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 大田基在 于 2019-08-19 设计创作，主要内容包括：本发明提供一种在整个变焦区域内良好地抑制对焦时的像面弯曲的变动来保持高光学性能且实现高倍率化的变焦透镜及具备该变焦透镜的摄像装置。本发明的变焦透镜从物体侧依次包括对焦组、变倍组及后续组。对焦组从物体侧依次包括变倍时及对焦时不动的对焦组前组、包括对焦时移动的1个或2个正的透镜组的对焦组中组、以及包括变倍时及对焦时移动的负的透镜组的对焦组后组。关于对焦组后组,对焦时的移动量根据变焦位置而发生变化,且具有在从无限远物体向最近物体对焦时向像侧移动的变焦区域。满足与对焦组后组的移动量相关的规定的条件式。(The invention provides a zoom lens which can well restrain the variation of field curvature in focusing in the whole zoom area, keep high optical performance and realize high magnification and an imaging device with the zoom lens. The zoom lens of the present invention includes a focusing group, a variable power group, and a subsequent group in this order from an object side. The focusing group comprises a focusing group front group which is immovable in zooming and focusing, a focusing group middle group comprising 1 or 2 positive lens groups which move in focusing and a focusing group rear group comprising a negative lens group which moves in zooming and focusing in sequence from the object side. The focus group rear group has a zoom region in which the amount of movement in focusing changes depending on the zoom position and which moves to the image side when focusing from an object at infinity to the nearest object. A predetermined conditional expression relating to the movement amount of the rear group of the focus group is satisfied.)

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 focusing group including a lens group which moves at the time of focusing, a variable power group including 2 or more lens groups which move along the optical axis while changing an interval with an adjacent group at the time of variable power, and a subsequent group having a lens group including a diaphragm on the most object side,

the focusing group comprises the following components in sequence from an object side to an image side: a front group of focusing groups including negative lenses and fixed with respect to an image plane at the time of magnification change and at the time of focusing, a middle group of focusing groups including 1 or 2 lens groups having positive refractive power which move along an optical axis by changing an interval with an adjacent group at the time of focusing, and a rear group of focusing groups including 1 lens group having negative refractive power which move along the optical axis by changing an interval with an adjacent group at the time of magnification change and at the time of focusing,

a moving amount at the time of focusing of the focusing group rear group having a zoom region that moves from the object side to the image side at the time of focusing from an infinity object to a closest object changes depending on the zoom position,

when the moving amount of the focusing group rear group when zooming from the wide-angle end to the telephoto end in a state of focusing on an object at infinity is DFrinf, the moving amount of the focusing group rear group when focusing from the object at infinity to the nearest object at a zoom position at which the moving amount of the focusing group rear group becomes maximum is DFrmax, the sign of the moving amount of the focusing group rear group when focusing from the object side to the image side is positive, and when moving from the image side to the object side is negative,

satisfies the conditional expression (1) shown below,

0.2＜DFrinf/DFrmax＜50 (1)。

2. the variable focus lens according to claim 1,

when the lateral magnification of the rear group of the focusing group in a state of focusing on an object at infinity is β Fr, the following conditional expression (2) is satisfied in the entire zoom region,

0.5＜1/βFr＜0.995 (2)。

3. zoom lens according to claim 1 or 2,

the focal group front group has a negative refractive power.

4. Zoom lens according to claim 1 or 2,

the sign of the refractive power of the focusing group in a state of focusing on an object at infinity is positive in the entire zoom region.

5. Zoom lens according to claim 1 or 2,

all lens groups within a group in the focusing group move from the image side to the object side upon focusing from an infinity object to a closest object.

6. Zoom lens according to claim 1 or 2,

the zoom position at which the amount of movement of the rear group of the focus group becomes maximum when focusing from an object at infinity to the nearest object is located on the wider angle side than the telephoto end.

7. Zoom lens according to claim 1 or 2,

the most object side lens group in the variable power group has negative refractive power and always moves from the object side to the image side when the power is changed from the wide angle end to the telephoto end.

8. The zoom lens of claim 7,

when the focal length of the most object side lens group in the zoom group is set to fV1 and the focal length of the rear group of the focusing group is set to fFr,

satisfies the conditional expression (3) shown below,

0.001＜fV1/fFr＜0.4 (3)。

9. zoom lens according to claim 1 or 2,

the rear group of the focusing group comprises 1 negative lens.

10. Zoom lens according to claim 1 or 2,

the rear group of the focusing group comprises a joint lens formed by jointing 1 negative lens and 1 positive lens.

11. Zoom lens according to claim 1 or 2,

the amount of movement in focusing of at least 1 lens group in the group of the focusing group varies depending on the zoom position.

12. Zoom lens according to claim 1 or 2,

at least 1 lens group of lens groups closer to the image side than the lens group closest to the object side among the lens groups in the variable power group moves at the time of focusing, and a moving amount at the time of focusing changes depending on a zoom position.

13. Zoom lens according to claim 1 or 2,

at least 1 lens group in the subsequent group moves at the time of focusing, and the amount of movement at the time of focusing changes according to the zoom position.

14. The variable focus lens according to claim 1,

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

0.3＜DFrinf/DFrmax＜10 (1-1)。

15. the variable focus lens according to claim 2,

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

0.55＜1/βFr＜0.995 (2-1)。

16. the zoom lens of claim 8,

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

0.002＜fV1/fFr＜0.3 (3-1)。

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

Technical Field

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

Background

Conventionally, as zoom lenses used in broadcasting cameras, movie cameras, digital cameras, and the like, there are known zoom lenses in which a focus group including a focus lens group, a zoom group including a zoom lens group, and a relay group are arranged in this order from the most object side. For example, patent document 1 listed below describes a zoom lens including, in order from the object side, a 1 st lens group including a focusing lens group and not moving during magnification, a 2 nd lens group moving during magnification, 1 or more lens groups moving during magnification, an aperture stop, and an imaging lens group. Patent document 2 describes a zoom lens including, in order from the object side, a 1 st lens group that does not move during magnification variation and a 2 nd lens group that moves during magnification variation, and a part or the whole of the 1 st lens group and a part of the 2 nd lens group move during focusing.

Patent document 1: japanese patent laid-open publication No. 2015-212724

Patent document 2: japanese patent laid-open publication No. 2017-203916

The zoom lens used for the above-described video camera is required to have high magnification and high performance. In the above type, if the magnification is increased, the amount of fluctuation of field curvature in focus varies depending on the zoom region, and therefore it is difficult to achieve the magnification while satisfactorily suppressing the fluctuation of field curvature in focus over the entire zoom region and maintaining satisfactory performance.

In the lens system described in patent document 1, since a configuration in which the focusing lens group having negative refractive power closest to the image side is moved according to the zoom position is not adopted, it is difficult to achieve both suppression of fluctuation of field curvature at the time of focusing at the zoom position of the intermediate focal length and correction of spherical aberration at the telephoto end. In the lens system described in patent document 2, suppression of aberration variation in focusing at the zoom position of the intermediate focal length is not sufficient.

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 that can achieve a high magnification while satisfactorily suppressing fluctuation of field curvature during focusing over the entire zoom region to maintain satisfactory optical performance, and an imaging device 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 to an image side: a focusing group including a lens group which moves at the time of focusing, a variable power group including 2 or more lens groups which move along an optical axis while changing an interval with an adjacent group at the time of variable power, and a subsequent group having a lens group including a diaphragm on the most object side, the focusing group including, in order from the object side toward the image side: a focusing group front group including a negative lens and fixed relative to an image surface at the time of magnification change and at the time of focusing, a focusing group rear group including a focusing group front group including 1 or 2 lens groups having positive refractive power which move along an optical axis while changing an interval with an adjacent group at the time of focusing, and a focusing group rear group including 1 lens group having negative refractive power which moves along an optical axis while changing an interval with an adjacent group at the time of magnification change and at the time of focusing, a moving amount at the time of focusing of the focusing group rear group being changed depending on a zoom position, the focusing group rear group including a zoom region which moves from an object side to an image side at the time of focusing from an infinity object to a closest object, a moving amount of the focusing group rear group at the time of magnification change from a wide angle end to a telephoto end in a state of focusing on the infinity object being set as DFrinf, and a zoom position at which the moving amount of the focusing group rear group becomes maximum at the time of focusing from the infinity object, When the amount of movement of the rear group of the focusing group when focusing from the object at infinity to the nearest object is set to DFrm ax, and the sign of the amount of movement of the rear group of the focusing group is positive when the rear group of the focusing group is moved from the object side to the image side and negative when the rear group of the focusing group is moved from the image side to the object side,

satisfies the conditional expression (1) shown below,

0.2＜DFrinf/DFrmax＜50 (1)。

<2> the zoom lens according to <1>, which has a focal group rear group having a lateral magnification of β Fr in a state of focusing on an object at infinity, within the entire zoom region,

satisfies the conditional expression (2) shown below,

0.5＜1/β Fr＜0.995 (2)。

<3> the zoom lens according to <1> or <2>, wherein the focus group front group has a negative refractive power.

<4> the zoom lens according to any one of <1> to <3>, wherein a sign of a refractive power of a focus group in a state of focusing on an object at infinity is positive in the entire zoom region.

<5> the zoom lens according to any one of <1> to <4>, wherein all lens groups within a group in a focus group move from the image side to the object side upon focusing from an infinity object to a closest object.

<6> the zoom lens according to any one of <1> to <5>, wherein a zoom position at which a moving amount of the focus group rear group becomes maximum upon focusing from an infinity object to a closest object is located at a position on a wider angle side than a telephoto end.

<7> a zoom lens according to any one of <1> to <6>, wherein a most object side lens group within the variable power group has a negative refractive power and always moves from the object side to the image side when varying power from a wide-angle end to a telephoto end.

<8> the zoom lens according to any one of <1> to <7>, which has a focal length of a most object side lens group in the variable power group set to fV1 and a focal length of a focus group rear group set to fFr,

satisfies the conditional expression (3) shown below,

0.001＜fV1/fFr＜0.4 (3)。

<9> the zoom lens according to any one of <1> to <8>, wherein the focus group rear group includes 1 negative lens.

<10> the zoom lens according to any one of <1> to <8>, wherein the focus group rear group includes a cemented lens in which 1 negative lens and 1 positive lens are cemented.

<11> the zoom lens according to any one of <1> to <10>, wherein a moving amount in focusing of at least 1 lens group within a group in a focusing group varies depending on a zoom position.

<12> a zoom lens according to any one of <1> to <11>, wherein at least 1 lens group of lens groups on the image side of the lens group on the most object side among the lens groups within the variable power group moves at the time of focusing, and a moving amount at the time of focusing varies depending on a zoom position.

<13> a zoom lens according to any one of <1> to <11>, wherein at least 1 lens group in the subsequent group moves at the time of focusing, and an amount of movement at the time of focusing varies according to a zoom position.

<14> the zoom lens according to <1>, which satisfies conditional expression (1-1) shown below,

0.3＜DFrinf/DFrmax＜10 (1-1)。

<15> the zoom lens according to <2>, which satisfies conditional expression (2-1) shown below,

0.55＜1/β Fr＜0.995 (2-1)。

<16> the zoom lens according to <8>, which satisfies conditional expression (3-1) shown below,

0.002＜fV1/fFr＜0.3 (3-1)。

<17> an image pickup apparatus including the zoom lens according to any one of <1> to <16 >.

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 a lens flange, a lens barrel, an imaging element, and a handshake correction mechanism.

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 refractive power symbol and the surface shape of the lens surface relating to the lens including the aspherical surface are considered in the paraxial region unless otherwise specified.

The "lens group", "focusing group front group", "focusing group middle group", and "focusing group rear group" are not limited to a structure including a plurality of lenses, and may be a structure including only 1 lens. Regarding the "1 lens group", a lens group in which the interval in the optical axis direction between adjacent groups changes at least one of at the time of magnification change and at the time of focusing is regarded as "1 lens group". That is, the lens groups included in 1 division when the lens groups are divided at intervals that vary at least one of at the time of magnification change and at the time of focusing are regarded as 1 lens group.

The "entire zoom region" is a variable magnification region from the wide angle end to the telephoto end. The "zoom position" indicates, for example, a wide-angle end, a telephoto end, and a variable magnification state between the wide-angle end and the telephoto end. The "zoom position of the intermediate focal length" is not limited to the intermediate point between the wide-angle end and the telephoto end, and may represent an arbitrary zoom position between the wide-angle end and the telephoto end. The "movement in focus" is not limited to the case of moving when all zoom positions are in focus, but means moving when at least 1 zoom position is in focus.

The "focal length" used in the conditional expression is a paraxial focal length. The value used in the conditional expression is a value based on the d-line. 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 that can achieve a high magnification while favorably suppressing variation in field curvature during focusing over the entire zoom region and maintaining favorable optical performance, 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 conceptual diagram illustrating a change in the height of the off-axis chief ray in the focus group.

Fig. 4 is a diagram showing an example of DFrinf and DFrmax in conditional expression (1).

Fig. 5 is a sectional view showing a configuration of a zoom lens according to embodiment 2 of the present invention and a diagram showing a movement locus.

Fig. 6 is a sectional view showing a configuration of a zoom lens according to embodiment 3 of the present invention and a diagram showing a movement locus.

Fig. 7 is a sectional view showing a configuration of a zoom lens according to embodiment 4 of the present invention and a diagram showing a movement locus.

Fig. 8 is a sectional view showing a configuration of a zoom lens according to embodiment 5 of the present invention and a diagram showing a movement locus.

Fig. 9 is a sectional view showing a configuration and a movement locus of a zoom lens according to embodiment 6 of the present invention.

Fig. 10 is a sectional view showing a configuration and a movement locus of a zoom lens according to embodiment 7 of the present invention.

Fig. 11 is each aberration diagram of the zoom lens according to embodiment 1 of the present invention in a state of focusing on an object at infinity.

Fig. 12 is each aberration diagram of the zoom lens according to embodiment 1 of the present invention in a state of focusing on the closest object.

Fig. 13 is each aberration diagram of the zoom lens according to embodiment 2 of the present invention in a state of focusing on an object at infinity.

Fig. 14 is each aberration diagram of the zoom lens according to embodiment 2 of the present invention in a state of focusing on the closest object.

Fig. 15 is each aberration diagram of the zoom lens according to embodiment 3 of the present invention in a state of focusing on an object at infinity.

Fig. 16 is each aberration diagram of the zoom lens according to embodiment 3 of the present invention in a state of focusing on the closest object.

Fig. 17 is aberration diagrams in a state where the zoom lens according to embodiment 4 of the present invention is focused on an object at infinity.

Fig. 18 is each aberration diagram of the zoom lens according to embodiment 4 of the present invention in a state of focusing on the closest object.

Fig. 19 is aberration diagrams in a state where the zoom lens according to embodiment 5 of the present invention is focused on an object at infinity.

Fig. 20 is each aberration diagram of the zoom lens according to embodiment 5 of the present invention in a state of focusing on the closest object.

Fig. 21 is each aberration diagram of the zoom lens according to embodiment 6 of the present invention in a state of focusing on an object at infinity.

Fig. 22 is each aberration diagram of the zoom lens according to embodiment 6 of the present invention in a state of focusing on the closest object.

Fig. 23 is aberration diagrams in a state where the zoom lens according to embodiment 7 of the present invention is focused on an object at infinity.

Fig. 24 is each aberration diagram of the zoom lens according to embodiment 7 of the present invention in a state of focusing on the closest object.

Fig. 25 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-optical filter, 3-imaging element, 5-signal processing section, 6-display section, 7-magnification-varying control section, 8-focus control section, 10-off-axis chief ray, 100-image pickup device, GF-focus group, GFf-focus group front group, GFm-focus group middle group, GFm 1-focus group 1 middle group, GFm 2-focus group 2 middle group, GFr-focus group rear group, GR-following group, GR 1-1 St following group, GR 2-2 nd following group, GV-magnification-varying group, GV 1-1 St magnification-varying group, GV 2-2 nd magnification-varying group, GV 3-3 rd magnification-varying group, ma, ta, wa-on-axis light beam, mb, tb, wb-maximum angle-view beam, PP-optical component, Sim-image plane, St-aperture stop, z-smooth vehicle is composed of a chassis.

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. 1, the moving locus of each lens group at the time of varying magnification from the wide angle end to the telephoto end is schematically shown by an arrow below each lens group moving at the time of varying magnification and/or focusing. Among these arrows, the solid line arrow indicates a movement locus in a state of focusing on an infinite object, and the dotted line arrow indicates a movement locus in a state of focusing on a closest object. In fig. 1, a grounding mark is shown below the lens group fixed to the image plane Sim during magnification variation and focusing.

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, assuming that the zoom lens is applied to an imaging apparatus. 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 includes, in order from the object side toward the image side along an optical axis Z, a focus group GF including a lens group which moves during focusing, a magnification-varying group GV including 2 or more lens groups which change the interval with an adjacent group during magnification-varying and move along the optical axis Z, and a subsequent group GR including a lens group including an aperture stop St on the most object side. In the subsequent group GR, when 1 lens group is set as a group in which the distance in the optical axis Z direction between the adjacent groups changes at least one of at the time of magnification change and at the time of focusing, the lens group on the most object side in the subsequent group GR is a lens group including the aperture stop St.

For example, in the example shown in fig. 1, the focusing group GF includes 6 lenses, the magnification-varying group GV includes 9 lenses, and the subsequent group GR includes the aperture stop St and 13 lenses. In the example shown in fig. 1, the variable magnification group GV includes 3 groups, that is, the 1 st variable magnification group GV1, the 2 nd variable magnification group GV2, and the 3 rd variable magnification group GV3, and the 3 groups are moved along the optical axis Z while changing the interval between adjacent groups during variable magnification. However, in the zoom lens of the present invention, the number of lenses constituting each group and the number of lens groups constituting the variable power group GV may be different from those in the example shown in fig. 1.

Focusing is performed by using a group closer to the object side than the variable magnification group GV, so that the amount of movement of the lens group that moves during focusing can be suppressed, which is advantageous in achieving both downsizing and high magnification. If focusing is performed using only the group on the image side of the variable magnification group GV, the amount of movement for focusing increases on the telephoto side with increasing magnification, and therefore it is difficult to achieve both downsizing and increasing magnification.

In the variable magnification group GV, the variable magnification group GV is constituted by 2 or more lens groups, and thus a lens group that is responsible for a main variable magnification function and a lens group that performs focus correction at the time of variable magnification can be made different from each other, and the functions can be shared.

The following group GR can be mainly configured as a group having an imaging effect. In the example shown in fig. 1, the aperture stop St is disposed on the most object side of the subsequent group GR. However, in the zoom lens of the present invention, as long as the most object side lens group of the subsequent group GR includes the aperture stop St, the position of the aperture stop St may be different from the example shown in fig. 1.

The sign of the refractive power of the focusing group GF in the state of focusing on the object at infinity is preferably positive throughout the entire zoom region. With such a configuration, the height of the light beam on the axis of the variable magnification group GV can be reduced, and spherical aberration can be easily corrected in the entire zoom region, which is advantageous for increasing magnification.

The focus group GF includes, in order from the object side toward the image side, a focus group front group GFf, a focus group middle group GFm, and a focus group rear group GFr. The focusing group front group GFf includes a negative lens, and is fixed with respect to the image plane Sim at the time of magnification change and at the time of focusing. The group GFm in the focusing group includes 1 or 2 lens groups having positive refractive power that change the interval with the adjacent group to move along the optical axis Z upon focusing. The focusing group rear group GFr includes 1 lens group having a negative refractive power that moves along the optical axis Z while changing the interval between adjacent groups at the time of magnification change and at the time of focusing.

By having the focus group front group GFf have a negative lens, it is advantageous to wide angle and to correct chromatic aberration of magnification at the wide angle end, spherical aberration at the telephoto end, and on-axis chromatic aberration at the telephoto end. By making the focusing group front group GFf stationary with respect to the image plane Sim at the time of magnification change and at the time of focusing, 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) at the time of magnification change and at the time of focusing is kept constant, and thus the variation in the center of gravity of the lens system can be reduced, so that the convenience at the time of shooting can be improved.

Preferably, focal group anterior group GFf has negative refractive power, which, when so configured, facilitates wide angle viewing.

Group GFm of the focus group can be responsible for the primary focusing action by including a lens group of positive refractive power that moves during focusing.

It is preferable that all lens groups within group GFm in the focusing group move from the image side to the object side upon focusing from an infinity object to a closest object. With such a configuration, the group GFm in the focusing group can perform a main focusing action.

The lens groups in the group GFm in the focusing group may be moved at the time of magnification change or may be fixed with respect to the image plane Sim at the time of magnification change. When the lens groups in the group GFm in the focusing group move at the time of magnification change, it is advantageous to suppress aberration variation at the time of magnification change. When the lens groups within the group GFm in the focusing group are fixed with respect to the image plane Sim at the time of magnification change, simplification of the mechanism for driving the lens groups is facilitated.

The focus group rear group GFr has negative refractive power and moves at zoom and focus. The amount of movement in focusing of the focus group rear group GFr changes depending on the zoom position, and the focus group rear group GFr has a zoom region that moves from the object side to the image side when focusing from an infinity object to a closest object.

For example, the movement locus of the focusing group rear group GFr of fig. 1 has a zoom region in which the movement locus in the state of focusing on the closest object indicated by the broken line is located on the image side than the movement locus in the state of focusing on the infinity object indicated by the solid line. In this zoom region, the focal group rear group GFr moves from the object side to the image side when focusing from an object at infinity to the nearest object.

By moving the focus group rear group GFr at the time of zooming, it is possible to suppress the variation of field curvature at the time of zooming in the zoom region from the wide-angle end to the zoom position of the intermediate focal length. Further, if the focal group rear group GFr is not moved during magnification change, it is difficult to achieve both suppression of field curvature on the wide angle side and suppression of spherical aberration on the telephoto side, and it is difficult to increase the magnification. Further, by moving the focus group rear group GFr from the object side to the image side when focusing from the object at infinity to the object at the closest in the zoom position at the intermediate focal length, it is easy to suppress the variation in field curvature at the time of focusing over the entire zoom region. That is, by configuring the focus group rear group GFr as described above, it is possible to suppress aberration variation at the time of magnification change and at the time of focusing, and particularly, it is possible to suppress variation in field curvature in a zoom region from the wide angle end to the zoom position of the intermediate focal length.

Here, the suppression of the aberration variation in the focus group rear group GFr will be described with reference to fig. 3(a) to 3 (C). Fig. 3(a) to 3(C) are conceptual views showing changes in the height of the off-axis chief ray 10 in the focus group GF. Fig. 3(a) to 3(C) conceptually show the focus group front group GFf, the focus group middle group GFm, and the focus group rear group GFr, with the left side being the object side and the right side being the image side. Fig. 3(a) to 3(C) each show a state of the zoom position at the intermediate focal length where the off-axis light beam becomes high.

Fig. 3(a) shows a state of focusing on an object at infinity. Fig. 3(B) shows a state where the group GFm in the focusing group is moved from the state of fig. 3(a) to the object side and focused on the nearest object. When focusing from an object at infinity to the nearest object, the height of the off-axis chief ray 10 passing through the most object-side focusing group front group GFf changes. In a general high-magnification zoom lens, in a zoom region from the wide-angle end to the zoom position of the intermediate focal length, the height HFf _ mod of the off-axis chief ray 10 of the focus group front group GFf in a state of being focused on the nearest object is higher than the height HFf _ inf of the off-axis chief ray 10 of the focus group front group GFf in a state of being focused on the infinity object. I.e., HFf _ inf < HFf _ mod.

At the zoom position of the intermediate focal length where the off-axis ray becomes high, the lens group where the off-axis chief ray 10 is the highest is the focusing group front group GFf. In a configuration in which the focus group front group GFf includes a negative lens as in the zoom lens of the present invention, when focusing from an object at infinity to a closest object, the height of the light beam at the focus group front group GFf becomes high, and the curvature of the image plane fluctuates upward due to the strong influence of the negative refractive power.

Therefore, as shown in fig. 3(C), when focusing from an infinitely distant object to the nearest object, if the focusing group rear group GFr is moved to the image side, the height HPr _ mod2 of the off-axis chief ray 10 passing through the focusing group rear group GFr after the movement can be made lower than the height HFr _ mod1 of the off-axis chief ray 10 passing through the focusing group rear group GFr before the movement. That is, HFr _ mod2 < HFr _ mod1 can be made. Since the focus group rear group GFr is a lens group having negative refractive power, the influence of negative refractive power is reduced as long as the height of the off-axis chief ray 10 passing through the focus group rear group GFr becomes lower. This can suppress the fluctuation of field curvature at the time of focusing.

In addition, it is preferable that the rear group of the focus group (zoom position at which the amount of movement of the mirror becomes maximum is located on the wider angle side than the telephoto end) is focused from the object at infinity to the nearest object.

In the zoom lens of the present invention, the following conditional expression (1) is satisfied where DFrinf is a moving amount of the focus group rear group GFr when zooming from the wide-angle end to the telephoto end in a state of focusing on an object at infinity, DFrmax is a moving amount of the focus group rear group GFr when focusing on the object from the object at a zoom position at which the moving amount of the focus group rear group GFr becomes maximum when focusing on the object from the object at infinity, and a sign of the moving amount of the focus group rear group GFr is positive when the focus group rear group GFr moves from the object side to the image side and negative when moving from the image side to the object side.

0.2＜DFrinf/DFrmax＜50 (1)

Fig. 4 shows, as an example, a movement locus of the focus group rear group GFr when zooming from the wide angle end to the telephoto end, and DFrinf and DFrmax on the locus. In fig. 4, the solid line indicates a movement locus at the time of magnification change in a state of focusing on an object at infinity, the broken line indicates a movement locus at the time of magnification change in a state of focusing on a nearest object, and the upper end indicates a state at the wide-angle end and the lower end indicates a state at the telephoto end.

By not being equal to or less than the lower limit of conditional expression (1), the amount of movement at the time of magnification change of the focus group rear group GFr can be secured, and variation in field curvature at the zoom position of the intermediate focal length can be easily suppressed. Alternatively, since the movement amount of the focus group rear group GFr during focusing is not excessively increased, the effect of suppressing the aberration variation during focusing by the movement of the focus group rear group GFr is not excessive, and the aberration variation can be appropriately suppressed. By not being equal to or more than the upper limit of conditional expression (1), the amount of movement of the focus group rear group GFr at the time of focusing can be secured, and the effect of suppressing aberration variation at the time of focusing can be obtained appropriately. Alternatively, the amount of movement of the focus group rear group GFr during magnification change can be suppressed, and the focus group rear group GFr can be made not to be excessively distant from the focus group middle group GFm on the telephoto side, so that spherical aberration on the telephoto side can be corrected favorably. Further, when the following conditional expression (1-1) is satisfied, more favorable characteristics can be obtained, and when the following conditional expression (1-2) is satisfied, further more favorable characteristics can be obtained.

0.3＜DFrinf/DFrmax＜10 (1-1)

0.4＜DFrinf/DFrmax＜7 (1-2)

When the lateral magnification of the focus group rear group GFr in a state of focusing on an object at infinity is Fr, the zoom lens preferably satisfies the following conditional expression (2) over the entire zoom region. By not being equal to or less than the lower limit of conditional expression (2), the negative refractive power of the focus group rear group GFr is not excessively increased, and therefore the effect of suppressing the variation in field curvature at the time of magnification change and at the time of focusing is not excessive, and the variation can be appropriately suppressed. Further, the color difference generated in the focusing group rear group GFr is easily suppressed. By not being equal to or more than the upper limit of conditional expression (2), the negative refractive power of the focus group rear group GFr is not excessively weakened, and therefore the effect of suppressing the variation in field curvature at the time of magnification change and at the time of focusing can be ensured satisfactorily. Alternatively, since the amount of movement of the focus group rear group GFr required for aberration correction during magnification change and focusing is not excessively large, interference with adjacent lens groups can be avoided. Further, when the following conditional expression (2-1) is satisfied, more favorable characteristics can be obtained, and when the following conditional expression (2-2) is satisfied, further more favorable characteristics can be obtained.

0.5＜1/β Fr＜0.995 (2)

0.55＜1/β Fr＜0.995 (2-1)

0.6＜1/β Fr＜0.98 (2-2)

Preferably, the lens group closest to the object side in the variable power group GV has negative refractive power and always moves from the object side to the image side when varying power from the wide angle end to the telephoto end. By having negative refractive power, the most object side lens group in the variable power group GV can perform a main variable power function. Further, by always moving the lens group to the image side when zooming from the wide angle end to the telephoto end, it is possible to prevent a reduction in zoom magnification on the telephoto side, which is advantageous for increasing the magnification. Further, the space for movement of the focus group rear group GFr during focusing can be secured, which is advantageous for downsizing, increasing magnification, and suppressing aberration variation.

In the configuration in which the lens group closest to the object side in the variable power group GV has negative refractive power and always moves from the object side to the image side when performing variable power from the wide angle end to the telephoto end, the following conditional expression (3) is preferable when the focal length of the lens group closest to the object side in the variable power group GV is fV1 and the focal length of the focus group rear group GFr is fFr. Since the negative refractive power of the focus group rear group GFr is not excessively reduced by not being equal to or less than the lower limit of the conditional expression (3), the effect of suppressing the fluctuation of the field curvature at the time of magnification change and at the time of focusing by the focus group rear group GFr can be ensured. Alternatively, the refractive power of the lens group closest to the object side in the variable power group GV is not excessively increased, and thus variation in spherical aberration during variable power is easily suppressed. Since the negative refractive power of the focus group rear group GFr is not excessively increased by not being equal to or more than the upper limit of the conditional expression (3), the effect of suppressing the fluctuation of the field curvature at the time of magnification change and at the time of focusing by the focus group rear group GFr is not excessive, and it is possible to appropriately suppress the fluctuation. Further, the color difference generated in the focusing group rear group GFr is easily suppressed. Alternatively, the refractive power of the most object-side lens group in the variable power group GV can be ensured, and thus both high power and downsizing can be easily achieved. Further, when the following conditional expression (3-1) is satisfied, more favorable characteristics can be obtained, and when the following conditional expression (3-2) is satisfied, further more favorable characteristics can be obtained.

0.001＜fV1/fFr＜0.4 (3)

0.002＜fV1/fFr＜0.3 (3-1)

0.003＜fV1/fFr＜0.2 (3-2)

The focus group rear group GFr has a configuration in which the amount of movement during focusing changes depending on the zoom position, but other groups may have a configuration in which the amount of movement during focusing changes depending on the zoom position. For example, the moving amount of at least 1 lens group in the group GFm in the focusing group during focusing may be changed depending on the zoom position. With such a configuration, it is possible to correct a variation in focal position due to movement of the focus group rear group GFr by the lens group of the focus group intermediate group GFm. Further, when the configuration is adopted in which only 1 lens group in the focus group rear group GFr and the focus group middle group GFm moves at the time of focusing, the number of lens groups that move at the time of focusing can be reduced, which is advantageous for simplification of the mechanism and miniaturization of the device.

Further, at least 1 of the lens groups closest to the object side among the lens groups in the variable magnification group GV and closer to the image side may be moved at the time of focusing, and the amount of movement at the time of focusing may be changed depending on the zoom position. With such a configuration, the lens group of the variable magnification group GV can correct the variation in the focal position due to the movement of the focus group rear group GFr. By using a part of the lens groups of the magnification-varying group GV having a smaller lens diameter than the focusing group GF for focusing, the load on the driving mechanism for driving the lens groups can be reduced at the time of magnification variation and at the time of focusing.

Further, at least 1 lens group in the subsequent group GR may be moved at the time of focusing, and the amount of movement at the time of focusing may be changed depending on the zoom position. With such a configuration, the lens group of the subsequent group GR can correct the fluctuation of the focal position due to the movement of the focus group rear group GFr. By using a part of the lens groups of the subsequent group GR having a smaller lens diameter than the focusing group GF for focusing, the load of the driving mechanism for driving the lens groups can be reduced at the time of magnification change and at the time of focusing. Further, the amount of movement can be reduced.

Each of the focus groups GF can have the following structure, for example. The focus group front group GFf can include 2 lenses, a negative lens and a positive lens. With such a configuration, it is advantageous to correct chromatic aberration. More specifically, the focus group front group GFf may include 2 lenses, i.e., a negative lens and a positive lens, in order from the object side to the image side. With such a configuration, correction of a wide angle and chromatic aberration is facilitated.

The group GFm in the focus group can include 3 positive lenses. In the case of such a configuration, the positive refractive power can be dispersed to 3 positive lenses, which is advantageous for correcting spherical aberration.

The focus group rear group GFr may include 1 negative lens. In the case of such a configuration, the movement space for magnification change of the lens group closest to the object side in the magnification change group GV can be secured wide, which is advantageous for higher magnification. When the lens group closest to the object side in the variable power group GV is a lens group that is responsible for the main variable power, it is more advantageous to increase the power.

Alternatively, the focusing group rear group GFr may include a cemented lens in which 1 negative lens and 1 positive lens are cemented. With such a configuration, it is easy to correct chromatic aberration on the telephoto side on-axis by having the positive lens and the negative lens. Further, the space can be shortened by the cemented lens, and the movement space of the lens group closest to the object side in the variable power group GV can be secured wide, which is advantageous for increasing the power.

The variable magnification group GV and the subsequent group GR can have the following structures, for example. The variable magnification group GV can include 2 lens groups having negative refractive power, and the subsequent group GR can have positive refractive power. 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 variable magnification group GV can include 3 lens groups having negative refractive power, and the subsequent group GR can have positive refractive power. 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 spherical aberration at the time of magnification change.

Alternatively, the variable magnification group GV may include, in order from the object side toward the image side, a lens group having negative refractive power, 2 lens groups having positive refractive power, and the subsequent group GR may include a lens group having positive refractive power. 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.

In addition, although the above description has been given of the case where the focus group rear group GFr moves during magnification change and during focusing, the focus group rear group GFr may be moved along the optical axis Z to correct a variation in field curvature due to a manufacturing error. Also, the focus group rear group GFr can be moved along the optical axis Z in accordance with a change in temperature and/or the aperture value of the aperture stop St.

The above-described preferred configurations and realizable configurations can be arbitrarily combined and preferably selectively employed as appropriate in accordance with the required specifications. According to the technique of the present invention, a zoom lens having a high magnification ratio while maintaining good optical performance by satisfactorily suppressing the variation of field curvature in focusing over the entire zoom region can be realized. The "high magnification" described herein means that the zoom magnification is 20 times or more.

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

[ example 1]

Fig. 1 shows a cross-sectional view and a movement locus of the zoom lens of example 1, and the method and the structure thereof are as described above, and therefore, a part of the description thereof will be omitted. The zoom lens according to embodiment 1 includes, in order from the object side toward the image side, a focus group GF, a variable magnification group GV, and a subsequent group GR. The focus group GF includes, in order from the object side toward the image side, a focus group front group GFf, a focus group middle group GFm, and a focus group rear group GFr. The focusing group front group GFf is fixed with respect to the image plane Sim at the time of magnification change and at the time of focusing. The group GFm in the focusing group includes 1 lens group, and moves along the optical axis Z at the time of magnification change and at the time of focusing. The focus group rear group GFr moves along the optical axis Z during zooming and focusing. The variable magnification group GV includes 3 lens groups of a 1 st variable magnification group GV1, a 2 nd variable magnification group GV2, and a 3 rd variable magnification group GV3 in order from the object side toward the image side, and the 3 groups change their intervals to move along the optical axis Z at the time of variable magnification. The subsequent group GR is fixed with respect to the image plane Sim at the time of magnification change and at the time of focusing.

Table 1A and table 1B show the basic lens data of the zoom lens of example 1, table 2 shows the specifications, table 3 shows the group interval, and table 4 shows the amount of movement in focus of the group that moves in focus. In order to avoid lengthening 1 table, the basic lens data in tables 1A and 1B are shown in 2 tables. 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 Z 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-reference 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. Also, for ease of understanding, each group is enclosed with a frame and symbols of the groups are shown in the rightmost 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 is marked with DD [ ], and the object-side surface number of the interval is marked with [ ], and is 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 are shown on a 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 columns labeled "wide-angle end", "intermediate", and "telephoto end", respectively. The table of the specification shows values in a state of focusing on an object at infinity.

In table 3, the values of the variable surface intervals in the state of focusing on an object at infinity are shown in the upper row, and the values of the variable surface intervals in the state of focusing on the closest object are shown in the lower row. In table 3, 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 the data of example 1, the object distance of the nearest object was set to 2.8m (meters).

Table 4 shows the amount of movement of each group when focusing from an object at infinity to the nearest object. The positive and negative signs of the movement amount are positive when moving from the object side to the image side, and negative when moving from the image side to the object side. In table 4, the moving amounts of the group GFm in the focus group and the group GFr behind the focus group are shown in the columns labeled "GFm" and "GFr", respectively.

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 ]