阅读说明：本技术 变焦镜头及摄像装置 (Zoom lens and image pickup apparatus ) 是由 富冈右恭 于 2020-02-20 设计创作，主要内容包括：本发明提供一种实现长焦侧下的长焦距化的同时实现小型化、具备防振透镜组及直径小的聚焦透镜组、且具有良好的光学性能的变焦镜头及具备该变焦镜头的摄像装置。变焦镜头从物体侧依次包括正的第1透镜组、负的第2透镜组、负的第3透镜组、正的第4透镜组。在从广角端向长焦端变倍时,第2透镜组向像侧移动,第3透镜组在向物体侧移动之后向像侧移动。第4透镜组从物体侧依次包括正的第4A透镜组、像抖动校正时移动的负的第4B透镜组、正的第4C透镜组、对焦时移动的第4D透镜组、具有不同于第4D透镜组的屈光力的符号的屈光力的第4E透镜组。(The invention provides a zoom lens which realizes miniaturization while realizing long focal length on a long focal side, has a vibration-proof lens group and a focusing lens group with small diameter and has good optical performance, and an image pickup device with the zoom lens. The zoom lens comprises a positive 1 st lens group, a negative 2 nd lens group, a negative 3 rd lens group and a positive 4 th lens group in sequence from the object side. When zooming from the wide-angle end to the telephoto end, the 2 nd lens group moves to the image side, and the 3 rd lens group moves to the image side after moving to the object side. The 4 th lens group includes, in order from the object side, a positive 4A lens group, a negative 4B lens group that moves at the time of image shake correction, a positive 4C lens group, a 4D lens group that moves at the time of focusing, and a 4E lens group having a refractive power different in sign from that of the 4D lens group.)

1. A zoom lens comprising, in order from an object side toward an image side, a1 st lens group having positive refractive power, a 2 nd lens group having negative refractive power, a 3 rd lens group having negative refractive power, and a4 th lens group having positive refractive power,

the 4 th lens group includes only 5 lens groups as lens groups, the 5 lens groups including, in order from the object side toward the image side, a 4A lens group having positive refractive power, a 4B lens group having negative refractive power moving in a direction intersecting the optical axis at the time of image shake correction, a 4C lens group having positive refractive power, a 4D lens group moving along the optical axis at the time of focusing, and a 4E lens group having refractive power different in sign from that of the 4D lens group,

a stop is disposed on the image side of the surface closest to the image side of the 3 rd lens group,

the 2 nd lens group moves to the image side, the 3 rd lens group moves to the image side after moving to the object side, and the 1 st lens group, the stop, the 4 th A lens group, the 4 th B lens group, the 4C lens group, and the 4E lens group are fixed with respect to the image plane,

the 4A lens group and the 4C lens group are fixed relative to an image surface when image shake correction is performed,

in focusing, the lens groups except the 4D lens group are fixed relative to the image surface,

the focal length of the 4A lens group, the 4B lens group and the 4C lens group is f4ABC,

In the case where the focal length of the 4D lens group is set to f4D,

satisfies the following conditional formula (1),

0.5＜f4ABC/|f4D|＜3 (1)。

2. the zoom lens according to claim 1,

the focal length of the 2 nd lens group is f2,

In the case where the focal length of the 3 rd lens group is set to f3,

satisfies the following conditional expression (2),

0.4＜f2/f3＜1.5 (2)。

3. the zoom lens according to claim 1 or 2,

the 2 nd lens group includes a cemented lens composed of a positive lens and a negative lens cemented in this order from the object side and having a cemented surface with a concave surface facing the object side.

4. The zoom lens according to claim 1 or 2,

the lateral magnification of the 4B lens group at the telephoto end in a state of focusing on an object at infinity is set to be beta 4B,

When the combined lateral magnification of the 4C lens group, the 4D lens group, and the 4E lens group at the telephoto end in a state of focusing on an infinitely distant object is β 4CDE,

satisfies the following conditional expression (3),

-5＜(1-β 4B)×β 4CDE＜-1 (3)。

5. the zoom lens according to claim 1 or 2,

the lateral magnification of the 4D lens group at the telephoto end in a state focused on an object at infinity is set to be beta 4D,

When the lateral magnification of the 4E lens group at the telephoto end in a state focused on an object at infinity is β 4E,

satisfies the following conditional expression (4),

0.5＜|(1-β 4D²)×β 4E²|＜4 (4)。

6. the zoom lens according to claim 1 or 2,

the stop is disposed between the 4A lens group and the 4B lens group.

7. The zoom lens according to claim 1 or 2,

the number of lenses constituting the 4D lens group is 4 or less.

8. The zoom lens according to claim 1 or 2,

the 4D lens group has a negative refractive power, and the 4E lens group has a positive refractive power.

9. The zoom lens according to claim 8,

satisfies the following conditional expression (5),

-3＜f4ABC/f4D＜-0.6 (5)。

10. the zoom lens according to claim 1 or 2,

the 4A lens group includes, in order from the object side to the image side, a single lens having positive refractive power, a cemented lens having positive refractive power as a whole, and a single lens having positive refractive power,

the cemented lens of the 4A lens group is composed of a biconvex lens and a negative lens cemented in this order from the object side.

11. The zoom lens according to claim 1 or 2,

the 4B lens group comprises 3 single lenses with negative refractive power and 1 positive lens,

2 single lenses out of the 3 single lenses having negative refractive power are arranged in series in order from the most object side of the 4B lens group.

12. The zoom lens according to claim 1,

satisfies the following conditional expression (1-1),

0.8＜f4ABC/|f4D|＜1.5 (1-1)。

13. the zoom lens according to claim 2,

satisfies the following conditional expression (2-1),

0.5＜f2/f3＜0.9 (2-1)。

14. the zoom lens according to claim 4,

satisfies the following conditional expression (3-1),

-4＜(1-β 4B)×β 4CDE＜-1.5 (3-1)。

15. the zoom lens according to claim 5,

satisfies the following conditional expression (4-1),

1.5＜|(1-β 4D²)×β 4E²|＜2.8 (4-1)。

16. the zoom lens according to claim 9,

satisfies the following conditional expression (5-1),

-1.4＜f4ABC/f4D＜-0.7 (5-1)。

17. an imaging device comprising the zoom lens according to any one of claims 1 to 16.

Technical Field

The present invention relates to a zoom lens and an imaging device.

Background

Conventionally, various zoom lenses have been proposed as lens systems used for television cameras, video cameras, monitoring cameras, and the like. For example, patent document 1 listed below describes, as a zoom lens applicable to a television camera, a zoom lens having a 4-group configuration including, in order from the object side, a1 st group having positive refractive power, a 2 nd group having negative refractive power which moves during magnification change, a 3 rd group having negative refractive power which moves during magnification change, and a4 th group having positive refractive power which is fixed during magnification change.

Patent document 1: japanese patent laid-open publication No. 2004-126631

In the zoom lens having the 4-group configuration in which the refractive powers of the 2 nd group and the 3 rd group that move during magnification change are negative as described in patent document 1, the divergent effect of the 2 lens groups is improved, and the 4 th group disposed on the image side is likely to be increased in diameter, and therefore, it is expected that the configuration is optimized to achieve downsizing of the lens system. Since an optical system is easily increased in size as the focal length becomes longer, it is an important problem to reduce the size particularly in a zoom lens having a long focal length.

A zoom lens having a long focal length is one of problems to correct image blur due to vibration, hand shake, and the like caused by a photographing environment, and it is desirable to provide a lens group (hereinafter, referred to as an anti-vibration lens group) that moves when image blur correction is performed.

On the other hand, a zoom lens generally has a focusing function. Patent document 1 does not describe a lens group (hereinafter, referred to as a focusing lens group) that moves in focusing, but some lens systems similar to the lens system of patent document 1 have a configuration in which the focusing lens group is provided in group 1. However, the configuration in which the focusing lens group is provided in the 1 st group having a large diameter and a large mass is disadvantageous for speeding up of auto focusing and for monitoring camera applications in which durability of the focusing mechanism is required.

Disclosure of Invention

The present invention has been made in view of the above circumstances, and an object thereof is to provide a zoom lens having a reduced size while achieving a longer focal length on the telephoto side, and having a vibration-proof lens group and a small-diameter focus lens group and having excellent optical performance, and an image pickup apparatus including the zoom lens.

A zoom lens according to one aspect of the present invention includes, in order from an object side to an image side, a1 st lens group having positive refractive power, a 2 nd lens group having negative refractive power, a 3 rd lens group having negative refractive power, and a4 th lens group having positive refractive power, the 4 th lens group including only 5 lens groups as lens groups, the 5 lens groups including, in order from the object side to the image side, a4 th A lens group having positive refractive power, a4 th B lens group having negative refractive power moving in a direction intersecting with an optical axis at the time of image blur correction, a 4C lens group having positive refractive power, a 4D lens group moving along the optical axis at the time of focusing, and a 4E lens group having refractive power different in sign from that of the 4D lens group, the lens group being disposed on the image side of a surface closest to the image side of the 3 rd lens group, and being variable in magnification from a wide-angle end, the 2 nd lens group moves to the image side, the 3 rd lens group moves to the image side after moving to the object side, the 1 st lens group, the stop, the 4 th A lens group, the 4 th B lens group, the 4C lens group, and the 4E lens group are fixed to the image plane, the 4 th A lens group and the 4C lens group are fixed to the image plane during image blur correction, the lens groups other than the 4D lens group are fixed to the image plane during focusing, and the following conditional expression (1) is satisfied when the combined focal length of the 4 th A lens group, the 4 th B lens group, and the 4C lens group is f4ABC and the focal length of the 4D lens group is f 4D.

0.5＜f4ABC/|f4D|＜3 (1)

The zoom lens according to the above aspect of the present invention preferably satisfies the following conditional expression (1-1).

0.8＜f4ABC/|f4D|＜1.5 (1-1)

In the zoom lens according to the above aspect of the present invention, when the focal length of the 2 nd lens group is f2 and the focal length of the 3 rd lens group is f3, the following conditional expression (2) is preferably satisfied, and the following conditional expression (2-1) is more preferably satisfied.

0.4＜f2/f3＜1.5 (2)

0.5＜f2/f3＜0.9 (2-1)

In the zoom lens according to the above aspect of the present invention, it is preferable that the 2 nd lens group includes a cemented lens configured by a positive lens and a negative lens cemented in this order from the object side and having a cemented surface with a concave surface facing the object side.

In the zoom lens according to the above aspect of the present invention, when a lateral magnification of the 4B lens group at a telephoto end in a state focused on an object at infinity is β 4B, and a combined lateral magnification of the 4C lens group, the 4D lens group, and the 4E lens group at a telephoto end in a state focused on an object at infinity is β 4CDE, the following conditional expression (3) is preferably satisfied, and the following conditional expression (3-1) is more preferably satisfied.

-5＜(1-β4B)×β4CDE＜-1 (3)

-4＜(1-β4B)×β4CDE＜-1.5 (3-1)

In the zoom lens according to the above aspect of the present invention, when the lateral magnification of the 4D lens group at the telephoto end in the state focused on the object at infinity is β 4D, and the lateral magnification of the 4E lens group at the telephoto end in the state focused on the object at infinity is β 4E, the following conditional expression (4) is preferably satisfied, and the following conditional expression (4-1) is more preferably satisfied.

0.5＜|(1-β4D²)×β4E²|＜4 (4)

1.5＜|(1-β4D²)×β4E²|＜2.8 (4-1)

In the zoom lens according to the above aspect of the present invention, it is preferable that the stop be disposed between the 4A lens group and the 4B lens group.

In the zoom lens according to the above aspect of the present invention, the number of lenses constituting the 4D lens group is preferably 4 or less.

In the zoom lens according to the above aspect of the present invention, the zoom lens may be configured such that: the 4D lens group has negative refractive power, and the 4E lens group has positive refractive power. In this configuration, when the combined focal length of the 4A lens group, the 4B lens group, and the 4C lens group is f4ABC, and the focal length of the 4D lens group is f4D, the following conditional expression (5) is preferably satisfied, and the following conditional expression (5-1) is more preferably satisfied.

-3＜f4ABC/f4D＜-0.6 (5)

-1.4＜f4ABC/f4D＜-0.7 (5-1)

In the zoom lens according to the above aspect of the present invention, the zoom lens may be configured such that: the 4A lens group includes, in order from the object side to the image side, a single lens having positive refractive power, a cemented lens having positive refractive power as a whole, and a single lens having positive refractive power, and the cemented lens of the 4A lens group is composed of a double convex lens and a negative lens cemented in order from the object side.

In the zoom lens according to the above aspect of the present invention, the zoom lens may be configured such that: the 4B lens group comprises 3 single lenses with negative refractive power and 1 positive lens, and 2 single lenses in the 3 single lenses with negative refractive power are sequentially arranged from the most object side of the 4B lens group.

An imaging device according to another aspect of the present invention includes the zoom lens according to the above aspect of the present invention.

In addition, the expressions "include" and "including" in the present specification may include, in addition to the components listed below: a lens having substantially no optical power; optical elements other than lenses, such as a diaphragm, a filter, and a cover glass; and mechanism parts such as lens flanges, lens barrels, imaging elements, and hand shake correction mechanisms.

In the present specification, "group having positive refractive power" means that the entire group has positive refractive power. Similarly, "group having negative refractive power" means that the group as a whole has negative refractive power. "a lens having positive refractive power" means the same as "a positive lens". The "lens having negative refractive power" has the same meaning as the "negative lens". The "lens group" is not limited to a configuration including a plurality of lenses, and may be a configuration including only 1 lens.

The singlet lens is an unbonded 1-piece lens. However, a compound aspherical lens (a lens in which a spherical lens and an aspherical film formed on the spherical lens are integrally formed and which functions as 1 aspherical lens as a whole) is used as 1 lens and is not regarded as a cemented lens. The signs of the refractive power and the surface shape of the lens surface of a lens including an aspherical surface are considered in the paraxial region unless otherwise specified.

The "focal length" used in the conditional expression is a paraxial focal length. The value used in the conditional expression is a value when the d-line is used as a reference in a state of focusing on an object at infinity. The "d line", "C line", "F line" and "g line" described in the present specification are open lines, the wavelength of the d line is 587.56nm (nm), the wavelength of the C line is 656.27nm (nm), the wavelength of the F line is 486.13nm (nm), and the wavelength of the g line is 435.84nm (nm). The "higher order" related to the aberration means 5 th order or more.

Effects of the invention

According to the present invention, it is possible to provide a zoom lens having a reduced size while achieving a long focal length on the telephoto side, and having excellent optical performance and including an anti-vibration lens group and a small-diameter focus lens group, and an image pickup apparatus including the zoom lens.

Drawings

Fig. 1 corresponds to a zoom lens system according to embodiment 1 of the present invention, and is a diagram showing a cross-sectional view and a movement locus of a zoom lens system according to an embodiment of the present invention.

Fig. 2 is a sectional view showing a structure of a4 th lens group of the zoom lens shown in fig. 1.

Fig. 3 is a cross-sectional view showing a structure and light beams in each magnification varying state of the zoom lens shown in fig. 1.

Fig. 4 is a sectional view and a movement locus showing the configuration of a zoom lens system according to embodiment 2 of the present invention.

Fig. 5 is a sectional view and a movement locus diagram showing a configuration of a zoom lens system according to embodiment 3 of the present invention.

Fig. 6 is a sectional view and a movement locus showing the configuration of a zoom lens system according to embodiment 4 of the present invention.

Fig. 7 is a sectional view and a movement locus diagram showing a configuration of a zoom lens system according to embodiment 5 of the present invention.

Fig. 8 is a spherical aberration diagram, an astigmatism diagram, a distortion aberration diagram, and a magnification chromatic aberration diagram of the zoom lens according to embodiment 1 of the present invention.

Fig. 9 is a lateral aberration diagram at the telephoto end of the zoom lens according to embodiment 1 of the present invention when the optical system is not tilted and when the optical system is tilted to perform image shake correction.

Fig. 10 is a spherical aberration diagram, an astigmatism diagram, a distortion aberration diagram, and a magnification chromatic aberration diagram of the zoom lens according to embodiment 2 of the present invention.

Fig. 11 is a lateral aberration diagram at the telephoto end of the zoom lens system according to embodiment 2 of the present invention when the optical system is not tilted and when the optical system is tilted to perform image shake correction.

Fig. 12 is a spherical aberration diagram, an astigmatism diagram, a distortion aberration diagram, and a magnification chromatic aberration diagram of the zoom lens according to embodiment 3 of the present invention.

Fig. 13 is a lateral aberration diagram at the telephoto end of the zoom lens system according to embodiment 3 of the present invention when the optical system is not tilted and when the optical system is tilted to perform image shake correction.

Fig. 14 is a spherical aberration diagram, an astigmatism diagram, a distortion aberration diagram, and a magnification chromatic aberration diagram of the zoom lens according to embodiment 4 of the present invention.

Fig. 15 is a lateral aberration diagram at the telephoto end of the zoom lens system according to embodiment 4 of the present invention when the optical system is not tilted and when the optical system is tilted to perform image shake correction.

Fig. 16 is a spherical aberration diagram, an astigmatism diagram, a distortion aberration diagram, and a magnification chromatic aberration diagram of the zoom lens according to embodiment 5 of the present invention.

Fig. 17 is a lateral aberration diagram at the telephoto end in the zoom lens according to embodiment 5 of the present invention when the optical system is not tilted and when the optical system is tilted to perform image shake correction.

Fig. 18 is a schematic configuration diagram of an imaging apparatus according to an embodiment of the present invention.

Description of the symbols

1-zoom lens, 2-filter, 3-imaging element, 4-signal processing section, 5-zoom control section, 6-image shake correction control section, 7-focus control section, 10-image pickup device, G1-1 lens group, G2-2 nd lens group, G3-3 rd lens group, G4-4 th lens group, G4A-4 th lens group, G4B-4B lens group, G4C-4C lens group, G4D-4D lens group, G4E-4E lens group, L11-L15, L21-L25, L31-L32, La 1-La 4, Lb 1-Lb 4, Lc 1-Lc 5, Ld 1-Ld 4, Le 1-Le 2-lens, light beam on-axis, Simb-aperture, maximum aperture, Siwa-PP-image plane, image plane-PP-image plane, z-optical axis.

Detailed Description

Hereinafter, embodiments of a zoom lens according to the present invention will be described in detail with reference to the drawings. Fig. 1 illustrates a configuration of a zoom lens according to an embodiment of the present invention, a sectional view of the zoom lens at a wide-angle end and a trajectory. Fig. 2 is a partially enlarged view of the zoom lens. Fig. 3 is a cross-sectional view showing a lens structure and light beams in each magnification varying state of the zoom lens. The examples shown in fig. 1 to 3 correspond to the zoom lens system of embodiment 1 described later. Fig. 1 to 3 show a state of focusing on an object at infinity, where the left side is the object side and the right side is the image side. In fig. 3, the WIDE-angle end state is shown in the upper row labeled with "WIDE", the intermediate focal length state is shown in the MIDDLE row labeled with "MIDDLE", and the TELE end state is shown in the lower row labeled with "TELE". Fig. 3 shows, as luminous fluxes, an on-axis luminous flux wa and a luminous flux wb at the maximum viewing angle in the wide-angle end state, an on-axis luminous flux ma and a luminous flux mb at the maximum viewing angle in the intermediate focal length state, and an on-axis luminous flux ta and a luminous flux tb at the maximum viewing angle in the telephoto end state.

Fig. 1 and 3 show an example in which the zoom lens is applied to an image pickup apparatus, and the optical member PP having a parallel flat plate shape is arranged between the zoom lens and the image plane Sim. The optical member PP is a member assumed to be various filters, cover glass, or the like. Examples of the various filters include a low-pass filter, an infrared cut filter, and a filter for cutting off a specific wavelength region. The optical member PP has no optical power, and the optical member PP may be omitted in the present invention.

The zoom lens of the present invention includes, in order from the object side toward the image side along the optical axis Z, a1 st lens group G1 having positive refractive power, a 2 nd lens group G2 having negative refractive power, a 3 rd lens group G3 having negative refractive power, and a4 th lens group G4 having positive refractive power. An aperture stop St is disposed on the image side of the most image side surface of the 3 rd lens group G3. Note that the aperture stop St in fig. 1 to 3 indicates a position in the optical axis direction, and does not indicate a shape. When zooming from the wide angle end to the telephoto end, the 2 nd lens group G2 always moves to the image side, the 3 rd lens group G3 moves to the object side and then moves to the image side, and the 1 St lens group G1 and the aperture stop St are fixed to the image plane Sim. In fig. 1, trajectories of the respective lens groups at the time of varying magnification from the wide-angle end to the telephoto end are schematically shown by arrows below the 2 nd lens group G2 and the 3 rd lens group G3, respectively.

The configuration in which the 1 st lens group G1 closest to the object side is fixed at the time of magnification change can reduce the variation in the center of gravity of the lens system without changing the total optical length at the time of magnification change, and therefore can improve the convenience in photographing. The total optical length is the sum of the distance on the optical axis from the lens surface closest to the object side to the lens surface closest to the image side and the back focal length in terms of the air-converted distance.

By providing two lens groups, i.e., the 2 nd lens group G2 and the 3 rd lens group G3, which are movable during magnification change, as lens groups having negative refractive power, the 3 rd lens group G3 can form a locus of movement toward the image side in the vicinity of the telephoto end during magnification change from the wide-angle end to the telephoto end. Therefore, the moving range of the 2 nd lens group G2 at the time of magnification change can be increased without increasing the optical total length, and hence it is advantageous to achieve miniaturization of the optical total length while achieving a high magnification change ratio. Further, since the moving range of the 2 nd lens group G2 can be increased, the refractive power of the 2 nd lens group G2 can be suppressed, and thus aberration variation (particularly, variation in distortion aberration and variation in chromatic aberration of magnification) accompanying magnification variation can be suppressed.

The refractive power of the 2 nd lens group G2 can be suppressed even with the configuration of the present invention in which the 2 nd lens group G2 and the 3 rd lens group G3 are lens groups having negative refractive power, from the viewpoint that the negative refractive power can be shared by the 2 nd group. Therefore, compared with the structure in which the 2 nd lens group G2 has negative refractive power and the 3 rd lens group G3 has positive refractive power, the structure of the present invention can reduce the height of the on-axis marginal ray passing through the 3 rd lens group G3, and is therefore advantageous for the reduction in diameter of the 3 rd lens group G3. In addition, since the configuration in which the positive, negative, and positive lens groups are arranged in order from the object side toward the image side can easily suppress distortion aberration at the wide angle end in the wide angle, the configuration can be applied to a wide-angle type zoom lens in which the refractive power of the 2 nd lens group G2 can be suppressed.

In the example shown in fig. 1, the 1 st lens group G1 includes 5 lenses, i.e., lenses L11 to L15, in order from the object side to the image side, the 2 nd lens group G2 includes 4 lenses, i.e., lenses L21 to L24, in order from the object side to the image side, the 3 rd lens group G3 includes 2 lenses, i.e., lenses L31 to L32, in order from the object side to the image side, and the 4 th lens group G4 includes 19 lenses. However, in the zoom lens of the present invention, the number of lenses constituting each lens group may be different from the example shown in fig. 1.

The zoom lens of the present invention has a large feature in the 4 th lens group G4, and therefore the 4 th lens group G4 is first described in detail. The 4 th lens group G4 includes only 5 lens groups as lens groups, and the 5 lens groups include, in order from the object side toward the image side, a 4A lens group G4A having positive refractive power, a 4B lens group G4B having negative refractive power which moves in a direction intersecting the optical axis Z during image blur correction, a 4C lens group G4C having positive refractive power, a 4D lens group G4D which moves along the optical axis Z during focusing, and a 4E lens group G4E. The 4D lens group G4D and the 4E lens group G4E have refractive powers of different signs from each other. At the time of magnification change, the 4 th a lens group G4A, the 4 th B lens group G4B, the 4 th C lens group G4C, and the 4 th E lens group G4E are fixed with respect to the image plane Sim.

The 4 th lens group G4 of the zoom lens of fig. 1 is shown enlarged in fig. 2. In the example shown in fig. 2, the 4A lens group G4A includes 4 lenses, i.e., lenses La1 to La4, in order from the object side to the image side, the 4B lens group G4B includes 4 lenses, i.e., lenses Lb1 to Lb4, in order from the object side to the image side, the 4C lens group G4C includes 5 lenses, i.e., lenses Lc1 to Lc5, in order from the object side to the image side, the 4D lens group G4D includes 4 lenses, i.e., lenses Ld1 to Ld4, in order from the object side to the image side, and the 4E lens group G4E includes 2 lenses, i.e., lenses Le1 to Le2, in order from the object side to the image side. The aperture stop St is disposed between the 4A lens group G4A and the 4B lens group G4B. However, in the zoom lens of the present invention, the number of lenses constituting each lens group in the 4 th lens group G4 may be different from the example shown in fig. 2, or the aperture stop St may be disposed at a position different from the example shown in fig. 2.

By providing the 4A lens group G4A with a positive refractive power, the light flux diverged by the 2 nd lens group G2 and the 3 rd lens group G3 can be converged and incident on the 4B lens group G4B, and therefore the lens of the 4B lens group G4B can be reduced in diameter.

Preferably, the 4A lens group G4A includes, in order from the object side to the image side, a single lens having positive refractive power, a cemented lens having positive refractive power as a whole, and a single lens having positive refractive power, and the cemented lens is formed by a biconvex lens and a negative lens cemented together in order from the object side. With such a configuration, by making divergent light from the 3 rd lens group G3 incident on the single lens having positive refractive power on the most object side of the 4A lens group G4A, it is possible to correct spherical aberration that increases in the tendency to transition on the wide angle side due to the 2 nd lens group G2 and the 3 rd lens group G3. Further, the cemented lens having the cemented surface with the convex surface facing the image side can correct axial chromatic aberration satisfactorily by utilizing high-order spherical aberration occurring for each wavelength. Further, by disposing a single lens having a positive refractive power on the image side of the cemented lens, the negative lens in the cemented lens easily secures a negative refractive power necessary for correcting the on-axis chromatic aberration, and good optical performance can be obtained.

The 4B-th lens group G4B can change the image position in the direction perpendicular to the optical axis Z by moving in the direction intersecting the optical axis Z, thereby enabling image shake correction. In the zoom lens of the present invention, the 4A lens group G4A and the 4C lens group G4C, which are lens groups on both sides of the 4B lens group G4B, are fixed with respect to the image plane Sim at the time of image shake correction. In the example shown in fig. 1, the vibration-proof lens group includes only the 4B lens group G4B, and the lens groups other than the 4B lens group G4B are fixed with respect to the image plane Sim at the time of image shake correction. The double arrow in the vertical direction drawn below the 4B lens group G4B in fig. 1 indicates that the 4B lens group G4B is an anti-vibration lens group.

By providing the 4B lens group G4B as a lens group having a negative refractive power, the refractive power of the 4B lens group G4B can be strengthened, and a large vibration-proof angle is favorably obtained even if the moving amount of the 4B lens group G4B is reduced at the time of image shake correction. Here, the vibration-proof angle is a correction angle of image blur that can be corrected by moving the vibration-proof lens group. Further, by setting the refractive power of the 4B lens group G4B to negative, even if the refractive power of the 4B lens group G4B is strengthened in order to obtain a large vibration-proof angle by a small amount of movement of the 4B lens group G4B, an increase in the beam diameter passing through the 4B lens group G4B can be suppressed, and the diameter of the 4B lens group G4B can be reduced. If the refractive power of the 4B lens group G4B is set to be positive, the effect of converging light beams needs to be estimated and the beam diameter needs to be increased in advance, and the height of the off-axis light beam from the optical axis Z needs to be secured in advance in order to realize an image size, so that it is difficult to reduce the diameter of the 4B lens group G4B.

Preferably, the 4B lens group G4B includes 3 negative-power single lenses and 1 positive lens, and 2 single lenses out of the 3 negative-power single lenses are arranged in series from the most object side of the 4B lens group G4B. In this way, by disposing 2 negative lenses having a divergent effect on the object side in the 4B lens group G4B, the occurrence of high-order spherical aberration in the 4B lens group G4B can be suppressed. Further, by disposing a single lens having a negative refractive power and a single lens having a positive refractive power on the image side of these 2 negative lenses, it is possible to suppress variation in chromatic aberration accompanying movement of the 4B lens group G4B at the time of image shake correction.

The 4C lens group G4C is a lens group having positive refractive power. The light flux diverged by the 4B lens group G4B can be converged by the 4C lens group G4C disposed on the image side of the 4B lens group G4B, and thus an increase in the light flux diameter incident on the 4D lens group G4D can be suppressed.

The 4D lens group G4D performs focusing by moving along the optical axis Z. In the zoom lens of the present invention, the focusing lens group includes only the 4D lens group G4D, and lens groups other than the 4D lens group G4D are fixed with respect to the image plane Sim upon focusing. Therefore, the zoom lens of the present invention does not use a lens of the 1 st lens group G1, which has a large lens diameter and is liable to be heavy, at the time of focusing, and is therefore advantageous for speedup of auto focusing and also advantageous for applications in a monitoring camera requiring durability of a focusing mechanism. A double arrow in the horizontal direction drawn below the 4D lens group G4D in fig. 1 indicates that the 4D lens group G4D is a focusing lens group.

The number of lenses constituting the 4D lens group G4D is preferably 4 or less. In the case of such a configuration, the weight of the focusing lens group can be suppressed, which is advantageous for speeding up of the auto-focusing. For example, the 4D lens group G4D may be configured to include 2 negative lenses and 2 positive lenses, and in such a configuration, it is easy to suppress aberration variation in focusing. More specifically, the 4D lens group G4D may include, in order from the object side to the image side, a negative lens, a positive lens, a negative lens, and a positive lens.

A 4D lens group G4D, which is a focusing lens group, is disposed on the image side of the 4C lens group G4C, and a 4E lens group G4E having a refractive power different from the sign of the refractive power of the 4D lens group G4D is disposed on the image side of the 4D lens group G4D. With this configuration, the refractive power of the 4D lens group G4D can be strengthened, and the moving amount of the 4D lens group G4D in focusing can be reduced. Also, even if the refractive power of the 4D lens group G4D is strengthened in order to reduce the moving amount of the 4D lens group G4D at the time of focusing, whereby the amount of aberration generated in the 4D lens group G4D increases, it is possible to correct aberration by the 4E lens group G4E having a refractive power of a different sign from that of the 4D lens group G4D.

Regarding the distribution of refractive powers in the 4 th lens group G4, in the zoom lens of the present invention, when the combined focal length of the 4 th a lens group G4A, the 4 th B lens group G4B, and the 4 th C lens group G4C is f4ABC, and the focal length of the 4 th D lens group G4D is f4D, the following conditional expression (1) is satisfied.

0.5＜f4ABC/|f4D|＜3 (1)

The operation and effect of conditional expression (1) will be described in each case with reference to the signs of refractive power of the 4D lens group G4D. When the 4D lens group G4D has a negative refractive power, the refractive power of the 4D lens group G4D is not excessively reduced by not being equal to or less than the lower limit of conditional expression (1), and therefore the moving amount of the 4D lens group G4D during focusing can be reduced. When the 4D lens group G4D has a negative refractive power, the refractive power of the 4D lens group G4D is not excessively increased by not being equal to or more than the upper limit of the conditional expression (1), and thus variation in aberrations during focusing can be suppressed.

When the 4D lens group G4D has positive refractive power, the moving amount of the 4D lens group G4D in focusing can be reduced while securing a back focal length of an appropriate length by not being equal to or less than the lower limit of conditional expression (1). This is for the reason described below. If the 4D lens group G4D has positive refractive power and is equal to or less than the lower limit of conditional expression (1), the combined refractive power of the 4A lens group G4A, the 4B lens group G4B, and the 4C lens group G4C becomes strong, causing divergent light from the 3 lens group G3 to be converted into large convergent light in the 3 lens groups. If a back focus of an appropriate length is to be secured in this state, the positive refractive power of the 4D lens group G4D cannot be strengthened, which leads to an increase in the moving amount of the 4D lens group G4D during focusing. When the 4D lens group G4D has a positive refractive power, the refractive power of the 4D lens group G4D is not excessively increased by not being equal to or higher than the upper limit of the conditional expression (1), and thus variation in aberrations during focusing can be suppressed.

Further, if the following conditional expression (1-1) is further satisfied within the range satisfying the conditional expression (1), more favorable characteristics can be obtained.

0.8＜f4ABC/|f4D|＜1.5 (1-1)

Further, when the lateral magnification of the 4B lens group G4B at the telephoto end in the state focused on the infinity object is β 4B, and the combined lateral magnification of the 4C lens group G4C, the 4D lens group G4D, and the 4E lens group G4E at the telephoto end in the state focused on the infinity object is β 4CDE, it is preferable that the following conditional expression (3) is satisfied. By setting the lower limit of conditional expression (3) or less, coma aberration generated in image blur correction can be suppressed. By setting the upper limit of conditional expression (3) or more, the amount of movement of the 4B lens group G4B required for image shake correction can be reduced, and thereby the amount of peripheral light can be easily secured for image shake correction. Further, a structure satisfying the following conditional expression (3-1) can provide more favorable characteristics.

-5＜(1-β4B)×β4CDE＜-1 (3)

-4＜(1-β4B)×β4CDE＜-1.5 (3-1)

Further, when the lateral magnification of the 4D lens group G4D at the telephoto end in the state focused on the object at infinity is β 4D, and the lateral magnification of the 4E lens group 64E at the telephoto end in the state focused on the object at infinity is β 4E, it is preferable that the following conditional expression (4) is satisfied. By setting the lower limit of conditional expression (4) or less, the increase in the movement amount of the 4D lens group G4D in focusing can be suppressed. Therefore, the back focus mode is advantageously realized. By setting the refractive power of the 4D lens group G4D not to be equal to or higher than the upper limit of the conditional expression (4), the variation of each aberration during focusing can be suppressed. Further, when the 4D lens group G4D has negative refractive power, the effect of easily and favorably correcting field curvature can be exhibited by not being equal to or more than the upper limit of conditional expression (4). Further, a structure satisfying the following conditional expression (4-1) can provide more favorable characteristics.

0.5＜|(1-β4D²)×β4E²|＜4 (4)

1.5＜|(1-β4D²)×β4E²|＜2.8 (4-1)

The configuration may be such that: the 4D lens group G4D has negative refractive power, and the 4E lens group G4E has positive refractive power. In the case of such a configuration, since the 4E lens group G4E having positive refractive power can provide a converging action to the light flux rising through the 4D lens group G4D, an increase in the incident angle of the principal ray of the off-axis light flux to the image plane Sim can be suppressed.

In the configuration in which the 4D lens group G4D has a negative refractive power, it is preferable that the following conditional expression (5) is satisfied when a combined focal length of the 4A lens group G4A, the 4B lens group G4B, and the 4C lens group G4C is f4ABC, and a focal length of the 4D lens group G4D is f 4D. By not being equal to or less than the lower limit of conditional expression (5), the refractive power of the 4D lens group G4D is not excessively increased, and therefore, the field curvature can be corrected well. By setting the refractive power of the 4D lens group G4D not to be equal to or higher than the upper limit of the conditional expression (5), the moving amount of the 4D lens group G4D necessary for focusing can be suppressed. Further, in order to satisfy conditional expression (5), by setting the range of f4ABC/f4D negative and the refractive power of the 4D lens group G4D negative, the 4E lens group G4E provides a converging action to the light flux rising through the 4D lens group G4D, and the light flux is easily incident on the image plane Sim at an appropriate angle. Therefore, when it is necessary to increase the image size for electronic vibration isolation, the conditional expression (5) is a preferable condition. Further, a structure satisfying the following conditional expression (5-1) can provide more favorable characteristics.

-3＜f4ABC/f4D＜-0.6 (5)

-1.4＜f4ABC/f4D＜-0.7 (5-1)

The aperture stop St is preferably disposed between the 4A lens group G4A and the 4B lens group G4B. In the configuration in which the 2 nd lens group G2 and the 3 rd lens group G3 movable at the time of magnification change are lens groups having negative refractive power, the interval between the 3 rd lens group G3 and the 4 th lens group G4 at the time of magnification change is smallest below the telephoto end. If the aperture stop St is disposed adjacent to the 4 th a lens group G4A on the object side of the 4 th a lens group G4A, it is necessary to provide a space for avoiding interference between the 3 rd lens group G3 and the aperture stop St and interference between the aperture stop St and the 4 th a lens group G4A, respectively. In contrast, by disposing the aperture stop St on the image side of the 4A lens group G4A instead of the object side of the 4A lens group G4A, the above-described space is not required, and high zoom ratio can be facilitated. Further, the light flux diverged by the 2 nd lens group G2 and the 3 rd lens group G3 can be passed through the aperture stop St after being converged by the 4A lens group G4A, and therefore, it is possible to suppress the diameter of the aperture stop St from becoming larger. When the aperture stop St is extremely disposed on the image side, the peripheral light amount decreases.

Next, a description will be given of a preferable configuration and an achievable configuration of the 1 st lens group G1, the 2 nd lens group G2, and the 3 rd lens group G3. The 1 st lens group G1 can be configured to include, for example, a cemented lens formed by a negative meniscus lens and a double convex lens cemented together, a cemented lens formed by a negative meniscus lens and a positive meniscus lens cemented together, and a positive meniscus lens in order from the object side to the image side. Alternatively, the 1 st lens group G1 may be configured to include, in order from the object side toward the image side, a cemented lens formed by a negative meniscus lens and a double convex lens cemented together, and a cemented lens formed by a double convex lens and a double concave lens cemented together.

Preferably, the 2 nd lens group G2 includes a cemented lens. In this case, the cemented lens included in the 2 nd lens group G2 is preferably composed of a positive lens and a negative lens cemented in this order from the object side, and has a cemented surface with a concave surface facing the object side. By setting the joint surface to such a shape, it is possible to excellently correct on-axis chromatic aberration generated in the 1 st lens group G1 on the telephoto side.

The 2 nd lens group G2 can be configured to include, for example, a negative meniscus lens, a cemented lens in which a positive meniscus lens and a biconcave lens are cemented, and a positive meniscus lens in this order from the object side to the image side. Alternatively, the 2 nd lens group G2 may be configured to include, in order from the object side to the image side, a double convex lens, a negative meniscus lens, a double concave lens, and a cemented lens in which a positive meniscus lens and a double concave lens are cemented.

When the focal length of the 2 nd lens group G2 is f2 and the focal length of the 3 rd lens group G3 is f3, the following conditional expression (2) is preferably satisfied. By setting the refractive power of the 2 nd lens group G2 to be not too high as the lower limit of the conditional expression (2) or less, it is possible to suppress excessive correction of spherical aberration on the telephoto side, which is advantageous for obtaining high optical performance. Since the refractive power of the 2 nd lens group G2 is not excessively reduced by not being equal to or more than the upper limit of the conditional expression (2), the moving amount of the 2 nd lens group G2 at the time of magnification change is easily shortened, which is advantageous in shortening the total optical length. Further, a structure satisfying the following conditional expression (2-1) can provide more favorable characteristics.

0.4＜f2/f3＜1.5 (2)

0.5＜f2/f3＜0.9 (2-1)

The 3 rd lens group G3 may be configured to include, for example, a cemented lens in which a biconcave lens and a positive meniscus lens are cemented together in order from the object side to the image side.

In the example shown in fig. 1, the optical member PP is disposed between the zoom lens and the image plane Sim, but when the optical member PP is an infrared cut filter or a filter that cuts off a specific wavelength region of visible light, the optical member PP can be disposed at an arbitrary position in the optical path. For example, the filter may be disposed on the object side or the image side of the 4E lens group G4E adjacent to the 4E lens group 64E.

The above-described preferred configurations and realizable configurations can be arbitrarily combined and preferably selectively employed as appropriate in accordance with the required specifications. According to the technique of the present invention, a zoom lens which is compact while achieving a long focal length on the telephoto side, and which has a vibration-proof lens group and a focusing lens group having a small diameter and has excellent optical performance can be realized. Here, "long focus on the telephoto side" means that the focal length at the telephoto end is 500mm or more.

Next, numerical embodiments of the zoom lens of the present invention will be described.

[ example 1]