阅读说明：本技术 变焦透镜及摄像装置 (Zoom lens and imaging device ) 是由 米泽贤 小松大树 椚濑高志 于 2019-08-19 设计创作，主要内容包括：本发明提供一种变倍时的色差的变动及球面像差的变动得到抑制而具有高光学性能的变焦透镜及具备该变焦透镜的摄像装置。变焦透镜从物体侧依次包括变倍时不动的正的第1透镜组、包括变倍时移动的2个以上的移动透镜组的中间组及在最靠物体侧具有包括光圈的透镜组的后续组。中间组至少具有2个负的移动透镜组。中间组内的至少1个负的移动透镜组至少包括1个满足与折射率、色散系数及部分色散比相关的预定的条件式的负的LN透镜。(The invention provides a zoom lens with high optical performance and suppressed variation of chromatic aberration and variation of spherical aberration during zooming, and an imaging device provided with the zoom lens. The zoom lens includes, in order from the object side, a positive 1 st lens group which is not moved at the time of magnification change, an intermediate group including 2 or more moving lens groups which move at the time of magnification change, and a subsequent group having a lens group including a diaphragm on the most object side. The intermediate group has at least 2 negative moving lens groups. The at least 1 negative moving lens group in the intermediate group includes at least 1 negative LN lens that satisfies predetermined conditions concerning refractive index, Abbe number, and partial dispersion ratio.)

1. A zoom lens characterized in that a lens element is provided,

the image pickup device includes, in order from an object side to an image side: a 1 st lens group having positive refractive power which is fixed with respect to an image surface at the time of variable magnification, an intermediate group including 2 or more moving lens groups which move along an optical axis while changing an interval with an adjacent group at the time of variable magnification, and a subsequent group including a lens group including a stop on the most object side,

at least 2 of the moving lens groups within the intermediate group have negative refractive power,

at least 1 of the moving lens groups having negative refractive power within the intermediate group includes at least 1 negative lens (LN lens),

when the refractive index under the d-line of the LN lens is Ndn, the d-line reference Abbe number of the LN lens is ν dn, and the partial dispersion ratio between the g-line and the F-line of the LN lens is θ gFn,

the LN lens satisfies conditional expressions (1), (2), (3), and (4) shown below,

1.72＜Ndn＜1.8 (1)；

43＜νdn＜57 (2)；

0.6355＜θgFn+0.001625×νdn＜0.66 (3)；

2.21＜Ndn+0.01×νdn (4)。

2. the variable focus lens according to claim 1,

the moving lens group having a negative refractive power in the intermediate group on the more object side than the moving lens group having a negative refractive power in the most image side in the intermediate group includes the LN lens,

when a focal length of the moving lens group having negative refractive power in the intermediate group including the LN lens having the strongest negative refractive power among the LN lenses included in the moving lens group having negative refractive power in the intermediate group located on the object side more than the moving lens group having negative refractive power on the most image side in the intermediate group is set to fA, and a focal length of the moving lens group having negative refractive power on the most image side in the intermediate group is set to fB,

the zoom lens satisfies conditional expression (5) shown below,

0.6＜fB/fA＜4.5 (5)。

3. zoom lens according to claim 1 or 2,

the moving lens group having a negative refractive power in the intermediate group on the more object side than the moving lens group having a negative refractive power in the most image side in the intermediate group includes the LN lens,

when a focal length of the moving lens group having negative refractive power in the intermediate group including the LN lens having the strongest negative refractive power among the LN lenses included in the moving lens group having negative refractive power in the intermediate group positioned on the object side more than the moving lens group having negative refractive power in the image side most in the intermediate group is set to fA, and a focal length of the LN lens having the strongest negative refractive power among the LN lenses included in the moving lens group having negative refractive power in the intermediate group is set to fnmm,

the zoom lens satisfies conditional expression (6) shown below,

0.5＜fLNm/fA＜40 (6)。

4. zoom lens according to claim 1 or 2,

at least 1 of the moving lens groups in the intermediate group includes a cemented lens in which at least 1 of the LN lenses and at least 1 of the positive lenses are cemented.

5. Zoom lens according to claim 4,

when the d-line reference Abbe number of at least 1 of the positive lenses of the cemented lens is set to vdcp and the d-line reference Abbe number of at least 1 of the negative lenses of the cemented lens is set to vdcp,

at least 1 of the cemented lenses satisfies conditional expression (7) shown below,

18＜νden-νdcp＜35 (7)。

6. zoom lens according to claim 1 or 2,

the moving lens group having the strongest negative refractive power among the moving lens groups having negative refractive powers within the intermediate group includes the LN lens.

7. Zoom lens according to claim 1 or 2,

focusing is performed by moving at least a part of the lenses in the 1 st lens group along an optical axis.

8. Zoom lens according to claim 1 or 2,

the moving lens group closest to the image side within the intermediate group has a negative refractive power.

9. The zoom lens of claim 8,

the intermediate group comprises 2 of said moving lens groups having negative refractive power,

the subsequent group includes a lens group having positive refractive power that is fixed relative to an image surface when variable in magnification.

10. The zoom lens of claim 8,

the intermediate group comprises 2 of said moving lens groups having negative refractive power,

the subsequent group includes, in order from the object side toward the image side, a lens group having positive refractive power that moves along the optical axis while changing the interval between adjacent groups at the time of magnification, and a lens group having positive refractive power that is fixed with respect to the image plane at the time of magnification change.

11. The zoom lens of claim 8,

the intermediate group includes, in order from the object side toward the image side, the moving lens group having a positive refractive power and 2 moving lens groups having a negative refractive power,

the subsequent group includes a lens group having positive refractive power that is fixed relative to an image surface when variable in magnification.

12. The zoom lens of claim 8,

the intermediate group comprises 3 of said moving lens groups having negative refractive power,

the subsequent group includes a lens group having refractive power fixed relative to an image surface at the time of variable magnification.

13. The zoom lens of claim 8,

the intermediate group comprises 4 of said moving lens groups having negative refractive power,

the subsequent group includes a lens group having positive refractive power that is fixed relative to an image surface when variable in magnification.

14. Zoom lens according to claim 1 or 2,

the LN lens further satisfies the conditional expression (2-1) shown below,

45＜νdn＜55 (2-1)。

15. zoom lens according to claim 1 or 2,

the LN lens further satisfies the conditional expression (3-1) shown below,

0.637＜θgFn+0.001625×νdn＜0.65 (3-1)。

16. zoom lens according to claim 1 or 2,

the LN lens further satisfies the conditional expression (4-1) shown below,

2.21＜Ndn+0.01×νdn＜2.33 (4-1)。

17. the variable focus lens according to claim 2,

satisfies the conditional expression (5-1) shown below,

2＜fB/fA＜4 (5-1)。

18. zoom lens according to claim 3,

satisfies the conditional expression (6-1) shown below,

0.5＜fLNm/fA＜4 (6-1)。

19. an imaging device comprising the zoom lens according to any one of claims 1 to 18.

Technical Field

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

Background

Conventionally, as a zoom lens used in a broadcasting camera, a movie camera, a digital camera, and the like, there is known a zoom lens in which a lens group having a positive refractive power is disposed on the most object side, and a moving lens group that moves at the time of magnification change is disposed on the image side, and the total length of the lens system is kept constant at the time of magnification change. For example, the zoom lenses having the 5-group or 6-group structure of the above type are described in patent document 1 and patent document 2 below.

Patent document 1: japanese patent laid-open publication No. 2017-078770

Patent document 2: japanese patent laid-open publication No. 2017-083563

The zoom lens used in the camera is required to have small aberration variation at the time of magnification change and high performance. In order to secure the zoom magnification, it is necessary to strengthen the refractive power of the moving lens group, and thus, the variation of chromatic aberration and the variation of spherical aberration at the time of magnification change tend to become large. In order to suppress variation in chromatic aberration at the time of magnification change, it is preferable to suppress chromatic aberration independently for the lens group having positive refractive power on the most object side and the moving lens group. At this time, the refractive power configuration and the material selection of the lens of the moving lens group for suppressing the variation of the secondary chromatic aberration are particularly important.

On the other hand, if the suppression of the variation of the spherical aberration during the magnification change is insufficient, there is a problem that the F value cannot be reduced at the telephoto end. The lens systems described in patent documents 1 and 2 are not sufficient in suppressing the variation of spherical aberration at the time of magnification change, and there is still room for improvement.

Disclosure of Invention

The present invention has been made in view of the above circumstances. An object of one embodiment of the present invention is to provide a zoom lens having high optical performance with suppressed variation in chromatic aberration and variation in spherical aberration during magnification variation, and an imaging apparatus including the zoom lens.

Specific methods for solving the above problems include the following ways.

<1> a zoom lens comprising, in order from an object side toward an image side: a first lens group having positive refractive power which is fixed to an image surface at the time of variable magnification, an intermediate group including 2 or more moving lens groups which move along an optical axis while changing an interval between the moving lens groups and an adjacent group at the time of variable magnification, and a subsequent group including a lens group including a stop on the most object side, wherein at least 2 moving lens groups in the intermediate group have negative refractive power, at least 1 moving lens group having negative refractive power in the intermediate group includes at least an LN lens which is a negative lens, and the LN lens satisfies conditional expressions (1), (2), (3), and (4) shown below when a refractive index at a d line of the LN lens is Ndn, an abbe number of a d line reference of the LN lens is ν dn, and a partial dispersion ratio between a g line and an F line of the LN lens is θ gFn,

1.72＜Ndn＜1.8 (1)；

43＜νdn＜57 (2)；

0.6355＜θgFn+0.001625×νdn＜0.66 (3)；

2.21＜Ndn+0.01×ν dn (4)。

<2> the zoom lens according to <1>, wherein the moving lens group having negative refractive power in the intermediate group on the object side of the moving lens group having negative refractive power on the most image side in the intermediate group includes an LN lens, and when a focal length of the moving lens group having negative refractive power in the intermediate group including an LN lens having the strongest negative refractive power among LN lenses included in the moving lens group having negative refractive power in the intermediate group on the object side of the moving lens group having negative refractive power on the most image side in the intermediate group is fA, and a focal length of the moving lens group having negative refractive power on the most image side in the intermediate group is fB,

the zoom lens satisfies the conditional expression (5) shown below,

0.6＜fB/fA＜4.5 (5)。

<3> the zoom lens according to <1> or <2>, wherein the moving lens group having negative refractive power in the intermediate group on the object side of the moving lens group having negative refractive power on the most image side in the intermediate group includes an LN lens, and when a focal length of the moving lens group having negative refractive power in the intermediate group including an LN lens having the strongest negative refractive power among LN lenses included in the moving lens group having negative refractive power in the intermediate group on the object side of the moving lens group having negative refractive power on the most image side in the intermediate group is fA and a focal length of the LN lens having negative refractive power among LN lenses included in the moving lens group having negative refractive power in the intermediate group is fLN,

the zoom lens satisfies conditional expression (6) shown below,

0.5＜fLNm/fA＜40 (6)。

<4> a zoom lens according to any one of <1> to <3>, wherein the at least 1 moving lens group within the intermediate group includes a cemented lens in which at least 1 LN lens and at least 1 positive lens are cemented.

<5> the zoom lens according to <4>, wherein when the Abbe number of d-line reference of at least 1 LN lens of the cemented lens is set to ν dcn and the Abbe number of d-line reference of at least 1 positive lens of the cemented lens is set to ν dcp, at least 1 cemented lens satisfies the conditional expression (7) shown below,

18＜v dcn-v dcp＜35 (7)。

<6> a zoom lens according to any one of <1> to <5>, wherein a moving lens group having a strongest negative refractive power among moving lens groups having negative refractive powers within the intermediate group includes an LN lens.

<7> the zoom lens according to any one of <1> to <6>, which performs focusing by moving at least a part of lenses within the 1 st lens group along an optical axis.

<8> the zoom lens according to any one of <1> to <7>, wherein a moving lens group closest to the image side within the intermediate group has a negative refractive power.

<9> a zoom lens according to <8>, wherein the intermediate group comprises 2 moving lens groups having negative refractive power, and the subsequent group comprises a lens group having positive refractive power which is fixed with respect to the image surface at the time of varying magnification.

<10> a zoom lens according to <8>, wherein the intermediate group includes 2 moving lens groups having negative refractive power, and the subsequent groups include, in order from the object side toward the image side, a lens group having positive refractive power that moves along the optical axis while changing an interval between the adjacent groups at the time of magnification, and a lens group having positive refractive power that is fixed with respect to the image surface at the time of magnification.

<11> the zoom lens according to <8>, wherein the intermediate group includes, in order from the object side toward the image side, a moving lens group having a positive refractive power and 2 moving lens groups having a negative refractive power, and the subsequent group includes a lens group having a positive refractive power which is fixed with respect to the image surface at the time of varying magnification.

<12> a zoom lens according to <8>, wherein the intermediate group comprises 3 moving lens groups having negative refractive power, and the subsequent group comprises a lens group having refractive power which is fixed with respect to the image surface at the time of varying magnification.

<13> a zoom lens according to <8>, wherein the intermediate group comprises 4 moving lens groups having negative refractive power, and the subsequent group comprises a lens group having positive refractive power which is fixed with respect to the image surface at the time of varying magnification.

<14> the zoom lens according to any one of <1> to <13>, wherein the LN lens further satisfies conditional expression (2-1) shown below,

45＜νdn＜55 (2-1)。

<15> the zoom lens according to any one of <1> to <14>, wherein the LN lens further satisfies conditional expression (3-1) shown below,

0.637＜0gFn+0.001625×νdn＜0.65 (3-1)。

<16> the zoom lens according to any one of <1> to <15>, wherein the LN lens further satisfies conditional expression (4-1) shown below,

2.21＜Ndn+0.01×νdn＜2.33 (4-1)。

<17> the zoom lens according to <2>, which satisfies conditional expression (5-1) shown below,

2＜fB/fA＜4 (5-1)。

<18> the zoom lens according to <3>, which satisfies conditional expression (6-1) shown below,

0.5<fLNm/fA＜4 (6-1)。

<19> an image pickup apparatus comprising the zoom lens according to any one of <1> to <18 >.

In addition, the terms "include" and "include" in the present specification mean that, in addition to the components listed above, the components may include: a lens having substantially no optical power; optical elements other than lenses such as an aperture, a filter, and 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 group as a whole 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 structure including a plurality of lenses, and may be a structure including only 1 lens. Further, regarding "1 lens group", a lens group that changes an interval in the optical axis direction between adjacent groups at the time of magnification change is taken as "1 lens group". That is, a lens group included in 1 division when dividing the lens group at intervals that vary at the time of magnification variation is taken as 1 lens group.

A compound aspherical lens (a lens in which a spherical lens and an aspherical film formed on the spherical lens are integrally configured to function as 1 aspherical lens as a whole) is handled as 1 lens, and is not regarded as a cemented lens. The refractive power symbol 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. When the refractive indices of a lens with respect to g, F and C lines are Ng, NF and NC, respectively, the partial dispersion ratio θ gF between the g and F lines of the lens is defined by (Ng-NF)/(NF-NC). 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).

Effects of the invention

According to one embodiment of the present invention, it is possible to provide a zoom lens having high optical performance with suppressed variation in chromatic aberration and variation in spherical aberration during magnification variation, and an imaging apparatus including the zoom lens.

Drawings

Fig. 1 corresponds to a zoom lens according to example 1 of the present invention, and is a sectional view showing a configuration and a movement locus of the zoom lens according to an embodiment of the present invention.

Fig. 2 is a sectional view showing the structure and light flux of the zoom lens shown in fig. 1.

Fig. 3 is a sectional view showing a configuration and a movement locus of a zoom lens according to embodiment 2 of the present invention.

Fig. 4 is a sectional view showing a configuration and a movement locus of a zoom lens according to embodiment 3 of the present invention.

Fig. 5 is a sectional view showing a configuration and a movement locus of a zoom lens according to embodiment 4 of the present invention.

Fig. 6 is a sectional view showing a configuration and a movement locus of a zoom lens according to embodiment 5 of the present invention.

Fig. 7 is each aberration diagram of a zoom lens according to embodiment 1 of the present invention.

Fig. 8 is each aberration diagram of a zoom lens according to embodiment 2 of the present invention.

Fig. 9 is each aberration diagram of a zoom lens according to embodiment 3 of the present invention.

Fig. 10 is each aberration diagram of a zoom lens according to embodiment 4 of the present invention.

Fig. 11 is each aberration diagram of a zoom lens according to embodiment 5 of the present invention.

Fig. 12 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, 5-signal processing section, 6-display section, 7-zoom control section, 100-image pickup device, G1-1 St lens group, G2-2 nd lens group, G3-3 rd lens group, G4-4 th lens group, G5-5 th lens group, G6-6 th lens group, Gm-intermediate group, Gs-subsequent group, L1 a-L6 j-lens, LN-LN lens, ma, ta, wa-on-axis beam, mb, tb, wb-maximum angle of view beam, PP-optical component, Sim-image plane, St-aperture stop, Z-optical axis.

Detailed Description

Hereinafter, embodiments of the zoom lens of the present invention will be described in detail with reference to the drawings. Fig. 1 is a cross-sectional view showing a configuration and a movement locus of a zoom lens according to an embodiment of the present invention. Fig. 2 is a cross-sectional view showing a lens structure and a light flux in each state of the zoom lens. The examples shown in fig. 1 and 2 correspond to a zoom lens of example 1 described later. Fig. 1 and 2 show a state where the object is focused on an object at infinity, and the left side is the object side and the right side is the image side. In fig. 1, the wide-angle end state is shown. In fig. 2, the wide-angle end state is shown in the upper row labeled "wide-angle end", the intermediate focal length state is shown in the middle row labeled "middle", and the telephoto end state is shown in the lower row labeled "telephoto end". Fig. 2 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 2 show an example in which an optical member PP having an incident surface and an exit surface parallel to each other is disposed between the zoom lens and the image plane Sim in the case where the zoom lens is applied to an imaging device. The optical member PP is a member assumed to be various filters, prisms, cover glass, and 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 may be omitted. Hereinafter, description will be made mainly with reference to fig. 1.

The zoom lens of the present invention includes, in order from the object side toward the image side along the optical axis Z, a 1 st lens group G1, an intermediate group Gm, and a subsequent group Gs. The 1 st lens group G1 is a lens group having positive refractive power and fixed relative to the image plane Sim at the time of magnification change. The intermediate group Gm includes 2 or more moving lens groups that move along the optical axis Z while changing the interval between adjacent groups when changing magnification. That is, the intermediate group Gm includes 2 or more moving lens groups that move along the optical axis Z in mutually different trajectories at the time of magnification change. At least 2 moving lens groups within the intermediate group Gm have negative refractive power. The subsequent group Gs has a lens group including an aperture stop St on the most object side.

By setting the lens group closest to the object side to a lens group having positive refractive power, the total length of the lens system (the distance on the optical axis from the lens surface closest to the object side to the image plane Sim) can be reduced, which is advantageous for downsizing. Further, by configuring the lens group having positive refractive power closest to the object side to be fixed at the time of magnification variation, it is possible to reduce variation in the center of gravity of the lens system without changing the total length of the lens system at the time of magnification variation, and therefore, it is possible to improve convenience at the time of photographing. Further, by disposing 2 or more moving lens groups having negative refractive power on the object side of the lens group including the aperture stop St, the refractive power of the negative moving lens group having a magnification function can be dispersed, and variation in spherical aberration and variation in chromatic aberration during magnification change can be reduced. This is advantageous in that both a small F value and a high magnification ratio can be achieved.

The zoom lens of the example shown in fig. 1 includes, in order from the object side toward the image side, a 1 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 a 4 th lens group G4 having refractive power. At the time of magnification change, the 1 st lens group G1 and the 4 th lens group G4 are fixed with respect to the image plane Sim. The 2 nd lens group G2 and the 3 rd lens group G3 are moving lens groups that move along the optical axis Z while changing the interval between adjacent groups when varying magnification. The 4 th lens group G4 is provided with an aperture stop St on the most object side. The aperture stop St shown in fig. 1 indicates a position in the optical axis direction, and does not indicate a shape. In the example shown in fig. 1, a group including the 2 nd lens group G2 and the 3 rd lens group G3 corresponds to the middle group Gm, and the 4 th lens group G4 corresponds to the subsequent group Gs. In fig. 1, moving loci of respective moving lens groups upon varying magnification from the wide-angle end to the telephoto end are schematically shown by arrows below the moving lens groups.

In the example shown in fig. 1, the 1 St lens group G1 includes 11 lenses, i.e., lenses L1a to L1k, in order from the object side to the image side, the 2 nd lens group G2 includes 6 lenses, i.e., lenses L2a to L2f, in order from the object side to the image side, the 3 rd lens group G3 includes 2 lenses, i.e., lenses L3a to L3b, in order from the object side to the image side, and the 4 th lens group G4 includes 9 lenses, i.e., an aperture stop St and lenses L4a to L4i, in order from the object side to the image side. However, in the zoom lens of the present invention, the number of lens groups constituting the intermediate group Gm and the subsequent group Gs, the number of lenses constituting each lens group, and the position of the aperture stop St may be different from those in the example shown in fig. 1.

In the zoom lens of the present invention, at least 1 moving lens group having a negative refractive power in the intermediate group Gm includes at least 1 negative lens, i.e., LN lens LN. When the refractive index of the LN lens LN in the d-line is Ndn, the d-line reference dispersion coefficient of the LN lens LN is ν dn, and the partial dispersion ratio between the g-line and the F-line of the LN lens LN is θ gFn, the LN lens LN is a lens that satisfies the following conditional expressions (1), (2), (3), and (4).

1.72＜Ndn＜1.8 (1)

43＜ν dn＜57 (2)

0.6355＜θgFn+0.001625×ν dn<0.66 (3)

2.21<Ndn+0.01×ν dn (4)

The conditional expressions (1), (2), (3), and (4) are conditional expressions relating to the material of the LN lens LN. Since a material having a high refractive index can be selected without being lower than the lower limit of conditional expression (1), miniaturization and high magnification can be easily achieved, and variation of each aberration during magnification change can be easily and favorably suppressed. Since the material having a low dispersion can be selected by not being equal to or more than the upper limit of conditional expression (1), the variation in color difference at the time of magnification variation can be easily suppressed.

Since the material having a low dispersion can be selected by not being equal to or less than the lower limit of conditional expression (2), the variation in color difference during magnification variation can be easily suppressed. Since the material having a high refractive index can be selected by not being equal to or more than the upper limit of conditional expression (2), miniaturization and high magnification can be easily achieved, and variation of each aberration at the time of magnification change can be easily and favorably suppressed. Further, a structure satisfying the following conditional expression (2-1) can provide more favorable characteristics.

45＜ν dn＜55 (2-1)

By satisfying the conditional expression (3), the variation of the secondary color difference at the time of magnification change can be easily suppressed satisfactorily. Further, a structure satisfying the following conditional expression (3-1) can provide more favorable characteristics.

0.637＜θgFn+0.001625×ν dn＜0.65 (3-1)

By satisfying the conditional expressions (1) and (2) and not being equal to or less than the lower limit of the conditional expression (4), it is possible to easily realize downsizing and high magnification, and to easily suppress variation of each aberration including chromatic aberration at the time of magnification variation. In order to select an appropriate material satisfying the above conditional expressions (1) and (2) from existing optical materials, it is preferable to satisfy the following conditional expression (4-1).

2.21＜Ndn+0.01×ν dn＜2.33 (4-1)

For example, in the example shown in fig. 1, the lens L2d of the 2 nd lens group G2 corresponds to the LN lens LN. However, in the zoom lens of the present invention, the LN lens LN may be a lens different from the example shown in fig. 1.

It is preferable that the moving lens group having the strongest negative refractive power among the moving lens groups having negative refractive power in the intermediate group Gm include the LN lens LN. With such a configuration, it is easy to suppress the variation of the chromatic aberration during the magnification change.

Further, it is preferable that the moving lens group having negative refractive power (the 2 nd lens group G2 in the example shown in fig. 1) in the intermediate group Gm on the object side of the moving lens group having negative refractive power (the 3 rd lens group G3 in the example shown in fig. 1) closest to the image side in the intermediate group Gm include an LN lens LN. With such a configuration, it is possible to favorably suppress variation in chromatic aberration of magnification at the time of magnification variation from the wide-angle end to the zoom intermediate region.

In the configuration in which the moving lens group having negative refractive power in the intermediate group Gm on the object side of the moving lens group having negative refractive power closest to the image side in the intermediate group Gm includes the LN lens LN, it is preferable that the following conditional expression (5) is satisfied when a focal length of the moving lens group having negative refractive power in the intermediate group Gm including the LN lens LN strongest in negative refractive power among the LN lenses LN included in the moving lens group having negative refractive power closest to the image side in the intermediate group Gm on the object side of the moving lens group having negative refractive power closest to the image side in the intermediate group Gm is fA, and a focal length of the moving lens group having negative refractive power closest to the image side in the intermediate group Gm is fB. By not being equal to or less than the lower limit of conditional expression (5), the effects of correcting the on-axis chromatic aberration and chromatic aberration of magnification at the time of magnification change by the LN lens LN can be ensured, and variations in these aberrations at the time of magnification change can be easily suppressed well. By not being equal to or more than the upper limit of conditional expression (5), the negative refractive power of the lens group including the LN lens LN does not become excessively strong, and variation in the on-axis chromatic aberration and chromatic aberration of magnification at the time of magnification change can be easily suppressed well. Further, a structure satisfying the following conditional expression (5-1) can provide more favorable characteristics.

0.6＜fB/fA＜4.5 (5)

2＜fB/fA＜4 (5-1)

In the configuration in which the moving lens group having negative refractive power in the intermediate group Gm on the object side of the moving lens group having negative refractive power on the most image side in the intermediate group Gm includes the LN lens LN, it is preferable that the following conditional expression (6) is satisfied when a focal length of the moving lens group having negative refractive power in the intermediate group Gm including the LN lens LN having the strongest negative refractive power among the LN lenses LN included in the moving lens group having negative refractive power on the most image side in the intermediate group Gm on the object side of the moving lens group having negative refractive power on the most image side in the intermediate group Gm is fA, and a focal length of the LN lens LN having the strongest negative refractive power among the LN lenses included in the moving lens group having negative refractive power in the intermediate group Gm is lnfm. By satisfying the conditional expression (6), the variation of the primary color difference and the variation of the secondary color difference at the time of magnification change can be easily suppressed. Further, a structure satisfying the following conditional expression (6-1) can provide more favorable characteristics.

0.5＜fLNm/fA＜40 (6)

0.5＜fLNm/fA＜4 (6-1)

Further, it is preferable that at least 1 moving lens group in the intermediate group Gm includes a cemented lens in which at least 1 LN lens LN and at least 1 positive lens are cemented. With such a configuration, it is easy to suppress the variation of the chromatic aberration during the magnification change. The cemented lens referred to herein may be a cemented lens including 2 lenses or may be a cemented lens including 3 lenses.

In a configuration in which at least 1 of the movable lens groups in the intermediate group Gm includes a cemented lens formed by a LN lens LN and a positive lens cemented together, when the d-line reference abbe number of at least 1 LN lens LN of the cemented lens is ν dcn and the d-line reference abbe number of at least 1 positive lens of the cemented lens is ν dcp, it is preferable that at least 1 of the cemented lenses satisfies the following conditional expression (7). Here, the LN lens LN and the positive lens satisfying the conditional expression (7) are lenses in the same cemented lens. By satisfying the conditional expression (7), the variation of the primary color difference at the time of magnification change can be easily suppressed.

18＜ν dcn-ν dcp＜35 (7)

Preferably, the 1 st lens group G1 includes a lens group that moves upon focusing, i.e., a focusing group. That is, it is preferable to perform focusing by moving at least a part of the lenses in the 1 st lens group G1 along the optical axis Z. Since the 1 st lens group G1 does not move during magnification change, if at least a part of the lenses in the 1 st lens group G1 are set as a focus group, the image point of the focus group does not move during magnification change, and thus, focus shift during magnification change can be suppressed.

The most image side moving lens group in the intermediate group Gm preferably has a negative refractive power. In the case of such a configuration, when correcting a variation in image position during magnification change, the movable lens group can be moved toward the image side on the telephoto side, and it is easy to secure a zoom stroke of the movable lens group mainly responsible for the magnification change, which is advantageous for downsizing and increasing magnification.

The intermediate group Gm and the subsequent group Gs can have the following structure, for example. The following configuration can be adopted: the intermediate group Gm comprises 2 moving lens groups of negative refractive power, the subsequent group Gs comprises lens groups of positive refractive power which contain the aperture stop St and which are fixed in relation to the image plane Sim when zoomed. In the case of such a configuration, the zoom stroke for moving the lens group becomes small, and the total length of the lens system can be shortened, which is advantageous for downsizing.

Alternatively, the following configuration can be adopted: the intermediate group Gm includes 2 moving lens groups having negative refractive power, and the subsequent group Gs includes, in order from the object side toward the image side, a lens group having positive refractive power that includes an aperture stop St and moves along the optical axis Z while changing an interval between adjacent groups at the time of magnification, and a lens group having positive refractive power that is fixed with respect to the image plane Sim at the time of magnification. With such a configuration, it is easy to reduce the size and increase the magnification, and to suppress the variation of each aberration during magnification variation. Further, in the zoom intermediate region where the off-axis light flux becomes highest, the moving lens group having positive refractive power including the aperture stop St can be thrown to the object side, and therefore the lens diameter of the 1 St lens group G1 can be suppressed, which is advantageous for downsizing the 1 St lens group G1.

Alternatively, the following configuration can be adopted: the intermediate group Gm includes, in order from the object side toward the image side, a moving lens group having positive refractive power and 2 moving lens groups having negative refractive power, and the subsequent group Gs includes a lens group having positive refractive power that includes the aperture stop St and is fixed relative to the image plane Sim when multiplied. With such a configuration, it is easy to reduce the size and increase the magnification, and to suppress the variation of each aberration during magnification variation. In particular, it is advantageous to suppress variation in spherical aberration at the time of magnification change.

Alternatively, the following configuration can be adopted: the intermediate group Gm comprises 3 moving lens groups of negative refractive power, the subsequent group Gs comprising lens groups of refractive power which contain the aperture stop St and which are fixed in relation to the image plane Sim when zoomed. With such a configuration, it is easy to reduce the size and increase the magnification, and to suppress the variation of each aberration during magnification variation. In particular, it is advantageous to suppress the variation of field curvature at the time of magnification change.

Alternatively, the following configuration can be adopted: the intermediate group Gm includes 4 moving lens groups of negative refractive power, and the subsequent group Gs includes lens groups of positive refractive power that include the aperture stop St and are fixed relative to the image plane Sim when zoomed. With such a configuration, it is easy to reduce the size and increase the magnification, and to suppress the variation of each aberration during magnification variation. In particular, it is advantageous to suppress the variation of field curvature and the variation of spherical aberration during magnification variation.

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, it is possible to realize a zoom lens having high optical performance with suppressed variation in chromatic aberration and variation in spherical aberration at the time of magnification variation.

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

[ example 1]

A cross-sectional view showing the structure of the zoom lens of example 1 is shown in fig. 1, and the method and structure thereof are as described above, and therefore, a part of the redundant description is omitted here. The zoom lens of embodiment 1 includes, in order from the object side toward the image side, a 1 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 a 4 th lens group G4 having positive refractive power. The intermediate group Gm includes a 2 nd lens group G2 and a 3 rd lens group G3. The subsequent group Gs includes the 4 th lens group G4. At the time of magnification change, the 1 st lens group G1 and the 4 th lens group G4 are fixed with respect to the image plane Sim, and the 2 nd lens group G2 and the 3 rd lens group G3 move along the optical axis Z while changing the interval between the lens groups adjacent to each other.

The 1 st lens group G1 includes 11 lenses, i.e., lenses L1a to L1k, in order from the object side to the image side. The 2 nd lens group G2 includes 6 lenses L2a to L2f in order from the object side to the image side. The 3 rd lens group G3 includes 2 lenses, i.e., lenses L3a to L3b, in order from the object side to the image side. The 4 th lens group G4 includes 9 lenses, i.e., an aperture stop St and lenses L4a to L4i, in order from the object side to the image side. The lens L2d corresponds to the LN lens LN. The focus group includes lens L1 e.

Table 1A and table 1B show the basic lens data of the zoom lens of example 1, table 2 shows the specifications and the variable surface distances, and table 3 shows the aspherical coefficients. In order to avoid lengthening 1 table, the basic lens data is divided into 2 tables of table 1A and table 1B. In tables 1A and 1B, the surface number is shown in the column Sn when the surface closest to the object side is the 1 st surface and the numbers are increased one by one toward the image side, the curvature radius of each surface is shown in the column R, and the surface interval on the optical axis between each surface and the surface adjacent to the image side is shown in the column D. The refractive index of each component element with respect to the d-line is shown in the Nd column, the d-line-based dispersion coefficient of each component element is shown in the vd column, and the partial dispersion ratio between the g-line and the F-line of each component element is shown in the θ gF column.

In table 1A and table 1B, the sign of the radius of curvature of the surface of the shape in which the convex surface faces the object side is positive, and the sign of the radius of curvature of the surface of the shape in which the convex surface faces the image side is negative. Table 1B also shows the aperture stop St and the optical member PP, and the column of the surface number corresponding to the surface of the aperture stop St describes the terms of the surface number (St) and (St). The value in the lowermost column of D in table 1B is the distance between the image plane Sim and the surface closest to the image side in the table. In tables 1A and 1B, the variable surface interval at the time of magnification change is denoted by DD [ ], and the object-side surface number of the interval is denoted by [ ]andis shown in the column D.

In table 2, values of zoom magnification Zr, focal length F, F value fno, maximum full view angle 2 ω, and variable surface interval are shown on the d-line basis. The (°) column 2 ω represents units of degrees. In table 2, the respective values of the wide-angle end state, the intermediate focal length state, and the telephoto end state are shown in the columns labeled wide-angle end, intermediate, and telephoto end, respectively.

In tables 1A and 1B, the number of the aspheric surface is denoted by a symbol, and the column of the curvature radius of the aspheric surface shows the numerical value of the paraxial curvature radius. In table 3, the column of Sn shows the surface number of the aspherical surface, and the columns of KA and Am (m is an integer of 3 or more) show the numerical values of the aspherical surface coefficients of the respective aspherical surfaces. "E. + -. n" (n: integer) of numerical values of aspherical surface coefficients of Table 3 represents ". times.10^±n". KA and Am are aspheric coefficients in an aspheric expression represented by the following expression.

Zd＝C×h²/{1+(1-KA×C²×h²)^1/2}+∑Am×h^m

Wherein the content of the first and second substances,

and (d) is as follows: aspheric depth (length of a perpendicular line that depends from a point on the aspheric surface of height h to a plane tangent to the aspheric vertex and perpendicular to the optical axis);

h: height (distance from the optical axis to the lens surface);

c: the reciprocal of the paraxial radius of curvature;

KA. Am, and (2): the coefficient of the aspherical surface is,

the aspherical Σ represents a sum associated with m.

In the data of each table, degrees are used as a unit of angle and mm (millimeter) is used as a unit of length, but the optical system can be used in an enlarged scale or in a reduced scale, and therefore other appropriate units can be used. In each table shown below, numerical values rounded to a predetermined number of digits are shown.

[ Table 1A ]