Zoom lens system, imaging apparatus, and method for zooming the zoom lens system   

Abstract: Providing a zoom lens system having excellent optical performance with a high zoom ratio, an imaging apparatus, and a method for zooming the zoom lens system. The system including, in order from an object, a first group G1 having negative refractive power, a second group G2 having positive refractive power, a third group G3 having negative refractive power, and a fourth group G4 having positive refractive power. An aperture stop S is disposed between the second group G2 and the fourth group G4. Upon zooming from a wide-angle end state to a telephoto end state, each group is moved such that a distance between the second group G2 and the third group G3 increases, a distance between the third group G3 and the fourth group G4 decreases, and the aperture stop S is moved together with the third group G3. Given conditions are satisfied.

TECHNICAL FIELD

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

BACKGROUND ART

A zoom lens system suitable for a film camera, an electronic still camera, and a video camera has been proposed (for example, Japanese Patent Application Laid-Open Nos. 2004-61910, and 11-174329).

However, conventional zoom lens system has a zoom ratio of about two, so that a requirement for a high zoom ratio cannot be sufficiently satisfied. Moreover, since the position of an aperture stop is not optimized, excellent optical performance cannot be accomplished.

DISCLOSURE OF THE INVENTION

The present invention is made in view of the aforementioned problems and has an object to provide a zoom lens system having excellent optical performance with a high zoom ratio, an imaging apparatus, and a method for zooming the zoom lens system.

According to a first aspect of the present invention, there is provided a zoom lens system comprising, in order from an object: a first lens group having negative refractive power; a second lens group having positive refractive power; a third lens group having negative refractive power; and a fourth lens group having positive refractive power; an aperture stop being disposed between the second lens group and the fourth lens group, upon zooming from a wide-angle end state to a telephoto end state, each lens group being moved such that a distance between the second lens group and the third lens group varies, and a distance between the third lens group and the fourth lens group varies, and the aperture stop being moved together with the third lens group, and the following conditional expressions (1) and (2) being satisfied:

1.20<f2/fw<2.50  (1)

−2.10<f3/fw<−0.80  (2)

where f2 denotes a focal length of the second lens group, f3 denotes a focal length of the third lens group, and fw denotes a focal length of the zoom lens system in the wide-angle end state.

According to a second aspect of the present invention, there is provided an imaging apparatus equipped with the zoom lens system according the first aspect.

According to a third aspect of the present invention, there is provided a zoom lens system comprising, in order from an object: a first lens group having negative refractive power; a second lens group having positive refractive power; a third lens group having negative refractive power; and a fourth lens group having positive refractive power; an aperture stop being disposed between the second lens group and the fourth lens group, upon zooming from a wide-angle end state to a telephoto end state, each lens group being moved such that a distance between the second lens group and the third lens group varies and a distance between the third lens group and the fourth lens group varies, and the aperture stop being moved together with the third lens group, each of the second lens group, the third lens group, and the fourth lens group including at least one cemented lens, the cemented lens in the fourth lens group being composed of, in order from the object, a positive lens cemented with a negative lens, the most image plane side lens surface of the zoom lens system being a convex shape facing the image plane, and the following conditional expression (3) being satisfied:

−0.3<(d1w−d1t)/Ymax<0.17  (3)

where d1w denotes a distance along an optical axis between the most object side lens surface of the zoom lens system to the image plane in the wide-angle end state, d1t denotes a distance along the optical axis between the most object side lens surface of the zoom lens system to the image plane in the telephoto end state, and Ymax denotes the maximum image height.

According to a fourth aspect of the present invention, there is provided a zoom lens system comprising, in order from an object: a first lens group having negative refractive power; a second lens group having positive refractive power; a third lens group having negative refractive power; and a fourth lens group having positive refractive power; upon zooming from a wide-angle end state to a telephoto end state, a distance between the second lens group and the third lens group varying and a distance between the third lens group and the fourth lens group varying, the third lens group or a portion of the third lens group being moved as a vibration reduction lens group in a direction perpendicular to the optical axis, and the following conditional expression (5) being satisfied:

0.12<(r2+r1)/(r2−r1)<1.30  (5)

where r1 denotes a radius of curvature of the object side of the vibration reduction lens group, and r2 denotes a radius of curvature of the image side of the vibration reduction lens group.

According to a fifth aspect of the present invention, there is provided an imaging apparatus equipped with the zoom lens system according fourth aspect.

According to a sixth aspect of the present invention, there is provided a method for zooming a zoom lens system including, in order from an object, a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group having negative refractive power, and a fourth lens group having positive refractive power, the method comprising steps of: providing an aperture stop between the second lens group and the fourth lens group; moving each lens group upon zooming from a wide-angle end state to a telephoto end state such that a distance between the second lens group and the third lens group varies, and a distance between the third lens group and the fourth lens group varies; moving aperture stop together with the third lens group upon zooming from the wide-angle end state to the telephoto end state; and satisfying the following conditional expressions (1) and (2):

1.20<f2/fw<2.50  (1)

−2.10<f3/fw<−0.80  (2)

where f2 denotes a focal length of the second lens group, f3 denotes a focal length of the third lens group, and fw denotes a focal length of the zoom lens system in the wide-angle end state.

According to a seventh aspect of the present invention, there is provided a method for zooming a zoom lens system including, in order from an object, a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group having negative refractive power, and a fourth lens group having positive refractive power, the method comprising steps of: providing an aperture stop between the second lens group and the fourth lens group; moving each lens group upon zooming from a wide-angle end state to a telephoto end state such that a distance between the second lens group and the third lens group varies, a distance between the third lens group and the fourth lens group varies; moving the aperture stop together with the third lens group upon zooming from the wide-angle end state to the telephoto end state; providing each of the second lens group, the third lens group, and the fourth lens group including at least one cemented lens; providing the cemented lens in the fourth lens group composed of, in order from the object, a positive lens cemented with a negative lens; providing the most image plane side lens surface being convex shape facing the image plane; and satisfying the following conditional expression (3):

−0.3<(d1w−d1t)/Ymax<0.17  (3)

where d1w denotes a distance between the most object side lens surface of the zoom lens system to the image plane in the wide-angle end state, d1t denotes a distance between the most object side lens surface of the zoom lens system to the image plane in the telephoto end state, and Ymax denotes the maximum image height.

According to a eighth aspect of the present invention, there is provided a method for zooming a zoom lens system including, in order from an object, a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group having negative refractive power, and a fourth lens group having positive refractive power, the method comprising steps of: varying a distance between the second lens group and the third lens group, and a distance between the third lens group and the fourth lens group upon zooming from a wide-angle end state to a telephoto end state; shifting the third lens group or a portion of the third lens group in a direction perpendicular to an optical axis as a vibration reduction lens group; and satisfying the following conditional expression (5):

0.12<(r2+r1)/(r2−r1)<1.30  (5)

where r1 denotes a radius of curvature of the object side of the vibration reduction lens group, and r2 denotes a radius of curvature of the image side of the vibration reduction lens group.

The present invention makes it possible to provide a zoom lens system having a vibration reduction function with excellent optical performance capable of correcting an image blur on the image plane caused by a camera shake with keeping a high zoom ratio.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing a lens configuration of a zoom lens system according to Example 1 of a first embodiment in a wide-angle end state.

FIGS. 2A and 2B are graphs showing various aberrations of the zoom lens system according to Example 1 of the first embodiment in the wide-angle end state upon focusing on infinity, and coma upon correcting rotational camera shake of 0.734 degrees, respectively.

FIG. 3 is graphs showing various aberrations of the zoom lens system according to Example 1 of the first embodiment in an intermediate focal length state upon focusing on infinity.

FIGS. 4A and 4B are graphs showing various aberrations of the zoom lens system according to Example 1 of the first embodiment in a telephoto end state upon focusing on infinity, and coma upon correcting rotational camera shake of 0.432 degrees, respectively.

FIG. 5 is a sectional view showing a lens configuration of a zoom lens system according to Example 2 of the first embodiment in the wide-angle end state.

FIGS. 6A and 6B are graphs showing various aberrations of the zoom lens system according to Example 2 of the first embodiment in the wide-angle end state upon focusing on infinity, and coma upon correcting rotational camera shake of 0.734 degrees, respectively.

FIG. 7 is graphs showing various aberrations of the zoom lens system according to Example 2 of the first embodiment in the intermediate focal length state upon focusing on infinity.

FIGS. 8A and 8B are graphs showing various aberrations of the zoom lens system according to Example 2 of the first embodiment in the telephoto end state upon focusing on infinity, and coma upon correcting rotational camera shake of 0.432 degrees, respectively.

FIG. 9 is a sectional view showing a lens configuration of a zoom lens system according to Example 3 of the first embodiment in the wide-angle end state.

FIGS. 10A and 10B are graphs showing various aberrations of the zoom lens system according to Example 3 of the first embodiment in the wide-angle end state upon focusing on infinity, and coma upon correcting rotational camera shake of 0.734 degrees, respectively.

FIG. 11 is graphs showing various aberrations of the zoom lens system according to Example 3 of the first embodiment in the intermediate focal length state upon focusing on infinity.

FIGS. 12A and 12B are graphs showing various aberrations of the zoom lens system according to Example 3 of the first embodiment in the telephoto end state upon focusing on infinity, and coma upon correcting rotational camera shake of 0.432 degrees, respectively.

FIG. 13 is a sectional view showing a lens configuration of a zoom lens system according to Example 4 of the first embodiment in the wide-angle end state.

FIGS. 14A and 14B are graphs showing various aberrations of the zoom lens system according to Example 4 of the first embodiment in the wide-angle end state upon focusing on infinity, and coma upon correcting rotational camera shake of 0.734 degrees, respectively.

FIG. 15 is graphs showing various aberrations of the zoom lens system according to Example 4 of the first embodiment in the intermediate focal length state upon focusing on infinity.

FIGS. 16A and 165 are graphs showing various aberrations of the zoom lens system according to Example 4 of the first embodiment in the telephoto end state upon focusing on infinity, and coma upon correcting rotational camera shake of 0.432 degrees, respectively.

FIG. 17 is a sectional view showing a lens configuration of a zoom lens system according to Example 5 of the first embodiment in the wide-angle end state.

FIGS. 18A and 18B are graphs showing various aberrations of the zoom lens system according to Example 5 of the first embodiment in the wide-angle end state upon focusing on infinity, and coma upon correcting camera shake, respectively.

FIG. 19 is graphs showing various aberrations of the zoom lens system according to Example 5 of the first embodiment in the intermediate focal length state upon focusing on infinity.

FIGS. 20A and 20B are graphs showing various aberrations of the zoom lens system according to Example 5 of the first embodiment in the telephoto end state upon focusing on infinity, and coma upon correcting camera shake, respectively.

FIG. 21 is a sectional view showing a lens configuration of a zoom lens system according to Example 6 of the first embodiment in the wide-angle end state.

FIGS. 22A and 22B are graphs showing various aberrations of the zoom lens system according to Example 6 of the first embodiment in the wide-angle end state upon focusing on infinity, and coma upon correcting camera shake, respectively.

FIG. 23 is graphs showing various aberrations of the zoom lens system according to Example 6 of the first embodiment in the intermediate focal length state upon focusing on infinity.

FIGS. 24A and 24B are graphs showing various aberrations of the zoom lens system according to Example 6 of the first embodiment in the telephoto end state upon focusing on infinity, and coma upon correcting camera shake, respectively.

FIG. 25 is a sectional view showing a lens configuration of a zoom lens system according to Example 7 of a second embodiment in the wide-angle end state.

FIGS. 26A and 26B are graphs showing various aberrations of the zoom lens system according to Example 7 of the second embodiment in the wide-angle end state upon focusing on infinity, and coma upon correcting camera shake, respectively.

FIG. 27 is graphs showing various aberrations of the zoom lens system according to Example 7 of the first embodiment in the intermediate focal length state upon focusing on infinity.

FIGS. 28A and 28B are graphs showing various aberrations of the zoom lens system according to Example 7 of the second embodiment in the telephoto end state upon focusing on infinity, and coma upon correcting camera shake, respectively.

FIG. 29 is a sectional view showing a lens configuration of a zoom lens system according to Example 8 of the second embodiment in the wide-angle end state.

FIGS. 30A and 30B are graphs showing various aberrations of the zoom lens system according to Example 8 of the second embodiment in the wide-angle end state upon focusing on infinity, and coma upon correcting camera shake, respectively.

FIG. 31 is graphs showing various aberrations of the zoom lens system according to Example 8 of the second embodiment in the intermediate focal length state upon focusing on infinity.

FIGS. 32A and 32B are graphs showing various aberrations of the zoom lens system according to Example 8 of the second embodiment in the telephoto end state upon focusing on infinity, and coma upon correcting camera shake, respectively.

FIG. 33 is a sectional view showing a lens configuration of a zoom lens system according to Example 9 of the second embodiment in the wide-angle end state.

FIGS. 34A and 34B are graphs showing various aberrations of the zoom lens system according to Example 9 of the second embodiment in the wide-angle end state upon focusing on infinity, and coma upon correcting camera shake, respectively.

FIG. 35 is graphs showing various aberrations of the zoom lens system according to Example 9 of the second embodiment in the intermediate focal length state upon focusing on infinity.

FIGS. 36A and 36B are graphs showing various aberrations of the zoom lens system according to Example 9 of the second embodiment in the telephoto end state upon focusing on infinity, and coma upon correcting camera shake, respectively.

FIG. 37 is a sectional view showing a lens configuration of a zoom lens system according to Example 10 of a third embodiment in the wide-angle end state.

FIGS. 38A and 38B are graphs showing various aberrations of the zoom lens system according to Example 10 of the third embodiment in the wide-angle end state upon focusing on infinity, and coma upon correcting camera shake, respectively.

FIG. 39 is graphs showing various aberrations of the zoom lens system according to Example 10 of the third embodiment in the intermediate focal length state upon focusing on infinity.

FIGS. 40A and 40B are graphs showing various aberrations of the zoom lens system according to Example 10 of the third embodiment in the telephoto end state upon focusing on infinity, and coma upon correcting camera shake, respectively.

FIG. 41 is a sectional view showing a lens configuration of a zoom lens system according to Example 11 of the third embodiment in the wide-angle end state.

FIGS. 42A and 42B are graphs showing various aberrations of the zoom lens system according to Example 11 of the third embodiment in the wide-angle end state upon focusing on infinity, and coma upon correcting camera shake, respectively.

FIG. 43 is graphs showing various aberrations of the zoom lens system according to Example 11 of the third embodiment in the intermediate focal length state upon focusing on infinity.

FIGS. 44A and 44B are graphs showing various aberrations of the zoom lens system according to Example 11 of the third embodiment in the telephoto end state upon focusing on infinity, and coma upon correcting camera shake, respectively.

FIG. 45 is a sectional view showing a lens configuration of a zoom lens system according to Example 12 of the third embodiment in the wide-angle end state.

FIGS. 46A and 46B are graphs showing various aberrations of the zoom lens system according to Example 12 of the third embodiment in the wide-angle end state upon focusing on infinity, and coma upon correcting camera shake, respectively.

FIG. 47 is graphs showing various aberrations of the zoom lens system according to Example 12 of the third embodiment in the intermediate focal length state upon focusing on infinity.

FIGS. 48A and 48B are graphs showing various aberrations of the zoom lens system according to Example 12 of the third embodiment in the telephoto end state upon focusing on infinity, and coma upon correcting camera shake, respectively.

FIG. 49 is a diagram showing an imaging apparatus (camera) equipped with the zoom lens system with a vibration reduction function according to Example 1 of the first embodiment.

A zoom lens system, an imaging apparatus, and a method for zooming the zoom lens system according to the first embodiment of the present application are explained.

The zoom lens system includes, in order from an object, a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group having negative refractive power, a fourth lens group having positive refractive power. An aperture stop is disposed between the second lens group and the fourth lens group. Upon zooming from a wide-angle end state to a telephoto end state, each lens group is moved such that a distance between the second lens group and the third lens group increases, and a distance between the third lens group and the fourth lens group decreases, and the aperture stop is moved together with the third lens group. The following conditional expressions (1) and (2) are satisfied:

1.20<f2/fw<2.50  (1)

−2.10<f3/fw<−0.80  (2)

where f2 denotes a focal length of the second lens group, f3 denotes a focal length of the third lens group, and fw denotes a focal length of the zoom lens system in the wide-angle end state.

The zoom lens system carries out vibration reduction by shifting the third lens group in a direction perpendicular to the optical axis.

Conditional expression (1) defines an appropriate range of refractive power of the second lens group. With satisfying conditional expression (1), the zoom lens system makes it possible to realize excellent optical performance, even upon performing vibration reduction with effectively securing a given zoom ratio.

When the value is equal to or falls below the lower limit of conditional expression (1), refractive power of the second lens group becomes too large, so that coma becomes worse. Moreover, decentered aberration upon vibration reduction, in other words, coma or astigmatism become worse.

In order to secure the effect of the present invention, it is preferable to set the lower limit of conditional expression (1) to 1.30.

On the other hand, when the value is equal to or exceeds the upper limit of conditional expression (1), refractive power of the second lens group becomes too small, so that moving amount of each lens group upon zooming increases. Accordingly, it becomes difficult to correct curvature of field and chromatic aberration upon zooming from a wide-angle end state to a telephoto end state.

In order to secure the effect of the present invention, it is preferable to set the upper limit of conditional expression (1) to 1.80.

Conditional expression (2) defines refractive power of the third lens group. In the present zoom lens system, with satisfying conditional expression (2), it becomes possible to realize excellent optical performance even upon performing vibration reduction with effectively securing a given zoom ratio.

When the value is equal to or falls below the lower limit of conditional expression (2), refractive power of the third lens group becomes too small, so that moving amount of the third lens group upon zooming becomes large. Accordingly, variation in curvature of field upon zooming becomes large, so that it becomes difficult to correct this.

On the other hand, when the value is equal to or exceeds the upper limit of conditional expression (2), refractive power of the third lens group becomes too large, so that spherical aberration becomes worse. Moreover, decentered aberration upon vibration reduction such as coma and astigmatism become worse.

In order to secure the effect of the present invention, it is preferable to set the upper limit of conditional expression (2) to −1.50. In order to secure the effect of the present invention, it is preferable to set the lower limit of conditional expression (2) to −2.00.

As described above in the present zoom lens system, an aperture stop is disposed between the second lens group and the fourth lens group, and moved together with the third lens group upon zooming from a wide-angle end state to a telephoto end state.

With this construction, it becomes possible to correct off-axis coma with good balance upon zooming, and to realize excellent optical performance.

In the present zoom lens system, it is preferable that the third lens group has a cemented lens.

With this configuration, it becomes possible to excellently correct variation in lateral chromatic aberration upon zooming.

In the present zoom lens system, it is preferable that the fourth lens group is composed of, in order from an image side, a cemented lens constructed by a negative lens and a positive lens, and a single lens having positive refractive power.

With this configuration, it becomes possible to excellently correct lateral chromatic aberration and spherical aberration with securing sufficient space between the third lens group and the fourth lens group. Moreover, with constructing the third lens group to be a vibration reduction lens group, it becomes possible to excellently correct coma and astigmatism upon vibration reduction.

In the present zoom lens system, it is preferable that each of the second lens group, the third lens group and the fourth lens group has at least one cemented lens.

With this configuration, it becomes possible to excellently correct variation in lateral chromatic aberration upon zooming.

In the present zoom lens system, it is preferable that the first lens group moves at first to the image side then to the object side upon zooming from the wide-angle end state to the telephoto end state.

With this configuration, the present zoom lens system makes it possible to become compact and have a high zoom ratio.

The present zoom lens system preferably satisfies the following conditional expression (3):

−0.3<(d1w−d1t)/Ymax<0.17  (3)

where d1w denotes a distance between the most object side lens surface of the zoom lens system to the image plane in the wide-angle end state, d1t denotes a distance between the most object side lens surface of the zoom lens system to the image plane in the telephoto end state, and Ymax denotes the maximum image height.

Conditional expression (3) defines moving condition of the first lens group upon zooming from the wide-angle end state to the telephoto end state. With satisfying conditional expression (3), the present zoom lens system makes it possible to realize excellent optical performance and compactness with effectively securing a given zoom ratio.

When the value is equal to or falls below the lower limit of conditional expression (3), moving amount of the first lens group having large refractive power upon zooming becomes too large, so that it becomes impossible to excellently correct spherical aberration from the wide-angle end state to the telephoto end state.

In order to secure the effect of the present invention, it is preferable to set the lower limit of conditional expression (3) to −0.15.

On the other hand, when the value is equal to or exceeds the upper limit of conditional expression (3), moving amounts of the second lens group and the third lens group become small, so that refractive power of the second lens group and the third lens group becomes too large, and spherical aberration becomes worse. Moreover, decentered aberration upon vibration reduction, in other words, coma and astigmatism become worse.

In order to secure the effect of the present invention, it is preferable to set the upper limit of conditional expression (3) to 0.05.

In the present zoom lens system, it is preferable that the most image side lens surface of the zoom lens system has a convex shape facing the image.

With this configuration, it becomes possible to reduce ghost images by the reflection light from the image plane.

Moreover, the zoom lens system comprises, in order from an object: a first lens group having negative refractive power; a second lens group having positive refractive power; a third lens group having negative refractive power; and a fourth lens group having positive refractive power. An aperture stop is disposed between the second lens group and the fourth lens group. Upon zooming from a wide-angle end state to a telephoto end state, the first lens group is moved at first to an image side and then to the object side, each lens group is moved such that a distance between the second lens group and the third lens group increases, and a distance between the third lens group and the fourth lens group decreases, the aperture stop is moved together with the third lens group. Each of the second lens group, the third lens group, and the fourth lens group has at least one cemented lens. The cemented lens in the fourth lens group is composed of, in order from the object, a positive lens and a negative lens. The most image side lens surface of the zoom lens system is a convex shape facing the image, and the following conditional expression (3) is satisfied:

−0.3<(d1w−d1t)/Ymax<0.17  (3)

where d1w denotes a distance between the most object side lens surface of the zoom lens system to the image plane in the wide-angle end state, d1t denotes a distance between the most object side lens surface of the zoom lens system to the image plane in the telephoto end state, and Ymax denotes the maximum image height.

As described above, in the present zoom lens system, upon zooming from the wide-angle end state to the telephoto end state, the first lens group is moved at first to the image and then to the object. With this configuration, it becomes possible to make the zoom lens system compact and to realize a high zoom ratio.

As described above, in the present zoom lens system, upon zooming from the wide-angle end state to the telephoto end state, the aperture stop is moved together with the third lens group. With this configuration, it becomes possible to correct off-axis coma upon zooming with good balance, and to realize excellent optical performance.

As described above, in the present zoom lens system, each of the second lens group, the third lens group, and the fourth lens group has at least one cemented lens. With this configuration, it becomes possible to excellently correct variation in lateral chromatic aberration upon zooming.

As described above, in the present zoom lens system, the fourth lens group is composed of, in order from the image side, a cemented lens constructed by a negative lens cemented with a positive lens, and a single lens having positive refractive power. With this configuration, it becomes possible to excellently correct lateral chromatic aberration, spherical aberration and coma with securing sufficient space between the third lens group and the fourth lens group. Moreover, with constructing the third lens group as the vibration reduction lens group, it becomes possible to excellently correct coma and astigmatism upon vibration reduction.

As described above, in the present zoom lens system, the most image side lens surface of the zoom lens system has a convex shape facing the image. With this configuration it becomes possible to reduce ghost images by the reflection light from the image plane.

Regarding conditional expression (3), explanation is the same as described above, so that duplicated explanation is omitted.

In the present zoom lens system, the following conditional expression (4) is preferably satisfied:

0.72<f2/(−f3)<1.5  (4)

where f2 denotes a focal length of the second lens group, and f3 denotes a focal length of the third lens group.

Conditional expression (4) suitably defines refractive power of the second lens group and refractive power of the third lens group. In the present zoom lens system, with satisfying conditional expression (4), it becomes possible to realize excellent optical performance.

When the value is equal to or falls below the lower limit of conditional expression (4), refractive power of the second lens group becomes too large, so that it becomes impossible to excellently correct coma upon zooming.

In order to secure the effect of the present invention, it is preferable to set the lower limit of conditional expression (4) to 0.75.

On the other hand, when the value is equal to or exceeds the upper limit of conditional expression (4), absolute value of refractive power of the third lens group becomes too large, so that it becomes difficult to excellently correct spherical aberration with realizing a high zoom ratio.

In order to secure the effect of the present invention, it is preferable to set the upper limit of conditional expression (4) to 1.1.

The present imaging apparatus is equipped with the zoom lens system described above.

With this construction, it becomes possible to realize an imaging apparatus having excellent optical performance with a high zoom ratio.

A method for zooming the present zoom lens system comprising, in order from an object, a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group having negative refractive power, and a fourth lens group having positive refractive power; the method comprising steps of: providing an aperture stop between the second lens group and the fourth lens group; moving each lens group such that a distance between the second lens group and the third lens group increases, a distance between the third lens group and the fourth lens group decreases upon zooming from a wide-angle end state to a telephoto end state; moving the aperture stop together with the third lens group upon zooming from the wide-angle end state to the telephoto end state; and satisfying the following conditional expressions (1) and (2):

1.20<f2/fw<2.50  (1)

−2.10<f3/fw<−0.80  (2)

where f2 denotes a focal length of the second lens group, f3 denotes a focal length of the third lens group, and fw denotes a focal length of the zoom lens system in the wide-angle end state.

With this configuration, the zoom lens system makes it possible to realize excellent optical performance and a high zoom ratio.

A method for zooming the zoom lens system comprising, in order from an object, a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group having negative refractive power, and a fourth lens group having positive refractive power, each of the second lens group, third lens group, and the fourth lens group including at least one cemented lens, the cemented lens in the fourth lens group composed of, in order from the object, a positive lens and a negative lens, and the most image side lens surface of the zoom lens system having a convex shape facing the image; the method comprising steps of: providing an aperture stop between the second lens group and the fourth lens group; moving the first lens group at first to an image side then to the object side, the aperture stop together with the third lens group, and each lens group such that a distance between the second lens group and the third lens group increases, and a distance between the third lens group and the fourth lens group decreases upon zooming from a wide-angle end state to a telephoto end state; and satisfying the following conditional expression (3):

−0.3<(d1w−d1t)/Ymax<0.17  (3)

where d1w denotes a distance between the most object side lens surface of the zoom lens system to the image plane in the wide-angle end state, d1t denotes a distance between the most object side lens surface of the zoom lens system to the image plane in the telephoto end state, and Ymax denotes the maximum image height.

With this configuration, it becomes possible to realize excellent optical performance and a high zoom ratio.

A zoom lens system according to each numerical example of the first embodiment is explained below with reference to accompanying drawings.

FIG. 1 is a sectional view showing a lens configuration of a zoom lens system according to Example 1 of a first embodiment in a wide-angle end state.

The zoom lens system according to Example 1 is composed of, in order from an object, a first lens group G1 having negative refractive power, a second lens group G2 having positive refractive power, a third lens group G3 having negative refractive power, and a fourth lens group G4 having positive refractive power.

The first lens group G1 is composed of, in order from the object, a negative meniscus lens L11 having a convex surface facing the object, and a cemented lens constructed by a negative meniscus lens L12 having a convex surface facing the object cemented with a positive meniscus lens L13 having a convex surface facing the object. The negative meniscus lens L11 is an aspherical lens on which an aspherical surface is formed by forming a resin layer on the image side glass surface.

The second lens group G2 is composed of, in order from the object, a double convex positive lens L21, and a cemented lens constructed by a double convex positive lens L22 cemented with a double concave negative lens L23.

The third lens group G3 is composed of a cemented lens constructed by, in order from the object, a positive meniscus lens L31 having a concave surface facing the object cemented with a double concave negative lens L32.

The fourth lens group G4 is composed of, in order from the object, a positive meniscus lens L41 having a concave surface facing the object, and a cemented lens constructed by a double convex positive lens L42 cemented with a negative meniscus lens L43 having a convex surface facing to the image.

In the zoom lens system according to Example 1, upon zooming from the wide-angle end state to the telephoto end state, the first lens group G1 is moved at first to the image side and then to the object side, and the second lens group G2, the third lens group G3, and the fourth lens group G4 are moved to the object such that a distance between the second lens group G2 and the third lend group G3 increases, and a distance between the third lens group G3 and the fourth lens group G4 decreases.

The aperture stop S is disposed between the second lens group G2 and the third lens group G3, and is moved together with the third lens group G3 upon zooming from the wide-angle end state to the telephoto end state.

In the zoom lens system according to Example 1, image plane correction upon occurring an image blur is carried out by shifting the third lens group G3 in a direction perpendicular to the optical axis.

Various values associated with the zoom lens system according to Example 1 of the present application are listed in Table 1.

In [Specifications], f denotes a focal length, FNO denotes an f-number, W denotes a wide-angle end state, M denotes an intermediate focal length state, T denotes a telephoto end state.

In [Lens Data], the first column “N” shows the lens surface number counted in order from the object side, the second column “r” shows a radius of curvature of each lens surface, the third column “d” shows a distance to the next surface, the fourth column “νd” shows an Abbe number of the lens material at d-line (wavelength λ=587.6 nm), and the fifth column “nd” shows a refractive index of the lens material at d-line (wavelength λ=587.6 nm). Moreover, r=0.0000 denotes a plane surface. Refractive index of the air nd=1.000000 is omitted from the Lens Data, and Bf denotes a back focal length.

In [Aspherical Data], aspherical coefficients when the aspherical surface is exhibited by the following expression are shown:

x=(h2/r)/[1+[1−κ(h2/r2)]1/2]+C4×h4+C6×h6+C8×h8+C10×h10

where h denotes a vertical height from the optical axis, x denotes a sag amount which is a distance along the optical axis from the tangent surface at the vertex of the aspherical surface to the aspherical surface at the vertical height h from the optical axis, r denotes a radius of curvature of a reference sphere (paraxial radius of curvature), κ denotes a conical coefficient, C4, C6, C8, C10 denote aspherical coefficients.

“E-n” (n: integer) denotes “×10−n”, for example, “1.234E-05” means “1.234×10−5”.

In [Variable Distances], a focal length f, and each variable distance are shown.

In the tables for various values, “mm” is generally used for the unit of length such as a focal length f, a radius of curvature r, a surface distance d and the like. However, since similar optical performance can be obtained by an optical system proportionally enlarged or reduced its dimension, the unit is not necessarily to be limited to “mm”, and any other suitable unit can be used. The explanation of reference symbols is the same in the other Examples, so that duplicated explanations are omitted.

In a zoom lens system having a focal length of f, a vibration reduction coefficient, which is a ratio of a moving amount of an image on the image plane I to that of the vibration reduction lens group perpendicularly to the optical axis upon correcting a camera shake, of K, in order to correct rotational camera shake of an angle of 8, the vibration reduction lens group for correcting the camera shake may be moved by the amount of (f·tan θ)/K perpendicularly to the optical axis.

In the wide-angle end state (W) in Example 1, the vibration reduction coefficient K is 1.321, and the focal length is 18.5 (mm), so that the moving amount of the third lens group G3 for correcting a rotational camera shake of 0.734 degrees is 0.179 (mm). In the telephoto end state (T), the vibration reduction coefficient K is 2.2, and the focal length is 53.4 (mm), so that the moving amount of the third lens group G3 for correcting a rotational camera shake of 0.432 degrees is 0.183 (mm).

TABLE 1 [Specifications]

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