examples, a variable focal length lens is shown in which at least one gradient index lens is used only in the first negative lens group. However, it is obvious that gradient index lenses may be used in lens groups other than the first negative lens group, which enables further aberration correction effects and a reduction in the overall system size.

According to the present invention, at least one lens is provided in at least the first negative lens group.
By using two gradient index disc lenses, it is possible to reduce barrel distortion at the wide-angle end and to suppress the occurrence of spherical aberration and coma aberration at the telephoto end. That is, at least the first
The number of negative lenses is small to correct the aberrations mentioned above by nine lines.

The first negative lens group can be made more compact, and the entire variable focal length lens system can be made shorter and lighter.

Furthermore, if refractive index gradient lenses are used in a plurality of lens groups, the number of variable focal length lenses can be significantly reduced, and ghosting can be significantly improved. Furthermore, the light loss of the entire system due to surface reflection and internal absorption is small, the T number can be made brighter, and a sufficient amount of transmitted light can be ensured even without a multilayer coating. Of course, since the number of components is small, assembly and adjustment work becomes easier, and it can also be mounted on ultra-compact optical equipment, such as ultra-compact cameras and gastrocameras, which require the incorporation of variable focal length lenses. It becomes possible.

(5) As described in detail, the variable focal length lens according to the present invention includes:
It is a lightweight and compact lens, and it is also easy to assemble and adjust since the number of lenses in each group is small.

FIG. 3 is a cross-sectional view and an aberration diagram showing a configuration example.

A...First lens group B...Second lens group C...Third lens group D...4th lens group

Claims (4)

[Claims] (1) Consisting of multiple lens groups, in order from the object side, the first lens group is a negative lens group and the second lens group is a positive lens group, and the distance between the first lens group and the second lens group is changed. What is claimed is: 1. A variable focal length lens that changes magnification by changing the magnification of the variable focal length lens, the variable focal length lens having at least one gradient index lens in at least the first lens group. (2) At least one gradient index lens in the first lens group has a refractive index distribution such that the refractive index at the outer periphery is smaller than the refractive index near the optical axis in the direction perpendicular to the optical axis. A variable focal length lens according to claim (1). (3) At least one gradient index lens of the first lens group has a refractive index distribution such that the refractive index increases from the object side to the image side along the optical axis of the lens. A variable focal length lens according to claim (1). (4) Let the refractive index on the optical axis of the gradient index lens be No, and let the height from the optical axis be, and the refractive index distribution of the lens is N(h)-No+N_1h^2+N_2h^4+N_3
h^6・・・・・・・・・(N_1, N_2, N_3,
. . . is a coefficient), N_2<0. The variable focal length lens according to claim (2).