JPH09133863A - Variable power lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To compensate various aberrations sufficiently excellently from the wide-angle end to the telephoto end and make the number of constituent lens elements extremely small although the power variation rate is about 3.5, or large. SOLUTION: The variable power lens which consists of plural lens groups G1-G3 and varies in power by varying the interval of at least one of the lens groups has the lens group G2 with negative refracting power most on the image plane side, and at least one lens having positive refracting power in the lens group G2 having the negative refracting power is composed of a gradient index lens which varies in refractive index at right angles to the optical axis. Then at least one surface of the gradient index lens is made aspherical and at least one lens with negative refracting power is arranged on the image plane side of this gradient index lens.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a variable power lens, and more particularly to a variable power lens for a lens shutter camera which has a small number of lenses and a high variable power ratio.

[0002]

2. Description of the Related Art Generally, in a variable power lens, aberration is favorably corrected in a reference state, and it is necessary to reduce aberration fluctuation during zooming. Therefore, it is desirable that spherical aberration, coma aberration, chromatic aberration, etc. be corrected well in each lens group. For that purpose, the number of lenses in each lens group is inevitably large, and the lens system becomes large.

In recent years, along with the miniaturization of cameras, zoom lenses have been reduced in size and weight. In particular, even for lens shutter cameras in which the lenses cannot be exchanged, there is a demand for a camera that is compact and has a variable power lens with a variable power ratio of 3 or more. On the other hand, there is also a great demand for cost reduction.

By the way, as described in JP-A-61-159612, the front lens group has a positive refractive power and the rear lens group has a negative refractive power, and the distance between the front lens group and the rear lens group is changed to change the magnification. There is known a variable power lens having a two-group configuration for performing. In order to make the lens system more compact and have a high zoom ratio with such a lens configuration, the radius of curvature of each lens may be reduced to increase the refracting power. However, in that case, the number of lenses must be increased in order to reduce aberration fluctuation during zooming to obtain good aberration correction and a sufficient zoom ratio, and the entire lens system becomes large. Further, as the number of lenses increases, it becomes difficult to achieve cost reduction. Further, if the refracting power of each lens is relaxed to reduce the aberration variation during zooming, the amount of movement of each group becomes large, which makes it impossible to achieve compactness.

In order to solve the above problems, as a prior art in which the number of lenses is reduced to 4 by using an aspherical surface, Japanese Patent Laid-Open Nos. 3-127008 and 3-1998.
As described in JP-A-274516 and JP-A-6-67092, there are lenses in which the first group is composed of negative and positive lenses, and the second group is composed of positive and negative lenses, but the zoom ratio is large. It is about 2.6 times, which is not enough in terms of high spec.

Further, as described in JP-A-61-148414, JP-A-61-259216 and JP-A-61-126515, a variable power lens having a two-group or three-group structure has a refractive index. It has been proposed to introduce a distributed lens, but the variable power ratio is about 1.5 to 2, which is not sufficient in terms of achieving high specifications.

Here, let us consider a variable power lens having a two-group structure as an example. In order to further increase the magnification with a variable power lens having a two-group structure while the number of lenses is small, it is necessary to increase the refractive power of each group or increase the amount of movement of the final group.
When the refractive power of each group is increased, the aberration generated in each group becomes large and the aberration of the entire optical system becomes large. In particular, since the negative refractive power of the final group becomes strong, positive spherical aberration occurs at the telephoto end. Further, the positive distortion becomes large, and its influence is great especially at the wide-angle end. Further, coma also becomes worse. Similarly, when the amount of movement of the last lens unit is increased, the aberration at the telephoto end becomes worse.

Further, as a variable power lens aiming at a high variable power ratio, there are disclosed in Japanese Patent Laid-Open Nos. 63-43115 and 1-252.
As described in No. 916 and the like, a variable power lens having a three-group or four-group structure has been proposed, and the variable power ratio has been increased to about 3, but the number of lens components is the minimum even if an aspherical surface is used. It is 11 sheets, which is not sufficiently satisfactory in terms of compactness.

Further, as an example in which a gradient index lens is used as a variable power lens having a variable power ratio of about 3, Japanese Patent Laid-Open No. 63-159.
No. 818 and Japanese Patent Application Laid-Open No. 63-161423, the number of lens components is 11 at the minimum, which is not sufficiently satisfactory in terms of compactness.

Further, even in a variable power lens having a three-group structure,
If an attempt is made to further increase the zoom ratio, the refractive power of the lens unit having the negative refractive power closest to the image surface side becomes strong, so that the same problem as the above-described variable power lens having the two-group structure occurs.

[0011]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art. The object of the present invention is to provide a wide-angle lens despite a large zoom ratio of about 3.4. It is an object of the present invention to provide a variable power lens in which various aberrations are sufficiently corrected from the end to the telephoto end and the number of constituent lenses is very small.

[0012]

A variable power lens of the present invention for solving the above-mentioned problems comprises a plurality of lens groups, and at least one lens group among the plurality of lens groups is varied to change the distance. In a variable power lens that performs magnification, a lens group having a negative refractive power is arranged closest to the image surface side, and at least one lens having a positive refractive power in the lens group having a negative refractive power is It is composed of a gradient index lens whose refractive index changes in the direction perpendicular to the axis, at least one surface of the gradient index lens has an aspherical surface, and at least one lens is closer to the image surface side than the gradient index lens. It is characterized in that a lens having a negative refracting power is arranged.

In this case, the gradient index lens having a positive refractive power may have aspherical surfaces on both sides.

In the present invention, the reason and action for taking the above configuration will be described. The gradient index lens includes a so-called axial gradient index lens having a refractive index change in the optical axis direction and a so-called radial gradient index gradient lens having a refractive index change in the direction perpendicular to the optical axis. . The present invention uses a radial type gradient index lens having a high optical potential.

The refractive index distribution of the reference wavelength of the radial type gradient index lens used in the present invention is expressed by the following equation. n (y) = N ₀ + N ₁ y ² + N ₂ y ⁴ + ... (1) where N ₀ is the refractive index of the reference wavelength at the center of the lens, y
Is the radial distance from the center of the lens, n (y) is the refractive index of the reference wavelength at the radius y from the center of the lens, N ₁ , N ₂
... is a constant.

Further, the shape of the aspherical surface used in the present invention is expressed by the following formula when the Z axis is in the traveling direction of light on the optical axis and the Y axis is in the direction orthogonal to the optical axis. ^{Z = (Y 2 / r)} / {1+ [1- (K + 1) (Y / r) 2 ] _{^{1/2} + A 4 Y 4 +}} A 6 Y 6 + A 8 Y 8 + A 10 Y 10 + ·· ··· (2) where r is the paraxial radius of curvature, K, A ₄ , A ₆ , A ₈ , A
₁₀ is an aspheric coefficient.

Further, according to the present invention, the above-mentioned gradient index lens having a positive refractive power is a variable power lens having an aspherical surface on at least one surface, preferably on both surfaces.

This will be described below. The gradient index lens also has a refractive power in its medium. If the refractive power of the surface and the refractive power of the medium have the same sign, the entire surface can be made even if the shape of the surface is loose compared to a homogeneous lens. Can have the same refractive power as a homogeneous lens.

Further, the refractive power of the medium of the gradient index lens is mainly the quadratic coefficient N of the above gradient index formula (1).
_If the coefficient N ₁ has a positive sign, the medium acts as a negative refractive power, and if the coefficient N ₁ has a negative sign, the medium has a positive refractive power. Therefore, it becomes possible to control the refracting power between the surface and the medium, the degree of freedom in aberration correction is increased, and the number of lenses can be reduced.

Further, since the gradient index lens has a refractive power in its medium, it is possible to correct Petzval sum. Petzval sum P of the gradient index lens unit
S is represented by the following equation. PS = (φ _S / N ₀ ) + (φ _M / N ₀ ² ) (3) where φ _S is the refractive power of the surface of the gradient index lens, φ _M
Is the refractive power of the medium of the gradient index lens.

As is clear from the above equation, in the gradient index lens, the Petzval sum can be freely changed to some extent by manipulating the refractive power of its surface and the refractive power of the medium. Therefore, by applying such a gradient index lens to the lens system of the present invention, the Petzval sum in the entire system can be satisfactorily corrected even if the number of lenses is reduced. Furthermore, because the medium and the surface have a refractive index distribution, aberrations can be corrected by the correction term on the surface that behaves differently from the homogeneous system, so that the performance of the entire system is improved. Is possible.

As described above, the gradient index lens can share the refracting power of the lens by the medium, so that it is effective to use it in a group having a particularly strong refracting power. If an attempt is made to increase the zoom ratio in the lens system as in the present invention, the negative refracting power of the negative lens group closest to the image surface side becomes strong, and particularly positive spherical aberration occurs at the telephoto end. For these reasons, it is effective to use a gradient index lens as the lens in the lens group having the most negative refractive power on the image plane side.

At this time, the coefficient N ₁ of the gradient index lens
Should satisfy the following equation. N ₁ > 0 (4) This is because the refractive power of the medium is made negative by setting the coefficient N ₁ of the gradient index lens to be N ₁ > 0. This is to reduce the aberration generated in the entire negative lens group.

By the way, in the variable power lens, since it is necessary to reduce various aberrations generated in each lens group, it is necessary to configure each group with at least two lenses, and the negative lens group closest to the image plane of the present invention. But at least one positive lens and at least one
It will consist of one negative lens.

Furthermore, when the number of lens elements of the optical system is further reduced and various aberrations are corrected well, the negative lens group closest to the image surface side is composed of at least one negative lens element closer to the image surface side than the positive lens element. It is advantageous to arrange the lens. With such a configuration, the negative lens group becomes a so-called telephoto type and the rear principal point of the entire system can be moved to the object side, which is also advantageous in terms of compactness.

Now, let us consider a case where a gradient index lens is used as the negative lens in the negative lens group and a case where the gradient index lens is used as the positive lens in the negative lens group.

The coefficient N ₁ of the gradient index lens is set to N ₁ > 0.
As described above, by changing the refractive power of the medium to a negative refractive power, the negative refractive power of the entire negative lens group is dispersed in the medium. This means that even if a gradient index lens is used as a negative lens, But it is possible, but with negative lens N ₁
When a gradient index lens of> 0 is used, positive spherical aberration occurs in the medium, and the spherical aberration generated in the correction term of the surface becomes positive spherical aberration. If it is used for a lens, it results in promoting the generation of positive spherical aberration in the entire system, especially at the telephoto end, which is not preferable.

On the contrary, when a gradient index lens of N ₁ > 0 is used as the positive lens, positive spherical aberration occurs in the medium, but negative spherical aberration occurs in the correction term of the surface. By using the gradient index lens, it is possible to cancel positive spherical aberration that increases as the negative refractive power of the negative lens group increases. Therefore, it becomes possible to correct positive spherical aberration at the telephoto end.

As described above, the present invention is characterized in that the gradient index lens is used as at least one lens having the positive refractive power in the lens group having the negative refractive power on the most image side.

As described above, by making the positive lens in the negative lens group a gradient index lens, it becomes possible to correct spherical aberration particularly at the telephoto end. However, if an attempt is made to increase the zoom ratio while correcting various aberrations, refraction of the reference wavelength at the position of the refractive index n (0) at the lens center of the gradient index lens and the maximum effective radius y _MAX of the lens. It becomes necessary to increase the difference Δnd from the index n (y _MAX ), which makes it difficult to manufacture the gradient index lens itself.

Therefore, in the present invention, at least one surface of the gradient index lens element is formed into an aspherical surface to generate negative spherical aberration, correct spherical aberration that tends to become large in the positive direction, and reduce the negative lens group. As the refracting power becomes stronger, positive distortion that occurs particularly at the wide-angle end is effectively corrected.

As described above, the negative lens group is composed of at least one positive lens and at least one negative lens on the image plane side of the positive lens. Then, in the positive lens, the ray height of the marginal ray becomes relatively high and the off-axis ray height becomes relatively low. On the contrary, in the negative lens, the height of the marginal ray is relatively low and the height of the off-axis ray is relatively high. That is,
The use of an aspherical surface for the positive lens is particularly effective for spherical aberration, and the use of an aspherical surface for the negative lens is particularly effective for off-axis aberrations such as distortion and astigmatism.

As in the present invention, when the focal length at the telephoto end of the variable power lens is extended to obtain a high zoom ratio, positive spherical aberration particularly at the telephoto end poses a problem. Is preferably arranged in the positive lens of the negative lens group.

At this time, if the shape of the aspherical surface is such that the positive refractive power becomes stronger as the distance from the optical axis increases, not only the correction of the positive spherical aberration at the telephoto end but also the positive distortion aberration at the wide angle end. Can be corrected well.

Furthermore, since the positive lens in the negative lens group has a smaller effective diameter than at least one negative lens on the image plane side of the positive lens, using an aspherical surface for this lens also contributes to processing. preferable.

Further, in the present invention, both surfaces of this gradient index positive lens may be aspherical. As described above, by using an aspherical surface for at least one surface of this gradient index positive lens, it is possible to satisfactorily correct spherical aberration especially at the telephoto end. It is possible to more effectively correct these various aberrations by using the above. At this time, if the shape of the aspherical surface is such that the positive refracting power becomes stronger as the distance from both sides of the optical axis increases, it becomes possible to satisfactorily correct the positive spherical aberration at the telephoto end.

The present invention is not limited to the variable power lens having the two-group configuration and the three-group configuration, and may be applied to an optical system of four or more groups in which the lens group closest to the image plane has negative refractive power. It is valid.

[0038]

Embodiments 1 to 3 of a variable power lens of the present invention will be described below with reference to the drawings. In order to achieve that purpose, the following three embodiments are shown in FIG.
As shown in FIG. 7, in a variable power lens that includes a plurality of lens groups G1 to G2 and performs zooming by changing the distance between at least one lens group among the plurality of lens groups, the negative refraction closest to the image plane side. A lens group G2 having a power is arranged, and at least one lens having a positive refractive power in the lens group G2 having a negative refractive power is a refractive index distribution type in which a refractive index changes in a direction perpendicular to an optical axis. It is configured by a lens, and at least one surface of the gradient index lens has an aspherical surface, and at least one lens having a negative refractive power is arranged on the image plane side of the gradient index lens. I am trying. Furthermore, this gradient index lens having a positive refractive power is characterized by having aspherical surfaces on both sides.

The respective embodiments will be described below. In the first embodiment, as shown in FIG. 1 in which the cross section at the wide-angle end (a), the intermediate focal length (b), and the telephoto end (c) is shown, the objects are sequentially arranged from the object side. , A first group G1 having positive refractive power and a second group G2 having negative refractive power,
The zooming is performed by changing the lens group interval between the first group G1 and the second group G2. The first group G1 is composed of a negative meniscus lens having a convex surface directed toward the object side and a biconvex positive lens, and an aperture is integrally arranged on the image side thereof. The second group G2 includes a negative meniscus lens similar to the positive meniscus lens having a convex surface facing the image plane side, and both surfaces of the negative meniscus lens of the first group G1 are aspherical surfaces.

Here, the lens (positive meniscus lens) having a positive refractive power, which is arranged on the most object side of the second group G2, is constituted by a gradient index lens. Both surfaces of this gradient index lens are aspherical. The positive lens of the first group G1 is also composed of a gradient index lens. With this configuration, it is possible to achieve a compact variable power lens having a high variable power ratio with a small number of lenses.

The cross-sectional shape of the second embodiment is substantially the same as that of the first embodiment, so the illustration thereof is omitted. However, the second embodiment is composed of a first group G1 having a positive refractive power and a second group G2 having a negative refractive power in order from the object side. , First group G
The zooming is performed by changing the lens group interval between the first and second lens groups G2. The first group G1 is composed of a negative meniscus lens having a convex surface directed toward the object side and a biconvex positive lens,
A diaphragm is integrally arranged on the image plane side. Also, the second
The group G2 is composed of a positive meniscus lens having a convex surface facing the image plane side and a negative meniscus lens similar to the positive meniscus lens, and both surfaces of the negative meniscus lens of the first group G1 are aspherical.

Here, the lens (positive meniscus lens) having a positive refractive power, which is arranged on the most object side of the second group G2, is formed of a gradient index lens. Further, the surface of the gradient index lens on the object side has an aspherical shape. The positive lens of the first group G1 is also composed of a gradient index lens. With this configuration, it is possible to achieve a compact variable power lens having a high variable power ratio with a small number of lenses. Furthermore, the second group G2
Since only the object side surface of the gradient index lens in the inside has an aspherical shape, it is advantageous in processing.

In the third embodiment, as shown in FIG. 2 at the wide-angle end (a), the intermediate focal length (b), and the telephoto end (c), the first group G1 having a positive refractive power is arranged in order from the object side. And positive refractive power second
It is composed of a group G2 and a third group G3 having negative refractive power, and zooming is performed by changing the lens group spacing between the first group G1 and the second group G2 and between the second group G2 and the third group G3. ing. The first group G1 is composed of a biconcave negative lens and a positive meniscus lens having a convex surface facing the object side, and the second group G2 is composed of a biconcave negative lens and a biconvex positive lens. , A diaphragm is integrally disposed between both lenses. The third group G3 is composed of a positive meniscus lens having a convex surface facing the image plane side and a negative meniscus lens similar to the positive meniscus lens.

Here, the lens (positive meniscus lens) having a positive refractive power, which is arranged on the most object side of the third group G3, is composed of a gradient index lens. Further, the surface of the gradient index lens on the object side has an aspherical shape. With this configuration, it is possible to achieve a compact variable power lens having a high variable power ratio with a small number of lenses.

Numerical data of each of the above-mentioned embodiments will be shown below. Symbols are other than the above, f is the focal length of the entire system, F _NO is the F number, ω is the half angle of view, and f _B is at infinity. Back focus, r ₁ , r ₂ ... Is the radius of curvature of each lens surface, d ₁ , d
₂ is the distance between the lens surfaces, n _d1 , n _d2 ... Is the d-line refractive index of each lens, and ν _d1 , ν _d2 are the Abbe numbers of each lens. The aspherical shape is expressed by the following equation, where Z is a traveling direction of light on the optical axis and Y is a direction orthogonal to the optical axis. ^{Z = (Y 2 / r)} / {1+ [1- (K + 1) (Y / r) 2 ] ^{_{1/2} + A 4 Y 4 +}} A 6 Y 6 + A 8 Y 8 + A 10 Y 10 + ·· ··· (2) where r is the paraxial radius of curvature, K, A ₄ , A ₆ , A ₈ , A
₁₀ is an aspheric coefficient.

The so-called radial type gradient index lens (indicated by "GRIN" in the numerical data) having a gradient index in the direction perpendicular to the optical axis in each example is a refraction expressed by the following equation. It has a rate distribution. n (y) = N ₀ + N ₁ y ² + N ₂ y ⁴ + ... (1) where N ₀ is the refractive index of the reference wavelength at the center of the lens, y
Is the radial distance from the center of the lens, n (y) is the refractive index of the reference wavelength at the radius y from the center of the lens, N ₁ , N ₂
... is a constant.

Ν _0d for the gradient index lens,
ν _id is a constant represented by the following equation. ν _0d = (N _0d -1) / (N _0F -N _0C ) ... (5) ν _id = N _id / (N _iF -N _iC ) ... (6) It should be noted that the above ν _0d , ν _In the formula of _id , N _0d , N _0F , and N _0C are the refractive indices of the d-line, F-line, and C-line on the optical axis, N _id ,
N _iF and N _iC are the d-line, F-line, and
It is the i-th order distribution coefficient of the C line. Next, Examples 1 to 3 above
The numerical data of is shown.

Example 1 f = 39.01 to 72.30 to 133.78 F _NO = 3.60 to 5.87 to 9.50 ω = 29.01 to 16.67 to 9.18 ° f _B = 4.46 to 33.91 to 88.31 r ₁ = 25.8987 (aspherical surface) d ₁ = 2.7744 n _d1 = 1.84666 ν _d1 = 23.78 r ₂ = 19.3356 (aspherical surface) d ₂ = 3.7238 r ₃ = 83.1780 d ₃ = 6.6456 GRIN-1 r ₄ = -15.3783 d ₄ = 0.1000 r ₅ = ∞ (aperture) d ₅ = ( Variable) r ₆ = -146.7940 (aspherical surface) d ₆ = 5.3221 GRIN-2 r ₇ = -37.4853 (aspherical surface) d ₇ = 5.5968 r ₈ = -11.9204 d ₈ = 4.0993 n _d4 = 1.77250 ν _d4 = 49.60 r ₉ = -42.6851 Aspheric surface coefficient 1st surface K = 0 A ₄ = -1.1999 × 10 ^-4 A ₆ = -7.0203 × 10 ^-7 A ₈ = 2.2850 × 10 ^-9 A ₁₀ = 3.8162 × 10 ^-15 2nd surface K = 0 A ₄ = -1.0246 × 10 ^-4 A ₆ = -5.2145 × 10 ^-7 A ₈ = 6.5715 × 10 ^-9 A ₁₀ = 3.7930 × 10 ^-13 6th surface K = 0 A ₄ = 3.8168 × 10 ^-5 A ₆ = 4.7 400 × 10 ^-9 A ₈ = 7.9294 × 10 ^-10 A ₁₀ = 1.0991 × 10 ^-13 7th surface K = 0 A ₄ = 3.3331 × 10 ^-6 A ₆ = -2.6277 × 10 ^-8 A ₈ = -9.6421 × _{^{10 -10 A 10 = 1.0146 × 10}} -13 GRIN-1 N 0 = 1.563370 N 1 = 9.7518 × 10 -5 N 2 = 1.0454 × 10 -6 ν 0d = 60.00 ν 1d = 8.6905 ν 2d = 6.3160 _{^{× 10 +1 GRIN-2 N 0}} = 1.574990 N 1 = 4.9692 × 10 -4 N 2 = 1.5545 × 10 -7 ν 0d = 37.00 ν 1d = 9.8014 × 10 +1 ν 2d = 3.0490 × 10 +1
.

Example 2 f = 39.01 to 72.30 to 133.78 F _NO = 3.60 to 5.87 to 9.50 ω = 29.01 to 16.67 to 9.18 ° f _B = 4.45 to 33.89 to 88.25 r ₁ = 25.8624 (aspherical surface) d ₁ = 2.7745 n _d1 = 1.84666 ν _d1 = 23.78 r ₂ = 19.3414 (aspherical surface) d ₂ = 3.7238 r ₃ = 83.5721 d ₃ = 6.6454 GRIN-1 r ₄ = -15.3854 d ₄ = 0.1000 r ₅ = ∞ (aperture) d ₅ = ( Variable) r ₆ = -146.6621 (aspherical surface) d ₆ = 5.3219 GRIN-2 r ₇ = -37.4942 d ₇ = 5.5968 r ₈ = -11.9237 d ₈ = 4.1001 n _d4 = 1.77250 ν _d4 = 49.60 r ₉ = -42.7350 Aspheric surface coefficient 1st surface K = 0 A ₄ = -1.2029 × 10 ^-4 A ₆ = -8.8969 × 10 ^-7 A ₈ = 6.8070 × 10 ^-9 A ₁₀ = -2.5204 × 10 ^-11 2nd surface K = 0 A ₄ = -1.0338 × 10 ^-4 A ₆ = -8.4262 × 10 ^-7 A ₈ = 1.5758 × 10 ^-8 A ₁₀ = -5.9487 × 10 ^-11 6th surface K = 0 A ₄ = 3.6152 × 10 ^-5 A ^{_{6 = -1.8326 × 10 -7 A 8}} = 7.0651 × 10 -9 A 10 = -3.6443 × 10 -11 GRIN-1 N 0 = 1.563370 N 1 = 9.7518 × 10 -5 N 2 = 1.0454 × 10 -6 ν 0d _{= 60.00 ν 1d = 8.6905 ν 2d} = 6.3160 × 10 +1 GRIN-2 N 0 = 1.574990 N 1 = 4.9692 × 10 -4 N 2 = 1.5545 × 10 -7 ν 0d = 37.00 ν 1d = 9.8014 × 10 +1 ν _2d = 3.0490 × 10 ⁺¹
.

Example 3 f = 36.75 ~ 70.68 ~ 135.82 F _NO = 3.60 ~ 5.90 ~ 9.85 ω = 30.48 ~ 17.02 ~ 9.05 ° f _B = 5.19 ~ 28.75 ~ 72.03 r ₁ = -222.3525 d ₁ = 2.1440 n _d1 = 1.84666 ν _d1 = 23.78 r ₂ = 153.7652 d ₂ = 0.1200 r ₃ = 19.3933 d ₃ = 3.0773 n _d2 = 1.69680 ν _d2 = 55.53 r ₄ = 110.4690 d ₄ = (variable) r ₅ = -41.5543 d ₅ = 4.8827 GRIN-1 r ₆ = 634.1938 d ₆ = 0.7116 r ₇ = ∞ (aperture) d ₇ = 1.9919 r ₈ = 112.4261 d ₈ = 6.9769 GRIN-2 r ₉ = -20.4783 d ₉ = (variable) r ₁₀ = -18.4369 (aspherical surface) d ₁₀ = 4.6366 GRIN-3 r ₁₁ = -16.3872 d ₁₁ = 2.1753 r ₁₂ = -14.7410 d ₁₂ = 1.9874 n _d6 = 1.69680 ν _d6 = 55.53 r ₁₃ = -246.2346 Aspherical surface 10th surface K = 0 A ₄ = 8.3268 × 10 ^-6 A ₆ = 1.5647 × 10 ^-7 A ₈ = -1.3259 × 10 ^-9 A ₁₀ = 6.4565 × 10 ^-12 GRIN-1 N ₀ = 1.840700 N ^{_{1 = 1.9724 × 10 -4 N 2}} = 5.4363 × 10 -6 ν 0d = 43.42 ν 1d = -3.6893 ν 2d = 1.9788 × 10 +1 GRIN-2 N 0 = 1.573310 N 1 = -7.6013 × 10 -4 N 2 _{^{= -2.4574 × 10 -6 ν 0d =}} 61.83 ν 1d = -3.6527 × 10 +1 ν 2d = -7.1944 GRIN-3 N 0 = 1.764930 N 1 = 6.5194 × 10 -4 N 2 = 4.8191 × 10 -9 ν 0d = 21.19 ν _1d = 2.7770 × 10 ⁺¹ ν _2d = -9.6653 × 10 ⁺³
.

Aberration diagrams of Examples 1 to 3 when focusing on an object at infinity are shown in FIGS. In each of the aberration diagrams, (a) shows the wide-angle end, (b) shows the intermediate focal length, and (c) shows the spherical aberration, astigmatism, distortion, and chromatic aberration of magnification at the telephoto end, respectively.

[0052]

As described above, according to the configuration of the present invention, various aberrations are sufficiently corrected from the wide-angle end to the telephoto end despite the large zoom ratio of 3.4 or more. Moreover, it is possible to construct a variable power lens having a very small number of constituent lenses.

[Brief description of the drawings]

FIG. 1 is a sectional view of a zoom lens according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a variable power lens according to a third embodiment of the present invention.

FIG. 3 is an aberration diagram of Example 1.

FIG. 4 is an aberration diagram of the second embodiment.

FIG. 5 is an aberration diagram for Example 3.

[Explanation of symbols]

 G1: first lens group G2: second lens group G3: third lens group

Claims (2)

[Claims] 1. A variable power lens composed of a plurality of lens groups, wherein at least one lens group among the plurality of lens groups is varied to perform a magnification change, having a negative refractive power closest to the image plane side. A lens group is arranged, and at least one lens having a positive refractive power in the lens group having a negative refractive power is constituted by a gradient index lens whose refractive index changes in a direction perpendicular to an optical axis, A variable power lens characterized in that at least one surface of the gradient index lens has an aspherical surface, and at least one lens having a negative refractive power is arranged on the image plane side of the gradient index lens. . 2. The variable power lens according to claim 1, wherein the gradient index lens element having a positive refractive power has aspherical surfaces on both sides.