阅读说明：本技术 变焦透镜以及拍摄装置 (Zoom lens and imaging device ) 是由 林俊秀 于 2018-11-23 设计创作，主要内容包括：本发明的课题在于,提供一种小型且高性能的变焦透镜以及拍摄装置。为了解决上述课题,变焦透镜,从物体侧起依次由负的第一透镜组(G1)、正的第二透镜组(G2)、负的第三透镜组(G3)和负的第四透镜组(G4)而实质性地构成,在变焦时,各个透镜组分别在光轴方向上进行移动,以使相互邻接的透镜组之间的间隔改变,通过使所述第三透镜组沿着光轴进行移动而进行对焦,并且满足预定的条件。此外,在拍摄装置中具备该变焦透镜。(The invention provides a zoom lens and an imaging device which are small and high in performance. In order to solve the above problem, a zoom lens is substantially composed of, in order from the object side, a negative first lens group (G1), a positive second lens group (G2), a negative third lens group (G3), and a negative fourth lens group (G4), wherein each lens group is moved in the optical axis direction during zooming so that the interval between the adjacent lens groups is changed, and the third lens group is moved along the optical axis to perform focusing, and predetermined conditions are satisfied. The imaging device is provided with the zoom lens.)

1. A zoom lens comprising, in order from an object side, a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group having negative refractive power, and a fourth lens group having negative refractive power, wherein each of the lens groups is moved in an optical axis direction to change an interval between the lens groups adjacent to each other during zooming,

focusing is performed by moving the third lens group along the optical axis, and the following conditions are satisfied:

2.30≤β_3t≤3.50…(3)

wherein, beta_3tIs a lateral magnification of the third lens group at infinity focusing at the telephoto end.

2. Zoom lens according to claim 1,

the following conditions are satisfied:

3.00≤|(1-β_3t ²)×β_4t ²|≤15.00…(1)

wherein the content of the first and second substances,

β_3tis a lateral magnification of the third lens group at infinity focusing at the telephoto end,

β_4tis a lateral magnification of the fourth lens group at infinity focusing at the telephoto end.

3. Zoom lens according to claim 1,

the following conditions are satisfied:

0.40≤f3/f1≤3.00…(2)

wherein the content of the first and second substances,

f1 is the focal length of the first lens group,

f3 is the focal length of the third lens group.

4. Zoom lens according to claim 1,

the following conditions are satisfied:

0.30≤f2/|f1|≤0.90…(4)

wherein the content of the first and second substances,

f1 is the focal length of the first lens group,

f2 is the focal length of the second lens group.

5. Zoom lens according to claim 1,

the following conditions are satisfied:

3.00≤f4/f1≤500.00…(5)

wherein the content of the first and second substances,

f1 is the focal length of the first lens group,

f4 is the focal length of the fourth lens group.

6. Zoom lens according to claim 1,

the following conditions are satisfied:

0.80≤|f3|/f2≤2.00…(6)

wherein the content of the first and second substances,

f2 is the focal length of the second lens group,

f3 is the focal length of the third lens group.

7. Zoom lens according to claim 1,

the following conditions are satisfied:

nd_max≥1.85…(7)

wherein the content of the first and second substances,

nd _ max is a refractive index of a lens made of a glass material having the highest refractive index among lenses constituting the zoom lens with respect to the d-line.

8. Zoom lens according to claim 1,

the following conditions are satisfied:

0.08≤R4n/f4n≤1.00…(8)

wherein the content of the first and second substances,

r4n represents a radius of curvature of an object side surface of a negative lens disposed on the most object side among negative lenses included in the fourth lens group,

f4n is a focal length of a negative lens disposed on the most object side among negative lenses included in the fourth lens group.

9. Zoom lens according to claim 1,

the second lens group includes at least two positive lenses.

10. Zoom lens according to claim 1,

the third lens group includes at least one positive lens and at least one negative lens.

11. An imaging device is characterized by comprising:

a variable focus lens as claimed in any one of claims 1 to 10; and

and a photographing element for receiving an optical image formed by the zoom lens and converting the optical image into an electrical image signal.

Technical Field

The present invention relates to a zoom lens and an imaging apparatus, and more particularly, to a zoom lens and an imaging apparatus suitable for an imaging apparatus using a solid-state imaging Device such as a CCD (Charge Coupled Device) or a CMOS (Complementary Metal Oxide Semiconductor) that receives an optical image and converts the optical image into an electrical image signal.

Background

Conventionally, in a solid-state imaging device such as a CCD or a CMOS, on-chip micro mirrors (or the like) are provided in each pixel in order to efficiently receive incident light from an imaging lens or the like. If the angle of inclination of the incident light with respect to the optical axis becomes large, vignetting occurs and the etendue of the on-chip micromirror decreases. Therefore, in the conventional technology, there is a limit that an inclination angle of incident light with respect to an optical axis must be made small, and it is required to maintain an exit pupil diameter of a photographing lens at a constant or more and to secure image-side telecentricity.

However, in recent years, the effective aperture ratio of the on-chip micromirror has been remarkably improved, and halation is less likely to occur even when light is obliquely incident on the light receiving surface of the solid-state imaging device, and peripheral dimming (shading) is hardly noticeable. Therefore, although a positive lens is disposed on the image side of the imaging lens in order to ensure image-side telecentricity, in recent years, the restriction on the exit pupil diameter of the imaging lens is reduced, and a negative lens can be disposed on the image side of the imaging lens. Therefore, in recent years, the imaging lens is downsized by disposing a negative lens on the image side of the imaging lens.

As such a photographic lens, a zoom lens having a four-group structure in which negative positive, negative, and negative refractive power are arranged in order from the object side is known (for example, see patent documents 1 to 3). In these zoom lenses, the negative lens group is disposed closest to the image side, and thereby shortening the total optical length, particularly at the wide-angle end. However, in the zoom lens, the focal length is changed by changing the intervals on the optical axis between the respective lens groups at the time of zooming, and aberration correction is carried out per focal length. In this case, it is preferable that all the lens groups are movable groups because the zoom ratio is easily increased and aberration correction for each focal length is easily performed.

Disclosure of Invention

Problems to be solved by the invention

However, in the zoom lens disclosed in patent document 1, since the first group and the fourth group are fixed on the optical axis at the time of zooming, it is difficult to increase the zoom ratio, and it is also disadvantageous in aberration correction. In the zoom lens having a negative positive/negative four-group structure disclosed in patent document 1 (numerical embodiment 1, numerical embodiment 2, and numerical embodiment 5), the fourth group is a fixed group, and therefore, the optical structure is not favorable for correction of field curvature and distortion aberration.

Further, in the zoom lenses (examples 7 and 8) having the negative-positive-negative four-group structure disclosed in patent document 2, since the fourth lens group is fixed on the optical axis during zooming, it is also difficult to correct curvature of field and distortion aberration.

In contrast, the zoom lens disclosed in patent document 3 is advantageous in aberration correction as well as in that it is easy to achieve a larger zoom ratio than the zoom lenses disclosed in patent documents 1 and 2 because the fourth lens group moves along the optical axis during zooming. However, in the zoom lens disclosed in patent document 3, the third lens group is formed of a lens having a relatively large diameter, and the zoom lens is not sufficiently downsized.

The invention provides a zoom lens and an imaging device which are small and high in performance.

Means for solving the problems

In order to solve the above-described problems, a zoom lens according to the present invention is a zoom lens substantially composed of, in order from an object side, a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group having negative refractive power, and a fourth lens group having negative refractive power, and moving each lens group in an optical axis direction so as to change an interval between the lens groups adjacent to each other when zooming is performed, the zoom lens being characterized in that focusing is performed by moving the third lens group along the optical axis, and the following conditions are satisfied:

2.30≤β_3t≤3.50…(3)

wherein, beta_3tIs a lateral magnification of the third lens group at infinity focusing at the telephoto end.

In order to solve the above problem, an imaging device according to the present invention includes: the zoom lens and the imaging element which receives an optical image formed by the zoom lens and converts the optical image into an electric image signal.

Effects of the invention

According to the present invention, a compact and high-performance zoom lens and an imaging apparatus can be provided.

Drawings

Fig. 1 is a cross-sectional view showing an example of a lens configuration of a zoom lens according to embodiment 1 of the present invention at infinity focusing at a wide-angle end (upper stage), an intermediate focal length position (middle stage), and a telephoto end (lower stage).

Fig. 2 is a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram of the zoom lens of example 1 at infinity focusing at the wide-angle end.

Fig. 3 is a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram in infinity focusing at an intermediate focal length position of the zoom lens according to example 1.

Fig. 4 is a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram in infinity focusing at the telephoto end of the zoom lens of example 1.

Fig. 5 is a sectional view showing an example of a lens configuration of a zoom lens according to embodiment 2 of the present invention at infinity focusing at a wide-angle end (upper stage), an intermediate focal length position (middle stage), and a telephoto end (lower stage).

Fig. 6 is a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram of the zoom lens of example 2 at infinity focusing at the wide-angle end.

Fig. 7 is a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram in infinity focusing at an intermediate focal length position of the zoom lens according to example 2.

Fig. 8 is a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram in infinity focusing at the telephoto end of the zoom lens of example 2.

Fig. 9 is a sectional view of an example of a lens configuration of a zoom lens according to embodiment 3 of the present invention at infinity focusing at a wide-angle end (upper stage), an intermediate focal length position (middle stage), and a telephoto end (lower stage).

Fig. 10 is a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram of the zoom lens of example 3 at infinity focusing at the wide-angle end.

Fig. 11 is a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram in infinity focusing at an intermediate focal length position of the zoom lens according to example 3.

Fig. 12 is a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram of the zoom lens of example 3 at infinity focusing at the telephoto end.

Fig. 13 is a sectional view of an example of a lens configuration of a zoom lens according to embodiment 4 of the present invention at infinity focusing at a wide-angle end (upper stage), an intermediate focal length position (middle stage), and a telephoto end (lower stage).

Fig. 14 is a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram of the zoom lens of example 4 at infinity focusing at the wide-angle end.

Fig. 15 is a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram in infinity focusing at an intermediate focal length position of the zoom lens according to example 4.

Fig. 16 is a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram in infinity focusing at the telephoto end of the zoom lens according to example 4.

Fig. 17 is a sectional view showing an example of a lens configuration of a zoom lens according to embodiment 5 of the present invention at infinity focusing at a wide-angle end (upper stage), an intermediate focal length position (middle stage), and a telephoto end (lower stage).

Fig. 18 is a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram at the wide-angle end in infinity focusing of the zoom lens of example 5.

Fig. 19 is a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram in infinity focusing at an intermediate focal length position of the zoom lens according to example 5.

Fig. 20 is a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram in infinity focusing at the telephoto end of the zoom lens according to example 5.

Fig. 21 is a sectional view showing an example of a lens configuration of a zoom lens according to embodiment 6 of the present invention at infinity focusing at a wide-angle end (upper stage), an intermediate focal length position (middle stage), and a telephoto end (lower stage).

Fig. 22 is a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram of the zoom lens of example 6 at infinity focusing at the wide-angle end.

Fig. 23 is a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram in infinity focusing at an intermediate focal length position of the zoom lens according to example 6.

Fig. 24 is a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram in infinity focusing at the telephoto end of the zoom lens according to example 6.

Fig. 25 is a sectional view showing an example of a lens configuration of the zoom lens according to embodiment 7 of the present invention at infinity focusing at the wide-angle end (upper stage), the intermediate focal length position (middle stage), and the telephoto end (lower stage).

Fig. 26 is a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram of the zoom lens of example 7 at infinity focusing at the wide-angle end.

Fig. 27 is a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram in infinity focusing at an intermediate focal length position of the zoom lens according to example 7.

Fig. 28 is a spherical aberration diagram, an astigmatism diagram, and a distortion aberration diagram in infinity focusing at the telephoto end of the zoom lens according to example 7.

Detailed Description

Embodiments of a zoom lens and an imaging device according to the present invention will be described below. However, the zoom lens and the imaging device described below are one embodiment of the zoom lens and the imaging device according to the present invention, and the zoom lens and the imaging device according to the present invention are not limited to the following embodiment.

1. Zoom lens

1-1. optical structure of zoom lens

First, an embodiment of the zoom lens according to the present invention will be described. The zoom lens of the present embodiment is substantially composed of, in order from the object side, a first lens group having negative refractive power, a second lens group having positive refractive power, a third lens group having negative refractive power, and a fourth lens group having negative refractive power. Here, the term "substantially constituted" means that the lens group substantially constituting the zoom lens is the four lens groups of the first lens group to the fourth lens group, but it is also permissible to include a lens group having substantially no refractive index, an optical element other than a lens such as a stop or a cover glass, or the like. In addition, each lens group comprises at least one lens.

In this zoom lens, the first lens group and the second lens group are set as an object side group having positive refractive power as a whole, and the third lens group and the fourth lens group are set as an image side group having negative refractive power as a whole, so that a remote (tele) type refractive power arrangement can be realized, and the total optical length of the zoom lens at the telephoto end can be made shorter than the focal length. Further, since the third lens group and the fourth lens group have negative refractive power, it is relatively easy to reduce the diameter of the lenses constituting the image side group compared to the size of the image pickup element. This facilitates the realization of a compact zoom lens. Hereinafter, the optical structure of each lens group will be described in more detail.

(1) First lens group

The first lens group is a lens group with negative refractive power. In this zoom lens, by disposing the negative refractive power in the first lens group disposed closest to the object side, a wide angle is achieved at the wide angle end, and it is also advantageous in achieving miniaturization of the zoom lens.

The first lens group at least comprises a negative lens. In particular, if the first lens group is configured by a plurality of negative lenses, it is possible to arrange an appropriate negative refractive power in the first lens group and to distribute the refractive power among the negative lenses, so that it is possible to suppress the occurrence of each aberration (spherical aberration, field curvature, etc.), which is preferable because it is easy to realize a zoom lens having high optical performance. Further, the embodiment in which the first lens group includes at least one positive lens is preferable in terms of performing aberration correction (spherical aberration, field curvature, chromatic aberration, and the like) well.

(2) Second lens group

The second lens group at least comprises a positive lens. In the zoom lens, the lens group having positive refractive power has only the second lens group. Therefore, by disposing a strong positive refractive power in the second lens group, a strong positive refractive power can be disposed in the object side group, and further, a refractive power disposition having a strong tendency to be remote can be realized. Here, it is preferable that the second lens group includes at least two positive lenses. By configuring the second lens group with a plurality of positive lenses, strong positive refractive power is arranged in the second lens group, and the refractive power is distributed and arranged in each positive lens, so that generation of spherical aberration can be suppressed, and the total optical length at the telephoto end is short, and the zoom lens is compact, and high performance can be easily realized. In addition, the embodiment in which the second lens group includes at least one negative lens is preferable in terms of favorably performing aberration correction.

(3) Third lens group

The third lens group at least comprises a negative lens. For example, it is preferable that the third lens group includes at least one positive lens and one negative lens, because spherical aberration and chromatic aberration can be corrected well. Here, if the third lens group is configured by two lenses of a positive lens and a negative lens, it is preferable to make the third lens group compact while achieving good optical performance. In particular, as described below, when the third lens group is used as the focusing group, the third lens group can be configured by two lenses, i.e., a positive lens and a negative lens, thereby achieving downsizing and weight reduction of the focusing group.

(4) Fourth lens group

And the fourth lens group at least comprises a negative lens. Here, it is preferable that, of the negative lenses included in the fourth lens group, an object side surface of the negative lens disposed on the most object side is a concave surface. By providing the object side surface of the negative lens with a concave surface, astigmatism can be corrected well.

Preferably, the fourth lens group includes at least one positive lens and one negative lens. By configuring the fourth lens group to include not only the negative lens but also at least one positive lens, distortion aberration and field curvature can be corrected satisfactorily.

Here, if the positive lens is disposed on the most image side of the fourth lens group, that is, on the most image side of the zoom lens, correction of the wraparound distortion aberration (positive distortion aberration) can be easily performed. Further, if the positive lens is disposed on the most image side of the fourth lens group, the incident angle of the principal ray with respect to the image plane can be suppressed from becoming excessively large, and therefore the condensing ratio of the on-chip micromirror can be improved. In order to achieve this effect, it is preferable that the positive lens closest to the image side disposed in the fourth lens group has a biconvex shape.

Further, it is preferable that the fourth lens group is configured by two lenses of a positive lens and a negative lens because good optical performance can be achieved and the fourth lens group can be configured to be compact.

(5) Aperture diaphragm

In the zoom lens according to the present invention, the arrangement of the aperture stop is not particularly limited. The aperture stop referred to herein is an aperture stop that defines the beam diameter of the zoom lens, that is, an aperture stop that defines the Fno (EFL (focal length)/D (aperture diameter)) of the zoom lens.

The aperture stop is disposed in a section from the object side of the second lens group to the image side of the third lens group, but is preferable in that light rays before and after the aperture stop are effectively blocked and high performance of the zoom lens is achieved. More preferably, the aperture stop is disposed on the object side than the focus group. By disposing the aperture stop on the object side rather than the focus group, the variation in angle of view at the time of wobbling (wobbling) can be suppressed. In this zoom lens, for example, when the third lens group is a focusing group, it is preferable that the aperture stop be disposed closer to the object side than the third lens group, and in particular, it is more preferable that the aperture stop be disposed closer to the object side than the second lens group, since a further reduction in the diameter of the front lens can be achieved.

1-2. actions

(1) Movement during zooming

In the zoom lens, upon zooming from a wide-angle end to a telephoto end, the respective lens groups are moved in an optical axis direction to change intervals between mutually adjacent lens groups, respectively. When zooming is performed in this manner, all the lens groups (first to fourth lens groups) constituting the zoom lens are set as movable groups, so that the zoom ratio is easily increased, and at the same time, aberration correction of each focal length is easily performed. In particular, by setting the fourth lens group as a movable group, correction of field curvature or distortion aberration is facilitated over the entire zoom range, and a high-performance zoom lens can be realized over the entire zoom range. The zoom ratio is not particularly limited as long as the desired zoom ratio can be achieved by the amount of movement or the direction of movement of each lens group in zooming. In particular, an embodiment in which the lens groups are moved such that the interval between the first lens group and the second lens group is small, the interval between the second lens group and the third lens group is large, the interval between the third lens group and the fourth lens group is changed, and the interval between the fourth lens group and the image plane is large is preferable in terms of realizing a high-performance zoom lens over the entire zoom range.

(2) Action at focusing

In this zoom lens, at the time of focusing from infinity to the closest object, any one of the first lens group to the fourth lens group is adopted as a focus group, and the focus group is moved in the optical axis direction to perform focusing. In particular, in the zoom lens, it is preferable that the third lens group is a focusing group. In this zoom lens, four groups of negative positive and negative configurations are adopted in order from the object side. The light flux converged by the second lens group is incident on the third lens group. Therefore, the third lens group is composed of lenses having a smaller diameter than the lenses constituting the other lens groups. In addition, since the third lens group has negative refractive power, weight reduction is easily achieved as compared with a lens group having positive refractive power. In this way, a rapid autofocus operation can be achieved by setting the third lens group as a focus group. Further, by reducing the size and weight of the focus group, the load on the focus drive mechanism for moving the focus group along the optical axis can be reduced. Therefore, the focus drive mechanism can be made smaller and lighter, and the entire zoom lens unit including the barrel portion can be made smaller and lighter.

Further, a fourth lens group having negative refractive power similar to the third lens group is disposed on the image side of the third lens group. Therefore, the image magnification of the focus group can be easily increased, and the amount of movement of the focus group in focusing can be reduced. This enables a more rapid autofocus operation to be achieved and the total optical length of the zoom lens to be shortened.

For example, when the zoom lens is used and wobbling occurs during a dynamic image capturing operation of the contrast AF (auto focus) system, in the zoom lens having the negative positive/negative refractive power arrangement, the third lens group disposed on the image side of the aperture stop is used as the focus group, so that rapid wobbling can be achieved and variation in the angle of view during wobbling can be suppressed. Therefore, even when the zoom lens is used for moving picture photographing, the image displayed on the liquid crystal monitor of the photographing device can be made less likely to have a sense of incongruity. The wobbling is an operation of maintaining an in-focus state by moving the focus group back and forth slightly and at a high speed along the optical axis during moving picture shooting in the contrast AF system.

1-3. conditional formula

Next, it is preferable that one or more conditional expressions described below are satisfied in the zoom lens.

1-3-1. conditional expression (1)

3.00≤|(1-β_3t ²)×β_4t ²|≤15.00……(1)

Wherein the content of the first and second substances,

β_3t: lateral magnification in infinity focusing of the telephoto-end third lens group

β_4t: lateral magnification in infinity focusing of the fourth lens group at the telephoto end

Conditional expression (1) is a mathematical expression for defining so-called focus sensitivity of the third lens group when the third lens group is used as a focusing group. By satisfying the conditional expression (1), the focus sensitivity of the third lens group when the third lens group is used as the focusing group becomes within a suitable range. Therefore, since the amount of movement of the third lens group in focusing can be reduced, rapid wobbling can be achieved, and the total optical length of the zoom lens can be shortened. Further, aberration variation in focusing is small, and a high-performance zoom lens can be realized in the entire focusing region regardless of the object distance.

On the other hand, if the value of conditional expression (1) is smaller than the lower limit value, the focus sensitivity of the third lens group becomes small when the third lens group is used as the focusing group. Therefore, the amount of movement of the third lens group in focusing becomes large, and therefore the total optical length of the zoom lens becomes long. On the other hand, if the value of conditional expression (1) exceeds the upper limit value, the focus sensitivity of the third lens group becomes large when the third lens group is used as the focusing group. In this case, since the amount of movement of the third lens group in focusing can be reduced, it is preferable in that a rapid wobbling is achieved and the total optical length of the zoom lens is shortened. However, if the focus sensitivity is too large, aberration variation in focusing becomes large. Therefore, in order to obtain good imaging performance in the entire focus region, a large number of lenses is required for aberration correction, and it is difficult to downsize the zoom lens, which is not preferable.

In addition to these effects, the lower limit of the conditional expression (1) is preferably 3.60, more preferably 4.20, and still more preferably 4.60. The upper limit value of conditional expression (1) is more preferably 14.00, still more preferably 13.00, and still more preferably 12.50.

1-3-2. conditional expression (2)

0.40≤f3/f1≤3.00……(2)

Wherein the content of the first and second substances,

f 1: focal length of the first lens group

f 3: focal length of the third lens group

Conditional expression (2) is a mathematical expression that defines a ratio of the focal length of the third lens group to the focal length of the first lens group. By satisfying the conditional expression (2), the refractive power of the third lens group with respect to the first lens group is within an appropriate range, so that the third lens group can be downsized, and a high-performance zoom lens can be realized. Further, if the third lens group is set as the focus group, rapid wobbling can be achieved by satisfying the conditional expression (2).

On the other hand, when the numerical value of the conditional expression (2) is smaller than the lower limit value, the refractive power of the third lens group with respect to the first lens group becomes strong, and it is preferable to miniaturize the third lens group, but it is difficult to correct spherical aberration. Therefore, it is not preferable because it is difficult to realize a high-performance zoom lens. On the other hand, when the value of conditional expression (2) exceeds the upper limit value, the refractive power of the third lens group with respect to the first lens group becomes weak, and it is necessary to increase the diameter of the lenses constituting the third lens group. Further, in this case, in order to achieve a desired zoom ratio, it is necessary to increase the amount of movement of the third lens group in zooming, and the total optical length of the zoom lens also increases. This is not preferable in terms of downsizing the zoom lens.

In addition to these effects, the lower limit value of conditional expression (2) is more preferably 0.43, and still more preferably 0.47. The upper limit of conditional expression (2) is preferably 2.00, more preferably 1.30, even more preferably 1.15, even more preferably 0.90, even more preferably 0.80, and even more preferably 0.72.

1-3-3. conditional expression (3)

1.50≤β_3t≤3.50…(3)

Wherein the content of the first and second substances,

β_3t: lateral magnification of the third lens group at infinity focusing at the telephoto end.

Conditional expression (3) is a mathematical expression that defines the lateral magnification of the third lens group at infinity focusing at the telephoto end. By satisfying the conditional expression (3), the refractive power of the third lens group is within an appropriate range, and the total optical length of the zoom lens at the telephoto end can be shortened, thereby realizing a zoom lens with higher performance in a smaller size.

On the other hand, when the numerical value of conditional expression (3) exceeds the upper limit value, the lateral magnification of the telephoto end of the third lens group becomes large, and correction of field curvature becomes difficult. Therefore, it is difficult to realize a high-performance zoom lens, which is not preferable. On the other hand, when the numerical value of conditional expression (3) is smaller than the lower limit value, since the lateral magnification of the third lens group at the telephoto end becomes small, the movement amount during zooming becomes large to realize a desired zoom ratio, and the total optical length becomes long, which is not preferable. Further, when the third lens group is set as the focus group, the amount of movement in focusing becomes large, and therefore, in this case, the total optical length also becomes long, which is not preferable.

In addition to these effects, the lower limit value of conditional expression (3) is more preferably 1.80, still more preferably 2.00, still more preferably 2.20, and still more preferably 2.30. The upper limit of conditional expression (3) is more preferably 3.40, still more preferably 3.30, yet more preferably 3.20, and yet more preferably 3.10.

1-3-4. conditional expression (4)

0.30≤f2/|f1|≤0.90……(4)

Wherein the content of the first and second substances,

f 1: focal length of the first lens group

f 2: focal length of the second lens group.

Conditional expression (4) is a mathematical expression which defines a ratio of the focal length of the second lens group to the focal length of the first lens group. By satisfying the conditional expression (4), the total optical length can be shortened by setting the refractive power of the second lens group to be within an appropriate range with respect to the refractive power of the first lens group, and a zoom lens having a smaller size and higher performance can be realized.

On the other hand, when the numerical value of conditional expression (4) is smaller than the lower limit value, the refractive power of the second lens group with respect to the first lens group becomes strong, and correction of spherical aberration becomes difficult. Therefore, it is difficult to realize a high-performance zoom lens, which is not preferable. On the other hand, when the value of conditional expression (4) exceeds the upper limit value, the refractive power of the second lens group with respect to the first lens group becomes weak, and the total optical length becomes long, which is not preferable.

In addition to these effects, the lower limit value of conditional expression (4) is more preferably 0.34, still more preferably 0.38, yet more preferably 0.40, still more preferably 0.44, and yet more preferably 0.48. The upper limit of conditional expression (4) is more preferably 0.80, still more preferably 0.75, yet more preferably 0.68, still more preferably 0.64, and yet more preferably 0.60.

1-3-5 conditional expression (5)

3.00≤f4/f1≤500.00……(5)

Wherein the content of the first and second substances,

f 1: focal length of the first lens group

f 4: focal length of the fourth lens group.

Conditional expression (5) is a mathematical expression which defines a ratio of the focal length of the fourth lens group to the focal length of the first lens group. By satisfying the conditional expression (5), the refractive power of the fourth lens group with respect to the first lens group is within an appropriate range, so that the fourth lens group can be downsized and a higher performance zoom lens can be realized.

On the other hand, when the numerical value of conditional expression (5) is smaller than the lower limit value, the refractive power of the fourth lens group with respect to the first lens group becomes strong, and correction of field curvature becomes difficult. Therefore, it is difficult to realize a high-performance zoom lens, and thus it is not preferable. On the other hand, when the value of conditional expression (5) exceeds the upper limit value, the refractive power of the fourth lens group with respect to the first lens group becomes weak, and the fourth lens group needs to be configured by a lens having a larger diameter, which is not preferable.

In addition to these effects, the lower limit value of conditional expression (5) is more preferably 3.5, still more preferably 4.0, still more preferably 4.5, still more preferably 5.0, yet more preferably 5.50, yet more preferably 6.00, still more preferably 7.00, and most preferably 9.00. The upper limit of conditional expression (5) is more preferably 100.00, and still more preferably 50.00.

1-3-6. conditional expression (6)

0.80≤|f3|/f2≤2.00……(6)

Wherein the content of the first and second substances,

f 2: focal length of the second lens group

f 3: focal length of the third lens group.

Conditional expression (6) is a mathematical expression which defines a ratio of the focal length of the third lens group to the focal length of the second lens group. By satisfying the conditional expression (6), the refractive power of the third lens group with respect to the second lens group is within an appropriate range, and the total optical length of the zoom lens can be shortened, and a zoom lens with higher performance can be realized in a smaller size.

On the other hand, when the numerical value of conditional expression (6) is smaller than the lower limit value, the refractive power of the third lens group with respect to the second lens group becomes strong, and correction of spherical aberration becomes difficult. Therefore, it is not preferable because it is difficult to realize a high-performance zoom lens. On the other hand, when the value of conditional expression (6) exceeds the upper limit value, the refractive power of the third lens group with respect to the second lens group becomes weak. Therefore, it is not preferable to increase the total optical length by increasing the amount of movement during zooming in order to achieve a desired zoom ratio. Further, when the third lens group is used as the focusing group, the amount of movement in focusing becomes large, and therefore, the total optical length becomes long in this case, which is not preferable.

In addition to these effects, the lower limit of conditional expression (6) is more preferably 0.90, and still more preferably 1.00. The upper limit of conditional expression (6) is preferably 1.80, and more preferably 1.60.

1-3-7. conditional expression (7)

nd_max≥1.85……(7)

Wherein the content of the first and second substances,

nd _ max: the refractive index of the lens made of glass material having the highest refractive index among the lenses constituting the zoom lens with respect to the d-line is higher.

The conditional expression (7) is a mathematical expression of the refractive index of the lens made of a glass material having the highest refractive index among the lenses constituting the zoom lens with respect to the d-line. When the conditional expression (7) is satisfied, since the refractive index of the lens made of a glass material having the highest refractive index among the zoom lenses is high with respect to the d-line, the curvature of the optical surface of the lens can be reduced, and a desired refractive power can be arranged in the lens. Therefore, generation of spherical aberration or field curvature can be suppressed, and a zoom lens of higher performance can be realized.

In contrast, when the numerical value of conditional expression (7) is smaller than the lower limit value, the refractive index of the entire lens constituting the zoom lens is lowered. Therefore, if a strong refractive power is required to be provided to the lens made of a glass material having the highest refractive index, the curvature of the lens becomes excessively large, and it becomes difficult to correct spherical aberration and field curvature, which is not preferable.

In addition to these effects, the lower limit of conditional expression (7) is more preferably 1.88, still more preferably 1.89, and still more preferably 1.90. Since the larger the numerical value of conditional expression (7) is, the more preferable, the upper limit value of conditional expression (7) need not be defined, but if the upper limit value is set, 2.30 is preferable.

1-3-8. conditional expression (8)

0.08≤R4n/f4n≤1.00……(8)

Wherein the content of the first and second substances,

r4 n: a radius of curvature of an object side surface of a negative lens disposed closest to the object side among negative lenses included in the fourth lens group

f4 n: a focal length of a negative lens disposed on the most object side among negative lenses included in the fourth lens group.

Conditional expression (8) is a mathematical expression for defining a ratio of a radius of curvature of an object side surface of a negative lens disposed most to the object side among negative lenses included in the fourth lens group to a focal length of the negative lens. Here, the "negative lens disposed on the most object side out of the negative lenses included in the fourth lens group" means a negative lens disposed on the most object side when viewed from the negative lenses included in the fourth lens group. Therefore, in the fourth lens group, the lens disposed on the most object side may be a positive lens.

By satisfying the conditional expression (8), the object-side surface of the negative lens disposed closest to the object side among the negative lenses included in the fourth lens group has a radius of curvature within an appropriate range with respect to the focal length of the negative lens, whereby astigmatism can be corrected favorably, and a zoom lens with higher performance can be realized.

On the other hand, when the numerical value of the conditional expression (8) is smaller than the lower limit, the curvature radius of the object-side surface of the negative lens is too small, and correction of astigmatism is difficult. Therefore, it is not preferable because it is difficult to realize a high-performance zoom lens. On the other hand, when the value of conditional expression (8) exceeds the upper limit, the curvature radius of the object-side surface of the negative lens becomes too large, and in this case, correction of astigmatism becomes difficult. Therefore, it is not preferable because it is difficult to realize a high-performance zoom lens.

In addition to these effects, the lower limit of conditional expression (8) is more preferably 0.12, and still more preferably 0.15. The upper limit of conditional expression (8) is more preferably 0.90, still more preferably 0.80, yet more preferably 0.70, and yet more preferably 0.65.

2. Image capturing apparatus

Next, an embodiment of the imaging device according to the present invention will be described. The imaging device of the present embodiment is characterized by comprising: the zoom lens and the imaging element convert an optical image formed on the image side of the lens by the zoom lens into an electrical signal.

The imaging element is not particularly limited, and a solid-state imaging element such as a ccd (charge Coupled device) sensor or a cmos (complementary Metal Oxide semiconductor) sensor may be used. The imaging device according to the present invention is suitable for imaging devices using these solid-state imaging elements, such as digital cameras and video cameras. The imaging device may be a lens-fixed imaging device in which a lens is fixed to a housing, or may be a lens-replaceable imaging device such as a single-lens reflex camera or a non-lens reflex camera. In particular, the zoom lens according to the present invention can shorten the back focal length, and is therefore particularly suitable for a small (thin) imaging device such as a camless camera that does not include an optical finder or a mirror for branching light to a finder.

Next, examples are shown and the present invention will be specifically explained. However, the present invention is not limited to the following examples. The zoom lenses of the following embodiments can be applied to imaging devices (optical devices) such as digital cameras, video cameras, and silver-salt film cameras. In each lens sectional view, the left side of the drawing is the object side, and the right side is the image side.

[ example 1]

(1) Optical structure of zoom lens

Fig. 1 shows lens structures of a WIDE-angle end state (WIDE), an intermediate focal length position state (MID), and a telephoto end state (TELE) of a zoom lens according to embodiment 1 of the present invention. In the figure, the movement locus of each lens group upon zooming is indicated by an arrow mark.