JP2003107353A - High variable power 4-group zoom lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a four-group zoom lens which is compact regardless of a high variable power rate. SOLUTION: In this zoom lens which consists of a first group G1 with positive refracting power, a second group G2 with positive refracting power, a third group G3 with negative refracting power, and a fourth group G4 with negative refracting power, and changes intervals of the respective groups to perform variable power, a high variable power four-group zoom lens moves the four groups to an object side in performing variable power from an wide angle area to a telephoto area to satisfy a conditional expression (6) about the average value of refractive indexes of negative lenses included in the third group and the fourth group.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-magnification four-group zoom lens, and more particularly to a zoom lens which is suitable for a lens shutter camera or the like having no limitation in back focus and which has a high zoom ratio and a small size.

[0002]

2. Description of the Related Art Conventionally, as zoom lenses used for lens shutter cameras, positive / negative two-group type, positive / positive / negative three-group type, negative / positive / negative three-group type, etc. are known. Have been made, and each has been commercialized.
Among these typical three types, when considering high zooming, the second group type of (3) has a large aberration variation due to zooming, and the field curvature at the intermediate focal length is particularly large, resulting in insufficient correction. Magnification scaling is basically impossible. Also,
Since the amount of movement of each group also increases, it is not preferable in downsizing the camera.

On the other hand, the three-group type and the three-group type can correct aberration fluctuations during zooming and can reduce the amount of movement of each group to some extent, so that higher zooming is possible compared to the two-group type. Becomes Known examples of prior art in which the zoom ratio is increased by using the three-group type are disclosed in Patent Document 1 and Patent Document 2. The former is a 3-group type of, 38-135
Has a zoom range of mm. The latter is a 3-group type of and has a zoom range of 35 to 135 mm.

Among the three group types, the type in which the group having negative refractive power precedes, the group spacing becomes maximum at the wide-angle end, so that the total lens length and the lens outer diameter become large, and the size is reduced. It is not preferable from the viewpoint.

On the other hand, the three-group type is a desirable zoom type because the lens having the positive refracting power precedes it and the total lens length and the lens outer diameter can be reduced. However, if further zooming is required, the amount of movement of each group must be large, and miniaturization of the camera body cannot be achieved.

Therefore, it is conceivable to further complicate the three-group type to supplement the degree of freedom in design. As an example in which the group preceded by a positive refractive power group is made into a four-group zoom as described above, Patent Document 3 Patent Document 4 and the like are known. Both are positive / negative / positive / negative four-group types, but the former is a positive / positive / negative three-group type in which the second group is divided into negative / positive. The zoom ratio was about 3 times, but it was a high zoom ratio at the time of application. The latter is a so-called double telephoto zoom type applied to a lens shutter camera. This type was originally developed for single-lens reflex cameras. This prior example has a zoom range of 38-135 mm.

[0007]

[Patent Document 1] Japanese Unexamined Patent Publication No. 2-135312 (pages 6 to 23)

[0008]

[Patent Document 2] JP-A-2-201410 (pages 4 to 13)

[0009]

[Patent Document 3] JP-A-63-43115 (pages 3 to 9)

[0010]

[Patent Document 4] Japanese Patent Application Laid-Open No. 2-223908 (pages 6 to 23)

[0011]

As described above, in order to achieve a high zoom ratio and compact size of the zoom lens,
The type preceded by a group of positive refracting power is desirable. However, since the one disclosed in Patent Document 1 is of the three-group type as described above, the amount of movement of the group during zooming is large and it is difficult to downsize the camera.
By the way, the telephoto ratio at the telephoto end is as large as 1.2.

In Patent Document 3, the telephoto ratio at the telephoto end is about 1.1. However, since the second group of positive, positive, and negative three-group type is divided, the eccentricity of these groups is high. Is very unfavorable because it becomes very strict.

In Patent Document 4, the telephoto ratio at the telephoto end is about 1.0, but since the distance between the second group and the third group is maximum at the wide-angle end, the entrance pupil position becomes far. This is not preferable because the outer diameters of the lenses of the first group and the second group become enormous. Further, although the amount of movement of the group is reduced, it is not preferable that the total lens length at the wide-angle end is increased.

The present invention has been made in view of such circumstances, and an object thereof is to provide a compact 4-group zoom lens having a high zoom ratio.

[0015]

A high-magnification four-group zoom lens of the present invention which achieves the above object, comprises a first group having a positive refractive power, a second group having a positive refractive power, and a negative group in order from the object side. Refractive power third
In a zoom lens that includes a group and a fourth group having negative refracting power, and varies the distance between the groups, the four groups move toward the object side when varying the magnification from the wide-angle range to the telephoto range, It is characterized in that the following conditional expression (6) is satisfied.

1.7 <N _N (6) where N _N is the average value of the refractive indices of the negative lenses included in the third and fourth groups.

[0017]

The reason why the above structure is adopted and the function of the present invention will be described below.

As described in the prior art, in order to achieve high zooming and miniaturization, it is preferable to use a zoom type in which positive refractive power precedes, such as a positive / positive / negative three-group type. preferable. However, if the zoom ratio is increased as it is, the amount of movement of the group increases and the total lens length at the telephoto end increases, so that the camera cannot be downsized. Also, the second
Even if the groups are divided into four groups, the accuracy of eccentricity between the divided groups becomes severe, which is not practical.

Therefore, in the present invention, a new 4-group zoom type is proposed.

In the positive / positive / negative three-group type described above, the third group bears most of the zooming action. The second group has a compensator function, and the first group functions to correct aberrations, particularly field curvature and distortion. Therefore, the total length of the lens at the telephoto end is substantially determined by the amount of movement of the third lens unit, and in order to shorten this, the power of the third lens unit must be increased. However, simply increasing the power of the third lens group makes it difficult to correct the aberration. That is, the power of the third lens unit is determined within a range in which practical aberration correction is possible after giving the required zooming action to the third lens unit, and thus the total lens length at the telephoto end is also determined. Will end up.

In the present invention, in order to solve the above problems, in the positive / positive / negative three-group type, the third group having negative refractive power is divided into four groups of positive / positive / negative / negative. Hereinafter, description will be given with reference to the drawings.

FIG. 2 shows the arrangement and movement locus of a conventional three-group type group. It is composed of a first lens group G1 having a positive refractive power, a second lens group G2 having a positive refractive power, and a third lens group G3 having a negative refractive power, and each lens group moves toward the object side during zooming from a wide-angle range to a telephoto range. . At this time, the distance between the first group G1 and the second group G2 is increased, and the distance between the second group G2 and the third group G3 is decreased so that the above-described action is obtained. .

FIG. 1 shows a four-group type according to the present invention. It is composed of a first group G1 having a positive refracting power, a second group G2 having a positive refracting power, a third group G3 having a negative refracting power, and a fourth group G4 having a negative refracting power, and is used for zooming from a wide-angle range to a telephoto range. As each group moves toward the object side, the distance between the first group G1 and the second group G2 increases, and the distance between the second group G2 and the third group G3 decreases. Further, when the magnification is changed from the wide-angle range to the telephoto range, the third group G3 and the fourth group G4 are moved so that the magnifications thereof are both increased, so that the magnification changing effect can be efficiently performed.

At this time, it is desirable that the following conditional expression be satisfied.

0.3 <| f ₃₄ | / f _W <1.1 ··· (1) 1 <β _3W ··· (2) 1 <β _4W ··· (3) where f _W is the focal length of the entire system at the wide-angle end, f ₃₄ is the combined focal length of the third group G3 and the fourth group G4 at the wide-angle end, and β _3W and β _4W are the third group G3 and the fourth group G4 at the wide-angle end, respectively. Is the paraxial lateral magnification of.

The conditional expression (1) is, as already described,
This is the most important condition for downsizing. When the upper limit of 1.1 is exceeded and the combined power of the third group G3 and the fourth group G4 becomes weak, miniaturization cannot be achieved. In addition, the lower limit of 0.
When the combined power exceeds 3 and becomes strong, even if the lens is divided into two groups, the power of each group becomes too strong, and it becomes difficult to perform sufficient aberration correction.

Conditional expressions (2) and (3) are conditions for ensuring the back focus at the wide-angle end, and beyond these ranges, the back focus becomes short and the third
The lens outer diameters of the group G3 and the fourth group G4 become large. Also, there is a problem that dust attached to the lens surface is reflected,
A flare problem due to reflection between the film surface and the like occurs, which is not preferable.

Further, in order to make good aberration correction, the second
It is desirable to use at least one aspherical surface in the group G2. At this time, at least 1 used in the second group G2
It is desirable that the aspherical surface should satisfy the following conditional expression.

0 <Δ _P / φ _P , φ _P = (n _{P ′} −n _P ) / r _P (4) where r _P is the paraxial radius of curvature of the aspherical surface, n _P and n _{P '} Is the refractive index of the medium before and after the aspheric surface, and Δ _P is the aspheric amount at the effective radius.

Conditional expression (4) indicates that the aspherical surface of the second lens group G2 has a shape in which the positive refractive power gradually becomes weaker (or the negative refractive power becomes stronger) as the distance from the optical axis increases. Such an aspherical surface of the second group G2 is effective in correcting spherical aberration and coma.

Further, it is desirable to use at least one aspherical surface also for the third group G3 or the fourth group G4. At this time, at least one aspherical surface used in the third group G3 or the fourth group G4 preferably satisfies the following conditional expression.

Δ _N / φ _N <0, φ _N = (n _{N ′} −n _N ) / r _N (5) where r _N is the paraxial radius of curvature of the aspherical surface, n _N , n _{N '} Is the refractive index of the medium before and after the aspherical surface, and Δ _N is the aspherical surface amount at the effective radius.

Conditional expression (5) is defined by the third group G3 or the fourth group.
It is shown that the aspherical surface of the group G4 has a shape in which the negative refracting power gradually becomes weaker (or the positive refracting power becomes stronger) with distance from the optical axis. Such an aspherical surface of the third group G3 or the fourth group G4 is effective for correction of field curvature and distortion.

Further, in the present invention, the Petzval image plane is likely to be overcorrected because the number of the groups having negative refractive power is increased. Therefore, it is desirable to satisfy the following conditional expression.

1.7 <N _N (6) where N _N is the average value of the refractive indices of the negative lenses included in the third group G3 and the fourth group G4. By satisfying the conditional expression (6), it is possible to excellently correct the field curvature, and it is possible to obtain a photograph excellent in depiction on the entire screen.

[0036]

EXAMPLES Examples 1 to 4 of the high variable power four-group zoom lens according to the present invention will be described below. 3 to 6 are lens cross-sectional views of Examples 1 to 4 at the wide-angle end (a) and the telephoto end (b), respectively.

The first embodiment has a focal length of 38 to 135 mm, and when zooming from the wide-angle end to the telephoto end, the first lens unit G1
And the distance between the second group G2 and the second group G2 increases.
The groups move toward the object side such that the distance between the groups decreases and the distance between the third group G3 and the fourth group G4 increases. The first group G1 is
A negative meniscus lens having a convex surface directed toward the object side, a positive meniscus lens having a convex surface directed toward the object side, two groups, and a second group G2
Is a biconcave lens, a negative meniscus lens having a convex surface directed toward the object side, a biconvex lens, a diaphragm, a biconvex lens, a cemented lens of a biconcave lens and a biconvex lens, 5 groups and 6 groups, 3rd group G3
Is a positive meniscus lens having a convex surface directed to the image side, two groups of two lenses, and the fourth group G4 is a positive meniscus lens having a convex surface directed to the image side, and a biconcave lens is two groups of two elements. Has been done. The diaphragm is included in the second group G2. Further, the aspherical surfaces are used for two surfaces in total, that is, the image side surface of the biconvex lens after the stop of the second group G2 and the object side surface of the biconcave lens of the third group G3.

The second embodiment has a focal length of 38 to 150 mm, and when zooming from the wide-angle end to the telephoto end, the first lens unit G1
And the distance between the second group G2 and the second group G2 increases.
The groups move toward the object side such that the distance between the groups decreases and the distance between the third group G3 and the fourth group G4 increases and then decreases. First
The second group G2 is a biconcave lens, a biconvex lens, a diaphragm, a biconvex lens, a biconcave lens, and a biconvex lens. The group G1 is a cemented lens of a negative meniscus lens and a positive meniscus lens having a convex surface facing the object side. Cemented lens of 5 groups of positive meniscus lens with convex surface facing the image side, 3rd
The group G3 is a positive meniscus lens having a convex surface directed toward the image side,
The second group of two biconcave lenses and the fourth group G4 are composed of one group of negative meniscus lenses each having a convex surface facing the image side. The diaphragm is included in the second group G2. Also, the aspherical surface is
The first surface of the first group G1, the image side surface of the biconvex lens after the aperture stop of the second group G2, and the object side surface of the biconcave lens of the third group G3 are used for all three surfaces.

The third embodiment has a focal length of 38 to 150 mm, and when zooming from the wide-angle end to the telephoto end, the first lens unit G1
And the distance between the second group G2 and the second group G2 increases.
The groups move toward the object side such that the distance between the groups decreases and the distance between the third group G3 and the fourth group G4 increases. The first group G1 is
A negative meniscus lens having a convex surface directed toward the object side, a positive meniscus lens having a convex surface directed toward the object side, two groups, and a second group G2
Is a biconcave lens, a biconvex lens, a negative meniscus lens with a convex surface facing the image side, a diaphragm, a biconvex lens, a biconvex lens, and a cemented lens of a negative meniscus lens with a convex surface facing the object side and a biconvex lens, 7 elements in 6 groups The third group G3 is a second group 2 of a positive meniscus lens having a convex surface facing the image side and a biconcave lens.
The fourth lens group G4 is composed of a biconvex lens and a biconcave lens. The diaphragm is included in the second group G2.
Further, the aspherical surfaces are used for the last three surfaces of the second lens group G1, the object-side surface of the biconcave lens of the third lens group G3, and the object-side surface of the biconcave lens of the fourth lens group G4. .

The fourth embodiment has a focal length of 28 to 105 mm, and when zooming from the wide-angle end to the telephoto end, the first lens unit G1
And the distance between the second group G2 and the second group G2 increases.
The respective groups move toward the object side such that the distance between the groups is decreased and the distance between the third group G3 and the fourth group G4 is decreased and then increased. First
The group G1 is a cemented lens of a biconcave lens and a biconvex lens, two groups of three lenses of a biconvex lens, and the second group G2 is a biconcave lens, a biconvex lens, a diaphragm, a biconvex lens, and a biconcave lens and a biconvex lens cemented lens Group 5 sheets, the third group G3,
A positive meniscus lens having a convex surface directed toward the image surface side, and a negative meniscus lens having a convex surface directed toward the image surface side, two groups, and a fourth group G4.
Is a first group 1 of negative meniscus lenses with the convex surface facing the image side.
It is composed of one sheet. The diaphragm is included in the second group G2. The aspherical surface is used only on the image-side surface of the biconvex lens after the stop of the second group G1.

The lens data of each embodiment are shown below. The symbols are the above, f is the focal length of the entire system, F _NO is the F number, 2ω is the angle of view, f _B is the back focus, and β ₃ is β _3. The paraxial lateral magnification of the third group G3, β ₄ is the paraxial lateral magnification of the fourth group G4, r ₁ , r ₂ ... Are the radii of curvature of the respective lens surfaces, and d ₁ and d _2.
... is the distance between the lens surfaces, n _d1 , n _d2 ... is the d of each lens
The refractive indices of the lines, ν _d1 , ν _d2, ... Are the Abbe numbers of each lens. The aspherical shape is expressed by the following equation, where x is the optical axis direction and y is the direction orthogonal to the optical axis.

X = (y ² / r) / [1+ {1-P (y /
r) ² } ^1/2 ] + A ₄ y ⁴ + A ₆ y ⁶ + A ₈ y ⁸ + A ₁₀ y ¹⁰ However, r is a paraxial radius of curvature, P is a conic coefficient, A ₄ , A ₆ ,
A ₈ and A ₁₀ are aspherical coefficients.

Example 1 f = 39.1 to 71.4 to 130.3 F _NO = 4.6 to 6.1 to 8.0 2ω = 57.84 to 33.66 to 18.82 ° f _B = 6.9 to 19.3 to 53.8 β ₃ = 1.34 to 1.75 to 2.21 β ₄ = 1.08 to 1.24 to 1.67 r ₁ = 35.2420 d ₁ = 2.000 n _d1 = 1.84666 ν _d1 = 23.78 r ₂ = 29.9510 d ₂ = 0.500 r ₃ = 25.6000 d ₃ = 4.500 n _d2 = 1.49700 ν _d2 = 81.61 r ₄ = 128.6170 d ₄ = (Variable) r ₅ = -30.3720 d ₅ = 1.000 n _d3 = 1.88300 ν _d3 = 40.78 r ₆ = 28.0770 d ₆ = 0.980 r ₇ = 61.1210 d ₇ = 1.000 n _d4 = 1.77250 ν _d4 = 49.66 r ₈ = 15.6480 d _{8 = 0.920 r 9 = 20.1570 d 9} = 3.500 n d5 = 1.78472 ν d5 = 25.68 r 10 = -57.1010 d 10 = 1.500 r 11 = ∞ ( _{stop) d 11 = 1.500 r 12 =} 28.2340 d 12 = 4.000 n d6 = 1.53172 ν _d6 = 48.90 r ₁₃ = -36.7070 (aspherical surface) d ₁₃ = 1.200 r ₁₄ = -165.7780 d ₁₄ = 1.500 n _d7 = 1.80518 ν _d7 = 25.43 r ₁₅ = 16.9400 d ₁₅ = 5.500 n _d8 = 1.56873 ν _d8 = 63.16 r ₁₆ = -15.3930 d ₁₆ = (variable) r ₁₇ = -54.2 730 d ₁₇ = 4.000 n _d9 = 1.76180 ν _d9 = 27.11 r ₁₈ = -23.9700 d ₁₈ = 2.170 r ₁₉ = -19.1930 (aspherical) d ₁₉ = 2.000 n _d10 = 1.80400 ν _d10 = 46.57 r ₂₀ = 322.2970 d ₂₀ = _{(variable) r 21 = -354.2300 d 21 =} 3.500 n d11 = 1.76182 ν d11 = 26.52 r 22 = -34.5340 d 22 = 1.210 r 23 = -25.0470 d 23 = 2.000 n d12 = 1.80400 ν d = 46.57 r 24 = 718.3720 Aspherical coefficient 13th surface P = 1.0000 A ₄ = 0.48167 × 10 ^-4 A ₆ = 0.26683 × 10 ^-7 A ₈ = 0.16257 × 10 ^-8 A ₁₀ = -0.84437 × 10 ^-11 19th surface P = 1.0012 A ₄ = 0.14608 × 10 ^-4 A ₆ = 0.28754 × 10 ^-7 A ₈ = 0.32531 × 10 ^-10 A ₁₀ = 0.

Example 2 f = 39.1 to 75.5 to 145.5 F _NO = 4.6 to 6.1 to 8.0 2ω = 57.84 to 31.93 to 16.89 ° f _B = 7.0 to 24.1 to 63.4 β ₃ = 1.17 to 1.45 to 1.60 β ₄ = 1.19 to 1.59 to 2.51 r ₁ = 27.3940 (aspherical surface) d ₁ = 2.000 n _d1 = 1.80518 ν _d1 = 25.43 r ₂ = 21.5300 d ₂ = 5.000 n _d2 = 1.48749 ν _d2 = 70.20 r ₃ = 75.0810 d ₃ = (variable) r ₄ = -34.6580 d ₄ = 1.500 n _d3 = 1.77250 ν _d3 = 49.66 r ₅ = 14.6990 d ₅ = 1.160 r ₆ = 22.0690 d ₆ = 3.000 n _d4 = 1.76182 ν _d4 = 26.52 r ₇ = -55.9830 d ₇ = 1.500 r ₈ = ∞ (aperture) d ₈ = 1.500 r ₉ = 63.5910 d ₉ = 3.000 n _d5 = 1.51633 ν _d5 = 64.15 r ₁₀ = -22.7880 (aspherical surface) d ₁₀ = 1.320 r ₁₁ = -20.9070 d ₁₁ = 1.500 n _d6 = 1.78470 ν _d6 = 26.30 r ₁₂ = 49.5720 d ₁₂ = 5.000 n _d7 = 1.51633 ν _d7 = 64.15 r ₁₃ = -15.8000 d ₁₃ = 0.200 r ₁₄ = -74.2190 d ₁₄ = 3.000 n _d8 = 1.51633 ν _d8 = 64.15 r ₁₅ = -18.5730 d ₁₅ = (Variable) r ₁₆ = -78.4020 d ₁₆ = 4.000 n _d9 = 1.80518 ν _d9 = 25.43 r ₁₇ = -23.0330 d ₁₇ = 1.880 r ₁₈ = -18.3240 (aspherical surface) d ₁₈ = 1.800 n _d10 = 1.77250 ν _d10 = 49.66 r ₁₉ = 316.7320 d ₁₉ = (variable) r ₂₀ = -31.8430 d ₂₀ = 2.000 n _d11 = 1.80400 ν _d11 = 46.57 r ₂₁ = -436.2390 Aspheric surface coefficient 1st surface P = 1.0000 A ₄ = 0.30725 × 10 ^-7 A ₆ = -0.24 135 × 10 ^-9 A ₈ = 0.25687 × 10 ^-11 A ₁₀ = 0 10th surface P = 1.0000 A ₄ = 0.48250 × 10 ^-4 A ₆ = 0.81447 × 10 ^-7 A ₈ = -0.43664 × 10 ^-9 A ₁₀ = 0.11008 × 10 ^-11 18th surface P = 1.0000 A ₄ = 0.11855 × 10 ^-4 A ₆ = 0.32106 × 10 ^-7 A ₈ = -0.444419 x 10 ^-9 A ₁₀ = 0.20139 x 10 ^-11 .

Example 3 f = 39.1 to 75.5 to 145.5 F _NO = 3.6 to 5.4 to 8.0 2ω = 57.84 to 31.93 to 16.89 ° f _B = 7.0 to 22.3 to 65.5 β ₃ = 1.36 to 1.79 to 2.27 β ₄ = 1.07 to 1.27 to 1.83 r ₁ = 43.7150 d ₁ = 2.000 n _d1 = 1.84666 ν _d1 = 23.78 r ₂ = 31.7650 d ₂ = 0.920 r ₃ = 27.2710 d ₃ = 5.000 n _d2 = 1.51454 ν _d2 = 54.69 r ₄ = 270.8610 d ₄ = _{(variable) r 5 = -30.0870 d 5 =} 1.300 n d3 = 1.88300 ν d3 = 40.78 r 6 = 18.5320 d 6 = 1.690 r 7 = 33.8190 d 7 = 3.500 n d4 = 1.84666 ν d4 = 23.78 r 8 = -59.0100 d _{8 = 1.450 r 9 = -27.1000 d} 9 = 1.200 n d5 = 1.72916 ν d5 = 54.68 r 10 = -35.0200 d 10 = 2.120 r 11 = ∞ ( _{stop) d 11 = 1.700 r 12 =} 78.9010 d 12 = 3.000 n d6 = 1.56732 ν _d6 = 42.83 r ₁₃ = -54.2940 d ₁₃ = 0.200 r ₁₄ = 33.5370 d ₁₄ = 3.000 n _d7 = 1.56732 ν _d7 = 42.83 r ₁₅ = -71.2530 d ₁₅ = 0.650 r ₁₆ = 481.5710 d ₁₆ = 1.500 n _d8 = 1.80518 ν _d8 = 25.43 r ₁₇ = 16.3100 d ₁₇ = 6.0 00 n _d9 = 1.51633 ν _d9 = 64.15 r ₁₈ = -21.3560 (aspherical surface) d ₁₈ = (variable) r ₁₉ = -45.3540 d ₁₉ = 3.500 n _d10 = 1.76182 ν _d10 = 26.52 r ₂₀ = -25.2940 d ₂₀ = 2.050 r ₂₁ = -30.8570 _{(aspherical) d 21 = 1.800 n d11 =} 1.80400 ν d11 = 46.57 r 22 = 66.1420 d 22 = ( _{variable) r 23 = 323.3140 d 23 =} 3.500 n d12 = 1.76182 ν d12 = 26.52 r 24 = -47.6200 d ₂₄ = 1.800 r ₂₅ = -26.6440 (aspherical surface) d ₂₅ = 2.000 n _d13 = 1.80400 ν _d13 = 46.57 r ₂₆ = 330.6980 Aspheric coefficient 18th surface P = 1.0000 A ₄ = 0.15660 × 10 ^-4 A ₆ = 0.15389 × 10 ^-7 A ₈ = -0.34018 × 10 ^-9 A ₁₀ = 0.23221 × 10 ^-11 21st surface P = 1.0000 A ₄ = -0.69516 × 10 ^-5 A ₆ = -0.37838 × 10 ^-7 A ₈ = 0.18367 × 10 ^-9 A ₁₀ = -0.15531 × 10 ^-11 25th surface P = 1.0000 A ₄ = 0.79001 × 10 ^-5 A ₆ = 0.17288 x 10 ^-7 A ₈ = -0.75567 x 10 ^-10 A ₁₀ = 0.52462 x 10 ^-12 .

Example 4 f = 28.8 to 54.2 to 101.9 F _NO = 4.6 to 6.1 to 8.0 2ω = 73.74 to 43.46 to 23.94 ° f _B = 4.5 to 23.7 to 50.4 β ₃ = 1.10 to 1.19 to 1.24 β ₄ = 1.20 to 1.86 to 2.78 r ₁ = -104.8750 d ₁ = 2.000 n _d1 = 1.83400 ν _d1 = 37.16 r ₂ = 37.2890 d ₂ = 5.000 n _d2 = 1.51742 ν _d2 = 52.41 r ₃ = -81.2180 d ₃ = 0.200 r ₄ = 36.4760 d ₄ = 4.500 n _d3 = 1.58904 ν _d3 = 53.20 r ₅ = -143.1600 d ₅ = (variable) r ₆ = -30.7210 d ₆ = 1.000 n _d4 = 1.77250 ν _d4 = 49.66 r ₇ = 12.8240 d ₇ = 0.790 r ₈ = 17.3610 d ₈ = 3.000 n _d5 = 1.78472 ν _d5 = 25.68 r ₉ = -92.8180 d ₉ = 1.500 r ₁₀ = ∞ (aperture) d ₁₀ = 2.500 r ₁₁ = 41.2990 d ₁₁ = 3.880 n _d6 = 1.51633 ν _d6 = 64.15 r ₁₂ = -24.7180 (aspherical surface) d ₁₂ = 0.750 r ₁₃ = -30.9670 d ₁₃ = 1.200 n _d7 = 1.80518 ν _d7 = 25.43 r ₁₄ = 21.6900 d ₁₄ = 5.200 n _d8 = 1.69680 ν _d8 = 55.52 r ₁₅ = -14.2150 d ₁₅ = (variable) r ₁₆ = -52.4040 d ₁₆ = 3.500 n _d9 = 1. 78472 ν _d9 = 25.68 r ₁₇ = -19.5360 d ₁₇ = 1.250 r ₁₈ = -20.0760 d ₁₈ = 1.600 n _d10 = 1.77250 ν _d10 = 49.66 r ₁₉ = -393.6420 d ₁₉ = (variable) r ₂₀ = -18.3260 d ₂₀ = 2.200 n _d11 = 1.72916 ν _d11 = 54.68 r ₂₁ = -140.0870 Aspheric coefficient 12th surface P = 1.0000 A ₄ = 0.77132 × 10 ^-4 A ₆ = 0.33027 × 10 ^-6 A ₈ = -0.24906 × 10 ^-8 A ₁₀ = 0.38477 × 10 ^-10 .

Aberrations representing spherical aberration, astigmatism, distortion, and chromatic aberration of magnification with respect to the object point at infinity at the wide-angle end (a), the intermediate focal length (b), and the telephoto end (c) of Examples 1 to 4 above. The figures are shown in FIGS. 7 to 10, respectively.

The following table shows the numerical values of the conditional expressions (1) to (6) in each example. In the table, Ri the lens surface number, Y denotes an effective radius when calculating the aspherical amount Δ _P, Δ _N.

[0049]

[0050]

According to the structure of the present invention, in the positive / positive / negative / negative 4-group zoom lens type, it is possible to obtain a compact zoom lens having a high zoom ratio.

[Brief description of drawings]

FIG. 1 is a diagram showing the arrangement and movement loci of groups of a four-group type zoom lens according to the present invention.

FIG. 2 is a diagram showing the arrangement and movement loci of groups of a conventional three-group type zoom lens.

FIG. 3 is a lens cross-sectional view of a wide-angle end (a) and a telephoto end (b) of the first embodiment.

4 is a lens cross-sectional view similar to FIG. 3 of Example 2. FIG.

FIG. 5 is a lens sectional view similar to FIG. 3 of Example 3;

6 is a lens cross-sectional view similar to FIG. 3 of Example 4. FIG.

FIG. 7 is an aberration diagram showing spherical aberration, astigmatism, distortion, and chromatic aberration of magnification for an object point at infinity at the wide-angle end (a), the intermediate focal length (b), and the telephoto end (c) in Example 1. .

FIG. 8 is an aberration diagram similar to FIG. 7 of Example 2.

FIG. 9 is an aberration diagram similar to FIG. 7 of Example 3.

FIG. 10 is an aberration diagram similar to FIG. 7 of Example 4.

[Explanation of symbols]

G1 ... 1st group G2 ... Second group G3 ... Group 3 G4 ... Group 4

Continued front page    F term (reference) 2H087 KA02 KA03 LA01 PA09 PA11                       PA12 PA18 PA19 PB11 PB12                       PB13 QA02 QA03 QA06 QA07                       QA17 QA19 QA21 QA25 QA26                       QA37 QA39 QA41 QA42 QA45                       QA46 RA05 RA13 RA32 SA23                       SA26 SA30 SA33 SA62 SA63                       SA64 SA65 SB03 SB04 SB16                       SB17 SB23 SB32 SB33

Claims (8)

[Claims] 1. A first group having positive refracting power in order from the object side,
In a zoom lens that includes a second lens unit having a positive refractive power, a third lens unit having a negative refractive power, and a fourth lens unit having a negative refractive power, and varying the distance between the respective lens units, zooming from a wide-angle range to a telephoto range. A high-magnification four-group zoom lens, characterized in that these four groups move toward the object side during zooming and satisfy the following conditional expression (6). 1.7 <N _N (6) where N _N is the average value of the refractive indices of the negative lenses included in the third group and the fourth group. 2. A high-magnification four-group zoom lens according to claim 1, wherein the third lens group and the fourth lens group move so that the magnifications of both the third lens group and the fourth lens group increase during zooming from the wide-angle range to the telephoto range. 3. The high variable power four-group zoom lens according to claim 1 or 2, wherein at least one aspherical surface is included in the second group. 4. When zooming from a wide-angle range to a telephoto range, the distance between the first group and the second group increases and the distance between the second group and the third group decreases. The high-magnification 4-group zoom lens according to claim 1. 5. The high variable power 4 group zoom lens according to claim 4, wherein the following conditional expressions (1), (2) and (3) are satisfied. 0.3 <| f ₃₄ | / f _W <1.1 ··· (1) 1 <β _3W ··· (2) 1 <β _4W ··· (3) where f _W is wide angle The focal length of the entire system at the edge, f ₃₄ is the combined focal length of the third group and the fourth group at the wide-angle end, β _3W ,
β _4W is the paraxial lateral magnification of the third group and the fourth group at the wide-angle end, respectively. 6. At least one used in said second group
4. The high-magnification 4-group zoom lens according to claim 3, wherein the aspherical surface satisfies the following conditional expression (4). _{0 <Δ P / φ P,} φ P = (n P '-n P) / r P ···· (4) However, r _P is a paraxial radius of curvature of the aspherical surface, n _P, n _P' non Refractive index of the medium before and after the spherical surface, Δ _P is the amount of aspherical surface at the effective radius. 7. The at least one aspherical surface is also used for the third group or the fourth group.
The high-magnification 4-group zoom lens described. 8. The high variable power 4th group according to claim 7, wherein at least one aspherical surface used in said 3rd group or 4th group satisfies the following conditional expression (5). Zoom lens. _{Δ N / φ N <0,} φ N = (n N '-n N) / r N ···· (5) However, r _N is the paraxial radius of curvature of the aspherical surface, n _N, n _N' Non Refractive index of the medium before and after the spherical surface, Δ _N is the amount of aspherical surface at the effective radius.