JPH085919A - Two-group zoom lens - Google Patents

Abstract

PURPOSE:To provide the standard zoom lens which has a high power variation ratio, simple constitution, and excellent image forming performance and is small in size and inexpensive. CONSTITUTION:The zoom lens is equipped with a 1st lens group G1 which has negative refracting power on the whole and a 2nd lens group G2 which has positive refracting power on the whole in order from the object side; and the 1st lens group G1 has a negative meniscus lens L1 which has a convex surface on its object side, a biconcave lens L2, and a positive lens L3 in order from the object side and the 2nd lens group G2 has a positive lens L4, a positive lens L5, a biconcave lens L6, and a positive lens L7 in order from the object side. This zoom lens is varied in power by varying the interval between the 1st lens group G1 and 2nd lens and satisfys conditions 0.6<= ¦f1¦/(fw.ft)<1/2=1, $1<=q2<=0, and 0.04<=d4/dI<=0.4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-group zoom lens, and more particularly to a compact standard zoom lens for single-lens reflex cameras and video cameras.

[0002]

2. Description of the Related Art In recent years, in a conversion lens for a 35 mm still camera, a zoom lens having a zoom ratio of about 2 times including a standard angle of view among zoom lenses having a two-group structure having negative and positive refracting powers in order from the object side. (Hereafter, "standard zoom lens"
However, there is a feeling that it has been completely fixed as a standard equipment lens instead of the standard lens (a lens having a focal length of about 50 mm in the case of 35 mm size).

Therefore, since the standard zoom lens as described above is carried as a regular lens while being mounted on the camera body, not only the minimum size is an essential condition, but also sufficient imaging performance is secured. However, it is also necessary to be compact and inexpensive. like this,
To realize a so-called standard zoom lens, the negative / positive two-group zoom lens described above is the most suitable lens type, and various proposals have been made.

For example, Japanese Unexamined Patent Publication No. 1-185607 and Japanese Unexamined Patent Publication No. 56-158315 propose a two-group zoom lens having seven lenses. In addition, JP-A-6
Japanese Unexamined Patent Publication No. 1-80214 proposes a two-group zoom lens which has a configuration of 7 to 8 elements and is made compact.

[0005]

However, in the zoom lens disclosed in Japanese Patent Application Laid-Open No. 1-185607, a two-group zoom lens having a seven-element structure is realized without using an aspherical surface or the like. With this 2 group zoom lens,
There is a disadvantage that the zoom ratio is small and the total lens length at the wide-angle end (hereinafter, simply referred to as “total length”) is large, and compactness is not sufficiently achieved. Further, each lens of the first lens group is also large, and it is necessary to improve it in terms of downsizing and cost reduction. Further, in terms of performance, there is a disadvantage in that the spherical aberration at the telephoto end and the fluctuation of the lower coma aberration due to zooming remain.

On the other hand, the zoom lens disclosed in Japanese Unexamined Patent Publication No. 56-158315 has a disadvantage that it is relatively large in size and has a small zoom ratio, like the zoom lens disclosed in the above-mentioned publication. The negative lens located second from the object side in the first lens group has a plano-concave shape and a negative meniscus shape. Therefore, the diameter of the front lens is increased, which is contrary to the compactness and leads to an increase in cost.

Further, in the zoom lens disclosed in Japanese Patent Laid-Open No. 61-80214, the zoom ratio is comparatively small, and a negative lens and a positive lens out of the negative, negative and positive lenses constituting the first lens group are formed. The air gap is small. Therefore, there is a problem that the field curvature, astigmatism, and downward coma are not sufficiently corrected.

The present invention has been made in view of the above problems, and is a two-group zoom lens having a high zoom ratio, a small size, a simple structure, an inexpensive price, and good image forming performance. The purpose is to provide.

[0009]

In order to solve the above-mentioned problems, in the present invention, in order from the object side, a first lens group G1 having a negative refractive power as a whole and a positive lens power having a positive refractive power as a whole. A second lens group G2, and the first lens group G1 includes, in order from the object side, a negative meniscus lens L1 having a convex surface facing the object side, a biconcave lens L2, and a positive lens L3. The second lens group G2 includes, in order from the object side, a positive lens L4, a positive lens L5, and a biconcave lens L.
6 and a positive lens L7, and in the zoom lens which performs zooming by changing the distance between the first lens group G1 and the second lens, the focal length of the first lens group G1 is f1.
The focal length of the entire lens system at the wide-angle end is fw, the focal length of the entire lens system at the telephoto end is ft, and the shape factor of the biconcave lens L2 in the first lens group G1 is q2. The axial air space between the biconcave lens L2 and the positive lens L3 in the group G1 is d4.
And the total axial thickness of the first lens group G1 is dI: 0.6 ≦ | f1 | / (fw · ft) ^1/2 ≦ 1 −1 ≦ q2 ≦ 0 0.04 ≦ d4 / dI ≦ Provided is a zoom lens which satisfies the condition of 0.4.

According to a preferred embodiment of the present invention, the first
When the focal length of the lens group G1 is f1 and the focal length of the second lens group G2 is f2, the condition of 0.7 ≦ f2 / | f1 | ≦ 0.95 is satisfied. Further, when the focal length of the negative meniscus lens L1 in the first lens group G1 is f11 and the focal length of the biconcave lens L2 in the first lens group G1 is f12, 0.5 ≦ f11 / f12 ≦ 1 It is preferable to satisfy the condition of.

[0011]

In general, in a negative / positive two-group zoom lens, the focal length of the entire lens system at the wide-angle end is fw, the focal length of the entire lens system at the telephoto end is ft, and the focal length of the first lens group G1 is If f1 is set, the total length at the wide-angle end and the total length at the telephoto end are equal when the relationship shown in the following expression (a) is established, and the change in the total length of the lens due to zooming is minimized. f1 =-(fw · ft) ^1/2 (a)

Therefore, it is not preferable to select the focal length f1 of the first lens group G1 so as to deviate significantly from the relationship shown in the expression (a) because the change in the total length of the lens due to the magnification change becomes too large. Further, when the magnification at the telephoto end of the second lens group G2, which is a converging lens group, is βt, the relationship shown in the following expression (b) is established. ft = f1 · βt (b)

In order to make the zoom lens compact (miniaturization), it is necessary to use the second lens group G2 at the telephoto end at a magnification exceeding 1 ×. Further, in order to satisfy the relations of the above expressions (a) and (b) while performing compact and excellent aberration correction, each lens group should be used with a relatively strong refractive power. Therefore, in the conventional zoom lens, there is a tendency that each lens group is configured with a large number of lenses. As a result, each lens group would have become thicker, and the effect of miniaturization would be diminished.

However, in the zoom lens of the present invention, unlike the prior art, the refractive power arrangement suitable for miniaturization is set by considering the relationship between the above two expressions (a) and (b). The first divergent lens group
By configuring the lens group G1 with three negative, negative, and positive lenses having the negative lens L1, the negative lens L2, and the positive lens L3, the zoom lens is compact, and the total length change due to zooming is small, and the zoom is low cost. The lens is realized.

The conditional expression of the present invention will be described below.
The zoom lens of the present invention satisfies the following conditional expressions (1) to (3). 0.6 ≦ | f1 | / (fw · ft) ^1/2 ≦ 1 (1) −1 ≦ q2 ≦ 0 (2) 0.04 ≦ d4 / dI ≦ 0.4 (3)

Where f1: focal length of the first lens group G1 fw: focal length of the entire system at the wide-angle end ft: focal length of the entire system at the telephoto end q2: shape of the biconcave lens L2 in the first lens group G1 Factor d4: axial air distance between biconcave lens L2 and positive lens L3 in first lens group G1 dI: total axial thickness of first lens group G1

The shape factor (shape factor) q of the lens is defined by the following equation (c). q = (r2 + r1) / (r2-r1) (c) Here, r1: radius of curvature of surface of object side of lens r2: radius of curvature of surface of reduction side of lens Further, total axial thickness of first lens group G1 Is the distance along the optical axis between the most object side surface and the most reduction side surface of the first lens group G1.

Conditional expression (1) is a conditional expression relating to the change in the total length in the entire range of the above-mentioned magnification change. When the value of this conditional expression exceeds 1.0, the total length becomes maximum at the wide-angle end, and this conditional expression When the value is less than 1.0, it means that the total length is maximum at the telephoto end.

If the upper limit of conditional expression (1) is exceeded, the total length at the wide-angle end becomes the longest. In this case, not only the diameter of the front lens increases, the diameter of the filter increases, but also the weight and cost increase. In addition, when it is regularly used in a camera with a built-in flash, it is necessary to reduce the total length at the wide-angle end where the angle of view is large because of the problem of vignetting of the built-in flash. In this respect, too, the upper limit of conditional expression (1) should be exceeded. Is at a disadvantage. Further, if the front lens diameter is forcibly reduced, the peripheral light amount becomes insufficient, which is not preferable.

On the contrary, when the value goes below the lower limit of the conditional expression (1), the total length becomes the longest at the telephoto end. in this case,
In particular, it becomes difficult to correct downward coma on the wide-angle side, spherical aberration on the telephoto side, and astigmatism and field curvature, and further, the fluctuation of the downward coma due to zooming increases significantly, which is not preferable. Therefore, in reality, it is desirable to determine the power (refractive power) arrangement within the range defined by the conditional expression (1).

Conditional expression (2) is a condition regarding the shape factor of the second negative lens L2 from the object side of the first lens group G1. The lower limit value and the upper limit value of the conditional expression (2) correspond to a plano-concave lens having a concave surface facing the reduction side and a biconcave lens having the same absolute value of the radius of curvature on both sides, and a lens shape satisfying the conditional expression (2) is It is within the range defined by the plano-concave lens and the biconcave lens.

If the lower limit of conditional expression (2) is not reached, the first
The negative lens L2 in the lens group G1 changes from a plano-concave lens to a meniscus shape. In the case of a zoom lens having a large angle of view at the wide-angle end, it is advantageous to make the negative lens L2 a meniscus shape in order to correct downward coma aberration and the like. However, in the case of the present invention, it is necessary to particularly advance the miniaturization of the negative meniscus lens L1 and the negative lens L2 of the first lens group G1 in order to achieve compactness and cost reduction. Negative lens L2
Is a negative meniscus lens shape, the incident height of oblique rays becomes higher especially at the wide-angle end, so that the front lens diameter increases and the total weight increases, which is not preferable because it leads to an increase in cost. Further, the larger the zoom ratio and the larger aperture zoom lens are, the more disadvantageous the correction of the spherical aberration at the telephoto end becomes, which is not preferable. The effect of the present invention can be further enhanced by setting the lower limit of conditional expression (2) to -0.9 or more, more preferably -0.8 or more.

On the contrary, when the upper limit of conditional expression (2) is exceeded, in the negative lens L2, the absolute value of the radius of curvature of the object side surface is smaller than the absolute value of the radius of curvature of the reduction side surface. It becomes a concave lens shape. In this case, it is difficult to correct lower coma and chromatic aberration of magnification at the wide-angle end, which is inconvenient. In addition, the fluctuation of the lower coma aberration due to zooming increases, which is not preferable. The effect of the present invention can be further enhanced by setting the upper limit of conditional expression (2) to -0.2 or less.

Conditional expression (3) is a condition related to the axial air gap between the biconcave lens L2 and the positive lens L3 of the first lens group G1. If the lower limit of conditional expression (3) is not reached, the distance between the biconcave lens L2 and the positive lens L3 becomes too small, and it becomes difficult to correct lower coma. Moreover, since the incident height of the oblique rays becomes higher, the diameter of the front lens is increased. In this case, if the diameter of the front lens is forcibly reduced, the amount of peripheral light decreases, which is not preferable. The lower limit of conditional expression (3) is set to 0.
By setting the ratio to 06 or more, and more preferably to 0.07 or more, it is possible to perform better aberration correction and compactness.

On the other hand, when the upper limit of conditional expression (3) is exceeded, the distance between the biconcave lens L2 and the positive lens L3 becomes too large, and the dead space between the first lens group G1 and the second lens group G2 becomes large. This is not preferable because the amount of the variable power decreases and it becomes impossible to increase the variable power ratio. The effect of the present invention can be further enhanced by setting the upper limit of conditional expression (3) to 0.3 or less, and more preferably 0.19 or less.

In order to achieve better imaging performance and size reduction, it is preferable to satisfy the following conditional expression (4). 0.7 ≦ f2 / | f1 | ≦ 0.95 (4) where, f2: focal length of the second lens group G2

Conditional expression (4) is a condition for setting an appropriate range for the focal length f2 of the second lens group G2. In the conditional expression (4), since the magnitude | f1 | of the focal length of the first lens group G1 has already been set by the conditional expression (1), the description will be made focusing on the change of the focal length f2 of the second lens group G2. To do.

If the lower limit of conditional expression (4) is not reached, the second
Although the refractive power of the lens group G2 is remarkably strong and the change in the entire length is small, the spherical aberration on the telephoto side is remarkably deteriorated,
The variation of spherical aberration due to zooming also increases, which is not preferable. Further, in order to obtain a good balance with other aberrations while correcting this spherical aberration, the number of constituent lenses of the second lens group G2 increases, and the effect of downsizing is diminished by increasing the thickness. This is not desirable. In addition,
In order to further enhance the effect of the present invention, the lower limit of conditional expression (4) is set to 0.77 or more, whereby the correction of spherical aberration and upper coma becomes even better.

On the contrary, if the upper limit of conditional expression (4) is exceeded, the back focus of the lens system becomes remarkably large because the refracting power of the second lens group G2 becomes weak, and as a result the overall length becomes long and compact. It is not preferable because it is against the conversion. In addition, the change in the total length becomes extremely large, resulting in an increase in size, which is not preferable. In order to further enhance the effect of the present invention, by setting the upper limit of conditional expression (4) to 0.9 or less, it is possible to realize a more compact zoom lens with a smaller total length change and a lower cost. .

In order to realize better imaging performance and size reduction, it is preferable that the following conditional expression (5) is satisfied. 0.5 ≦ f11 / f12 ≦ 1 (5) where, f11: focal length of negative meniscus lens L1 in first lens group G1 f12: focal length of biconcave lens L2 in first lens group G1

Conditional expression (5) is a condition for defining an appropriate range for the ratio between the focal length of the negative meniscus lens L1 and the focal length of the biconcave lens L2 in the first lens group G1. In order to satisfactorily suppress the change of the lower coma aberration during zooming and the difference due to the difference in the incident height, and to satisfactorily correct the field curvature and the distortion aberration, a low-cost and compact zoom lens like the present invention is used. If two negative lenses L1 and L2
Appropriate power allocation is required for.

When the value goes below the lower limit of conditional expression (5), the power of the negative lens L1 becomes remarkably strong, and it becomes difficult to correct lower coma, field curvature and astigmatism, which is not preferable. By setting the lower limit of conditional expression (5) to 0.6 or more, and more preferably 0.7 or more, better aberration correction can be achieved.

On the contrary, when the value exceeds the upper limit of the conditional expression (5), the power of the negative lens L2 becomes stronger than that of the negative lens L1, so that the incident height of the oblique ray becomes remarkably high, resulting in a large size, which is preferable. Absent. By setting the upper limit of conditional expression (5) to 0.9 or less, a more compact and low-cost zoom lens can be realized.

To further enhance the effect of the present invention, it is preferable to satisfy the following conditional expressions (6) and (7). 0 <r10 (6) 0.15 <d12 / dII (7) where, r10: radius of curvature of reduction side surface of positive lens L5 in second lens group G2 d12: biconcave lens in second lens group G2 On-axis air distance between L6 and the positive lens L7 dII: Total axial thickness of the second lens group G1 The total axial thickness dII of the second lens group G2 is the most object-side surface of the second lens group G2. Is the distance along the optical axis between and the surface on the most reduction side.

Conditional expression (6) is a condition that the radius of curvature of the surface of the positive lens L5 on the reduction side in the second lens group G2 is positive, that is, the positive lens L5 is concave on the reduction side. In other words, it means that the air lens between the positive lens L5 and the biconcave lens L6 has a biconvex shape. In the case of a two-group zoom lens composed of a very small number of lenses, the biconvex air lens is necessary to increase the degree of freedom of spherical aberration correction. Therefore, if the range defined by the conditional expression (6) is exceeded, it becomes difficult to correct spherical aberration particularly on the telephoto side, which is not preferable.

Conditional expression (7) is a condition for defining an appropriate range for the axial air distance between the biconcave lens L6 and the positive lens L7 in the second lens group G2. If the range defined by the conditional expression (7) is exceeded, it becomes difficult to correct the upper coma aberration in the case of a zoom lens having a small number of components as in the present invention, which is not preferable.

The positive lens L4 in the second lens group G2
Is advantageous in correcting spherical aberration on the telephoto side, and the positive lens L7 has a positive lens shape with a convex surface facing the reduction side (that is, r14 <0, where r14: on the reduction side of the positive lens L7). It is advantageous to correct the upper coma aberration by setting the radius of curvature). Further, the center thickness of the biconcave lens L6 (the thickness along the optical axis between the object side surface and the reduction side surface of the lens) is larger than the center thickness of the positive lens L4 or the positive lens L5. It is particularly effective for favorably correcting spherical aberration on the telephoto side.

The positive lens L4 in the second lens group G2
And the material of the positive lens L5 is d line (λ = 587.
Use of a glass material having a refractive index of 1.5 or more with respect to 6 nm) is effective in correcting spherical aberration. Furthermore, the positive lens L
The upper coma aberration can be satisfactorily corrected by setting the material used so that the refractive index of 7 for the d-line is also 1.5 or more. In addition, setting the materials to be used so that the refractive index of the negative meniscus lens L1 and the biconcave lens L2 of the first lens group G1 with respect to the d-line is 1.7 or more is advantageous for correction of the lower coma aberration. The positive lens L3 preferably has a meniscus shape.

[0039]

Embodiments of the present invention will be described below with reference to the accompanying drawings. The zoom lens according to each embodiment of the present invention includes, in order from the object side, a first lens group G1 having a negative refractive power as a whole and a second lens group G1 having a positive refractive power as a whole.
The first lens group G1 includes, in order from the object side, a negative meniscus lens L1 having a convex surface directed toward the object side, a biconcave lens L2, and a positive lens L3. The group G2 includes, in order from the object side, the positive lens L4.
, Positive lens L5, biconcave lens L6, and positive lens L7
And the distance between the first lens group G1 and the second lens is changed to perform zooming.

In each embodiment, the second lens group G
An aperture stop S is provided between the positive lens L4 and the positive lens L5 in the second lens. Further, in the third embodiment, the fixed diaphragm SF is arranged immediately on the object side and immediately on the reduction side of the second lens group G2. Aperture stop S and fixed stop SF
Moves along the optical axis together with the second lens group G2 during zooming.

[Embodiment 1] FIG. 1 is a diagram showing a lens configuration of a zoom lens according to a first embodiment of the present invention and a movement of each lens unit during zooming. In FIG. 1, W indicates the wide-angle end, M indicates the intermediate focal length state, and T indicates the telephoto end. The zoom lens of FIG. 1 has, in order from the object side, a negative meniscus lens L1 having a convex surface directed toward the object side, a biconcave lens L2 having a smaller absolute value of the radius of curvature of the reduction side surface than the object side, and a convex surface directed toward the object side. A first lens group G1 including a positive meniscus lens L3, a biconvex lens L4 having a smaller radius of curvature on the object side than the reduction side, a positive meniscus lens L5 having a convex surface facing the object side, and a lens on the reduction side from the object side. It is composed of a biconcave lens L6 having a small absolute value of the radius of curvature of the surface, and a second lens group G2 composed of a positive meniscus lens L7 having a convex surface facing the reduction side.

The following table (1) lists the values of specifications of the first embodiment of the present invention. In Table (1), f is the focal length and F is
NO represents the F number and 2ω represents the angle of view. Furthermore, the surface number indicates the order of the lens surfaces from the object side, and the refractive index and the Abbe number indicate values for the d-line (λ = 587.6 nm).

[0043]

[Table 1] f = 36 to 77.6 mm FNO = 4.1 to 5.9 2ω = 64.4 to 31.1 ° (Variable interval during zooming) f 36.0000 50.0000 77.6000 d6 31.1548 15.4265 1.0417 d14 48.2356 59.3130 81.1517 (Conformance value) (1) | f1 | / (fw · ft) ^1/2 = 0.96 (2) q2 = -0 .61 (3) d4 / dI = 0.166 (4) f2 / | f1 | = 0.79 (5) f11 / f12 = 0.76 (6) r10 = 628.5 (7) d12 / dII = 0 .301

2 to 4 are graphs showing various aberrations of the first embodiment, FIG. 2 is graphs showing various aberrations at the wide-angle end, FIG. 3 is graphs showing various aberrations at an intermediate focal length state, and FIG. FIG. 7 is a diagram of various aberrations at the edge. In each aberration diagram, FNO is the F number, Y is the image height, and D is the d line (λ = 587.6n).
m), and G indicates the g-line (λ = 435.8 nm). Further, in the aberration diagram showing astigmatism, the solid line shows the sagittal image plane and the broken line shows the meridional image plane. Further, in the aberration diagram showing the spherical aberration, the broken line shows the sine condition. As is clear from each aberration diagram, it is understood that various aberrations are satisfactorily corrected in each focal length state in the present embodiment.

[Embodiment 2] FIG. 5 is a diagram showing a lens configuration of a zoom lens according to a second embodiment of the present invention and a movement of each lens unit during zooming. In FIG. 5, W indicates the wide-angle end, M indicates the intermediate focal length state, and T indicates the telephoto end. The zoom lens of FIG. 5 has, in order from the object side, a negative meniscus lens L1 having a convex surface directed toward the object side, a biconcave lens L2 having a smaller absolute value of the radius of curvature of the reduction side surface than the object side, and a convex surface directed toward the object side. A first lens group G1 including a positive meniscus lens L3, a biconvex lens L4 having a smaller radius of curvature on the object side than the reduction side, a positive meniscus lens L5 having a convex surface facing the object side, and a lens on the reduction side from the object side. It is composed of a biconcave lens L6 having a small absolute value of the radius of curvature of the surface, and a second lens group G2 composed of a positive meniscus lens L7 having a convex surface facing the reduction side.

The following table (2) lists the values of specifications of the second embodiment of the present invention. In Table (2), f is the focal length, F
NO represents the F number and 2ω represents the angle of view. Furthermore, the surface number indicates the order of the lens surfaces from the object side, and the refractive index and the Abbe number indicate values for the d-line (λ = 587.6 nm).

[0047]

[Table 2] f = 36 to 77.6 mm FNO = 4.1 to 5.94 2ω = 64.3 to 31.1 ° (Variable interval during zooming) f 36.0000 50.0000 77.6000 d6 25.7478 12.7973 0.9535 d14 48.3308 59.8423 82.5360 (Conformance value) (1) | f1 | / (fw · ft) ^1/2 = 0.85 (2) q2 = -0 .60 (3) d4 / dI = 0.125 (4) f2 / | f1 | = 0.82 (5) f11 / f12 = 0.77 (6) r10 = 317.3 (7) d12 / dII = 0 .285

6 to 8 are aberration diagrams of the second embodiment, FIG. 6 is an aberration diagram at the wide-angle end, FIG. 7 is an aberration diagram at the intermediate focal length state, and FIG. FIG. 7 is a diagram of various aberrations at the edge. In each aberration diagram, FNO is the F number, Y is the image height, and D is the d line (λ = 587.6n).
m), and G indicates the g-line (λ = 435.8 nm). Further, in the aberration diagram showing astigmatism, the solid line shows the sagittal image plane and the broken line shows the meridional image plane. Further, in the aberration diagram showing the spherical aberration, the broken line shows the sine condition. As is clear from each aberration diagram, it is understood that various aberrations are satisfactorily corrected in each focal length state in the present embodiment.

[Embodiment 3] FIG. 9 is a diagram showing a lens configuration of a zoom lens according to a third embodiment of the present invention and the movement of each lens unit during zooming. In FIG. 9, W indicates the wide-angle end, M indicates the intermediate focal length state, and T indicates the telephoto end. The zoom lens of FIG. 9 has, in order from the object side, a negative meniscus lens L1 having a convex surface directed toward the object side, a biconcave lens L2 having a smaller absolute value of the radius of curvature of the reduction side surface than the object side, and a convex surface directed toward the object side. A first lens group G1 including a positive meniscus lens L3, a biconvex lens L4 having a smaller radius of curvature on the object side than the reduction side, a positive meniscus lens L5 having a convex surface facing the object side, and a lens on the reduction side from the object side. It is composed of a biconcave lens L6 having a small absolute value of the radius of curvature of the surface, and a second lens group G2 including a biconvex lens L7 having a smaller radius of curvature of the surface on the reduction side than the object side.

The following table (3) lists the values of specifications of the third embodiment of the present invention. In Table (3), f is the focal length, F
NO represents the F number and 2ω represents the angle of view. Furthermore, the surface number indicates the order of the lens surfaces from the object side, and the refractive index and the Abbe number indicate values for the d-line (λ = 587.6 nm).

[0051]

[Table 3] f = 36 to 77.6 mm FNO = 4.1 to 5.9 2ω = 64 to 31 ° (Variable interval during zooming) f 36.0000 50.0000 77.6000 d6 24.3228 12.0723 0.8687 d16 42.9869 53.8750 75.3392 (Values corresponding to conditions) (1) | f1 | / (fw · ft) ^1/2 = 0.85 (2) q2 = -0 .63 (3) d4 / dI = 0.092 (4) f2 / | f1 | = 0.778 (5) f11 / f12 = 0.678 (6) r10 = 136.21 (7) d12 / dII = 0 .201

10 to 12 are aberration diagrams of Example 3, and FIG. 10 is an aberration diagram at the wide-angle end.
1 is a diagram of various aberrations in the intermediate focal length state, and FIG.
[Fig. 6] is a diagram of various types of aberration at the telephoto end. In each aberration diagram,
FNO is the F number, Y is the image height, and D is the d line (λ = 58
7.6 nm) and G indicates the g-line (λ = 435.8 nm). Further, in the aberration diagram showing astigmatism, the solid line shows the sagittal image plane and the broken line shows the meridional image plane. Further, in the aberration diagram showing the spherical aberration, the broken line shows the sine condition. As is clear from each aberration diagram, it is understood that various aberrations are satisfactorily corrected in each focal length state in the present embodiment.

[0053]

As described above, according to the present invention, the variable power ratio is 2.1 times or more, and the entire variable power range is small in size and has a simple structure, but excellent image formation is achieved. It is possible to realize a two-group zoom lens having performance.

[Brief description of drawings]

FIG. 1 is a diagram showing a lens configuration of a zoom lens according to Example 1 of the present invention and movement of each lens group during zooming.

FIG. 2 is a diagram of various types of aberration at the wide-angle end of Example 1.

FIG. 3 is a diagram of various types of aberration in the intermediate focal length state of Example 1.

FIG. 4 is a diagram of various types of aberration at the telephoto end of the first example.

FIG. 5 is a diagram showing a lens configuration of a zoom lens according to Example 2 of the present invention and movement of each lens unit during zooming.

FIG. 6 is a diagram of various types of aberration at the wide-angle end of Example 2.

FIG. 7 is a diagram of various types of aberration in the intermediate focal length state of Example 2.

FIG. 8 is a diagram of various types of aberration at the telephoto end of the second example.

FIG. 9 is a diagram showing a lens configuration of a zoom lens according to Example 3 of the present invention, and movement of each lens unit during zooming.

FIG. 10 is a diagram of various types of aberration at the wide angle end of Example 3;

FIG. 11 is a diagram of various types of aberration in the intermediate focal length state of Example 3.

FIG. 12 is a diagram of various types of aberration at the telephoto end of Example 3;

[Explanation of symbols]

 G1 First lens group G2 Second lens group L Each lens component S Aperture stop SF Fixed stop

Claims (3)

[Claims] 1. A first lens group G1 having a negative refracting power as a whole and a second lens group G2 having a positive refracting power as a whole are provided in order from the object side, and the first lens group G1 is A negative meniscus lens L1 having a convex surface directed toward the object side and a biconcave lens L2 in order from the object side.
And a positive lens L3, and the second lens group G2 includes the positive lens L in order from the object side.
4, a positive lens L5, a biconcave lens L6, and a positive lens L
And a zoom lens which has a zoom distance of 7 and changes the distance between the first lens group G1 and the second lens to change the magnification, wherein the focal length of the first lens group G1 is f1 and the entire lens system at the wide angle end. Is fw, the focal length of the entire lens system at the telephoto end is ft, and the shape factor of the biconcave lens L2 in the first lens group G1 is q2.
When the axial air distance between the biconcave lens L2 and the positive lens L3 in the first lens group G1 is d4 and the total axial thickness of the first lens group G1 is dI, 0.6 ≦ | A zoom lens characterized by satisfying a condition of f1 | / (fw · ft) ^1/2 ≦ 1 −1 ≦ q2 ≦ 0 0.04 ≦ d4 / dI ≦ 0.4. 2. The focal length of the first lens group G1 is f1
The zoom lens according to claim 1, wherein when the focal length of the second lens group G2 is f2, the condition of 0.7 ≦ f2 / | f1 | ≦ 0.95 is satisfied. 3. The focal length of the negative meniscus lens L1 in the first lens group G1 is f11, and the first lens group G1.
The zoom lens according to claim 1 or 2, wherein, when the focal length of the biconcave lens L2 in 1 is f12, the condition of 0.5≤f11 / f12≤1 is satisfied.