JPS62196614A - Zoom lens - Google Patents

Abstract

PURPOSE:To reduce the number of lenses, to reduce troubles due to an error between relative positions of lenses and to simplify assembling adjusting work by arranging at least one axial refractive index distribution type lens in a front group and arranging at least one radial refractive index distribution type lens in a rear group. CONSTITUTION:The zoom lens is provided with plural lens groups consisting of a zooming part for executing zooming by changing the intervals of these lenses on the axis and an image formation lens part arranged successively and the image formation lens part is divided on the border of the longest axial interval so that the zooming part side and the other side are set up as the front group and the rear group respectively. At least one axial refractive index distribution type lens whose refractive index is changed in the optical axis direction is arranged in the front group and at least one radial refractive index distribution type lens whose refractive index is changed in the direction rectangular to the optical axis is arranged in the rear group. Even if the front group of the final fixing lens group of the zoom lens is constituted of only one axial refractive index distribution type lens or two lenses added by a uniform lens and the rear group is constituted of only one radial refractive index distribution type lens, aberration can be efficiently corrected.

Description

[Detailed Description of the Invention] Field of Application The present invention relates to a zoom lens, and in particular improves the fixed lens group disposed following the zoom section to make the entire system more compact without deteriorating image quality. be.

<Prior Art> In recent years, there has been an increasing demand for zoom lenses for photography to be smaller and lighter. Current photographic lens systems, especially zoom lenses for photography or video cameras, have the first lens group as a positive lens group, the second lens group as a negative lens group, and the third lens group as a positive or negative lens group, in order from the object side. It is composed of a lens group, and the distance between the first positive lens group and the second negative lens group and the distance between the second negative lens group and the third lens group are changed to perform magnification, and the lens closest to the image side is In most cases, a variable focal length optical system consisting of a final fixed lens group that is fixed during zooming is used. In photographic zoom lenses, it is necessary to correct not only aberrations at a specific focal length, but also aberration fluctuations during zooming, and one way to do this is to have each lens group individually share the desired amount of aberration. It's a standard.

Among these, in the type where the final fixed lens group is divided into two groups, the front group and the rear group, with the largest air gap as the boundary, the front group is
Mainly spherical aberration, Hosochromatic aberration, and coma aberration remaining in the zoom section are effectively corrected, and the rear group mainly suppresses the occurrence of astigmatism and coma aberration, especially outward coma aberration as much as possible. Therefore, each lens group is generally composed of a large number of lenses, which is a factor that hinders the above requirements.

Conventionally, in order to make a zoom lens more compact, (1) the power of each lens group in the zoom section was increased; (2) Decrease the telephoto ratio of the relay lens group. This method is typical. Although the above method is suitable as a first-order approximation, it causes various problems in an actual lens system. That is, (1,
) In order to increase the power of the zoom section, the Petzval sum shared by the negative second lens group, which has a strong power, becomes negative and thick (occurs), resulting in a significantly excessive curvature of field.

Further, manufacturing problems arise, such as the need to assemble the zoom section with greater precision.

Similarly, in the method (2) of reducing the telephoto ratio of the relay lens group, the curvature of field becomes excessive in the direction in which the Petzval sum shared by the relay lens group takes a negative value. If the refractive index of the positive lens is lowered as a means of correcting this Petzval sum, or if a positive lens with strong power is combined with a negative lens, spherical aberration and higher-order aberrations will occur significantly, making correction difficult. becomes. Further, in (1), it is possible to correct the above aberration by increasing the number of lenses constituting the zoom section, but this increases the thickness of the lens group and requires a longer principal point interval. Therefore, as a result, it becomes difficult to shorten the total optical length of the entire system. In other words, the number of lenses in the relay (which is constructed to eliminate various aberrations generated by the zoom section) increases, which hinders miniaturization and weight reduction as well as simplification of assembly and adjustment. Therefore, ordinary spherical lens systems have limitations in meeting the above requirements.

Purpose of the present invention: The purpose of the present invention is to solve the above-mentioned problems and make the entire system compact.By reducing the number of lenses, the relative position error between lenses, that is, the pull caused by optical eccentricity, is reduced, and assembly adjustment is facilitated. This brings out the effect of simplifying the work.

The above purpose is to have a zoom section that has a plurality of lens groups, perform zooming by changing the axial spacing between them, and an imaging lens section, and to arrange the imaging lens section with the largest axial spacing as the boundary. The zoom section side is the front group, and the other side is the rear group.The front group is provided with at least one axial gradient index lens whose refractive index changes in the optical axis direction, and the rear group is provided with at least one axial gradient index lens.
This is achieved by arranging two radial gradient index lenses whose refractive index changes in a direction perpendicular to the optical axis. It is believed that further features will become clear in the description below. Furthermore, in the text section of the embodiment described below, a configuration is mentioned in which a positive focusing lens, a negative variator, and a convencator are arranged in order. Various types can be adopted, such as a double lens type, or a type in which the first positive lens is fixed and the third lens and third lens move simultaneously for zooming.

First, a general rotation when a gradient index lens is used in an imaging lens system will be described, and then embodiments will be described.

The third-order aberration coefficients of the gradient index lens are P, J, 5an
Although it is guided by the ds, the well logging "lens design method" (
Expression A1 ~ using the symbols of Kyoritsu Publishing Co., Ltd.
It becomes A15.

Here, the aberration coefficient of a gradient index lens is the refraction terms A1 to A5 that occur when the medium is homogeneous, and the refraction terms A1 to A5 that occur when the medium is homogeneous. Refraction term A that appears due to the action
6 ~ Transfer order of aberration terms that occur when light is refracted while traveling inside the AIO and gradient index lens Al1-
It is expressed by adding A15.

Third-order aberration coefficient (spherical system, homogeneous medium) ■. =h: Q crown (Ns) Alm
,=6,,Q,Q volume("'T')A2m,=h,h,"
Q,”A, (+) A3P= ~
ψ" A4 rV, = m, +P, , H, N4m
,=h,h,,'o,+Δ' (+) +””Δ,(+
) A5 (gradient index lens refraction term) I, =h: ψIn,,
A6m,=h5. ψin, u
A7m, =hyu2ψ,
,, A8V,
=h, h:ψIn, u
A9ψIn,. = ÷ (ΔN1.) ΔTh
0. ) Al0 (gradient index lens transfer order) This will be explained by taking spherical aberration as an example.

First, the inhomogeneity term ψin, ν in the radial gradient index lens is ψin, ν=4 (ΔNty)/γv A 16
becomes. Here, ΔNi represents the difference between Nl of the medium after the ν plane and N1 of the medium before the ν plane.

This formula indicates that when the medium in front of the radial refraction multiple distribution type lens is homogeneous (N1=O in a homogeneous medium), and when the coefficient N1 of h8 representing the refractive index distribution is Nl<O, it is a convex surface. ψIn < O and h4ψ1nto (hereinafter the subscript ν is omitted) has the effect of generating spherical aberration in over one direction. If it is a concave surface, ψIn > O and h4ψ1n>0
This has the effect of under-producing spherical aberration.

On the other hand, if the coefficient Nl of h2 is Nl>0, if it is a convex surface, ψ
in > O, and h4φ1n〉0, which has the effect of generating spherical aberration in the under direction, and if it is concave, ψin
<O, and h4ψin <O, which has the effect of generating excessive spherical aberration. Conversely, when the medium after the radial gradient index lens is homogeneous, the value of ΔN1ν has the opposite sign from that in the above case.

Next, the inhomogeneity term ψ, n, in the axial gradient index lens becomes ψin, ν=(ΔNoν)/γ2 A17. Here, y is the differential value of the refractive index in the optical axis direction, and Δ
The eclipse oν represents the difference between the front and rear of the ν plane.

This formula shows that when the media before and after an axial gradient index lens are homogeneous (Moν=0 in a homogeneous medium), focusing on an arbitrary surface of the lens, the refractive index decreases from that surface to the other surface ( That is, the slope Nov of the distribution change is No, <
O), when the surface shape is not flat, ψin < O, and h4φin < O, which has the effect of generating spherical aberration in one direction, and the refractive index increases from that surface to the other. (That is, when the eclipse 0ν>0), ψ1n>0 when the surface shape is other than a flat surface, which has the effect of generating h4ψ1n>0 and under-spherical aberration. ,Also,
When the surface shape is flat, ψin'' is 0 and there is no effect.

Next, the effect when a gradient index lens is used as a zoom lens will be explained.

For a normal zoom lens with a bright F number of about 1.2 to 1.4, a large number of lenses are normally used in the final fixed (relay) lens group. In contrast, the front group of the final fixed lens group of a zoom lens is composed of one axial gradient index lens or two homogeneous lenses.
Even if the rear group is composed of one radial index gradient lens, it is possible to satisfactorily correct aberrations.

In other words, when an axial gradient index lens is placed in the front group of the final fixed lens group, the spherical aberration and coma aberration that occur largely in the downward direction when constructed with a small number of homogeneous lenses as in the past can be avoided. This makes it possible to make it smaller. In particular, if a convex surface with a steeper curvature than the other surface is directed toward the side where the absolute value of the inclination angle with respect to the optical axis of the axial ray entering the lens and the axial ray exiting the lens is smaller, the refractive index on the lens surface can be adjusted arbitrarily. Effective correction can be realized based on the fact that the value of .

If a radial graded index lens is used in the rear group, the positive power can be shared with the internal condensing action, so the curvature of the refracting surface can be relaxed, and the position on the lens surface can be Since the refractive indexes are different, the occurrence of spherical aberration is reduced.

In addition, as in the first embodiment of the present invention shown in FIG. 1, an axial refractive index distribution type in which a convex surface faces the image side in the final fixed lens group and the refractive index gradually decreases from the convex surface side to the other surface. It is clear from the explanation of formula A17I that a similar aberration correction effect can be obtained by using a lens.

Furthermore, since the axial gradient index lens is used in the lens group with high axial rays, the occurrence of comatic aberration is reduced, so lenses with small occurrence of coma aberration are also required in the rear group.

Therefore, the most suitable combination is to use a radial gradient index lens in the rear group. If the rear group has negative power, if a radial gradient index lens is used in which the rear group has a distribution in which the refractive index gradually increases,
Since the negative power can be shared with the internal diverging effect, the curvature of the refractive surface can be relaxed, and since the refractive index differs depending on the position on the lens surface, other aberrations can be reduced as well as in the rear group. It is possible to reduce the occurrence of spherical aberration without affecting the

As shown in Figure 1, in order from the object side, there is a positive lens group with a focusing function, a negative second lens group with a variable power function, and a correction for image plane position fluctuations due to variable power. This is a zoom lens consisting of a negative third lens group that has a function, and a fourth positive lens group that is the final fixed lens group during zooming. An afocal 6-convex positive lens and a prism that guides some of the light to the viewfinder are provided, and after that, a Petzval multi-beam configuration with 6 convex and 2 groups is one of the appropriate solutions for correcting aberrations. , a low-pass filter is placed just in front of the image plane.

It has a stripe filter and an image pickup tube faceplate, and the light beam exiting the lens is almost telecentric.

Embodiment 2 shown in FIG. 3 includes, in order from the object side, a positive lens group having a focusing function, a negative fourth lens group having a variable power function, and a negative fourth lens group having a variable power function. This zoom lens includes a third positive lens group having a correction function, and a fourth positive lens group which is a final fixed lens group that is fixed during zooming.

Configuring the third lens group with a positive lens group in this way means that
Although this is advantageous for correcting the Petzval sum, the amount of spherical aberration generated becomes too large, and the amount of coma aberration also increases. Therefore, in order to correct these aberrations, a large number of lenses were required in the final fixed lens group. Therefore,
The front group of the final fixed lens group was composed of one axial gradient index lens, and the rear group was composed of one radial gradient index lens, and as in Example 1, spherical aberration and coma aberration were well corrected. Ta.

In the embodiments of the present invention, the front group of the final fixed lens group is composed of two lenses and the rear group is composed of one lens, as an example of constructing the lens group with the minimum necessary number. In the example, the front group and the rear group each consist of one lens, but it goes without saying that performance can be further improved by configuring these in combination with multiple gradient index lenses or homogeneous lenses. stomach.

Lens data of Examples is shown below.

For convenience, as an expression to express the refractive index distribution, if the refractive index changes depending on the distance from the optical axis, the refractive index is N(h), and N (, h) = No + N + h' + N2h' + N3h'
+ ---- If the lens has a refractive index distribution in the optical axis direction, the object-side vertex of the lens is the relative coordinate origin, and the refractive index when the distance from the origin is X is N (x), N
(X)=NO+NIX+N2X”+N3X”+7
--- Expressed together.

R22 in Numerical Example 1. R23 indicates the face plate, filter, etc. of the image pickup tube of the video camera.

R15 in Numerical Example 1. R16 indicates a glass block for dividing a light beam for a finder optical system or the like.

Numerical Example 1 (see Figure 1) Focal length F=100-570F number 1: 1.2
2 to 1.39 angle of view 2ω = 48.8° to 9.1° variable interval Ni (x) =NO+N+ X+N2 X” 10N3
x3λ NoNI N2to1゜(
X) d 1.88867 -4.15256
X10-'-1,53134X10-'g 1
．． 91683 -3.12392 mowing 0 -6.028
11XIO-'2.05803XlOi1.76137X10-' Ni (h) =No +N+ h"+Nzh'λ
NoNI Ni 1'i, (h) d 1.85 -3.
65201X10 2.86314X10-”g
1.87525 -s: ao43s kari Q -'
3.00721 x 10-” Numerical Example 2 (see Figure 3) Focal length F = 100-284F number 1:1
．． ．． 0 angle of view 2ω=44.6°~16.4°K l'/-232,6;l;1 Variable interval Ni (x) =N6+N1x+Nzx"λ No
NI N2N8(x) d 1
．． 85426 -9.6901X10″″”,
-1,09226XIO-'g 1.87933
-1.01943X10 6.64091X10-
'2.05803X10-7 1.76137X10-6 Ni (h) =No 10N1 h"+N2h'λ
NoNI N2 N, (h) d 1.85099 -2.69
575X10-3.14357X10-”g
1.89677 -2.65437X10 -3.3
9781
The second lens group is a negative lens group, and the third lens group is a positive or negative lens group, and the distance between the first positive lens group and the second positive lens group, and the distance between the second negative lens group and the third lens. In a variable focal length optical system that performs magnification by changing the distance between the groups and has a final fixed lens group closest to the image side that remains fixed during the magnification change,
The final fixed lens group is divided into two groups, a front group and a rear group, using the largest air gap as a boundary, and at least one axial gradient index lens is used in the front group, and at least one axial gradient index lens is used in the rear group. By using one radial refractive index gradient lens, a high-performance zoom lens could be achieved even if the number of constituent lenses was reduced. Furthermore, by reducing the number of constituent lenses, we were able to create a zoom lens that is small, lightweight, and easy to assemble and adjust.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a lens showing the first embodiment of the present invention, FIG. 2 is a diagram of its various aberrations, FIG. 3 is a sectional view of a lens showing the second embodiment, and FIG. 4 is a diagram of its various aberrations. . In the figure, Ri is the radius of curvature, Di is the distance between lens surfaces, M is the meridional surface, and S is the sagittal surface.

Claims (5)

[Claims] (1) A zoom section that has multiple lens groups and performs zooming by changing their axial spacing, and an imaging lens section, and the imaging lens section is divided based on the largest axial spacing and zoomed. One side is the front group, the other side is the rear group, and at least one
There are two axial gradient index lenses whose refractive index changes in the direction of the optical axis, and at least one radial gradient index lens whose refractive index changes in the direction perpendicular to the optical axis in the rear group. A zoom lens characterized by the (2) The axial gradient index lens arranged in the front group has a smaller absolute value of the inclination angle with respect to the optical axis of the axial ray entering the lens and the axial ray exiting the lens, compared to the other surface. 2. The zoom lens according to claim 1, wherein the zoom lens has a convex surface with a steep curvature, and has a distribution in which the refractive index decreases from the convex surface to the other surface. (3) The zoom lens according to claim 1, wherein the axial gradient index lens is a positive meniscus lens. (4) The zoom lens according to claim 1, wherein the radial gradient index lens has a distribution that decreases as it moves away from the optical axis. (5) The zoom unit includes, in order from the object side, a positive first lens group, a negative second lens group, and a positive or negative third lens group, and is on the axis between the first lens group and the second lens group. The zoom lens according to claim 1, wherein zooming is performed by changing the distance and the axial distance between the second lens group and the third lens group.