CN102346293B

CN102346293B - Zoom lens, optical device and the method for the manufacture of zoom lens

Info

Publication number: CN102346293B
Application number: CN201110220267.8A
Authority: CN
Inventors: 小滨昭彦; 横井规和; 田中一政
Original assignee: Nikon Corp
Current assignee: Nikon Corp
Priority date: 2010-07-30
Filing date: 2011-08-01
Publication date: 2015-12-09
Anticipated expiration: 2031-08-01
Also published as: CN102346293A

Abstract

A kind of zoom lens, to comprise along the order of optical axis from thing: the first lens combination G1 with positive refraction focal power, the second lens combination G2 with negative refractive power and have the 3rd lens combination G3 of positive refraction focal power.From wide-angle side state W to dolly-out, dolly-back end state T zoom time, distance between the first lens combination G1 and the second lens combination G2 increases, and the distance between the second lens combination G2 and the 3rd lens combination G3 reduces.Meet the condition provided.Therefore, provide and there is high optical property and suppress the zoom lens of change on aberration, be equipped with the optical device of zoom lens and the method for the manufacture of zoom lens.

Description

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

The disclosures of the following priority applications are hereby incorporated by reference:

japanese laid-open patent application No.2010-171323 filed on 30/7/2010;

japanese laid-open patent application No.2010-171324 filed on 30/7/2010;

japanese laid-open patent application No.2010-171336 filed on 30/7/2010;

japanese published patent application No.2010-097333, filed on 25/4/2011;

japanese published patent application No.2011-151892 filed on 8/7/2011;

japanese published patent application No.2011-151899, filed on 8/7/2011; and

japanese published patent application No.2011-151906, filed on 8/7/2011.

Technical Field

The invention relates to a zoom lens, an optical apparatus equipped with the zoom lens, and a method for manufacturing the zoom lens.

Background

Various zoom lenses having a lens group with positive refractive power arranged to the most object side have been proposed (for example, see japanese laid-open patent application No. 2008-. With such a zoom lens, the demand for suppressing ghost images and flare, which deteriorate optical performance, and aberrations becomes stronger. Therefore, high optical performance is required for the antireflection coating applied to the lens surface, and thus in order to meet such requirements, multilayer design techniques and multilayer coating techniques are continuously developed (see, for example, japanese laid-open patent application No. 2000-356704).

When the conventional zoom lens is forcibly made to have a high zoom ratio, variation in aberrations increases, and thus sufficiently high optical performance cannot be obtained. In addition, there are the following problems: reflected light that produces ghost images and flare is easily generated from optical surfaces in such a zoom lens.

Disclosure of Invention

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a zoom lens which has good optical performance and suppresses variations in various aberrations as well as ghost images and flare, an optical apparatus equipped with the zoom lens, and a method of manufacturing the zoom lens.

According to a first aspect of the present invention, there is provided a zoom lens including, in order from an object along an optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power, a distance between the first lens group and the second lens group increasing and a distance between the second lens group and the third lens group decreasing upon zooming from a wide-angle end state to a telephoto end state, the first lens group including a positive lens a satisfying the following conditional expression (1):

85.0＜νdA(1)

wherein ν dA denotes an abbe number at d-line of a material of the positive lens a in the first lens group, and

the following conditional expression (2) is satisfied:

3.90＜f1/fw＜11.00(2)

where fw denotes a focal length of the zoom lens in the wide-angle end state, and f1 denotes a focal length of the first lens group.

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

According to a third aspect of the present invention, there is provided a zoom lens including, in order from an object along an optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power, 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 increasing, and a distance between the second lens group and the third lens group decreasing, the zoom lens including a positive lens a' satisfying the following conditional expressions (14) and (15):

1.540＜ndA’(14)

66.5＜νdA’(15)

wherein ndA 'represents a refractive index of the material of the positive lens a', and ν dA 'represents an abbe number of the material of the positive lens a', and the following conditional expression (2) is satisfied:

3.90＜f1/fw＜11.00(2)

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

According to a fifth aspect of the present invention, there is provided a zoom lens comprising, in order from an object along an optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power, a distance between the first lens group and the second lens group increasing and a distance between the second lens group and the third lens group decreasing upon zooming from a wide-angle end state to a telephoto end state, the first lens group comprising a plurality of positive lenses a ″ satisfying the following conditional expression (22):

66.5< vd when 1.540 ≦ ndA ″.

When ndA "< 1.540, 75.0< ν dA" (22)

Wherein ndA 'represents a refractive index at a d-line of a material of each of the plurality of positive lenses in the first lens group, ν dA represents an Abbe's number at a d-line of a material of each of the plurality of positive lenses in the first lens group, and

the following conditional expressions (23) and (3) are satisfied:

4.75＜f1/fw＜11.0(23)

0.28＜f1/ft＜0.52(3)

where fw denotes a focal length of the zoom lens in the wide-angle end state, ft denotes a focal length of the zoom lens in the telephoto end state, and f1 denotes a focal length of the first lens group.

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

According to a seventh aspect of the present invention, there is provided a method for manufacturing a zoom lens including, in order from an object side along an optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power, the method comprising the steps of: movably arranging the first lens group, the second lens group, and the third lens group such that a distance between the first lens group and the second lens group increases and a distance between the second lens group and the third lens group decreases; a positive lens a satisfying the following conditional expression (1) is arranged:

85.0＜νdA(1)

wherein ν dA denotes an abbe number at a d-line of a material of the positive lens a in the first lens group; and, each lens is arranged satisfying the following conditional expression (2):

3.90＜f1/fw＜11.00(2)

According to an eighth aspect of the present invention, there is provided a method for manufacturing a zoom lens including, in order from an object side along an optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power, the method comprising the steps of: movably arranging the first lens group, the second lens group, and the third lens group such that a distance between the first lens group and the second lens group increases and a distance between the second lens group and the third lens group decreases; a positive lens a' satisfying the following conditional expressions (14) and (15) is arranged:

1.540＜ndA’(14)

66.5＜νdA’(15)

wherein ndA 'represents a refractive index of a material of the positive lens A', and ν dA 'represents an Abbe number of the material of the positive lens A', and

each lens is arranged satisfying the following conditional expression (2):

3.90＜f1/fw＜11.00(2)

According to a ninth aspect of the present invention, there is provided a method for manufacturing a zoom lens including, in order from an object side along an optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power, the method comprising the steps of: movably arranging the first lens group, the second lens group, and the third lens group such that a distance between the first lens group and the second lens group increases and a distance between the second lens group and the third lens group decreases; arranging a plurality of positive lenses a ″ that satisfy the following conditional expression (22):

66.5< vd when 1.540 ≦ ndA ″.

When ndA "< 1.540, 75.0< ν dA" (22)

Wherein ndA 'represents a refractive index at a d-line of a material of each of the plurality of positive lenses in the first lens group, and ν dA' represents an Abbe number at the d-line of the material of each of the plurality of positive lenses in the first lens group; and, the following conditional expressions (23) and

(3) arranging each lens:

4.75＜f1/fw＜11.0(23)

0.28＜f1/ft＜0.52(3)

The present invention makes it possible to provide a zoom lens that has good optical performance and suppresses variations in various aberrations as well as ghost images and flare, an optical apparatus equipped with the zoom lens, and a method of manufacturing the zoom lens.

Drawings

Fig. 1 is a sectional view showing a lens configuration of a zoom lens according to example 1 of the first embodiment and example 4 of the second embodiment of the present application.

Fig. 2A, 2B, and 2C are graphs showing various aberrations of the zoom lens according to example 1 of the first embodiment and example 4 of the second embodiment, in which fig. 2A is a wide-angle end state, fig. 2B is an intermediate focal length state, and fig. 2C is a telephoto end state, upon focusing on an object at infinity.

Fig. 3 is a sectional view showing a lens configuration of a lens system according to example 1 of the first embodiment and example 4 of the second embodiment, and is an explanatory view in which light rays reflected from a first ghost-generating surface are reflected by a second ghost-generating surface.

Fig. 4 is a sectional view showing a lens configuration of a zoom lens according to example 2 of the first embodiment of the present application.

Fig. 5A, 5B, and 5C are graphs showing various aberrations of the zoom lens according to example 2 of the first embodiment, in which fig. 5A is a wide-angle end state, fig. 5B is an intermediate focal length state, and fig. 5C is a telephoto end state.

Fig. 6 is a sectional view showing a lens configuration of a zoom lens according to example 3 of the first embodiment and example 8 of the second embodiment of the present application.

Fig. 7A, 7B, and 7C are graphs showing various aberrations of the zoom lens according to example 3 of the first embodiment and example 8 of the second embodiment, in which fig. 7A is a wide-angle end state, fig. 7B is an intermediate focal length state, and fig. 7C is a telephoto end state, upon focusing on an object at infinity.

Fig. 8 is a sectional view showing a lens configuration of a zoom lens according to example 5 of the second embodiment and example 10 of the third embodiment of the present application.

Fig. 9A, 9B, and 9C are graphs showing various aberrations of the zoom lenses according to example 5 of the second embodiment and example 10 of the third embodiment, in which fig. 9A is the wide-angle end state, fig. 9B is the intermediate focal length state, and fig. 9C is the telephoto end state, upon focusing on an object at infinity.

Fig. 10 is a sectional view showing a lens configuration of a zoom lens according to example 6 of the second embodiment and example 11 of the third embodiment of the present application.

Fig. 11A, 11B, and 11C are graphs showing various aberrations of the zoom lenses according to example 6 of the second embodiment and example 11 of the third embodiment, when focusing on an object at infinity, wherein fig. 11A is the wide-angle end state, fig. 11B is the intermediate focal length state, and fig. 11C is the telephoto end state.

Fig. 12 is a sectional view showing a lens configuration of a zoom lens according to example 7 of the second embodiment and example 9 of the third embodiment of the present application.

Fig. 13A, 13B, and 13C are graphs showing various aberrations of the zoom lenses according to example 7 of the second embodiment and example 9 of the third embodiment, in which fig. 13A is the wide-angle end state, fig. 13B is the intermediate focal length state, and fig. 13C is the telephoto end state, upon focusing on an object at infinity.

Fig. 14 is a sectional view showing a lens configuration of a lens system according to example 9 of the third embodiment, and is an explanatory view in which the second ghost generation surface reflects light rays reflected from the first ghost generation surface.

Fig. 15 is a sectional view showing a lens configuration of a zoom lens according to example 12 of the third embodiment of the present application.

Fig. 16A, 16B, and 16C are graphs showing various aberrations of the zoom lens according to example 12 of the third embodiment, in which fig. 16A is the wide-angle end state, fig. 16B is the intermediate focal length state, and fig. 16C is the telephoto end state.

Fig. 17 is an explanatory view of the configuration of the antireflection coating according to the present application.

Fig. 18 is a graph showing the spectral reflectance of the anti-reflection coating according to the present embodiment.

Fig. 19 is a graph showing the spectral reflectance of the anti-reflection coating according to the variation of the present application.

Fig. 20 is a graph relating incident angles according to spectral reflectances of the antireflection coatings in the modified forms.

Fig. 21 is a graph showing the spectral reflectance of the anti-reflection coating according to the conventional example.

Fig. 22 is a graph showing incidence angle dependence of spectral reflectance of the anti-reflection coating according to the conventional example.

Fig. 23 is a diagram showing a configuration of a camera equipped with the zoom lens according to example 1 of the first embodiment.

Fig. 24 is a flowchart schematically describing a method for manufacturing a zoom lens according to the first embodiment.

Fig. 25 is a flowchart schematically describing a method for manufacturing a zoom lens according to the second embodiment.

Fig. 26 is a flowchart schematically describing a method for manufacturing a zoom lens according to the third embodiment.

Detailed Description

(first embodiment)

A zoom lens according to a first embodiment of the present application is described below.

A zoom lens according to a first embodiment of the present application includes, in order from an object side along an optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power. 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 increases, and a distance between the second lens group and the third lens group decreases. With this configuration, it becomes possible to realize an optical system capable of zooming while suppressing variation in distortion generated upon zooming.

In a zoom lens according to the first embodiment, the first lens group includes a positive lens a satisfying the following conditional expression (1), and satisfies the following conditional expression (2):

85.0＜νdA(1)

3.90＜f1/fw＜11.00(2)

where ν dA denotes an abbe number at a d-line (wavelength λ 587.6nm) of the positive lens a in the first lens group, fw denotes a focal length of the zoom lens in the wide-angle end state, and f1 denotes a focal length of the first lens group.

Conditional expression (1) defines an optimum abbe number of the positive lens a in the first lens group, and is for achieving high optical performance and suppressing variation in chromatic aberration generated upon zooming from the wide-angle end state to the telephoto end state.

When the value ν dA is equal to or smaller than the lower limit of the conditional expression (1), it becomes difficult to suppress variations in longitudinal chromatic aberration and lateral chromatic aberration. The material becomes a material having small anomalous dispersion, so that it becomes difficult to suppress variations in second-order chromatic aberration. In addition, longitudinal chromatic aberration and lateral chromatic aberration in the visible light range become large in the telephoto end state, and thus high optical performance cannot be obtained.

Conditional expression (2) defines an appropriate range of the focal length of the first lens group, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming from the wide-angle end state to the telephoto end state.

When the ratio f1/fw is equal to or smaller than the lower limit of conditional expression (2), refractive power of the first lens group becomes strong, and therefore it becomes difficult to suppress variations in transverse chromatic aberration and off-axis aberration, particularly astigmatism. Therefore, high optical performance cannot be obtained.

On the other hand, when the ratio f1/fw is equal to or exceeds the upper limit of conditional expression (2), refractive power of the first lens group becomes weak, and therefore, in order to obtain a given zoom ratio, the moving amount of the first lens group with respect to the image plane must be increased. As a result, variation in height with respect to the optical axis of off-axis rays passing through the first lens group becomes large, and therefore it becomes difficult to suppress variation in lateral chromatic aberration and off-axis aberration, particularly astigmatism. Therefore, high optical performance cannot be obtained.

In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (2) to 4.75. In order to further secure the effect of the present embodiment, it is most preferable to set the lower limit of conditional expression (2) to 5.10.

In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (2) to 8.80. In order to further secure the effect of the present embodiment, it is most preferable to set the upper limit of conditional expression (2) to 7.60.

In the zoom lens according to the first embodiment, the following conditional expression (3) is preferably satisfied:

0.28＜f1/ft＜0.52(3)

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

Conditional expression (3) defines an appropriate range of the optimum focal length of the first lens group, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming from the wide-angle end state to the telephoto end state.

When the ratio f1/ft is equal to or smaller than the lower limit of conditional expression (3), refractive power of the first lens group becomes strong, and therefore it becomes difficult to suppress variations in longitudinal chromatic aberration and spherical aberration. Therefore, high optical performance cannot be obtained.

On the other hand, when the ratio f1/ft is equal to or exceeds the upper limit of conditional expression (3), refractive power of the first lens group becomes weak, and the moving amount of the first lens group with respect to the image plane must be increased in order to obtain a given zoom ratio. As a result, variation in height with respect to the optical axis of off-axis rays passing through the first lens group becomes large, and therefore it becomes difficult to suppress variation in lateral chromatic aberration and off-axis aberration, particularly astigmatism. Therefore, high optical performance cannot be obtained.

In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (3) to 0.31.

In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (3) to 0.48. To further secure the effect of the present embodiment, it is most preferable to set the upper limit of conditional expression (3) to 0.44.

In the zoom lens according to the first embodiment, the following conditional expression (4) is preferably satisfied:

0.25＜Δ1/f1＜1.10(4)

where Δ 1 denotes a moving amount of the first lens group with respect to the image plane upon zooming from the wide-angle end state to the telephoto end state.

Conditional expression (4) defines an optimum moving amount of the first lens group with respect to the image plane upon zooming from the wide-angle end state to the telephoto end state, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming.

When the ratio Δ 1/f1 is equal to or smaller than the lower limit of conditional expression (4), the moving amount of the first lens group with respect to the image plane becomes small, and therefore refractive power of the first lens group must be large in order to obtain a given zoom ratio. As a result, upon zooming from the wide-angle end state to the telephoto end state, variation in refractive power corresponding to variation in height with respect to the optical axis of off-axis rays passing through the first lens group becomes large, and thus it becomes difficult to suppress variation in lateral chromatic aberration and off-axis aberration, particularly astigmatism. Therefore, high optical performance cannot be obtained.

On the other hand, when the ratio Δ 1/f1 is equal to or exceeds the upper limit of conditional expression (4), the moving amount of the first lens group with respect to the image plane becomes large, so upon zooming from the wide-angle end state to the telephoto end state, the variation in height with respect to the optical axis of the off-axis ray passing through the first lens group becomes large. As a result, it becomes difficult to suppress variations in lateral chromatic aberration and off-axis aberration, particularly astigmatism. Therefore, high optical performance cannot be obtained.

In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (4) to 0.36. In order to further secure the effect of the present embodiment, it is most preferable to set the lower limit of conditional expression (4) to 0.48.

In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (4) to 0.95.

In the zoom lens according to the first embodiment, the following conditional expression (5) is preferably satisfied:

0.65＜f1A/f1＜1.75(5)

where f1A denotes the focal length of the positive lens a in the first lens group.

Conditional expression (5) defines the optimum focal length of the positive lens a in the first lens group, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming.

When the ratio f1A/f1 is equal to or less than the lower limit of conditional expression (5), refractive power of the positive lens a becomes strong, and therefore, upon zooming from the wide-angle end state to the telephoto end state, a variation in refractive power corresponding to a variation in height of off-axis rays passing through the positive lens a becomes large. As a result, it becomes difficult to suppress variations in lateral chromatic aberration and off-axis aberration, particularly astigmatism, and therefore high optical performance cannot be obtained.

On the other hand, when the ratio f1A/f1 is equal to or exceeds the upper limit of conditional expression (5), the refractive power of the positive lens a becomes weak, the positive refractive power of the positive lens a in the first lens group other than the positive lens a becomes strong, and therefore, upon zooming from the wide-angle end state to the telephoto end state, the variation in refractive power corresponding to the variation in height of the off-axis rays passing through the positive lens a becomes large. As a result, it becomes difficult to suppress variations in lateral chromatic aberration and off-axis aberration, particularly astigmatism, and therefore high optical performance cannot be obtained.

In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (5) to 0.80.

In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (5) to 1.35.

In the zoom lens according to the first embodiment, the following conditional expression (6) is preferably satisfied:

wherein,an effective diameter (effective diameter) of the positive lens a in the first lens group is indicated.

Conditional expression (6) defines an optimum effective diameter of the positive lens a in the first lens group, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming.

When ratio ofEqual to or less than the lower limit of conditional expression (6), upon zooming from the wide-angle end state to the telephoto end state, variation in height with respect to the optical axis of off-axis rays passing through the positive lens a in the first lens group becomes small. As a result, it becomes difficult to suppress variations in off-axis aberrations, particularly astigmatism, and therefore high optical performance cannot be obtained.

On the other hand, when the ratio isEqual to or exceeding the upper limit of conditional expression (6), upon zooming from the wide-angle end state to the telephoto end state, variation in height with respect to the optical axis of off-axis rays passing through the positive lens a in the first lens group becomes large. As a result, it becomes difficult to suppress variations in lateral chromatic aberration and off-axis aberration, particularly astigmatism, and therefore high optical performance cannot be obtained.

In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (6) to 2.45.

In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (6) to 3.80.

In the zoom lens according to the first embodiment, the first lens group preferably includes a positive lens B satisfying the following conditional expression (7):

1.580＜ndB(7)

where ndB denotes a refractive index at a d-line (wavelength λ 587.6nm) of the material of the positive lens B in the first lens group.

Conditional expression (7) defines the optimum refractive index of the material of the positive lens B in the first lens group, and is for achieving high optical performance and suppressing variation in off-axis aberration generated upon zooming.

When the value ndB is equal to or smaller than the lower limit of conditional expression (7), the curvature of the surface of the positive lens B becomes strong, and therefore, upon zooming from the wide-angle end state to the telephoto end state, a variation in the deflection angle corresponding to a variation in height with respect to the optical axis of off-axis rays passing through the positive lens B becomes large. As a result, it becomes difficult to suppress variations in off-axis aberrations, particularly astigmatism, and therefore high optical performance cannot be obtained.

In the zoom lens according to the first embodiment, the first lens group preferably includes a positive lens B satisfying the following conditional expression (8):

40.0＜νdB＜66.5(8)

where ν dB denotes an abbe number at a d-line (wavelength λ 587.6nm) of the material of the positive lens B in the first lens group.

Conditional expression (8) defines the optimum abbe number of the material of the positive lens B in the first lens group, and is for achieving high optical performance and suppressing variation in chromatic aberration generated upon zooming.

When the value ν dB is equal to or smaller than the lower limit of conditional expression (8), the dispersion of the material of the positive lens B becomes large, and therefore, upon zooming from the wide-angle end state to the telephoto end state, the variation in dispersion corresponding to the variation in height with respect to the optical axis of the off-axis ray passing through the positive lens B becomes large. As a result, it becomes difficult to suppress the variation in lateral chromatic aberration, and therefore, high optical performance cannot be obtained.

On the other hand, when the value ν dB is equal to or exceeds the upper limit of conditional expression (8), the dispersion of the material of the positive lens B becomes small, and therefore when a negative lens is included in the first lens group, correction of chromatic aberration becomes excessively large. As a result, it becomes difficult to suppress the variation in lateral chromatic aberration. When the negative lens is not included in the first lens group, since chromatic aberration still exists, it becomes difficult to suppress variation in chromatic aberration, and therefore, high optical performance cannot be obtained. Therefore, in either case, high optical performance cannot be achieved.

In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (8) to 49.0.

In the zoom lens according to the first embodiment, the following conditional expression (9) is preferably satisfied:

0.65＜f1B/f1＜1.75(9)

where f1B denotes the focal length of the positive lens B in the first lens group.

Conditional expression (9) defines the optimum focal length of the positive lens B in the first lens group.

When the ratio f1B/f1 is equal to or less than the lower limit of conditional expression (9), refractive power of the positive lens B becomes strong, and therefore, upon zooming from the wide-angle end state to the telephoto end state, a change in refractive power corresponding to a change in height with respect to the optical axis of off-axis rays passing through the positive lens B becomes large. As a result, it becomes difficult to suppress variations in lateral chromatic aberration and off-axis aberration, particularly astigmatism, and therefore high optical performance cannot be obtained.

On the other hand, when the ratio f1B/f1 is equal to or exceeds the upper limit of conditional expression (9), refractive power of the positive lens B becomes weak, and therefore refractive power of positive lenses other than the positive lens B in the first lens group becomes strong. As a result, upon zooming from the wide-angle end state to the telephoto end state, a variation in refractive power corresponding to a variation in height with respect to the optical axis of the off-axis rays passing through the positive lens B becomes large. Therefore, it becomes difficult to suppress variations in lateral chromatic aberration and off-axis aberration, particularly astigmatism, and therefore high optical performance cannot be obtained.

In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (9) to 0.77.

In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (9) to 1.42.

In the zoom lens according to the first embodiment, the following conditional expression (10) is preferably satisfied:

wherein,the effective diameter of the positive lens B in the first lens group is indicated.

Conditional expression (10) defines the optimum diameter of the positive lens B in the first lens group, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming.

When ratio ofEqual to or less than the lower limit of conditional expression (10), upon zooming from the wide-angle end state to the telephoto end state, variation in height with respect to the optical axis of off-axis rays passing through the positive lens B in the first lens group becomes small, and thus it becomes difficult to suppress variation in off-axis aberration, particularly astigmatism. Therefore, high optical performance cannot be obtained.

On the other hand, when the ratio isEqual to or above the upper limit of conditional expression (10), in the range from the wide-angle end state to the telephoto end stateUpon zooming, variation in height with respect to the optical axis of off-axis rays passing through the positive lens B in the first lens group becomes large, and therefore it becomes difficult to suppress variation in lateral chromatic aberration and off-axis aberration, particularly astigmatism. Therefore, high optical performance cannot be obtained.

In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (10) to 2.45.

In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (10) to 3.80.

In the zoom lens according to the first embodiment, the first lens group preferably includes a negative lens that satisfies the following conditional expressions (11) and (12):

1.750＜ndN(11)

28.0＜νdN＜50.0(12)

where ndN denotes a refractive index at a d-line (wavelength λ 587.6nm) of a material of the negative lens in the first lens group, and ν dN denotes an abbe number at a d-line (wavelength λ 587.6nm) of a material of the negative lens in the first lens group.

Conditional expression (11) defines an optimum range of refractive index in the negative lens in the first lens group, and is for achieving high optical performance and suppressing variation in off-axis aberration generated upon zooming from the wide-angle end state to the telephoto end state.

When the value ν dN is equal to or smaller than the lower limit of conditional expression (11), the curvature of the surface of the negative lens in the first lens group becomes large, so that upon zooming from the wide-angle end state to the telephoto end state, variation in off-axis aberration, particularly astigmatism, corresponding to variation in height with respect to the optical axis of off-axis rays passing through the negative lens becomes difficult to suppress. Therefore, high optical performance cannot be achieved.

In order to secure the effect of the present embodiment, it is preferable to set the lower limit of conditional expression (11) to 1.780.

Conditional expression (12) defines an optimum abbe number of the material of the negative lens in the first lens group, and is for achieving high optical performance and suppressing variation in chromatic aberration generated upon zooming from the wide-angle end state to the telephoto end state.

When the value ν dN is equal to or smaller than the lower limit of conditional expression (12), it becomes difficult to suppress variation in second-order chromatic aberration generated upon zooming from the wide-angle end state to the telephoto end state, and therefore high optical performance cannot be obtained.

On the other hand, when the value ν dN equals or exceeds the upper limit of conditional expression (12), and when a given achromatization is to be performed in the first lens group, refractive power of each of the positive lens and the negative lens becomes large. As a result, upon zooming from the wide-angle end state to the telephoto end state, variation in off-axis aberration, particularly astigmatism, corresponding to variation in height with respect to the optical axis of off-axis rays passing through the negative lens becomes difficult to be suppressed, and therefore, high optical performance cannot be obtained.

In order to secure the effect of the present embodiment, it is preferable to set the upper limit of conditional expression (12) to 43.0.

In the zoom lens according to the first embodiment, the first lens group is preferably composed of one negative lens and two positive lenses.

With this configuration, the thickness of the first lens group can be suppressed. Accordingly, upon zooming from the wide-angle end state to the telephoto end state, variation in height relative to the optical axis of off-axis rays passing through the most object-side surface of the first lens group can be suppressed, so that variation in off-axis aberrations, particularly astigmatism, can be suppressed. As a result, high optical performance can be achieved.

In the zoom lens according to the first embodiment, the third lens group preferably includes a positive lens satisfying the following conditional expression (13):

when nd3 is more than or equal to 1.540, v d3 is more than 65.5

75.0< ν d3(13) when nd3<1.540

Where nd3 denotes a refractive index at a d-line (wavelength λ 587.6nm) of the material of the positive lens in the third lens group, and vd 3 denotes an abbe number at the d-line (wavelength λ 587.6nm) of the material of the positive lens in the third lens group.

Conditional expression (13) defines an optimum abbe number of the material of the positive lens in the first lens group, and is for achieving high optical performance and suppressing variation in chromatic aberration generated upon zooming from the wide-angle end state to the telephoto end state.

When the value ν d3 is equal to or smaller than the lower limit of conditional expression (13), it becomes difficult to suppress variations in longitudinal chromatic aberration and lateral chromatic aberration. The material becomes a material having small anomalous dispersion, so that it becomes difficult to suppress variations in second-order chromatic aberration. In addition, longitudinal chromatic aberration and lateral chromatic aberration in the visible light range become large in the telephoto end state, and thus high optical performance cannot be obtained.

In order to secure the effect of the present embodiment, when 1.540. ltoreq. nd3, it is preferable to set the lower limit of conditional expression (13) to 67.5. In order to secure the effect of the present embodiment, when nd3<1.540, the lower limit of conditional expression (13) is preferably set to 80.5.

In the zoom lens according to the first embodiment, it is preferable that the third lens group includes, in order from the object side, a front lens group having positive refractive power and a rear lens group having positive refractive power, and a distance between the front lens group and the rear lens group upon zooming from the wide-angle end state to the telephoto end state decreases.

With this configuration, the zooming efficiency of the third lens group can be enhanced better than a configuration in which the third lens group is integrally moved upon zooming. Also, it is possible to achieve high optical performance and suppress variations in spherical aberration, coma, and astigmatism.

In the zoom lens according to the first embodiment, it is preferable that the third lens group includes, in order from the object side, a front lens group having positive refractive power, an intermediate lens group having negative refractive power, and a rear lens group having positive refractive power, and upon zooming from a wide-angle end state to a telephoto end state, a distance between the front lens group and the intermediate lens group varies, and a distance between the intermediate lens group and the rear lens group varies.

With this configuration, it is possible to suppress variation in aberration generated in the third lens group better than a configuration in which the third lens group is integrally moved at the time of zooming, so that it is possible to achieve high optical performance, and particularly suppress spherical aberration, coma, and astigmatism.

In the zoom lens according to the first embodiment, it is preferable that a distance between the front lens group and the intermediate lens group increases, and a distance between the intermediate lens group and the rear lens group decreases.

With this configuration, it is possible to enhance the zooming efficiency of the third lens group, and therefore it is possible to achieve high optical performance and suppress variations in spherical aberration, coma, and astigmatism.

Then, a zoom lens seen from another point of view according to the first embodiment of the present application includes, in order from the object side along the optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens having positive refractive power. 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 increases, and a distance between the second lens group and the third lens group decreases, thereby realizing an optical system capable of zooming while suppressing variation in distortion upon zooming.

In a zoom lens seen from another point of view according to the first embodiment, the first lens group includes a positive lens a satisfying the following conditional expression (1), and satisfies the following conditional expression (2):

85.0＜νdA(1)

3.90＜f1/fw＜11.00(2)

wherein ν dA denotes an abbe number at a d-line (wavelength λ 587.6nm) of a material of the positive lens a in the first lens group, fw denotes a focal length of the zoom lens in the wide-angle end state, and f1 denotes a focal length of the first lens group.

Conditional expression (1) defines an optimum abbe number of the positive lens a in the first lens group, and is for achieving high optical performance and suppressing variation in chromatic aberration generated upon zooming from the wide-angle end state to the telephoto end state. However, the conditional expression (1) has already been described above, and therefore, a repetitive description is omitted.

Conditional expression (2) defines an appropriate range of the focal length of the first lens group, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming from the wide-angle end state to the telephoto end state. However, the conditional expression (2) has already been described above, and therefore, a repetitive description is omitted.

In a zoom lens seen from another point of view according to the first embodiment of the present application, an antireflection coating is applied to at least one optical surface among the first lens group and the second lens group, and the antireflection coating includes at least one layer formed by a wet process. With this configuration, the zoom lens seen from another point of view according to the first embodiment of the present application makes it possible to suppress ghost images and flare generated by light rays from an object reflected from an optical surface, thereby achieving good optical performance.

Further, in a zoom lens seen from another point of view according to the first embodiment of the present application, the antireflection coating is a multilayer film, and the layer formed by the wet process is preferably an outermost layer among the layers including the multilayer film. With this configuration, since the difference in refractive index with respect to air may be small, the reflectance of light may be small, so that ghost images and flare may be further suppressed.

In a zoom lens seen from another point of view according to the first embodiment of the present application, when a refractive index at d-line of a layer formed by a wet process is denoted by nd, the refractive index nd is preferably 1.30 or less. With this configuration, since the difference in refractive index with respect to air may be small, the reflectance of light may be small, so that ghost images and flare may be further suppressed.

Moreover, in a zoom lens seen from another point of view according to the first embodiment of the present application, the optical surface on which the antireflection coating is formed is preferably a concave surface seen from an aperture stop. Since reflected light rays are liable to be generated on a concave surface seen from the aperture stop among optical surfaces in the first lens group and the second lens group, ghost images and flare can be effectively suppressed by applying an antireflection coating on such optical surfaces.

In a zoom lens seen from another point of view according to the first embodiment of the present application, it is desirable that the concave surface on which the antireflection coating is applied seen from the aperture stop is an image side lens surface. Since the image side concave surface seen from the aperture stop among the optical surfaces in the first lens group and the second lens group tends to generate reflected light, with applying the antireflection coating on such optical surfaces, ghost images and flare can be effectively suppressed.

In a zoom lens seen from another point of view according to the first embodiment of the present application, it is desirable that the concave surface on which the antireflection coating is applied seen from the aperture stop is an object side lens surface. Since the object side concave surface seen from the aperture stop among the optical surfaces in the first lens group and the second lens group tends to generate reflected light, with applying the antireflection coating on such optical surfaces, ghost images and flare can be effectively suppressed.

Moreover, in a zoom lens seen from another point of view according to the first embodiment of the present application, the optical surface on which the antireflection coating is formed is preferably a concave surface seen from an object. Since reflected light is liable to be generated on a concave surface seen from an object among optical surfaces in the first lens group and the second lens group, ghost images and flare can be effectively suppressed by applying an antireflection coating on such optical surfaces.

Moreover, in a zoom lens seen from another point of view according to the first embodiment of the present application, the concave optical surface seen from the object on which the antireflection coating is formed is preferably an image side lens surface of the image side second lens from the most object side lens in the first lens group. Since reflected light rays are liable to be generated on the image side lens surface of the image side second lens from the most object side lens in the first lens group, ghost images and flare can be effectively suppressed by applying the antireflection coating on such an optical surface.

Moreover, in a zoom lens seen from another point of view according to the first embodiment of the present application, the concave optical surface seen from the object on which the antireflection coating is formed is preferably an object side lens surface of the image side second lens from the most object side lens in the second lens group. Since reflected light rays are liable to be generated on the object side lens surface of the image side second lens from the most object side lens in the second lens group, ghost images and flare can be effectively suppressed by applying the antireflection coating on such an optical surface.

Moreover, in a zoom lens seen from another point of view according to the first embodiment of the present application, the concave optical surface seen from the object on which the antireflection coating is formed is preferably an image side lens surface of the image side third lens from the most object side lens in the second lens group. Since reflected light rays are liable to be generated on the image side lens surface of the image side third lens from the most object side lens in the second lens group, ghost images and flare can be effectively suppressed by applying the antireflection coating on such an optical surface.

Moreover, in a zoom lens seen from another point of view according to the first embodiment of the present application, the concave optical surface seen from the object on which the antireflection coating is formed is preferably an object side lens surface of the image side fourth lens from the most object side lens in the second lens group. Since reflected light rays are liable to be generated on the object side lens surface of the image side fourth lens from the most object side lens in the second lens group, ghost images and flare can be effectively suppressed by applying the antireflection coating on such an optical surface.

In the zoom lens seen from another point of view according to the first embodiment, the antireflection coating may also be formed by a dry process, not limited to a wet process. In this case, it is preferable that the antireflection coating contains at least one layer whose refractive index is equal to 1.30 or less. Therefore, the same effect as in the case of using the wet method can be obtained by forming the antireflection coating based on the dry method or the like. Note that at this time, the layer whose refractive index is equal to 1.30 or less is preferably a layer constituting the outermost surface of the layers of the multilayer film.

In the zoom lens seen from another point of view according to the first embodiment, the following conditional expression (3) is preferably satisfied:

0.28＜f1/ft＜0.52(3)

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

Conditional expression (3) defines an appropriate range of the optimum focal length of the first lens group, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming from the wide-angle end state to the telephoto end state. However, conditional expression (3) has already been described above, and therefore, a repetitive description is omitted.

In the zoom lens seen from another point of view according to the first embodiment, it is preferable that conditional expression (4) is satisfied:

0.25＜Δ1/f1＜1.10(4)

Conditional expression (4) defines an optimum moving amount of the first lens group with respect to the image plane upon zooming from the wide-angle end state to the telephoto end state. However, conditional expression (4) has already been described above, and therefore, a repetitive description is omitted.

In the zoom lens seen from another point of view according to the first embodiment, the following conditional expression (5) is preferably satisfied:

0.65＜f1A/f1＜1.75(5)

Conditional expression (5) defines the optimum focal length of the positive lens a in the first lens group, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming. However, conditional expression (5) has already been described above, and therefore, a repetitive description is omitted.

In the zoom lens seen from another point of view according to the first embodiment, the following conditional expression (6) is preferably satisfied:

wherein,the effective diameter of the positive lens a in the first lens group is indicated.

Conditional expression (6) defines an optimum effective diameter of the positive lens a in the first lens group, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming. However, conditional expression (6) has already been described above, and therefore, a repetitive description is omitted.

In a zoom lens seen from another point of view according to the first embodiment, the first lens group preferably includes a positive lens B satisfying the following conditional expression (7):

1.580＜ndB(7)

Conditional expression (7) defines the optimum refractive index of the material of the positive lens B in the first lens group, and is for achieving high optical performance and suppressing variation in off-axis aberration generated upon zooming. However, conditional expression (7) has already been described above, and therefore, a repetitive description is omitted.

In a zoom lens seen from another point of view according to the first embodiment, the first lens group preferably includes a positive lens B satisfying the following conditional expression (8):

40.0＜νdB＜66.5(8)

Conditional expression (8) defines the optimum abbe number of the material of the positive lens B in the first lens group, and is for achieving high optical performance and suppressing variation in chromatic aberration generated upon zooming. However, conditional expression (8) has already been described above, and therefore, a repetitive description is omitted.

In the zoom lens seen from another point of view according to the first embodiment, the following conditional expression (9) is preferably satisfied:

0.65＜f1B/f1＜1.75(9)

Conditional expression (9) defines the optimum focal length of the positive lens B in the first lens group. However, conditional expression (9) has already been described above, and therefore, a repetitive description is omitted.

In the zoom lens seen from another point of view according to the first embodiment, the following conditional expression (10) is preferably satisfied:

Conditional expression (10) defines the optimum diameter of the positive lens B in the first lens group, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming. However, the conditional expression (10) has already been described above, and therefore, a repetitive description is omitted.

In a zoom lens seen from another point of view according to the first embodiment, the first lens group preferably includes a negative lens that satisfies the following conditional expressions (11) and (12):

1.750＜ndN(11)

28.0＜νdN＜50.0(12)

Conditional expression (11) defines an optimum range of refractive index in the negative lens in the first lens group, and is for achieving high optical performance and suppressing variation in off-axis aberration generated upon zooming from the wide-angle end state to the telephoto end state. However, conditional expression (11) has already been described above, and therefore, a repetitive description is omitted.

Conditional expression (12) defines an optimum abbe number of the material of the negative lens in the first lens group, and is for achieving high optical performance and suppressing variation in chromatic aberration generated upon zooming from the wide-angle end state to the telephoto end state. However, conditional expression (12) has already been described above, and therefore, a repetitive description is omitted.

In a zoom lens seen from another point of view according to the first embodiment, the first lens group is preferably composed of one negative lens and two positive lenses.

With this configuration, the thickness of the first lens group can be suppressed. Accordingly, upon zooming from the wide-angle end state to the telephoto end state, variation in height relative to the optical axis of off-axis rays passing through the most object-side surface of the first lens group can be suppressed, and thus variation in off-axis aberrations, particularly astigmatism, can be suppressed. As a result, high optical performance can be achieved.

In a zoom lens seen from another point of view according to the first embodiment, the third lens group preferably includes a positive lens satisfying the following conditional expression (13):

when nd3 is more than or equal to 1.540, v d3 is more than 65.5

75.0< ν d3(13) when nd3<1.540

Conditional expression (13) defines an optimum abbe number of the material of the positive lens in the third lens group, and is for achieving high optical performance and suppressing variation in chromatic aberration generated upon zooming from the wide-angle end state to the telephoto end state. However, conditional expression (13) has already been described above, and therefore, a repetitive description is omitted.

In a zoom lens seen from another point of view according to the first embodiment, it is preferable that the third lens group includes, in order from the object side, a front lens group having positive refractive power and a rear lens group having positive refractive power, and a distance between the front lens group and the rear lens group decreases upon zooming from a wide-angle end state to a telephoto end state.

In a zoom lens seen from another point of view according to the first embodiment, it is preferable that the third lens group includes, in order from the object side, a front lens group having positive refractive power, an intermediate lens group having negative refractive power, and a rear lens group having positive refractive power, and upon zooming from a wide-angle end state to a telephoto end state, a distance between the front lens group and the intermediate lens group varies, and a distance between the intermediate lens group and the rear lens group varies.

In a zoom lens seen from another point of view according to the first embodiment, it is preferable that a distance between the front lens group and the intermediate lens group increases, and a distance between the intermediate lens group and the rear lens group decreases.

Next, a zoom lens according to each example of the first embodiment will be described below with reference to the drawings. Incidentally, after example 12 of the third embodiment, detailed description of the antireflection coating will be separately described.

< example 1>

Fig. 1 is a sectional view showing a lens configuration of a zoom lens according to example 1 of the first embodiment of the present application.

As shown in fig. 1, the zoom lens according to example 1 of the first embodiment is composed of, in order from the object side along the optical axis: a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power. The third lens group G3 is composed of, in order from the object side along the optical axis: a front lens group G31 having positive refractive power, an intermediate lens group G32 having negative refractive power, and a rear lens group G33 having positive refractive power.

Upon zooming from a wide-angle end state to a telephoto end state, the first lens group G1 is monotonously moved to the object side, the second lens group G2 is first moved to the image side and then moved to the object side, and the third lens group G3 is monotonously moved to the object side with respect to the image plane I, so that a distance between the first lens group G1 and the second lens group G2 increases, and a distance between the second lens group G2 and the third lens group G3 decreases. Further, the front lens group G31, the intermediate lens group G32, and the rear lens group G33 are monotonously moved toward the object side with respect to the image plane I, so that a distance between the front lens group G31 and the intermediate lens group G32 increases, and a distance between the intermediate lens group G32 and the rear lens group G33 decreases. Further, the front lens group G31 and the rear lens group G33 integrally move with respect to the image plane I.

The aperture stop S is disposed to the most object side of the third lens group G3, and is integrally formed with the front lens group G31, with the third lens group G3 disposed to the image side of the second lens group G2.

The first lens group G1 is composed of, in order from the object side along the optical axis: a cemented lens constructed by a negative meniscus lens L11 having a convex surface facing the object side cemented with a double convex positive lens L12; and a biconvex positive lens L13.

The second lens group G2 is composed of, in order from the object side along the optical axis: a negative meniscus lens L21 having a convex surface facing the object side; a biconcave negative lens L22; a biconvex positive lens L23; and a cemented lens constructed by a double concave negative lens L24 cemented with a double convex positive lens L25. The negative meniscus lens L21 disposed to the most object side of the second lens group G2 is a compound type aspherical lens, and its object side lens surface is formed to be aspherical by applying a resin layer.

The front lens group G31 is composed of, in order from the object side along the optical axis: a biconvex positive lens L31; a biconvex positive lens L32; a cemented lens constructed by a double convex positive lens L33 cemented with a negative meniscus lens L34 having a concave surface facing the object side.

The intermediate lens group G32 is composed of, in order from the object side along the optical axis: a cemented lens constructed by a double concave negative lens L41 cemented with a positive meniscus lens L42 having a convex surface facing the object side; and a negative meniscus lens L43 having a concave surface facing the object side. The double concave negative lens L41 disposed to the most object side of the intermediate lens group G32 is a glass-molded type aspherical lens whose object side lens surface is an aspherical surface.

The rear lens group G33 is composed of, in order from the object side along the optical axis: a positive meniscus lens L51 having a concave surface facing the object side; a biconvex positive lens L52; and a cemented lens constructed by a double concave negative lens L53 cemented with a double convex positive lens L54. The positive meniscus lens L51 disposed to the most object side of the rear lens group G33 is a glass-molded type aspherical lens whose object side lens surface is an aspherical surface. The light rays from the biconvex positive lens L54 form an image on the image plane I.

The image plane I is formed on an imaging device not shown. The imaging device is constructed of a CCD, a CMOS, and the like. This is the same in the following examples.

In the zoom lens seen from another point of view according to example 1 of the first embodiment, an antireflection coating described below is applied to the image plane side lens surface of the negative meniscus lens L21 in the second lens group G2 and the object side lens surface of the double concave negative lens L22 in the second lens group G2.

Various values associated with the zoom lens according to example 1 of the first embodiment are listed in table 1.

In (specification), W denotes a wide-angle end state, M denotes an intermediate focal length state, T denotes a telephoto end state, F denotes a focal length of the zoom lens, FNO denotes an F number, ω denotes a half angle of view (unit: degree), Y denotes an image height, TL denotes a total lens length, which is a distance between the most object side lens surface of the first lens group G1 and the image plane I when focused on infinity, and Bf denotes a back focal length.

In (lens data), "OP" denotes an object plane, "I" denotes an image plane, the leftmost column "I" denotes an optical surface number, the second column "r" denotes a radius of curvature of each optical surface, the third column "d" denotes a surface distance, the fourth column "nd" denotes a refractive index at a d-line (wavelength λ 587.6nm), and the fifth column "vd" denotes an abbe number at a d-line (wavelength λ 587.6 nm). In the fifth column "nd", the refractive index nd of air is omitted to be 1.000000. In the second column "r", r ═ infinity indicates a plane.

The aspherical surfaces are expressed by the following expression, where y is the height in the direction perpendicular to the optical axis, x (y) is the distance (sag amount) from a tangent plane at the vertex of each aspherical surface to each aspherical surface at the height y along the optical axis, r is the radius of curvature (paraxial radius of curvature) of a reference sphere, κ is a conic coefficient, and Cn is an aspherical surface coefficient of the nth order. Note that in the examples that follow, [ E-n]Is represented by [. times.10 [)^-n]。

X(y)＝(y²/r)/[1+(1-k×y²/r²)^1/2]

+A4×y⁴+A6×y⁶+A8×y⁸+A10×y¹⁰

In (aspherical surface data), "E-n" represents ". times.10^-n", wherein" n "is an integer, and for example," 1.234E-05 "means" 1.234X 10^-5". Each aspheric surface is expressed in (lens data) by appending a "+" to the right side of the surface number.

In (variable distance), di ("i" is a surface number) represents a variable distance, and Bf represents a back focal distance.

In (lens group data), a starting surface number "ST" of each lens group and a focal length of each lens group are shown. In (values of conditional expressions), values of the respective conditional expressions are shown.

In each table for multiple values, "mm" is typically used for units of length such as focal length, radius of curvature, and distance to the next lens surface. However, since similar optical performance can be obtained by proportionally enlarging or reducing the size of the optical system, the unit is not necessarily limited to "mm", and any other appropriate unit may be used. The description of the reference numerals is the same in other examples of the examples included in the second and third embodiments.

TABLE 1

Fig. 2A, 2B, and 2C are graphs showing various aberrations of the zoom lens according to example 1 of the first embodiment, in which fig. 2A is a wide-angle end state, fig. 2B is an intermediate focal length state, and fig. 2C is a telephoto end state, upon focusing on an object at infinity.

In each graph, FNO denotes an F number, a denotes a half angle of view (unit: degree), d denotes an aberration curve at a d-line (wavelength λ 587.6nm), and g denotes an aberration curve at a g-line (wavelength λ 435.8 nm). The unspecified aberration curve is an aberration curve with respect to the d-line. In the graph showing astigmatism, the solid line indicates a sagittal image surface, and the broken line indicates a meridional image surface. In other examples including the examples in the second and third embodiments, the description of the reference numerals is the same.

As is apparent from the respective graphs, the zoom lens according to example 1 of the first embodiment shows superior optical performance as a result of good correction for respective aberrations.

Fig. 3 is a sectional view showing a lens configuration of a lens system according to example 1 of the first embodiment, and is an explanatory view in which light rays reflected from a first ghost-generating surface are reflected by a second ghost-generating surface.

As shown in fig. 3, when a light ray BM from an object is incident on the zoom lens, the light ray is reflected by the object side lens surface (the first ghost generation surface whose surface number is 9) of the double concave negative lens L22, and the reflected light ray is reflected again by the image plane I side lens surface (the second ghost generation surface whose surface number is 8) of the negative meniscus lens L21 to reach the image plane I, and a ghost is generated. Incidentally, the first ghost generation surface 9 is a concave surface as viewed from the object side, and the second ghost generation surface 8 is a concave surface as viewed from the aperture stop S side. By forming an antireflection coating corresponding to a wide wavelength range on the surface of such a lens, ghost images and flare can be effectively suppressed.

< example 2>

As shown in fig. 4, the zoom lens according to example 2 of the first embodiment is composed of, in order from the object side along the optical axis: a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power. The third lens group G3 is composed of, in order from the object side along the optical axis: a front lens group G31 having positive refractive power, and a rear lens group G32 having positive refractive power.

Upon zooming from a wide-angle end state to a telephoto end state, the first lens group G1 monotonously moves to the object side, the second lens group G2 monotonously moves to the object side, and the third lens group G3 monotonously moves to the object side with respect to the image plane I, so that a distance between the first lens group G1 and the second lens group G2 increases, and a distance between the second lens group G2 and the third lens group G3 decreases. Further, the front lens group G31 and the rear lens group G32 are monotonously moved toward the object side with respect to the image plane I such that a distance between the front lens group G31 and the rear lens group G32 decreases.

The first lens group G1 is composed of, in order from the object side along the optical axis: a cemented lens constructed by a negative meniscus lens L11 having a convex surface facing the object side cemented with a double convex positive lens L12; and a positive meniscus lens L13 having a convex surface facing the object side.

The second lens group G2 is composed of, in order from the object side along the optical axis: a negative meniscus lens L21 having a convex surface facing the object side; a biconcave negative lens L22; a biconvex positive lens L23; and a double concave negative lens L24. The negative meniscus lens L21 disposed to the most object side of the second lens group G2 is a compound type aspherical lens, the object side lens surface of which is formed to be aspherical by applying a resin layer.

The front lens group G31 is composed of, in order from the object side along the optical axis: a biconvex positive lens L31; a cemented lens constructed by a double convex positive lens L32 cemented with a negative meniscus lens L33 having a concave surface facing the object side; and a cemented lens constructed by a double concave negative lens L34 cemented with a positive meniscus lens L35 having a convex surface facing the object side. The double concave negative lens L34 is a compound type aspherical lens, and its object side lens surface is formed to be aspherical by applying a resin layer.

The rear lens group G32 is composed of, in order from the object side along the optical axis: a biconvex positive lens L41; a cemented lens constructed by a double convex positive lens L42 cemented with a double concave negative lens L43; and a biconvex positive lens L44. The double convex positive lens L41 disposed to the most object side of the rear lens group G32 is a glass-molded type aspherical lens whose object side lens surface is an aspherical surface. The light rays from the biconvex positive lens L44 form an image on the image plane I.

In the zoom lens seen from another point of view according to example 2 of the first embodiment, an antireflection coating described after firing is applied to the object side lens surface of the positive meniscus lens L13 in the first lens group G1 and the image side lens surface of the double convex positive lens L23 in the second lens group G2.

Various values associated with the zoom lens according to example 2 of the first embodiment are listed in table 2.

TABLE 2

As is apparent from the respective graphs, the zoom lens according to example 2 of the first embodiment shows superior optical performance as a result of good correction for respective aberrations.

< example 3>

Fig. 6 is a sectional view showing a lens configuration of a zoom lens according to example 3 of the first embodiment of the present application.

As shown in fig. 6, the zoom lens according to example 3 of the first embodiment is composed of, in order from the object side along the optical axis: a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power. The third lens group G3 is composed of, in order from the object side along the optical axis: a front lens group G31 having positive refractive power, an intermediate lens group G32 having negative refractive power, and a rear lens group G33 having positive refractive power.

Upon zooming from a wide-angle end state to a telephoto end state, the first lens group G1 is monotonously moved to the object side, the second lens group G2 is first moved to the image side and then moved to the object side, and the third lens group G3 is monotonously moved to the object side with respect to the image plane I, so that a distance between the first lens group G1 and the second lens group G2 increases, and a distance between the second lens group G2 and the third lens group G3 decreases. Further, the front lens group G31, the intermediate lens group G32, and the rear lens group G33 are monotonously moved toward the object side with respect to the image plane I, so that a distance between the front lens group G31 and the intermediate lens group G32 increases, and a distance between the intermediate lens group G32 and the rear lens group G33 decreases.

The aperture stop S is disposed to the most object side of the third lens group G3, and is integrally formed with the front lens group G31, wherein the third lens group G3 is disposed to the image side of the second lens group G2.

The second lens group G2 is composed of, in order from the object side along the optical axis: a negative meniscus lens L21 having a convex surface facing the object side; a biconcave negative lens L22; a biconvex positive lens L23; and a cemented lens constructed by a double concave negative lens L24 cemented with a double convex positive lens L25. The negative meniscus lens L21 disposed to the most object side of the second lens group G2 is a compound type aspherical lens, the object side lens surface of which is formed to be aspherical by applying a resin layer.

The front lens group G31 is composed of, in order from the object side along the optical axis: a biconvex positive lens L31; a biconvex positive lens L32; and a cemented lens constructed by a double convex positive lens L33 cemented with a negative meniscus lens L34 having a concave surface facing the object side.

In the zoom lens seen from another point of view according to example 3 of the first embodiment, an antireflection coating described later is applied to the image side lens surface of the double convex positive lens L12 in the first lens group G1 and the object side lens surface of the double concave negative lens L24 in the second lens group G2.

Various values associated with the zoom lens according to example 3 of the first embodiment are listed in table 3.

TABLE 3

Fig. 7A, 7B, and 7C are graphs showing various aberrations of the zoom lens according to example 3 of the first embodiment, in which fig. 7A is a wide-angle end state, fig. 7B is an intermediate focal length state, and fig. 7C is a telephoto end state.

As is apparent from the respective graphs, the zoom lens according to example 3 of the first embodiment shows superior optical performance as a result of good correction for respective aberrations.

Next, an outline of a method for manufacturing a zoom lens according to the first embodiment will be described.

A method for manufacturing a zoom lens according to the first embodiment is a method for manufacturing a zoom lens including, in order from an object side along an optical axis: a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power, and configured such that an antireflection coating is applied to at least one optical surface in the first lens group and the second lens group, and the antireflection coating includes at least one layer formed by a wet process, the method including steps S11 to S13.

Step S11: the first lens group, the second lens group, and the third lens group are movably arranged such that 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 increases, and a distance between the second lens group and the third lens group decreases.

Step S12: a positive lens a satisfying the following conditional expression (1) is arranged into the first lens group:

85.0＜νdA(1)

where ν dA denotes an abbe number at a d-line (wavelength λ 587.6nm) of the positive lens a in the first lens group.

Step S13: disposing each lens satisfying conditional expression (2):

3.90＜f1/fw＜11.00(2)

With this method for manufacturing a zoom lens according to the first embodiment, it becomes possible to manufacture a zoom lens having good optical performance, and suppress variations in aberrations as well as ghost images and flare.

(second embodiment)

A zoom lens according to a second embodiment of the present application is described below.

A zoom lens according to a second embodiment of the present application includes, in order from an object side along an optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power. 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 increases, and a distance between the second lens group and the third lens group decreases. With this configuration, it becomes possible to realize a zoom lens, and at the same time, suppress variations in distortion generated upon zooming.

The zoom lens according to the second embodiment includes a positive lens a' satisfying the following conditional expressions (14) and (15), and satisfies the following conditional expression (2):

1.540＜ndA’(14)

66.5＜νdA’(15)

3.90＜f1/fw＜11.00(2)

where ndA 'denotes a refractive index at the d-line (wavelength λ 587.6nm) of the material of the positive lens a', ν dA 'denotes an abbe number at the d-line (wavelength λ 587.6nm) of the material of the positive lens a', fw denotes a focal length of the zoom lens in the wide-angle end state, and f1 denotes a focal length of the first lens group.

Conditional expression (14) defines the optimum refractive index of the material of the positive lens a', and is for achieving high optical performance and suppressing variations in spherical aberration and curvature of field generated upon zooming from the wide-angle end state to the telephoto end state.

When the value ndA' is equal to or smaller than the lower limit of conditional expression (14), it becomes difficult to suppress variations in spherical aberration and curvature of field, and thus high optical performance cannot be obtained.

In order to secure the effect of the second embodiment, the lower limit of conditional expression (14) is preferably set to 1.550.

Conditional expression (15) defines the optimum abbe number of the material of the positive lens a', and is for achieving high optical performance and suppressing variation in chromatic aberration generated upon zooming from the wide-angle end state to the telephoto end state.

When the value ν dA' is equal to or smaller than the lower limit of conditional expression (15), it becomes difficult to suppress variations in longitudinal chromatic aberration and lateral chromatic aberration. The material becomes a material having small anomalous dispersion, so that it becomes difficult to suppress variations in second-order chromatic aberration. In addition, longitudinal chromatic aberration and lateral chromatic aberration in the visible light range become large in the telephoto end state, and thus high optical performance cannot be obtained.

In order to secure the effect of the second embodiment, the lower limit of conditional expression (15) is preferably set to 67.5.

In the zoom lens according to the second embodiment, the following conditional expression (3) is preferably satisfied:

0.28＜f1/ft＜0.52(3)

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

Conditional expression (3) defines an appropriate range of the optimum focal length of the first lens group, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming from the wide-angle end state to the telephoto end state. However, the conditional expression (3) has already been described above, and therefore, a repetitive description is omitted.

In the zoom lens according to the second embodiment, the following conditional expression (4) is preferably satisfied:

0.25＜Δ1/f1＜1.10(4)

In the zoom lens according to the second embodiment, the third lens group preferably includes a positive lens a'.

With this configuration, it becomes possible to suppress variations in longitudinal chromatic aberration and spherical aberration that occur upon zooming from the wide-angle end state to the telephoto end state, and thus high optical performance can be achieved.

In the zoom lens according to the second embodiment, the following conditional expression (16) is preferably satisfied:

0.75＜f3A’/f3＜2.25(16)

where f3 denotes a focal length of the third lens group, and f3A 'denotes a focal length of the positive lens a' in the third lens group.

Conditional expression (16) defines the optimum focal length of the positive lens a' in the third lens group, and is for achieving high optical performance and suppressing chromatic aberration generated upon zooming and variations in on-axis aberration.

When the ratio f3A '/f 3 is equal to or less than the lower limit of conditional expression (16), refractive power of the positive lens a ' becomes strong, and therefore, upon zooming from the wide-angle end state to the telephoto end state, a change in refractive power corresponding to a change in height of a ray with respect to the optical axis on an axis passing through the positive lens a ' becomes large. As a result, it becomes difficult to suppress variations in longitudinal chromatic aberration and spherical aberration. Therefore, high optical performance cannot be obtained.

On the other hand, when the ratio f3A '/f 3 is equal to or exceeds the upper limit of conditional expression (16), the refractive power of the positive lens a ' becomes small, and therefore, the refractive power of the positive lenses other than the positive lens a ' in the third lens group becomes strong. As a result, upon zooming from the wide-angle end state to the telephoto end state, variation in refractive power corresponding to variation in height with respect to the optical axis of off-axis rays passing through the positive lens a' becomes large, and thus it becomes difficult to suppress variation in longitudinal chromatic aberration and spherical aberration. Therefore, high optical performance cannot be obtained.

In order to secure the effect of the second embodiment, the lower limit of conditional expression (16) is preferably set to 0.90.

In order to secure the effect of the second embodiment, it is preferable to set the upper limit of conditional expression (16) to 1.95.

In the zoom lens according to the second embodiment, the first lens group preferably includes a positive lens a'.

With this configuration, it becomes possible to suppress variation in longitudinal chromatic aberration generated upon zooming from the wide-angle end state to the telephoto end state, and thus high optical performance can be achieved.

In the zoom lens according to the second embodiment, the following conditional expression (17) is preferably satisfied:

0.65＜f1A’/f1＜1.75(17)

where f1A 'denotes a focal length of the positive lens a' in the first lens group.

Conditional expression (17) defines the optimum focal length of the positive lens a' in the first lens group, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming.

When the ratio f1A '/f 1 is equal to or less than the lower limit of conditional expression (17), refractive power of the positive lens a' becomes strong, and therefore, upon zooming from the wide-angle end state to the telephoto end state, a change in refractive power corresponding to a change in height of off-axis rays with respect to the optical axis becomes large. As a result, it becomes difficult to suppress variations in lateral chromatic aberration and off-axis aberration, particularly astigmatism. Therefore, high optical performance cannot be obtained.

On the other hand, when the ratio f1A '/f 1 is equal to or exceeds the upper limit of conditional expression (17), the refractive power of the positive lens a ' becomes weak, and the refractive power of the positive lenses other than the positive lens a ' in the first lens group becomes strong. As a result, upon zooming from the wide-angle end state to the telephoto end state, variation in refractive power corresponding to variation in height relative to the optical axis of off-axis rays passing through the positive lens a' becomes large, and thus it becomes difficult to suppress variation in lateral chromatic aberration and off-axis aberration, particularly astigmatism. Therefore, high optical performance cannot be obtained.

In order to secure the effect of the second embodiment, the lower limit of conditional expression (17) is preferably set to 0.80.

In order to secure the effect of the second embodiment, it is preferable to set the upper limit of conditional expression (17) to 1.35.

In the zoom lens according to the second embodiment, the following conditional expression (18) is preferably satisfied:

wherein,the effective diameter of the positive lens a' in the first lens group is indicated.

Conditional expression (18) defines the optimum effective diameter of the positive lens a' in the first lens group, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming.

When ratio ofEqual to or less than the lower limit of conditional expression (18), upon zooming from the wide-angle end state to the telephoto end stateIn the first lens group, the positive lens a 'has a positive refractive power, and the positive lens a' has a negative refractive power. As a result, high optical performance cannot be obtained.

On the other hand, when the ratio isEqual to or exceeding the upper limit of conditional expression (18), upon zooming from the wide-angle end state to the telephoto end state, variation in height with respect to the optical axis of off-axis rays passing through the positive lens a' in the first lens group becomes large, and therefore, it becomes difficult to suppress variation in lateral chromatic aberration and off-axis aberration, particularly astigmatism. As a result, high optical performance cannot be obtained.

In order to secure the effect of the second embodiment, the lower limit of conditional expression (18) is preferably 2.45.

In order to secure the effect of the second embodiment, it is preferable to set the upper limit of conditional expression (18) to 3.80.

In the zoom lens according to the second embodiment, the following conditional expression (19) is preferably satisfied:

wherein ft denotes a focal length of the zoom lens in the telephoto end state, andthe effective diameter of the positive lens a' in the first lens group is indicated.

Conditional expression (19) defines the optimum effective diameter of the positive lens a' in the first lens group, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming.

When ratio ofEqual to or less than the lower limit of conditional expression (19), upon zooming from the wide-angle end state to the telephoto end state, variation in height with respect to the optical axis of off-axis rays passing through the positive lens a' in the first lens group becomes small, and therefore, it becomes difficult to suppress variation in off-axis aberration, particularly astigmatism. As a result, high optical performance cannot be obtained.

On the other hand, when the ratio isEqual to or exceeding the upper limit of conditional expression (19), upon zooming from the wide-angle end state to the telephoto end state, variation in height with respect to the optical axis of off-axis rays passing through the positive lens a' in the first lens group becomes large, and therefore, it becomes difficult to suppress variation in lateral chromatic aberration and off-axis aberration, particularly astigmatism. As a result, high optical performance cannot be obtained.

In order to secure the effect of the second embodiment, the lower limit of conditional expression (19) is preferably 0.080.

In order to secure the effect of the second embodiment, it is preferable to set the upper limit of conditional expression (19) to 0.350.

In the zoom lens according to the second embodiment, the first lens group preferably includes two positive lenses.

With this configuration, the thickness of the first lens group can be suppressed, so that upon zooming from the wide-angle end state to the telephoto end state, variation in height with respect to the optical axis of off-axis rays passing through the most object side lens surface in the first lens group can be suppressed, and as a result, variation in off-axis aberration, particularly astigmatism, can be suppressed, and therefore, high optical performance can be achieved.

In the zoom lens according to the second embodiment, the following conditional expressions (11) and (12) are preferably satisfied:

1.750＜ndN(11)

28.0＜νdN＜50.0(12)

Conditional expression (11) defines an optimum range of refractive index in the negative lens in the first lens group, and is for achieving high optical performance and suppressing variation in off-axis aberration generated upon zooming from the wide-angle end state to the telephoto end state. However, the conditional expression (11) has already been described above, and therefore, a repetitive description is omitted.

Conditional expression (12) defines an optimum abbe number of the material of the negative lens in the first lens group, and is for achieving high optical performance and suppressing variation in chromatic aberration generated upon zooming from the wide-angle end state to the telephoto end state. However, conditional expression (12) has already been described above, and therefore, duplicate description is omitted.

In the zoom lens according to the second embodiment, the first lens group preferably has only one negative lens.

With this configuration, the thickness of the first lens group can be suppressed. Accordingly, upon zooming from the wide-angle end state to the telephoto end state, variation in height with respect to the optical axis of off-axis rays passing through the most object side lens surface of the first lens group can be suppressed. As a result, variations in off-axis aberrations, particularly astigmatism, can be suppressed, and therefore, high optical performance can be achieved.

In the zoom lens according to the second embodiment, the following conditional expression (20) is preferably satisfied:

75.0＜νdB’(20)

where ν dB 'denotes an abbe number at a d-line (wavelength λ 587.6nm) of the material of the positive lens B' in the first lens group.

Conditional expression (20) defines the optimum abbe number of the material of the positive lens B', and is for achieving high optical performance and suppressing variation in chromatic aberration generated upon zooming from the wide-angle end state to the telephoto end state.

When the value ν dB' is equal to or smaller than the lower limit of the conditional expression (20), it becomes difficult to suppress variations in longitudinal chromatic aberration and lateral chromatic aberration. The material becomes a material having small anomalous dispersion, so that it becomes difficult to suppress variations in second-order chromatic aberration. In addition, longitudinal chromatic aberration and lateral chromatic aberration in the visible light range become large in the telephoto end state, and thus high optical performance cannot be obtained.

In the zoom lens according to the second embodiment, it is preferable that the third lens group includes, in order from the object side, a front lens group having positive refractive power and a rear lens group having positive refractive power, and a distance between the front lens group and the rear lens group upon zooming from the wide-angle end state to the telephoto end state decreases.

In the zoom lens according to the second embodiment, it is preferable that the third lens group includes, in order from the object side, a front lens group having positive refractive power, an intermediate lens group having negative refractive power, and a rear lens group having positive refractive power, and upon zooming from a wide-angle end state to a telephoto end state, a distance between the front lens group and the intermediate lens group varies, and a distance between the intermediate lens group and the rear lens group varies.

In the zoom lens according to the second embodiment, it is preferable that a distance between the front lens group and the intermediate lens group increases, and a distance between the intermediate lens group and the rear lens group decreases.

In the zoom lens according to the second embodiment, the front lens group preferably includes a positive lens a'.

With this configuration, it becomes possible to suppress variations in longitudinal chromatic aberration and spherical aberration generated upon zooming from the wide-angle end state to the telephoto end state, and thus high optical performance can be achieved.

In the zoom lens according to the second embodiment, the following conditional expression (21) is preferably satisfied:

0.55＜f31A’/f31＜2.45(21)

where f31 denotes a focal length of the front lens group, and f31A 'denotes a focal length of the positive lens a' in the front lens group.

Conditional expression (21) defines the optimum focal length of the positive lens a' in the first lens group, and is for achieving high optical performance and suppressing chromatic aberration generated upon zooming and variations in on-axis aberration.

When the ratio f31A '/f 31 is equal to or less than the lower limit of conditional expression (21), refractive power of the positive lens a ' becomes strong, and therefore, upon zooming from the wide-angle end state to the telephoto end state, a variation in refractive power corresponding to a variation in height of rays on the axis passing through the positive lens a ' becomes large. As a result, it becomes difficult to suppress variations in longitudinal chromatic aberration and spherical aberration. Therefore, high optical performance cannot be obtained.

On the other hand, when the ratio f31A '/f 31 is equal to or exceeds the upper limit of conditional expression (21), refractive power of the positive lens a' becomes weak, positive refractive power other than the positive lens a 'in the front lens group becomes strong, and therefore, upon zooming from the wide-angle end state to the telephoto end state, variation in refractive power corresponding to variation in height of off-axis rays passing through the positive lens a' becomes large. As a result, it becomes difficult to suppress variations in longitudinal chromatic aberration and spherical aberration. Therefore, high optical performance cannot be obtained.

In order to secure the effect of the second embodiment, the lower limit of conditional expression (21) is preferably set to 0.73.

In order to secure the effect of the second embodiment, it is preferable to set the upper limit of conditional expression (21) to 1.95.

Then, a zoom lens seen from another point of view according to the second embodiment of the present application includes, in order from the object side along the optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power. 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 increases, and a distance between the second lens group and the third lens group decreases. With this configuration, it becomes possible to realize a zoom lens, and at the same time, suppress variation in distortion upon zooming.

A zoom lens seen from another point of view according to the second embodiment includes a positive lens a' satisfying the following conditional expressions (14) and (15), and satisfies the following conditional expression (2):

1.540＜ndA’(14)

66.5＜νdA’(15)

3.90＜f1/fw＜11.00(2)

Conditional expression (14) defines the optimum refractive index of the material of the positive lens a', and is for achieving high optical performance and suppressing variations in spherical aberration and curvature of field generated upon zooming from the wide-angle end state to the telephoto end state. However, the conditional expression (14) has already been described above, and therefore, a repetitive description is omitted.

Conditional expression (15) defines the optimum abbe number of the material of the positive lens a', and is for achieving high optical performance and suppressing variation in chromatic aberration generated upon zooming from the wide-angle end state to the telephoto end state. However, conditional expression (15) has already been described above, and therefore, duplicate description is omitted.

In a zoom lens seen from another point of view according to the second embodiment of the present application, an antireflection coating is applied to at least one optical surface among the first lens group and the second lens group, and the antireflection coating includes at least one layer formed by a wet process. With this configuration, the zoom lens seen from another point of view according to the second embodiment of the present application makes it possible to suppress ghost images and flare generated by light rays from an object reflected from an optical surface, thereby achieving good optical performance.

Moreover, in a zoom lens seen from another point of view according to the second embodiment of the present application, the antireflection coating is a multilayer film, and the layer formed by the wet process is preferably an outermost layer among the layers constituting the multilayer film. With this configuration, since the difference in refractive index with respect to air can be small, the reflectance of light can be small, so that ghost images and flare can be further suppressed.

In a zoom lens seen from another point of view according to the second embodiment of the present application, when a refractive index at d-line of a layer formed by a wet process is denoted by nd, the refractive index nd is preferably 1.30 or less. With this configuration, since the difference in refractive index with respect to air can be small, the reflectance of light can be small, so that ghost images and flare can be further suppressed.

Moreover, in a zoom lens seen from another point of view according to the second embodiment of the present application, the optical surface on which the antireflection coating is formed is preferably a concave surface seen from an aperture stop. Since reflected light rays are liable to be generated on a concave surface seen from the aperture stop among optical surfaces in the first lens group and the second lens group, ghost images and flare can be effectively suppressed by applying an antireflection coating on such optical surfaces.

In a zoom lens seen from another point of view according to the second embodiment, it is desirable that the concave surface on which the antireflection coating is applied seen from the aperture stop is an image side lens surface. Since the image side concave surface seen from the aperture stop among the optical surfaces in the first lens group and the second lens group tends to generate reflected light, with applying the antireflection coating on such optical surfaces, ghost images and flare can be effectively suppressed.

In a zoom lens seen from another point of view according to the second embodiment, it is desirable that the concave surface on which the antireflection coating is applied seen from the aperture stop is an object side lens surface. Since the object side concave surface seen from the aperture stop among the optical surfaces in the first lens group and the second lens group tends to generate reflected light, with applying the antireflection coating on such optical surfaces, ghost images and flare can be effectively suppressed.

Moreover, in a zoom lens seen from another point of view according to the second embodiment of the present application, an optical surface on which the antireflection coating is formed is preferably a concave surface seen from the object side. Since reflected light is liable to be generated on a concave surface seen from an object among optical surfaces in the first lens group and the second lens group, ghost images and flare can be effectively suppressed by applying an antireflection coating on such optical surfaces.

Moreover, in a zoom lens seen from another point of view according to the second embodiment of the present application, the concave optical surface seen from the object on which the antireflection coating is formed is preferably an image side lens surface of the image side second lens from the most object side lens in the first lens group. Since reflected light rays are liable to be generated on the image side lens surface of the image side second lens from the most object side lens in the first lens group, ghost images and flare can be effectively suppressed by applying the antireflection coating on such an optical surface.

Moreover, in a zoom lens seen from another point of view according to the second embodiment of the present application, the concave optical surface seen from the object on which the antireflection coating is formed is preferably an object side lens surface of the image side second lens from the most object side lens in the second lens group. Since reflected light rays are liable to be generated on the object side lens surface of the image side second lens from the most object side lens in the second lens group, ghost images and flare can be effectively suppressed by applying the antireflection coating on such an optical surface.

Moreover, in a zoom lens seen from another point of view according to the second embodiment of the present application, the concave optical surface seen from the object on which the antireflection coating is formed is preferably an image side lens surface of the image side third lens from the most object side lens in the second lens group. Since reflected light rays are liable to be generated on the image side lens surface of the image side third lens from the most object side lens in the second lens group, ghost images and flare can be effectively suppressed by applying the antireflection coating on such an optical surface.

Moreover, in a zoom lens seen from another point of view according to the second embodiment of the present application, the concave optical surface seen from the object on which the antireflection coating is formed is preferably an object side lens surface of the image side fourth lens from the most object side lens in the second lens group. Since reflected light rays are liable to be generated on the object side lens surface of the image side fourth lens from the most object side lens in the second lens group, ghost images and flare can be effectively suppressed by applying the antireflection coating on such an optical surface.

In the zoom lens seen from another point of view according to the second embodiment, the antireflection coating may also be formed by a dry process, not limited to a wet process. In this case, it is preferable that the antireflection coating contains at least one layer whose refractive index is equal to 1.30 or less. Therefore, the same effect as in the case of using the wet method can be obtained by forming the antireflection coating based on the dry method or the like. Note that at this time, the layer whose refractive index is equal to 1.30 or less is preferably a layer constituting the outermost surface of the layers of the multilayer film.

In the zoom lens seen from another point of view according to the second embodiment, the following conditional expression (3) is preferably satisfied:

0.28＜f1/ft＜0.52(3)

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

In the zoom lens seen from another point of view according to the second embodiment, it is preferable that conditional expression (4) is satisfied:

0.25＜Δ1/f1＜1.10(4)

In a zoom lens seen from another point of view according to the second embodiment, the third lens group preferably includes a positive lens a'.

With this configuration, it becomes possible to suppress variations in longitudinal chromatic aberration and spherical aberration generated upon zooming from the wide-angle end state to the telephoto end state, so that high optical performance can be achieved.

In the zoom lens seen from another point of view according to the second embodiment, the following conditional expression (16) is preferably satisfied:

0.75＜f3A’/f3＜2.25(16)

Conditional expression (16) defines the optimum focal length of the positive lens a' in the third lens group, and is for achieving high optical performance and suppressing chromatic aberration generated upon zooming and variations in on-axis aberration. However, conditional expression (16) has already been described above, and therefore, duplicate description is omitted.

In a zoom lens seen from another point of view according to the second embodiment, the first lens group preferably includes a positive lens a'.

In the zoom lens seen from another point of view according to the second embodiment, the following conditional expression (17) is preferably satisfied:

0.65＜f1A’/f1＜1.75(17)

Conditional expression (17) defines the optimum focal length of the positive lens a' in the first lens group, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming. However, the conditional expression (17) has already been described above, and therefore, duplicate description is omitted.

In the zoom lens seen from another point of view according to the second embodiment, the following conditional expression (18) is preferably satisfied:

Conditional expression (18) defines the optimum effective diameter of the positive lens a' in the first lens group, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming. However, the conditional expression (18) has already been described above, and therefore, a repetitive description is omitted.

In the zoom lens seen from another point of view according to the second embodiment, the following conditional expression (19) is preferably satisfied:

Conditional expression (19) defines the optimum effective diameter of the positive lens a' in the first lens group, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming. However, the conditional expression (19) has already been described above, and therefore, duplicate description is omitted.

In a zoom lens seen from another point of view according to the second embodiment, the first lens group preferably includes two positive lenses.

With this configuration, the thickness of the first lens group can be suppressed, so that upon zooming from the wide-angle end state to the telephoto end state, variation in height with respect to the optical axis of off-axis rays passing through the most object side lens surface in the first lens group can be suppressed. As a result, variations in off-axis aberrations, particularly astigmatism, can be suppressed, and therefore, high optical performance can be achieved.

In a zoom lens seen from another point of view according to the second embodiment, the following conditional expressions (11) and (12) are preferably satisfied:

1.750＜ndN(11)

28.0＜νdN＜50.0(12)

Conditional expression (11) defines an optimum range of refractive index of the negative lens in the first lens group, and is for achieving high optical performance and suppressing variation in off-axis aberration generated upon zooming from the wide-angle end state to the telephoto end state. However, conditional expression (11) has already been described above, and therefore, a repetitive description is omitted.

In a zoom lens seen from another point of view according to the second embodiment, the first lens group preferably has only one negative lens.

With this configuration, the thickness of the first lens group can be suppressed. Accordingly, upon zooming from the wide-angle end state to the telephoto end state, variation in height with respect to the optical axis of off-axis rays passing through the most object side lens surface of the first lens group can be suppressed. As a result, variations in off-axis aberrations, particularly astigmatism, can be suppressed, and thus high optical performance can be achieved.

In the zoom lens seen from another point of view according to the second embodiment, the following conditional expression (20) is preferably satisfied:

75.0＜νdB’(20)

Conditional expression (20) defines the optimum abbe number of the material of the positive lens B', and is for achieving high optical performance and suppressing variation in chromatic aberration generated upon zooming from the wide-angle end state to the telephoto end state. However, the conditional expression (20) has already been described above, and therefore, a repetitive description is omitted.

In a zoom lens seen from another point of view according to the second embodiment, it is preferable that the third lens group includes, in order from the object side, a front lens group having positive refractive power and a rear lens group having positive refractive power, and a distance between the front lens group and the rear lens group upon zooming from the wide-angle end state to the telephoto end state decreases.

In a zoom lens seen from another point of view according to the second embodiment, it is preferable that the third lens group includes, in order from the object side, a front lens group having positive refractive power, an intermediate lens group having negative refractive power, and a rear lens group having positive refractive power, and upon zooming from a wide-angle end state to a telephoto end state, a distance between the front lens group and the intermediate lens group varies, and a distance between the intermediate lens group and the rear lens group varies.

In a zoom lens seen from another point of view according to the second embodiment, it is preferable that a distance between the front lens group and the intermediate lens group increases, and a distance between the intermediate lens group and the rear lens group decreases.

In the zoom lens seen from another point of view according to the second embodiment, the following conditional expression (21) is preferably satisfied:

0.55＜f31A’/f31＜2.45(21)

Conditional expression (21) defines the optimum focal length of the positive lens a' in the front lens group, and is for achieving high optical performance and suppressing chromatic aberration generated upon zooming and variations in on-axis aberration. However, the conditional expression (21) has already been described above, and therefore, duplicate description is omitted.

Next, a zoom lens according to each example of the second embodiment will be described below with reference to the drawings. Incidentally, after example 12 of the third embodiment, the antireflection coating will be separately described in detail.

< example 4>

Fig. 1 is a sectional view showing a lens configuration of a zoom lens according to example 4 of the second embodiment of the present application.

As shown in fig. 1, the zoom lens according to example 4 of the second embodiment is composed of, in order from the object side along the optical axis: a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power. The third lens group G3 is composed of, in order from the object side along the optical axis: a front lens group G31 having positive refractive power, an intermediate lens group G32 having negative refractive power, and a rear lens group G33 having positive refractive power.

Upon zooming from a wide-angle end state to a telephoto end state, the first lens group G1 is monotonously moved to the object side, the second lens group G2 is first moved to the image side and then moved to the object side, and the third lens group G3 is monotonously moved to the object side with respect to the image plane I, so that a distance between the first lens group G1 and the second lens group G2 increases, and a distance between the second lens group G2 and the third lens group G3 decreases. Further, the front lens group G31, the intermediate lens group G32, and the rear lens group G33 are monotonously moved toward the object side with respect to the image plane I, so that a distance between the front lens group G31 and the intermediate lens group G32 increases, and a distance between the intermediate lens group G32 and the rear lens group G33 decreases. Further, the front lens group G31 and the rear lens group G33 move integrally with respect to the image plane I.

The front lens group G31 is composed of, in order from the object side along the optical axis: a biconvex positive lens L31; a biconvex positive lens L32; a cemented lens constructed by a double convex positive lens L33 cemented with a negative meniscus lens L34 having a concave surface facing the object side. The biconvex positive lens L31 is a positive lens a' satisfying the conditional expressions (14) and (15).

In the zoom lens seen from another point of view according to example 4 of the second embodiment, an antireflection coating described later is applied to the image plane side lens surface of the negative meniscus lens L21 in the second lens group G2 and the object side lens surface of the double concave negative lens L22 in the second lens group G2.

Various values associated with the zoom lens according to example 4 of the second embodiment are listed in table 4.

TABLE 4

Fig. 2A, 2B, and 2C are graphs showing various aberrations of the zoom lens according to example 4 of the second embodiment, in which fig. 2A is a wide-angle end state, fig. 2B is an intermediate focal length state, and fig. 2C is a telephoto end state.

As is apparent from the respective graphs, the zoom lens according to example 4 of the second embodiment shows superior optical performance as a result of good correction for respective aberrations.

Fig. 3 is a sectional view showing a lens configuration of a zoom lens seen from another point of view according to example 4 of the second embodiment, and is an explanatory view in which light rays reflected from the first ghost-generating surface are reflected by the second ghost-generating surface. As shown in fig. 3, when a light ray BM from an object is incident on the zoom lens, the light ray is reflected by the object side lens surface (the first ghost generation surface whose surface number is 9) of the double concave negative lens L22, and the reflected light ray is reflected again by the image plane I side lens surface (the second ghost generation surface whose surface number is 8) of the negative meniscus lens L21 to reach the image plane I, and a ghost is generated. Incidentally, the first ghost generation surface 9 is a concave surface seen from the object side, and the second ghost generation surface 8 is a concave surface seen from the aperture stop S. By forming an antireflection coating corresponding to a wide wavelength range on the surface of such a lens, ghost images and flare can be effectively suppressed.

< example 5>

Fig. 8 is a sectional view showing a lens configuration of a zoom lens according to example 5 of the second embodiment of the present application.

As shown in fig. 8, the zoom lens according to example 5 of the second embodiment is composed of, in order from the object side along the optical axis: a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power. The third lens group G3 is composed of, in order from the object side along the optical axis: a front lens group G31 having positive refractive power, and a rear lens group G32 having positive refractive power.

Upon zooming from a wide-angle end state to a telephoto end state, the first lens group G1 is monotonously moved to the object side, the second lens group G2 is first moved to the image side and then moved to the object side, and the third lens group G3 is monotonously moved to the object side with respect to the image plane I, so that a distance between the first lens group G1 and the second lens group G2 increases, and a distance between the second lens group G2 and the third lens group G3 decreases. Further, the front lens group G31 and the rear lens group G32 are monotonously moved toward the object side with respect to the image plane I such that a distance between the front lens group G31 and the rear lens group G32 decreases.

The first lens group G1 is composed of, in order from the object side along the optical axis: a cemented lens constructed by a negative meniscus lens L11 having a convex surface facing the object side cemented with a double convex positive lens L12; and a positive meniscus lens L13 having a convex surface facing the object side. The positive meniscus lens L13 is a positive lens a' satisfying the conditional expressions (14) and (15).

The second lens group G2 is composed of, in order from the object side along the optical axis: a negative meniscus lens L21 having a convex surface facing the object side; a biconcave negative lens L22; a biconvex positive lens L23; and a cemented lens constructed by a negative meniscus lens L24 having a convex surface facing the image side cemented with a positive meniscus lens L25 having a convex surface facing the image side. The negative meniscus lens L21 disposed to the most object side of the second lens group G2 is a compound type aspherical lens, the object side lens surface of which is formed to be aspherical by applying a resin layer.

The front lens group G31 is composed of, in order from the object side along the optical axis: a biconvex positive lens L31; a biconvex positive lens L32; a cemented lens constructed by a double convex positive lens L33 cemented with a double concave negative lens L34; a cemented lens constructed by a double concave negative lens L35 cemented with a positive meniscus lens L36 having a convex surface facing the object side; and a negative meniscus lens L37 having a concave surface facing the object side. The double concave negative lens L35 is a glass-molded type aspherical lens, and its object side lens surface is formed to be aspherical. The biconvex positive lens L31 is a positive lens a' satisfying the conditional expressions (14) and (15).

The rear lens group G32 is composed of, in order from the object side along the optical axis: a biconvex positive lens L41; and a cemented lens constructed by a double concave negative lens L42 cemented with a double convex positive lens L43. The double convex positive lens L41 disposed to the most object side of the rear lens group G32 is a glass-molded type aspherical lens whose object side lens surface is an aspherical surface. The light rays from the biconvex positive lens L43 form an image on the image plane I.

In the zoom lens seen from another point of view according to example 5 of the second embodiment, an antireflection coating described later is applied to the object side lens surface of the positive meniscus lens L13 in the first lens group G1 and the image side lens surface of the double convex positive lens L23 in the second lens group G2.

Various values associated with the zoom lens according to example 5 of the second embodiment are listed in table 5.

TABLE 5

Fig. 9A, 9B, and 9C are graphs showing various aberrations of the zoom lens according to example 5 of the second embodiment, in which fig. 9A is a wide-angle end state, fig. 9B is an intermediate focal length state, and fig. 9C is a telephoto end state.

As is apparent from the respective graphs, the zoom lens according to example 5 of the second embodiment shows superior optical performance as a result of good correction for respective aberrations.

< example 6>

Fig. 10 is a sectional view showing a lens configuration of a zoom lens according to example 6 of the second embodiment of the present application.

As shown in fig. 10, the zoom lens according to example 6 of the second embodiment is composed of, in order from the object side along the optical axis: a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power. The third lens group G3 is composed of, in order from the object side along the optical axis: a front lens group G31 having positive refractive power, an intermediate lens group G32 having negative refractive power, and a rear lens group G33 having positive refractive power.

Upon zooming from a wide-angle end state W to a telephoto end state T, the first lens group G1 is monotonously moved to the object side, the second lens group G2 is first moved to the image side and then moved to the object side, and the third lens group G3 is monotonously moved to the object side with respect to the image plane I, so that a distance between the first lens group G1 and the second lens group G2 increases, and a distance between the second lens group G2 and the third lens group G3 decreases. Further, the front lens group G31, the intermediate lens group G32, and the rear lens group G33 are monotonously moved toward the object side with respect to the image plane I, so that a distance between the front lens group G31 and the intermediate lens group G32 increases, and a distance between the intermediate lens group G32 and the rear lens group G33 decreases.

The intermediate lens group G32 is composed of, in order from the object side along the optical axis: a cemented lens constructed by a double concave negative lens L41 cemented with a positive meniscus lens L42 having a convex surface facing the object side; and a negative meniscus lens L43 having a concave surface facing the object side. The double concave negative lens L41 disposed to the most object side of the intermediate lens group G32 is a compound type aspherical lens whose object side lens surface is an aspherical surface formed by applying a resin layer.

The rear lens group G33 is composed of, in order from the object side along the optical axis: a biconvex positive lens L51; a biconvex positive lens L52; and a cemented lens constructed by a double concave negative lens L53 cemented with a double convex positive lens L54. The double convex positive lens L51 disposed to the most object side of the rear lens group G33 is a glass-molded type aspherical lens whose object side lens surface is an aspherical surface. The light rays from the biconvex positive lens L54 form an image on the image plane I.

In the zoom lens seen from another point of view according to example 6 of the second embodiment, an antireflection coating described below is applied to the object side lens surface of the positive meniscus lens L13 in the first lens group G1 and the object side lens surface of the double concave negative lens L24 in the second lens group G2.

Various values associated with the zoom lens according to example 6 of the second embodiment are listed in table 6.

TABLE 6

Fig. 11A, 11B, and 11C are graphs showing various aberrations of the zoom lens according to example 6 of the second embodiment, in which fig. 11A is a wide-angle end state, fig. 11B is an intermediate focal length state, and fig. 11C is a telephoto end state.

As is apparent from the respective graphs, the zoom lens according to example 6 of the second embodiment shows superior optical performance as a result of good correction for respective aberrations.

< example 7>

Fig. 12 is a sectional view showing a lens configuration of a zoom lens according to example 7 of the second embodiment of the present application.

As shown in fig. 12, the zoom lens according to example 7 of the second embodiment is composed of, in order from the object side along the optical axis: a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power. The third lens group G3 is composed of, in order from the object side along the optical axis: a front lens group G31 having positive refractive power, an intermediate lens group G32 having negative refractive power, and a rear lens group G33 having positive refractive power.

In the zoom lens seen from another point of view according to example 7 of the second embodiment, an antireflection coating described later is applied to the image side lens surface of the negative meniscus lens L21 in the second lens group G2 and the object side lens surface of the double concave negative lens L22 in the second lens group G2.

Various values associated with the zoom lens according to example 7 of the second embodiment are listed in table 7.

TABLE 7

Fig. 13A, 13B, and 13C are graphs showing various aberrations of the zoom lens according to example 7 of the second embodiment, in which fig. 13A is a wide-angle end state, fig. 13B is an intermediate focal length state, and fig. 13C is a telephoto end state.

As is apparent from the respective graphs, the zoom lens according to example 7 of the second embodiment shows superior optical performance as a result of good correction for respective aberrations.

< example 8>

Fig. 6 is a sectional view showing a lens configuration of a zoom lens according to example 8 of the second embodiment of the present application.

As shown in fig. 6, the zoom lens according to example 8 of the second embodiment is composed of, in order from the object side along the optical axis: a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power. The third lens group G3 is composed of, in order from the object side along the optical axis: a front lens group G31 having positive refractive power, an intermediate lens group G32 having negative refractive power, and a rear lens group G33 having positive refractive power.

In the zoom lens seen from another point of view according to example 8 of the second embodiment, an antireflection coating described later is applied to the image side lens surface of the double convex positive lens L12 in the first lens group G1 and the object side lens surface of the double concave negative lens L24 in the second lens group G2.

Various values associated with the zoom lens according to example 8 of the second embodiment are listed in table 8.

TABLE 8

Fig. 7A, 7B, and 7C are graphs showing various aberrations of the zoom lens according to example 8 of the second embodiment, in which fig. 7A is a wide-angle end state, fig. 7B is an intermediate focal length state, and fig. 7C is a telephoto end state.

As is apparent from the respective graphs, the zoom lens according to example 8 of the second embodiment shows superior optical performance as a result of good correction for respective aberrations.

Next, an outline of a method for manufacturing a zoom lens according to the second embodiment will be described.

A method for manufacturing a zoom lens according to the second embodiment is a method for manufacturing a zoom lens that includes, in order from an object side along an optical axis, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power, and is configured such that an antireflection coating is applied to at least one optical surface in the first lens group and the second lens group, and the antireflection coating includes at least one layer formed by a wet process, the method including steps S21 to S23 shown in fig. 25.

Step S21: disposing the first lens group G1, the second lens group G2, and the third lens group G3 movably such that 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 increases, and a distance between the second lens group and the third lens group decreases;

step S22: a positive lens a' satisfying the following conditional expressions (14) and (15) is arranged:

1.540＜ndA’(14)

66.5＜νdA’(15)

where ndA 'denotes a refractive index at the d-line (wavelength λ 587.6nm) of the material of the positive lens a', and ν dA 'denotes an abbe number at the d-line (wavelength λ 587.6nm) of the material of the positive lens a'.

Step S23: each lens is arranged satisfying the following conditional expression (2):

3.90＜f1/fw＜11.00(2)

With this method for manufacturing a zoom lens according to the second embodiment, it becomes possible to manufacture a zoom lens having good optical performance, and suppress variations in aberrations as well as ghost images and flare.

(third embodiment)

A zoom lens according to a third embodiment of the present application is described below.

A zoom lens according to a third embodiment of the present application includes, in order from an object side along an optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power. 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 increases, and a distance between the second lens group and the third lens group decreases. With this configuration, it becomes possible to realize a zoom lens, and at the same time, suppress variations in distortion generated upon zooming.

In a zoom lens according to the third embodiment, the first lens group includes a plurality of positive lenses satisfying the following conditional expressions (22) and (23), and the following conditional expression (3) is satisfied:

66.5< vd when 1.540 ≦ ndA ″.

When ndA "< 1.540, 75.0< ν dA" (22)

4.75＜f1/fw＜11.00(23)

0.28＜f1/ft＜0.52(3)

Where ndA 'denotes a refractive index at a d-line (wavelength λ 587.6nm) of a material of each of the plurality of positive lenses in the first lens group, ν dA' denotes an abbe number at the d-line (wavelength λ 587.6nm) of the material of each of the plurality of positive lenses of the first lens group, fw denotes a focal length of the zoom lens in the wide-angle end state, ft denotes a focal length of the zoom lens in the telephoto end state, and f1 denotes a focal length of the first lens group.

Conditional expression (22) defines an optimum abbe number of a material of each of the plurality of positive lenses of the first lens group, and is for achieving high optical performance and suppressing variations in longitudinal chromatic aberration and transverse chromatic aberration generated upon zooming from the wide-angle end state to the telephoto end state.

When the value ν dA "is equal to or smaller than the lower limit of conditional expression (22), it becomes difficult to suppress variations in longitudinal chromatic aberration and lateral chromatic aberration. The material becomes a material having small anomalous dispersion, so that it becomes difficult to suppress variations in second-order chromatic aberration. In addition, longitudinal chromatic aberration and lateral chromatic aberration in the visible light range become large in the telephoto end state, and thus high optical performance cannot be obtained.

In order to secure the effect of the third embodiment, it is preferable to set the lower limit of conditional expression (22) to 67.5 when 1.540. ltoreq. ndA ". In order to secure the effect of the third embodiment, it is preferable to set the lower limit of conditional expression (22) to 80.5 when ndA "< 1.540.

Conditional expression (23) defines an optimum range of the focal length of the first lens group, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming from the wide-angle end state to the telephoto end state.

When the ratio f1/fw is equal to or smaller than the lower limit of conditional expression (23), refractive power of the first lens group becomes strong, and therefore it becomes difficult to suppress variations in transverse chromatic aberration and off-axis aberration, particularly astigmatism. Therefore, high optical performance cannot be obtained.

On the other hand, when the ratio f1/fw is equal to or exceeds the upper limit of conditional expression (23), refractive power of the first lens group becomes weak, and therefore, in order to obtain a given zoom ratio, the moving amount of the first lens group with respect to the image plane must be increased. Therefore, the variation in height of the off-axis rays with respect to the optical axis becomes large. As a result, variations in lateral chromatic aberration and off-axis aberration, particularly astigmatism, cannot be suppressed, and therefore high optical performance cannot be achieved.

In order to secure the effect of the third embodiment, the lower limit of conditional expression (23) is preferably set to 5.10.

In order to secure the effect of the third embodiment, it is preferable to set the upper limit of conditional expression (23) to 8.80. In order to further secure the effect of the present embodiment, it is most preferable to set the upper limit of conditional expression (23) to 7.60.

In the zoom lens according to the third embodiment, conditional expression (4) is preferably satisfied:

0.25＜Δ1/f1＜1.10(4)

Conditional expression (4) defines an optimum moving amount of the first lens group with respect to the image plane upon zooming from the wide-angle end state to the telephoto end state, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming. However, conditional expression (4) has already been described above, and therefore, a repetitive description is omitted.

In the zoom lens according to the third embodiment, it is preferable that conditional expression (24) is satisfied:

0.65＜f1A”/f1＜1.75(24)

where f1A ″ represents a focal length of each of the plurality of positive lenses in the first lens group.

Conditional expression (24) defines an optimum focal length of each of the plurality of positive lenses in the first lens group, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming.

When the ratio f1A "/f 1 is equal to or less than the lower limit of conditional expression (24), refractive power of each of the plurality of positive lenses becomes strong, and therefore, upon zooming from the wide-angle end state to the telephoto end state, a variation in refractive power corresponding to a variation in height with respect to the optical axis of off-axis rays passing through the first lens group becomes large. As a result, it becomes difficult to suppress variations in lateral chromatic aberration and off-axis aberration, particularly astigmatism, and therefore high optical performance cannot be achieved.

On the other hand, when the ratio f1A "/f 1 is equal to or exceeds the upper limit of conditional expression (24), the refractive power of each of the plurality of positive lenses becomes weak, and therefore it becomes difficult to suppress variations in chromatic aberration and off-axis aberration, particularly astigmatism, and therefore high optical performance cannot be achieved.

In order to secure the effect of the third embodiment, the lower limit of conditional expression (24) is preferably set to 0.80.

In order to secure the effect of the third embodiment, it is preferable to set the upper limit of conditional expression (24) to 1.35.

In the zoom lens according to the third embodiment, the following conditional expression (25) is preferably satisfied:

wherein,an effective diameter of each of the plurality of positive lenses in the first lens group is indicated.

Conditional expression (25) defines an optimum effective diameter of each of the plurality of positive lenses in the first lens group, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming.

When ratio ofEqual to or less than the lower limit of conditional expression (25), upon zooming from the wide-angle end state to the telephoto end state, variation in height with respect to the optical axis of off-axis rays passing through the plurality of positive lenses in the first lens group becomes small, and therefore, it becomes difficult to suppress variation in off-axis aberration, particularly astigmatism. As a result, high optical performance cannot be achieved.

On the other hand, when the ratio isEqual to or exceeding the upper limit of conditional expression (25), upon zooming from the wide-angle end state to the telephoto end state, variation in height with respect to the optical axis of off-axis rays passing through the plurality of positive lenses in the first lens group becomes large, and therefore, it becomes difficult to suppress variation in lateral chromatic aberration and off-axis aberration, particularly astigmatism. As a result, high optical performance cannot be achieved.

In order to secure the effect of the third embodiment, the lower limit of conditional expression (25) is preferably 2.45.

In order to secure the effect of the third embodiment, it is preferable to set the upper limit of conditional expression (25) to 3.80.

In the zoom lens according to the third embodiment, the number of the plurality of positive lenses in the first lens group is preferably 2.

With this configuration, it becomes possible to suppress the thickness of the first lens group, and therefore, it becomes possible to suppress variation in height with respect to the optical axis of off-axis rays passing through the most object-side surface in the first lens group, and as a result, it becomes possible to suppress variation in off-axis aberration, particularly astigmatism, and therefore, high optical performance can be achieved.

In the zoom lens according to the third embodiment, the first lens group preferably includes a negative lens that satisfies the following conditional expressions (11) and (12):

1.750＜ndN(11)

28.0＜νdN＜50.0(12)

In the zoom lens according to the third embodiment, the number of negative lenses in the first lens group is preferably one.

With this configuration, it becomes possible to suppress the thickness of the first lens group, and therefore, upon zooming from the wide-angle end state to the telephoto end state, it is possible to suppress variation in height with respect to the optical axis of off-axis rays passing through the most object side surface of the first lens group. Variations in off-axis aberrations, particularly astigmatism, can be suppressed, and therefore, high optical performance can be achieved.

In the zoom lens according to the third embodiment, the third lens group preferably satisfies the following conditional expression (26):

65.5＜νd3(26)

where vd 3 denotes an abbe number at the d-line (wavelength λ 587.6nm) of the material of the positive lens in the third lens group.

Conditional expression (26) defines an optimum abbe number of the material of the positive lens in the third lens group, and is for achieving high optical performance and suppressing variation in chromatic aberration generated upon zooming from the wide-angle end state to the telephoto end state.

When the value ν d3 is equal to or smaller than the lower limit of conditional expression (26), it becomes difficult to suppress variations in longitudinal chromatic aberration and lateral chromatic aberration. The material becomes a material having small anomalous dispersion, so that it becomes difficult to suppress variations in second-order chromatic aberration. In addition, longitudinal chromatic aberration and lateral chromatic aberration in the visible light range become large in the telephoto end state, and thus high optical performance cannot be obtained.

In the zoom lens according to the third embodiment, it is preferable that the third lens group includes, in order from the object side, a front lens group having positive refractive power and a rear lens group having positive refractive power, and a distance between the front lens group and the rear lens group upon zooming from the wide-angle end state to the telephoto end state decreases.

In the zoom lens according to the third embodiment, it is preferable that the third lens group includes, in order from the object side, a front lens group having positive refractive power, an intermediate lens group having negative refractive power, and a rear lens group having positive refractive power, and upon zooming from a wide-angle end state to a telephoto end state, a distance between the front lens group and the intermediate lens group varies, and a distance between the intermediate lens group and the rear lens group varies.

In the zoom lens according to the third embodiment, it is preferable that a distance between the front lens group and the intermediate lens group increases, and a distance between the intermediate lens group and the rear lens group decreases.

Then, a zoom lens seen from another point of view according to the third embodiment of the present application is described below.

A zoom lens seen from another point of view according to the third embodiment of the present application includes, in order from an object side along an optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens having positive refractive power. 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 increases, and a distance between the second lens group and the third lens group decreases. With this configuration, it becomes possible to realize a zoom lens, and at the same time, suppress variation in distortion generated upon zooming.

In a zoom lens seen from another point of view according to the third embodiment, the first lens group includes a plurality of positive lenses satisfying the following conditional expressions (22) and (23), and the following conditional expression (3) is satisfied:

66.5< vd when 1.540 ≦ ndA ″.

When ndA "< 1.540, 75.0< ν dA" (22)

4.75＜f1/fw＜11.00(23)

0.28＜f1/ft＜0.52(3)

Conditional expression (22) defines an optimum abbe number of a material of each of the plurality of positive lenses of the first lens group, and is for achieving high optical performance and suppressing variations in longitudinal chromatic aberration and transverse chromatic aberration generated upon zooming from the wide-angle end state to the telephoto end state. However, the conditional expression (22) has already been described above, and therefore, a repetitive description is omitted.

Conditional expression (23) defines an optimum range of the focal length of the first lens group, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming from the wide-angle end state to the telephoto end state. However, conditional expression (23) has already been described above, and therefore, duplicate description is omitted.

In a zoom lens seen from another point of view according to the third embodiment of the present application, an antireflection coating is applied to at least one optical surface among the first lens group and the second lens group, and the antireflection coating includes at least one layer formed by a wet process. With this configuration, the zoom lens seen from another point of view according to the third embodiment of the present application makes it possible to suppress ghost images and flare generated by light rays from an object reflected from an optical surface, thereby achieving good optical performance.

Moreover, in a zoom lens seen from another point of view according to the third embodiment of the present application, the antireflection coating is a multilayer film, and the layer formed by the wet process is preferably an outermost layer among the layers constituting the multilayer film. With this configuration, since the difference in refractive index with respect to air can be small, the reflectance of light can be small, so that ghost images and flare can be further suppressed.

In a zoom lens seen from another point of view according to the third embodiment of the present application, when a refractive index at d-line of a layer formed by a wet process is denoted by nd, the refractive index nd is preferably 1.30 or less. With this configuration, since the difference in refractive index with respect to air can be small, the reflectance of light can be small, so that ghost images and flare can be further suppressed.

Moreover, in a zoom lens seen from another point of view according to the third embodiment of the present application, the optical surface on which the antireflection coating is formed is preferably a concave surface seen from an aperture stop. Since reflected light rays are liable to be generated on a concave surface seen from the aperture stop among optical surfaces in the first lens group and the second lens group, ghost images and flare can be effectively suppressed by applying an antireflection coating on such optical surfaces.

In a zoom lens seen from another point of view according to the third embodiment, it is desirable that the concave surface on which the antireflection coating is applied seen from the aperture stop is an image side lens surface. Since the image side concave surface seen from the aperture stop among the optical surfaces in the first lens group and the second lens group tends to generate reflected light, with applying the antireflection coating on such optical surfaces, ghost images and flare can be effectively suppressed.

In a zoom lens seen from another point of view according to the third embodiment, it is desirable that the concave surface on which the antireflection coating is applied seen from the aperture stop is an object side lens surface. Since the object side concave surface seen from the aperture stop among the optical surfaces in the first lens group and the second lens group tends to generate reflected light, with applying the antireflection coating on such optical surfaces, ghost images and flare can be effectively suppressed.

Moreover, in a zoom lens seen from another point of view according to the third embodiment of the present application, an optical surface on which the antireflection coating is formed is preferably a concave surface seen from the object side. Since reflected light is liable to be generated on a concave surface seen from an object among optical surfaces in the first lens group and the second lens group, ghost images and flare can be effectively suppressed by applying an antireflection coating on such optical surfaces.

Moreover, in a zoom lens seen from another point of view according to the third embodiment of the present application, the concave optical surface seen from the object on which the antireflection coating is formed is preferably an image side lens surface of the image side second lens from the most object side lens in the first lens group. Since reflected light rays are liable to be generated on the image side lens surface of the image side second lens from the most object side lens in the first lens group, ghost images and flare can be effectively suppressed by applying the antireflection coating on such an optical surface.

Moreover, in a zoom lens seen from another point of view according to the third embodiment of the present application, the concave optical surface seen from the object on which the antireflection coating is formed is preferably an object side lens surface of the image side second lens from the most object side lens in the second lens group. Since reflected light rays are liable to be generated on the object side lens surface of the image side second lens from the most object side lens in the second lens group, ghost images and flare can be effectively suppressed by applying the antireflection coating on such an optical surface.

Moreover, in a zoom lens seen from another point of view according to the third embodiment of the present application, the concave optical surface seen from the object on which the antireflection coating is formed is preferably an image side lens surface of the image side third lens from the most object side lens in the second lens group. Since reflected light rays are liable to be generated on the image side lens surface of the image side third lens from the most object side lens in the second lens group, ghost images and flare can be effectively suppressed by applying the antireflection coating on such an optical surface.

Moreover, in a zoom lens seen from another point of view according to the third embodiment of the present application, the concave optical surface seen from the object on which the antireflection coating is formed is preferably an object side lens surface of the image side fourth lens from the most object side lens in the second lens group. Since reflected light rays are liable to be generated on the object side lens surface of the image side fourth lens from the most object side lens in the second lens group, ghost images and flare can be effectively suppressed by applying the antireflection coating on such an optical surface.

In the zoom lens seen from another point of view according to the third embodiment, the antireflection coating may also be formed by a dry process, not limited to a wet process. In this case, it is preferable that the antireflection coating contains at least one layer whose refractive index is equal to 1.30 or less. Therefore, the same effect as in the case of using the wet method can be obtained by forming the antireflection coating based on the dry method or the like. Note that at this time, the layer whose refractive index is equal to 1.30 or less is preferably a layer constituting the outermost surface of the layers of the multilayer film.

0.25＜Δ1/f1＜1.10(4)

In the zoom lens according to the third embodiment, the following conditional expression (24) is preferably satisfied:

0.65＜f1A”/f1＜1.75(24)

Conditional expression (24) defines an optimum focal length of each of the plurality of positive lenses in the first lens group, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming. However, the conditional expression (24) has already been described above, and therefore, a repetitive description is omitted.

In a zoom lens seen from another point of view according to the third embodiment, the following conditional expression (25) is preferably satisfied:

Conditional expression (25) defines an optimum effective diameter of each of the plurality of positive lenses in the first lens group, and is for achieving high optical performance and suppressing variations in chromatic aberration and off-axis aberration generated upon zooming. However, the conditional expression (25) has already been described above, and therefore, duplicate description is omitted.

In a zoom lens seen from another point of view according to the third embodiment, the number of the plurality of positive lenses in the first lens group is preferably 2.

In a zoom lens seen from another point of view according to the third embodiment, the first lens group preferably includes a negative lens that satisfies the following conditional expressions (11) and (12):

1.750＜ndN(11)

28.0＜νdN＜50.0(12)

In a zoom lens seen from another point of view according to the third embodiment, the number of negative lenses in the first lens group is preferably one.

With this configuration, it becomes possible to suppress the thickness of the first lens group, and therefore, upon zooming from the wide-angle end state to the telephoto end state, it is possible to suppress variation in height with respect to the optical axis of off-axis rays passing through the most object side surface of the first lens group. As a result, variations in off-axis aberrations, particularly astigmatism, can be suppressed, and therefore, high optical performance can be achieved.

In a zoom lens seen from another point of view according to the third embodiment, the third lens group preferably satisfies the following conditional expression (26):

65.5＜νd3(26)

Conditional expression (26) defines an optimum abbe number of the material of the positive lens in the third lens group, and is for achieving high optical performance and suppressing variation in chromatic aberration generated upon zooming from the wide-angle end state to the telephoto end state. However, the conditional expression (26) has already been described above, and therefore, duplicate description is omitted.

In a zoom lens seen from another point of view according to the third embodiment, it is preferable that the third lens group includes, in order from the object side, a front lens group having positive refractive power and a rear lens group having positive refractive power, and a distance between the front lens group and the rear lens group upon zooming from the wide-angle end state to the telephoto end state decreases.

In a zoom lens seen from another point of view according to the third embodiment, it is preferable that the third lens group includes, in order from the object side, a front lens group having positive refractive power, an intermediate lens group having negative refractive power, and a rear lens group having positive refractive power, and upon zooming from a wide-angle end state to a telephoto end state, a distance between the front lens group and the intermediate lens group varies, and a distance between the intermediate lens group and the rear lens group varies.

In a zoom lens seen from another point of view according to the third embodiment, it is preferable that, upon zooming from a wide-angle end state to a telephoto end state, a distance between the front lens group and the intermediate lens group increases, and a distance between the intermediate lens group and the rear lens group decreases.

Next, a zoom lens according to each example of the third embodiment will be described below with reference to the drawings. Incidentally, after example 12 of the third embodiment, the antireflection coating will be separately described in detail.

< example 9>

Fig. 12 is a sectional view showing a lens configuration of a zoom lens according to example 9 of the third embodiment of the present application.

As shown in fig. 12, the zoom lens according to example 9 of the third embodiment is composed of, in order from the object side along the optical axis: a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power. The third lens group G3 is composed of, in order from the object side along the optical axis: a front lens group G31 having positive refractive power, an intermediate lens group G32 having negative refractive power, and a rear lens group G33 having positive refractive power.

The intermediate lens group G32 is composed of, in order from the object side along the optical axis: a cemented lens constructed by a double concave negative lens L41 cemented with a positive meniscus lens L42 having a convex surface facing the object side; and a negative meniscus lens L43 having a concave surface facing the object side. The double concave negative lens L41 disposed to the most object side of the rear lens group G32 is a compound type aspherical lens whose object side lens surface is an aspherical surface formed by applying a resin layer.

In the zoom lens seen from another point of view according to example 9 of the third embodiment, an antireflection coating described later is applied to the image side lens surface of the negative meniscus lens L21 in the second lens group G2 and the object side lens surface of the double concave negative lens L22 in the second lens group G2.

Various values associated with the zoom lens according to example 9 of the third embodiment are listed in table 9.

TABLE 9

Fig. 13A, 13B, and 13C are graphs showing various aberrations of the zoom lens according to example 9 of the third embodiment, in which fig. 13A is a wide-angle end state, fig. 13B is an intermediate focal length state, and fig. 13C is a telephoto end state.

As is apparent from the respective graphs, the zoom lens according to example 9 of the second embodiment shows superior optical performance as a result of good correction for respective aberrations.

Fig. 14 is a sectional view showing a lens configuration of a lens system of example 9 seen from another point of view according to a third embodiment, and is an explanatory view in which the second ghost generation surface reflects light rays reflected from the first ghost generation surface.

As shown in fig. 14, when a light ray BM from an object is incident on the zoom lens, the light ray is reflected by the object side lens surface (the first ghost generation surface whose surface number is 9) of the double concave negative lens L22, and the reflected light ray is reflected again by the image plane I side lens surface (the second ghost generation surface whose surface number is 8) of the negative meniscus lens L21 to reach the image plane I, and a ghost is generated. Incidentally, the first ghost generation surface 9 is a concave surface as viewed from the object side, and the second ghost generation surface 8 is a concave surface as viewed from the aperture stop S side. By forming an antireflection coating corresponding to a wide wavelength range on the surface of such a lens, ghost images and flare can be effectively reduced.

< example 10>

Fig. 8 is a sectional view showing a lens configuration of a zoom lens according to example 10 of the third embodiment of the present application.

As shown in fig. 8, the zoom lens according to example 10 of the third embodiment is composed of, in order from the object side along the optical axis: a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power. The third lens group G3 is composed of, in order from the object side along the optical axis: a front lens group G31 having positive refractive power, and a rear lens group G32 having positive refractive power.

The front lens group G31 is composed of, in order from the object side along the optical axis: a biconvex positive lens L31; a biconvex positive lens L32; a cemented lens constructed by a double convex positive lens L33 cemented with a double concave negative lens L34; a cemented lens constructed by a double concave negative lens L35 cemented with a positive meniscus lens L36 having a convex surface facing the object side; and a negative meniscus lens L37 having a concave surface facing the object side. The double concave negative lens L35 is a glass-molded type aspherical lens, and its object side lens surface is formed to be aspherical.

In the zoom lens seen from another point of view according to example 10 of the third embodiment, an antireflection coating described later is applied to the object side lens surface of the positive meniscus lens L13 in the first lens group G1 and the image side lens surface of the double convex positive lens L23 in the second lens group G2.

Various values associated with the zoom lens according to example 10 of the third embodiment are listed in table 10.

Watch 10

Fig. 9A, 9B, and 9C are graphs showing various aberrations of the zoom lens according to example 10 of the third embodiment, in which fig. 9A is a wide-angle end state, fig. 9B is an intermediate focal length state, and fig. 9C is a telephoto end state.

As is apparent from the respective graphs, the zoom lens according to example 10 of the third embodiment shows superior optical performance as a result of good correction for respective aberrations.

< example 11>

Fig. 10 is a sectional view showing a lens configuration of a zoom lens according to example 11 of the third embodiment of the present application.

As shown in fig. 10, the zoom lens according to example 11 of the third embodiment is composed of, in order from the object side along the optical axis: a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power. The third lens group G3 is composed of, in order from the object side along the optical axis: a front lens group G31 having positive refractive power, an intermediate lens group G32 having negative refractive power, and a rear lens group G33 having positive refractive power.

An aperture stop S is disposed to the most object side of the third lens group G3, and is integrally formed with the front lens group G31, and the third lens group G3 is disposed to the image side of the second lens group G2.

In the zoom lens seen from another point of view according to example 11 of the third embodiment, an antireflection coating described later is applied to the object side lens surface of the positive meniscus lens L13 in the first lens group G1 and the object side lens surface of the double concave negative lens L24 in the second lens group G2.

Various values associated with the zoom lens according to example 11 of the third embodiment are listed in table 11.

TABLE 11

Fig. 11A, 11B, and 11C are graphs showing various aberrations of the zoom lens according to example 11 of the third embodiment, in which fig. 11A is a wide-angle end state, fig. 11B is an intermediate focal length state, and fig. 11C is a telephoto end state.

As is apparent from the respective graphs, the zoom lens according to example 11 of the third embodiment shows superior optical performance as a result of good correction for respective aberrations.

< example 12>

As shown in fig. 15, the zoom lens according to example 12 of the third embodiment is composed of, in order from the object side along the optical axis: a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power. The third lens group G3 is composed of, in order from the object side along the optical axis: a front lens group G31 having positive refractive power, and a rear lens group G32 having positive refractive power.

The front lens group G31 is composed of, in order from the object side along the optical axis: a biconvex positive lens L31; a biconvex positive lens L32; a cemented lens constructed by a double convex positive lens L33 cemented with a double concave negative lens L34; a cemented lens constructed by a double concave negative lens L35 cemented with a double convex positive lens L36; and a negative meniscus lens L37 having a concave surface facing the object side. The double concave negative lens L35 is a glass-molded type aspherical lens, and its object side lens surface is formed to be aspherical.

The rear lens group G32 is composed of, in order from the object side along the optical axis: a biconvex positive lens L41; and a cemented lens constructed by a negative meniscus lens L42 having a convex surface facing the object side cemented with a double convex positive lens L43. The double convex positive lens L41 disposed to the most object side of the rear lens group G32 is a glass-molded type aspherical lens whose object side lens surface is an aspherical surface. The light rays from the biconvex positive lens L43 form an image on the image plane I.

In the zoom lens seen from another point of view according to example 12 of the third embodiment, an antireflection coating described below is applied to the image side lens surface of the double convex positive lens L12 in the first lens group G1 and the image side lens surface of the negative meniscus lens L21 in the second lens group G2.

Various values associated with the zoom lens according to example 12 of the third embodiment are listed in table 12.

TABLE 12

As is apparent from the respective graphs, the zoom lens according to example 12 of the third embodiment shows superior optical performance as a result of good correction for respective aberrations.

Next, an outline of a method for manufacturing a zoom lens according to the third embodiment is described.

A method for manufacturing a zoom lens according to the third embodiment is a method for manufacturing a zoom lens that includes, in order from an object along an optical axis, a first lens group G1 having positive refractive power, a second lens group G2 having negative refractive power, and a third lens group G3 having positive refractive power, and is configured such that an antireflection coating is applied to at least one optical surface in the first lens group and the second lens group, and the antireflection coating includes at least one layer formed by a wet process, the method including steps S31 to S33 shown in fig. 26.

Step S31: the first lens group G1, the second lens group G2, and the third lens group G3 are movably arranged such that, 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 increases, and a distance between the second lens group and the third lens group decreases.

Step S32: disposing a plurality of positive lenses satisfying the following conditional expression (22) within the first lens group:

66.5< vd when 1.540 ≦ ndA ″.

When ndA "< 1.540, 75.0< ν dA" (22)

Wherein ndA 'represents a refractive index at a d-line (wavelength λ 587.6nm) of a material of each of the plurality of positive lenses in the first lens group, and ν dA' represents an abbe number at the d-line (wavelength λ 587.6nm) of the material of each of the plurality of positive lenses in the first lens group.

Step S33: each lens is arranged satisfying the following conditional expressions (23) and (3):

4.75＜f1/fw＜11.0(23)

0.28＜f1/ft＜0.52(3)

With this method for manufacturing a zoom lens according to the third embodiment, it becomes possible to manufacture a zoom lens having good optical performance, and suppress variations in aberrations as well as ghost images and flare.

Next, an antireflection coating used in the zoom lens seen from another point of view according to each example of the first to third embodiments is explained.

Fig. 17 is an explanatory view of the configuration of an antireflection coating (also referred to as a multilayer broadband antireflection coating) used in the zoom lens according to the present embodiment. The antireflection coating 101 is composed of seven layers, and is formed on the optical surface of the optical member 102 such as a lens. The first layer 101a is formed using alumina by a vacuum evaporation method. On the first layer 101a, a second layer 101b formed using a mixture of titanium oxide and zirconium oxide by a vacuum evaporation method is formed. Further, a third layer 101c formed using alumina by a vacuum evaporation method is formed on the second layer 101 b. Further, a fourth layer 101f formed using a mixture of titanium oxide and zirconium oxide by a vacuum evaporation method is formed on the third layer 101 c. Further, a fifth layer 101e formed using alumina by a vacuum evaporation method is formed on the fourth layer 101 d. On the fifth layer 101e, a sixth layer 101f formed using a mixture of titanium oxide and zirconium oxide by a vacuum evaporation method is formed.

Then, on the sixth layer 101f formed in this way, a seventh layer 101g formed using a mixture of silicon dioxide and magnesium fluoride is formed by a wet process to form an antireflection coating according to the present embodiment. To form the seventh layer 101g, a sol-gel method as a wet treatment was used. The sol-gel method is the following treatment: the sol obtained by mixing is converted into a gel without fluidity by a hydrolytic polycondensation reaction, and the product is obtained by thermally decomposing this gel. In the manufacture of optical films, the film may be produced by: a material sol of an optical thin film is coated on an optical surface of an optical member, and the sol is dried and cured into a gel film. Note that the wet method may include a process of using a solid film that is not obtained by a gel state, and is not limited to the sol-gel process.

In this way, the first layer 101a to the sixth layer 101f are formed by electron beam evaporation as a drying process, and the seventh layer 101g as the uppermost layer is formed by a subsequent wet process using a sol liquid prepared by a hydrofluoric acid/magnesium acetate method. First, a film is formed on the film formation surface (the above optical surface of the optical member 102) by a vacuum evaporation apparatus in the following order: an aluminum oxide layer which becomes the first layer 101 a; a mixture layer of titanium oxide and zirconium oxide, which becomes the second layer 101 b; an aluminum oxide layer which becomes the third layer 101 a; a mixture layer of titanium oxide and zirconium oxide, which becomes the fourth layer 101 b; an aluminum oxide layer which becomes the fifth layer 101 a; and a mixture layer of titanium oxide and zirconium oxide, which becomes the sixth layer 101 b. Then, after being taken out from the vacuum evaporation apparatus, the sol liquid prepared by the hydrofluoric acid/magnesium acetate method was applied to the optical member 102 by the spray coating method, thereby forming a layer formed of a mixture of silicon dioxide and magnesium fluoride, which became the seventh layer 101 g. The reaction formula prepared by the hydrofluoric acid/magnesium acetate method is shown by the expression (a):

2HF+Mg(CH3COO)2→MgF2+2CH3COOH(a)

the sol liquid is used to form a film after mixing the components through a high-temperature, high-pressure aging treatment performed at 140 ℃ for 24 hours in an autoclave. After the formation of the seventh layer 101g was completed, the optical member 102 was processed using heat treatment at 160 ℃ for one hour under atmospheric pressure, thereby completing. Using such a sol-gel method, atoms or molecules from several to several tens of nanometers are aggregated to become particles of several nanometers to several tens of nanometers, and several such particles are established to form secondary particles. As a result, the secondary fine particles are stacked to form the seventh layer 101 g.

The optical performance of the optical member including the thus formed antireflection coating 101 is described below by using the spectral characteristics shown in fig. 18.

The optical member (lens) including the antireflection coating according to each of the first to third embodiments was formed under the conditions shown in table 13 below. Here, table 13 shows the respective optical film thicknesses of the layers 101a (first layer) to 101g (seventh layer) of the antireflection coating 101 obtained under the following conditions: λ denotes a reference wavelength, and the refractive indices of the substrate (optical member) are set to 1.62, 1.74, and 1.85. Note that table 13 shows Al expressed as alumina₂O₃ZrO expressed as a mixture of titanium oxide and zirconium oxide₂+TiO₂And MgF expressed as a mixture of magnesium fluoride and silica₂+SiO₂。

Watch 13

Fig. 18 shows spectral characteristics when a light beam is perpendicularly incident on an optical member in which the optical film thickness of each of the layers of the antireflection coating 101 is designed, and the reference wavelength λ is set to 550nm in table 13.

As is apparent from fig. 18, the optical member including the antireflection coating 101 designed in the case where the reference wavelength is set to 550nm can limit the reflectance to be as low as 0.2% or less in the entire range where the wavelength of the light beam is 420nm to 720 nm. Also, in table 13, even the optical member including the antireflection coating 101 has substantially the same spectral characteristics as in the case where the reference wavelength λ shown in fig. 18 is 550nm, in a manner not to substantially affect the spectral characteristics thereof, wherein each optical film thickness is designed with the reference wavelength λ set to the d-line (wavelength 587.6 nm).

Next, a modified example of the antireflection coating will be described. The antireflection coating was a 5-layer film, and the optical film thickness of each layer with respect to the reference wavelength λ was designed under the conditions shown in table 14 below, similarly to table 13. In this modified example, the formation of the fifth layer involves using the dissolving gel process as described above.

TABLE 14

Fig. 19 shows spectral characteristics when a light beam is perpendicularly incident on the optical member, in which the optical film thickness of each layer is designed with the substrate refractive index set to 1.52 and the reference wavelength λ set to 550nm in table 14. As is apparent from fig. 19, the antireflection coating in the modified example can limit the reflectance to be as low as 0.2% or less over the entire range in which the wavelength of the light beam is 420nm-720 nm. Note that in table 14, even the optical member including the antireflection coating has substantially the same spectral characteristics as those shown in fig. 19 in such a manner that the spectral characteristics thereof are not substantially affected, wherein each optical film thickness is designed with the reference wavelength λ set to the d-line (wavelength 587.6 nm).

Fig. 20 shows spectral characteristics in the case where the incident angles of the light beams incident on the optical member having the spectral characteristics shown in fig. 19 are 30 degrees, 45 degrees, and 60 degrees, respectively. Note that fig. 19 and 20 do not show the spectral characteristics of the optical member including the antireflection coating in which the substrate refractive index is 1.46 shown in fig. 14, however, it is understood that the optical member has the spectral characteristics substantially the same as the substrate refractive index is 1.52.

Also, fig. 21 shows, by comparison, one example of an antireflection coating by only a drying method such as a conventional vacuum evaporation method. Fig. 21 shows spectral characteristics when a light beam was incident on the optical member, in which the antireflection coating configured under the conditions shown in table 13 below was designed, and the substrate refractive index was set to 1.52 in the same manner as in table 12. Further, fig. 22 shows spectral characteristics in the following cases: the incident angles of the light beams on the optical member having the spectral characteristics shown in fig. 21 are 30 degrees, 45 degrees, and 60 degrees, respectively.

Watch 15

Comparing the spectral characteristics of the optical member including the antireflection coating according to the present embodiment shown in fig. 18 to 20 with those in the conventional examples shown in fig. 21 and 22, it can be understood that the current antireflection coating has much lower reflectance at any incident angle and has low reflectance over a wider frequency band.

Next, an example of applying the antireflection coating shown in table 13 to example 1 of the first embodiment to example 12 of the third embodiment as described above is explained.

In the zoom lens seen from another point of view according to example 1 of the first embodiment, as shown in table 1, the refractive index nd of the negative meniscus lens L21 of the second lens group G2 is 1.834807(nd ═ 1.834807), and the refractive index nd of the double concave negative lens L22 of the second lens group G2 is 1.816000(nd ═ 1.816000), whereby it is feasible to reduce light reflected from each lens surface and reduce ghost images and flare by: an antireflection coating 101 corresponding to 1.85 as the substrate refractive index is applied to the image side lens surface of the negative meniscus lens L21 (see table 13), and an antireflection coating corresponding to 1.85 as the substrate refractive index is applied to the object side lens surface of the double concave negative lens L22 (see table 13).

In the zoom lens seen from another point of view according to example 2 of the first embodiment, as shown in table 2, the refractive index nd of the positive meniscus lens L13 of the first lens group G1 is 1.603001(nd ═ 1.603001), and the refractive index nd of the biconvex positive lens L23 of the second lens group G2 is 1.846660(nd ═ 1.846660), whereby it is feasible to reduce light reflected from each lens surface and reduce ghost images and flare by: an antireflection coating 101 corresponding to 1.62 as the substrate refractive index was applied to the object side lens surface of the positive meniscus lens L13 (see table 13), and an antireflection coating corresponding to 1.85 as the substrate refractive index was applied to the image side lens surface of the double convex positive lens L23 (see table 13).

In the zoom lens seen from another point of view according to example 3 of the first embodiment, as shown in table 3, the refractive index nd of the double convex positive lens L12 of the first lens group G1 is 1.437000(nd ═ 1.437000), and the refractive index nd of the double concave negative lens L24 of the second lens group G2 is 1.816000(nd ═ 1.816000), whereby it is feasible to reduce light reflected from each lens surface and reduce ghost images and flare by: an antireflection coating 101 corresponding to 1.46 as the substrate refractive index is applied to the image side lens surface of the double convex positive lens L12 (see table 14), and an antireflection coating corresponding to 1.85 as the substrate refractive index is applied to the object side lens surface of the double concave negative lens L24 (see table 13).

In the zoom lens seen from another point of view according to example 4 of the second embodiment, as shown in table 4, the refractive index nd of the negative meniscus lens L21 of the second lens group G2 is 1.834807(nd ═ 1.834807), and the refractive index nd of the double concave negative lens L22 of the second lens group G2 is 1.816000(nd ═ 1.816000), whereby it is feasible to reduce light reflected from each lens surface and reduce ghost images and flare by: an antireflection coating 101 corresponding to 1.85 as the substrate refractive index is applied to the image side lens surface of the negative meniscus lens L21 (see table 13), and an antireflection coating corresponding to 1.85 as the substrate refractive index is applied to the object side lens surface of the double concave negative lens L22 (see table 13).

In the zoom lens seen from another point of view according to example 5 of the second embodiment, as shown in table 5, the refractive index nd of the positive meniscus lens L13 of the first lens group G1 is 1.593190(nd ═ 1.593190), and the refractive index nd of the biconvex positive lens L23 of the second lens group G2 is 1.846660(nd ═ 1.846660), whereby it is feasible to reduce light reflected from each lens surface and reduce ghost images and flare by: an antireflection coating 101 corresponding to 1.62 as the substrate refractive index was applied to the object side lens surface of the positive meniscus lens L13 (see table 13), and an antireflection coating corresponding to 1.85 as the substrate refractive index was applied to the image side lens surface of the double convex positive lens L23 (see table 13).

In the zoom lens seen from another point of view according to example 6 of the second embodiment, as shown in table 6, the refractive index nd of the positive meniscus lens L13 of the first lens group G1 is 1.593190(nd ═ 1.593190), and the refractive index nd of the double concave negative lens L24 of the second lens group G2 is 1.816000(nd ═ 1.816000), whereby it is feasible to reduce light reflected from each lens surface and reduce ghost images and flare by: an antireflection coating 101 corresponding to 1.62 as the substrate refractive index was applied to the object side lens surface of the positive meniscus lens L13 (see table 13), and an antireflection coating corresponding to 1.85 as the substrate refractive index was applied to the object side lens surface of the double concave negative lens L24 (see table 13).

In the zoom lens seen from another point of view according to example 7 of the second embodiment, as shown in table 7, the refractive index nd of the negative meniscus lens L21 of the second lens group G2 is 1.834810(nd ═ 1.834810), and the refractive index nd of the double concave negative lens L22 of the second lens group G2 is 1.816000(nd ═ 1.816000), whereby it is feasible to reduce light reflected from each lens surface and reduce ghost images and flare by: an antireflection coating 101 corresponding to 1.85 as the substrate refractive index is applied to the image side lens surface of the negative meniscus lens L21 (see table 13), and an antireflection coating corresponding to 1.85 as the substrate refractive index is applied to the object side lens surface of the double concave negative lens L22 (see table 13).

In the zoom lens seen from another point of view according to example 8 of the second embodiment, as shown in table 8, the refractive index nd of the double convex positive lens L12 of the first lens group G1 is 1.437000(nd1.437000), and the refractive index nd of the double concave negative lens L24 of the second lens group G2 is 1.816000(nd 1.816000), whereby it is feasible to reduce light reflected from each lens surface and reduce ghost images and flare by: an antireflection coating 101 corresponding to 1.46 as the substrate refractive index is applied to the image side lens surface of the double convex positive lens L12 (see table 14), and an antireflection coating corresponding to 1.85 as the substrate refractive index is applied to the object side lens surface of the double concave negative lens L24 (see table 13).

In the zoom lens seen from another point of view according to example 9 of the third embodiment, as shown in table 9, the refractive index nd of the negative meniscus lens L21 of the second lens group G2 is 1.834810(nd ═ 1.834810), and the refractive index nd of the double concave negative lens L22 of the second lens group G2 is 1.816000(nd ═ 1.816000), whereby it is feasible to reduce light reflected from each lens surface and reduce ghost images and flare by: an antireflection coating 101 corresponding to 1.85 as the substrate refractive index is applied to the image side lens surface of the negative meniscus lens L21 (see table 13), and an antireflection coating corresponding to 1.85 as the substrate refractive index is applied to the object side lens surface of the double concave negative lens L22 (see table 13).

In the zoom lens seen from another point of view according to example 10 of the third embodiment, as shown in table 10, the refractive index nd of the positive meniscus lens L13 of the first lens group G1 is 1.593190(nd ═ 1.593190), and the refractive index nd of the biconvex positive lens L23 of the second lens group G2 is 1.846660(nd ═ 1.846660), whereby it is feasible to reduce light reflected from each lens surface and reduce ghost images and flare by: an antireflection coating 101 corresponding to 1.62 as the substrate refractive index was applied to the object side lens surface of the positive meniscus lens L13 (see table 13), and an antireflection coating corresponding to 1.85 as the substrate refractive index was applied to the image side lens surface of the double convex positive lens L23 (see table 13).

In the zoom lens seen from another point of view according to example 11 of the third embodiment, as shown in table 11, the refractive index nd of the positive meniscus lens L13 of the first lens group G1 is 1.593190(nd ═ 1.593190), and the refractive index nd of the double concave negative lens L24 of the second lens group G2 is 1.816000(nd ═ 1.816000), whereby it is feasible to reduce light reflected from each lens surface and reduce ghost images and flare by: an antireflection coating 101 corresponding to 1.62 as the substrate refractive index was applied to the object side lens surface of the positive meniscus lens L13 (see table 13), and an antireflection coating corresponding to 1.85 as the substrate refractive index was applied to the object side lens surface of the double concave negative lens L24 (see table 13).

In the zoom lens seen from another point of view according to example 12 of the third embodiment, as shown in table 12, the refractive index nd of the biconvex positive lens L12 of the first lens group G1 is 1.497820(nd ═ 1.497820), and the refractive index nd of the negative meniscus lens L21 of the second lens group G2 is 1.804000(nd ═ 1.804000), whereby it is feasible to reduce light reflected from each lens surface and reduce ghost images and flare by: an antireflection coating 101 corresponding to 1.52 as a substrate refractive index is applied to the image side lens surface of the double convex positive lens L12 (see table 13), and an antireflection coating corresponding to 1.85 as a substrate refractive index is applied to the image side lens surface of the negative meniscus lens L21 (see table 13).

As described above, the first to third embodiments make it possible to provide a zoom lens having high optical performance and suppressing variations in aberrations.

Next, a camera as an optical apparatus equipped with the zoom lens according to the first embodiment is explained. Although a case where the zoom lens according to example 1 of the first embodiment is mounted is described, the same result can be obtained by the zoom lens according to any other example of the first to third embodiments.

Fig. 23 is a sectional view showing a single-lens reflex digital camera equipped with the zoom lens according to example 1 of the first embodiment.

In fig. 23, a camera 1 is a single-lens reflex digital camera 1 equipped with the zoom lens according to example 1 of the first embodiment as an imaging lens 2. In the camera 1, light rays emitted from an object, not shown, are converged by an imaging lens 2, reflected by a quick return mirror 3, and focused on a focusing screen 4. The light focused on the focusing screen 4 is reflected multiple times within the pentagonal roof prism 5 and is guided to the eyepiece 6. Therefore, the photographer can observe the object image as an erect image through the eyepiece 6.

When the photographer presses a release button, not shown, to the bottom, the quick return mirror 3 is retracted from the optical path, and light from an object, not shown, forms an object image on the imaging device 7. Thus, the light emitted from the object is captured by the imaging device 7 and stored as a photographed object image in a memory, not shown. In this way, the photographer can take an object image by the camera 1.

By mounting the zoom lens according to example 1 of the first embodiment as the imaging lens 2 to the camera 1, it becomes possible to realize a camera having high optical performance.

Incidentally, the same effect as that of the above-described camera 1 can be obtained by a camera that does not include the quick return mirror 3.

Incidentally, the following description may be suitably applied within the limit of not deteriorating the optical performance.

In the above description and examples, although a zoom lens having a 3-lens group configuration has been shown, the present application may be applied to other lens group configurations such as a 4-lens group configuration. In particular, a lens configuration is possible in which a lens or a lens group is added to the most object side or the most image side of the zoom lens. Incidentally, a lens group is defined as including a portion of at least one lens separated by an air space that changes upon zooming.

In a zoom lens according to the present application, in order to change focus from infinity to a close object, a part of a lens group, a single lens group, or a plurality of lens groups may be moved along an optical axis as a focusing lens group. In this case, the focusing lens group may be used for auto focusing, and is adapted to be driven by a motor such as an ultrasonic motor. It is particularly preferred that at least a part of the second lens group moves as a focusing lens group.

Also, in a zoom lens according to the present application, a lens group or a part of a lens group may be moved in a direction including a component perpendicular to the optical axis as a vibration reduction lens group, or tilted (wobbling) in a direction including the optical axis, thereby correcting image blur caused by camera shake. Specifically, at least a part of the third lens group is preferably made to function as a vibration reduction lens group.

In a zoom lens according to the present application, any lens surface may be a spherical surface, a planar surface, or an aspherical surface.

When the lens surface is a spherical surface or a flat surface, lens processing, assembly, and adjustment become easy, and deterioration in optical performance caused by lens processing, assembly, and adjustment errors can be prevented, so that it is preferable. Also, even if the image surface is displaced, the deterioration in optical performance is small, so that it is preferable.

When the lens surface is an aspherical surface, the aspherical surface may be manufactured by a fine grinding process, a glass molding process of forming a glass material into an aspherical shape by a mold, or a complex process of forming a resin material into an aspherical shape on the surface of a glass lens. The lens surface may be a diffractive optical surface, and the lens may be a gradient index type lens (GRIN lens) or a plastic lens.

In a zoom lens according to the present application, the zoom ratio is about 7 to 25.

In a zoom lens according to the present application, the first lens group preferably includes two positive lens components. The first lens group preferably arranges these lens components in order from the object side positively, and arranges an air space therebetween.

Also, the second lens group preferably includes one positive lens component and three negative lens components. The second lens group preferably arranges these lens components in order from the object side, negative-positive-negative, and arranges an air space therebetween.

Also, the third lens group includes at least three positive lens components and at least one negative lens component.

Also, the third lens group preferably includes six or seven positive lens components and three or four negative lens components.

The above examples of each embodiment of the present application show only specific examples for better understanding of the present application. It is therefore needless to say that the application in its broader aspects is not limited to the specific details and representative devices described.

Claims

1. A zoom lens comprising, in order from an object along an optical axis:

a first lens group having positive refractive power;

a second lens group having negative refractive power; and

a third lens group having positive refractive power,

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 increasing, and a distance between the second lens group and the third lens group decreasing,

the first lens group includes a positive lens a satisfying the following conditional expression:

85.0<νdA

wherein ν dA denotes an abbe number at a d-line of a material of the positive lens a in the first lens group, and

the following conditional expression is satisfied:

5.10<f1/fw<8.80

2. The zoom lens according to claim 1, wherein the following conditional expression is satisfied:

0.28<f1/ft<0.52

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

3. The zoom lens according to claim 1, wherein the following conditional expression is satisfied:

0.25<Δ1/f1<1.10

where Δ 1 denotes a moving amount of the first lens group with respect to an image plane from the wide-angle end state to the telephoto end state.

4. The zoom lens according to claim 1, wherein the following conditional expression is satisfied:

0.65<f1A/f1<1.75

wherein f1A denotes a focal length of the positive lens a in the first lens group.

5. The zoom lens according to claim 1, wherein the following conditional expression is satisfied:

wherein，Denotes an effective diameter of the positive lens a in the first lens group.

6. The zoom lens according to claim 1, wherein the first lens group includes a positive lens B that satisfies the following conditional expression:

1.580<ndB

wherein ndB denotes a refractive index at a d-line of a material of the positive lens B in the first lens group.

7. The zoom lens according to claim 6, wherein the first lens group comprises a positive lens B satisfying the following conditional expression:

40.0<νdB<66.5

wherein ν dB represents an Abbe number at a d-line of a material of the positive lens B in the first lens group.

8. The zoom lens according to claim 6, wherein the following conditional expression is satisfied:

0.65<f1B/f1<1.75

wherein fiB denotes a focal length of the positive lens B in the first lens group.

9. The zoom lens according to claim 6, wherein the following conditional expression is satisfied:

wherein,denotes an effective diameter of the positive lens B in the first lens group.

10. The zoom lens according to claim 1, wherein the first lens group comprises a negative lens that satisfies the following conditional expression:

1.750<ndN

28.0<νdN<50.0

wherein ndN represents a refractive index at a d-line of a material of the negative lens in the first lens group, and ν dN represents an abbe number at the d-line of the material of the negative lens in the first lens group.

11. The zoom lens according to claim 1, wherein the first lens group is composed of one negative lens and two positive lenses.

12. The zoom lens according to claim 1, wherein the third lens group comprises a positive lens satisfying the following conditional expression:

when nd3 is more than or equal to 1.540, 65.5 nu d3

75.0< vd 3 when nd3<1.540

Where nd3 denotes a refractive index at a d-line of a material of the positive lens in the third lens group, and vd 3 denotes an abbe number at the d-line of the material of the positive lens in the third lens group.

13. The zoom lens according to claim 1, wherein the third lens group includes, in order from the object side along the optical axis, a front lens group having positive refractive power and a rear lens group having positive refractive power, and upon zooming from a wide-angle end state to a telephoto end state, a distance between the front lens group and the rear lens group decreases.

14. A zoom lens according to claim 1, wherein the third lens group includes, in order from the object side along the optical axis, a front lens group having positive refractive power, an intermediate lens group having negative refractive power, and a rear lens group having positive refractive power, and upon zooming from a wide-angle end state to a telephoto end state, a distance between the front lens group and the intermediate lens group varies, and a distance between the intermediate lens group and the rear lens group varies.

15. A zoom lens according to claim 14, wherein upon zooming from a wide-angle end state to a telephoto end state, a distance between the front lens group and the intermediate lens group increases, and a distance between the intermediate lens group and the rear lens group decreases.

16. The zoom lens according to claim 1, wherein an antireflection coating is applied on at least one optical surface of the first lens group and the second lens group, and the antireflection coating includes at least one layer formed by a wet process.

17. The zoom lens according to claim 16, wherein the antireflection coating is a multilayer film, and the layer formed by a wet process is an outermost layer among layers constituting the multilayer film.

18. The zoom lens according to claim 16, wherein when a refractive index at a d-line of the layer formed by a wet process is denoted by nd, the refractive index nd is 1.30 or less.

19. The zoom lens according to claim 16, wherein the optical surface on which the antireflection coating is applied is a concave surface as viewed from an aperture stop.

20. The zoom lens according to claim 19, wherein the concave surface seen from the aperture stop, on which the antireflection coating is applied, is an image side lens surface.

21. The zoom lens according to claim 19, wherein the concave surface seen from the aperture stop, on which the antireflection coating is applied, is an object side lens surface.

22. The zoom lens according to claim 16, wherein the optical surface on which the antireflection coating is applied is a concave surface as viewed from an object side.

23. The zoom lens according to claim 22, wherein the concave optical surface as viewed from the object side is an image side lens surface of an image side second lens from a most object side lens in the first lens group.

24. The zoom lens according to claim 22, wherein the concave optical surface as viewed from the object side is an object side lens surface of an image side second lens from a most object side lens in the second lens group.

25. The zoom lens according to claim 22, wherein the concave optical surface as viewed from the object side is an image side lens surface of an image side third lens from a most object side lens in the second lens group.

26. The zoom lens according to claim 22, wherein the concave optical surface as viewed from the object side is an object side lens surface of an image side fourth lens from a most object side lens in the second lens group.

27. An optical apparatus equipped with the zoom lens according to claim 1.

28. A zoom lens comprising, in order from an object along an optical axis:

a first lens group having positive refractive power;

a second lens group having negative refractive power; and

a third lens group having positive refractive power,

the zoom lens includes a positive lens a' satisfying the following conditional expression:

1.540<ndA’

66.5<νdA’

wherein ndA 'represents a refractive index at a d-line of a material of the positive lens A', and ν dA 'represents an Abbe number at the d-line of the material of the positive lens A', and

the following conditional expression is satisfied:

5.10<f1/fw<8.80

29. The zoom lens according to claim 28, wherein the following conditional expression is satisfied:

0.28<f1/ft<0.52

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

30. The zoom lens according to claim 28, wherein the following conditional expression is satisfied:

0.25<Δ1/f1<1.10

31. The zoom lens of claim 28, wherein the third lens group comprises the positive lens a'.

32. The zoom lens according to claim 31, wherein the following conditional expression is satisfied:

0.75<f3A’/f3<2.25

wherein f3 denotes a focal length of the third lens group, and f3A 'denotes a focal length of the positive lens a' in the third lens group.

33. The zoom lens of claim 28, wherein the first lens group comprises the positive lens a'.

34. The zoom lens according to claim 33, wherein the following conditional expression is satisfied:

0.65<f1A’/f1<1.75

wherein f1A 'denotes a focal length of the positive lens a' in the first lens group.

35. The zoom lens according to claim 33, wherein the following conditional expression is satisfied:

wherein,denotes an effective diameter of the positive lens a' in the first lens group.

36. The zoom lens according to claim 33, wherein the following conditional expression is satisfied:

wherein ft denotes a focal length of the zoom lens in a telephoto end state, and,denotes an effective diameter of the positive lens a' in the first lens group.

37. The zoom lens of claim 28, wherein the first lens group comprises two positive lenses.

38. The zoom lens according to claim 28, wherein the first lens group comprises a negative lens satisfying the following conditional expression:

1.750<ndN

28.0<νdN<50.0

39. The zoom lens of claim 38, wherein the number of negative lenses in the first lens group is 1.

40. The zoom lens according to claim 28, wherein the first lens group comprises a positive lens B' satisfying the following conditional expression:

75.0<νdB’

wherein ν dB 'represents an abbe number at a d-line of a material of the positive lens B' in the first lens group.

41. The zoom lens according to claim 28, wherein the third lens group includes, in order from the object side along the optical axis, a front lens group having positive refractive power and a rear lens group having positive refractive power, and upon zooming from a wide-angle end state to a telephoto end state, a distance between the front lens group and the rear lens group decreases.

42. A zoom lens according to claim 28, wherein the third lens group comprises, in order from the object side along the optical axis, a front lens group having positive refractive power, an intermediate lens group having negative refractive power, and a rear lens group having positive refractive power, and upon zooming from a wide-angle end state to a telephoto end state, a distance between the front lens group and the intermediate lens group varies, and a distance between the intermediate lens group and the rear lens group varies.

43. A zoom lens according to claim 42, wherein upon zooming from a wide-angle end state to a telephoto end state, a distance between the front lens group and the intermediate lens group increases, and a distance between the intermediate lens group and the rear lens group decreases.

44. The zoom lens according to claim 42, wherein the front lens group comprises the positive lens A'.

45. The zoom lens according to claim 44, wherein the following conditional expression is satisfied:

0.55<f31A’/f31<2.45

wherein f31 denotes a focal length of the front lens group, and f31A 'denotes a focal length of the positive lens a' in the front lens group.

46. The zoom lens according to claim 28, wherein an antireflection coating is applied on at least one optical surface of the first lens group and the second lens group, and the antireflection coating includes at least one layer formed by a wet process.

47. An optical apparatus equipped with the zoom lens according to claim 28.

48. A zoom lens comprising, in order from an object along an optical axis:

a first lens group having positive refractive power;

a second lens group having negative refractive power; and

a third lens group having positive refractive power,

the first lens group includes a plurality of positive lenses a ″ satisfying the following conditional expression:

66.5< vdA' when 1.540 ≦ ndA ″.

75.0< vda' when ndA "< 1.540"

Wherein ndA' represents a refractive index at a d-line of a material of each of the plurality of positive lenses in the first lens group, ν dA represents an Abbe number at a d-line of a material of each of the plurality of positive lenses in the first lens group, and

the following conditional expression is satisfied:

5.10<f1/fw<8.80

0.28<f1/ft<0.52

49. The zoom lens according to claim 48, wherein the following conditional expression is satisfied:

0.25<Δ1/f1<1.10

where Δ 1 denotes a moving amount of the first lens group with respect to an image plane upon zooming from a wide-angle end state to a telephoto end state.

50. The zoom lens according to claim 48, wherein the following conditional expression is satisfied:

0.65<f1A”/f1<1.75

wherein f 1A' represents a focal length of each of the plurality of positive lenses in the first lens group.

51. The zoom lens according to claim 48, wherein an antireflection coating is applied on at least one optical surface of the first lens group and the second lens group, and the antireflection coating includes at least one layer formed by a wet process.

52. An optical apparatus equipped with the zoom lens according to claim 48.

53. A method for manufacturing a zoom lens including, in order from an object side along an optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power, the method comprising the steps of:

movably arranging the first lens group, the second lens group, and the third lens group such that a distance between the first lens group and the second lens group increases and a distance between the second lens group and the third lens group decreases;

a positive lens a satisfying the following conditional expression is arranged:

85.0<νdA

wherein ν dA denotes an abbe number at a d-line of a material of the positive lens a in the first lens group; and is

Each lens is arranged satisfying the following conditional expression:

5.10<f1/fw<8.80

54. The method of claim 53, further comprising the step of:

each lens is arranged satisfying the following conditional expression:

0.28<f1/ft<0.52

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

55. The method of claim 53, further comprising the step of:

each lens is arranged satisfying the following conditional expression:

0.25<Δ1/f1<1.10

56. The method of claim 53, further comprising the step of:

each lens is arranged satisfying the following conditional expression:

0.65<f1A/f1<1.75

57. The method of claim 53, further comprising the step of:

disposing the first lens group including a positive lens B satisfying the following conditional expression:

1.580<ndB

58. The method of claim 53, further comprising the step of:

an antireflection coating is applied on at least one optical surface of the first lens group and the second lens group, and the antireflection coating includes at least one layer formed by a wet process.

59. The method of claim 58, further comprising the step of:

applying the layer formed by the wet process having a refractive index of 1.30 or less when a refractive index at d-line of the layer formed by the wet process is denoted as nd.

60. The method of claim 58, further comprising the step of:

the anti-reflection coating is applied on an optical surface having a concave surface as viewed from an aperture stop.

61. The method of claim 58, further comprising the step of:

the antireflection coating is applied on an optical surface having a concave surface as viewed from the object side.

62. A method for manufacturing a zoom lens including, in order from an object side along an optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power, the method comprising the steps of:

a positive lens a' satisfying the following conditional expression is arranged:

1.540<ndA’

66.5<νdA’

each lens is arranged satisfying the following conditional expression:

5.10<f1/fw<8.80

63. The method of claim 62, further comprising the step of:

each lens is arranged satisfying the following conditional expression:

0.28<f1/ft<0.52

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

64. The method of claim 62, further comprising the step of:

each lens is arranged satisfying the following conditional expression:

0.25<Δ1/f1<1.10

65. The method of claim 62, further comprising the step of:

arranging the third lens group including the positive lens a'.

66. The method of claim 62, further comprising the step of:

arranging the first lens group including the positive lens a'.

67. The method of claim 62, further comprising the step of:

68. A method for manufacturing a zoom lens including, in order from an object side along an optical axis, a first lens group having positive refractive power, a second lens group having negative refractive power, and a third lens group having positive refractive power, the method comprising the steps of:

a plurality of positive lenses a ″ satisfying the following conditional expressions are arranged:

66.5< vdA' when 1.540 ≦ ndA ″.

75.0< vda' when ndA "< 1.540"

Wherein ndA' represents a refractive index at a d-line of a material of each of the plurality of positive lenses in the first lens group, and ν dA represents an Abbe number at the d-line of the material of each of the plurality of positive lenses in the first lens group; and,

each lens is arranged satisfying the following conditional expression:

5.10<f1/fw<8.80

0.28<f1/ft<0.52