JP2569302B2 - Compact zoom lens - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zoom lens, and more particularly to a zoom lens having a telephoto type optical arrangement.

(Prior Art) In recent years, with the miniaturization of cameras, a small zoom lens having a short overall length has been demanded. In the field of small cameras that do not have interchangeable lenses such as lens shutter cameras, zoom lens devices have become desired, for example, rather than those that are large and inconvenient to carry, such as single-lens reflex cameras with interchangeable lenses. There is a growing demand for portable devices that are small enough to fit in a pocket.

In order to meet such demands, the present applicant has disclosed in
In Japanese Patent Application Laid-Open No. 201213, etc., the refractive power of the first lens group is positive, the refractive power of the lens group located on the image side is negative, and the distance between these two lens groups is changed. We have proposed a lens to double.

However, in the case of the above-described configuration, it is one way to make the lenses compact by using a tight power device for each lens group. However, doing so increases aberration variation during zooming. To reduce the amount of aberration fluctuation, it is effective to increase the number of lenses to suppress the occurrence of aberration, but in that case, the entire lens must be enlarged. In addition, when the power is reduced to suppress the fluctuation of aberration, there is a great difficulty in downsizing as it is against the demand that the moving amount of the lens group must be increased.

Further, in this type of zoom lens, the 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 groups of focus, variator, compensator, and relay are arranged. , First
Unless the focal length of the positive lens group is equal to or shorter than the entire focal length at the zooming wide-angle end, there is a problem that it is difficult to make the lens compact. If the refractive power of the first lens group is increased to reduce the size, the Petzval sum will take a large positive value, and the refractive power of the negative lens group will also increase to obtain a desired value of the focal length of the entire system. Therefore, there is a problem that aberration fluctuation due to zooming becomes large as a whole.

(Object) It is an object of the present invention to provide a zoom lens which can suppress aberration fluctuations extremely small, is compact, and has a small number of lenses.

In order to achieve the above object, a lens portion having a positive refractive power and a lens portion having a negative refractive power are arranged in order, and the lens portion having a positive refractive power is composed of a lens group having a positive refractive power or a first lens having a positive refractive power. A lens unit having a negative refractive power has a second lens unit having a negative refractive power, and a lens unit having a negative refractive power has a second lens unit having a negative refractive power. The distance between the first lens unit and the second lens unit is reduced. At least one gradient index lens which shares an optical axis with another lens is provided in a lens portion having a positive refractive power of a lens performing zooming. The lens portion having a negative refractive power is the second lens portion.
It is assumed that a negative lens group may be provided behind the lens group.

The refractive index distribution type lens is well known in the literature and the like, but is a lens in which the refractive index is unevenly distributed in the lens based on a predetermined rule. More specifically, it includes a radial type in which the refractive index changes in a direction perpendicular to the optical axis of the lens, that is, a radial direction, and an axial type in which the refractive index changes in the optical axis direction of the lens.

In the case of the radial type, the inside of the lens also has refractive power, and when this lens is used, besides refraction of the surface, there is bending of light both in the light passage stage and the light passage stage in the lens, so that the glass Considering a lens having the same refractive power as a lens, the radius of curvature of the lens is reduced, which is effective for correcting spherical aberration and the like. In addition, Petzval sum P inside the lens
The inside of the converging refractive power of the lens when the normalized power of the focal length of the entire system 1 by diverging action, occurring in P = / N ² when the refractive index N ₀ on the axis, usually Is smaller than P = / N on the surface of the lens, and the field curvature can be reduced. The axial type also has a different refractive index depending on the incident position of the light beam, and is effective for correcting spherical aberration and higher-order aberrations.

In particular, a compact zoom lens of this type tends to have an image plane under, and therefore, if a lens having a refractive index distribution in the radial direction is used as the positive lens, the Petzval sum becomes small and the field curvature can be corrected.

In addition, the spherical aberration tends to occur in the lens surface on the image side in the portion having the positive refractive power on the object side, and outward coma tends to occur on this lens surface. By introducing a gradient index lens into the first lens group or the positive fixed lens group behind it (or both), spherical aberration and coma can be corrected through the entire system, and aberration fluctuations due to zooming can be suppressed. Becomes

As described above, by using at least one gradient index lens, a small zoom lens with small aberration fluctuation during zooming is realized. Regarding the specific refractive index distribution shape, it is desirable that the negative refractive power becomes stronger or the positive refractive power becomes weaker toward the periphery. Thereby, high-order spherical aberration and coma generated on the final lens surface of the positive refractive power portion can be removed.

In particular, when a gradient index lens is introduced at the rear of the positive refractive power portion, that is, before the stop, it is preferable that the positive refractive power increases as it goes to the periphery. When the lens before the aperture is made a lens with a distribution in the radial direction, the refractive index decreases as it goes to the periphery. For a lens with a refractive index distribution in the optical axis direction, the positive refractive power becomes stronger near the final surface. What should I do? For example, if the rear surface of the final lens of the first lens group has a convex surface facing the image plane, the refractive index of the final lens of the first lens group decreases as the direction of the optical axis moves toward the image plane. desirable. Then, the refractive index at the vertex of the final surface of the first lens that is convex toward the image surface is the lowest, the peripheral portion is the highest, and the positive refractive power is stronger at the peripheral portion. With this configuration, the curvature of the final surface of the first lens group, which is effective for aberration correction, is reduced, and the spherical aberration and coma generated during refraction are reduced.

As described above, the configuration of the gradient index lens in the positive refractive power portion is particularly effective for correcting spherical aberration and coma over the entire focal length.

FIG. 1 illustrates a first embodiment of the present invention. This lens has a two-group configuration including a movable positive first lens group 11 and a movable negative second lens group 12. The first lens group 11 has a first positive meniscus lens that is convex toward the object side. It has a refractive index distribution in the direction of the distance from the axis (radial direction). In this distribution, the refractive index decreases toward the periphery,
Rather than falling monotonically, the periphery is more gentle than the gradient of the refractive index at the center. That is, the absolute value of the differential value with respect to the radius of the refractive index near the center is larger than that at the periphery, and the positive refractive power is weaker at the periphery.

Due to this distribution, outward coma aberration is generated on the final surface of the first lens group with spherical aberration under the entire focal length, but spherical aberration and coma are corrected on the object side surface of the gradient index lens. doing. Further, as described above, the Petzval sum is reduced by the refractive index distribution type lens, which has the effect of suppressing the curvature of field to a small value. As a result, a zoom lens having good aberration from the wide-angle end to the telephoto end is realized.

In general, a zoom lens of the type as in the present embodiment requires four or more first lens groups if they have the same power. However, in the present embodiment, the zoom lens extends from the optical axis to the outer periphery. By introducing one refractive index distribution type lens having a tendency to decrease the refractive index, the overall length of the first lens group is shortened by the simple configuration, thereby shortening the optical overall length of the entire system.

In the second embodiment, as shown in FIG. 3, the first lens group 21 includes a first positive meniscus lens having a convex surface facing the object side, a radial refractive index distribution, and a third biconvex lens. A refractive index distribution is provided in the optical axis direction, and the magnification from the wide-angle end to the telephoto end is increased (2ω = 56.8 ° to 30.3 °). In this distribution, 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:
It is larger than that near the center, and the negative refractive power is stronger at the periphery than at the center. The refractive index of the third biconvex lens decreases as the direction of the optical axis moves toward the image plane. The refractive power of the surface on the image plane side is stronger at the periphery than at the vertex.

According to the distribution described above, on the image side surface of the third biconvex lens of the first lens unit, the correction of the spherical aberration and the outgoing coma, which have been corrected by the gradient index lens but still remain, remain. Correction is made by the refractive index distribution of one positive meniscus lens. In particular, on the telephoto side, the astigmatism (ΔM−ΔS), which is particularly likely to occur on the final surface of the first lens group, is corrected by the refractive index distribution of the first positive meniscus lens. The burden on is reduced. As a result, it has become possible to provide a zoom lens having good aberration from the wide-angle end to the telephoto end.

The third embodiment shown in FIG. 5 is a two-group configuration in which the biconcave lens of the first lens group 31 has a refractive index distribution in the optical axis direction.

This distribution is of a type in which the refractive index decreases toward the image plane in the optical axis direction.On the object side surface having a small radius of curvature of the biconcave lens, the refractive index is higher near the periphery than near the optical axis, The negative refractive power becomes stronger near the periphery.

Conventionally, spherical aberration tends to be under, particularly on the telephoto side, but it has become possible to correct the spherical aberration on the object side surface of the gradient index lens.

The fourth embodiment shown in FIG. 7 is a first lens unit having a positive focal length which does not move to the image side of the positive first lens unit during zooming.
The zoom lens includes a movable first lens group 41 and a movable second lens group 43 so as to perform zooming by changing the distance between the movable first lens group 41 and the movable second lens group 43. This is an example in which a positive meniscus lens has a refractive index distribution in the radial direction. In this distribution, the refractive index increases toward the periphery, and the refractive index increases more in the periphery than in the center. That is, 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.

Due to this distribution, insufficient correction of spherical aberration mainly occurring on the last surface of the first lens group 42, and correction of outgoing coma by changing the refractive index inside the gradient index lens over the entire focal length. doing. In addition, the fact that the astigmatism (ΔM−ΔS) generated on the final surface of the first lens group 42 is under becomes particularly corrected inside the gradient index lens.

As a result, from the wide-angle end to the telephoto end, it has become possible to provide a zoom lens with good aberration.

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

The refractive index distribution of this lens decreases toward the periphery and becomes a positive refractive power distribution, and the first refractive index distribution in which the occurrence of aberration is large is large.
The radius of curvature of the last surface of the lens group is reduced, so that aberration is easily corrected.

Conventionally, the spherical aberration is under in the final surface of the first lens group, but the spherical aberration is corrected over the entire focal length by the image side surface of the biconvex lens having the refractive index distribution. Also, regarding the field curvature, the Petzval sum is reduced by the refractive power of the gradient index lens, and the aberration fluctuation due to zooming is corrected to be small.

As a result, it is possible to provide a zoom lens having good aberration from the wide-angle end to the telephoto end.

With the configuration as described above, a zoom lens having a small number of constituent lenses and being compact, and having small aberration fluctuations during zooming is realized.

Hereinafter, numerical examples will be described. Ri is the radius of curvature of the lens surface, Di is the lens thickness or surface interval, Ni is the refractive index, and νi is the Abbe number. H is the height from the optical axis, and x is the distance on the optical axis.

(Effects) According to the present invention described above, the number of components of each lens group of the zoom lens can be reduced, so that the weight and size can be reduced, and the number of lenses can be reduced. The spacing can be reduced, which has a significant effect on shortening the overall length.

Further, the number of components of each lens group of the zoom lens can be reduced, and the length of the lens groups can be reduced, so that there is a margin in the space between the lens groups and the moving range of the moving group can be increased. , High magnification can be easily achieved. Alternatively, since the aberration can be corrected smaller for each lens group, it is possible to achieve a zoom lens with small aberration fluctuation due to zooming.

[Brief description of the drawings]

FIG. 1 is a lens sectional view showing a first embodiment of the present invention, and FIG.
The figure shows the aberration curve. FIG. 3 is a lens sectional view showing a second embodiment, and FIG. 4 is an aberration curve diagram thereof. FIG. 5 is a lens sectional view showing a third embodiment, and FIG. 6 is an aberration curve diagram thereof. FIG. 7 is a lens sectional view showing a fourth embodiment, and FIG. 8 is an aberration curve diagram thereof. FIG. 9 is a lens sectional view showing a fifth embodiment, and FIG. 10 is an aberration curve diagram thereof. In the figure, 11, 21, 31, 41, 51 ... the movable first positive lens group, 12,
22, 32, 43, 52 ... movable second negative lens group, 42 ... fixed positive lens group.

Continuing on the front page (72) Inventor Akinaga Horiuchi 770 Shimonoge, Takatsu-ku, Kawasaki Canon Inc. Tamagawa Works (72) Inventor Jun Hattori 3-2-2 Shimomaruko Ota-ku, Tokyo Canon Inc. (72 ) Inventor Shigeyuki Suda 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-60-48009 (JP, A) JP-A-57-168209 (JP, A) JP-A-58-184916 (JP, A) JP-A-58-220115 (JP, A) JP-A-59-149312 (JP, A)

Claims (4)

(57) [Claims] 1. A zoom lens system comprising: a first positive lens unit and a second negative lens unit in order from the object side; the distance between both lens units is reduced from the wide-angle end to the telephoto end; In the compact zoom lens that performs the above, the first positive meniscus lens having the convex surface facing the object side of the first lens group has a refractive index that decreases toward the periphery, and a refractive index with respect to the radius of the refractive index near the center of the optical axis. A compact zoom lens, wherein the absolute value of the differential value has a larger refractive index distribution than that of the surroundings. 2. A zoom lens system having a first positive lens unit and a second negative lens unit in order from the object side to reduce the distance between the two lens units and move both lens units from the wide-angle end to the telephoto end. In the compact zoom lens that performs the above, the first positive meniscus lens having a convex surface facing the object side of the first lens group has a refractive index that increases as the distance from the optical axis increases, and the radius of the refractive index at the periphery increases. The differential value has a refractive index distribution larger than that near the optical axis center, and the biconvex lens of the first lens group has a refractive index distribution in which the refractive index decreases as the optical axis direction moves toward the image plane side. Features a compact zoom lens. 3. A zoom lens system comprising: a first positive lens unit and a second negative lens unit in order from the object side; the distance between the two lens units is reduced from the wide-angle end to the telephoto end; In the compact zoom lens to perform, the first
The biconcave lens of the lens group has a refractive index that decreases toward the image plane, and has a refractive index distribution in which the refractive index is higher near the periphery than near the optical axis on the object side where the radius of curvature of the biconcave lens is small. And a compact zoom lens. 4. A positive first lens group, a positive first 'lens group that does not move during zooming, and a movable second negative lens group, in order from the object side, wherein the first first lens group extends from the wide-angle end to the telephoto end. In a zoom lens that moves a lens group and the second lens group and reduces the distance between the two lens groups to perform zooming, the positive meniscus lens having a convex surface facing the object side of the first lens group has a peripheral portion. A compact zoom lens characterized in that the refractive index increases as the distance from the optical axis increases, and the differential value of the refractive index with respect to the radius has a larger refractive index distribution at the periphery than at the center of the optical axis.