Zoom lens, imaging apparatus, and method for manufacturing zoom lens

This invention claims the benefit of Japanese Patent Application Nos. 2011-180957 and 2011-180958 which are hereby incorporated by reference.

The present invention relates to a zoom lens, an imaging apparatus, and a method for manufacturing the zoom lens.

In recent years, higher zoom ratio, higher performance and smaller size are demanded for imaging optical systems, including a video camera and a digital still camera. A zoom lens that is proposed to meet such demands is a zoom lens comprising, in order from an object: a first lens group having positive refractive power; a second lens group having negative refractive power; a third lens group having positive refractive power; and a fourth lens group having positive refractive power, wherein zooming is performed by moving each lens group (e.g. see Japanese Laid-Open Patent Publication No. 2008-152288(A)).

However a zoom lens that is even more compact and has higher performance is demanded.

With the foregoing in view, it is an object of the present invention to provide a zoom lens that has a compactness and excellent optical performance, even if the zoom ratio is high, an imaging apparatus using the zoom lens, and a method for manufacturing the zoom lens.

To achieve this object, a first zoom lens according to the present invention is a zoom lens comprising, in order from an object: a first lens group having positive refractive power; a second lens group having negative refractive power; a third lens group having positive refractive power; and a fourth lens group having positive refractive power, wherein upon zooming from a wide-angle end state to a telephoto end state, a distance between the first lens group and the second lens group is changed, a distance between the second lens group and the third lens group is changed and the fourth lens group is moved toward the object first, then moved toward an image, the third lens group includes, in order from the object, a first positive lens, a negative lens and a second positive lens, the fourth lens group includes two lens components, and the following conditional expressions are satisfied.

2.0< f 3/ fw< 3.0

0.6<(− f 3 b )/ f 3<1.0

where

f 3 denotes a focal length of the third lens group,

fw denotes a focal length of the zoom lens in the wide-angle end state, and

f 3 b denotes a focal length of the negative lens of the third lens group.

In the first zoom lens, it is preferable that the following conditional expression is satisfied.

0.3< f 3/ f 4<0.6

Where

f 3 denotes a focal length of the third lens group, and

f 4 denotes a focal length of the fourth lens group.

In the first zoom lens, it is preferable that the following conditional expression is satisfied.

1.0<(− f 2)/ fw< 1.5

Where

f 2 denotes a focal length of the second lens group, and

fw denotes a focal length of the zoom lens in the wide-angle end state.

In the first zoom lens, it is preferable that the following conditional expression is satisfied.

1.0< TLt/ft< 1.2

Where

TLt denotes a total length of the zoom lens in the telephoto end state, and

ft denotes a focal length of the zoom lens in the telephoto end state.

In the first zoom lens, it is preferable that the following conditional expression is satisfied.

1.0< D 1/ fw< 1.6

Where

D 1 denotes a thickness of the first lens group on the optical axis, and

fw denotes a focal length of the zoom lens in the wide-angle end state.

In the first zoom lens, it is preferable that the following conditional expression is satisfied.

1.5< f 3 c/f 3 a< 2.5

Where

f 3 c denotes a focal length of the second positive lens of the third lens group, and

f 3 a denotes a focal length of the first positive lens of the third lens group.

In the first zoom lens, it is preferable that the fourth lens group is formed of, in order from the object, a first lens component constituted by a positive lens and a second lens component constituted by a negative lens, and at least one of the positive lens and the negative lens has an aspherical surface.

In the first zoom lens, it is preferable that the following conditional expression is satisfied.

0.1<(− f 2)/ f 1<0.2

Where

f 2 denotes a focal length of the second lens group, and

f 1 denotes a focal length of the first lens group.

In the first zoom lens, it is preferable that the fourth lens group includes a first lens component, and a second lens component that is disposed on the image side of the first lens component via an air space.

In this case, it is also preferable that the following conditional expression is satisfied.

−11.5<( R 42 a+R 41 b )/( R 42 a−R 41 b )<−3.5

Where

R 41 b denotes a paraxial radius of curvature of a lens surface closest to the image in the first lens component of the fourth lens group, and

R 42 a denotes a paraxial radius of curvature of a lens surface closest to the object in the second lens component of the fourth lens group.

In the first zoom lens, it is preferable that an aperture stop is disposed near the object side of the first positive lens of the third lens group, and the third lens group and the aperture stop move together along the optical axis upon zooming from the wide-angle end state to the telephoto end state.

In the first zoom lens, it is preferable that at least a part of the third lens group can move so as to have a component in a vertical direction with respect to the optical axis.

In the first zoom lens, it is preferable that the fourth lens group moves along the optical axis upon focusing from an object at infinity to an object at a finite distance.

A first imaging apparatus according to the present invention is an imaging apparatus comprising a zoom lens that forms an image of an object on a predetermined surface, and the zoom lens is the first zoom lens according to the present invention.

A second zoom lens according to the present invention is a zoom lens having, in order from an object: a first lens group having positive refractive power; a second lens group having negative refractive power; a third lens group having positive refractive power; and a fourth lens group having positive refractive power, wherein upon zooming from a wide-angle end state to a telephoto end state, a distance between the first lens group and the second lens group is changed, a distance between the second lens group and the third lens group is changed, and the fourth lens group is moved toward the object first, then moved toward an image, the third lens group includes, in order from the object, a first positive lens, a negative lens, and a second positive lens, and the fourth lens group includes a first lens component and a second lens component that is disposed on the image side of the first lens component via an air space.

In the second zoom lens, it is preferable that the following conditional expression is satisfied.

−11.5<( R 42 a+R 41 b )/( R 42 a−R 41 b )<−3.5

Where

R 41 b denotes a paraxial radius of curvature of a lens surface closest to the image in the first lens component of the fourth lens group, and

R 42 a denotes a paraxial radius of curvature of a lens surface closest to the object in the second lens component of the fourth lens group.

In the second zoom lens, it is preferable that the following conditional expression is satisfied.

2.0< f 3/ fw< 3.0

Where

f 3 denotes a focal length of the third lens group, and

fw denotes a focal length of the zoom lens in the wide-angle end state.

In the second zoom lens, it is preferable that the following conditional expression is satisfied.

0.6<(− f 3 b )/ f 3<1.0

Where

f 3 denotes a focal length of the third lens group, and

f 3 b denotes a focal length of the negative lens of the third lens group.

A second imaging apparatus according to the present invention is an imaging apparatus comprising a zoom lens that forms an image of an object on a predetermined surface, and the zoom lens is the second zoom lens according to the present invention.

A first method for manufacturing a zoom lens according to the present invention is a method for manufacturing a zoom lens having, in order from an object: a first lens group having positive refractive power; a second lens group having negative refractive power; a third lens group having positive refractive power; and a fourth lens group having positive refractive power, wherein upon zooming from a wide-angle end state to a telephoto end state, a distance between the first lens group and the second lens group is changed, a distance between the second lens group and the third lens group is changed and the fourth lens group is moved toward the object first, then moved toward an image, the third lens group includes, in order from the object, a first positive lens, a negative lens and a second positive lens, the fourth lens group includes two lens components, and the following conditional expressions are satisfied.

2.0< f 3/ fw< 3.0

0.6<(− f 3 b )/ f 3<1.0

Where

f 3 denotes a focal length of the third lens group,

fw denotes a focal length of the zoom lens in the wide-angle end state, and

f 3 b denotes a focal length of the negative lens of the third lens group.

In the first method for manufacturing the zoom lens, it is preferable that the following conditional expression is satisfied.

0.3< f 3/ f 4<0.6

Where

f 3 denotes a focal length of the third lens group, and

f 4 denotes a focal length of the fourth lens group.

In the first method for manufacturing the zoom lens, it is preferable that the following conditional expression is satisfied.

1.0<(− f 2)/ fw< 1.5

Where

f 2 denotes a focal length of the second lens group, and

fw denotes a focal length of the zoom lens in the wide-angle end state.

In the first method for manufacturing the zoom lens, it is preferable that the fourth lens group includes a first lens component, and a second lens component that is disposed on the image side of the first lens component via an air space.

A second method for manufacturing a zoom lens is a method for manufacturing a zoom lens having, in order from an object: a first lens group having positive refractive power; a second lens group having negative refractive power; a third lens group having positive refractive power; and a fourth lens group having positive refractive power, wherein upon zooming from a wide-angle end state to a telephoto end state, a distance between the first lens group and the second lens group is changed, a distance between the second lens group and the third lens group is changed, and the fourth lens group is moved toward the object first, then moved toward an image, the third lens group includes, in order from the object, a first positive lens, a negative lens, and a second positive lens, and the fourth lens group includes a first lens component and a second lens component that is disposed on the image side of the first lens component via an air space.

In the second method for manufacturing the zoom lens, it is preferable that the following conditional expression is satisfied.

−11.5<( R 42 a+R 41 b )/( R 42 a−R 41 b )<−3.5

where R 41 b denotes a paraxial radius of curvature of a lens surface closest to the image in the first lens component of the fourth lens group, and R 42 a denotes a paraxial radius of curvature of a lens surface closest to the object in the second lens component of the fourth lens group.

According to the present invention, a compactness and excellent optical performance can be implemented even if the zoom ratio is high.

Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only and thus are not limitative of the present invention.

FIG. 1 shows a cross-section and a zoom locus of a zoom lens according to Example 1;

FIG. 2A are graphs showing various aberrations of the zoom lens according to Example 1 upon focusing on infinity in the wide-angle end state, FIG. 2B are graphs showing various aberrations of the zoom lens upon focusing on infinity in the intermediate focal length state, and FIG. 2C are graphs showing various aberrations of the zoom lens upon focusing on infinity in the telephoto end state;

FIG. 3 shows a cross-section and a zoom locus of a zoom lens according to Example 2;

FIG. 4A are graphs showing various aberrations of the zoom lens according to Example 2 upon focusing on infinity in the wide-angle end state, FIG. 4B are graphs showing various aberrations of the zoom lens upon focusing on infinity in the intermediate focal length state, and FIG. 4C are graphs showing various aberrations of the zoom lens upon focusing on infinity in the telephoto end state;

FIG. 5 shows a cross-section and a zoom locus of a zoom lens according to Example 3;

FIG. 6A are graphs showing various aberrations of the zoom lens according to Example 3 upon focusing on infinity in the wide-angle end state, FIG. 6B are graphs showing various aberrations of the zoom lens upon focusing on infinity in the intermediate focal length state, and FIG. 6C are graphs showing various aberrations of the zoom lens upon focusing on infinity in the telephoto end state;

FIG. 7 shows a cross-section and a zoom locus of a zoom lens according to Example 4;

FIG. 8A are graphs showing various aberrations of the zoom lens according to Example 4 upon focusing on infinity in the wide-angle end state, FIG. 8B are graphs showing various aberrations of the zoom lens upon focusing on infinity in the intermediate focal length state, and FIG. 8C are graphs showing various aberrations of the zoom lens upon focusing on infinity in the telephoto end state;

FIG. 9A is a front view of a digital still camera, and FIG. 9B is a rear view of the digital still camera;

FIG. 10 is a cross-sectional view along a line indicated by the arrows A and A′ in FIG. 9A ; and

FIG. 11 is a flow chart depicting a method for manufacturing the zoom lens.

Embodiments of the present invention will now be described with reference to the drawings. FIG. 9 and FIG. 10 show a digital still camera CAM with a zoom lens according to the present invention. FIG. 9A shows a front view of the digital still camera CAM, and FIG. 9B shows a rear view of the digital still camera CAM. FIG. 10 is a cross-sectional view along a line indicated by the arrows A and A′ in FIG. 9A .

If a power button (not illustrated) is pressed on the digital still camera CAM shown in FIG. 9 and FIG. 10 , a shutter (not illustrated) of an image capturing lens (Z) is released, and lights from an object are collected by the image capturing lens (ZL) and form an image on a picture element C (not illustrated) (e.g. CCD and CMOS), which is disposed on an image plane I. The object image formed on the picture element C is displayed on a liquid crystal monitor M disposed on the back of the digital still camera CAM. The user determines the composition of the object image while viewing the liquid crystal monitor M, then presses a release button B 1 to capture the object image by the picture element C, and stores it in memory (not illustrated).

The image capturing lens is constituted by a later mentioned zoom lens ZL according to the embodiment. The digital still camera CAM has an auxiliary light emitting unit D, which emits auxiliary light when the object is dark, a wide (W) tele (T) button B 2 for zooming the image capturing lens (zoom lens ZL) from a wide-angle end state (W) to a telephoto end state (T), and a function button B 3 , which is used for setting various conditions for the digital still camera CAM.

A zoom lens ZL according to a first embodiment is, for example, a zoom lens comprising, in order from an object, a first lens group G 1 having positive refractive power, a second lens group G 2 having negative refractive power, a third lens group G 3 having positive refractive power and a fourth lens group G 4 having positive refractive power. Upon zooming from a wide-angle end state to a telephoto end state, a distance between the first lens group G 1 and the second lens group G 2 changes, a distance between the second lens group G 2 and the third lens group G 3 changes, and the fourth lens group G 4 moves toward the object first, then moves toward an image. The third lens group G 3 includes, in order from the object, a first positive lens, a negative lens and a second positive lens. The fourth lens group G 4 includes two lens components.

In the zoom lens ZL having this configuration, it is preferable that the following conditional expression (1) and conditional expression (2) are satisfied.

2.0< f 3/ fw< 3.0  (1)

0.6<(− f 3 b )/ f 3<1.0  (2)

where f 3 denotes a focal length of the third lens group G 3 , fw denotes a focal length of the zoom lens ZL in the wide-angle end state, and f 3 b denotes a focal length of the negative lens of the third lens group G 3 .

The conditional expression (1) specifies a relationship between the focal length of the third lens group G 3 and the focal length of the zoom lens ZL in the wide-angle end state. Spherical aberration and fluctuations of aberrations due to zooming can be controlled by satisfying these conditional expressions. If the upper limit value of the conditional expression (1) is exceeded, power of the third lens group G 3 becomes too weak, which makes it difficult to correct coma aberration. Furthermore, the total length of the zoom lens increases because the moving distance of the lens increases upon zooming, which makes it impossible to implement compactness. If the lower limit value of the conditional expression (1) is not reached, power of the third lens group G 3 becomes too strong, and spherical aberration in the telephone end state is excessively corrected by the third lens group G 3 , which makes it difficult to correct coma aberration and curvature of field.

To demonstrate the effect of the first embodiment well, it is preferable that the upper limit value of the conditional expression (1) is 2.7. It is even better that the upper limit value of the conditional expression (1) is 2.5. To demonstrate the effect of the first embodiment well, it is preferable that the lower limit value of the conditional expression (1) is 2.05. It is even better that the lower limit value of the conditional expression (1) is 2.1.

The conditional expression (2) specifies the focal length of the negative lens in the third lens group G 3 . If the upper limit value of the conditional expression (2) is exceeded, power of the negative lens in the third lens group G 3 becomes weak, which makes it difficult to correct spherical aberration, coma aberration and astigmatism. If the lower limit value of the conditional expression (2) is not reached, power of the entire third lens group G 3 becomes weak, which makes it difficult to correct spherical aberration. Furthermore, power of the negative lens of the third lens group G 3 becomes strong, which makes it difficult to correct coma aberration.

To demonstrate the effect of the first embodiment well, it is preferable that the upper limit value of the conditional expression (2) is 0.9. It is even better that the upper limit value of the conditional expression (2) is 0.8. To demonstrate the effect of the first embodiment well, it is preferable that the lower limit value of the conditional expression (2) is 0.605. It is even better that the lower limit value of the conditional expression (2) is 0.61.

In the zoom lens ZL according to the first embodiment, it is preferable that the following conditional expression (3) is satisfied.

0.3< f 3/ f 4<0.6  (3)

where f 3 denotes a focal length of the third lens group G 3 , and f 4 denotes a focal length of the fourth lens group G 4 .

The conditional expression (3) specifies a relationship between the focal length of the third lens group G 3 and the focal length of the fourth lens group G 4 . If the upper limit value of the conditional expression (3) is exceeded, power of the fourth lens group G 4 becomes too strong, which makes it difficult to correct spherical aberration and longitudinal chromatic aberration in the telephoto end state. Furthermore, the total length of the zoom lens increases because the moving distance of the third lens group G 3 increases upon zooming, which makes it impossible to implement compactness. If the lower limit value of the conditional expression (3) is not reached, power of the fourth lens group G 4 becomes too weak, which makes it difficult to correct curvature of field and coma aberration in the wide-angle end state, and coma aberration in the telephoto end state.

To demonstrate the effect of the first embodiment well, it is preferable that the upper limit value of the conditional expression (3) is 0.5. It is even better that the upper limit value of the conditional expression (3) is 0.45. To demonstrate the effect of the first embodiment well, it is preferable that the lower limit value of the conditional expression (3) is 0.31. It is even better that the lower limit value of the conditional expression (3) is 0.33.

In the zoom lens ZL according to the first embodiment, it is preferable that the following conditional expression (4) is satisfied.

1.0<(− f 2)/ fw< 1.5  (4)

where f 2 denotes a focal length of the second lens group G 2 , and fw denotes a focal length of the zoom lens ZL in the wide-angle end state.

The conditional expression (4) specifies a relationship between the focal length of the second lens group G 2 and the focal length of the zoom lens ZL in the wide-angle end state. If the upper limit value of the conditional expression (4) is exceeded, power of the second lens group G 2 becomes too weak, hence power of the other lens groups must be increased, which makes it difficult to correct spherical aberration and curvature of field. Furthermore, the total length of the zoom lens increases, and the front lens diameter increases as well, because the moving distance of the lens increases upon zooming, which makes it impossible to implement compactness. If the lower limit value of the conditional expression (4) is not reached, power of the second lens group G 2 becomes strong, which decreases the moving distance but makes it difficult to correct astigmatism and curvature of field.

To demonstrate the effect of the first embodiment well, it is preferable that the upper limit value of the conditional expression (4) is 1.4. It is even better that the upper limit value of the conditional expression (4) is 1.35. To demonstrate the effect of the first embodiment well, it is preferable that the lower limit value of the conditional expression (4) is 1.05. It is even better that the lower limit value of the conditional expression (4) is 1.1.

In the zoom lens ZL according to the first embodiment, it is preferable that the following conditional expression (5) is satisfied.

1.0< TLt/ft< 1.2  (5)

where TLt denotes a total length of the zoom lens ZL in the telephoto end state, and ft denotes a focal length of the zoom lens ZL in the telephoto end state.

The conditional expression (5) specifies a total length of the zoom lens ZL in the telephoto end state. If the upper limit value of the conditional expression (5) is exceeded, the total length becomes too long, which makes it impossible to implement compactness. If power of the third lens group G 3 is increased to relax this problem, it becomes difficult to correct spherical aberration and chromatic aberration. If the lower limit value of the conditional expression (5) is not reached, power of the first lens group G 1 becomes too strong, which makes it difficult to correct curvature of field.

To demonstrate the effect of the first embodiment well, it is preferable that the upper limit value of the conditional expression (5) is 1.18. It is even better that the upper limit value of the conditional expression (5) is 1.17. To demonstrate the effect of the first embodiment well, it is preferable that the lower limit value of the conditional expression (5) is 1.02. It is even better that the lower limit value of the conditional expression (5) is 1.05.

In the zoom lens ZL according to the first embodiment, it is preferable that the following conditional expression (6) is satisfied.

1.0< D 1/ fw< 1.6  (6)

where D 1 denotes a thickness of the first lens group G 1 on the optical axis, and fw denotes a focal length of the zoom lens ZL in the wide-angle end state.

The conditional expression (6) specifies a thickness of the first lens group G 1 on the optical axis. If the upper limit value of the conditional expression (6) is exceeded, the thickness of the first lens group G 1 becomes too thick, and the zoom lens in a retracted state cannot be compact, and correction of astigmatism and curvature of field becomes difficult. If the lower limit value of the conditional expression (6) is not reached, thickness of the zoom lens in the retracted state becomes thin, but correction of the longitudinal chromatic aberration becomes difficult due to the change of the refractive index, and correction of astigmatism and curvature of field in the wide-angle end state becomes difficult.

To demonstrate the effect of the first embodiment well, it is preferable that the upper limit value of the conditional expression (6) is 1.4. It is even better that the upper limit value of the conditional expression (6) is 1.3. To demonstrate the effect of the first embodiment well, it is preferable that the lower limit value of the conditional expression (6) is 1.02. It is even better that the lower limit value of the conditional expression (6) is 1.05.

In the zoom lens ZL according to the first embodiment, it is preferable that the following conditional expression (7) is satisfied.

1.5< f 3 c/f 3 a< 2.5  (7)

where f 3 c denotes a focal length of the second positive lens of the third lens group G 3 , and f 3 a denotes a focal length of the first positive lens of the third lens group G 3 .

The conditional expression (7) specifies a relationship between the focal length of the front side positive lens (first positive lens) and that of the rear side positive lens (second positive lens) of the third lens group G 3 . If the upper limit value of the conditional expression (7) is exceeded, power of the front side positive lens becomes strong, which makes it easy to correct spherical aberration, but power of the rear side positive lens becomes weak, which makes it difficult to correct coma aberration. If the lower limit value of the conditional expression (7) is not reached, power of the front side positive lens becomes weak, which makes it difficult to correct spherical aberration.

To demonstrate the effect of the first embodiment well, it is preferable that the upper limit value of the conditional expression (7) is 2.495. It is even better that the upper limit value of the conditional expression (7) is 2.492. To demonstrate the effect of the first embodiment well, it is preferable that the lower limit value of the conditional expression (7) is 1.6. It is even better that the lower limit value of the conditional expression (7) is 1.8

In the zoom lens ZL according to the first embodiment, it is preferable that the fourth lens group G 4 includes, in order from the object, a first lens component that is constituted by a positive lens, and a second lens component that is constituted by a negative lens, and at least one of the positive lens and the negative lens has an aspherical surface. Thereby abaxial astigmatism, coma aberration and curvature of field can be corrected well.

In the zoom lens ZL according to the first embodiment, it is preferable that the following conditional expression (8) is satisfied.

0.1<(− f 2)/ f 1<0.2  (8)

where f 2 denotes a focal length of the second lens group G 2 , and f 1 denotes a focal length of the first lens group G 1 .

The conditional expression (8) specifies a relationship between a focal length of the first lens group G 1 and that of the second lens group G 2 . If the upper limit value of the conditional expression (8) is exceeded, power of the first lens group G 1 becomes strong, which makes it difficult to correct spherical aberration in the telephoto end state. Power of the second lens group G 2 becomes weak, and total length increases because the moving distance of the lens increases upon zooming. If the lower limit value of the conditional expression (8) is not reached, power of the second lens group G 2 becomes too strong, which makes it difficult to correct astigmatism and curvature of field.

To demonstrate the effect of the first embodiment well, it is preferable that the upper limit value of the conditional expression (8) is 0.18. It is even better that the upper limit value of the conditional expression (8) is 0.16. To demonstrate the effect of the first embodiment well, it is preferable that the lower limit value of the conditional expression (8) is 0.12. It is even better that the lower limit value of the conditional expression (8) is 0.14.

In the zoom lens ZL according to the first embodiment, it is preferable that the fourth lens group G 4 includes a first lens component, and a second lens component that is disposed on the image side of the first lens component via an air space. Since there is the air space between the first lens component and the second lens component of the fourth lens group G 4 , coma aberration can be effectively corrected in the intermediate area to the telephoto end state. In the case of cementing the first lens component and the second lens component, there is one more surface that is free, which is advantageous to correct aberrations for peripheral image height in the telephoto area.

In this case, it is preferable that the following conditional expression (9) is satisfied.

−11.5<( R 42 a+R 41 b )/( R 42 a−R 41 b )<−3.5  (9)

where R 41 b denotes a paraxial radius of curvature of a lens surface closest to the image in the first lens component of the fourth lens group G 4 , and R 42 a denotes a paraxial radius of curvature of a lens surface closest to the object in the second lens component of the fourth lens group G 4 .

The conditional expression (9) specifies a shape factor of an air lens between the two lenses of the fourth lens group G 4 . If the upper limit value of the conditional expression (9) is exceeded, power of the first lens component of the fourth lens group G 4 becomes weak, which makes it difficult to correct coma aberration and astigmatism in the telephoto end state. If the lower limit value of the conditional expression (9) is not reached, power of the first lens component of the fourth lens group G 4 becomes too strong, which makes it difficult to correct coma aberration in the intermediate area to the telephoto end state. Correction of lateral chromatic aberration in the telephoto side also becomes difficult.

To demonstrate the effect of the first embodiment well, it is preferable that the upper limit value of the conditional expression (9) is −3.6. It is even better that the upper limit value of the conditional expression (9) is −3.7. To demonstrate the effect of the first embodiment well, it is preferable that the lower limit value of the conditional expression (9) is −11.4. It is even better that the lower limit value of the conditional expression (9) is −11.3.

According to the first embodiment, a zoom lens ZL that has compactness and excellent optical performance, even if the zoom ratio is high, and an imaging apparatus (digital still camera CAM) having this zoom lens ZL, can be implemented.

It is preferable that an aperture stop S is disposed near the object side of the first positive lens of the third lens group G 3 , and the third lens group G 3 and the aperture stop S move together along the optical axis upon zooming from the wide-angle end state to the telephoto end state.

It is preferable that at least a part of the third lens group G 3 can move so as to have a component in a vertical direction to the optical axis.

It is preferable that the fourth lens group G 4 moves along the optical axis upon focusing from an object at infinity to an object at a finite distance.

A method for manufacturing the zoom lens ZL according to the first embodiment will now be described with reference to FIG. 11 . First the first lens group G 1 , the second lens group G 2 , the third lens group G 3 and the fourth lens group G 4 are assembled, in order from the object, in a cylindrical lens barrel (step ST 10 ). Each lens is driveably constituted so that upon zooming from the wide-angle end state to the telephoto end state, the distance between the first lens group G 1 and the second lens group G 2 changes, the distance between the second lens group G 2 and the third lens group G 3 changes, and the fourth lens group G 4 moves toward the object first, then moves toward an image (step ST 20 ).

In step ST 10 in which the lenses are assembled, each lens is disposed so that the first lens group G 1 has positive refractive power, the second lens group G 2 has negative refractive power, the third lens group G 3 has positive refractive power, and the fourth lens group G 4 has positive refractive power. For the third lens group G 3 , the first positive lens, the negative lens and the second positive lens are disposed in order from the object. For the fourth lens group G 4 , the two lens components are disposed. Each lens is disposed so as to satisfy the above mentioned conditional expression (1) and conditional expression (2) among others. According to this manufacturing method, the mechanical mechanism can be simplified, and the zoom lens ZL that has compactness and excellent optical performance, even if the zoom ratio is high, can be implemented.

The second embodiment of the present invention will now be described. A zoom lens ZL according to the second embodiment has a similar configuration as the zoom lens ZL according to the first embodiment, and comprises, in order from an object, a first lens group G 1 having positive refractive power, a second lens group G 2 having negative refractive power, a third lens group G 3 having positive refractive power and a fourth lens group G 4 having positive refractive power, as shown in FIG. 1 . Upon zooming from a wide-angle end state to a telephoto end state, a distance between the first lens group G 1 and the second lens group G 2 changes, the second lens group G 2 and the third lens group G 3 changes, and the fourth lens group G 4 moves toward the object first, then moves toward an image. The third lens group G 3 further comprises, in order from the object, a first positive lens, a negative lens and a second positive lens. The fourth lens group G 4 has a first lens component, and a second lens component that is disposed on the image side of the first lens component via an air space.

In the zoom lens ZL having this configuration, there is an air space between the first lens component and the second lens component of the fourth lens group G 4 , hence coma aberration can be effectively corrected in the intermediate area to the telephoto end state. In the case of cementing the first lens component and the second lens component, there is one more surface that is free, which is advantageous to correct aberrations for the peripheral image height in the telephoto area.

In the zoom lens ZL according to the second embodiment, it is preferable that the above mentioned conditional expression (9) is satisfied. Thereby a similar effect as the first embodiment can be Implemented. To demonstrate the effect of the second embodiment well, it is preferable that the upper limit value of the conditional expression (9) is −3.6. It is even better that the upper limit value of the conditional expression (9) is −3.7. To demonstrate the effect of the second embodiment well, it is preferable that the lower limit value of the conditional expression (9) is −11.4. It is even better that the lower limit value of the conditional expression (9) is −11.3.

In the zoom lens ZL according to the second embodiment, it is preferable that the above mentioned conditional expression (1) is satisfied. Thereby a similar effect as the first embodiment can be Implemented. To demonstrate the effect of the second embodiment well, it is preferable that the upper limit value of the conditional expression (1) is 2.7. It is even better that the upper limit value of the conditional expression (1) is 2.5. To demonstrate the effect of the second embodiment well, it is preferable that the lower limit value of the conditional expression (1) is 2.05. It is even better that the lower limit value of the conditional expression (1) is 2.1.

In the zoom lens ZL according to the second embodiment, it is preferable that the above mentioned conditional expression (2) is satisfied. Thereby a similar effect as the first embodiment can be Implemented. To demonstrate the effect of the second embodiment well, it is preferable that the upper limit value of the conditional expression (2) is 0.9. It is even better that the upper limit value of the conditional expression (2) is 0.8. To demonstrate the effect of the second embodiment well, it is preferable that the lower limit value of the conditional expression (2) is 0.605. It is even better that the lower limit value of the conditional expression (2) is 0.61.

In the zoom lens ZL according to the second embodiment, it is preferable that the above mentioned conditional expression (3) is satisfied. Thereby a similar effect as the first embodiment can be implemented. To demonstrate the effect of the second embodiment well, it is preferable that the upper limit value of the conditional expression (3) is 0.5. It is even better that the upper limit value of the conditional expression (3) is 0.45. To demonstrate the effect of the second embodiment well, it is preferable that the lower limit value of the conditional expression (3) is 0.31. It is even better that the lower limit value of the conditional expression (3) is 0.33.

In the zoom lens ZL according to the second embodiment, it is preferable that the above mentioned conditional expression (4) is satisfied. Thereby a similar effect as the first embodiment can be implemented. To demonstrate the effect of the second embodiment well, it is preferable that the upper limit value of the conditional expression (4) is 1.4. It is even better that the upper limit value of the conditional expression (4) is 1.35. To demonstrate the effect of the second embodiment well, it is preferable that the lower limit value of the conditional expression (4) is 1.05. It is even better that the lower limit value of the conditional expression (4) is 1.1.

In the zoom lens ZL according to the second embodiment, it is preferable that the above mentioned conditional expression (5) is satisfied. Thereby a similar effect as the first embodiment can be implemented. To demonstrate the effect of the second embodiment well, it is preferable that the upper limit value of the conditional expression (5) is 1.18. It is even better that the upper limit value of the conditional expression (5) is 1.17. To demonstrate the effect of the second embodiment well, it is preferable that the lower limit value of the conditional expression (5) is 1.02. It is even better that the lower limit value of the conditional expression (5) is 1.05.

In the zoom lens ZL according to the second embodiment, it is preferable that the above mentioned conditional expression (6) is satisfied. Thereby a similar effect as the first embodiment can be implemented. To demonstrate the effect of the second embodiment well, it is preferable that the upper limit value of the conditional expression (6) is 1.4. It is even better that the upper limit value of the conditional expression (6) is 1.3. To demonstrate the effect of the second embodiment well, it is preferable that the lower limit value of the conditional expression (6) is 1.02. It is even better that the lower limit value of the conditional expression (6) is 1.05.

In the zoom lens ZL according to the second embodiment, it is preferable that the above mentioned conditional expression (7) is satisfied. Thereby a similar effect as the first embodiment can be implemented. To demonstrate the effect of the second embodiment well, it is preferable that the upper limit value of the conditional expression (7) is 2.495. It is even better that the upper limit value of the conditional expression (7) is 2.492. To demonstrate the effect of the second embodiment well, it is preferable that the lower limit value of the conditional expression (7) is 1.6. It is even better that the lower limit value of the conditional expression (7) is 1.8.

In the zoom lens ZL according to the second embodiment, it is preferable that the first lens component of the fourth lens group G 4 is constituted by a positive lens, the second lens component of the fourth lens group G 4 is constituted by a negative lens, and at least one of the positive lens and the negative lens has an aspherical surface. This makes it possible to correct abaxial astigmatism, coma aberration and curvature of field ideally.

In the zoom lens ZL according to the second embodiment, it is preferable that the above mentioned conditional expression (8) is satisfied. Thereby a similar affect as the first embodiment can be implemented. To demonstrate the effect of the second embodiment well, it is preferable that the upper limit value of the conditional expression (8) is 0.18. It is even better that the upper limit value of the conditional expression (8) is 0.16. To demonstrate the effect of the second embodiment well, it is preferable that the lower limit value of the conditional expression (8) is 0.12. It is even better that the lower limit value of conditional expression (8) is 0.14.

According to the second embodiment, a zoom lens ZL that has compactness and excellent optical performance, even if the zoom ratio is high, and an imaging apparatus (digital still camera CAM) having this zoom lens ZL, can be implemented.

It is preferable that an aperture stop S is disposed near the object side of the first positive lens of the third lens group G 3 , and the third lens group G 3 and the aperture stop S move together along the optical axis upon zooming from the wide-angle end state to the telephoto end state.

It is preferable that at least a part of the third lens group G 3 can move so as to have a component in a vertical direction to the optical axis.

It is preferable that the fourth lens group G 4 moves along the optical axis upon focusing from an object at infinity to an object at a finite distance.

Now a method for manufacturing the zoom lens ZL according to the second embodiment will be described with reference to FIG. 11 , just like the first embodiment. First the first lens group G 1 , the second lens group G 2 , the third lens group G 3 and the fourth lens group G 4 are assembled, in order from the object, in a cylindrical lens barrel (step ST 10 ). Each lens is driveably constituted so that upon zooming from the wide-angle end state to the telephoto end state, the distance between the first lens group G 1 and the second lens group G 2 changes, the distance between the second lens group G 2 and the third lens group G 3 changes, and the fourth lens group G 4 moves toward the object first, then moves toward an image (step ST 20 ).

In step ST 10 in which the lenses are assembled, each lens is disposed so that the first lens group G 1 has positive refractive power, the second lens group G 2 has negative refractive power, the third lens group G 3 has positive refractive power, and the fourth lens group G 4 has positive refractive power. For the third lens group G 3 , the first positive lens, the negative lens and the second positive lens are disposed in order from the object. For the fourth lens group G 4 , the first lens component and the second lens component are disposed, and the second lens component is disposed on the image side of the first lens component via an air space. Each lens is disposed so as to satisfy the above mentioned conditional expression (9) among others. According to this manufacturing method, the mechanical mechanism can be simplified, and the zoom lens ZL that has compactness and excellent optical performance, even if the zoom ratio is high, can be implemented.