JPS61259216A - Compact zoom lens - Google Patents

Abstract

PURPOSE:To obtain a compact zoom lens system of less variance of aberrations by providing lens parts having a positive refracting power and a negative refracting power and providing one distributed index lens at least in the lens part having the positive refracting power. CONSTITUTION:A lens part 11 having the positive refracting power and a lens part 12 having the negative refracting power are arranged in order, and the lens part 11 having the positive refracting power has the first lens group having a positive refracting power, and the lens part 12 having the negative refracting power has a lens group having a negative refracting power. The interval between the first lens group and the lens group having the negative refracting power is shortened from the wide angle and to the telephoto end to perform zooming. The lens part 11 having the positive refracting power has one distributed index lens which shares the optical axis with the other lenses at least. Either of a radial type and axial type is used as the distributed index lens.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Application) The present invention relates to a zoom lens, and particularly to a zoom lens having a telephoto optical arrangement.

(Prior Art) In recent years, with the miniaturization of cameras, there has been a demand for compact zoom lenses with a short overall length. Even in the field of small cameras where lenses cannot be changed, such as lens-shutter cameras, the use of zoom lenses has become desirable, rather than large and inconvenient cameras such as single-lens reflex cameras that can have interchangeable lenses. There is a growing demand for something that is large enough to fit inside a bag and is easy to carry.

In order to meet these demands, this silk applicant
201213, etc., the first lens group has a positive refractive power, the lens group located on the image side has a negative refractive power, and the distance between these two lens groups is changed. We have proposed a lens that doubles.

However, in the case of the above-mentioned configuration, one way to make the lens compact is to tighten the power arrangement of each lens group, but this increases aberration fluctuations during zooming. To reduce the amount of aberration fluctuation, it is effective to increase the number of lenses to suppress the occurrence of aberrations, but this would inevitably increase the size of the entire lens. Furthermore, if the power is to be reduced to suppress aberration fluctuations, the amount of movement of the lens group must also be increased, which is contrary to the requirements, and there is a great difficulty in making the lens compact.

This type of zoom lens also has focus.

The focal length of the first positive lens group tends to be higher because the degree of convergence of the light beam exiting the first positive lens group tends to be stronger than that of an orthodox zoom lens in which the variator, convencator, and relay groups are arranged in order. There is a problem in that it is difficult to make the lens compact unless it is made shorter than the overall focal length at the zooming wide-angle end. The Petzval sum, which strengthens the refractive power of the first lens group in order to make it compact, must take a large positive value, and the refractive power of the lens group must also be negative in order to make the focal length of the entire system the desired value. Since it is necessary to make the lens strong, there is a problem in that aberration fluctuations due to zooming become large overall.

(Objective) An object of the present invention is to provide a zoom lens that is capable of suppressing fluctuations in aberrations to an extremely low level, is compact, and has a small number of lenses.

In order to achieve the above object, a lens section with positive refractive power and a lens section with negative refractive power are arranged side by side, and the lens section with positive refractive power consists of a group of lenses with positive refractive power, or the lens section with positive refractive power consists of a lens group with positive refractive power, or Consists of a lens group and a subsequent lens group that is fixed during zooming.
The lens part with negative refractive power has a second lens group with negative refractive power, and the distance between the first lens group and the second lens group is reduced to perform zooming. At least one refractive wealth distribution type lens that shares an optical axis with other lenses is provided.

Note that the lens section with negative refractive power may have a negative lens group behind the second lens group.

A highly distributed refractive lens is already well known in the literature, and is a lens in which refractive indexes are distributed non-uniformly within the lens based on a predetermined law. Specifically, in the case of the radial type, in which the refraction height changes in the direction perpendicular to the optical axis of the lens, that is, the radial direction, and the axial type, in which the refraction height changes in the direction of the optical axis of the lens, there is also a change in the inside of the lens. It has a refractive power, and when this lens is used, in addition to surface refraction, there is also bending of light both at the stage of light passing through the lens and at the stage of light passing through the lens. When considering a lens with a spherical aberration, the base radius of the lens becomes looser, which is effective for correcting spherical aberrations, etc. Also, inside the lens, Petzval sum P
is generated as P=ψ/N2 when the power due to internal convergence and divergence is taken as the refractive power ψ of the lens when the focal length of the entire system is IVC normalized, and the refractive end No on the axis. The occurrence of P=ψ/N in the plane is also smaller, and the field curvature can be reduced. The axial type is also effective in correcting spherical aberrations and higher-order aberrations in which the refraction height varies depending on the incident position of the light beam.

In particular, in this type of compact zoom lens, the image plane tends to be undersized υ, so if a lens having a refractive height distribution in the radial direction is used as the positive lens, the Petzval sum becomes smaller and the field curvature can be corrected.

In addition, under-spherical aberration occurs on the image side lens surface of the portion that bears positive refractive power on the object side, and outward coma aberration tends to occur on this lens surface, which deteriorates the positive refractive power. By introducing a refractive distribution lens in the first lens group, the positive fixed lens group behind it, or both, spherical aberration and comatic aberration can be corrected throughout the system, and aberration fluctuations due to zooming can be suppressed. It becomes possible.

As described above, by using at least one gradient index lens, a compact zoom lens with small aberration fluctuations during zooming can be realized. Regarding the specific distribution shape of the refractive groups, it is desirable that the negative refractive power becomes stronger or the positive refractive power becomes weaker toward the periphery. This makes it possible to eliminate high-order spherical aberration and comatic aberration that occur at the final lens surface of the positive refractive power section.

In addition, especially when introducing a gradient index lens at the rear of the positive refractive power section, that is, in front of the diaphragm, it is desirable that the positive refractive power becomes stronger toward the periphery. If the lens before the aperture is a lens with distribution in the radial direction, the refractive index decreases toward the periphery.If the lens has a main refraction distribution in the optical axis direction, the positive refractive power becomes stronger toward the periphery of the final surface. You should do it. For example, if the rear surface of the last lens in the first lens group has a convex surface facing the image plane, it is desirable that the refractive index of the last lens in the first lens group decreases as the optical axis direction moves toward the image plane. . Then, the final surface of the first lens, which faces the image plane convexly, will have the lowest refractive index at its apex.
The peripheral part is the highest, and the positive refractive power is stronger in the peripheral part. With this configuration, the curvature of the final surface of the first lens group, which is effective in correcting aberrations, becomes gentler, which occurs during refraction.
Spherical aberration and coma aberration are also reduced.

As described above, configuring the refractive/high distribution lens in the positive refractive power section is particularly effective in correcting spherical aberration and coma aberration over the entire focal length.

(Example) FIG. 1 depicts a first embodiment of the invention.

This lens consists of a movable positive first lens group 11 and a movable negative second lens group 1202.
The convex part is facing the object side].

Distance direction (radial direction) from the optical axis to a positive meniscus lens
with a refractive index distribution added to it. In the zero distribution, the refractive index decreases toward the periphery, but it does not fall monotonically, but the slope of the refractive index is gentler at the periphery than at the center. In other words, the absolute value of the differential value of the refractive index with respect to the radius near the center is larger than that at the periphery, and the positive refractive power is weaker at the periphery.

Due to this distribution, conventionally, extroverted coma aberration with under spherical aberration occurs at the final surface of the first lens group at all focal lengths, but spherical aberration and coma aberration occur on the object side surface of the refractive distribution type lens. is being corrected. Further, as mentioned above, the Petzval sum is reduced by the refractive distribution type lens, which has the effect of suppressing the curvature of field to a small level. As a result of these efforts, a zoom lens with good aberrations from the wide-angle end to the telephoto end was realized.

It should be noted that normally in a zoom lens of the type used in this example,
If the power is the same, the first lens group must have four or more lenses, but in this example, one gradient index lens, which has a tendency for the refractive index to decrease from the optical axis to the outer periphery, is used. By introducing the lenses, the total length of the first lens group is shortened by the simple structure, and the total optical length of the entire system is shortened.

The II2 embodiment has a two-group configuration as shown in FIG. It has a refractive index distribution in the axial direction and increases the magnification from the wide-angle end to the telephoto end (2ω = 56.8 to 30.3
). This distribution shows that in the first positive meniscus lens, the refractive index increases toward the periphery, and the differential value of the refractive index at the periphery with respect to the radius is larger than that near the center, and the refractive power at the periphery is more negative than that at the center. is getting stronger.

Further, the refractive index of the third biconvex lens decreases toward the image plane in the optical axis direction, and the refractive power of the surface on the image plane side is stronger at the periphery than at the apex.

Due to the distribution explained above, although it has been corrected by the gradient index lens on the side surface of the third biconvex lens in the first lens group, there is still residual spherical aberration under-correction and extroversion coma. is corrected by the refractive index distribution of the first positive meniscus lens.

In addition, the under-astigmatism (ΔM-ΔS) that tends to occur at the final surface of the first lens group, especially on the telephoto side, is corrected to the refractive index distribution of the first positive meniscus lens, and the second lens This reduces the burden on the group. These features make it possible to provide a zoom lens with good aberrations from the wide-angle end to the telephoto end.

The third embodiment shown in FIG. 5 has a two-group configuration, with the first lens group 310
'It is a biconcave lens with a refraction book distribution in the optical axis direction.

This distribution is a conical type in which the refractive index decreases as it goes toward the larger surface in the optical axis direction, and on the object side of a biconcave lens with a small white base radius, the refractive index is higher near the periphery than near the optical axis. It is high, and the negative refractive power is strong in the periphery.

Conventionally, spherical aberration has tended to be undersized, especially at the telephoto end, but it has become possible to correct this on the object side of a gradient index lens.

In the fourth embodiment shown in FIG. 7, a first lens group 42 with a positive focal length that does not move toward the image side of the first positive lens group during zooming is shown.
The lens group 41 has a movable first lens group 41 and a movable second lens group 43. This is an example of a positive meniscus lens with a radial refractive index distribution. In this distribution, the refractive index increases toward the periphery, and the refractive index is larger at the periphery than at the center. In other words, the differential value of the refractive index with respect to the radius is larger at the periphery, and the negative refractive power is stronger at the periphery.

With this distribution, insufficient correction of spherical aberration and extroverted coma, which mainly occur at the final surface of the first lens group 42, are corrected by changes in the refractive index inside the gradient index lens over the entire focal length.

Furthermore, the fact that the astigmatism (ΔM−ΔS) that occurs particularly at the final surface of the first lens group 42 is undercorrected is also corrected within the gradient index lens.

These features have made it possible to provide a zoom lens with good aberrations from the wide-angle end to the telephoto end.

In the fifth embodiment, a biconvex lens in a first lens group 51 having a two-group configuration is provided with a radial refractive index distribution.

The refractive index distribution of this lens is such that the refractive index decreases toward the periphery, resulting in a positive refractive power distribution.The radius of the vehicle at the final surface of the first lens group, where large aberrations occur, is not loose, making it easy to correct aberrations. are doing.

Conventionally, the spherical aberration becomes undersized at the final surface of the first lens group, but the spherical aberration is corrected over the entire focal length by using the image side surface of a biconvex lens having a refractive index distribution. Furthermore, regarding the large-plane curvature, the refractive power of the gradient index lens allows the Schpetzval sum to be reduced, and aberration fluctuations due to zooming to be reduced.

These features have made it possible to provide a zoom lens with good aberrations from the wide-angle end to the telephoto end.

With the configuration described above, a compact zoom lens with a small number of constituent lenses and small aberration fluctuations during zooming has been realized.

Numerical examples will be described below. Ri represents the curved radius of the lens surface, Di represents the lens thickness or surface spacing, Ni represents the refractive index, and νi represents the Abbe number. Further, h is the height from the optical axis, and X is the distance on the optical axis.

0 x Since it can be reduced, the distance between the principal points between each lens group can be reduced, which has a significant effect on shortening the overall length.

Furthermore, the number of elements in each lens group of the zoom lens can be reduced, and the length of the lens group can be reduced, creating more space between each lens group and increasing the range of movement of the movable group. , high variable power groups can be easily achieved. Alternatively, since aberrations can be corrected to a smaller value in each lens group, a zoom lens with small aberration fluctuations due to zooming can be achieved.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a lens showing a first embodiment of the present invention;
The figure shows the aberration curve. FIG. 3 is a sectional view of a lens showing the second embodiment, and FIG. 4 is an aberration curve diagram thereof. FIG. 5 is a sectional view of a lens showing the third embodiment, and FIG. 6 is an aberration curve diagram thereof. FIG. 7 is a sectional view of a lens showing the fourth embodiment, and FIG. 8 is an aberration curve diagram thereof. FIG. 9 is a cross-sectional view of the lens showing the fifth embodiment;
The figure shows the aberration curve. In the figure, 11.21.31.41.51... movable first
Positive lens group, 12, 22, 32, 43°52...Movable second negative lens group, 42...Fixed positive lens group. Rtl? tt Rq Rv 7Z・]1721

Claims (4)

[Claims] (1) A lens section with a positive refractive power and a lens section with a negative refractive power are placed side by side, the lens section with a positive refractive power has a first lens group with a positive refractive power, and the lens section with a negative refractive power has a negative refractive power. The lens has a lens group of A compact zoom lens comprising at least one lens having a distributed refractive index and sharing an optical axis with the lens. (2) A compact zoom lens according to claim 1, wherein the refractive index of the lens with distributed refractive index changes in the radial direction. (3) The compact zoom lens according to claim 1, wherein the refractive index of the lens with distributed refractive index changes in the optical axis direction. (4) The compact zoom lens according to claim 1, wherein the lens portion with positive refractive power comprises a lens group with positive refractive power that is fixed during zooming, following the first lens group.