JP2015163927A - Inner focus lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an inner focus lens configured to reduce the entire length and aperture, while improving imaging performance.SOLUTION: An inner focus lens includes from an object side: a first lens group Ghaving positive refractive power; a second lens group Ghaving negative refractive power; and a third lens group Ghaving negative refractive power. The second lens group Gmoves along an optical axis, to focus from infinity to MOD(minimum object distance). A predetermined condition is satisfied, to achieve a compact inner focus lens having high imaging performance, which is suitable for a compact camera having a video function.

Description

  The present invention relates to an inner focus lens having a small size and high imaging performance.

  Conventionally, lenses for single-lens reflex cameras in particular have adopted a configuration that facilitates ensuring back focus by arranging a positive lens group behind the optical system in order to ensure a long flange back with respect to the focal length. There were a lot of things. However, in recent years, there has been an increase in cases where it is not necessary to ensure a long flange back due to the progress of miniaturization of camera bodies and the spread of digital cameras.

  In addition, since a digital camera can also shoot moving images, high-speed autofocus processing corresponding to moving image shooting is desired. In autofocus, first, a part of lens groups (focus group) are vibrated at high speed in the optical axis direction (wobbling) to create a non-focus state → a focus state → a non-focus state. Then, a signal component in a specific frequency band in a partial image region is detected from the output signal of the image sensor, the optimum position of the focus group that is in focus is obtained, and the focus group is moved to the optimum position. In particular, in moving image shooting, it is required to continuously repeat these series of operations at a high speed. In order to execute wobbling, the focus group is required to be as small and light as possible so that the focus group can be driven at high speed.

  In order to meet such a demand, an inner focus lens that can sufficiently handle moving image shooting has been proposed (see, for example, Patent Document 1).

JP 2013-97212 A

  The inner focus type lens disclosed in Patent Document 1 has a mid-telephoto focal length in terms of a 35 mm film camera, and has a small and light focus group inside, so that good wobbling can be performed.

  By the way, conventionally, in an imaging sensor that receives an optical image and converts it into an electrical image signal, there is a limitation for efficiently capturing incident light with an on-chip microlens or the like, and an exit pupil is formed on the lens side. It has been desired to ensure the telecentricity of the incident light beam to the image sensor by increasing it to a certain value or more.

  However, in recent image sensors, the aperture ratio has been improved and the degree of freedom in designing on-chip microlenses has progressed, and the restriction on the exit pupil required on the photographing lens side has been reduced. Furthermore, due to recent advances and improvements in software and camera systems, distortion aberration is large to some extent, and it has become possible to correct even conspicuous ones by image processing.

  For this reason, in conventional photographic lenses, a positive lens component is arranged on the most image side of the optical system to ensure telecentricity, but in recent years this has become unnecessary, and it is no longer necessary on the most image side of the optical system. Even if the negative lens component is arranged and the light beam is obliquely incident on the image sensor, the peripheral light reduction (shading) due to the mismatch of the pupil with the on-chip microlens has become inconspicuous. Further, since the negative lens component can be disposed on the most image side of the optical system, it is possible to expect a reduction in the diameter of the optical system.

  On the other hand, in the inner focus type lens disclosed in Patent Document 1, although the total length of the optical system is shortened, the positive lens component is disposed on the most image side of the optical system. The size of the (most image side lens) is not sufficiently small. For this reason, it is difficult to deal with cameras in which the optical system has been downsized in the aperture direction, such as mirrorless single-lens cameras that have been widely spread in recent years. In order to suppress aberration fluctuations and zooming effects due to wobbling during focusing, it is more preferable to dispose a negative lens component on the most image side of the optical system.

  Further, since the inner focus lens disclosed in Patent Document 1 is not intended for widening the angle, correction of curvature of field and distortion and securing of the amount of peripheral light necessary for widening the angle are required. Such points are not taken into consideration.

  An object of the present invention is to provide an inner focus type lens in which a reduction in the overall length and the aperture diameter is achieved and a high imaging performance is achieved in order to eliminate the above-described problems caused by the prior art. It is another object of the present invention to provide an inner focus type lens having a focal length from a wide angle to a standard angle of view and having high imaging performance.

In order to solve the above-described problems and achieve the object, an inner focus lens according to a first aspect of the present invention includes a first lens group having a positive refractive power arranged in order from the object side, and negative refraction. A second lens group having a power and a third lens group having a negative refractive power, and by moving the second lens group along the optical axis, the closest distance from the infinite object focus state It is an inner focus type lens that performs focusing to an object in-focus state, and a single lens component having a negative refractive power is disposed on the most image side of the third lens group, and satisfies the following conditional expression: Features.
(1) (R1 + R2) / (R1-R2) ≦ 0.0
Here, R1 represents the radius of curvature of the object side air boundary surface of the single lens component having the negative refractive power, and R2 represents the radius of curvature of the image side air boundary surface of the single lens component having the negative refractive power.

  According to the first aspect of the present invention, it is possible to provide an inner focus lens that achieves downsizing of the overall length and aperture and has high imaging performance. In particular, the aperture of the third lens group (most image side lens) can be reduced, and off-axis coma can be favorably corrected.

An inner focus type lens according to a second aspect of the present invention is the inner focus type lens according to the first aspect, wherein the single lens component having the negative refractive power and disposed on the most image side of the third lens group is composed of a single glass material. And satisfying the following conditional expression.
(2) 30 ≦ νen
Here, νen represents the Abbe number with respect to the e-line of a single lens component having a negative refractive power disposed on the most image side of the third lens group.

  According to the second aspect of the present invention, the single lens component having the negative refractive power disposed on the most image side of the third lens group can be easily reduced in size and weight, and the lateral chromatic aberration can be corrected well. Can do.

An inner focus type lens according to a third aspect of the present invention is characterized in that, in the first or second aspect of the invention, the following conditional expression is satisfied.
(3) 0.18 ≦ f1 / f ≦ 0.99
Here, f1 represents the focal length of the first lens group in the infinite object focusing state, and f represents the focal length of the entire optical system in the infinite object focusing state.

  According to the invention of claim 3, it is possible to provide an inner focus lens having a high imaging performance and having a focal length from a wide angle to a standard angle of view.

An inner focus type lens according to a fourth aspect of the present invention is characterized in that, in any one of the first to third aspects, the following conditional expression is satisfied.
(4) −29.0 ≦ f3 / f ≦ −5.4
Here, f3 represents the focal length of the third lens group in the infinite object focusing state, and f represents the focal length of the entire optical system in the infinite object focusing state.

  According to the fourth aspect of the present invention, it is possible to provide an inner focus type lens that achieves downsizing of the overall length and aperture and has high imaging performance.

An inner focus type lens according to a fifth aspect of the present invention is characterized in that, in any one of the first to fourth aspects, the following conditional expression is satisfied.
(5) 0.51 ≦ βinf / βmod ≦ 2.07
Where βinf is the paraxial magnification of the second lens group in the infinite object focusing state, and βmod is the paraxial magnification of the second lens group in the closest object focusing state.

  According to the fifth aspect of the present invention, it is possible to improve the imaging performance by suppressing the angle of view variation due to focusing.

  An inner focus type lens according to a sixth aspect of the present invention is the front sub lens according to any one of the first to fifth aspects, wherein the third lens group is disposed in order from the object side and has a positive refractive power. A lens group and a rear sub-lens group having negative refractive power, and the air space on the widest axis in the third lens group is between the front sub-lens group and the rear sub-lens group. It is formed.

  According to the sixth aspect of the present invention, it is possible to further reduce the aperture of the lens close to the image plane and correct axial aberrations and off-axis aberrations (particularly distortion aberrations).

An inner focus type lens according to a seventh aspect of the present invention is characterized in that, in any one of the first to sixth aspects, the following conditional expression is satisfied.
(6) 0.01 ≦ L1s / L ≦ 0.53
Here, L1s indicates the axial distance from the most object side surface of the first lens group to the aperture stop, and L indicates the total length of the optical system (the air-converted optical path length from the apex of the lens surface on the most object side to the imaging surface).

  According to the seventh aspect of the present invention, it is possible to promote downsizing of the optical system by reducing the front lens diameter and the rear lens diameter while maintaining the imaging performance.

  An inner focus type lens according to an eighth aspect of the present invention is the inner focus type lens according to any one of the first to seventh aspects, wherein the second lens group is composed of a single lens component having a negative refractive power. And

  According to the eighth aspect of the invention, an inner focus lens suitable for moving image shooting can be provided by reducing the size and weight of the second lens group that is the focus group.

An inner focus type lens according to a ninth aspect of the present invention is characterized in that, in any one of the first to eighth aspects, the following conditional expression is satisfied.
(7) −2.12 ≦ f2 / f ≦ −0.18
Here, f2 represents the focal length of the second lens group in the infinite object focusing state, and f represents the focal length of the entire optical system in the infinite object focusing state.

  According to the ninth aspect of the present invention, it is possible to further shorten the overall length of the optical system and improve the imaging performance.

An inner focus lens according to a tenth aspect of the present invention is the lens according to any one of the first to ninth aspects, wherein a lens group including lenses other than the lens arranged closest to the object side is arranged with respect to the optical axis. The image is shifted by moving in the vertical direction, and the following conditional expression is satisfied.
(8) 0.15 ≦ (1-βp) × βr ≦ 4.50
Here, βp represents the lateral magnification of the lens group moved in the direction perpendicular to the optical axis, and βr represents the combined lateral magnification of the lens disposed on the image side of the lens group moved in the direction perpendicular to the optical axis.

  According to the tenth aspect of the present invention, it is possible to provide a small inner focus lens having an image stabilization function. In particular, it is possible to reduce the moving amount of the image stabilizing group at the time of image stabilization and to reduce the size of the optical system, and to improve the image stabilization capability.

  According to the present invention, there is an effect that it is possible to provide an inner focus lens in which the overall length and the aperture size are reduced and the imaging performance is high. Furthermore, there is an effect that it is possible to provide an inner focus lens that has a focal length from a wide angle to a standard angle of view and has high imaging performance. According to the present invention, it is possible to provide a small inner focus lens suitable for moving image shooting.

1 is a cross-sectional view along the optical axis showing the configuration of an inner focus lens according to Example 1. FIG. FIG. 5 is a diagram illustrating all aberrations of the inner focus lens according to Example 1; FIG. 6 is a cross-sectional view along the optical axis showing the configuration of the inner focus lens according to Example 2. FIG. 10 is a diagram illustrating all aberrations of the inner focus lens according to Example 2; FIG. 6 is a cross-sectional view along the optical axis showing the configuration of an inner focus lens according to Example 3; FIG. 9 is a diagram illustrating all aberrations of the inner focus lens according to Example 3;

  Hereinafter, a preferred embodiment of an inner focus type lens according to the present invention will be described in detail.

  The inner focus type lens according to the present invention includes a first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens having a negative refractive power, which are arranged in order from the object side. And a lens group.

  In the inner focus type lens according to the present invention, focusing is performed from the infinitely focused object state to the closest object focused state by moving the second lens group along the optical axis. Thus, by performing the focusing by moving the second lens group, there is no change in the overall length of the optical system, and the dustproof and soundproof performance is enhanced.

  Further, by arranging the first lens group having the positive refractive power closest to the object side, the diameter of the light beam guided to the subsequent second lens group can be reduced. For this reason, the aperture of the second lens group, which is the focus group, can be reduced to reduce the weight of the second lens group. As a result, high-speed and quiet focusing is possible, which is effective for moving image shooting. Moreover, since the aperture of the second lens group can be reduced, it is advantageous for reducing the aperture of the optical system.

  Furthermore, by disposing the third lens group having the negative refractive power closest to the image side, it is possible to improve the telephoto property and shorten the back focus, thereby promoting the downsizing of the optical system.

  An object of the present invention is to provide an inner focus lens that is also suitable for a small camera capable of moving image shooting, that is, an inner focus lens that achieves a reduction in overall length and aperture and has high imaging performance. It is said. It is another object of the present invention to provide an inner focus type lens having a focal length from a wide angle to a standard angle of view and having high imaging performance. Therefore, in order to achieve such an object, various conditions as shown below are set in addition to the above characteristics.

  First, in the inner focus lens according to the present invention, it is preferable to dispose a single lens component having a negative refractive power on the most image side of the third lens group. By doing so, it is possible to further reduce the aperture of the third lens group (most image side lens), and it is suitable for small cameras such as mirrorless single-lens cameras that are widely used in recent years.

  The single lens component includes a single polished lens, an aspheric lens, a composite aspheric lens, and a cemented lens, and does not include, for example, two positive and negative lenses that have an air layer and are not bonded to each other.

In the inner focus type lens according to the present invention, in addition to disposing the single lens component having negative refractive power on the most image side of the third lens group, the object side air boundary of the single lens component having negative refractive power When the radius of curvature of the surface is R1, and the radius of curvature of the image side air boundary surface of the single lens component having the negative refractive power is R2, it is preferable that the following conditional expression is satisfied.
(1) (R1 + R2) / (R1-R2) ≦ 0.0

  Conditional expression (1) is an expression that defines the shape of a single lens component having a negative refractive power, which is disposed closest to the image side of the third lens group. When the conditional expression (1) is satisfied, the radius of curvature of the object side surface of the single lens component becomes smaller than the radius of curvature of the image side surface. As a result, good correction of off-axis coma is possible.

In addition, the said conditional expression (1) can anticipate a more preferable effect, if the range shown next is satisfied.
(1a) (R1 + R2) / (R1-R2) ≦ −1.0
By satisfying the range defined by the conditional expression (1a), better correction of off-axis coma aberration becomes possible.

Furthermore, the conditional expression (1a) exhibits an effect by correcting off-axis coma aberration when the following range is satisfied.
(1b) −100.00 ≦ (R1 + R2) / (R1−R2) ≦ −1.02

  Furthermore, in the inner focus type lens according to the present invention, it is preferable that the single lens component having the negative refractive power disposed on the most image side of the third lens group is composed of a single glass material. If the single lens component in the third lens group is composed of a single glass material, that is, a single lens, the single lens component can be easily downsized in the optical axis direction and the radial direction. In addition, the single lens component can be reduced in weight.

In the inner focus type lens according to the present invention, when the Abbe number with respect to the e-line of the single lens component having the negative refractive power arranged on the most image side of the third lens group is νen, the following conditional expression is satisfied. It is preferable to satisfy.
(2) 30 ≦ νen

  If the lower limit of conditional expression (2) is not reached, the lateral chromatic aberration will be overcorrected, and it will be difficult to maintain high imaging performance.

Furthermore, in the inner focus lens according to the present invention, when the focal length of the first lens group in the infinite object focusing state is f1, and the focal length of the entire optical system in the infinite object focusing state is f, It is preferable to satisfy the following conditional expression.
(3) 0.18 ≦ f1 / f ≦ 0.99

  Conditional expression (3) is an expression that prescribes the ratio of the focal length of the first lens unit and the focal length of the entire optical system in the state of focusing on an object at infinity. By satisfying conditional expression (3), the refractive power of the first lens unit becomes appropriate, and the front lens diameter is reduced and the total length of the optical system is shortened. A bright inner focus lens can be realized.

  If the lower limit of conditional expression (3) is not reached, the focal length of the first lens group becomes short and the spherical aberration becomes excessive on the under side, and the paraxial imaging magnification of the subsequent lens group becomes large. This is not preferable because the ball diameter increases and the optical system becomes larger. On the other hand, if the upper limit in conditional expression (3) is exceeded, the focal length of the first lens group becomes long and the entire length of the optical system is extended, making it difficult to reduce the size of the optical system.

In addition, if the said conditional expression (3) satisfies the range shown next, a more preferable effect can be anticipated.
(3a) 0.22 ≦ f1 / f ≦ 0.90
By satisfying the range defined by the conditional expression (3a), it is possible to realize a bright inner focus type lens having a small size, a wide angle, and a better imaging performance.

Further, when the conditional expression (3a) satisfies the following range, a small, wide-angle, and higher-performance inner focus lens can be realized.
(3b) 0.30 ≦ f1 / f ≦ 0.80

Furthermore, in the inner focus type lens according to the present invention, when the focal length of the third lens group in the infinite object focusing state is f3 and the focal length of the entire optical system in the infinite object focusing state is f, It is preferable to satisfy the following conditional expression.
(4) −29.0 ≦ f3 / f ≦ −5.4

  Conditional expression (4) is an expression that prescribes the ratio of the focal length of the third lens group and the focal length of the entire optical system in an infinitely focused object state. By satisfying this conditional expression (4), the refractive power of the third lens group is optimized, and the overall length and aperture of the optical system can be reduced without deteriorating the imaging performance.

  If the lower limit of conditional expression (4) is not reached, the refractive power of the third lens group will become weak. For this reason, the back focus is extended and it is difficult to reduce the size of the optical system. On the other hand, if the upper limit of conditional expression (4) is exceeded, the refractive power of the third lens group becomes strong. In this case, the F number in the entire optical system tends to increase, and a bright optical system cannot be obtained. In order to realize a bright optical system in this state, it is necessary to widen the aperture stop. However, when the aperture stop is opened wide, the occurrence of various aberrations becomes significant. Therefore, in order to realize an optical system with good imaging performance, it is necessary to increase the number of lenses in order to correct aberrations. In particular, it is necessary to increase the number of lenses constituting the first lens group. If the number of lenses constituting the optical system increases, it is difficult to reduce the size and weight of the optical system, which is not preferable.

In addition, if the said conditional expression (4) satisfies the range shown next, a more preferable effect can be anticipated.
(4a) −26.0 ≦ f3 / f ≦ −5.4
By satisfying the range defined by the conditional expression (1a), it is possible to realize an inner focus type lens that is small in size and has superior imaging performance.

Furthermore, when the conditional expression (4a) satisfies the following range, a smaller and higher performance inner focus lens can be realized.
(4b) −24.0 ≦ f3 / f ≦ −5.4

Furthermore, in the inner focus lens according to the present invention, the paraxial magnification of the second lens group in the infinite object focusing state is βinf, and the paraxial magnification of the second lens group in the closest object focusing state is βmod. It is preferable that the following conditional expression is satisfied.
(5) 0.51 ≦ βinf / βmod ≦ 2.07

  Conditional expression (5) is an expression that prescribes the ratio of the paraxial lateral magnification of the second lens group in the infinite object focusing state and the closest object focusing state. By satisfying conditional expression (5), it is possible to suppress a change in magnification even when the focus group (second lens group) is operated, and to suppress a change in the angle of view during focusing. If the value deviates from the range defined by the conditional expression (5), it becomes impossible to suppress the angle of view variation during focusing. If the angle of view changes during the movement of the focus group, the image appears to be shaken and the quality of the image is degraded.

In addition, the said conditional expression (5) can anticipate a more preferable effect, if the range shown next is satisfied.
(5a) 0.60 ≦ βinf / βmod ≦ 1.80
By satisfying the range defined by the conditional expression (5a), it is possible to further suppress the angle of view variation during focusing.

Furthermore, when the conditional expression (5a) satisfies the following range, it is possible to further reduce the field angle fluctuation during focusing.
(5b) 0.68 ≦ βinf / βmod ≦ 1.60

Furthermore, when the conditional expression (5b) satisfies the following range, the field angle fluctuation during focusing can be extremely reduced.
(5c) 0.80 ≦ βinf / βmod ≦ 1.40

  Furthermore, in the inner focus type lens according to the present invention, the third lens group is arranged in order from the object side, a front sub lens group having a positive refractive power, a rear sub lens group having a negative refractive power, And the widest air space on the axis in the third lens group is formed between the front sub lens group and the rear sub lens group.

  By doing so, it is possible to reduce the lens aperture close to the imaging plane and improve the imaging performance. That is, it has a positive refracting power on the object side of the third lens group, with an increase in the lens aperture on the image side, which is a problem in miniaturizing the optical system of the short flange back intended to be mounted on a small camera such as a mirrorless single-lens camera. This can be suppressed by arranging the front sub lens group. Furthermore, by arranging the rear sub lens group having negative refractive power with an air space on the image side of the front sub lens group, while correcting axial aberration with the front sub lens group having positive refractive power, In the rear sub-lens group, off-axis aberrations, particularly distortion aberrations can be corrected satisfactorily.

Further, in the inner focus type lens according to the present invention, the axial distance from the most object side surface of the first lens group to the aperture stop is L1s, and the total length of the optical system (the air conversion from the apex of the lens surface on the most object side to the imaging surface) When the optical path length is L, it is preferable that the following conditional expression is satisfied.
(6) 0.01 ≦ L1s / L ≦ 0.53

  Conditional expression (6) is an expression that defines the ratio of the axial distance from the most object side surface of the first lens group to the aperture stop and the total length of the optical system. By satisfying the conditional expression (6), it is possible to define an appropriate position of the aperture stop with respect to the entire length of the optical system and to reduce the aperture of the optical system while maintaining high imaging performance.

  If the lower limit of conditional expression (6) is not reached, the aperture stop is too close to the object side and the lens aperture on the image side is enlarged, and off-axis aberrations in the rear group, mainly distortion, become prominent. It is not preferable. On the other hand, if the upper limit of conditional expression (6) is exceeded, the aperture stop will be too close to the image side, leading to an increase in the effective diameter of the front lens, making it difficult to reduce the size of the optical system.

In addition, when the conditional expression (6) satisfies the following range, a more preferable effect can be expected.
(6a) 0.012 ≦ L1s / L ≦ 0.500
By satisfying the range defined by this conditional expression (6a), it is possible to realize a smaller optical system aperture while maintaining high imaging performance.

Furthermore, when the conditional expression (6a) satisfies the following range, the optical system aperture can be further reduced.
(6b) 0.013 ≦ L1s / L ≦ 0.400

Furthermore, when the conditional expression (6b) satisfies the following range, the optical system aperture can be further reduced.
(6c) 0.013 ≦ L1s / L ≦ 0.300

  Furthermore, in the inner focus type lens according to the present invention, it is preferable that the second lens group is composed of a single lens component having a negative refractive power.

  By configuring the second lens group with a single lens component having a negative refractive power, the focus group can be reduced in size and weight, enabling high-speed focusing, which is effective for moving image shooting. Further, by reducing the size and weight of the focus group, the load on the driving means such as an actuator that controls the focus group is reduced, which contributes to power saving. Further, further downsizing of the driving means can be promoted.

Furthermore, in the inner focus type lens according to the present invention, when the focal length of the second lens group in the infinite object focusing state is f2, and the focal length of the entire optical system in the infinite object focusing state is f, It is preferable to satisfy the following conditional expression.
(7) −2.12 ≦ f2 / f ≦ −0.18

  Conditional expression (7) is an expression that prescribes the ratio of the focal length of the second lens group and the focal length of the entire optical system in an infinitely focused object state. By satisfying conditional expression (7), it is possible to maintain high imaging performance while realizing downsizing of the optical system (especially effective for correcting curvature of field).

  If the lower limit of conditional expression (7) is not reached, the focal length of the second lens group becomes long, and the negative power of the second lens group becomes too weak. As a result, the amount of movement of the second lens group during focusing increases, the overall length of the optical system increases, and it becomes difficult to reduce the size of the optical system. On the other hand, if the upper limit in conditional expression (7) is exceeded, the focal length of the second lens group becomes short, and the negative power of the second lens group becomes too strong. As a result, aberration fluctuations (particularly field curvature fluctuations) and field angle fluctuations accompanying movement of the second lens group during focusing become excessive, which is not preferable.

In addition, when the conditional expression (7) satisfies the following range, a more preferable effect can be expected.
(7a) -1.90 ≦ f2 / f ≦ −0.19
By satisfying the range defined by the conditional expression (7a), it is possible to realize an inner focus lens having a smaller size and excellent imaging performance.

Furthermore, when the conditional expression (7a) satisfies the following range, a smaller and higher performance inner focus lens can be realized.
(7b) -1.50 ≦ f2 / f ≦ −0.20

Further, in the inner focus type lens according to the present invention, the image is shifted by moving a lens group (anti-vibration group) composed of lenses other than the lens disposed closest to the object side in a direction perpendicular to the optical axis. Then, image stabilization correction is performed. When the lateral magnification of the lens group moved in the direction perpendicular to the optical axis is βp, and the combined lateral magnification of the lens arranged on the image side of the lens group moved in the direction perpendicular to the optical axis is βr. It is preferable that the following conditional expression is satisfied.
(8) 0.15 ≦ (1-βp) × βr ≦ 4.50

  Conditional expression (8) defines the image shift ratio with respect to the moving amount of the lens group moved during the image stabilization correction. By satisfying conditional expression (8), it is possible to reduce the amount of movement of the image stabilization group during image stabilization correction, to reduce the size of the optical system aperture, and to improve image stabilization capability. When the image stabilizing group includes a lens arranged closest to the image side, the value of βr in conditional expression (7) is 1.

  If the lower limit of conditional expression (8) is not reached, the amount of movement of the image stabilizing group necessary for shifting the image by a predetermined amount increases in the vertical direction, the optical system aperture increases, and the optical system becomes smaller. Is inhibited. On the other hand, if the upper limit is exceeded in the conditional expression (8), the image is greatly shifted even when the image stabilizing group is slightly moved, so that the image stabilization capability is deteriorated. In order to maintain high image stabilization capability in this state, extremely high accuracy is required for controlling the image stabilization group during image stabilization. As a result, the structure of the drive unit for the vibration proof group becomes complicated and rebounds to the manufacturing cost of the lens unit, which is not preferable.

  Note that the image stabilization effect does not change even if the image stabilization group is composed of a plurality of lenses or a single lens. If the anti-vibration group is composed of a single lens, the anti-vibration group can be reduced in size and weight, which is effective in reducing the size and weight of the entire optical system. By reducing the size and weight of the anti-vibration group, the load on the driving means that controls the anti-vibration group is reduced, which contributes to power saving. In addition, if an aspheric lens having a shape that weakens the power of the paraxial curvature is used in the vibration proof group, it is possible to suppress the one-side blur and the fluctuation of the center frame during the vibration proof correction.

In addition, the said conditional expression (8) can anticipate a more preferable effect, if the range shown next is satisfied.
(8a) 0.16 ≦ (1-βp) × βr ≦ 4.30
By satisfying the range defined by the conditional expression (8a), it is possible to realize an inner focus type lens that is small in size and has a superior anti-shake correction capability.

Further, when the conditional expression (8a) satisfies the following range, it is possible to realize an inner focus type lens that is small and has an extremely excellent image stabilization capability.
(8b) 0.16 ≦ (1-βp) × βr ≦ 4.00

Further, in the inner focus type lens according to the present invention, when the radius of curvature of the outermost object side surface of the second lens group is R21 and the radius of curvature of the outermost image side surface of the second lens group is R22, the following conditional expression is satisfied. It is preferable.
(9) 0 ≦ (R21 + R22) / (R21−R22)

  Conditional expression (9) defines the shape of the most object side surface and the shape of the most image side surface in the second lens group. By satisfying conditional expression (9), the radius of curvature of the most image side surface in the second lens group becomes smaller than the radius of curvature of the most object side surface. As a result, it is possible to reduce the change in the angle of the light ray incident on the surface having strong power, and to suppress the variation in field curvature during focusing.

In addition, if the said conditional expression (9) satisfies the range shown next, a more preferable effect can be anticipated.
(9a) 1 ≦ (R21 + R22) / (R21−R22)
By satisfying the range defined by the conditional expression (9a), it is possible to further suppress fluctuations in the field curvature during focusing.

Furthermore, if the conditional expression (9a) satisfies the following range, the variation in field curvature during focusing can be made extremely small.
(9b) 1 ≦ (R21 + R22) / (R21−R22) ≦ 300

  In the inner focus lens according to the present invention, it is effective to correct spherical aberration if a positive lens having an aspheric surface is disposed in the first lens group. In particular, when an aspheric surface having a shape that weakens the power of paraxial curvature is formed on the positive lens, the effect of correcting spherical aberration is improved.

  In the inner focus type lens according to the present invention, it is more effective to correct field curvature if an aspheric surface is formed on the lenses constituting the second lens group. In particular, when an aspheric surface having a shape that weakens the power of paraxial curvature is formed on the lenses constituting the second lens group, the effect of correcting the curvature of field is further improved and the effect of suppressing fluctuations in the curvature of field during focusing is improved. Get higher.

  In the inner focus type lens according to the present invention, if an aspherical surface is formed on the lenses constituting the third lens group, it is effective for correcting curvature of field. In particular, if an aspheric surface having a shape that weakens the power of paraxial curvature is formed on the lenses constituting the third lens group, the field curvature correction effect is improved.

  In addition, it is preferable that the lens arrange | positioned on the image side through air with respect to the 2nd lens group is a single lens component which has positive refractive power. By disposing such a single lens component on the image side of the second lens group, the magnification of the second lens group can be increased, and the amount of movement of the second lens group during focusing can be reduced. As a result, not only miniaturization of the optical system but also high-speed focusing becomes possible.

  As described above, according to the present invention, it is possible to provide an inner focus lens that achieves a reduction in the overall length and the aperture size and has high imaging performance. Furthermore, it is possible to provide an inner focus type lens having high imaging performance and having a focal length from a wide angle to a standard angle of view. In addition, it is possible to provide a small inner focus lens having excellent image stabilization capability. As described above, according to the present invention, it is possible to provide an inner focus lens that can be easily mounted on a small camera capable of moving image shooting. In particular, by satisfying the above conditional expressions, it is possible to realize an inner focus type lens that is suitable for moving image shooting and has a smaller size and high imaging performance.

  Embodiments of an inner focus lens according to the present invention will be described below in detail with reference to the drawings. The present invention is not limited to the following examples.

FIG. 1 is a cross-sectional view along the optical axis showing the configuration of the inner focus lens according to the first embodiment. FIG. 1 shows an infinite object focusing state. The inner focus type lens includes a first lens group G ₁₁ having a positive refractive power, a second lens group G ₁₂ having a negative refractive power, and a third lens having a negative refractive power in order from an object side (not shown). a lens group G _13, is formed is disposed.

The first lens group G ₁₁ includes, in order from the object side, a lens L ₁₁₁ having no refractive power, an aperture stop S that defines a predetermined aperture, a positive lens L ₁₁₂ , a negative lens L _113, and a positive lens L. ₁₁₄ is arranged. The positive lens L ₁₁₂ and the negative lens L ₁₁₃ are cemented. The both surfaces of the positive lens L _114, aspheric surface is formed.

The second lens group G ₁₂ includes, is composed of a negative lens L _121. On both surfaces of the negative lens L _121, aspheric surface is formed. The second lens group G ₁₂ includes, by moving from the object side to the image side along the optical axis to perform focusing from infinity in-focus state to a closest distance object in-focus state.

The third lens group G ₁₃ is constituted, in order from the object side, a positive lens L ₁₃₁ (front sub-lens group), a negative lens L ₁₃₂ (rear sub-lens group), is the arrangement. Aspherical surfaces are formed on both surfaces of the positive lens _L131 . In addition, an air gap is formed between the positive lens L ₁₃₁ and the negative lens L ₁₃₂ .

In the inner focus type lens according to Example 1, the positive lens L ₁₁₄ included in the first lens group G ₁₁ or the positive lens L ₁₃₁ included in the third lens group G ₁₃ is moved in the direction perpendicular to the optical axis. To correct the image stabilization. It is also possible to perform the image stabilization correction by moving all the lenses except the lens L ₁₁₁ having no refractive power of the first lens group G _{11 in} the direction perpendicular to the optical axis. .

  Various numerical data related to the inner focus lens according to Example 1 will be described below.

(Lens data)
r ₁ = ∞
d ₁ = 0.6500 ne ₁ = 1.51872 νe ₁ = 64.00
r ₂ = ∞
d ₂ = 0.5000
r ₃ = ∞ (aperture stop)
d ₃ = 3.8293
r ₄ = -9.4944
d ₄ = 2.8640 ne ₂ = 1.83945 nu ₂ = 42.47
r ₅ = -5.8201
d ₅ = 0.6500 ne ₃ = 1.81184 νe ₃ = 33.03
r ₆ = -16.1384
d ₆ = 0.2000
r ₇ = 22.3959 (Aspherical surface)
d ₇ = 3.2615 ne ₄ = 1.85639 νe ₄ = 39.85
r ₈ = -18.3976 (aspherical surface)
d ₈ = D (8) (variable)
r ₉ = 19.3324 (aspherical surface)
d ₉ = 0.6500 ne ₅ = 1.82917 νe ₅ = 23.86
r ₁₀ = 10.5762 (aspherical surface)
d ₁₀ = D (10) (variable)
r ₁₁ = -17.1418 (aspherical surface)
d ₁₁ = 4.1419 ne ₆ = 1.74689 νe ₆ = 49.07
r ₁₂ = -12.0908 (aspherical surface)
d ₁₂ = 2.8770
r ₁₃ = -22.5833
d ₁₃ = 1.0000 ne ₇ = 1.83930 νe ₇ = 37.09
r ₁₄ = -77.3086
d ₁₄ = Bf

Conical coefficient (k) and aspheric coefficient (A ₄ , A ₆ , A ₈ , A ₁₀ )
(Seventh side)
k = 0,
A ₄ = -4.44632 × 10 ^-5 , A ₆ = -3.60976 × 10 ^-8 ,
A ₈ = 9.18001 × 10 ^-9 , A ₁₀ = -2.80183 × 10 ^-11
(8th page)
k = 0,
A ₄ = 5.44540 × 10 ⁻⁵ , A ₆ = 2.72131 × 10 ⁻⁷ ,
A ₈ = 3.22891 × 10 ^-9 , A ₁₀ = 9.43255 × 10 ^-12
(9th page)
k = 0,
A ₄ = -2.70854 × 10 ⁻⁵ , A ₆ = −2.61994 × 10 ⁻⁶ ,
A ₈ = 2.06465 × 10 ^-8 , A ₁₀ = -1.04244 × 10 ^-10
(Tenth aspect)
k = 0,
A ₄ = 3.25644 × 10 ^-5 , A ₆ = -3.06186 × 10 ^-6 ,
A ₈ = -3.22202 × 10 ^-9 , A ₁₀ = 7.42390 × 10 ^-11
(11th page)
k = 0,
A ₄ = 1.76311 × 10 ^-4 , A ₆ = 1.34885 × 10 ^-6 ,
A ₈ = -1.04265 × 10 ⁻⁸ , A ₁₀ = 3.35661 × 10 ⁻¹²
(Twelfth surface)
k = 0,
A ₄ = 1.119215 × 10 ⁻⁴ , A ₆ = 5.79903 × 10 ⁻⁷ ,
A ₈ = 2.49765 × 10 ^-9 , A ₁₀ = -1.46183 × 10 ^-11

(Numeric data for each in-focus state)
Infinite distance Closest distance (object distance 300mm)
D (8) 1.0688 1.8929
D (10) 6.8075 5.9834
f (focal length of the entire optical system) 27.5462 26.0246
Fno. (F number) 2.8840 2.8985
ω (half angle of view) 38.5881 38.3233
Y (image height) 20.29 21.07
Bf (back focus) 15.6482 15.6482

(Numerical values related to conditional expression (1))
R1 (the radius of curvature of the object-side air boundary surface of the negative lens L ₁₃₂ ) = − 22.5833
R2 (the radius of curvature of the image side air interface of the negative lens L ₁₃₂₎ = - 77.3086
(R1 + R2) / (R1-R2) =-1.83

(Numerical value related to conditional expression (2))
νen (the Abbe number with respect to the e-line of the negative lens L ₁₃₂ ) = 37.09

(Numerical values related to conditional expression (3))
f1 (the focal length of the first lens group G ₁₁ in the infinite object in-focus state) = 13.6190
f1 / f = 0.49

(Numerical values related to conditional expression (4))
f3 (the focal length of the third lens group G ₁₃ in the infinite object in-focus state) = - 400.0000
f3 / f = -14.52

(Numerical values related to conditional expression (5))
Betainf (paraxial magnification of the second lens group G ₁₂ in the infinite object in-focus state) = 1.87
β mod (paraxial magnification of the second lens group G _{12 when} the object is in closest focus) = 1.85
βinf / βmod = 1.01

(Numerical values related to conditional expression (6))
L1s (axial distance from the most object side surface to the aperture stop S in the first lens group G ₁₁₎ = 1.1500
L (total length of optical system) = 44.1482
L1s / L = 0.03

(Numerical values related to conditional expression (7))
f2 (the focal length of the second lens group G ₁₂ in the infinite object in-focus state) = - 29.1423
f2 / f = -1.06

(Numerical value related to conditional expression (8))
When the lens group to be moved (anti-vibration group) is the positive lens L ₁₁₄ of the first lens group G ₁₁ βp (lateral magnification of the lens group moved in the direction perpendicular to the optical axis) = − 0.33
βr (combined lateral magnification of the lens arranged on the image side of the lens group moved in the direction perpendicular to the optical axis) = 2.02
(1-βp) × βr = 2.69
When the lens group to be moved (anti-vibration group) is the positive lens L ₁₃₁ of the third lens group G ₁₃ βp (lateral magnification of the lens group moved in the direction perpendicular to the optical axis) = 0.76
βr (combined lateral magnification of the lens arranged on the image side of the lens group moved in the direction perpendicular to the optical axis) = 1.43
(1-βp) × βr = 0.35
When the lens group to be moved (anti-vibration group) is all lenses except for the lens L ₁₁₁ having no refractive power of the first lens group G ₁₁ , βp (the lens group to be moved in the direction perpendicular to the optical axis) (Horizontal magnification) = 0
βr (the combined lateral magnification of the lens arranged on the image side of the lens group moved in the direction perpendicular to the optical axis) = 1
(1-βp) × βr = 1

(Numerical values related to conditional expression (9))
R21 (radius of curvature of the most object side surface of the negative lens L ₁₂₁₎ = 19.3324
R22 (radius of curvature of the most image side surface of the negative lens L ₁₂₁₎ = 10.5762
(R21 + R22) / (R21-R22) = 3.42

  FIG. 2 is a diagram illustrating various aberrations of the inner focus lens according to Example 1. In the figure, the curve represents the aberration of the wavelength corresponding to the e-line (λ = 546.074 nm). Further, S and M in the astigmatism diagram represent aberrations with respect to the sagittal image surface and the meridional image surface, respectively.

FIG. 3 is a cross-sectional view along the optical axis showing the configuration of the inner focus lens according to the second embodiment. FIG. 3 shows an infinite object focusing state. The inner focus type lens includes a first lens group G ₂₁ having a positive refractive power, a second lens group G ₂₂ having a negative refractive power, and a third lens having a negative refractive power in order from an object side (not shown). a lens group G _23, is formed are disposed.

In the first lens group G ₂₁ , a positive lens L ₂₁₁ , an aperture stop S that defines a predetermined aperture, a positive lens L ₂₁₂ , a negative lens L _213, and a positive lens L ₂₁₄ are arranged in order from the object side. Configured. The positive lens L ₂₁₂ and the negative lens L ₂₁₃ are cemented. Aspherical surfaces are formed on both surfaces of the positive lens L ₂₁₄ .

The second lens group G ₂₂ includes, is composed of a negative lens L _221. An aspheric surface is formed on both surfaces of the negative lens L ₂₂₁ . The second lens group G ₂₂ moves from the object side to the image side along the optical axis, thereby performing focusing from an infinite object focusing state to a closest object focusing state.

The third lens group G ₂₃ is constituted, in order from the object side, a positive lens L ₂₃₁ (front sub-lens group), a negative lens L ₂₃₂ (rear sub-lens group), is the arrangement. Aspherical surfaces are formed on both surfaces of the positive lens _L231 . In addition, an air gap is formed between the positive lens L ₂₃₁ and the negative lens L ₂₃₂ .

In the inner focus type lens according to Example 2, the positive lens L ₂₁₄ included in the first lens group G ₂₁ or the positive lens L ₂₃₁ included in the third lens group G ₂₃ is moved in the direction perpendicular to the optical axis. To correct the image stabilization.

  Various numerical data related to the inner focus lens according to Example 2 will be described below.

(Lens data)
r ₁ = 17.9780
d ₁ = 3.1723 ne ₁ = 1.49845 νe ₁ = 81.21
r ₂ = -179.8468
d ₂ = 0.5000
r ₃ = ∞ (aperture stop)
d ₃ = 3.7714
r ₄ = -24.8117
d ₄ = 1.6114 ne ₂ = 1.49845 νe ₂ = 81.21
r ₅ = -17.9439
d ₅ = 0.6500 ne ₃ = 1.73432 νe ₃ = 28.10
r ₆ = 47.4504
d ₆ = 0.6736
r ₇ = 28.5683 (aspherical surface)
d ₇ = 2.9298 ne ₄ = 1.88765 νe ₄ = 36.97
r ₈ = -23.6412 (aspherical surface)
d ₈ = D (8) (variable)
r ₉ = 38.5730 (aspherical surface)
d ₉ = 0.6500 ne ₅ = 1.62518 νe ₅ = 57.96
r ₁₀ = 12.3652 (aspherical surface)
d ₁₀ = D (10) (variable)
r ₁₁ = -19.3415 (aspherical surface)
d ₁₁ = 1.4124 ne ₆ = 2.00912 νe ₆ = 28.91
r ₁₂ = -17.3396 (aspherical surface)
d ₁₂ = 8.4378
r ₁₃ = -13.9954
d ₁₃ = 1.0000 ne ₇ = 1.58481 νe ₇ = 40.61
r ₁₄ = -20.2884
d ₁₄ = Bf

Conical coefficient (k) and aspheric coefficient (A ₄ , A ₆ , A ₈ , A ₁₀ )
(Seventh side)
k = 0,
A ₄ = -5.31140 × 10 ⁻⁵ , A ₆ = 1.77167 × 10 ⁻⁸ ,
A ₈ = -2.98858 × 10 ⁻¹⁰ , A ₁₀ = 2.27493 × 10 ⁻¹¹
(8th page)
k = 0,
A ₄ = 3.99440 × 10 ⁻⁶ , A ₆ = −5.26041 × 10 ⁻⁸ ,
A ₈ = -8.87342 × 10 ^-11 , A ₁₀ = 1.87394 × 10 ^-11
(9th page)
k = 0,
A ₄ = 7.42096 × 10 ^-6 , A ₆ = -1.53328 × 10 ^-6 ,
A ₈ = 1.49734 × 10 ⁻⁸ , A ₁₀ = −4.71441 × 10 ⁻¹¹
(Tenth aspect)
k = 0,
A ₄ = 1.80928 × 10 ^-5 , A ₆ = -1.60282 × 10 ^-6 ,
A ₈ = 6.53719 × 10 ^-9 , A ₁₀ = 3.47436 × 10 ^-12
(11th page)
k = 0,
A ₄ = 1.40765 × 10 ⁻⁴ , A ₆ = 4.99455 × 10 ⁻⁷ ,
A ₈ = -1.94373 × 10 ^-9 , A ₁₀ = -9.37987 × 10 ^-12
(Twelfth surface)
k = 0,
A ₄ = 1.04350 × 10 ⁻⁴ , A ₆ = 3.22665 × 10 ⁻⁷ ,
A ₈ = 6.06200 × 10 ^-10 , A ₁₀ = -1.72843 × 10 ^-11

(Numeric data for each in-focus state)
Infinite distance Closest distance (object distance 300mm)
D (8) 1.2021 3.4333
D (10) 6.9558 4.7246
f (focal length of the entire optical system) 48.4962 40.8401
Fno. (F number) 2.8840 2.9589
ω (half angle of view) 21.9113 20.7990
Y (image height) 21.63 21.63
Bf (back focus) 16.1817 16.1817

(Numerical values related to conditional expression (1))
R1 (the radius of curvature of the object-side air boundary surface of the negative lens L ₂₃₂ ) =-13.9954
R2 (the radius of curvature of the image side air boundary surface of the negative lens L ₂₃₂ ) = − 20.2884
(R1 + R2) / (R1-R2) =-5.45

(Numerical value related to conditional expression (2))
νen (the Abbe number for the e-line of the negative lens L ₂₃₂ ) = 40.61

(Numerical values related to conditional expression (3))
f1 (the focal length of the first lens group G ₂₁ in the infinite object in-focus state) = 22.0829
f1 / f = 0.46

(Numerical values related to conditional expression (4))
f3 (the focal length of the third lens group G ₂₃ in the infinite object in-focus state) = - 263.2280
f3 / f = -5.43

(Numerical values related to conditional expression (5))
βinf (paraxial magnification of the second lens group G ₂₂ in the infinite object focusing state) = 2.09
β mod (paraxial magnification of the second lens group G _{22 in} the closest object focusing state) = 2.02
βinf / βmod = 1.04

(Numerical values related to conditional expression (6))
L1s (axial distance from the most object side surface to the aperture stop S in the first lens group G ₂₁₎ = 3.6723
L (total length of optical system) = 49.1482
L1s / L = 0.07

(Numerical values related to conditional expression (7))
f2 (the focal length of the second lens group G ₂₂ in the infinite object in-focus state) = - 29.3910
f2 / f = -0.61

(Numerical value related to conditional expression (8))
When the lens group to be moved (anti-vibration group) is the positive lens L ₂₁₄ of the first lens group G ₂₁ βp (lateral magnification of the lens group moved in the direction perpendicular to the optical axis) = − 0.19
βr (combined lateral magnification of the lens arranged on the image side of the lens group moved in the direction perpendicular to the optical axis) = 2.20
(1-βp) × βr = 2.62
When the lens group to be moved (anti-vibration group) is the positive lens L ₂₃₁ of the third lens group G ₂₃ βp (lateral magnification of the lens group moved in the direction perpendicular to the optical axis) = 0.86
βr (combined lateral magnification of the lens arranged on the image side of the lens group moved in the direction perpendicular to the optical axis) = 1.22
(1-βp) × βr = 0.17

(Numerical values related to conditional expression (9))
R21 (radius of curvature of the most object side surface of the negative lens L ₂₂₁₎ = 38.5730
R22 (radius of curvature of the most image side surface of the negative lens L ₂₂₁₎ = 12.3652
(R21 + R22) / (R21-R22) = 1.94

  FIG. 4 is a diagram illustrating various aberrations of the inner focus lens according to Example 2. In the figure, the curve represents the aberration of the wavelength corresponding to the e-line (λ = 546.074 nm). Further, S and M in the astigmatism diagram represent aberrations with respect to the sagittal image surface and the meridional image surface, respectively.

FIG. 5 is a cross-sectional view along the optical axis showing the configuration of the inner focus lens according to the third embodiment. FIG. 5 shows an infinite object focusing state. The inner focus type lens includes a first lens group G ₃₁ having a positive refractive power, a second lens group G ₃₂ having a negative refractive power, and a third lens having a negative refractive power in order from an object side (not shown). a lens group G _33, is formed are disposed.

The first lens group G ₃₁ includes a positive lens L ₃₁₁ , an aperture stop S that defines a predetermined aperture, a negative lens L _312, and a positive lens L _{313 in} order from the object side. Aspherical surfaces are formed on both surfaces of the positive lens _L313 .

The second lens group G ₃₂ is constituted by a negative lens L _321. Aspherical surfaces are formed on both surfaces of the negative lens _L321 . The second lens group G ₃₂ is, by moving from the object side to the image side along the optical axis to perform focusing from infinity in-focus state to a closest distance object in-focus state.

The third lens group G ₃₃ includes a positive lens L ₃₃₁ (front sub-lens group) and a negative lens L ₃₃₂ (rear sub-lens group) arranged in order from the object side. Aspherical surfaces are formed on both surfaces of the positive lens _L331 . In addition, an air gap is formed between the positive lens L ₃₃₁ and the negative lens L ₃₃₂ .

In the inner focus lens according to Example 3, the positive lens L ₃₁₃ included in the first lens group G ₃₁ or the positive lens L ₃₃₁ included in the third lens group G ₃₃ is moved in the direction perpendicular to the optical axis. To correct the image stabilization.

  Various numerical data relating to the inner focus lens according to Example 3 will be described below.

(Lens data)
r ₁ = 16.4363
d ₁ = 5.5000 ne ₁ = 1.49845 νe ₁ = 81.21
r ₂ = -300.0000
d ₂ = 0.5000
r ₃ = ∞ (aperture stop)
d ₃ = 1.8212
r ₄ = -44.7468
d ₄ = 0.7000 ne ₂ = 1.72310 νe ₂ = 29.27
r ₅ = 373.5699
d ₅ = 0.8417
r ₆ = 20.8910 (Aspherical surface)
d ₆ = 3.3714 ne ₃ = 1.49856 νe ₃ = 81.16
r ₇ = -33.7365 (aspherical surface)
d ₇ = D (7) (variable)
r ₈ = 90.3752 (aspherical surface)
d ₈ = 0.6500 ne ₄ = 1.58547 νe ₄ = 59.22
r ₉ = 11.0161 (aspherical surface)
d ₉ = D (9) (variable)
r ₁₀ = -23.8098 (aspherical surface)
d ₁₀ = 1.3706 ne ₅ = 1.82917 νe ₅ = 23.86
r ₁₁ = -18.3476 (aspherical surface)
d ₁₁ = 7.8919
r ₁₂ = -13.3351
d ₁₂ = 0.7000 ne ₆ = 1.49845 νe ₆ = 81.21
r ₁₃ = -22.5577
d ₁₃ = Bf

Conical coefficient (k) and aspheric coefficient (A ₄ , A ₆ , A ₈ , A ₁₀ )
(Sixth surface)
k = 0,
A ₄ = -6.66384 × 10 ⁻⁵ , A ₆ = −3.555330 × 10 ⁻⁷ ,
A ₈ = 6.24915 × 10 ^-10 , A ₁₀ = -8.69024 × 10 ^-12
(Seventh side)
k = 0,
A ₄ = 4.36278 × 10 ^-6 , A ₆ = -1.41704 × 10 ^-7 ,
A ₈ = -1.53397 × 10 ⁻¹⁰ , A ₁₀ = −3.28298 × 10 ⁻¹²
(8th page)
k = 0,
A ₄ = -1.17365 × 10 ⁻⁵ , A ₆ = −9.52960 × 10 ⁻⁸ ,
A ₈ = 5.84886 × 10 ^-10 , A ₁₀ = -3.14094 × 10 ^-12
(9th page)
k = 0,
A ₄ = -9.90628 × 10 ⁻⁶ , A ₆ = −6.68574 × 10 ⁻⁷ ,
A ₈ = 8.71141 × 10 ^-9 , A ₁₀ = -6.97618 × 10 ^-11
(Tenth aspect)
k = 0,
A ₄ = 8.77623 × 10 ^-5 , A ₆ = -4.76558 × 10 ^-7 ,
A ₈ = 1.66193 × 10 ^-8 , A ₁₀ = -8.96128 × 10 ^-11
(11th page)
k = 0,
A ₄ = 5.77887 × 10 ⁻⁵ , A ₆ = −5.330380 × 10 ⁻⁷ ,
A ₈ = 1.24226 × 10 ⁻⁸ , A ₁₀ = −7.91033 × 10 ⁻¹¹

(Numeric data for each in-focus state)
Infinite distance Closest distance (object distance 300mm)
D (7) 1.2117 3.0915
D (9) 6.4767 4.5969
f (focal length of the entire optical system) 58.5031 46.1351
Fno. (F number) 2.8840 3.0166
ω (half angle of view) 18.4621 17.3034
Y (image height) 21.63 21.63
Bf (Back focus) 20.1130 20.1130

(Numerical values related to conditional expression (1))
R1 (the radius of curvature of the object side air interface of the negative lens L ₃₃₂₎ = - 13.3351
R2 (the radius of curvature of the image side air interface of the negative lens L ₃₃₂₎ = - 22.5577
(R1 + R2) / (R1-R2) =-3.89

(Numerical value related to conditional expression (2))
νen (Abbe number with respect to the e-line of the negative lens L ₃₃₂ ) = 81.21

(Numerical values related to conditional expression (3))
f1 (the focal length of the first lens group G ₃₁ in the infinite object in-focus state) = 21.4980
f1 / f = 0.37

(Numerical values related to conditional expression (4))
f3 (the focal length of the third lens group G ₃₃ in the infinite object in-focus state) = - 400.0000
f3 / f = -6.84

(Numerical values related to conditional expression (5))
Betainf (paraxial magnification of the second lens group G ₃₂ in the infinite object in-focus state) = 2.73
β mod (paraxial magnification of the second lens group G _{32 in} the closest object focusing state) = 2.65
βinf / βmod = 1.03

(Numerical values related to conditional expression (6))
L1s (axial distance from the most object side surface to the aperture stop S in the first lens group G ₃₁₎ = 6.0000
L (total length of optical system) = 51.1482
L1s / L = 0.12

(Numerical values related to conditional expression (7))
f2 (the focal length of the second lens group G ₃₂ in the infinite object in-focus state) = - 21.4928
f2 / f = -0.37

(Numerical value related to conditional expression (8))
When the lens group to be moved (anti-vibration group) is the positive lens L ₃₁₃ of the first lens group G ₃₁ βp (lateral magnification of the lens group moved in the direction perpendicular to the optical axis) = 0.37
βr (combined lateral magnification of the lens arranged on the image side of the lens group moved in the direction perpendicular to the optical axis) = 2.72
(1-βp) × βr = 1.72
When the lens group to be moved (anti-vibration group) is the positive lens L ₃₃₁ of the third lens group G ₃₃ βp (lateral magnification of the lens group moved in the direction perpendicular to the optical axis) = 0.76
βr (combined lateral magnification of the lens arranged on the image side of the lens group moved in the direction perpendicular to the optical axis) = 1.32
(1-βp) × βr = 0.32

(Numerical values related to conditional expression (9))
R21 (radius of curvature of the most object side surface of the negative lens L ₃₂₁₎ = 90.3752
R22 (radius of curvature of the most image side surface of the negative lens L ₃₂₁₎ = 11.0161
(R21 + R22) / (R21-R22) = 1.28

  FIG. 6 is a diagram illustrating various aberrations of the inner focus lens according to Example 3. In the figure, the curve represents the aberration of the wavelength corresponding to the e-line (λ = 546.074 nm). Further, S and M in the astigmatism diagram represent aberrations with respect to the sagittal image surface and the meridional image surface, respectively.

In the numerical data in each of the above embodiments, r ₁ , r ₂ ,... Are the curvature radii of the respective lenses and diaphragm surfaces, and d ₁ , d ₂ ,. thickness or their surface separations, ne _1, ne _2, the refractive index with respect to ... the e-line of each lens _{(λ = 546.074nm), νe 1} , νe 2, ···· are each lens e The Abbe number for the line (λ = 587.56 nm) is shown. The unit of length is all “mm”, and the unit of angle is “°”.

In addition, each of the above aspheric shapes has a depth of the aspheric surface Z, a curvature c (1 / r), a height from the optical axis h, a cone coefficient k, 4th order, 6th order, 8th order, 10th order. When the following aspheric coefficients are A ₄ , A ₆ , A ₈ , and A ₁₀ , respectively, and the light traveling direction is positive, the following aspheric coefficients are expressed by the following equations.

  In each of the above embodiments, an example of an inner focus type lens having a focal length from a wide angle to a standard angle of view in terms of a 35 mm film camera is shown. The inner focus type lens in each of the above embodiments can perform high-speed autofocus processing that is indispensable for moving image shooting by reducing the size and weight of the focus group. Moreover, since the movement amount of the vibration proof group at the time of vibration proof correction can be suppressed, the expansion of the optical system aperture can be suppressed. In particular, by satisfying the above conditional expressions, it is possible to realize a small, wide-angle inner focus type lens suitable for moving image shooting and having high imaging performance.

  As described above, the inner focus type lens according to the present invention is useful for a small-sized imaging device such as a photographic camera or a video camera, and is particularly suitable for an imaging device for moving image shooting.

G ₁₁ , G ₂₁ , G ₃₁ 1st lens group G ₁₂ , G ₂₂ , G ₃₂ 2nd lens group G ₁₃ , G ₂₃ , G ₃₃ 3rd lens group L ₁₁₁ Lenses having no refractive power L ₁₁₂ , L ₁₁₄ , L ₁₃₁ , L ₂₁₁ , L ₂₁₂ , L ₂₁₄ , L ₂₃₁ , L ₃₁₁ , L ₃₁₃ , L ₃₃₁ positive lenses L ₁₁₃ , L ₁₂₁ , L ₁₃₂ , L ₂₁₃ , L ₂₂₁ , L ₂₃₂ , L ₃₁₂ , L ₃₂₁ , L ₃₃₂ Negative lens S Aperture stop

Claims (10)

A first lens group having a positive refractive power, a second lens group having a negative refractive power, and a third lens group having a negative refractive power, which are arranged in order from the object side, and An inner focus type lens that performs focusing from an infinite object focusing state to a closest object focusing state by moving a lens group along an optical axis,
A single lens component having negative refractive power is disposed on the most image side of the third lens group,
An inner focus type lens satisfying the following conditional expression:
(1) (R1 + R2) / (R1-R2) ≦ 0.0
Here, R1 represents the radius of curvature of the object side air boundary surface of the single lens component having the negative refractive power, and R2 represents the radius of curvature of the image side air boundary surface of the single lens component having the negative refractive power. The single lens component having negative refractive power arranged on the most image side of the third lens group is composed of a single glass material,
The inner focus type lens according to claim 1, which satisfies the following conditional expression.
(2) 30 ≦ νen
Here, νen represents the Abbe number with respect to the e-line of a single lens component having a negative refractive power disposed on the most image side of the third lens group. The inner focus lens according to claim 1, wherein the following conditional expression is satisfied.
(3) 0.18 ≦ f1 / f ≦ 0.99
Here, f1 represents the focal length of the first lens group in the infinite object focusing state, and f represents the focal length of the entire optical system in the infinite object focusing state. The inner focus type lens according to claim 1, wherein the following conditional expression is satisfied.
(4) −29.0 ≦ f3 / f ≦ −5.4
Here, f3 represents the focal length of the third lens group in the infinite object focusing state, and f represents the focal length of the entire optical system in the infinite object focusing state. 5. The inner focus lens according to claim 1, wherein the following conditional expression is satisfied.
(5) 0.51 ≦ βinf / βmod ≦ 2.07
Where βinf is the paraxial magnification of the second lens group in the infinite object focusing state, and βmod is the paraxial magnification of the second lens group in the closest object focusing state. The third lens group includes a front sub lens group having a positive refractive power and a rear sub lens group having a negative refractive power, which are arranged in order from the object side,
6. The widest axial air space in the third lens group is formed between the front sub lens group and the rear sub lens group. The inner focus lens described in 1. The inner focus type lens according to claim 1, wherein the following conditional expression is satisfied.
(6) 0.01 ≦ L1s / L ≦ 0.53
Here, L1s indicates the axial distance from the most object side surface of the first lens group to the aperture stop, and L indicates the total length of the optical system (the air-converted optical path length from the apex of the lens surface on the most object side to the imaging surface).   The inner focus lens according to any one of claims 1 to 7, wherein the second lens group includes a single lens component having a negative refractive power. The inner focus type lens according to claim 1, wherein the following conditional expression is satisfied.
(7) −2.12 ≦ f2 / f ≦ −0.18
Here, f2 represents the focal length of the second lens group in the infinite object focusing state, and f represents the focal length of the entire optical system in the infinite object focusing state. The image is shifted by moving a lens group composed of lenses other than the lens arranged closest to the object side in the direction perpendicular to the optical axis,
The inner focus type lens according to claim 1, wherein the following conditional expression is satisfied.
(8) 0.15 ≦ (1-βp) × βr ≦ 4.50
Here, βp represents the lateral magnification of the lens group moved in the direction perpendicular to the optical axis, and βr represents the combined lateral magnification of the lens disposed on the image side of the lens group moved in the direction perpendicular to the optical axis.

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