JP2015156038A - Rear focus lens system and imaging apparatus including the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a rear focus lens system capable of reducing an electrical load or noise in a focusing operation and, more preferably, in a wobbling operation.

SOLUTION: A rear focus lens system comprises, in order from an object side to an image side: a front side lens group LA having positive refractive power; an aperture stop S; and a rear side lens group LB having positive refractive power. The front side lens group LA comprises, in order from the object side: a front side negative lens group LA1 comprising one or a plurality of lens components having negative refractive power; and a front side positive lens group LA2. The front side positive lens group LA2 has a lens component, and the lens component is located closest to the object side and has a positive lens. The rear side lens group LB comprises, in order from the object side: a rear side positive lens group LB1; and a focusing lens group LB2. When focusing from a long-distance object to a short-distance object, the focusing lens group LB2 moves so that distance to the rear side positive lens group LB1 is changed. The focusing lens group LB2 comprises one lens component. The rear focus lens system satisfies predetermined conditional expressions.

COPYRIGHT: (C)2015,JPO&INPIT

Description

  The present invention relates to a rear focus lens system and an imaging apparatus including the same.

  In recent years, video shooting has become a trend in digital cameras. For this reason, the moving image shooting function is an important function for digital cameras. Therefore, an interchangeable lens optimized for moving image shooting is also demanded in an interchangeable lens digital camera.

  By the way, still image shooting is also performed in a digital camera. The purpose of still image shooting is to cut out a target subject (photograph the subject) in a moment of shooting. Therefore, after determining the composition, it would be good if the subject was focused on at the moment of shooting. Therefore, a so-called phase difference type autofocus has been adopted in a conventional camera for taking a still image. This phase difference type autofocus is an autofocus that combines high speed with high precision.

  On the other hand, in moving image shooting, it is necessary to always maintain an in-focus state by operating autofocus. Therefore, with the exception of some professional video cameras, many consumer video cameras always used autofocus. Contrast autofocus (so-called hill-climbing autofocus) is used for autofocus in video shooting. In contrast autofocus, the change in contrast is measured by always moving a focusing lens group by a minute amount before and after the in-focus position. A change in focus state (deviation from the focus state) is detected from the change in contrast. The operation of moving a minute amount is called wobbling.

  When it is determined that the in-focus state has changed, the in-focus state can be re-entered by appropriately moving the focus lens group. With such a wobbling function, even when the distance to the subject changes, the in-focus state can always be maintained. However, depending on the frame rate set on the camera body side, very high speed movement is required for wobbling, that is, movement of the focus lens group. For this reason, the focus lens group is required to reduce the weight, minimize the amount of movement, and the like.

  When wobbling is performed, a driving sound (operation sound) is generated with the movement of the focus lens group. If the volume of the drive sound is high, this drive sound is recorded as noise together with other sounds in moving image shooting. For this reason, reducing the volume of driving sound is also an important issue. Also, if the change in image magnification is large during wobbling, the image will always appear to fluctuate, and the displayed image will appear very unnatural. Accordingly, in moving image shooting, it is also important that the change in image magnification during wobbling is small.

  In order to satisfy the above-described solutions and demands, weight reduction is required particularly for the focusing lens group.

  There are several types of lens systems depending on the position of the focusing lens group. One of these is a rear focus type lens system. In the rear focus type lens system, a lens group located closest to the image side of the lens system is a focusing lens group. As this rear focus type lens system, those of Patent Documents 1 to 4 are known.

JP 2011-209377 A JP 2011-76022 A JP 2010-210883 A JP 2010-101979 A

  The lens system described in Patent Document 1 is a bright lens system, but is large as a lens system because the lens diameter of the front lens is large. Further, the lens systems described in Patent Document 2 and Patent Document 4 are difficult to say as bright lens systems. Since the lens system described in Patent Document 3 seems to be intended for use in a compact camera, the total length of the lens system is longer than the focal length.

  The present invention has been made in view of such a problem, and reduces the electric burden of the drive system during the focusing operation, more preferably during the wobbling operation, reduces the noise generated by the drive, and the lens system. An object of the present invention is to provide a rear focus lens system that is advantageous in ensuring predetermined brightness and optical performance and reducing the size of the lens system. Furthermore, it aims at provision of the imaging device provided with such a rear focus lens system.

In order to solve the above-described problems and achieve the object, the rear focus lens system of the present invention is:
From the object side to the image side,
A front lens unit having positive refractive power;
The aperture stop,
A rear lens unit having a positive refractive power,
The front lens group includes, in order from the object side, a front negative lens group composed of one or more lens components having a negative refractive power, and a front positive lens group.
The front positive lens group has a lens component, the lens component is disposed closest to the object side, and has a positive lens;
The rear lens group is composed of, in order from the object side, a rear positive lens group and a focusing lens group.
When focusing from a long-distance object to a short-distance object, the focusing lens group moves to change the distance from the rear positive lens group,
The focusing lens group consists of one lens component,
The following conditional expressions (1), (2), and (3) are satisfied.
4.0 <F _no × L _air / f _ent <8.0 (1)
1.0 <| f _Rfo | / f _ent <6.0 (2)
−2.6 <f _FN / f _ent <−0.2 (3)
However,
F _no is the minimum F number of the rear focus lens system,
L _air is the distance on the optical axis from the lens surface closest to the object side of the rear focus lens system to the image plane,
f _Rfo is the focal length of the focusing lens group,
f _FN is a focal length of the front negative lens unit,
f _ent is the focal length of the entire rear focus lens system,
The minimum F number and the focal length of the entire system are respectively the F number and focal length when an object at infinity is in focus,
The lens component includes a lens body having only two refracting surfaces in contact with air on the optical axis, the object side surface and the image side surface,
It is.

Further, another rear focus lens system of the present invention is
From the object side to the image side,
A front lens unit having positive refractive power;
The aperture stop,
A rear lens unit having a positive refractive power,
The front lens group includes, in order from the object side, a front negative lens group including a lens component having one negative refractive power, and a front positive lens group.
The front positive lens group has a lens component, the lens component is disposed closest to the object side, and has a positive lens;
The rear lens group, in order from the object side, consists of a rear positive lens group and a focusing lens group with positive refractive power,
When focusing from a long-distance object to a short-distance object, the focusing lens group moves to reduce the distance from the rear positive lens group,
The focusing lens group consists of one lens component,
The following conditional expressions (1) and (4) are satisfied.
4.0 <F _no × L _air / f _ent <8.0 (1)
1.0 <f _Rfo / f _ent <6.0 (4)
However,
F _no is the minimum F number of the rear focus lens system,
L _air is the distance on the optical axis from the lens surface closest to the object side of the rear focus lens system to the image plane,
f _Rfo is the focal length of the focusing lens group,
f _ent is the focal length of the entire rear focus lens system,
The minimum F number and the focal length of the entire system are respectively the F number and focal length when an object at infinity is in focus,
The lens component includes a lens body having only two refracting surfaces in contact with air on the optical axis, the object side surface and the image side surface,
It is.

Further, another rear focus lens system of the present invention is
From the object side to the image side,
A front lens unit having positive refractive power;
The aperture stop,
It consists of a rear lens group with positive refractive power,
The front lens group includes, in order from the object side, a front negative lens group composed of one or more lens components having a negative refractive power, and a front positive lens group.
The rear lens group, in order from the object side, consists of a rear positive lens group and a focusing lens group having negative refractive power,
When focusing from a long-distance object to a short-distance object, the focusing lens group moves to increase the distance from the rear positive lens group,
The focusing lens group consists of one lens component,
The following conditional expression (5) is satisfied.
−6.0 <f _Rfo / f _ent <−1.0 (5)
However,
f _Rfo is the focal length of the focusing lens group,
f _ent is the focal length of the entire rear focus lens system, and the focal length when focusing on an object at infinity,
The lens component includes a lens body having only two refracting surfaces in contact with air on the optical axis, the object side surface and the image side surface,
It is.

  According to the above configuration, the electric load of the drive system during the focusing operation, more preferably, the wobbling operation is reduced, the noise generated by the drive is reduced, the predetermined brightness and optical performance of the lens system are ensured, the lens It is possible to provide a rear focus lens system that is advantageous for downsizing the system.

The imaging apparatus of the present invention includes an imaging lens system, and an imaging element that is disposed on the image side of the imaging lens system and converts an image formed by the imaging lens system into an electrical signal,
The imaging lens system is any one of the rear focus lens systems described above.

  According to the above-described configuration, although it is small, the operation sound during the focusing operation, more preferably during the wobbling operation is quiet, and a high-resolution image can be obtained without degrading the image quality even in a dark shooting environment. An imaging device can be realized.

  According to the present invention, it is possible to reduce the electric load of the drive system during the focusing operation, more preferably during the wobbling operation, to reduce noise generated by the drive, to ensure the predetermined brightness and optical performance of the lens system, and to the lens system. It is possible to provide a rear focus lens system that is advantageous for downsizing and an imaging device including the rear focus lens system.

FIG. 2 is a lens cross-sectional view of the rear focus lens system of the present invention when focusing on an object at infinity, where (a) is a lens cross-sectional view of Example 1 and (b) is a lens cross-sectional view of Example 2. FIG. FIG. 4 is a lens cross-sectional view of the rear focus lens system of the present invention when focusing on an object at infinity, where (a) is a lens cross-sectional view of Example 3, and (b) is a lens cross-sectional view of Example 4. FIG. 6 is a lens cross-sectional view of the rear focus lens system of the present invention when focusing on an object at infinity, where (a) is a lens cross-sectional view of Example 5, and (b) is a lens cross-sectional view of Example 6. FIG. 6 is a lens cross-sectional view of the rear focus lens system of the present invention when focusing on an object at infinity, where (a) is a lens cross-sectional view of Example 7, and (b) is a lens cross-sectional view of Example 8. 10 is a lens cross-sectional view of a rear focus lens system of the present invention when an object at infinity is focused, and is a lens cross-sectional view of Example 9. FIG. (A)-(h) is an aberration diagram of the rear focus lens system of Example 1, and is an aberration diagram in two different in-focus states. (A)-(h) is an aberration diagram of the rear focus lens system of Example 2, and is an aberration diagram in two different in-focus states. (A)-(h) are aberration diagrams of the rear focus lens system of Example 3, and are aberration diagrams in two different in-focus states. (A)-(h) are aberration diagrams of the rear focus lens system of Example 4, and are aberration diagrams in two different in-focus states. (A) to (h) are aberration diagrams of the rear focus lens system of Example 5, and are aberration diagrams in two different in-focus states. (A) to (h) are aberration diagrams of the rear focus lens system of Example 6, and are aberration diagrams in two different in-focus states. (A)-(h) is an aberration figure of the rear-focus lens system of Example 7, Comprising: It is an aberration figure of two different focusing states. (A)-(h) are aberration diagrams of the rear focus lens system of Example 8, and are aberration diagrams in two different in-focus states. (A) to (h) are aberration diagrams of the rear focus lens system of Example 9, and are aberration diagrams in two different in-focus states. It is sectional drawing of the lens interchangeable camera which used the rear-focus lens system by this invention as an interchangeable lens. It is a front perspective view which shows the external appearance of the digital camera by this invention. FIG. 17 is a rear perspective view of the digital camera of FIG. 16. FIG. 17 is a configuration block diagram of an internal circuit of a main part of the digital camera of FIG. 16.

  Embodiments and examples of a rear focus lens system and an imaging apparatus according to the present invention will be described below in detail with reference to the drawings. In addition, this invention is not limited by this embodiment and an Example.

  The rear focus lens system according to the present embodiment includes, in order from the object side to the image side, a front lens unit having a positive refractive power, an aperture stop, and a rear lens unit having a positive refractive power. In order from the object side, it consists of a front negative lens group consisting of lens components of negative refractive power and a front positive lens group, and the rear lens group consists of a rear positive lens group and a focusing lens group in order from the object side. Thus, when focusing from a long-distance object to a short-distance object, the focusing lens group moves so as to change the distance from the rear positive lens group, and the focusing lens group consists of one lens component. This is the basic configuration of the rear focus lens system of this embodiment.

  In the above basic configuration, first, lens groups (front lens group and rear lens group) having positive refractive power are respectively arranged on the object side and the image side with the aperture stop interposed therebetween. Such an arrangement is advantageous for correcting various aberrations. Next, the front lens group is arranged from the object side in the order of a negative refractive power lens group (front negative lens group) and a positive refractive power lens group (front positive lens group). Such an arrangement is advantageous for securing a required angle of view and securing a predetermined back focus.

  Further, the rear lens group is composed of a positive refractive power lens group (rear positive lens group) and a focusing lens group, and the focusing lens group is disposed on the image side of the rear positive lens group. The focusing lens group is composed of one lens component. As described above, the lens group is moved during the focusing operation or the wobbling operation. Therefore, such an arrangement and configuration is advantageous for reducing the weight of the lens group to be moved, reducing the driving power and reducing the driving sound during the focusing operation and the wobbling operation due to the weight reduction. From the above, in the rear focus lens system, it is preferable that the rear lens group has the above arrangement and configuration.

In the rear focus lens system of the first embodiment, in addition to the basic configuration described above, the front negative lens unit includes one or more lens components having negative refractive power, and the front positive lens unit has a lens component. The lens component is arranged on the most object side, has a positive lens, and satisfies the following conditional expressions (1), (2), and (3).
4.0 <F _no × L _air / f _ent <8.0 (1)
1.0 <| f _Rfo | / f _ent <6.0 (2)
−2.6 <f _FN / f _ent <−0.2 (3)
However,
F _no is the minimum F number of the rear focus lens system,
L _air is the distance on the optical axis from the lens surface closest to the object side of the rear focus lens system to the image plane,
f _Rfo is the focal length of the focusing lens group,
f _FN is the focal length of the front negative lens unit,
f _ent is the focal length of the entire rear focus lens system,
The minimum F number and the focal length of the entire system are respectively the F number and focal length when an object at infinity is in focus,
The lens component is a lens body having only two refracting surfaces in contact with air on the optical axis, that is, the object side surface and the image side surface.
It is.

Note that L _air is equal to the distance obtained by adding the back focus to the axial distance from the most object side surface to the most image side surface of the rear focus lens system. Here, the axial distance from the most object side surface to the most image side surface is a distance not converted to air, and the back focus is a distance converted to air.

  In a lens system of a digital camera (lens exchange type, lens non-exchange type), optical filters are arranged in a space closer to the image side than the lens system. Further, in a system single lens camera (lens exchange type) in which an interchangeable lens is attached and detached, a filter is disposed on the camera body side. Therefore, when the interchangeable lens is attached to the camera body, it is necessary to prevent interference between the interchangeable lens and the filter on the body side. From the above, it is required for the lens system of a digital camera to ensure an appropriate length of back focus.

  Therefore, in the rear focus lens system of the present embodiment, the front negative lens group is disposed closest to the object side in the front lens group. The front negative lens group is composed of one or a plurality of negative lens components. Thus, the front lens group has a negative refractive power lens group on the front side and a positive refractive power lens group on the rear side. Thus, since the front lens group has a retrofocus type configuration, an appropriate back focus can be secured.

  Further, as described above, it is preferable that the front positive lens unit has a lens component, and the lens component is disposed closest to the object side and has a positive lens. A front negative lens group is disposed on the object side of the front positive lens group. This front negative lens group is composed only of lens components having negative refractive power. For this reason, the front positive lens group having such a configuration is advantageous for correcting aberrations occurring in the front negative lens group.

  Conditional expression (1) relates to the total length of the lens system. If an attempt is made to reduce the F-number in a bright and wide-angle lens system, the number of lenses increases in order to correct aberrations satisfactorily. As a result, the total length of the lens system tends to be long. However, considering the convenience of the user, the lens system is preferably small. Conditional expression (1) is a preferable condition for ensuring both good optical performance and shortening the overall length of the lens system.

  It is preferable not to exceed the upper limit of conditional expression (1), to prevent the total length of the lens system from becoming long, and to improve portability.

  It is preferable to ensure an optical path (lens thickness, lens interval) necessary to perform good aberration correction so as not to fall below the lower limit of conditional expression (1).

  Conditional expression (2) specifies a preferable refractive power of the focusing lens group.

  The amount of movement of the lens unit accompanying focusing can be suppressed by ensuring the refractive power of the focusing lens unit appropriately without exceeding the upper limit of conditional expression (2). Not exceeding the upper limit of conditional expression (2) is advantageous for shortening the overall length of the lens system.

  By avoiding falling below the lower limit of conditional expression (2) and appropriately suppressing the refractive power of the focusing lens group, it becomes easy to reduce aberration fluctuations associated with focusing. Further, even if the focusing lens group is composed of one lens component, aberration variation can be suppressed.

  Conditional expression (3) specifies a preferable refractive power of the front negative lens unit.

  Properly suppressing the refractive power of the front negative lens unit so as not to exceed the upper limit of conditional expression (3) is advantageous not only for shortening the overall length of the lens system but also for reducing aberrations.

  Properly securing the refractive power of the front negative lens unit so as not to fall below the lower limit of conditional expression (3) is advantageous for securing a predetermined back focus.

Further, in the rear focus lens system of the second embodiment, in addition to the basic configuration described above, the front negative lens group includes one lens component having a negative refractive power, and the front positive lens group includes a lens component. The lens component is arranged closest to the object side and has a positive lens. The refractive power of the focusing lens group is positive refractive power, and the movement of the focusing lens group is such that the distance from the rear positive lens group is shortened. The following conditional expressions (1) and (4) are satisfied.
4.0 <F _no × L _air / f _ent <8.0 (1)
1.0 <f _Rfo / f _ent <6.0 (4)
However,
F _no is the minimum F number of the rear focus lens system,
L _air is the distance on the optical axis from the lens surface closest to the object side of the rear focus lens system to the image plane,
f _Rfo is the focal length of the focusing lens group,
f _ent is the focal length of the entire rear focus lens system,
The minimum F number and the focal length of the entire system are respectively the F number and focal length when an object at infinity is in focus,
The lens component is a lens body having only two refracting surfaces in contact with air on the optical axis, that is, the object side surface and the image side surface.
It is.

  The configuration of the front positive lens group and the technical significance of conditional expression (1) are as described above.

  In addition, it is preferable to configure the front negative lens unit with a lens component having one negative refractive power in order to reduce the diameter of the lens closest to the object side and shorten the overall length of the lens system.

  In addition, when the refractive power of the focusing lens group is a positive refractive power, it is possible to focus from a long distance object to a short distance object by moving the focusing lens group so as to reduce the distance from the rear positive lens group. . With such a configuration, the exit pupil is easily separated from the image plane. Therefore, such a configuration is suitable for an imaging apparatus using an electronic imaging element, for example, a lens system of a digital camera.

  Conditional expression (4) specifies a preferable refractive power of the focusing lens group.

  By avoiding exceeding the upper limit of conditional expression (4) and ensuring the refractive power of the focusing lens group appropriately, an increase in the amount of movement of the lens group accompanying focusing can be suppressed. Not exceeding the upper limit of conditional expression (4) is advantageous for shortening the overall length of the lens system.

  By avoiding falling below the lower limit of conditional expression (4) and appropriately suppressing the refractive power of the focusing lens group, it becomes easy to reduce aberration fluctuations associated with focusing. Further, even if the focusing lens group is composed of one lens component, aberration variation can be suppressed.

In the rear focus lens system according to the third embodiment, in addition to the above basic configuration, the front negative lens unit includes one or more lens components having negative refractive power, and the refractive power of the focusing lens unit is negative refractive. The movement of the focusing lens group is a movement that widens the distance from the rear positive lens group, and satisfies the following conditional expression (5).
−6.0 <f _Rfo / f _ent <−1.0 (5)
However,
f _Rfo is the focal length of the focusing lens group,
f _ent is the focal length of the entire rear focus lens system, and is the focal length when focusing on an object at infinity,
The lens component includes a lens body having only two refracting surfaces in contact with air on the optical axis, the object side surface and the image side surface,
It is.

  The technical significance of configuring the front negative lens group with one or a plurality of lens components having a negative refractive power is as described above.

  In addition, when the refractive power of the focusing lens group is a negative refractive power, it is possible to focus from a long distance object to a short distance object by moving the focusing lens group so as to increase the distance from the rear positive lens group. . Such a configuration is advantageous for downsizing the entire lens system. In addition, since the arrangement of the sign of refractive power (positive and negative refractive power) can be made symmetric with respect to the aperture stop, the above configuration is advantageous for aberration correction.

  Conditional expression (5) specifies a preferable refractive power of the focusing lens group.

  By avoiding the upper limit of conditional expression (5) from being exceeded and appropriately suppressing the refractive power of the focusing lens group, it becomes easy to reduce aberration fluctuations caused by focusing. Further, even if the focusing lens group is composed of one lens component, aberration variation can be suppressed.

  By ensuring that the refractive power of the focusing lens group is appropriately ensured not to fall below the lower limit of conditional expression (5), an increase in the amount of movement of the lens group accompanying focusing can be suppressed. Not exceeding the upper limit of conditional expression (5) is advantageous for shortening the overall length of the lens system.

  In addition, the rear focus lens system of the above embodiment preferably has at most two lens components having negative refractive power.

  This is advantageous for shortening the lens diameter closest to the object side of the lens system and the overall length of the lens system.

  In the rear focus lens system of the above embodiment, it is preferable that there are two lens components having negative refractive power.

  This is advantageous for achieving both a wide angle of view and a reduction in off-axis aberration associated therewith.

  In the rear focus lens system of the above embodiment, it is preferable that each lens component having a negative refractive power is a single lens having a negative refractive power.

  This is advantageous for cost reduction.

  In the rear focus lens system of the above embodiment, it is preferable that there is one lens component having a negative refractive power.

  This is more advantageous for shortening the overall length of the lens system.

  In the rear focus lens system of the above embodiment, it is preferable that the lens component having a negative refractive power is a single lens.

  This is advantageous for cost reduction.

  In the rear focus lens system of the third embodiment, it is preferable that the front positive lens unit has a lens component, the lens component is disposed closest to the object side, and has a positive lens.

  This is advantageous for correcting aberrations occurring in the front negative lens group as described above.

  In the rear focus lens system of the above-described embodiment, it is preferable that the lens component in the front positive lens unit is a lens component having a positive refractive power.

  In this way, the height of the off-axis light beam passing through the lens component having the positive refractive power can be increased. Therefore, off-axis aberrations that occur in the front negative lens group can be easily canceled by the lens component having the positive refractive power.

  In the rear focus lens system of the above embodiment, it is preferable that the lens component having a positive refractive power is a single lens having a positive refractive power.

  This is advantageous for shortening the overall length of the lens system and reducing costs.

  In the rear focus lens system of the above-described embodiment, it is preferable that the lens component in the front positive lens group is a cemented lens component including a positive lens and a negative lens.

  This is advantageous for correcting chromatic aberration.

Moreover, it is preferable that the rear focus lens system of the above embodiment satisfies the following conditional expression (6).
0.75 <fb _air / f _ent <1.3 (6)
However,
fb _air is the back focus of the rear focus lens system,
f _ent is the focal length of the entire rear focus lens system,
It is.

  Conditional expression (6) is a conditional expression that specifies a preferable back focus length of the rear focus lens system.

  It is preferable to reduce the total length of the lens so as not to exceed the upper limit of conditional expression (6) while ensuring a space in which a filter or the like can be disposed without falling below the lower limit of conditional expression (6).

In the rear focus lens system of the above embodiment, it is preferable that the rear positive lens unit has an aspheric lens having a positive refractive power and satisfies the following conditional expression (7).
1.65 <nL _asp <1.95 (7)
However,
nL _asp is the refractive index at the d-line of the aspheric lens,
It is.

  This is advantageous for correcting spherical aberration and coma. Therefore, it is preferable that the aspheric lens satisfies the conditional expression (7).

  In order to suppress the refractive index so as not to exceed the upper limit of the conditional expression (7), a glass material with small dispersion is used among practical glass materials. Therefore, not exceeding the upper limit of conditional expression (7) is advantageous for correcting chromatic aberration.

  Securing the refractive index so that it does not fall below the lower limit of conditional expression (7) is advantageous for reducing the curvature of field by correcting the Petzval sum.

  In the rear focus lens system of the above-described embodiment, it is preferable that the aspherical lens is a lens positioned closest to the image side in the rear positive lens group.

  By doing in this way, the passage place of the axial light beam and the off-axis light beam on the aspherical surface can be made different. Therefore, this is advantageous for correcting various aberrations due to the aspherical surface.

  In the rear focus lens system of the above-described embodiment, it is preferable that the rear positive lens group includes a negative lens, a positive lens, and a positive lens in order from the object side.

  This is advantageous for correction of field curvature.

  In the rear focus lens system of the above-described embodiment, the rear positive lens group includes, in order from the object side, a negative lens whose object side surface has a concave surface facing the object side, and a positive lens whose image side surface faces a convex surface toward the image side. The image side surface is preferably a positive lens having a convex surface facing the image side.

  This is more advantageous for correction of field curvature and the like.

  In the rear focus lens system of the above embodiment, it is preferable that the focusing lens group has an aspheric lens.

  In the rear focus lens system of the present embodiment, the focusing lens group is composed of one lens component. One lens component includes one lens or one cemented lens. This focusing lens group tends to increase spherical aberration when focused on a short distance object. Therefore, in order to suppress the increase in spherical aberration, it is preferable to provide the focusing lens group with an aspheric lens. Since the focusing lens group includes an aspheric lens, it is possible to suppress a variation in spherical aberration associated with focusing on a short-distance object.

In the rear focus lens system of the above embodiment, it is preferable that the focusing lens group satisfies the following conditional expression (8).
1.65 <nL _Rfo <1.95 (8)
However,
nL _Rfo is the average value of the refractive indices at the d-line of all the lenses in the focusing lens group,
It is.

  By suppressing the refractive index so as not to exceed the upper limit of the conditional expression (8), a glass material having a small dispersion among the practical glass materials is used. Therefore, not exceeding the upper limit of conditional expression (8) is advantageous for correcting chromatic aberration.

  Securing the refractive index so that it does not fall below the lower limit of conditional expression (8) is advantageous for reducing the variation in spherical aberration associated with focusing.

  In the rear focus lens system of the above embodiment, it is preferable that the focusing lens group is a single lens.

  This is more advantageous for reducing the size of the focusing lens group. Further, this is advantageous for reducing the electric load of the drive system during the focusing operation (more preferably during the wobbling operation) and for reducing the noise generated by the drive.

  In addition, the imaging apparatus of the present embodiment includes an imaging lens system and an imaging element that is arranged on the image side of the imaging lens system and converts an image formed by the imaging lens system into an electrical signal, and the imaging lens system is the above It is the rear focus lens system of the embodiment.

  By doing in this way, it becomes an imaging device using the merit of the rear focus lens system of this embodiment. Therefore, this is preferable.

  The configuration of the rear focus lens system of the present embodiment is a configuration in a state in which an object at the farthest distance, for example, an object at infinity is in focus, unless otherwise specified.

  In addition, it is more preferable that a plurality of each constituent requirement is satisfied simultaneously.

For each conditional expression, it is preferable to set the upper limit value and the lower limit value as follows. If it does in this way, the effect can be acquired more certainly.
For conditional expression (1),
More preferably, the lower limit value is 5.0, more preferably 5.4.
More preferably, the upper limit value is 7.5, more preferably 7.0.
For conditional expression (2),
More preferably, the lower limit is 1.7, and more preferably 2.2.
More preferably, the upper limit value is 5.5, more preferably 5.2.
Conditional expression (3)
More preferably, the lower limit value is -2.4, more preferably -2.2.
More preferably, the upper limit value is -0.5, more preferably -0.8.
For conditional expression (4),
More preferably, the lower limit is 1.7, and more preferably 2.2.
More preferably, the upper limit value is 5.5, more preferably 5.2, and even more preferably 4.9.
For conditional expression (5),
More preferably, the lower limit value is −5.5, more preferably −5.2.
More preferably, the upper limit value is -1.7, more preferably -2.2, and even more preferably -2.6.
For conditional expression (6),
More preferably, the lower limit value is 0.8, more preferably 0.85.
More preferably, the upper limit value is 1.2, more preferably 1.15.
For conditional expression (7),
More preferably, the lower limit value is 1.70, more preferably 1.74.
More preferably, the upper limit value is 1.93, more preferably 1.92.
Conditional expression (8)
More preferably, the lower limit is 1.67, more preferably 1.69.
More preferably, the upper limit value is 1.93, more preferably 1.91.

  The above-described rear focus lens system may satisfy a plurality of configurations at the same time. This is preferable in obtaining a good rear focus lens system and an imaging apparatus. Moreover, the combination of a preferable structure is arbitrary. For each conditional expression, only the upper limit value or lower limit value of the numerical range of the more limited conditional expression may be limited.

  Embodiments of a rear focus lens system and an imaging apparatus according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments.

  The embodiment shown below is a compact, bright, high-performance, wide-field-of-view rear focus lens system that is optimal for wide-angle lenses, particularly for use in interchangeable lens systems of digital cameras. Further, the focusing lens group may be used also as the wobbling lens group.

  Examples 1 to 9 of the rear focus lens system of the present invention will be described below. FIGS. 1 to 5 show lens cross-sectional views when focusing on an object at infinity according to Examples 1 to 9, respectively. 1 to 5, the front lens group is indicated by LA, the aperture stop is indicated by S, the rear lens group is indicated by LB, the parallel plate is indicated by C, and the image plane is indicated by I. Furthermore, the front negative lens group is indicated by LA1, the front positive lens group is indicated by LA2, the rear positive lens group is indicated by LB1, and the focusing lens group is indicated by LB2. In FIGS. 1 to 5, a filter (dust removal filter, infrared cut filter, low-pass filter) and a cover glass that protects the imaging surface are illustrated as one optically equivalent parallel plate C.

  As shown in FIG. 1A, the rear focus lens system of Embodiment 1 includes, in order from the object side, a front lens unit LA having positive refractive power, an aperture stop S, and a rear lens unit LB having positive refractive power. It consists of and. Further, the front lens unit LA includes a front negative lens unit LA1 having negative refractive power and a front positive lens unit LA2 having positive refractive power. The rear lens unit LB includes a rear positive lens unit LB1 having a positive refractive power and a focusing lens unit LB2.

  When focusing from an object at infinity to a near object, the front lens unit LA is stationary, the aperture stop S is stationary, the rear positive lens unit LB1 is stationary, and the focusing lens unit LB2 is moved to the image side. .

  In order from the object side, the front negative lens unit LA1 includes a negative meniscus lens L1 having a convex surface directed toward the object side. The front positive lens unit LA2 includes a biconcave negative lens L2, a biconvex positive lens L3, a biconvex positive lens L4, and a biconcave negative lens L5. Here, the biconcave negative lens L2 and the biconvex positive lens L3 are cemented. The rear positive lens unit LB1 includes a biconcave negative lens L6, a biconvex positive lens L7, and a biconvex positive lens L8. Here, the biconcave negative lens L6 and the biconvex positive lens L7 are cemented. The focusing lens unit LB2 includes a negative meniscus lens L9 having a convex surface directed toward the image side.

  The aspheric surfaces are used for a total of six surfaces including both surfaces of the negative meniscus lens L1, both surfaces of the biconvex positive lens 8, and both surfaces of the negative meniscus lens L9.

  The rear focus lens system of Example 2 is shown in FIG. The order of arrangement of the lens groups and the refractive power of each lens group are the same as in the first embodiment.

  When focusing from an object at infinity to a close object, each lens group moves (moves and stops) in the same manner as in the first embodiment.

  In order from the object side, the front negative lens unit LA1 includes a biconcave negative lens L1 and a biconcave negative lens L2. The front positive lens unit LA2 includes a positive meniscus lens L3 having a convex surface facing the image side, a biconvex positive lens L4, and a positive meniscus lens L5 having a convex surface facing the image side. Here, the biconvex positive lens L4 and the positive meniscus lens L5 are cemented. The rear positive lens unit LB1 includes a biconcave negative lens L6, a biconvex positive lens L7, and a biconvex positive lens L8. Here, the biconcave negative lens L6 and the biconvex positive lens L7 are cemented. The focusing lens unit LB2 includes a negative meniscus lens L9 having a convex surface directed toward the image side.

  The aspheric surfaces are used for a total of four surfaces including both surfaces of the biconvex positive lens L8 and both surfaces of the negative meniscus lens L9.

  The rear focus lens system of Example 3 is shown in FIG. The order of arrangement of the lens groups and the refractive power of each lens group are the same as in the first embodiment.

  When focusing from an object at infinity to a close object, each lens group moves (moves and stops) in the same manner as in the first embodiment.

  In order from the object side, the front negative lens unit LA1 includes a negative meniscus lens L1 having a convex surface directed toward the object side. The front positive lens unit LA2 includes a convex plano positive lens L2 and a planoconcave negative lens L3. Here, the convex plano-positive lens L2 and the plano-concave negative lens L3 are cemented. The rear positive lens unit LB1 includes a biconcave negative lens L4, a biconvex positive lens L5, and a biconvex positive lens L6. Here, the biconcave negative lens L4 and the biconvex positive lens L5 are cemented. The focusing lens unit LB2 includes a negative meniscus lens L7 having a convex surface directed toward the object side.

  The aspheric surfaces are used for a total of four surfaces including both surfaces of the negative meniscus lens L1 and both surfaces of the biconvex positive lens L6.

  The rear focus lens system of Example 4 is shown in FIG. The order of arrangement of the lens groups and the refractive power of each lens group are the same as in the first embodiment.

  When focusing from an object at infinity to a close object, each lens group moves (moves and stops) in the same manner as in the first embodiment.

  In order from the object side, the front negative lens unit LA1 includes a negative meniscus lens L1 having a convex surface directed toward the object side. The front positive lens unit LA2 includes a positive meniscus lens L2 having a convex surface directed toward the object side. The rear positive lens unit LB1 includes a biconcave negative lens L3, a biconvex positive lens L4, and a biconvex positive lens L5. Here, the biconcave negative lens L3 and the biconvex positive lens L4 are cemented. The focusing lens unit LB2 includes a biconcave negative lens L6.

  The aspheric surfaces are used for a total of four surfaces including both surfaces of the negative meniscus lens L1 and both surfaces of the biconvex positive lens L5.

  The rear focus lens system of Example 5 is shown in FIG. The order of arrangement of the lens groups and the refractive power of each lens group are the same as in the first embodiment.

  When focusing from an object at infinity to a close object, each lens group moves (moves and stops) in the same manner as in the first embodiment.

  In order from the object side, the front negative lens unit LA1 includes a negative meniscus lens L1 having a convex surface directed toward the object side. The front positive lens unit LA2 includes a negative meniscus lens L2 having a convex surface facing the object side, and a positive meniscus lens L3 having a convex surface facing the object side. Here, the negative meniscus lens L2 and the positive meniscus lens L3 are cemented. The rear positive lens unit LB1 includes a biconcave negative lens L4, a biconvex positive lens L5, and a biconvex positive lens L6. Here, the biconcave negative lens L4 and the biconvex positive lens L5 are cemented. The focusing lens unit LB2 includes a negative meniscus lens L7 having a convex surface directed toward the object side.

  The aspheric surfaces are used for a total of four surfaces including both surfaces of the negative meniscus lens L1 and both surfaces of the biconvex positive lens L6.

  The rear focus lens system of Example 6 is shown in FIG. The order of arrangement of the lens groups and the refractive power of each lens group are the same as in the first embodiment.

  When focusing from an object at infinity to a close object, each lens group moves (moves and stops) in the same manner as in the first embodiment.

  In order from the object side, the front negative lens unit LA1 includes a negative meniscus lens L1 having a convex surface directed toward the object side. The front positive lens unit LA2 includes a positive meniscus lens L2 having a convex surface facing the object side, a positive meniscus lens L3 having a convex surface facing the image side, and a negative meniscus lens L4 having a convex surface facing the image side. . Here, the positive meniscus lens L3 and the negative meniscus lens L4 are cemented. The rear positive lens unit LB1 includes a biconcave negative lens L5, a biconvex positive lens L6, and a biconvex positive lens L7. Here, the biconcave negative lens L5 and the biconvex positive lens L6 are cemented. The focusing lens unit LB2 includes a negative meniscus lens L8 having a convex surface facing the image side.

  The aspheric surfaces are used for a total of six surfaces including both surfaces of the negative meniscus lens L1, both surfaces of the biconvex positive lens L7, and both surfaces of the negative meniscus lens L8.

  The rear focus lens system of Example 7 is shown in FIG. The order of arrangement of the lens groups and the refractive power of each lens group are the same as in the first embodiment.

  When focusing from an object at infinity to a close object, the front lens unit LA is stationary, the aperture stop S is stationary, the rear positive lens unit LB1 is stationary, and the focusing lens unit LB2 is moved to the object side. .

  In order from the object side, the front negative lens unit LA1 includes a negative meniscus lens L1 having a convex surface directed toward the object side. The front positive lens unit LA2 includes a biconvex positive lens L2, a biconcave negative lens L3, a biconvex positive lens L4, and a negative meniscus lens L5 having a convex surface facing the object side. The rear positive lens unit LB1 includes a biconcave negative lens L6, a biconvex positive lens L7, and a biconvex positive lens L8. Here, the biconcave negative lens L5 and the biconvex positive lens L6 are cemented. The focusing lens unit LB2 includes a biconvex positive lens L9.

  The aspheric surfaces are used for a total of four surfaces including both surfaces of the negative meniscus lens L1 and both surfaces of the biconvex positive lens L8.

  The rear focus lens system of Example 8 is shown in FIG. The order of arrangement of the lens groups and the refractive power of each lens group are the same as in the seventh embodiment.

  When focusing from an object at infinity to a close object, each lens unit moves (moves and stops) in the same manner as in the seventh embodiment.

  In order from the object side, the front negative lens unit LA1 includes a negative meniscus lens L1 having a convex surface directed toward the object side. The front positive lens unit LA2 includes a positive meniscus lens L2 having a convex surface facing the image side, a biconvex positive lens L3, and a biconcave negative lens L4. Here, the biconvex positive lens L3 and the biconcave negative lens L4 are cemented. The rear positive lens unit LB1 includes a biconcave negative lens L5, a biconvex positive lens L6, and a biconvex positive lens L7. Here, the biconcave negative lens L5 and the biconvex positive lens L6 are cemented. The focusing lens unit LB2 includes a biconvex positive lens L8.

  Aspheric surfaces are used for a total of five surfaces including both surfaces of the negative meniscus lens L1, both surfaces of the biconvex positive lens L7, and the object side surface of the biconvex positive lens L8.

  The rear focus lens system of Example 9 is shown in FIG. The order of arrangement of the lens groups and the refractive power of each lens group are the same as in the seventh embodiment.

  When focusing from an object at infinity to a close object, each lens unit moves (moves and stops) in the same manner as in the seventh embodiment.

  In order from the object side, the front negative lens unit LA1 includes a negative meniscus lens L1 having a convex surface directed toward the object side. The front positive lens group LA2 includes a biconvex positive lens L2, a biconcave negative lens L3, and a biconvex positive lens L4. The rear positive lens unit LB1 includes a negative meniscus lens L5 having a convex surface facing the image side, a biconvex positive lens L6, and a positive meniscus lens L7 having a convex surface facing the image side. The focusing lens unit LB2 includes a positive meniscus lens L8 having a convex surface directed toward the object side.

  The aspheric surfaces are used for a total of six surfaces including both surfaces of the negative meniscus lens L1, both surfaces of the positive meniscus lens L7, and both surfaces of the positive meniscus lens L8.

  In addition, L6 of Examples 1, 2, and 7, L4 of Examples 3 and 5, L3 of Example 4, and L5 of Examples 6, 8, and 9 all had the object side facing the concave surface on the object side. It is a negative lens. In each of the first, second, and seventh L7, the third and fifth L5, the fourth L4, and the sixth, eighth, and ninth L6, the positive lens has the convex side toward the image side. It is. Each of the first, second, and seventh L8, the third and fifth L6, the fourth L5, and the sixth, eighth, and ninth L7 is a positive lens in which the image side faces a convex surface toward the image side. It is.

  Below, the numerical data of each said Example are shown. Symbols are the above, r is the radius of curvature of each lens surface, d is the distance between the lens surfaces, nd is the refractive index of the d-line of each lens, and νd is the Abbe number of each lens. The focal length is the focal length of the entire system, Fno is the F number, and ω is the half angle of view. The total length is obtained by adding back focus to the distance from the lens front surface to the lens final surface. BF (back focus) represents the distance from the last lens surface to the paraxial image plane in terms of air.

  As for the in-focus state, when focusing on an object at infinity at infinity, when the distance between object images is 250 mm, it indicates when the object is focused when the distance between objects is 250 mm. Yes. Note that the state where the object is focused on a short distance object includes, for example, a state where the object-image distance is 250 mm. Further, in the group focal length, the value of the focal length of the rear lens unit LB is a value when the object is focused on an infinite object.

The aspherical shape is expressed by the following equation, where x is an optical axis with the light traveling direction being positive, and y is a direction orthogonal to the optical axis.
x = (y ² / R) / [1+ {1− (K + 1) (y / R) ² } ^1/2 ]
^{+ A4y 4 + A6y 6 + A8y} 8 + A10y 10 + A12y 12
Here, R is a paraxial radius of curvature, K is a conical coefficient, and A4, A6, A8, A10, and A12 are fourth, sixth, eighth, tenth, and twelfth aspheric coefficients, respectively. In the aspheric coefficient, “e−n” (n is an integer) indicates “10 ⁻ⁿ ”.

Numerical example 1
Unit mm

Surface data surface number rd nd νd
Object ∞ ∞
1 * 35.3707 1.200 1.58313 59.38
2 * 12.1077 5.188
3 -20.0898 1.000 1.92286 18.90
4 152.4567 3.162 1.90366 31.32
5 -22.4250 0.150
6 18.2374 3.000 2.00069 25.46
7 -111.7807 0.248
8 -67.2318 1.000 1.49700 81.54
9 42.0807 2.089
10 (Aperture) ∞ 4.958
11 -9.3487 0.800 1.84666 23.78
12 24.3538 3.432 1.59282 68.63
13 -13.6192 0.150
14 * 35.8615 4.638 1.80610 40.92
15 * -13.1962 variable
16 * -18.3575 1.234 1.80610 40.92
17 * -27.1640 variable
18 ∞ 4.000 1.51633 64.14
19 ∞ 1.000
Image plane (imaging plane) ∞

Aspheric data 1st surface
K = 2.2548
A4 = -4.9174E-06, A6 = -1.1263E-08, A8 = 0.0000E + 00, A10 = 0.0000E + 00
Second side
K = -0.8097
A4 = 2.6014E-05, A6 = 3.0364E-08, A8 = 0.0000E + 00, A10 = 0.0000E + 00
14th page
K = 3.3649
A4 = -4.7353E-05, A6 = 1.0148E-07, A8 = -3.7950E-10, A10 = 0.0000E + 00
15th page
K = 0.0787
A4 = 8.1510E-05, A6 = -5.0514E-09, A8 = 2.2062E-09, A10 = 0.0000E + 00
16th page
K = -5.0265
A4 = 2.2130E-04, A6 = -5.6885E-07, A8 = 0.0000E + 00, A10 = 0.0000E + 00
17th page
K = 0.0000
A4 = 2.8730E-04, A6 = -5.1837E-07, A8 = 0.0000E + 00, A10 = 0.0000E + 00

Various data
Focal length at infinity 15.818
Fno 2.040
Angle of view (2ω) 69.94
Statue height 10.820
BF 16.434
Total length 50.183

In-focus state
At infinity When object distance is 250mm
d15 1.500 3.769
d17 12.796 10.527
Moving distance of focusing lens unit LB2 2.269mm to the image side

Group Focal Length Front Lens Group LA Front Negative Lens Group LA1 Front Positive Lens Group LA2
32.700 -32.978 20.371
Rear lens group LB Rear positive lens group LB1 Focusing lens group LB2
22.536 16.157 -74.931

Numerical example 2
Unit mm

Surface data surface number rd nd νd
Object ∞ ∞
1 -190.7928 1.000 1.60311 60.64
2 17.0709 4.283
3 -65.6398 1.000 1.54072 47.23
4 29.1506 2.550
5 -59.8779 2.112 1.80400 46.57
6 -28.4422 0.195
7 17.8187 3.587 1.72916 54.68
8 -3613.4330 1.000 1.59270 35.31
9 -77.2778 1.971
10 (Aperture) ∞ 10.396
11 -9.6476 0.800 1.75520 27.51
12 39.4214 3.789 1.69680 55.53
13 -16.3094 0.150
14 * 36.7323 5.294 1.74320 49.34
15 * -15.2211 variable
16 * -12.7481 1.000 1.74320 49.34
17 * -17.7438 variable
18 ∞ 4.000 1.51633 64.14
19 ∞ 1.000
Image plane (imaging plane) ∞

Aspheric data 14th surface
K = 0.0000
A4 = -1.6842E-06, A6 = -2.2466E-07, A8 = 5.1823E-10, A10 = 0.0000E + 00
15th page
K = 0.0000
A4 = 9.5171E-05, A6 = -3.1876E-07, A8 = 1.1592E-09, A10 = 0.0000E + 00
16th page
K = 0.0000
A4 = 4.9819E-04, A6 = -2.3882E-06, A8 = 9.0718E-09, A10 = 0.0000E + 00
17th page
K = 0.0000
A4 = 4.0096E-04, A6 = -1.5898E-06, A8 = 3.6137E-09, A10 = 0.0000E + 00

Various data
Focal length at infinity 16.579
Fno 1.730
Angle of view (2ω) 71.46
Statue height 10.820
BF 18.399
Total length 59.420

In-focus state
At infinity When object distance is 250mm
d15 1.894 3.895
d17 14.761 12.760
Moving distance of focusing lens group LB2 To the image side: 2.001mm

Group Focal Length Front Lens Group LA Front Negative Lens Group LA1 Front Positive Lens Group LA2
39.668 -14.204 15.785
Rear lens group LB Rear positive lens group LB1 Focusing lens group LB2
25.993 17.649 -66.609

Numerical Example 3
Unit mm

Surface data surface number rd nd νd
Object ∞ ∞
1 * 202.0492 0.900 1.49700 81.54
2 * 12.1016 3.266
3 18.0250 2.605 1.90366 31.32
4 ∞ 0.800 1.76182 26.52
5 221.7383 2.307
6 (Aperture) ∞ 5.559
7 -8.6571 0.900 1.92286 18.90
8 93.4944 4.021 1.78590 44.20
9 -12.6425 0.174
10 * 40.9578 4.926 1.91082 35.25
11 * -16.9813 variable
12 157.1183 1.000 1.58913 61.14
13 45.4249 Variable
14 ∞ 4.000 1.51633 64.14
15 ∞ 1.000
Image plane (imaging plane) ∞

Aspheric data 1st surface
K = 0.0000
A4 = 2.0193E-05, A6 = -2.3044E-07, A8 = 7.5434E-10, A10 = 0.0000E + 00
Second side
K = 0.0220
A4 = -1.2525E-05, A6 = -1.6986E-07, A8 = -4.0538E-09, A10 = 0.0000E + 00
10th page
K = 0.9448
A4 = -3.1443E-05, A6 = 9.8803E-08, A8 = -1.2435E-10, A10 = 0.0000E + 00
11th page
K = -0.0882
A4 = 3.7209E-05, A6 = -3.3422E-09, A8 = 4.4759E-10, A10 = 0.0000E + 00

Various data
Focal length at infinity 16.999
Fno 2.040
Angle of view (2ω) 69.50
Statue height 10.820
BF 17.725
Total length 45.683

In-focus state
At infinity When object distance is 250mm
d11 1.500 3.599
d13 14.087 11.988
Moving distance of focusing lens group LB2 2.099mm to the image side

Group Focal Length Front Lens Group LA Front Negative Lens Group LA1 Front Positive Lens Group LA2
71.066 -25.942 21.271
Rear lens group LB Rear positive lens group LB1 Focusing lens group LB2
19.509 14.163 -59.703

Numerical Example 4
Unit mm

Surface data surface number rd nd νd
Object ∞ ∞
1 * 101.4317 1.000 1.58313 59.38
2 * 8.1591 0.350
3 10.5158 2.308 1.91082 35.25
4 110.2627 1.054
5 (Aperture) ∞ 4.370
6 -7.2727 0.800 1.84666 23.78
7 50.4515 4.681 1.77250 49.60
8 -11.0870 0.150
9 * 29.3851 7.022 1.74320 49.29
10 * -14.2838 variable
11 -46.9681 1.200 1.77250 49.60
12 179.0025 Variable
13 ∞ 4.000 1.51633 64.14
14 ∞ 1.000
Image plane (imaging plane) ∞

Aspheric data 1st surface
K = 0.0000
A4 = 3.5475E-05, A6 = -1.4892E-06, A8 = -3.3787E-08, A10 = 9.8311E-10
Second side
K = 0.5879
A4 = -1.9847E-04, A6 = -6.2865E-06, A8 = -2.1899E-07, A10 = 2.0709E-09
9th page
K = -0.3265
A4 = -3.8469E-05, A6 = 9.9942E-08, A8 = 7.1888E-11, A10 = 0.0000E + 00
10th page
K = -0.3223
A4 = 4.9650E-05, A6 = -2.7076E-08, A8 = 4.1331E-10, A10 = 2.1323E-12

Various data
Focal length at infinity 17.349
Fno 2.860
Angle of view (2ω) 68.71
Statue height 10.820
BF 17.118
Total length 41.153

In-focus state
At infinity When object distance is 250mm
d10 1.100 2.798
d12 13.480 11.782
Moving distance of focusing lens group LB2 1.698mm to image side

Group Focal Length Front Lens Group LA Front Negative Lens Group LA1 Front Positive Lens Group LA2
68.346 -15.276 12.623
Rear lens group LB Rear positive lens group LB1 Focusing lens group LB2
18.274 12.483 -48.052

Numerical Example 5
Unit mm

Surface data surface number rd nd νd
Object ∞ ∞
1 * 43.7949 1.000 1.58313 59.38
2 * 10.6265 4.183
3 16.8038 1.100 1.59282 68.63
4 8.5000 5.221 1.72000 43.69
5 105.7665 4.000
6 (Aperture) ∞ 4.168
7 -7.6266 0.900 1.80518 25.42
8 27.7547 4.174 1.75700 47.82
9 -12.3848 0.150
10 * 36.1934 4.695 1.83481 42.71
11 * -16.7266 variable
12 89.9921 1.200 1.90366 31.32
13 40.0519 Variable
14 ∞ 4.000 1.51633 64.14
15 ∞ 1.000
Image plane (imaging plane) ∞

Aspheric data 1st surface
K = 0.0000
A4 = 2.8426E-05, A6 = -3.7297E-07, A8 = 1.4123E-09, A10 = 0.0000E + 00
Second side
K = 0.0000
A4 = -1.1806E-05, A6 = -3.4503E-07, A8 = -6.2413E-09, A10 = 0.0000E + 00
10th page
K = 0.0000
A4 = -3.0172E-05, A6 = 1.2813E-07, A8 = -5.5945E-11, A10 = 0.0000E + 00
11th page
K = 0.0000
A4 = 4.7195E-05, A6 = -3.8668E-08, A8 = 9.9417E-10, A10 = 0.0000E + 00

Various data
Focal length at infinity 16.285
Fno 1.840
Angle of view (2ω) 70.81
Statue height 10.820
BF 18.392
Total length 50.683

In-focus state
At infinity When object distance is 250mm
d11 1.500 4.288
d13 14.754 11.966
Moving distance of focusing lens group LB2 2.788mm to image side

Group Focal Length Front Lens Group LA Front Negative Lens Group LA1 Front Positive Lens Group LA2
102.081 -24.332 22.591
Rear lens group LB Rear positive lens group LB1 Focusing lens group LB2
18.522 14.725 -80.789

Numerical Example 6
Unit mm

Surface data surface number rd nd νd
Object ∞ ∞
1 * 117.9211 1.338 1.49710 81.56
2 * 12.1579 2.749
3 21.2660 2.785 2.00069 25.46
4 145.3244 1.561
5 -89.9683 2.555 1.49700 81.54
6 -18.3424 1.162 1.69895 30.13
7 -38.1917 4.115
8 (Aperture) ∞ 3.550
9 -8.1530 0.984 1.80810 22.76
10 46.2680 5.788 1.72916 54.68
11 -12.9673 0.017
12 * 30.3731 5.805 1.80610 40.40
13 * -18.3695 variable
14 * -53.9241 1.228 1.73310 48.89
15 * -700.9583 Variable
16 ∞ 4.000 1.51633 64.14
17 ∞ 1.000
Image plane (imaging plane) ∞

Aspheric data 1st surface
K = 26.0388
A4 = -1.9088E-05, A6 = -1.1827E-08, A8 = -3.4935E-11, A10 = 0.0000E + 00
Second side
K = -0.6040
A4 = -3.2316E-05, A6 = -1.4898E-07, A8 = -1.3525E-09, A10 = 0.0000E + 00
12th page
K = -0.0251
A4 = -2.8303E-05, A6 = 4.4410E-08, A8 = -1.5724E-10, A10 = 0.0000E + 00
Side 13
K = -0.5158
A4 = 3.1993E-05, A6 = -6.5634E-08, A8 = 1.8233E-12, A10 = 0.0000E + 00
14th page
K = 0.3856
A4 = 1.7428E-04, A6 = -8.8776E-07, A8 = 7.0241E-10, A10 = 0.0000E + 00
15th page
K = -0.4547
A4 = 1.7590E-04, A6 = -7.5239E-07, A8 = -2.5509E-10, A10 = 0.0000E + 00

Various data
Focal length at infinity 15.984
Fno 2.040
Angle of view (2ω) 72.36
Statue height 10.820
BF 17.436
Total length 52.947

In-focus state
At infinity When object distance is 250mm
d13 1.874 4.454
d15 13.798 11.218
Moving distance of focusing lens group LB2 2.580mm to the image side

Group Focal Length Front Lens Group LA Front Negative Lens Group LA1 Front Positive Lens Group LA2
103.532 -27.384 24.167
Rear lens group LB Rear positive lens group LB1 Focusing lens group LB2
17.196 13.631 -79.751

Numerical Example 7
Unit mm

Surface data surface number rd nd νd
Object ∞ ∞
1 * 168.1123 1.200 1.58313 59.38
2 * 11.8795 7.678
3 21.5466 4.009 1.91082 35.25
4 -60.6439 0.915
5 -25.9904 0.800 1.62004 36.26
6 14.6445 0.200
7 13.8827 4.183 1.74400 44.78
8 -33.5510 0.200
9 43.6351 0.800 1.59270 35.31
10 22.6873 2.100
11 (Aperture) ∞ 4.576
12 -10.0260 0.800 1.84666 23.78
13 35.9093 2.879 1.88300 40.76
14 -41.1893 0.200
15 * 98.4378 3.974 1.86400 40.58
16 * -15.6770 Variable
17 57.7542 3.000 1.69350 53.21
18 -145.6899 Variable
19 ∞ 4.000 1.51633 64.14
20 ∞ 1.000
Image plane (imaging plane) ∞

Aspheric data 1st surface
K = 144.9293
A4 = -1.0666E-05, A6 = 3.4212E-08, A8 = -1.5519E-10, A10 = 0.0000E + 00
Second side
K = -0.2024
A4 = -2.1102E-05, A6 = -6.9102E-08, A8 = -2.3655E-10, A10 = 0.0000E + 00
15th page
K = -0.6305
A4 = -2.1605E-05, A6 = 2.3357E-07, A8 = -5.5691E-10, A10 = 0.0000E + 00
16th page
K = -1.1787
A4 = -1.5594E-06, A6 = 1.3092E-07, A8 = 7.6288E-10, A10 = 0.0000E + 00

Various data
Focal length at infinity 16.660
Fno 1.720
Angle of view (2ω) 70.77
Statue height 10.820
BF 15.235
Total length 57.182

In-focus state
At infinity When object distance is 250mm
d16 4.433 1.750
d18 11.596 14.279
Moving distance of focusing lens group LB2 2.683mm to the object side

Group Focal Length Front Lens Group LA Front Negative Lens Group LA1 Front Positive Lens Group LA2
34.859 -21.983 18.836
Rear lens group LB Rear positive lens group LB1 Focusing lens group LB2
23.923 44.778 60.000

Numerical Example 8
Unit mm

Surface data surface number rd nd νd
Object ∞ ∞
1 * 196.5522 1.200 1.58313 59.38
2 * 10.1274 5.095
3 -33.8189 1.367 2.00069 25.46
4 -29.6860 0.162
5 12.5469 5.138 1.81600 46.62
6 -36.4228 1.000 1.59270 35.31
7 44.4790 1.667
8 (Aperture) ∞ 6.000
9 -7.9245 0.800 1.80000 29.84
10 18.1350 3.000 1.72916 54.68
11 -24.8150 0.141
12 * 65.4178 3.901 1.74320 49.34
13 * -14.8165 variable
14 * 53.0196 3.074 1.69350 53.21
15 -56.3891 Variable
16 ∞ 4.000 1.51633 64.14
17 ∞ 1.000
Image plane (imaging plane) ∞

Aspheric data 1st surface
K = -10.0019
A4 = -2.8064E-05, A6 = 1.3835E-07, A8 = -2.2885E-10, A10 = 0.0000E + 00
Second side
K = -0.9256
A4 = 2.8961E-05, A6 = -9.3833E-08, A8 = 5.1634E-09, A10 = 0.0000E + 00
12th page
K = 8.0040
A4 = -3.8878E-06, A6 = 2.2640E-07, A8 = 9.9634E-11, A10 = 0.0000E + 00
Side 13
K = -0.9171
A4 = 1.9493E-05, A6 = 2.3813E-07, A8 = 1.9649E-09, A10 = 0.0000E + 00
14th page
K = -4.2677
A4 = -7.3765E-06, A6 = 3.8310E-08, A8 = -2.8740E-10, A10 = 0.0000E + 00

Various data
Focal length at infinity 16.735
Fno 2.040
Angle of view (2ω) 70.23
Statue height 10.820
BF 15.666
Total length 52.154

In-focus state
At infinity When object distance is 250mm
d13 3.943 1.980
d15 12.028 13.991
Moving distance of focusing lens group LB2 1.963mm to the object side

Group Focal Length Front Lens Group LA Front Negative Lens Group LA1 Front Positive Lens Group LA2
31.277 -18.354 15.186
Rear lens group LB Rear positive lens group LB1 Focusing lens group LB2
21.844 75.311 39.862

Numerical Example 9
Unit mm

Surface data surface number rd nd νd
Object ∞ ∞
1 * 46.2702 1.200 1.58313 59.38
2 * 9.2500 3.773
3 23.8604 3.266 1.90366 31.32
4 -629.7890 3.579
5 -19.6207 1.200 1.72151 29.23
6 55.7447 0.150
7 16.1220 3.171 1.88300 40.76
8 -38.8954 2.836
9 (Aperture) ∞ 3.886
10 -7.1093 0.800 1.84666 23.78
11 -50.0291 0.150
12 89.6178 3.426 1.72000 46.02
13 -9.0349 0.150
14 * -19.5391 1.868 1.80610 40.92
15 * -14.7852 variable
16 * 39.4016 2.320 1.80610 40.92
17 * 123.6390 Variable
18 ∞ 4.000 1.51633 64.14
19 ∞ 1.000
Image plane (imaging plane) ∞

Aspheric data 1st surface
K = 6.9901
A4 = -2.3898E-05, A6 = 1.4665E-07, A8 = 0.0000E + 00, A10 = 0.0000E + 00
Second side
K = -0.2147
A4 = -8.7419E-05, A6 = -4.1755E-07, A8 = 0.0000E + 00, A10 = 0.0000E + 00
14th page
K = 0.0000
A4 = -2.0238E-04, A6 = 1.3479E-06, A8 = -4.0204E-08, A10 = 0.0000E + 00
15th page
K = -0.5465
A4 = -7.0396E-05, A6 = 1.3019E-06, A8 = -9.9025E-09, A10 = 0.0000E + 00
16th page
K = -27.8427
A4 = -8.4185E-06, A6 = -7.2382E-07, A8 = 0.0000E + 00, A10 = 0.0000E + 00
17th page
K = 0.0000
A4 = -8.0718E-05, A6 = -4.7852E-07, A8 = 0.0000E + 00, A10 = 0.0000E + 00

Various data
Focal length at infinity 15.698
Fno 2.040
Angle of view (2ω) 69.39
Statue height 10.820
BF 14.197
Total length 50.182

In-focus state
At infinity When object distance is 250mm
d15 4.210 1.4870
d17 10.559 13.282
Moving distance of focusing lens unit LB2 2.723mm toward the object side

Group Focal Length Front Lens Group LA Front Negative Lens Group LA1 Front Positive Lens Group LA2
30.755 -20.066 16.897
Rear lens group LB Rear positive lens group LB1 Focusing lens group LB2
23.218 38.302 70.871

  The aberration diagrams of Examples 1 to 9 are shown in FIGS. 6 to 14, respectively. In each figure, “FIY” indicates the maximum image height.

  In these aberration diagrams, (a), (b), (c), and (d) are spherical aberration (SA), astigmatism (AS), distortion aberration (DT), and lateral chromatic aberration at infinity, respectively. (CC) is shown.

  Also, (e), (g), (g), and (h) are spherical aberration (SA), astigmatism (AS), distortion (DT), and lateral chromatic aberration (at a distance between object images of 250 mm, respectively). CC).

Next, the values of conditional expressions (1) to (8) in each example will be listed.
Example 1 Example 2 Example 3 Example 4 Example 5
(1) F _no・ L _air / f _ent 6.47 6.20 5.48 6.78 5.73
(2) | f _Rfo | / f _ent 4.74 4.02 3.51 2.77 4.96
(3) f _FN / f _ent -2.08 -0.86 -1.53 -0.88 -1.49
(4) f _Rfo / f _{ent -----}
(5) f _Rfo / f _ent -4.74 -4.02 -3.51 -2.77 -4.96
(6) fb _air / f _ent 1.04 1.11 1.04 0.99 1.13
(7) nL _asp 1.806 1.743 1.911 1.743 1.835
(8) nL _{Rfo 1.806} 1.743 1.589 1.773 1.904

Example 6 Example 7 Example 8 Example 9
(1) F _no・ L _air / f _ent 6.76 5.90 6.36 6.52
(2) | f _Rfo | / f _ent 4.99 3.60 2.38 4.51
(3) f _FN / f _ent -1.71 -1.32 -1.10 -1.28
(4) f _Rfo / f _ent -3.60 2.38 4.51
(5) f _Rfo / f _ent -4.99---
(6) fb _air / f _ent 1.09 0.91 0.94 0.90
(7) nL _asp 1.806 1.864 1.743 1.806
(8) nL _Rfo 1.733 1.694 1.694 1.806

The element values of conditional expressions (1) to (8) are shown below.
Example 1 Example 2 Example 3 Example 4 Example 5
F _no 2.040 1.730 2.040 2.860 1.840
L _air 50.183 59.420 45.683 41.153 50.683
f _Rfo -74.931 -66.609 -59.703 -48.052 -80.789
f _FN -32.978 -14.204 -25.942 -15.276 -24.332
f _ent 15.818 16.579 16.999 17.349 16.285
fb _air 16.434 18.399 17.725 17.118 18.392

Example 6 Example 7 Example 8 Example 9
F _no 2.040 1.720 2.040 2.040
L _air 52.947 57.182 52.154 50.182
f _Rfo -79.751 60.000 39.862 70.871
f _FN -27.384 -21.983 -18.354 -20.066
f _ent 15.984 16.660 16.735 15.698
fb _air 17.436 15.235 15.666 14.197

  FIG. 15 is a cross-sectional view of a single lens mirrorless camera as an electronic imaging apparatus. In FIG. 15, reference numeral 1 denotes a single-lens mirrorless camera, 2 denotes a photographing lens system disposed in the lens barrel, and 3 denotes a lens barrel mounting portion that allows the photographing lens system 2 to be attached to and detached from the single-lens mirrorless camera 1. As the mount unit 3, a screw type mount, a bayonet type mount, or the like is used. In this example, a bayonet type mount is used. Reference numeral 4 denotes an image sensor surface, and 5 denotes a back monitor. A small CCD or CMOS is used as the image sensor.

  For example, the rear focus lens system of the present invention shown in the first to ninth embodiments is used as the photographing lens system 2 of the single lens mirrorless camera 1.

  16 and 17 are conceptual diagrams of the configuration of the imaging apparatus according to the present invention. FIG. 16 is a front perspective view showing the appearance of a digital camera 40 as an image pickup apparatus, and FIG. 17 is a rear perspective view of the same. The rear focus lens system of the present invention is used for the photographing optical system 41 of the digital camera 40.

  The digital camera 40 of this embodiment includes a photographing optical system 41 positioned on the photographing optical path 42, a shutter button 45, a liquid crystal display monitor 47, and the like. When the shutter button 45 disposed on the upper part of the digital camera 40 is pressed, In conjunction with this, photographing is performed through the photographing optical system 41, for example, the rear focus lens system of the first embodiment. An object image formed by the photographing optical system 41 is formed on an image sensor (photoelectric conversion surface) provided in the vicinity of the imaging surface. The object image received by the image sensor is displayed on the liquid crystal display monitor 47 provided on the back of the camera as an electronic image by the processing means. In addition, the photographed electronic image can be recorded in a recording unit.

  FIG. 18 is a block diagram showing an internal circuit of a main part of the digital camera 40. In the following description, the processing means described above is configured by, for example, the CDS / ADC unit 24, the temporary storage memory 17, the image processing unit 18, and the like, and the storage unit is configured by the storage medium unit 19 or the like.

  As shown in FIG. 18, the digital camera 40 is connected to the operation unit 12, the control unit 13 connected to the operation unit 12, and the control signal output port of the control unit 13 via buses 14 and 15. An imaging drive circuit 16, a temporary storage memory 17, an image processing unit 18, a storage medium unit 19, a display unit 20, and a setting information storage memory unit 21 are provided.

  The temporary storage memory 17, the image processing unit 18, the storage medium unit 19, the display unit 20, and the setting information storage memory unit 21 can mutually input and output data via the bus 22. In addition, a CCD 49 and a CDS / ADC unit 24 are connected to the imaging drive circuit 16.

  The operation unit 12 includes various input buttons and switches, and notifies the control unit of event information input from the outside (camera user) via these buttons. The control unit 13 is a central processing unit composed of, for example, a CPU, and has a built-in program memory (not shown) and controls the entire digital camera 40 according to a program stored in the program memory.

  The CCD 49 is an image pickup device that is driven and controlled by the image pickup drive circuit 16, converts the light amount of each pixel of the object image formed via the image pickup optical system 41 into an electric signal, and outputs the electric signal to the CDS / ADC unit 24.

  The CDS / ADC unit 24 amplifies the electrical signal input from the CCD 49 and performs analog / digital conversion, and raw video data (Bayer data, hereinafter referred to as RAW data) obtained by performing the amplification and digital conversion. Is output to the temporary storage memory 17.

  The temporary storage memory 17 is a buffer made of, for example, SDRAM, and is a memory device that temporarily stores RAW data output from the CDS / ADC unit 24. The image processing unit 18 reads out the RAW data stored in the temporary storage memory 17 or the RAW data stored in the storage medium unit 19, and includes distortion correction based on the image quality parameter designated by the control unit 13. It is a circuit that performs various image processing electrically.

  The storage medium unit 19 is detachably mounted with a card-type or stick-type recording medium made of, for example, a flash memory, and the RAW data transferred from the temporary storage memory 17 or the image processing unit 18 to these flash memories. The image data that has been subjected to the image processing is recorded and held.

  The display unit 20 includes a liquid crystal display monitor 47 and the like, and displays captured RAW data, image data, an operation menu, and the like. The setting information storage memory unit 21 includes a ROM unit that stores various image quality parameters in advance, and a RAM unit that stores image quality parameters read from the ROM unit by an input operation of the operation unit 12.

  The digital camera 40 configured in this manner employs the rear focus lens system of the present invention as the photographing optical system 41, so that a high resolution image can be obtained without degrading the image quality while having a wide angle of view and a small size. An imaging device that is advantageous to obtain can be obtained.

  As described above, the rear focus lens system and the imaging apparatus according to the present invention reduce the electric load and noise during the focusing operation (more preferably during the wobbling operation), and can increase a wide range without degrading the image quality. This is useful for obtaining a resolution image.

LA ... front lens group LA1 ... front negative lens group LA2 ... front positive lens group LB ... rear lens group LB1 ... rear positive lens group LB2 ... focusing lens group S ... aperture stop C ... parallel plate I ... image plane 1 ... single lens Mirrorless camera 2 ... photographic lens system 3 ... lens mount 4 ... imaging element surface 5 ... back monitor 12 ... operation unit 13 ... control units 14 and 15 ... bus 16 ... imaging drive circuit 17 ... temporary storage memory 18 ... image Processing unit 19 ... Storage medium unit 20 ... Display unit 21 ... Setting information storage memory unit 22 ... Bus 24 ... CDS / ADC unit 40 ... Digital camera 41 ... Shooting optical system 42 ... Shooting optical path 45 ... Shutter button 47 ... Liquid crystal display monitor 49 ... CCD

In order to solve the above-described problems and achieve the object, the rear focus lens system of the present invention is:
From the object side to the image side,
A front lens unit having positive refractive power;
The aperture stop,
A rear lens unit having a positive refractive power,
The front lens group includes, in order from the object side, a front negative lens group including one or two lens components having negative refractive power, and a front positive lens group.
The rear lens group includes, in order from the object side, a rear positive lens group and a focusing lens group having negative refractive power,
When focusing from a long-distance object to a short-distance object, the focusing lens group moves to increase the distance from the rear positive lens group,
The focusing lens group consists of one lens component,
The following conditional expression (6-1) is satisfied.
0.75 <fb _air / f _ent ≦ 1.04 (6-1)
However,
fb _air is the back focus of the rear focus lens system,
f _ent is the focal length of the entire rear focus lens system,
It is.

Further, another rear focus lens system of the present invention is
From the object side to the image side,
A front lens unit having positive refractive power;
The aperture stop,
A rear lens unit having a positive refractive power,
The front lens group includes, in order from the object side, a front negative lens group including one or two lens components having negative refractive power, and a front positive lens group.
The rear lens group includes, in order from the object side, a rear positive lens group and a focusing lens group having negative refractive power,
When focusing from a long-distance object to a short-distance object, the focusing lens group moves to increase the distance from the rear positive lens group,
The focusing lens group consists of one lens component,
The focusing lens group is a negative meniscus lens having a convex surface facing the object side or a biconcave negative lens .

Therefore, in the rear focus lens system of the present embodiment, the front negative lens group is disposed closest to the object side in the front lens group. The front negative lens group is composed of one or a plurality of negative lens components. Thus, the front lens group has a negative refractive power lens group on the front side and a positive refractive power lens group on the rear side. Thus, since the front lens group has a retrofocus type configuration, an appropriate back focus can be secured. Here, the front negative lens group may be configured by one or two negative lens components.

Embodiments of a rear focus lens system and an imaging apparatus according to the present invention will be described below in detail with reference to the drawings. Note that the present invention is not limited to the embodiments. Examples 2 and 6-9 are reference examples.

In order from the object side, the front negative lens unit LA1 includes a negative meniscus lens L1 , a biconcave negative lens L2, and a biconvex positive lens L3 having a convex surface directed toward the object side. The front positive lens group LA2 includes a biconvex positive lens L4 and a biconcave negative lens L5. Here, the biconcave negative lens L2 and the biconvex positive lens L3 are cemented. The rear positive lens unit LB1 includes a biconcave negative lens L6, a biconvex positive lens L7, and a biconvex positive lens L8. Here, the biconcave negative lens L6 and the biconvex positive lens L7 are cemented. The focusing lens unit LB2 includes a negative meniscus lens L9 having a convex surface directed toward the image side.

As described above, the rear focus lens system and the imaging apparatus according to the present invention reduce the electric load and noise during the focusing operation (more preferably during the wobbling operation), and can increase a wide range without degrading the image quality. This is useful for obtaining a resolution image.
[Additional Item 1]
From the object side to the image side,
A front lens unit having positive refractive power;
The aperture stop,
It consists of a rear lens group with positive refractive power,
The front lens group includes, in order from the object side, a front negative lens group composed of one or more lens components having a negative refractive power, and a front positive lens group.
The rear lens group, in order from the object side, consists of a rear positive lens group and a focusing lens group having negative refractive power,
When focusing from a long-distance object to a short-distance object, the focusing lens group moves to increase the distance from the rear positive lens group,
The focusing lens group consists of one lens component,
The focusing lens group is a negative meniscus lens having a convex surface directed toward the object side, or a biconcave negative lens.
[Additional Item 2]
From the object side to the image side,
A front lens unit having positive refractive power;
The aperture stop,
It consists of a rear lens group with positive refractive power,
The front lens group includes, in order from the object side, a front negative lens group composed of one or more lens components having a negative refractive power, and a front positive lens group.
The rear lens group, in order from the object side, consists of a rear positive lens group and a focusing lens group having negative refractive power,
When focusing from a long-distance object to a short-distance object, the focusing lens group moves to increase the distance from the rear positive lens group,
The focusing lens group consists of one lens component,
The rear positive lens group has an aspheric lens having a positive refractive power,
The rear focus lens system, wherein the aspherical lens is a lens located closest to the image side in the rear positive lens group.
[Additional Item 3]
From the object side to the image side,
A front lens unit having positive refractive power;
The aperture stop,
It consists of a rear lens group with positive refractive power,
The front lens group includes, in order from the object side, a front negative lens group composed of one or more lens components having a negative refractive power, and a front positive lens group.
The rear lens group, in order from the object side, consists of a rear positive lens group and a focusing lens group having negative refractive power,
When focusing from a long-distance object to a short-distance object, the focusing lens group moves to increase the distance from the rear positive lens group,
The focusing lens group consists of one lens component,
A rear focus lens system satisfying the following conditional expression (6-1):
0.75 <fb _air / f _ent ≦ 1.04 (6-1)
However,
fb _air is the back focus of the rear focus lens system,
f _ent is the focal length of the entire rear focus lens system,
It is.
[Additional Item 4]
From the object side to the image side,
A front lens unit having positive refractive power;
The aperture stop,
It consists of a rear lens group with positive refractive power,
The front lens group includes, in order from the object side, a front negative lens group composed of one or more lens components having a negative refractive power, and a front positive lens group.
The rear lens group, in order from the object side, consists of a rear positive lens group and a focusing lens group having negative refractive power,
When focusing from a long-distance object to a short-distance object, the focusing lens group moves to increase the distance from the rear positive lens group,
The focusing lens group consists of one lens component,
The rear positive lens group has an aspheric lens having a positive refractive power,
A rear focus lens system satisfying the following conditional expression (7-1):
1.74 ≦ nL _asp <1.95 (7-1)
However,
nL _asp is the refractive index at the d-line of the aspheric lens,
It is.
[Additional Item 5]
From the object side to the image side,
A front lens unit having positive refractive power;
The aperture stop,
It consists of a rear lens group with positive refractive power,
The front lens group includes, in order from the object side, a front negative lens group composed of one or more lens components having a negative refractive power, and a front positive lens group.
The rear lens group, in order from the object side, consists of a rear positive lens group and a focusing lens group having negative refractive power,
When focusing from a long-distance object to a short-distance object, the focusing lens group moves to increase the distance from the rear positive lens group,
The focusing lens group consists of one lens component,
The focusing lens group satisfies the following conditional expression (8-1): Rear focus lens system
1.73 ≦ nL _Rfo <1.95 (8-1)
However,
nL _Rfo is the average value of the refractive indices at the d-line of all the lenses in the focusing lens group,
It is.
[Additional Item 6]
The rear focus lens system according to any one of additional items 1 to 5, which satisfies the following conditional expression (5):
−6.0 <f _Rfo / f _ent <−1.0 (5)
However,
f _Rfo is the focal length of the focusing lens group,
f _ent is the focal length of the entire rear focus lens system, and the focal length when focusing on an object at infinity,
The lens component includes a lens body having only two refracting surfaces in contact with air on the optical axis, the object side surface and the image side surface,
It is.
[Additional Item 7]
The rear focus lens system according to any one of appendices 1 to 6, wherein the lens component in the front positive lens group includes a lens component having a positive refractive power.
[Additional Item 8]
The rear focus lens system according to item 7, wherein the lens component having a positive refractive power is a single lens having a positive refractive power.
[Additional Item 9]
The rear focus lens system according to any one of appendices 1 to 8, wherein the front positive lens group includes a lens component, and the lens component is disposed closest to the object side and includes a positive lens.
[Additional Item 10]
Item 10. The rear focus lens system according to Item 9, wherein the lens component in the front positive lens group includes a lens component having a positive refractive power.
[Additional Item 11]
The rear focus lens system according to item 10, wherein the lens component having a positive refractive power is a single lens having a positive refractive power.
[Additional Item 12]
The rear focus lens system according to any one of Additional Items 1 to 11, wherein the following conditional expression (6) is satisfied.
0.75 <fb _air / f _ent <1.3 (6)
However,
fb _air is the back focus of the rear focus lens system,
f _ent is the focal length of the entire rear focus lens system,
It is.
[Additional Item 13]
The rear positive lens group has an aspheric lens having a positive refractive power,
The rear focus lens system according to any one of Additional Items 1 to 12, wherein the following conditional expression (7) is satisfied.
1.65 <nL _asp <1.95 (7)
However,
nL _asp is the refractive index at the d-line of the aspheric lens,
It is.
[Additional Item 14]
14. The rear focus lens system according to appendix 13, wherein the aspheric lens is a lens positioned closest to the image side in the rear positive lens group.
[Appendix 15]
The rear focus lens system according to any one of additional items 1 to 14, wherein the rear positive lens group includes a negative lens, a positive lens, and a positive lens in order from the object side.
[Additional Item 16]
The rear positive lens group includes, in order from the object side, a negative lens whose object side surface is concave toward the object side, a positive lens whose image side surface is convex toward the image side, and a positive lens whose image side surface is convex toward the image side. Item 15. The rear focus lens system according to Item 15, wherein the lens is composed of a lens.
[Additional Item 17]
The rear focus lens system according to any one of Additional Notes 1 to 16, wherein the focusing lens group satisfies the following conditional expression (8).
1.65 <nL _Rfo <1.95 (8)
However,
nL _Rfo is the average value of the refractive indices at the d-line of all the lenses in the focusing lens group,
It is.
[Additional Item 18]
The rear focus lens system according to any one of items 1 to 17, wherein the focusing lens group is a single lens.
[Appendix 19]
An imaging lens system; and an imaging element that is disposed on the image side of the imaging lens system and converts an image formed by the imaging lens system into an electrical signal;
An imaging apparatus, wherein the imaging lens system is the rear focus lens system according to any one of additional items 1 to 18.
[Appendix 1-1]
From the object side to the image side,
A front lens unit having positive refractive power;
The aperture stop,
A rear lens unit having a positive refractive power,
The front lens group includes, in order from the object side, a front negative lens group composed of one or more lens components having a negative refractive power, and a front positive lens group.
The front positive lens group has a lens component, the lens component is disposed closest to the object side, and has a positive lens;
The rear lens group is composed of, in order from the object side, a rear positive lens group and a focusing lens group.
When focusing from a long-distance object to a short-distance object, the focusing lens group moves to change the distance from the rear positive lens group,
The focusing lens group consists of one lens component,
A rear focus lens system satisfying the following conditional expressions (1), (2), and (3):
4.0 <F _no × L _air / f _ent <8.0 (1)
1.0 <| f _Rfo | / f _ent <6.0 (2)
−2.6 <f _FN / f _ent <−0.2 (3)
However,
F _no is the minimum F number of the rear focus lens system,
L _air is the distance on the optical axis from the lens surface closest to the object side of the rear focus lens system to the image plane,
f _Rfo is the focal length of the focusing lens group,
f _FN is a focal length of the front negative lens unit,
f _ent is the focal length of the entire rear focus lens system,
The minimum F number and the focal length of the entire system are respectively the F number and focal length when an object at infinity is in focus,
The lens component includes a lens body having only two refracting surfaces in contact with air on the optical axis, the object side surface and the image side surface,
It is.
[Appendix 2-1]
From the object side to the image side,
A front lens unit having positive refractive power;
The aperture stop,
A rear lens unit having a positive refractive power,
The front lens group includes, in order from the object side, a front negative lens group including a lens component having one negative refractive power, and a front positive lens group.
The front positive lens group has a lens component, the lens component is disposed closest to the object side, and has a positive lens;
The rear lens group, in order from the object side, consists of a rear positive lens group and a focusing lens group with positive refractive power,
When focusing from a long-distance object to a short-distance object, the focusing lens group moves to reduce the distance from the rear positive lens group,
The focusing lens group consists of one lens component,
A rear focus lens system characterized by satisfying the following conditional expressions (1) and (4):
4.0 <F _no × L _air / f _ent <8.0 (1)
1.0 <f _Rfo / f _ent <6.0 (4)
However,
F _no is the minimum F number of the rear focus lens system,
L _air is the distance on the optical axis from the lens surface closest to the object side of the rear focus lens system to the image plane,
f _Rfo is the focal length of the focusing lens group,
f _ent is the focal length of the entire rear focus lens system,
The minimum F number and the focal length of the entire system are respectively the F number and focal length when an object at infinity is in focus,
The lens component includes a lens body having only two refracting surfaces in contact with air on the optical axis, the object side surface and the image side surface,
It is.
[Appendix 3-1]
The rear focus lens system according to appendix 1-1, wherein the front negative lens group includes at most two lens components having the negative refractive power.
[Appendix 4-1]
The rear focus lens system according to Additional Statement 3-1, wherein the number of lens components having negative refractive power is two.
[Appendix 5-1]
The rear focus lens system according to Additional Item 4-1, wherein each of the lens components having negative refractive power is a single lens having negative refractive power.
[Appendix 6-1]
Item 3. The rear focus lens system according to Item 3-1, wherein there is one lens component having a negative refractive power.
[Additional Item 7-1]
Item 6. The rear focus lens system according to Item 2-1 or 6-1, wherein the lens component having a negative refractive power is a single lens.
[Appendix 8-1]
The rear focus lens system according to any one of appendices 1-1 to 7-1, wherein the lens component in the front positive lens group includes a lens component having a positive refractive power.
[Appendix 9-1]
Item 8. The rear focus lens system according to Item 8-1, wherein the lens component having a positive refractive power is a single lens having a positive refractive power.
[Appendix 10-1]
From the object side to the image side,
A front lens unit having positive refractive power;
The aperture stop,
It consists of a rear lens group with positive refractive power,
The front lens group includes, in order from the object side, a front negative lens group composed of one or more lens components having a negative refractive power, and a front positive lens group.
The rear lens group, in order from the object side, consists of a rear positive lens group and a focusing lens group having negative refractive power,
When focusing from a long-distance object to a short-distance object, the focusing lens group moves to increase the distance from the rear positive lens group,
The focusing lens group consists of one lens component,
A rear focus lens system characterized by satisfying the following conditional expression (5):
−6.0 <f _Rfo / f _ent <−1.0 (5)
However,
f _Rfo is the focal length of the focusing lens group,
f _ent is the focal length of the entire rear focus lens system, and the focal length when focusing on an object at infinity,
The lens component includes a lens body having only two refracting surfaces in contact with air on the optical axis, the object side surface and the image side surface,
It is.
[Additional Item 11-1]
The rear focus lens system according to Additional Statement 10-1, wherein the front negative lens group includes at most two lens components having the negative refractive power.
[Additional Item 12-1]
Item 11. The rear focus lens system according to Item 11-1, wherein there are two lens components having negative refractive power.
[Additional Item 13-1]
The rear focus lens system according to Additional Statement 12-1, wherein each of the lens components having negative refractive power is a single lens having negative refractive power.
[Additional Item 14-1]
Item 11. The rear focus lens system according to Item 11-1, wherein the number of lens components having negative refractive power is one.
[Appendix 15-1]
Item 14. The rear focus lens system according to Item 14-1, wherein the lens component having a negative refractive power is a single lens.
[Additional Item 16-1]
The rear according to any one of appendices 10-1 to 15-1, wherein the front positive lens group has a lens component, and the lens component is disposed closest to the object side and has a positive lens. Focus lens system.
[Additional Item 17-1]
Item 16. The rear focus lens system according to Item 16-1, wherein the lens component in the front positive lens group includes a lens component having a positive refractive power.
[Additional Item 18-1]
Item 18. The rear focus lens system according to Item 17-1, wherein the lens component having a positive refractive power is a single lens having a positive refractive power.
[Additional Item 19-1]
Item 16. The rear focus lens system according to Item 16, wherein the lens component in the front positive lens group includes a cemented lens component including a positive lens and a negative lens.
[Additional Item 20-1]
20. The rear focus lens system according to any one of additional items 1-1 to 19-1, wherein the following conditional expression (6) is satisfied.
0.75 <fb _air / f _ent <1.3 (6)
However,
fb _air is the back focus of the rear focus lens system,
f _ent is the focal length of the entire rear focus lens system,
It is.
[Additional Item 21-1]
The rear positive lens group has an aspheric lens having a positive refractive power,
The rear focus lens system according to any one of additional items 1-1 to 20-1, wherein the following conditional expression (7) is satisfied.
1.65 <nL _asp <1.95 (7)
However,
nL _asp is the refractive index at the d-line of the aspheric lens,
It is.
[Appendix 22-1]
The rear focus lens system according to Additional Item 21-1, wherein the aspheric lens is a lens positioned closest to the image side in the rear positive lens group.
[Additional Item 23-1]
The rear focus lens system according to any one of appendices 1-1 to 22-1, wherein the rear positive lens group includes a negative lens, a positive lens, and a positive lens in order from the object side.
[Additional Item 24-1]
The rear positive lens group includes, in order from the object side, a negative lens whose object side surface is concave toward the object side, a positive lens whose image side surface is convex toward the image side, and a positive lens whose image side surface is convex toward the image side. The rear focus lens system according to Additional Item 23-1, comprising a lens.
[Additional Item 25-1]
The rear focus lens system according to any one of appendices 1-1 to 24-1, wherein the focusing lens group includes an aspheric lens.
[Additional Item 26-1]
The rear focus lens system according to any one of appendices 1-1 to 22-1, wherein the focusing lens group satisfies the following conditional expression (8).
1.65 <nL _Rfo <1.95 (8)
However,
nL _Rfo is the average value of the refractive indices at the d-line of all the lenses in the focusing lens group,
It is.
[Additional Item 27-1]
The rear focus lens system according to any one of Supplementary Notes 1-1 to 26-1, wherein the focusing lens group is a single lens.
[Appendix 28-1]
An imaging lens system; and an imaging element that is disposed on the image side of the imaging lens system and converts an image formed by the imaging lens system into an electrical signal;
An imaging apparatus, wherein the imaging lens system is the rear focus lens system according to any one of additional items 1-1 to 27-1.

Claims (28)

From the object side to the image side,
A front lens unit having positive refractive power;
The aperture stop,
A rear lens unit having a positive refractive power,
The front lens group includes, in order from the object side, a front negative lens group composed of one or more lens components having a negative refractive power, and a front positive lens group.
The front positive lens group has a lens component, the lens component is disposed closest to the object side, and has a positive lens;
The rear lens group is composed of, in order from the object side, a rear positive lens group and a focusing lens group.
When focusing from a long-distance object to a short-distance object, the focusing lens group moves to change the distance from the rear positive lens group,
The focusing lens group consists of one lens component,
A rear focus lens system satisfying the following conditional expressions (1), (2), and (3):
4.0 <F _no × L _air / f _ent <8.0 (1)
1.0 <| f _Rfo | / f _ent <6.0 (2)
−2.6 <f _FN / f _ent <−0.2 (3)
However,
F _no is the minimum F number of the rear focus lens system,
L _air is the distance on the optical axis from the lens surface closest to the object side of the rear focus lens system to the image plane,
f _Rfo is the focal length of the focusing lens group,
f _FN is a focal length of the front negative lens unit,
f _ent is the focal length of the entire rear focus lens system,
The minimum F number and the focal length of the entire system are respectively the F number and focal length when an object at infinity is in focus,
The lens component includes a lens body having only two refracting surfaces in contact with air on the optical axis, the object side surface and the image side surface,
It is. From the object side to the image side,
A front lens unit having positive refractive power;
The aperture stop,
A rear lens unit having a positive refractive power,
The front lens group includes, in order from the object side, a front negative lens group including a lens component having one negative refractive power, and a front positive lens group.
The front positive lens group has a lens component, the lens component is disposed closest to the object side, and has a positive lens;
The rear lens group, in order from the object side, consists of a rear positive lens group and a focusing lens group with positive refractive power,
When focusing from a long-distance object to a short-distance object, the focusing lens group moves to reduce the distance from the rear positive lens group,
The focusing lens group consists of one lens component,
A rear focus lens system characterized by satisfying the following conditional expressions (1) and (4):
4.0 <F _no × L _air / f _ent <8.0 (1)
1.0 <f _Rfo / f _ent <6.0 (4)
However,
F _no is the minimum F number of the rear focus lens system,
L _air is the distance on the optical axis from the lens surface closest to the object side of the rear focus lens system to the image plane,
f _Rfo is the focal length of the focusing lens group,
f _ent is the focal length of the entire rear focus lens system,
The minimum F number and the focal length of the entire system are respectively the F number and focal length when an object at infinity is in focus,
The lens component includes a lens body having only two refracting surfaces in contact with air on the optical axis, the object side surface and the image side surface,
It is.   The rear focus lens system according to claim 1, wherein the front negative lens group includes at most two lens components having the negative refractive power.   4. The rear focus lens system according to claim 3, wherein there are two lens components having a negative refractive power.   5. The rear focus lens system according to claim 4, wherein each of the lens components having a negative refractive power is a single lens having a negative refractive power.   4. The rear focus lens system according to claim 3, wherein the number of the negative refractive power lens components is one.   7. The rear focus lens system according to claim 2, wherein the lens component having a negative refractive power is a single lens.   The rear focus lens system according to any one of claims 1 to 7, wherein the lens component in the front-side positive lens group includes a lens component having a positive refractive power.   9. The rear focus lens system according to claim 8, wherein the lens component having a positive refractive power is a single lens having a positive refractive power. From the object side to the image side,
A front lens unit having positive refractive power;
The aperture stop,
It consists of a rear lens group with positive refractive power,
The front lens group includes, in order from the object side, a front negative lens group composed of one or more lens components having a negative refractive power, and a front positive lens group.
The rear lens group, in order from the object side, consists of a rear positive lens group and a focusing lens group having negative refractive power,
When focusing from a long-distance object to a short-distance object, the focusing lens group moves to increase the distance from the rear positive lens group,
The focusing lens group consists of one lens component,
A rear focus lens system characterized by satisfying the following conditional expression (5):
−6.0 <f _Rfo / f _ent <−1.0 (5)
However,
f _Rfo is the focal length of the focusing lens group,
f _ent is the focal length of the entire rear focus lens system, and the focal length when focusing on an object at infinity,
The lens component includes a lens body having only two refracting surfaces in contact with air on the optical axis, the object side surface and the image side surface,
It is.   11. The rear focus lens system according to claim 10, wherein the front negative lens group includes at most two lens components having the negative refractive power.   The rear focus lens system according to claim 11, wherein the lens component having the negative refractive power is two.   13. The rear focus lens system according to claim 12, wherein each of the lens components having a negative refractive power is a single lens having a negative refractive power.   The rear focus lens system according to claim 11, wherein the lens component having the negative refractive power is one.   The rear focus lens system according to claim 14, wherein the lens component having a negative refractive power is a single lens.   The rear focus lens system according to any one of claims 10 to 15, wherein the front positive lens group includes a lens component, and the lens component is disposed closest to the object side and includes a positive lens.   The rear focus lens system according to claim 16, wherein the lens component in the front-side positive lens group includes a lens component having a positive refractive power.   The rear focus lens system according to claim 17, wherein the lens component having a positive refractive power is a single lens having a positive refractive power.   The rear focus lens system according to claim 16, wherein the lens component in the front positive lens group includes a cemented lens component including a positive lens and a negative lens. The rear focus lens system according to claim 1, wherein the following conditional expression (6) is satisfied.
0.75 <fb _air / f _ent <1.3 (6)
However,
fb _air is the back focus of the rear focus lens system,
f _ent is the focal length of the entire rear focus lens system,
It is. The rear positive lens group has an aspheric lens having a positive refractive power,
The rear focus lens system according to any one of claims 1 to 20, wherein the following conditional expression (7) is satisfied.
1.65 <nL _asp <1.95 (7)
However,
nL _asp is the refractive index at the d-line of the aspheric lens,
It is.   The rear focus lens system according to claim 21, wherein the aspherical lens is a lens located closest to the image side in the rear positive lens group.   The rear focus lens system according to any one of claims 1 to 22, wherein the rear positive lens group includes a negative lens, a positive lens, and a positive lens in order from the object side.   The rear positive lens group includes, in order from the object side, a negative lens whose object side surface is concave toward the object side, a positive lens whose image side surface is convex toward the image side, and a positive lens whose image side surface is convex toward the image side. The rear focus lens system according to claim 23, comprising a lens.   The rear focus lens system according to any one of claims 1 to 24, wherein the focusing lens group includes an aspheric lens. The rear focus lens system according to any one of claims 1 to 22, wherein the focusing lens group satisfies the following conditional expression (8).
1.65 <nL _Rfo <1.95 (8)
However,
nL _Rfo is the average value of the refractive indices at the d-line of all the lenses in the focusing lens group,
It is.   The rear focus lens system according to any one of claims 1 to 26, wherein the focusing lens group is a single lens. An imaging lens system; and an imaging element that is disposed on the image side of the imaging lens system and converts an image formed by the imaging lens system into an electrical signal;
An imaging apparatus, wherein the imaging lens system is the rear focus lens system according to any one of claims 1 to 27.

Images