# Patent

## Title
Zoom lens and imaging apparatus

## Abstract

A zoom lens consists of, in order from the object side, a positive first lens group that is fixed during magnification change, at least two movable lens groups that are moved during magnification change, and a positive end lens group that is disposed at the most image side and is fixed during magnification change. The first lens group consists of, in order from the object side, a negative first-a lens group that is fixed during focusing, a positive first-b lens group that is moved during focusing, and a positive first-c lens group. The first-a lens group includes at least two negative lenses, where the most object-side negative lens has a meniscus shape with the convex surface toward the object side, and a first-n lens, which is at least one negative lens of the rest of the negative lenses of the first-a lens group, satisfies given condition expressions (1) to (3).

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application claims priority under 35 U.S.C. §119 to Japanese Patent Application No. 2015-053563, filed on Mar. 17, 2015. The above application is hereby expressly incorporated by reference, in its entirety, into the present application.
BACKGROUND
The present disclosure relates to a zoom lens for use with electronic cameras, such as digital cameras, video cameras, broadcasting cameras, monitoring cameras, etc., and an imaging apparatus provided with the zoom lens.
For broadcasting cameras and motion picture cameras, change of the angle of view due to focusing is undesirable, and such cameras often employ a focusing system where the first lens group of the zoom lens is divided into a first-a lens group that has a negative refractive power and is fixed during focusing, a first-b lens group that has a positive refractive power, and a first-c lens group that has a positive refractive power, and the first-b lens group is moved to effect focusing. Zoom lenses having the above-described focusing system are proposed in Japanese Patent No. 5615143, and Japanese Unexamined Patent Publication Nos. 2012-013817 and 2014-016508 (hereinafter, Patent Documents 1 to 3, respectively).
SUMMARY
The lenses of Patent Documents 1 to 3, however, have a problem that the size of the first lens group is extremely large relative to the image size. Further, the entire length of the lens of Patent Document 1 is large, and, in order to reduce the entire length, it is necessary to increase the power of the first lens group, which will accompany a problem of insufficient chromatic aberration correction. Also, all the lenses of Patent Documents 2 and 3 have insufficient chromatic aberration correction. In recent years, there is an increasing demand for portable broadcasting lenses, and high performance lenses that are compact relative to large image sizes and have successfully corrected chromatic aberration are demanded.
In view of the above-described circumstances, the present disclosure is directed to providing a compact and high performance zoom lens with successfully corrected chromatic aberration, and an imaging apparatus provided with the zoom lens.
The zoom lens of the disclosure consists of, in order from the object side, a first lens group that has a positive refractive power and is fixed during magnification change, at least two movable lens groups that are moved during magnification change with changing the distances along the optical axis direction between adjacent lens groups, and an end lens group that has a positive refractive power, is disposed at the most image side, and is fixed during magnification change, wherein the first lens group consists of, in order from the object side, a first-a lens group that has a negative refractive power and is fixed during focusing, a first-b lens group that has a positive refractive power and is moved during focusing with changing the distances along the optical axis direction between adjacent lens groups, and a first-c lens group that has a positive refractive power, the first-a lens group includes at least two negative lenses, wherein the most object-side negative lens has a meniscus shape with the convex surface toward the object side, and a first-n lens, which is at least one negative lens of the rest of the negative lenses of the first-a lens group, satisfies the condition expressions (1), (2), and (3) below:

62<vdn  (1),

0.64<θgFn+0.001625×vdn<0.7  (2), and

1<fln/fla<2  (3),

where vdn is an Abbe number with respect to the d-line of the first-n lens, θgFn is a partial dispersion ratio of the first-n lens, fln is a focal length with respect to the d-line of the first-n lens, and fla is a focal length with respect to the d-line of the first-a lens group.

It is preferred that any one or all of the condition expressions (1-1), (1-2), (2-1), and (3-1) below be satisfied:

70<vdn  (1-1),

70<vdn<100  (1-2),

0.65<θgFn+0.001625×vdn<0.69  (2-1),

1.1<fln/fla<1.8  (3-1).

In the zoom lens of the disclosure, it is preferred that the first-a lens group include a cemented lens formed by, in order from the object side, the first-n lens and a first-p lens having a positive refractive power that are cemented together, and satisfy the condition expressions (4) and (5) below. It is more preferred that the condition expression (4-1) and/or (5-1) below be satisfied.

vdp<40  (4),

20<vdp<38  (4-1),

0.62<θgFp+0.001625×vdp<0.67  (5),

0.63<θgFp+0.001625×vdp<0.66  (5-1),

where vdp is an Abbe number with respect to the d-line of the first-p lens, and θgFp is a partial dispersion ratio of the first-p lens.

It is preferred that the condition expression (6) below be satisfied, and it is more preferred that the condition expression (6-1) below be satisfied:

1.2<ft/fl<2  (6),

1.3<ft/fl<1.8  (6-1),

where ft is a focal length of the entire system at the telephoto end, and fl is a focal length of the first lens group.

It is preferred that the condition expression (7) below be satisfied, and it is more preferred that the condition expression (7-1) below be satisfied:

2<flb/fl<4  (7),

2.5<flb/fl<3.5  (7-1),

where flb is a focal length of the first-b lens group, and fl is a focal length of the first lens group.

It is preferred that the first-a lens group consist of, in order from the object side, two negative lenses, and a cemented lens formed by, in order from the object side, the first-n lens and the first-p lens having a positive refractive power that are cemented together.
The first-c lens group may be fixed during focusing, or may be moved during focusing along a different locus of movement from that of the first-b lens group.
It is preferred that the movable lens groups comprise at least two lens groups having a negative refractive power.
It is preferred that the movable lens groups comprise at least three lens groups.
The movable lens groups of the zoom lens may consist of, in order from the object side, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens group having a negative refractive power, or may consist of, in order from the object side, a second lens group having a positive refractive power, a third lens group having a negative refractive power, a fourth lens group having a negative refractive power, and a fifth lens group having a positive refractive power.
The imaging apparatus of the disclosure comprises the above-described zoom lens of the disclosure.
It should be noted that the expression “consisting/consist of” as used herein means that the zoom lens may include, besides the elements recited above: lenses substantially without any power; optical elements other than lenses, such as a stop, a mask, a cover glass, and filters; and mechanical components, such as a lens flange, a lens barrel, an image sensor, a camera shake correction mechanism, etc.
The sign (positive or negative) with respect to the surface shape and the refractive power of any lens including an aspheric surface among the lenses described above is about the paraxial region.
The zoom lens of the disclosure consists of, in order from the object side, a first lens group that has a positive refractive power and is fixed during magnification change, at least two movable lens groups that are moved during magnification change with changing the distances along the optical axis direction between adjacent lens groups, and an end lens group that has a positive refractive power, is disposed at the most image side, and is fixed during magnification change, wherein the first lens group consists of, in order from the object side, a first-a lens group that has a negative refractive power and is fixed during focusing, a first-b lens group that has a positive refractive power and is moved during focusing with changing the distances along the optical axis direction between adjacent lens groups, and a first-c lens group that has a positive refractive power, the first-a lens group includes at least two negative lenses, wherein the most object-side negative lens has a meniscus shape with the convex surface toward the object side, and a first-n lens, which is at least one negative lens of the rest of the negative lenses of the first-a lens group, satisfies the condition expressions (1), (2), and (3) below:

62<vdn  (1),

0.64<θgFn+0.001625×vdn<0.7  (2),

1<fln/fla<2  (3).

This configuration allows providing a compact and high performance zoom lens with successfully corrected chromatic aberration.

The imaging apparatus of the disclosure, which is provided with the zoom lens of the disclosure, allows size reduction of the apparatus, and allows obtaining high image-quality images.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a sectional view illustrating the lens configuration of a zoom lens according to one embodiment of the disclosure (a zoom lens of Example 1),
FIG. 2 is a sectional view illustrating the lens configuration of a zoom lens of Example 2 of the disclosure,
FIG. 3 is a sectional view illustrating the lens configuration of a zoom lens of Example 3 of the disclosure,
FIG. 4 is a sectional view illustrating the lens configuration of a zoom lens of Example 4 of the disclosure,
FIG. 5 shows aberration diagrams of the zoom lens of Example 1 of the disclosure,
FIG. 6 shows aberration diagrams of the zoom lens of Example 2 of the disclosure,
FIG. 7 shows aberration diagrams of the zoom lens of Example 3 of the disclosure,
FIG. 8 shows aberration diagrams of the zoom lens of Example 4 of the disclosure,
FIG. 9 is a diagram illustrating the schematic configuration of an imaging apparatus according to an embodiment of the disclosure.



DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. FIG. 1 is a sectional view illustrating the lens configuration of a zoom lens according to one embodiment of the disclosure. The configuration example shown in FIG. 1 is the same as the configuration of a zoom lens of Example 1, which will be described later. In FIG. 1, the left side is the object side and the right side is the image plane side. An aperture stop St shown in the drawing does not necessarily represent the size and the shape thereof, but represents the position thereof along the optical axis Z. FIG. 1 also shows loci of movement of lens groups during magnification change, an axial bundle of rays wa, and a bundle of rays wb at the maximum angle of view.
The zoom lens of this embodiment consists of, in order from the object side, a first lens group G1 that has a positive refractive power and is fixed during magnification change, at least two movable lens groups that are moved during magnification change with changing the distances along the optical axis direction between adjacent lens groups, and an end lens group that has a positive refractive power, is disposed at the most image side, and is fixed during magnification change. In the example shown in FIG. 1, the zoom lens consists of the first lens group G1 that has a positive refractive power and is fixed during magnification change, second to fourth lens groups G2 to G4 (movable lens groups) that are moved during magnification change with changing the distances along the optical axis direction between adjacent lens groups, and a fifth lens group G5 (end lens group) that has a positive refractive power, is disposed at the most image side, and is fixed during magnification change. The first lens group G1 consists of ten lenses L1a to L1j, the second lens group G2 consists of a lens L2a, the third lens group G3 consists of five lenses L3a to L3e, the fourth lens group G4 consists of two lenses L4a and L4b, and the fifth lens group G5 consists of twelve lenses L5a to L5l. 
When this zoom lens is used with an imaging apparatus, it is preferred to provide a cover glass, a prism, and various filters, such as an infrared cutoff filter and a low-pass filter, between the optical system and the image plane Sim depending on the configuration of the camera on which the lens is mounted. In the example shown in FIG. 1, optical members PP1 and PP2 in the form of plane-parallel plates, which are assumed to represent the above-mentioned elements, are disposed between the lens system and the image plane Sim.
Providing the most object-side lens group with a positive refractive power in this manner allows reducing the entire length of the lens system, and this is advantageous for size reduction. Further, providing the most image-side lens group with a positive refractive power allows minimizing increase of the incidence angle of the principal ray of off-axis rays entering the image plane Sim, and this allows suppressing shading. Further, since the most object-side lens group and the most image-side lens group are fixed during magnification change, the entire length of the lens system does not change during magnification change, and this allows providing a zoom lens with small change of center of gravity during magnification change, and thus with good operability.
The first lens group G1 consists of, in order from the object side, a first-a lens group G1a that has a negative refractive power and is fixed during focusing, a first-b lens group G1b that has a positive refractive power and is moved during focusing with changing the distances along the optical axis direction between adjacent lens groups, and a first-c lens group G1c that has a positive refractive power. In this embodiment, the first-a lens group G1a consists of four lenses L1a to lens L1d, the first-b lens group G1b consists of a lens L1e, and the first-c lens group G1c consists of five lenses L1f to L1j. This configuration allows suppressing change of the angle of view during focusing.
The first-a lens group G1a includes at least two negative lenses, where the most object-side negative lens has a meniscus shape with the convex surface toward the object side, and a first-n lens, which is at least one negative lens of the rest of the negative lenses of the first-a lens group, satisfies the condition expressions (1), (2), and (3) below. In this embodiment, the lens L1c corresponds to the first-n lens.
Disposing at least two negative lenses in the first-a lens group G1a in this manner allows providing a negative refractive power necessary for achieving a wide angle of view. Providing the most object-side negative lens of the first-a lens group G1a with a meniscus shape with the convex surface toward the object side allows suppressing astigmatism and distortion. Further, providing the first-n lens that satisfies the condition expressions (1), (2), and (3) below in the first-a lens group G1a allows successfully correcting chromatic aberration at the first lens group G1, in particular, successfully correcting lateral chromatic aberration at the wide angle side and longitudinal chromatic aberration at the telephoto side.
Satisfying the condition expression (1) allows successfully correcting lateral chromatic aberration at the wide angle side and longitudinal chromatic aberration at the telephoto side during focusing. Further, satisfying the condition expression (2) together with the condition expression (1) allows successfully correcting secondary spectrum. Further, satisfying the condition expression (3) allows successfully correcting chromatic aberration, in particular, secondary spectrum of longitudinal chromatic aberration at the telephoto side.

62<vdn  (1),

0.64<θgFn+0.001625×vdn<0.7  (2), and

1<fln/fla<2  (3),

where vdn is an Abbe number with respect to the d-line of the first-n lens, θgFn is a partial dispersion ratio of the first-n lens, fln is a focal length with respect to the d-line of the first-n lens, and fla is a focal length with respect to the d-line of the first-a lens group.

It should be noted that higher performance can be obtained when any one or all of the condition expressions (1-1), (1-2), (2-1), and (3-1) below are satisfied. Setting the value of vdn such that it does not become equal to or greater than the upper limit of the condition expression (1-2) allows preventing the material forming the first-n lens from having excessively low dispersion, and this allows selecting a material having sufficient refractive index for successfully correcting distortion at the wide angle end.

70<vdn  (1-1),

70<vdn<100  (1-2),

0.65<θgFn+0.001625×vdn<0.69  (2-1),

1.1<fln/fla<1.8  (3-1).

In the zoom lens of the disclosure, it is preferred that the first-a lens group G1a include a cemented lens formed by, in order from the object side, the first-n lens and a first-p lens having a positive refractive power that are cemented together, and satisfy the condition expressions (4) and (5) below. In this embodiment, the lens L1c corresponds to the first-n lens, and the lens L1d corresponds to the first-p lens. Disposing the above-described cemented lens in the first-a lens group G1a allows successfully correcting chromatic aberration at the first-a lens group G1a, and suppressing change of longitudinal chromatic aberration and lateral chromatic aberration during focusing. Further, satisfying the condition expression (4) allows successfully correcting lateral chromatic aberration at the wide angle side and longitudinal chromatic aberration at the telephoto side during focusing. Satisfying the condition expression (5) together with the condition expression (4) allows successfully correcting secondary spectrum. It should be noted that higher performance can be obtained when the condition expression (4-1) and/or (5-1) below is satisfied.

vdp<40  (4),

20<vdp<38  (4-1),

0.62<θgFp+0.001625×vdp<0.67  (5),

0.63<θgFp+0.001625×vdp<0.66  (5-1),

where vdp is an Abbe number with respect to the d-line of the first-p lens, and θgFp is a partial dispersion ratio of the first-p lens.

Further, it is preferred that the condition expression (6) below be satisfied. Setting the value of ft/fl such that it does not become equal to or smaller than the lower limit of the condition expression (6) allows preventing the power of the first lens group G1 from becoming excessively weak, and this prevents increase of the entire length, thereby contributing to size reduction. Setting the value of ft/fl such that it does not become equal to or greater than the upper limit of the condition expression (6) allows preventing the power of the first lens group G1 from becoming excessively strong, and this allows successfully correcting chromatic aberration. It should be noted that higher performance can be obtained when the condition expression (6-1) below is satisfied.

1.2<ft/fl<2  (6),

1.3<ft/fl<1.8  (6-1),

where ft is a focal length of the entire system at the telephoto end, and fl is a focal length of the first lens group.

It is preferred that the condition expression (7) below be satisfied. Satisfying the condition expression (7) allows suppressing change of aberrations during focusing. In particular, setting the value of flb/fl such that it does not become equal to or smaller than the lower limit of the condition expression (7) allows preventing the power from becoming excessively strong, and this allows suppressing change of aberrations during focusing. Setting the value of flb/fl such that it does not become equal to or greater than the upper limit of condition expression (7) allows preventing the amount of movement of the first-b lens group G1b during focusing from becoming excessively large, and this contributes to size reduction of the first lens group G1. It should be noted that higher performance can be obtained when the condition expression (7-1) below is satisfied.

2<flb/fl<4  (7),

2.5<flb/fl<3.5  (7-1),

where flb is a focal length of the first-b lens group, and fl is a focal length of the first lens group.

Further, it is preferred that the first-a lens group G1a consist of, in order from the object side, two negative lenses, and a cemented lens formed by, in order from the object side, the first-n lens and the first-p lens having a positive refractive power that are cemented together. This configuration allows suppressing field curvature and distortion at the wide angle side, and successfully correcting spherical aberration at the telephoto side.
The first-c lens group G1c may be fixed during focusing. In this case, the first-b lens group G1b is the only movable group during focusing, and this allows weight reduction of the movable group that is moved during focusing.
The first-c lens group G1c may be moved during focusing along a different locus of movement from that of the first-b lens group G1b. This configuration facilitates suppressing change of aberrations during focusing, in particular, facilitates suppressing field curvature and distortion at the wide angle side, and spherical aberration at the telephoto side.
It is preferred that the movable lens groups include at least two lens groups having a negative refractive power. In general, when there are two movable lens groups having a negative refractive power, the amount of movement of the movable lens groups can be made smaller than that when there is one movable lens group having a negative refractive power. This configuration therefore leads to reduction of the entire length of the lens system.
It is preferred that the movable lens groups include at least three movable lens groups. This configuration facilitates correction of aberrations during magnification change, in particular, facilitates suppressing change of spherical aberration, field curvature, and distortion.
The movable lens groups of the zoom lens may consist of, in order from the object side, the second lens group G2 having a positive refractive power, the third lens group G3 having a negative refractive power, and the fourth lens group G4 having a negative refractive power. This configuration facilitates correction of aberrations during magnification change, in particular, facilitates suppressing change of spherical aberration, field curvature, and distortion. It should be noted that the zoom lens of this embodiment shows this aspect.
Alternatively, the movable lens groups of the zoom lens may consist of, in order from the object side, the second lens group having a positive refractive power, the third lens group having a negative refractive power, the fourth lens group having a negative refractive power, and the fifth lens group having a positive refractive power. This configuration allows more appropriate aberration correction than the above-described configuration where the movable lens groups consists of three lens groups.
In the example shown in FIG. 1, the optical members PP1 and PP2 are disposed between the lens system and the image plane Sim. However, in place of disposing the various filters, such as a low-pass filter and a filter that cuts off a specific wavelength range, between the lens system and the image plane Sim, the various filters may be disposed between the lenses, or coatings having the same functions as the various filters may be applied to the lens surfaces of some of the lenses.
Next, numerical examples of the zoom lens of the disclosure are described.
First, a zoom lens of Example 1 is described. FIG. 1 is a sectional view illustrating the lens configuration of the zoom lens of Example 1. It should be noted that, in FIG. 1, and FIGS. 2 to 4 corresponding to Examples 2 to 4, which will be described later, the left side is the object side and the right side is the image plane side. The aperture stop St shown in the drawings does not necessarily represent the size and the shape thereof, but represents the position thereof along the optical axis Z. FIG. 1 also shows loci of movement of the lens groups during magnification change, an axial bundle of rays wa, and a bundle of rays wb at the maximum angle of view.
The zoom lens of Example 1 consists of, in order from the object side, a first lens group G1 that has a positive refractive power and is fixed during magnification change, second to fourth lens groups G2 to G4 (movable lens groups) that are moved during magnification change with changing the distances along the optical axis direction between adjacent lens groups, and a fifth lens group G5 (end lens group) that has a positive refractive power, is disposed at the most image side, and is fixed during magnification change.
Table 1 shows basic lens data of the zoom lens of Example 1, Table 2 shows data about specifications of the zoom lens, Table 3 shows data about variable surface distances of the zoom lens, and Table 4 shows data about aspheric coefficients of the zoom lens. In the following description, meanings of symbols used in the tables are explained with respect to Example 1 as an example. The same explanations basically apply to those with respect to Examples 2 to 4.
In the lens data shown in Table 1, each value in the column of “Surface No.” represents a surface number, where the object-side surface of the most object-side element is the 1st surface and the number is sequentially increased toward the image plane side, each value in the column of “Radius of Curvature” represents the radius of curvature of the corresponding surface, and each value in the column of “Surface Distance” represents the distance along the optical axis Z between the corresponding surface and the next surface. Each value in the column of “nd” represents the refractive index with respect to the d-line (the wavelength of 587.6 nm) of the corresponding optical element, each value in the column of “vd” represents the Abbe number with respect to the d-line (the wavelength of 587.6 nm) of the corresponding optical element, and each value in the column of “θgF” represents the partial dispersion ratio of the corresponding optical element.
It should be noted that the partial dispersion ratio θgF is expressed by the formula below:

θgF=(Ng−NF)/(NF−NC),

where Ng is a refractive index with respect to the g-line, NF is a refractive index with respect to F-line, and NC is a refractive index with respect to the C-line.

The sign with respect to the radius of curvature is provided such that a positive radius of curvature indicates a surface shape that is convex toward the object side, and a negative radius of curvature indicates a surface shape that is convex toward the image plane side. The basic lens data also includes data about the aperture stop St and the optical members PP1 and PP2, and the surface number and the text “(stop)” are shown at the position in the column of the surface number corresponding to the aperture stop St. In the lens data shown in Table 1, each surface distance that is variable during magnification change is represented by the symbol “DD[surface number]”. The numerical value corresponding to each DD[surface number] is shown in Table 3.
The data about specifications shown in Table 2 show values of zoom magnification, focal length f, F-number FNo, and full angle of view 2ω.
With respect to the basic lens data, the data about specifications, and the data about variable surface distances, the unit of angle is degrees, and the unit of length is millimeters; however, any other suitable units may be used since optical systems are usable when they are proportionally enlarged or reduced.
In the lens data shown in Table 1, the symbol “*” is added to the surface number of each aspheric surface, and the numerical value of the paraxial radius of curvature is shown as the radius of curvature of each aspheric surface. In the data about aspheric coefficients shown in Table 4, the surface number of each aspheric surface and aspheric coefficients about each aspheric surface are shown. The aspheric coefficients are values of the coefficients KA and Am (where m=3, . . . , 20) in the formula of aspheric surface shown below:

Zd=C·h2/{1+(1−KA·C2·h2)1/2}+ΣAm·hm,

where Zd is a depth of the aspheric surface (a length of a perpendicular line from a point with a height h on the aspheric surface to a plane tangent to the apex of the aspheric surface and perpendicular to the optical axis), h is the height (a distance from the optical axis), C is a reciprocal of the paraxial radius of curvature, and KA and Am are aspheric coefficients (where m=3, . . . , 20).








TABLE 1







Example 1 - Lens Data













Radius of






Surface No.
Curvature
Surface Distance
nd
νd
θgF















 1
214.0485
3.6001
1.88300
40.76
0.56679


 2
75.1630
22.9827


 3
−597.4831
3.3000
1.73400
51.47
0.54874


 4
443.5473
12.9081


 5
−187.4186
5.8583
1.53775
74.70
0.53936


 6
122.1466
14.7216
1.91650
31.60
0.59117


 7
−1192.6629
2.6958


 *8
337.3004
13.7943
1.43875
94.94
0.53433


 9
−172.5134
13.4076


 10
192.0693
17.0129
1.49700
81.54
0.53748


 11
−139.9406
0.6538


 12
−133.1303
3.3500
1.85150
40.78
0.56958


 13
115.2733
15.2541
1.49700
81.54
0.53748


 14
−398.0807
6.0395


 15
459.0857
12.9020
1.53775
74.70
0.53936


 16
−156.6756
0.2000


 17
137.1994
15.6658
1.49700
81.54
0.53748


 18
−276.3776
DD[18]


 19
362.4361
2.9957
1.49700
81.54
0.53748


 20
−555.5230
DD[20]


*21
212.6957
2.4011
1.53775
74.70
0.53936


 22
27.2627
10.4426


 23
−42.9639
1.2004
2.00100
29.13
0.59952


 24
191.3068
2.4309


 25
−105.3359
6.7325
1.69895
30.13
0.60298


 26
−28.8119
2.4783
1.69560
59.05
0.54348


 27
−82.6623
0.3007


 28
161.3383
5.2491
1.83481
42.72
0.56486


 29
−80.5118
DD[29]


 30
−52.0619
1.3100
1.49700
81.54
0.53748


 31
1116.7924
1.9941
1.84666
23.83
0.61603


 32
−307.6714
DD[32]


 33 (stop)
∞
1.8275


 34
118.3571
3.8140
1.91082
35.25
0.58224


 35
−350.3523
2.5727


 36
−105.5123
3.0000
1.76182
26.52
0.61361


 37
−208.3315
11.3437


 38
59.9113
5.2848
1.65844
50.88
0.55612


 39
∞
0.3009


 40
42.0799
10.3271
1.43875
94.94
0.53433


 41
−78.3277
1.5500
1.95375
32.32
0.59015


 42
56.6019
4.9263


 43
−226.8790
6.1786
1.80518
25.43
0.61027


 44
−36.3203
1.4100
1.80400
46.58
0.55730


 45
−106.9554
0.4084


 46
64.4975
7.8638
1.48749
70.24
0.53007


 47
−64.4975
0.2001


 48
54.5207
2.0998
1.91082
35.25
0.58224


 49
20.5114
13.6195
1.49700
81.54
0.53748


 50
−42.0493
1.6000
1.90043
37.37
0.57720


 51
57.4339
0.6085


 52
48.2644
3.3704
1.84666
23.83
0.61603


 53
240.7851
3.0000


 54
∞
1.4000
1.51633
64.14
0.53531


 55
∞
1.0000


 56
∞
3.6900
1.51633
64.14
0.53531


 57
∞
54.0311
















TABLE 2







Example 1 - Specifications (d-line)











Wide Angle End
Middle
Telephoto End














Zoom Magnification
1.0
2.4
7.4


f′
19.91
46.80
146.33


FNo.
2.86
2.86
2.86


2ω[°]
73.6
33.2
11.0
















TABLE 3







Example 1 - Distances with respect to Zoom











Wide Angle End
Middle
Telephoto End
















DD[18]
1.4993
49.5135
85.3829



DD[20]
1.4865
6.8361
8.7457



DD[29]
62.9756
9.2695
21.2659



DD[32]
52.4033
52.7456
2.9702

















TABLE 4





Example 1 - Aspheric Coefficients


















Surface No.
8







KA
1.0000000E+00



A3
1.5064530E−07



A4
−1.5641141E−07 



A5
1.6501598E−09



A6
−3.9701428E−11 



A7
6.9263338E−13



A8
1.0556630E−17



A9
−7.0509369E−17 



A10
5.3287613E−19







Surface No.
21







KA
 1.0000000E+00



A4
 1.5045420E−06



A6
−4.1679388E−10



A8
−8.9800509E−12



A10
 7.0993908E−14



A12
−3.2299521E−16



A14
 8.7823289E−19



A16
−1.4036759E−21



A18
 1.2097861E−24



A20
−4.3023907E−28










FIG. 5 shows aberration diagrams of the zoom lens of Example 1. The aberration diagrams shown at the top of FIG. 5 are those of spherical aberration, astigmatism, distortion, and lateral chromatic aberration, in this order from the left side, at the wide-angle end. The aberration diagrams shown at the middle of FIG. 5 are those of spherical aberration, astigmatism, distortion, and lateral chromatic aberration, in this order from the left side, at the middle position. The aberration diagrams shown at the bottom of FIG. 5 are those of spherical aberration, distortion, and lateral chromatic aberration, in this order from the left side, at the telephoto end. These aberration diagrams show aberrations when the object distance is infinity. The aberration diagrams of spherical aberration, astigmatism, and distortion show those with respect to the d-line (the wavelength of 587.6 nm), which is used as a reference wavelength. The aberration diagrams of spherical aberration show those with respect to the d-line (the wavelength of 587.6 nm), the C-line (the wavelength of 656.3 nm), the F-line (the wavelength of 486.1 nm), and the g-line (the wavelength of 435.8 nm) in the solid line, the long dashed line, the short dashed line, and the gray solid line, respectively. The aberration diagrams of astigmatism show those in the sagittal direction and the tangential direction in the solid line, and the short dashed line, respectively. The aberration diagrams of lateral chromatic aberration show those with respect to the C-line (the wavelength of 656.3 nm), the F-line (the wavelength of 486.1 nm), and the g-line (the wavelength of 435.8 nm) in the long dashed line, the short dashed line, and the gray solid line, respectively. The symbol “FNo.” in the aberration diagrams of spherical aberration means “F-number”, and the symbol “ω” in the other aberration diagrams means “half angle of view”.
Next, a zoom lens of Example 2 is described. FIG. 2 is a sectional view illustrating the lens configuration of the zoom lens of Example 2. The zoom lens of Example 2 consists of in order from the object side, a first lens group G1 that has a positive refractive power and is fixed during magnification change, second to fifth lens groups G2 to G5 (movable lens groups) that are moved during magnification change with changing the distances along the optical axis direction between adjacent lens groups, and a sixth lens group G6 (end lens group) that has a positive refractive power, is disposed at the most image side, and is fixed during magnification change. The first lens group G1 consists of ten lenses L1a to L1j, the second lens group G2 consists of a lens L2a, the third lens group G3 consists of five lenses L1a to L3e, the fourth lens group G4 consists of two lenses L4a and L4b, the fifth lens group G5 consists of two lenses L5a and L5b, and the sixth lens group G6 consists of ten lenses L6a to L6j. Table 5 shows basic lens data of the zoom lens of Example 2, Table 6 shows data about specifications of the zoom lens, Table 7 shows data about variable surface distances of the zoom lens, Table 8 shows data about aspheric coefficients of the zoom lens, and FIG. 6 shows aberration diagrams of the zoom lens.







TABLE 5







Example 2 - Lens Data













Radius of






Surface No.
Curvature
Surface Distance
nd
νd
θgF















 1
204.5076
3.6001
1.88300
40.76
0.56679


 2
75.1577
26.8271


 3
−680.1918
3.3001
1.73400
51.47
0.54874


 4
394.2434
10.1996


 5
−194.8976
6.0275
1.53775
74.70
0.53936


 6
119.9249
14.7493
1.91650
31.60
0.59117


 7
−1395.5679
1.4975


 *8
334.5227
13.5447
1.43875
94.94
0.53433


 9
−178.4244
13.8156


 10
190.5673
16.5365
1.49700
81.54
0.53748


 11
−148.2904
0.8631


 12
−137.7176
3.3505
1.85150
40.78
0.56958


 13
113.9140
15.3310
1.49700
81.54
0.53748


 14
−407.0823
5.3500


 15
573.8699
13.3719
1.53775
74.70
0.53936


 16
−155.6554
0.2451


 17
138.0910
16.3580
1.49700
81.54
0.53748


 18
−248.2025
DD[18]


 19
331.9810
3.0337
1.49700
81.54
0.53748


 20
−566.9344
DD[20]


*21
236.4764
2.3725
1.53775
74.70
0.53936


 22
27.4357
10.1724


 23
−43.6440
1.2000
2.00100
29.13
0.59952


 24
196.3935
2.3659


 25
−105.3852
6.3996
1.69895
30.13
0.60298


 26
−29.4777
4.4704
1.69560
59.05
0.54348


 27
−84.3847
0.3005


 28
170.5472
5.1064
1.83481
42.72
0.56486


 29
−82.5546
DD[29]


 30
−52.8642
1.3101
1.49700
81.54
0.53748


 31
1177.9980
1.9548
1.84666
23.83
0.61603


 32
−319.2827
DD[32]


 33 (stop)
∞
1.1696


 34
117.8758
3.7936
1.91082
35.25
0.58224


 35
−345.2428
2.2403


 36
−103.1702
3.0000
1.76182
26.52
0.61361


 37
−203.4153
DD[37]


 38
60.3391
5.2627
1.65844
50.88
0.55612


 39
∞
0.8372


 40
41.6543
10.3088
1.43875
94.94
0.53433


 41
−77.6159
1.5892
1.95375
32.32
0.59015


 42
55.9588
4.8039


 43
−243.7036
6.2713
1.80518
25.43
0.61027


 44
−35.9951
1.4100
1.80400
46.58
0.55730


 45
−106.5175
0.6156


 46
63.7897
7.9106
1.48749
70.24
0.53007


 47
−63.7897
0.2007


 48
54.4770
1.6010
1.91082
35.25
0.58224


 49
20.5144
14.2437
1.49700
81.54
0.53748


 50
−41.6177
1.6006
1.90043
37.37
0.57720


 51
57.8925
0.3412


 52
48.5057
3.3350
1.84666
23.83
0.61603


 53
242.4352
3.0000


 54
∞
1.4000
1.51633
64.14
0.53531


 55
∞
1.0000


 56
∞
3.6900
1.51633
64.14
0.53531


 57
∞
52.9818
















TABLE 6







Example 2 - Specifications (d-line)











Wide Angle End
Middle
Telephoto End














Zoom Magnification
1.0
2.4
7.4


f′
19.88
46.74
146.14


FNo.
2.86
2.86
2.86


2ω[°]
73.8
33.2
11.0
















TABLE 7







Example 2 - Distances with respect to Zoom











Wide Angle End
Middle
Telephoto End
















DD[18]
1.4998
51.1925
88.2200



DD[20]
1.4938
6.8434
8.7530



DD[29]
64.3039
9.6273
20.8055



DD[32]
51.9906
52.1819
2.9978



DD[37]
10.1220
9.5650
8.6338

















TABLE 8





Example 2 - Aspheric Coefficients


















Surface No.
8







KA
1.0000000E+00



A3
1.5064530E−07



A4
−1.5641141E−07 



A5
1.6501598E−09



A6
−3.9701428E−11 



A7
6.9263338E−13



A8
1.0556630E−17



A9
−7.0509369E−17 



A10
5.3287613E−19







Surface No.
21







KA
 1.0000000E+00



A4
 1.5045420E−06



A6
−4.1679388E−10



A8
−8.9800509E−12



A10
 7.0993908E−14



A12
−3.2299521E−16



A14
 8.7823289E−19



A16
−1.4036759E−21



A18
 1.2097861E−24



A20
−4.3023907E−28










Next, a zoom lens of Example 3 is described. FIG. 3 is a sectional view illustrating the lens configuration of the zoom lens of Example 3. The zoom lens of Example 3 has the same lens group configuration as that of the zoom lens of Example 1. Table 9 shows basic lens data of the zoom lens of Example 3, Table 10 shows data about specifications of the zoom lens, Table 11 shows data about variable surface distances of the zoom lens, Table 12 shows data about aspheric coefficients of the zoom lens, and FIG. 7 shows aberration diagrams of the zoom lens.







TABLE 9







Example 3 - Lens Data













Radius of






Surface No.
Curvature
Surface Distance
nd
νd
θgF















 1
203.3033
3.6000
1.75500
52.32
0.54765


 2
70.9391
27.1004


 3
−338.7454
3.3001
1.77250
49.60
0.55212


 4
378.5456
10.5278


 5
−265.5030
3.5300
1.43875
94.66
0.53402


 6
122.8648
13.6010
1.91082
35.25
0.58224


 7
−19851.3347
3.6816


 *8
281.3047
12.9599
1.43875
94.94
0.53433


 9
−214.8359
14.8527


 10
238.5428
15.5435
1.49700
81.54
0.53748


 11
−142.9598
0.5234


 12
−137.9389
3.3500
1.83481
42.72
0.56486


 13
106.1360
17.0654
1.49700
81.54
0.53748


 14
−316.9974
0.4827


 15
543.8380
11.0182
1.53775
74.70
0.53936


 16
−177.9557
2.8866


 17
133.2953
17.4933
1.49700
81.54
0.53748


 18
−208.4111
DD[18]


 19
349.0362
3.0377
1.49700
81.54
0.53748


 20
−585.2849
DD[20]


*21
231.8394
2.3423
1.53775
74.70
0.53936


 22
27.2866
10.6024


 23
−43.2897
1.2000
2.00100
29.13
0.59952


 24
203.7558
2.8071


 25
−102.0549
6.6695
1.69895
30.13
0.60298


 26
−29.2108
1.7290
1.69560
59.05
0.54348


 27
−80.5930
0.3005


 28
161.3029
5.2395
1.83481
42.72
0.56486


 29
−80.8454
DD[29]


 30
−52.3914
1.3100
1.49700
81.54
0.53748


 31
3010.3139
1.9234
1.84666
23.83
0.61603


 32
−274.0259
DD[32]


 33 (stop)
∞
2.0283


 34
119.4012
3.5996
1.91082
35.25
0.58224


 35
−414.6305
1.6311


 36
−106.0887
3.0000
1.76182
26.52
0.61361


 37
−192.8743
11.6874


 38
62.8957
5.0727
1.65844
50.88
0.55612


 39
∞
0.3004


 40
42.0886
10.3576
1.43875
94.94
0.53433


 41
−78.0793
1.4003
1.95375
32.32
0.59015


 42
55.8551
6.2257


 43
−253.7994
6.5210
1.80518
25.43
0.61027


 44
−36.2933
1.4100
1.80400
46.58
0.55730


 45
−105.8885
0.2000


 46
64.2148
8.2858
1.48749
70.24
0.53007


 47
−64.2148
0.2000


 48
55.2351
2.2417
1.91082
35.25
0.58224


 49
20.9380
14.8846
1.49700
81.54
0.53748


 50
−43.1405
1.6000
1.90043
37.37
0.57720


 51
58.6237
0.2008


 52
46.2659
5.8212
1.84666
23.83
0.61603


 53
184.1153
3.0000


 54
∞
1.4000
1.51633
64.14
0.53531


 55
∞
1.0000


 56
∞
3.6900
1.51633
64.14
0.53531


 57
∞
51.2846
















TABLE 10







Example 3 - Specifications (d-line)











Wide Angle End
Middle
Telephoto End














Zoom Magnification
1.0
2.4
7.4


f′
19.90
46.79
146.29


FNo.
2.86
2.86
2.86


2ω[°]
73.8
33.2
11.0
















TABLE 11







Example 3 - Distances with respect to Zoom











Wide Angle End
Middle
Telephoto End
















DD[18]
1.4998
50.0802
86.4555



DD[20]
1.4969
6.8465
8.7561



DD[29]
64.0006
9.2167
21.7032



DD[32]
52.8723
53.7262
2.9548

















TABLE 12





Example 3 - Aspheric Coefficients


















Surface No.
8







KA
1.0000000E+00



A3
1.5064530E−07



A4
−1.5641141E−07 



A5
1.6501598E−09



A6
−3.9701428E−11 



A7
6.9263338E−13



A8
1.0556630E−17



A9
−7.0509369E−17 



A10
5.3287613E−19







Surface No.
21







KA
 1.0000000E+00



A4
 1.5045420E−06



A6
−4.1679388E−10



A8
−8.9800509E−12



A10
 7.0993908E−14



A12
−3.2299521E−16



A14
 8.7823289E−19



A16
−1.4036759E−21



A18
 1.2097861E−24



A20
−4.3023907E−28










Next, a zoom lens of Example 4 is described. FIG. 4 is a sectional view illustrating the lens configuration of the zoom lens of Example 4. The zoom lens of Example 4 has the same lens group configuration as that of the zoom lens of Example 1. Table 13 shows basic lens data of the zoom lens of Example 4, Table 14 shows data about specifications of the zoom lens, Table 15 shows data about variable surface distances of the zoom lens, Table 16 shows data about aspheric coefficients of the zoom lens, and FIG. 8 shows aberration diagrams of the zoom lens.







TABLE 13







Example 4 - Lens Data













Radius of






Surface No.
Curvature
Surface Distance
nd
νd
θgF















 1
206.2478
3.6000
1.83481
42.72
0.56486


 2
73.6755
28.3630


 3
−414.1587
3.3001
1.80400
46.58
0.55730


 4
378.1742
10.0697


 5
−203.7117
3.5307
1.49700
81.54
0.53748


 6
126.7830
14.8567
1.91650
31.60
0.59117


 7
−800.5290
1.4943


 *8
333.3336
13.3218
1.43875
94.94
0.53433


 9
−183.4719
14.0204


 10
199.5391
17.3922
1.49700
81.54
0.53748


 11
−131.2369
0.3242


 12
−128.6939
3.3505
1.85150
40.78
0.56958


 13
115.0910
15.6314
1.49700
81.54
0.53748


 14
−355.9889
6.5632


 15
459.3712
12.9818
1.53775
74.70
0.53936


 16
−156.5869
0.2014


 17
137.0094
15.6708
1.49700
81.54
0.53748


 18
−277.4188
DD[18]


 19
360.3858
3.0389
1.49700
81.54
0.53748


 20
−557.9596
DD[20]


*21
216.3200
2.4009
1.53775
74.70
0.53936


 22
27.2953
10.4367


 23
−42.9945
1.2000
2.00100
29.13
0.59952


 24
192.1280
2.4232


 25
−105.2604
6.7166
1.69895
30.13
0.60298


 26
−28.8310
2.6322
1.69560
59.05
0.54348


 27
−82.9675
0.3000


 28
162.6223
5.2344
1.83481
42.72
0.56486


 29
−80.5636
DD[29]


 30
−51.8139
1.3100
1.49700
81.54
0.53748


 31
1155.8690
1.9895
1.84666
23.83
0.61603


 32
−303.9788
DD[32]


 33 (stop)
∞
2.5109


 34
118.6003
3.8001
1.91082
35.25
0.58224


 35
−340.2735
2.5000


 36
−105.2797
3.0000
1.76182
26.52
0.61361


 37
−211.7385
10.7447


 38
59.6286
5.2859
1.65844
50.88
0.55612


 39
∞
0.7143


 40
42.1381
10.1467
1.43875
94.94
0.53433


 41
−79.4704
1.4000
1.95375
32.32
0.59015


 42
57.3111
4.8082


 43
−211.6643
5.9778
1.80518
25.43
0.61027


 44
−36.7566
1.4100
1.80400
46.58
0.55730


 45
−107.9111
0.2974


 46
65.4459
7.6951
1.48749
70.24
0.53007


 47
−65.4459
0.9133


 48
52.8061
1.6002
1.91082
35.25
0.58224


 49
20.4963
12.8564
1.49700
81.54
0.53748


 50
−42.9103
1.6003
1.90043
37.37
0.57720


 51
57.8695
1.1479


 52
49.7950
3.2238
1.84666
23.83
0.61603


 53
250.6338
3.0000


 54
∞
1.4000
1.51633
64.14
0.53531


 55
∞
1.0000


 56
∞
3.6900
1.51633
64.14
0.53531


 57
∞
54.3476
















TABLE 14







Example 4 - Specifications (d-line)











Wide Angle End
Middle
Telephoto End














Zoom Magnification
1.0
2.4
7.4


f′
19.85
46.66
145.88


FNo.
2.85
2.85
2.85


2ω[°]
73.8
33.4
11.0
















TABLE 15







Example 4 - Distances with respect to Zoom











Wide Angle End
Middle
Telephoto End
















DD[18]
1.4999
48.9126
84.7378



DD[20]
1.6030
7.3950
9.3351



DD[29]
62.7958
9.3474
21.1948



DD[32]
52.3243
52.5680
2.9554

















TABLE 16





Example 4 - Aspheric Coefficients


















Surface No.
8







KA
1.0000000E+00



A3
1.5064530E−07



A4
−1.5641141E−07 



A5
1.6501598E−09



A6
−3.9701428E−11 



A7
6.9263338E−13



A8
1.0556630E−17



A9
−7.0509369E−17 



A10
5.3287613E−19







Surface No.
21







KA
 1.0000000E+00



A4
 1.5045420E−06



A6
−4.1679388E−10



A8
−8.9800509E−12



A10
 7.0993908E−14



A12
−3.2299521E−16



A14
 8.7823289E−19



A16
−1.4036759E−21



A18
 1.2097861E−24



A20
−4.3023907E−28










Table 17 shows values corresponding to the condition expressions (1) to (7) of the zoom lenses of Examples 1 to 4. In all the examples, the d-line is used as a reference wavelength, and the values shown in the Table 17 below are with respect to the reference wavelength.












TABLE 17






Condition
Example
Example
Example
Example


No.
Expression
1
2
3
4




















(1)
62 < νdn
74.70
74.70
94.66
81.54


(2)
0.64 < θgFn +
0.66075
0.66075
0.68784
0.66999



0.001625 × νdn <



0.7


(3)
1 < fln/fla < 2
1.273
1.262
1.696
1.433


(4)
νdp < 40
31.60
31.60
35.25
31.60


(5)
0.62 < θgFp +
0.64253
0.64253
0.63953
0.64253



0.001625 × νdp <



0.67


(6)
1.2 < ft/fl < 2
1.592
1.543
1.537
1.585


(7)
2 < flb/fl < 4
2.854
2.823
2.940
2.954









As can be seen from the above-described data, all the zoom lenses of Examples 1 to 4 satisfy the condition expressions (1) to (7), and are compact and high performance zoom lenses with successfully corrected chromatic aberration, while ensuring a zoom ratio of around 7×.
Next, an imaging apparatus according to an embodiment of the disclosure is described. FIG. 9 is a diagram illustrating the schematic configuration of an imaging apparatus employing the zoom lens of the embodiment of the disclosure, which is one example of the imaging apparatus of the embodiment of the disclosure. It should be noted that the lens groups are schematically shown in FIG. 9. Examples of the imaging apparatus may include a video camera, an electronic still camera, etc., which include a solid-state image sensor, such as a CCD (Charge Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor), serving as a recording medium.
The imaging apparatus 10 shown in FIG. 9 includes: a zoom lens 1; a filter 6 having a function of a low-pass filter, etc., disposed on the image plane side of the zoom lens 1; an image sensor 7 disposed on the image plane side of the filter 6; and a signal processing circuit 8. The image sensor 7 converts an optical image formed by the zoom lens 1 into an electric signal. As the image sensor 7, a CCD or a CMOS, for example, may be used. The image sensor 7 is disposed such that the imaging surface thereof is positioned in the same position as the image plane of the zoom lens 1.
An image taken through the zoom lens 1 is formed on the imaging surface of the image sensor 7. Then, a signal about the image outputted from the image sensor 7 is processed by the signal processing circuit 8, and the image is displayed on a display unit 9.
The imaging apparatus 10 of this embodiment is provided with the zoom lens 1 of the disclosure, and therefore allows size reduction of the apparatus, and obtaining high image-quality images.
The present disclosure has been described with reference to the embodiments and the examples. However, the disclosure is not limited to the above-described embodiments and examples, and various modifications may be made to the disclosure. For example, the values of the radius of curvature, the surface distance, the refractive index, the Abbe number, etc., of each lens element are not limited to the values shown in the above-described numerical examples and may be different values.

## Claims

1. A zoom lens consists of, in order from the object side, a first lens group that has a positive refractive power and is fixed during magnification change, at least two movable lens groups that are moved during magnification change with changing the distances along the optical axis direction between adjacent lens groups, and an end lens group that has a positive refractive power, is disposed at the most image side, and is fixed during magnification change,
wherein the first lens group consists of, in order from the object side, a first-a lens group that has a negative refractive power and is fixed during focusing, a first-b lens group that has a positive refractive power and is moved during focusing with changing the distances along the optical axis direction between adjacent lens groups, and a first-c lens group that has a positive refractive power,
the first-a lens group includes at least two negative lenses, wherein the most object-side negative lens has a meniscus shape with the convex surface toward the object side, and a first-n lens, which is at least one negative lens of the rest of the negative lenses of the first-a lens group, satisfies the condition expressions (1), (2), and (3) below:


62<vdn  (1),



0.64<θgFn+0.001625×vdn<0.7  (2), and



1<fln/fla<2  (3),


where vdn is an Abbe number with respect to the d-line of the first-n lens, θgFn is a partial dispersion ratio of the first-n lens, fln is a focal length with respect to the d-line of the first-n lens, and fla is a focal length with respect to the d-line of the first-a lens group.

2. The zoom lens as claimed in claim 1, wherein the first-a lens group includes a cemented lens formed by, in order from the object side, the first-n lens and a first-p lens having a positive refractive power that are cemented together, and satisfies the condition expressions (4) and (5) below:


vdp<40  (4), and



0.62<θgFp+0.001625×vdp<0.67  (5),

where vdp is an Abbe number with respect to the d-line of the first-p lens, and θgFp is a partial dispersion ratio of the first-p lens.

3. The zoom lens as claimed in claim 2, wherein the condition expression (4-1) below is satisfied:


20<vdp<38  (4-1).

4. The zoom lens as claimed in claim 2, wherein the condition expression (5-1) below is satisfied:


0.63<θgFp+0.001625×vdp<0.66  (5-1).

5. The zoom lens as claimed in claim 1, wherein the condition expression (6) below is satisfied:


1.2<ft/fl<2  (6),

where ft is a focal length of the entire system at the telephoto end, and fl is a focal length of the first lens group.

6. The zoom lens as claimed in claim 5, wherein the condition expression (6-1) below is satisfied:


1.3<ft/fl<1.8  (6-1).

7. The zoom lens as claimed in claim 1, wherein the condition expression (7) below is satisfied:


2<flb/fl<4  (7),

where flb is a focal length of the first-b lens group, and fl is a focal length of the first lens group.

8. The zoom lens as claimed in claim 7, wherein the condition expression (7-1) below is satisfied:


2.5<flb/fl<3.5  (7-1).

9. The zoom lens as claimed in claim 1, wherein the first-a lens group consists of, in order from the object side, two negative lenses, and a cemented lens formed by, in order from the object side, the first-n lens and a first-p lens having a positive refractive power that are cemented together.

10. The zoom lens as claimed in claim 1, wherein the first-c lens group is fixed during focusing.

11. The zoom lens as claimed in claim 1, wherein the first-c lens group is moved during focusing along a different locus of movement from that of the first-b lens group.

12. The zoom lens as claimed in claim 1, wherein the movable lens groups comprises at least two lens groups having a negative refractive power.

13. The zoom lens as claimed in claim 1, wherein the movable lens groups comprises at least three lens groups.

14. The zoom lens as claimed in claim 1, wherein the at least two movable lens groups consists of, in order from the object side, a second lens group having a positive refractive power, a third lens group having a negative refractive power, and a fourth lens group having a negative refractive power.

15. The zoom lens as claimed in claim 1, wherein the at least two movable lens groups consists of, in order from the object side, a second lens group having a positive refractive power, a third lens group having a negative refractive power, a fourth lens group having a negative refractive power, and a fifth lens group having a positive refractive power.

16. The zoom lens as claimed in claim 1, wherein the condition expression (1-1) below is satisfied:


70<vdn  (1-1).

17. The zoom lens as claimed in claim 16, wherein the condition expression (1-2) below is satisfied:


70<vdn<100  (1-2).

18. The zoom lens as claimed in claim 1 wherein the condition expression (2-1) below is satisfied:


0.65<θgFn+0.001625×vdn<0.69  (2-1).

19. The zoom lens as claimed in claim 1, wherein the condition expression (3-1) below is satisfied:


1.1<fln/fla<1.8  (3-1).

20. An imaging apparatus comprising the zoom lens as claimed in claim 1.