JP2016188969A - Inner focusing lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact inner focusing lens having a compact light-weight focusing group, a wide angle focal length and high imaging performance.SOLUTION: The inner focusing lens has, sequentially from the object side, a first lens group Ghaving a positive refractive power, a second lens group Ghaving a negative refractive power, and a third lens group Ghaving a negative refractive power. The first lens group Ghas negative meniscus lenses L, Ldisposed closest on the object side. The second lens group Gis moved along the optical axis, thereby focusing from a focus state for an object at infinity to a focus state for the minimum object distance. The inner focusing lens satisfies predetermined conditions and thereby can realize a compact inner focusing lens having high imaging performance at wide angles, suitable for compact cameras having a function of capturing video.SELECTED DRAWING: Figure 1

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 addition, when the positive lens group is disposed on the most image side of the optical system, the refractive power of the focus group must be increased to some extent, so that aberration fluctuations and zooming effects due to wobbling during focusing tend to occur. In order to suppress aberration fluctuations and zooming effects due to wobbling during focusing, it is more preferable to dispose a negative lens group on the most image side of the optical system.

  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 includes, in order from the object side, 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. A lens group is arranged, and the second lens group is moved to perform focusing. This inner focus lens has a medium telephoto focal length in terms of a 35 mm film camera, and has a small and light focus group inside.

  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. In addition, with recent advances and improvements in software and camera systems, it has become possible to correct distortion by image processing even if the distortion aberration is large to a certain extent.

  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 arranged on the most image side of the optical system. Although suitable for realization, the aperture of the third lens group (most image side lens) is not sufficiently small. For this reason, it is difficult to apply to a camera in which the optical system has been downsized in the aperture direction, such as a mirrorless single-lens camera that has been widely spread in recent years.

  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.

  The present invention provides a small inner focus lens that has a small and light focus group, a wide angle focal length, and high imaging performance in order to eliminate the above-described problems caused by the prior art. The purpose is to do.

In order to solve the above-described problems and achieve the object, an inner focus type lens according to the present invention includes a first lens group having a positive refractive power and a first lens group having a negative refractive power arranged in order from the object side. And a third lens group having a negative refractive power. The first lens group includes at least one negative meniscus lens closest to the object side, and the most image side of the third lens group. Is arranged with a single lens component having a negative refractive power, and the distance between the first lens group and the second lens group is increased while the first lens group and the third lens group are fixed, By moving the second lens group from the object side to the image side along the optical axis so as to reduce the distance between the second lens group and the third lens group, the closest distance from the infinite object focus state Four until the object is in focus Perform single, characterized by satisfying the conditional expressions below.
(1) 0 ≦ (R1 + R2) / (R1−R2)
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 present invention, it is possible to realize a small inner focus lens having a small and light focus group, a wide-angle focal length, and high imaging performance. In particular, by satisfying conditional expression (1), it is possible to reduce the aperture of the third lens group (most image-side lens) and to correct off-axis coma favorably.

Furthermore, the inner focus type lens according to the present invention is the above-described invention, wherein the single lens component having a negative refractive power disposed on the most image side of the third lens group is formed of a single glass material, The following conditional expression is satisfied.
(2) 30 ≦ νdn
Here, νdn indicates the Abbe number with respect to the d-line of the single lens component having the negative refractive power.

  According to the present invention, the single lens component having negative refractive power included in the third lens group can be easily reduced in size and weight, and the lateral chromatic aberration can be favorably corrected.

Furthermore, the inner focus type lens according to the present invention is characterized in that, in the above invention, the following conditional expression is satisfied.
(3) 0.28 ≦ f1 / f ≦ 1.30
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 present invention, it is possible to realize an inner focus type lens that is smaller and has high imaging performance.

Furthermore, the inner focus type lens according to the present invention is characterized in that, in the above invention, the following conditional expression is satisfied.
(4) f3 / f ≦ −29.1
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 present invention, the overall length of the optical system can be shortened and the imaging performance can be improved.

Furthermore, the inner focus type lens according to the present invention is characterized in that, in the above invention, the following conditional expression is satisfied.
(5) 0.50 ≦ βinf / βmod ≦ 2.02
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 present invention, it is possible to improve the imaging performance by suppressing the angle of view variation due to focusing.

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

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

Furthermore, the inner focus type lens according to the present invention is characterized in that, in the above invention, an aperture stop for defining a predetermined aperture is provided, and the following conditional expression is satisfied.
(6) 0.24 ≦ L1s / L ≦ 0.95
Where L1s is the axial distance from the most object side surface of the first lens group to the aperture stop, and L is the axial distance from the apex of the lens surface on the most object side to the imaging surface in the optical system (total length of the optical system). Indicates.

  According to 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.

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

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

Furthermore, the inner focus type lens according to the present invention is characterized in that, in the above invention, the following conditional expression is satisfied.
(7) −7.46 ≦ f2 / f ≦ −2.11
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 present invention, the overall length of the optical system can be shortened and the imaging performance can be improved.

  According to the present invention, there is an effect that it is possible to provide a small inner focus type lens having a small and light focus group, a wide angle focal length, and a 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; FIG. 6 is a cross-sectional view along the optical axis showing the configuration of an inner focus lens according to Example 4; FIG. 10 is a diagram illustrating all aberrations of the inner focus lens according to Example 4;

  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, the distance between the first lens group and the second lens group is increased while the first lens group and the third lens group are fixed, and the second lens group and the third lens group are The second lens group is moved from the object side to the image side along the optical axis so as to reduce the distance between the infinite object focusing state and the closest object focusing state. Thus, by performing 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 can be 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.

  Further, by disposing at least one negative meniscus lens on the most object side of the first lens group, it is easy to widen the angle of the optical system.

  Furthermore, the third lens group having the negative refractive power closest to the image side can reduce the telephoto ratio (full length / focal length), shorten the back focus, and reduce the size of the optical system. Can be promoted.

  An object of the present invention is to provide a small inner focus type lens having a small and light focus group, a wide-angle focal length, and 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) 0 ≦ (R1 + R2) / (R1−R2)

  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. By satisfying conditional expression (1), high imaging performance can be provided. That is, when the conditional expression (1) is satisfied, in the single lens component, the radius of curvature of the object side surface becomes larger 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) 0.5 ≦ (R1 + R2) / (R1−R2)

Further, when the conditional expression (1a) satisfies the following range, a more preferable effect can be expected.
(1b) 0.7 ≦ (R1 + R2) / (R1−R2) ≦ 100

  Furthermore, in the inner focus 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 formed of a single glass material. If the single lens component in the third lens group is formed of a single glass material, it is easy to reduce the size of the single lens component in the optical axis direction and the radial direction. In addition, the single lens component can be easily reduced in weight.

In the inner focus type lens according to the present invention, it is preferable that the following conditional expression is satisfied when the Abbe number of the single lens component having negative refractive power with respect to the d-line is νdn.
(2) 30 ≦ νdn

  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) 0.28 ≦ f1 / f ≦ 1.30

  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 focal length of the first lens unit becomes appropriate with respect to the focal length of the entire optical system, and the rear lens diameter is reduced and the total length of the optical system is reduced. Image performance can be improved.

  If the lower limit of conditional expression (3) is not reached, not only will the focal length of the first lens group become short and the spherical aberration will be undercorrected, but the paraxial imaging magnification of the subsequent lens group will become large and the rear lens diameter will increase. Increases the size of the optical system, which is not preferable. 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) 0.37 ≦ f1 / f ≦ 0.97

Further, when the conditional expression (3a) satisfies the following range, a more preferable effect can be expected.
(3b) 0.45 ≦ 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) f3 / f ≦ −29.1

  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 upper limit in conditional expression (4) is exceeded, the refractive power of the third lens group will become 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) −12000 ≦ f3 / f ≦ −30.1

Further, when the conditional expression (4a) satisfies the following range, a more preferable effect can be expected.
(4b) −10000 ≦ f3 / f ≦ −31.1

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) 0.50 ≦ βinf / βmod ≦ 2.02

  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

Further, when the conditional expression (5a) satisfies the following range, a more preferable effect can be expected.
(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 on-axis air space 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 for mounting 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.

Furthermore, the inner focus type lens according to the present invention includes an aperture stop that defines a predetermined aperture, the axial distance from the most object side surface of the first lens group to the aperture stop is L1s, and the most object side in the optical system. When the on-axis distance from the lens surface apex to the imaging surface (total length of the optical system) is L, it is preferable that the following conditional expression is satisfied.
(6) 0.24 ≦ L1s / L ≦ 0.95

  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. The aperture stop is preferably disposed in the first lens group.

In addition, when the conditional expression (6) satisfies the following range, a more preferable effect can be expected.
(6a) 0.32 ≦ L1s / L ≦ 0.71

Further, when the conditional expression (6a) satisfies the following range, a more preferable effect can be expected.
(6b) 0.40 ≦ L1s / L ≦ 0.60

  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. The meaning of the single lens component is as described above.

  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) −7.46 ≦ f2 / f ≦ −2.11

  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) −5.60 ≦ f2 / f ≦ −1.80

Further, when the conditional expression (7a) satisfies the following range, a more preferable effect can be expected.
(7b) −5.00 ≦ f2 / f ≦ −1.62

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.
(8) 0 ≦ (R21 + R22) / (R21−R22)

  Conditional expression (8) 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 (8), 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, the said conditional expression (8) can anticipate a more preferable effect, if the range shown next is satisfied.
(8a) 1 ≦ (R21 + R22) / (R21−R22)

Further, when the conditional expression (8a) satisfies the following range, a more preferable effect can be expected.
(8b) 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.

  As described above, according to the present invention, it is possible to realize a small inner focus lens having a small and light focus group, a wide-angle focal length, and high imaging performance. . In particular, by satisfying the above conditional expressions, it is possible to realize an inner focus lens having a smaller size and higher imaging performance, which is suitable for moving image shooting.

  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. Between the third lens group G ₁₃ and the image plane IMG, a cover glass CG is disposed.

The first lens group G ₁₁ includes, in order from the object side, a negative meniscus lens L ₁₁₁ , a negative meniscus lens L ₁₁₂ , a negative lens L ₁₁₃ , a positive lens L ₁₁₄ , a negative lens L _115, and a positive lens L ₁₁₆ . An aperture stop STP that defines a predetermined aperture and a positive lens L ₁₁₇ are arranged. On both surfaces of the negative lens L _113, aspheric surface is formed. The negative lens L ₁₁₅ and the positive lens L ₁₁₆ are cemented. Aspherical surfaces are formed on both surfaces of the positive lens _L117 .

The second lens group G ₁₂ includes, formed by a negative lens L _121. On both surfaces of the negative lens L _121, aspheric surface is formed.

The third lens group G ₁₃ includes, in order from the object side, a front sub lens group G _13F having a positive refractive power and a rear sub lens group G _13R having a negative refractive power. Between the front sub-lens group G _13F and the rear sub-lens group G _13R , the widest axial air gap is formed in the third lens group G ₁₃ .

The front sub lens group G _13F is configured by arranging a positive lens L ₁₃₁ and a positive lens L _{132 in} order from the object side. The rear sub lens group G _13R includes a negative lens L ₁₃₃ . The negative lens L ₁₃₃ is formed of a single glass material. Aspherical surfaces are formed on both surfaces of the negative lens _L133 .

In this inner focus type lens, the distance between the first lens group G ₁₁ and the second lens group G ₁₂ is increased while the first lens group G ₁₁ and the third lens group G ₁₃ are fixed, and the second lens group G ₁₂ and the interval between the third lens group G ₁₃ is reduced, most from infinity in-focus state by making the second lens group G ₁₂ is moved from the object side along the optical axis to the image plane IMG side Focusing is performed until the object is in focus at close range.

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

(Lens data)
r ₁ = 28.832
d ₁ = 2.000 nd ₁ = 1.5935 νd ₁ = 67.00
r ₂ = 15.623
d ₂ = 6.886
r ₃ = 29.397
d ₃ = 1.500 nd ₂ = 1.4970 νd ₂ = 81.61
r ₄ = 13.122
d ₄ = 5.883
r ₅ = 52.568 (aspherical surface)
d ₅ = 1.300 nd ₃ = 1.5920 νd ₃ = 67.02
r ₆ = 12.910 (aspherical surface)
d ₆ = 3.068
r ₇ = 30.333
d ₇ = 2.265 nd ₄ = 1.8810 νd ₄ = 40.14
r ₈ = 141.737
d ₈ = 12.099
r ₉ = 24.676
d ₉ = 1.000 nd ₅ = 1.8810 νd ₅ = 40.14
r ₁₀ = 13.601
d ₁₀ = 5.292 nd ₆ = 1.4875 νd ₆ = 70.44
r ₁₁ = -35.502
d ₁₁ = 1.300
r ₁₂ = ∞ (aperture stop)
d ₁₂ = 2.425
r ₁₃ = 30.850 (aspherical surface)
d ₁₃ = 4.386 nd ₇ = 1.4971 νd ₇ = 81.56
r ₁₄ = -18.338 (aspherical surface)
d ₁₄ = D (14) (variable)
r ₁₅ = 45.781 (aspherical surface)
d ₁₅ = 0.800 nd ₈ = 1.7290 νd ₈ = 54.04
r ₁₆ = 19.193 (aspherical surface)
d ₁₆ = D (16) (variable)
r ₁₇ = -68.737
d ₁₇ = 2.535 nd ₉ = 1.4970 νd ₉ = 81.61
r ₁₈ = -25.555
d ₁₈ = 0.100
r ₁₉ = -329.577
d ₁₉ = 4.036 nd ₁₀ = 1.4970 νd ₁₀ = 81.61
r ₂₀ = -23.042
d ₂₀ = 0.329
r ₂₁ = -400.000 (aspherical surface)
d ₂₁ = 1.200 nd ₁₁ = 1.8820 νd ₁₁ = 37.22
r ₂₂ = 26.785 (aspherical surface)
d ₂₂ = 25.606
r ₂₃ = ∞
d ₂₃ = 2.500 nd ₁₂ = 1.5168 νd ₁₂ = 64.20
r ₂₄ = ∞
d ₂₄ = 1.000
r ₂₅ = ∞ (imaging plane)

Conical coefficient (k) and aspheric coefficient (A ₄ , A ₆ , A ₈ , A ₁₀ )
(5th page)
k = 0,
A ₄ = −2.6625 × 10 ⁻⁵ , A ₆ = 3.0031 × 10 ⁻⁷ ,
A ₈ = -1.7989 × 10 ⁻⁹ , A ₁₀ = 5.7847 × 10 ⁻¹²
(Sixth surface)
k = 0,
A ₄ = -6.8334 × 10 ^-5 , A ₆ = 8.4364 × 10 ^-9 ,
A ₈ = -1.2228 × 10 ^-9 , A ₁₀ = -9.8374 × 10 ^-12
(13th page)
k = 0,
A ₄ = -2.2269 × 10 ^-5 , A ₆ = 1.1253 × 10 ^-9 ,
A ₈ = -1.0562 × 10 ^-9 , A ₁₀ = -3.1969 × 10 ^-12
(14th page)
k = 0,
A ₄ = 5.1791 × 10 ⁻⁵ , A ₆ = −5.2286 × 10 ⁻⁷ ,
A ₈ = 4.00083 × 10 ⁻⁹ , A ₁₀ = 2.3692 × 10 ⁻¹¹
(15th page)
k = 0,
A ₄ = 2.0348 × 10 ⁻⁵ , A ₆ = −1.1141 × 10 ⁻⁶ ,
A ₈ = 1.4175 × 10 ⁻⁸ , A ₁₀ = −5.7786 × 10 ⁻¹¹
(16th surface)
k = 0,
A ₄ = 2.1580 × 10 ⁻⁵ , A ₆ = −8.9505 × 10 ⁻⁷ ,
A ₈ = 1.2780 × 10 ⁻⁸ , A ₁₀ = −5.7413 × 10 ⁻¹¹
(21st surface)
k = 0,
A ₄ = -2.4151 × 10 ^-5 , A ₆ = -1.3394 × 10 ^-7 ,
A ₈ = 2.2182 × 10 ⁻⁹ , A ₁₀ = −7.5852 × 10 ⁻¹²
(Twenty-second surface)
k = 0,
A ₄ = -3.5206 × 10 ^-6 , A ₆ = -1.2925 × 10 ^-7 ,
A ₈ = 2.2655 × 10 ⁻⁹ , A ₁₀ = −8.5817 × 10 ⁻¹²

(Numeric data for each in-focus state)
Infinity Closest distance (object distance 158.000mm)
D (14) 1.472 2.318
D (16) 6.519 5.674
f (focal length of the entire optical system) 18.54 17.88
FNO (F number) 2.88 2.92
ω (half angle of view) 50.29 49.76
f1 (the focal length of the first lens group G ₁₁₎ 10.28 10.28
f2 (the focal length of the second lens group G ₁₂₎ -45.92 -45.92
f3 (the focal length of the third lens group G ₁₃₎ -722.75 -722.75
BF (back focus) 29.106 29.106

(Numerical values related to conditional expression (1))
R1 (curvature radius of object side air interface of negative lens L ₁₃₃ ) = − 400.000
R2 (the radius of curvature of the image side air boundary surface of the negative lens L ₁₃₃ ) = 26.785
(R1 + R2) / (R1-R2) = 0.87

(Numerical value related to conditional expression (2))
νdn (Abbe number of the negative lens L ₁₃₃ with respect to the d-line) = 37.22

(Numerical values related to conditional expression (3))
f1 / f = 0.55

(Numerical values related to conditional expression (4))
f3 / f = -38.97

(Numerical values related to conditional expression (5))
Betainf (paraxial magnification of the second lens group G ₁₂ in the infinite object in-focus state) = 1.83
β mod (paraxial magnification of the second lens group G _{12 when} the object is in closest focus) = 1.81
βinf / βmod = 1.01

(Numerical values related to conditional expression (6))
L1s (axial distance from the most object side surface to the aperture stop STP of the first lens group G ₁₁₎ = 42.593
L (axial distance from the lens surface vertex of the most object side to the imaging surface IMG of the first lens group G ₁₁ (overall length of the optical system)) = 95.501
L1s / L = 0.45

(Numerical values related to conditional expression (7))
f2 / f = -2.48

(Numerical value related to conditional expression (8))
R21 (radius of curvature of the most object side surface of the negative lens L ₁₂₁₎ = 45.781
R22 (radius of curvature of the most image side surface of the negative lens L ₁₂₁₎ = 19.193
(R21 + R22) / (R21-R22) = 2.44

  FIG. 2 is a diagram illustrating various aberrations of the inner focus lens according to Example 1. In the spherical aberration diagram, the vertical axis represents the F number (indicated by FNO in the figure), the solid line is the d line (λ = 587.56 nm), the short broken line is the g line (λ = 435.84 nm), and the long broken line is the C line The characteristic of the wavelength corresponding to the line (λ = 656.28 nm) is shown. In the graph showing astigmatism, the vertical axis represents the image height (indicated by Y in the figure) and represents the wavelength characteristic corresponding to the d-line (λ = 587.56 nm). In the graph showing astigmatism, the solid line indicates the characteristics of the sagittal plane (indicated by S in the figure), and the broken line indicates the characteristics of the meridional plane (indicated by M in the figure). In the distortion diagram, the vertical axis represents the image height (indicated by Y in the figure) and represents the wavelength characteristic corresponding to the d-line (λ = 587.56 nm).

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. Between the third lens group G ₂₃ and the image plane IMG, a cover glass CG is disposed.

The first lens group G ₂₁ includes, in order from the object side, a negative meniscus lens L ₂₁₁ , a negative meniscus lens L ₂₁₂ , a negative lens L ₂₁₃ , a positive lens L ₂₁₄ , a negative lens L _215, and a positive lens L ₂₁₆ . An aperture stop STP that defines a predetermined aperture and a positive lens L ₂₁₇ are arranged. Aspherical surfaces are formed on both surfaces of the negative lens _L213 . The negative lens L ₂₁₅ and the positive lens L ₂₁₆ are cemented. Aspherical surfaces are formed on both surfaces of the positive lens _L217 .

The second lens group G ₂₂ includes, formed by a negative lens L _221. An aspheric surface is formed on both surfaces of the negative lens L ₂₂₁ .

The third lens group G ₂₃ is constituted in order from the object side, a front sub-lens group G _23F having a positive refractive power, and a rear sub-lens group G _23R having a negative refractive power, is the arrangement. Between the front sub-lens group G _23F and the rear sub-lens group G _23R , the widest axial air space in the third lens group G ₂₃ is formed.

The front sub lens group G _23F is configured by arranging a positive lens L ₂₃₁ and a positive lens L _{232 in} order from the object side. The rear sub lens group G _23R includes a negative lens L ₂₃₃ . The negative lens L ₂₃₃ is formed of a single glass material. Aspherical surfaces are formed on both surfaces of the negative lens _L233 .

In this inner focus type lens, the distance between the first lens group G ₂₁ and the second lens group G ₂₂ is increased while the first lens group G ₂₁ and the third lens group G ₂₃ are fixed, and the second lens group G The second lens group G ₂₂ is moved from the object side to the image plane IMG side along the optical axis so that the distance between the lens ₂₂ and the third lens group G ₂₃ is reduced. Focusing is performed until the object is in focus at close range.

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

(Lens data)
r ₁ = 30.152
d ₁ = 2.000 nd ₁ = 1.5935 νd ₁ = 67.00
r ₂ = 16.214
d ₂ = 6.369
r ₃ = 31.366
d ₃ = 1.500 nd ₂ = 1.4970 νd ₂ = 81.61
r ₄ = 13.499
d ₄ = 5.658
r ₅ = 51.837 (aspherical surface)
d ₅ = 1.300 nd ₃ = 1.5920 νd ₃ = 67.02
r ₆ = 13.285 (aspherical surface)
d ₆ = 2.866
r ₇ = 27.620
d ₇ = 2.238 nd ₄ = 1.8810 νd ₄ = 40.14
r ₈ = 87.188
d ₈ = 12.690
r ₉ = 23.272
d ₉ = 1.000 nd ₅ = 1.8810 νd ₅ = 40.14
r ₁₀ = 13.324
d ₁₀ = 5.334 nd ₆ = 1.4875 νd ₆ = 70.44
r ₁₁ = -43.127
d ₁₁ = 1.629
r ₁₂ = ∞ (aperture stop)
d ₁₂ = 1.822
r ₁₃ = 30.203 (aspherical surface)
d ₁₃ = 4.424 nd ₇ = 1.4971 νd ₇ = 81.56
r ₁₄ = -18.833 (aspherical surface)
d ₁₄ = D (14) (variable)
r ₁₅ = 42.496 (aspherical surface)
d ₁₅ = 0.800 nd ₈ = 1.7290 νd ₈ = 54.04
r ₁₆ = 18.812 (aspherical surface)
d ₁₆ = D (16) (variable)
r ₁₇ = 647.460
d ₁₇ = 3.783 nd ₉ = 1.4970 νd ₉ = 81.61
r ₁₈ = -19.801
d ₁₈ = 0.100
r ₁₉ = -48.734
d ₁₉ = 2.492 nd ₁₀ = 1.4970 νd ₁₀ = 81.61
r ₂₀ = -33.384
d ₂₀ = 0.761
r ₂₁ = -400.000 (aspherical surface)
d ₂₁ = 1.200 nd ₁₁ = 1.8820 νd ₁₁ = 37.22
r ₂₂ = 27.667 (aspherical surface)
d ₂₂ = 22.428
r ₂₃ = ∞
d ₂₃ = 2.500 nd ₁₂ = 1.5168 νd ₁₂ = 64.20
r ₂₄ = ∞
d ₂₄ = 1.000
r ₂₅ = ∞ (imaging plane)

Conical coefficient (k) and aspheric coefficient (A ₄ , A ₆ , A ₈ , A ₁₀ )
(5th page)
k = 0,
A ₄ = -2.7090 × 10 ^-5 , A ₆ = 2.6283 × 10 ^-7 ,
A ₈ = -1.4454 × 10 ^-9 , A ₁₀ = 4.3803 × 10 ^-12
(Sixth surface)
k = 0,
A ₄ = -6.1483 × 10 ⁻⁵ , A ₆ = 4.0703 × 10 ⁻⁸ ,
A ₈ = -1.1388 × 10 ^-9 , A ₁₀ = -6.0150 × 10 ^-12
(13th page)
k = 0,
A ₄ = -2.2964 × 10 ^-5 , A ₆ = -6.1034 × 10 ^-9 ,
A ₈ = −1.0258 × 10 ⁻⁹ , A ₁₀ = 2.5147 × 10 ⁻¹²
(14th page)
k = 0,
A ₄ = 4.6889 × 10 ⁻⁵ , A ₆ = −4.5934 × 10 ⁻⁷ ,
A ₈ = 3.4940 × 10 ⁻⁹ , A ₁₀ = −1.7504 × 10 ⁻¹¹
(15th page)
k = 0,
A ₄ = 2.0032 × 10 ⁻⁵ , A ₆ = −1.0580 × 10 ⁻⁶ ,
A ₈ = 1.3913 × 10 ⁻⁸ , A ₁₀ = −6.6138 × 10 ⁻¹¹
(16th surface)
k = 0,
A ₄ = 2.3359 × 10 ⁻⁵ , A ₆ = −8.33928 × 10 ⁻⁷ ,
A ₈ = 1.2186 × 10 ⁻⁸ , A ₁₀ = −6.4391 × 10 ⁻¹¹
(21st surface)
k = 0,
A ₄ = -2.3499 × 10 ^-5 , A ₆ = -1.2412 × 10 ^-7 ,
A ₈ = 2.2965 × 10 ^-9 , A ₁₀ = -8.5091 × 10 ^-12
(Twenty-second surface)
k = 0,
A ₄ = -2.5375 × 10 ^-6 , A ₆ = -1.1587 × 10 ^-7 ,
A ₈ = 2.1605 × 10 ⁻⁹ , A ₁₀ = −8.6835 × 10 ⁻¹²

(Numeric data for each in-focus state)
Infinity Closest distance (object distance 158.000mm)
D (14) 1.480 2.405
D (16) 6.626 5.702
f (focal length of the entire optical system) 19.41 18.66
FNO (F number) 2.88 2.92
ω (half angle of view) 49.11 48.48
f1 (the focal length of the first lens group G ₂₁₎ 10.82 10.82
f2 (the focal length of the second lens group G ₂₂₎ -46.97 -46.97
f3 (the focal length of the third lens group G ₂₃₎ -626.90 -626.90
BF (Back focus) 25.928 25.928

(Numerical values related to conditional expression (1))
R1 (the radius of curvature of the object side air interface of the negative lens L ₂₃₃₎ = - 400.000
R2 (the radius of curvature of the image side air interface of the negative lens L ₂₃₃₎ = 27.667
(R1 + R2) / (R1-R2) = 0.87

(Numerical value related to conditional expression (2))
νdn (Abbe number with respect to d-line of negative lens L ₂₃₃ ) = 37.22

(Numerical values related to conditional expression (3))
f1 / f = 0.56

(Numerical values related to conditional expression (4))
f3 / f = -32.30

(Numerical values related to conditional expression (5))
βinf (paraxial magnification of the second lens group G _{22 in} an infinite object focused state) = 1.85
β mod (paraxial magnification of the second lens group G _{22 in} the closest object focusing state) = 1.83
βinf / βmod = 1.01

(Numerical values related to conditional expression (6))
L1s (axial distance from the most object side surface to the aperture stop STP of the first lens group G ₂₁₎ = 42.584
L (on-axis distance from the lens surface vertex of the first lens group G _{21 on} the most object side to the imaging surface IMG (total length of the optical system)) = 92.000
L1s / L = 0.46

(Numerical values related to conditional expression (7))
f2 / f = -2.42

(Numerical value related to conditional expression (8))
R21 (radius of curvature of the most object side surface of the negative lens L ₂₂₁₎ = 42.496
R22 (radius of curvature of the most image side surface of the negative lens L ₂₂₁₎ = 18.812
(R21 + R22) / (R21-R22) = 2.59

  FIG. 4 is a diagram illustrating various aberrations of the inner focus lens according to Example 2. In the spherical aberration diagram, the vertical axis represents the F number (indicated by FNO in the figure), the solid line is the d line (λ = 587.56 nm), the short broken line is the g line (λ = 435.84 nm), and the long broken line is the C line The characteristic of the wavelength corresponding to the line (λ = 656.28 nm) is shown. In the graph showing astigmatism, the vertical axis represents the image height (indicated by Y in the figure) and represents the wavelength characteristic corresponding to the d-line (λ = 587.56 nm). In the graph showing astigmatism, the solid line indicates the characteristics of the sagittal plane (indicated by S in the figure), and the broken line indicates the characteristics of the meridional plane (indicated by M in the figure). In the distortion diagram, the vertical axis represents the image height (indicated by Y in the figure) and represents the wavelength characteristic corresponding to the d-line (λ = 587.56 nm).

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. A cover glass CG is disposed between the third lens group G ₃₃ and the imaging plane IMG.

The first lens group G ₃₁ includes a negative meniscus lens L ₃₁₁ , a negative meniscus lens L ₃₁₂ , a negative lens L ₃₁₃ , a positive lens L ₃₁₄ , a negative lens L _315, and a positive lens L _{316 in} order from the object side. An aperture stop STP that defines a predetermined aperture and a positive lens _L317 are arranged. Aspheric surfaces are formed on both surfaces of the negative lens _L313 . The negative lens L ₃₁₅ and the positive lens L ₃₁₆ are cemented. Aspherical surfaces are formed on both surfaces of the positive lens _L317 .

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 third lens group G ₃₃ includes, in order from the object side, a front sub lens group G _33F having a positive refractive power and a rear sub lens group G _33R having a negative refractive power. Between the front sub lens group G _33F and the rear sub lens group G _33R , the widest axial air space in the third lens group G ₃₃ is formed.

The front sub lens group G _33F includes a positive lens L ₃₃₁ and a positive lens L ₃₃₂ arranged in this order from the object side. The rear sub lens group G _33R includes a negative lens L ₃₃₃ . The negative lens L ₃₃₃ is formed of a single glass material. Aspheric surfaces are formed on both surfaces of the negative lens _L333 .

In this inner focus type lens, while the first lens group G ₃₁ and the third lens group G ₃₃ are fixed, the distance between the first lens group G ₃₁ and the second lens group G ₃₂ is increased, and the second lens group G ₃₂ and the interval between the third lens group G ₃₃ is reduced, from infinity in-focus state by making the second lens group G ₃₂ is moved from the object side along the optical axis to the image plane IMG side uppermost Focusing is performed until the object is in focus at close range.

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

(Lens data)
r ₁ = 29.863
d ₁ = 2.000 nd ₁ = 1.5935 νd ₁ = 67.00
r ₂ = 15.214
d ₂ = 7.108
r ₃ = 31.676
d ₃ = 1.500 nd ₂ = 1.4970 νd ₂ = 81.61
r ₄ = 12.821
d ₄ = 5.662
r ₅ = 56.855 (aspherical surface)
d ₅ = 1.300 nd ₃ = 1.5920 νd ₃ = 67.02
r ₆ = 12.496 (aspherical surface)
d ₆ = 4.710
r ₇ = 25.649
d ₇ = 2.736 nd ₄ = 1.8810 νd ₄ = 40.14
r ₈ = -2872.181
d ₈ = 10.427
r ₉ = 29.340
d ₉ = 1.000 nd ₅ = 1.8810 νd ₅ = 40.14
r ₁₀ = 11.062
d ₁₀ = 5.282 nd ₆ = 1.4875 νd ₆ = 70.44
r ₁₁ = -36.758
d ₁₁ = 1.300
r ₁₂ = ∞ (aperture stop)
d ₁₂ = 3.832
r ₁₃ = 32.994 (aspherical surface)
d ₁₃ = 4.343 nd ₇ = 1.4971 νd ₇ = 81.56
r ₁₄ = -16.586 (aspherical surface)
d ₁₄ = D (14) (variable)
r ₁₅ = 168.747 (aspherical surface)
d ₁₅ = 0.800 nd ₈ = 1.7290 νd ₈ = 54.04
r ₁₆ = 35.344 (aspherical surface)
d ₁₆ = D (16) (variable)
r ₁₇ = -47.172
d ₁₇ = 2.755 nd ₉ = 1.4970 νd ₉ = 81.61
r ₁₈ = -20.329
d ₁₈ = 0.100
r ₁₉ = -45.060
d ₁₉ = 3.412 nd ₁₀ = 1.4970 νd ₁₀ = 81.61
r ₂₀ = -20.831
d ₂₀ = 0.833
r ₂₁ = -400.000 (aspherical surface)
d ₂₁ = 1.200 nd ₁₁ = 1.8820 νd ₁₁ = 37.22
r ₂₂ = 34.153 (aspherical surface)
d ₂₂ = 20.338
r ₂₃ = ∞
d ₂₃ = 2.500 nd ₁₂ = 1.5168 νd ₁₂ = 64.20
r ₂₄ = ∞
d ₂₄ = 1.000
r ₂₅ = ∞ (imaging plane)

Conical coefficient (k) and aspheric coefficient (A ₄ , A ₆ , A ₈ , A ₁₀ )
(5th page)
k = 0,
A ₄ = -2.3716 × 10 ⁻⁵ , A ₆ = 1.7317 × 10 ⁻⁷ ,
A ₈ = −6.4139 × 10 ⁻¹⁰ , A ₁₀ = 1.5464 × 10 ⁻¹²
(Sixth surface)
k = 0,
A ₄ = -8.7141 × 10 ^-5 , A ₆ = -3.1834 × 10 ^-7 ,
A ₈ = 1.5577 × 10 ⁻⁹ , A ₁₀ = −2.7154 × 10 ⁻¹¹
(13th page)
k = 0,
A ₄ = -1.4834 × 10 ⁻⁵ , A ₆ = −1.6560 × 10 ⁻⁷ ,
A ₈ = 1.3132 × 10 ⁻⁹ , A ₁₀ = −1.6004 × 10 ⁻¹¹
(14th page)
k = 0,
A ₄ = 2.5383 × 10 ⁻⁵ , A ₆ = −2.6971 × 10 ⁻⁷ ,
A ₈ = 1.9137 × 10 ^-9 , A ₁₀ = -1.9738 × 10 ^-11
(15th page)
k = 0,
A ₄ = 4.8211 × 10 ⁻⁵ , A ₆ = −8.0172 × 10 ⁻⁷ ,
A ₈ = 1.0635 × 10 ^-8 , A ₁₀ = -4.7053 × 10 ^-11
(16th surface)
k = 0,
A ₄ = 5.9595 × 10 ^-5 , A ₆ = -8.2829 × 10 ^-7 ,
A ₈ = 1.1533 × 10 ⁻⁸ , A ₁₀ = −4.9667 × 10 ⁻¹¹
(21st surface)
k = 0,
A ₄ = -7.9720 × 10 ⁻⁵ , A ₆ = −2.0100 × 10 ⁻⁷ ,
A ₈ = 2.0113 × 10 ^-9 , A ₁₀ = 7.2706 × 10 ^-14
(Twenty-second surface)
k = 0,
A ₄ = -4.3301 × 10 ^-5 , A ₆ = -1.5941 × 10 ^-7 ,
A ₈ = 3.0911 × 10 ⁻⁹ , A ₁₀ = −7.0460 × 10 ⁻¹²

(Numeric data for each in-focus state)
Infinity Closest distance (object distance 158.000mm)
D (14) 1.489 2.539
D (16) 6.373 5.323
f (focal length of the entire optical system) 16.49 16.05
FNO (F number) 2.88 2.91
ω (half angle of view) 53.50 53.14
f1 (the focal length of the first lens group G ₃₁₎ 10.68 10.68
f2 (the focal length of the second lens group G ₃₂₎ -61.48 -61.48
f3 (the focal length of the third lens group G ₃₃₎ -126154 -126154
BF (back focus) 23.838 23.838

(Numerical values related to conditional expression (1))
R1 (the radius of curvature of the object side air interface of the negative lens L ₃₃₃₎ = - 400.000
R2 (the radius of curvature of the image side air interface of the negative lens L ₃₃₃₎ = 34.153
(R1 + R2) / (R1-R2) = 0.84

(Numerical value related to conditional expression (2))
dn (Abbe number at the d-line of the negative lens L ₃₃₃₎ = 37.22

(Numerical values related to conditional expression (3))
f1 / f = 0.65

(Numerical values related to conditional expression (4))
f3 / f = -7652.47

(Numerical values related to conditional expression (5))
Betainf (paraxial magnification of the second lens group G ₃₂ in the infinite object in-focus state) = 1.59
β mod (paraxial magnification of the second lens group G _{32 in} the closest object focusing state) = 1.57
βinf / βmod = 1.01

(Numerical values related to conditional expression (6))
L1s (axial distance from the most object side surface of the first lens group G ₃₁ to the aperture stop STP) = 43.025
L (on-axis distance from the apex of the lens surface on the most object side of the first lens group G ₃₁ to the imaging plane IMG (total length of the optical system)) = 92.000
L1s / L = 0.47

(Numerical values related to conditional expression (7))
f2 / f = -3.73

(Numerical value related to conditional expression (8))
R21 (radius of curvature of the most object side surface of the negative lens L ₃₂₁₎ = 168.747
R22 (radius of curvature of the most image side surface of the negative lens L ₃₂₁₎ = 35.344
(R21 + R22) / (R21-R22) = 1.53

  FIG. 6 is a diagram illustrating various aberrations of the inner focus lens according to Example 3. In the spherical aberration diagram, the vertical axis represents the F number (indicated by FNO in the figure), the solid line is the d line (λ = 587.56 nm), the short broken line is the g line (λ = 435.84 nm), and the long broken line is the C line The characteristic of the wavelength corresponding to the line (λ = 656.28 nm) is shown. In the graph showing astigmatism, the vertical axis represents the image height (indicated by Y in the figure) and represents the wavelength characteristic corresponding to the d-line (λ = 587.56 nm). In the graph showing astigmatism, the solid line indicates the characteristics of the sagittal plane (indicated by S in the figure), and the broken line indicates the characteristics of the meridional plane (indicated by M in the figure). In the distortion diagram, the vertical axis represents the image height (indicated by Y in the figure) and represents the wavelength characteristic corresponding to the d-line (λ = 587.56 nm).

FIG. 7 is a cross-sectional view along the optical axis showing the configuration of the inner focus lens according to the fourth example. FIG. 7 shows an infinite object focusing state. The inner focus type lens includes a first lens group G ₄₁ having a positive refractive power, a second lens group G ₄₂ 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 _43, is formed are disposed. Between the third lens group G ₄₃ and the image plane IMG, a cover glass CG is disposed.

The first lens group G ₄₁ includes, in order from the object side, a negative meniscus lens L ₄₁₁ , a negative meniscus lens L ₄₁₂ , a negative lens L ₄₁₃ , a positive lens L ₄₁₄ , a negative lens L _415, and a positive lens L ₄₁₆ . A positive lens L ₄₁₇ and an aperture stop STP that defines a predetermined aperture are arranged. An aspheric surface is formed on both surfaces of the negative lens L ₄₁₃ . The negative lens L ₄₁₅ and the positive lens L ₄₁₆ are cemented. Aspherical surfaces are formed on both surfaces of the positive lens _L417 .

The second lens group _G42 includes a negative lens _L421 . An aspheric surface is formed on both surfaces of the negative lens _L421 .

The third lens group G ₄₃ includes, in order from the object side, a front sub lens group G _43F having a positive refractive power and a rear sub lens group G _43R having a negative refractive power. Between the front sub-lens group G _43F and the rear sub-lens group G _43R , the widest axial air interval is formed in the third lens group G ₄₃ .

The front sub lens group G _43F includes a positive lens L ₄₃₁ and a positive lens L ₄₃₂ arranged in this order from the object side. The rear sub lens group G _43R includes a negative lens L ₄₃₃ . The negative lens L ₄₃₃ is formed of a single glass material. Aspherical surfaces are formed on both surfaces of the negative lens _L433 .

In this inner focus type lens, the distance between the first lens group G ₄₁ and the second lens group G ₄₂ is increased while the first lens group G ₄₁ and the third lens group G ₄₃ are fixed, and the second lens group G ₄₂ and the interval between the third lens group G ₄₃ is reduced, from infinity in-focus state by making the second lens group G ₄₂ is moved from the object side along the optical axis to the image plane IMG side uppermost Focusing is performed until the object is in focus at close range.

  Various numerical data relating to the inner focus lens according to Example 4 will be described below.

(Lens data)
r ₁ = 28.832
d ₁ = 2.0000 nd ₁ = 1.5935 νd ₁ = 67.00
r ₂ = 15.623
d ₂ = 6.8857
r ₃ = 29.397
d ₃ = 1.5000 nd ₂ = 1.4970 νd ₂ = 81.61
r ₄ = 13.122
d ₄ = 5.8831
r ₅ = 52.568 (aspherical surface)
d ₅ = 1.3000 nd ₃ = 1.5920 νd ₃ = 67.02
r ₆ = 12.910 (aspherical surface)
d ₆ = 3.0680
r ₇ = 30.333
d ₇ = 2.2648 nd ₄ = 1.8810 νd ₄ = 40.14
r ₈ = 141.737
d ₈ = 12.0987
r ₉ = 24.676
d ₉ = 1.000 nd ₅ = 1.8810 νd ₅ = 40.14
r ₁₀ = 13.601
d ₁₀ = 5.2921 nd ₆ = 1.4875 νd ₆ = 70.44
r ₁₁ = -35.502
d ₁₁ = 3.7248
r ₁₂ = 30.850 (aspherical surface)
d ₁₂ = 4.3865 nd ₇ = 1.4971 νd ₇ = 81.56
r ₁₃ = -18.338 (aspherical surface)
d ₁₃ = 1.000
r ₁₄ = ∞ (aperture stop)
d ₁₄ = D (14) (variable)
r ₁₅ = 45.781 (aspherical surface)
d ₁₅ = 0.8000 nd ₈ = 1.7290 νd ₈ = 54.04
r ₁₆ = 19.193 (aspherical surface)
d ₁₆ = D (16) (variable)
r ₁₇ = -68.737
d ₁₇ = 2.5350 nd ₉ = 1.4970 νd ₉ = 81.61
r ₁₈ = -25.555
d ₁₈ = 0.1000
r ₁₉ = -329.577
d ₁₉ = 4.0360 nd ₁₀ = 1.4970 νd ₁₀ = 81.61
r ₂₀ = -23.042
d ₂₀ = 0.3290
r ₂₁ = -400.000 (aspherical surface)
d ₂₁ = 1.2000 nd ₁₁ = 1.8820 νd ₁₁ = 37.22
r ₂₂ = 26.785 (aspherical surface)
d ₂₂ = 25.606
r ₂₃ = ∞
d ₂₃ = 2.5000 nd ₁₂ = 1.5168 νd ₁₂ = 64.20
r ₂₄ = ∞
d ₂₄ = 1.000
r ₂₅ = ∞ (imaging plane)

Conical coefficient (k) and aspheric coefficient (A ₄ , A ₆ , A ₈ , A ₁₀ )
(5th page)
k = 0,
A ₄ = −2.6625 × 10 ⁻⁵ , A ₆ = 3.0031 × 10 ⁻⁷ ,
A ₈ = -1.7989 × 10 ⁻⁹ , A ₁₀ = 5.7847 × 10 ⁻¹²
(Sixth surface)
k = 0,
A ₄ = -6.8334 × 10 ^-5 , A ₆ = 8.4364 × 10 ^-9 ,
A ₈ = -1.2228 × 10 ^-9 , A ₁₀ = -9.8374 × 10 ^-12
(Twelfth surface)
k = 0,
A ₄ = -2.2269 × 10 ^-5 , A ₆ = 1.1253 × 10 ^-9 ,
A ₈ = -1.0562 × 10 ^-9 , A ₁₀ = -3.1969 × 10 ^-12
(13th page)
k = 0,
A ₄ = 5.1791 × 10 ⁻⁵ , A ₆ = −5.2286 × 10 ⁻⁷ ,
A ₈ = 4.0083 × 10 ^-9 , A ₁₀ = -2.3692 × 10 ^-11
(15th page)
k = 0,
A ₄ = 2.0348 × 10 ⁻⁵ , A ₆ = −1.1141 × 10 ⁻⁶ ,
A ₈ = 1.4175 × 10 ⁻⁸ , A ₁₀ = −5.7786 × 10 ⁻¹¹
(16th surface)
k = 0,
A ₄ = 2.1580 × 10 ⁻⁵ , A ₆ = −8.9505 × 10 ⁻⁷ ,
A ₈ = 1.2780 × 10 ⁻⁸ , A ₁₀ = −5.7413 × 10 ⁻¹¹
(21st surface)
k = 0,
A ₄ = -2.4151 × 10 ^-5 , A ₆ = -1.3394 × 10 ^-7 ,
A ₈ = 2.2182 × 10 ⁻⁹ , A ₁₀ = −7.5852 × 10 ⁻¹²
(Twenty-second surface)
k = 0,
A ₄ = -3.5206 × 10 ^-6 , A ₆ = -1.2925 × 10 ^-7 ,
A ₈ = 2.2655 × 10 ⁻⁹ , A ₁₀ = −8.5817 × 10 ⁻¹²

(Numeric data for each in-focus state)
Infinity Closest distance (object distance 158.000mm)
D (14) 0.4719 1.3177
D (16) 5.8194 4.9736
f (focal length of the entire optical system) 18.54 17.89
FNO (F number) 2.88 2.93
ω (half angle of view) 50.29 49.47
f1 (the focal length of the first lens group G ₄₁₎ 10.28 10.28
f2 (the focal length of the second lens group G ₄₂₎ -45.92 -45.92
f3 (the focal length of the third lens group G ₄₃₎ -722.75 -722.75
BF (back focus) 29.106 29.106

(Numerical values related to conditional expression (1))
R1 (the radius of curvature of the object side air interface of the negative lens L ₄₃₃₎ = - 400.000
R2 (the radius of curvature of the image side air interface of the negative lens L ₄₃₃₎ = 26.785
(R1 + R2) / (R1-R2) = 0.87

(Numerical value related to conditional expression (2))
νdn (Abbe number with respect to d-line of negative lens L ₄₃₃ ) = 37.22

(Numerical values related to conditional expression (3))
f1 / f = 0.55

(Numerical values related to conditional expression (4))
f3 / f = -38.97

(Numerical values related to conditional expression (5))
Betainf (paraxial magnification of the second lens group G ₄₂ in the infinite object in-focus state) = 1.83
β mod (paraxial magnification of the second lens group G _{42 in} the closest object focusing state) = 1.81
βinf / βmod = 1.01

(Numerical values related to conditional expression (6))
L1s (axial distance from the most object side surface of the first lens group G ₄₁ to the aperture stop STP) = 50.4037
L (axial distance from the top of the first lens group G _{41 on} the most object side to the imaging surface IMG (total length of the optical system)) = 94.8010
L1s / L = 0.53

(Numerical values related to conditional expression (7))
f2 / f = -2.48

(Numerical value related to conditional expression (8))
R21 (radius of curvature of the most object side surface of the negative lens L ₄₂₁₎ = 45.781
R22 (radius of curvature of the most image side surface of the negative lens L ₄₂₁₎ = 19.193
(R21 + R22) / (R21-R22) = 2.44

  FIG. 8 is a diagram illustrating various aberrations of the inner focus lens according to Example 4. In the spherical aberration diagram, the vertical axis represents the F number (indicated by FNO in the figure), the solid line is the d line (λ = 587.56 nm), the short broken line is the g line (λ = 435.84 nm), and the long broken line is the C line The characteristic of the wavelength corresponding to the line (λ = 656.28 nm) is shown. In the graph showing astigmatism, the vertical axis represents the image height (indicated by Y in the figure) and represents the wavelength characteristic corresponding to the d-line (λ = 587.56 nm). In the graph showing astigmatism, the solid line indicates the characteristics of the sagittal plane (indicated by S in the figure), and the broken line indicates the characteristics of the meridional plane (indicated by M in the figure). In the distortion diagram, the vertical axis represents the image height (indicated by Y in the figure) and represents the wavelength characteristic corresponding to the d-line (λ = 587.56 nm).

In the numerical data in each of the above embodiments, r ₁ , r ₂ ,... Are the radii of curvature of the lenses and the diaphragm surface, and d ₁ , d ₂ ,. , Nd ₁ , nd ₂ ,... Is the refractive index of each lens with respect to the d-line (λ = 587.56 nm), and νd ₁ , νd ₂ ,. The Abbe number for the d-line (λ = 587.56 nm) is shown. Further, BF (back focus) represents the distance from the final surface of the optical system to the paraxial image surface. The total length of the optical system is obtained by adding BF to the distance from the most object side surface to the final lens surface. 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 lens having a wide-angle focal length 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. In particular, by satisfying the above conditional expressions, it is possible to realize an inner focus lens that is suitable for moving image shooting and has a small size, a wide angle, and 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 , G ₄₁ first lens group G ₁₂ , G ₂₂ , G ₃₂ , G ₄₂ second lens group G ₁₃ , G ₂₃ , G ₃₃ , G ₄₃ third lens group G _13F , G _23F , G _33F , G _43F front sub lens group G _13R , G _23R , G _33R , G _43R rear sub lens group L ₁₁₁ , L ₁₁₂ , L ₂₁₁ , L ₂₁₂ , L ₃₁₁ , L ₃₁₂ , L ₄₁₁ , L ₄₁₂ negative meniscus lens _{L 113, L 115, L 121} , L 133, L 213, L 215, L 221, L 233, L 313, L 315, L 321, L 333, L 413, L 415, L 421, L 433 negative lens _{L 114, L 116, L 117} , L 131, L 132, L 214, L 216, L 217, L 231, L 232, L 314, L 316, L 317, L 331, L 332, L 414, L 416 , L ₄₁₇ , L ₄₃₁ , L ₄₃₂ positive lens STP Aperture stop IMG Imaging surface CG Cover glass

Claims (9)

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,
The first lens group includes at least one negative meniscus lens closest to the object side,
A single lens component having negative refractive power is disposed on the most image side of the third lens group,
While the first lens group and the third lens group are fixed, an interval between the first lens group and the second lens group is enlarged, and an interval between the second lens group and the third lens group is reduced. As described above, focusing from the infinite object focusing state to the closest object focusing state is performed by moving the second lens group from the object side to the image side along the optical axis,
An inner focus type lens satisfying the following conditional expression:
(1) 0 ≦ (R1 + R2) / (R1−R2)
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 a negative refractive power disposed on the most image side of the third lens group is formed of a single glass material,
The inner focus type lens according to claim 1, wherein the following conditional expression is satisfied.
(2) 30 ≦ νdn
Here, νdn indicates the Abbe number with respect to the d-line of the single lens component having the negative refractive power. The inner focus lens according to claim 1, wherein the following conditional expression is satisfied.
(3) 0.28 ≦ f1 / f ≦ 1.30
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) f3 / f ≦ −29.1
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) 0.50 ≦ βinf / βmod ≦ 2.02
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 described inner focus lens. It has an aperture stop that defines a predetermined aperture,
The inner focus type lens according to claim 1, wherein the following conditional expression is satisfied.
(6) 0.24 ≦ L1s / L ≦ 0.95
Where L1s is the axial distance from the most object side surface of the first lens group to the aperture stop, and L is the axial distance from the apex of the lens surface on the most object side to the imaging surface in the optical system (total length of the optical system). Indicates.   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 any one of claims 1 to 8, which satisfies the following conditional expression.
(7) −7.46 ≦ f2 / f ≦ −2.11
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.

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