Patent Publication Number: US-2023136002-A1

Title: Optical device and image pickup apparatus

Description:
BACKGROUND 
     Field of the Disclosure 
     The present disclosure relates to an optical device and an image pickup apparatus that can change the focal length range of a master lens by insertion or withdrawal of an internal conversion lens. 
     Description of the Related Art 
     There is a known configuration in which, in optical devices, such as digital cameras, video cameras, and interchangeable lenses, a first focal length range of a master lens is changed to a second focal length range (either to the telephoto side or the wide-angle side) by inserting a conversion lens into optical path. 
     Japanese Patent Laid-Open No. 11-311828 discloses a technique in which an internal conversion lens in a camera body is moved between an insertion position at which the internal conversion lens is inserted into the optical path and a withdrawal position at which the internal conversion lens is withdrawn outward from the optical path. The internal conversion lens described here is withdrawn into a space between a prism configured to guide a subject image to a finder and a strobe light stored above a lens barrel. 
     For both first and second focal length ranges, a master lens described in Japanese Patent Laid-Open No. 11-311828 is fixed at substantially the same position in the optical axis direction. Therefore, a space for insertion of the internal conversion lens always needs to be left between the master lens and an image plane where light from a subject is formed into an image. This has been a hindrance to reducing the overall lens length. The master lens described in Japanese Patent Laid-Open No. 11-311828 is moved to the withdrawal position by a dedicated actuator. This means that the lens requires an internal space for accommodating the actuator. Accordingly, it has been difficult to prevent an increase in lens size. Also, the configuration described in Japanese Patent Laid-Open No. 11-311828 is applicable only to a type of lens-integrated camera that includes a prism and a strobe light. Therefore, for interchangeable lenses or cameras that do not include at least one of a prism and a strobe light, it has been difficult to prevent a size increase. 
     SUMMARY 
     The aspects of the present disclosure provide an optical device that includes an internal conversion lens, and can shorten the overall lens length while leaving a space for insertion or withdrawal of the internal conversion lens. 
     An optical device according to an aspect of the present disclosure includes a first lens group corresponding to a first optical axis, and a second lens group corresponding to a second optical axis and configured to change a focal length range of an optical system from a first focal length range to a second focal length range by being disposed on the first optical axis on a side of the first lens group adjacent to an image plane. The first lens group moves toward the image plane in a first direction parallel to the first optical axis. The second lens group moves in a second direction to allow at least part of the second lens group to overlap at least part of the first lens group in the first direction, and the second optical axis withdraws from the first optical axis. An overall length of the optical device in a direction of the first optical axis is shorter when the focal length range of the optical system is the first focal length range than when the focal length range of the optical system is the second focal length range. 
     Further features of the present disclosure will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a front perspective view of an interchangeable lens (second focal length range) and a camera body according to embodiments of the present disclosure. 
         FIG.  2    is a back perspective view of the interchangeable lens (second focal length range) and the camera body (with the interchangeable lens detached therefrom) according to embodiments of the present disclosure. 
         FIG.  3    is a cross-sectional view of the interchangeable lens (second focal length range) and the camera body according to embodiments of the present disclosure. 
         FIG.  4    is a cross-sectional view of the interchangeable lens (first focal length range) and the camera body according to embodiments of the present disclosure. 
         FIG.  5    is a cross-sectional view of each lens group in the interchangeable lens (second focal length range) according to embodiments of the present disclosure. 
         FIG.  6    is a cross-sectional view of each lens group in the interchangeable lens (during transition) according to a first embodiment. 
         FIG.  7    is a cross-sectional view of each lens group in the interchangeable lens (during transition) according to the first embodiment. 
         FIG.  8    is a cross-sectional view of each lens group in the interchangeable lens (during transition) according to the first embodiment. 
         FIG.  9    is a cross-sectional view of each lens group in the interchangeable lens (during transition) according to the first embodiment. 
         FIG.  10    is a cross-sectional view of each lens group in the interchangeable lens (during transition) according to the first embodiment. 
         FIG.  11    is a cross-sectional view of each lens group in the interchangeable lens (during transition) according to the first embodiment. 
         FIG.  12    is a cross-sectional view of each lens group in the interchangeable lens (first focal length range) according to the first embodiment. 
         FIG.  13 A  is a graph showing a distance between each lens group and an image plane of the interchangeable lens (during transition) in the optical axis direction according to the first embodiment, and  FIG.  13 B  is a graph showing a distance between each lens group and the optical axis of the interchangeable lens (during transition) in the radial direction according to the first embodiment. 
         FIG.  14    is an external view of each lens group in an interchangeable lens (second focal length range) according to a second embodiment. 
         FIG.  15    is an external view of each lens group in the interchangeable lens (during transition) according to the second embodiment. 
         FIG.  16    is an external view of each lens group in the interchangeable lens (during transition) according to the second embodiment. 
         FIG.  17    is an external view of each lens group in the interchangeable lens (during transition) according to the second embodiment. 
         FIG.  18    is an external view of each lens group in the interchangeable lens (during transition) according to the second embodiment. 
         FIG.  19    is an external view of each lens group in the interchangeable lens (during transition) according to the second embodiment. 
         FIG.  20    is an external view of each lens group in the interchangeable lens (during transition) according to the second embodiment. 
         FIG.  21    is an external view of each lens group in the interchangeable lens (first focal length range) according to the second embodiment. 
         FIG.  22    is a perspective view of each lens group in the interchangeable lens (second focal length range) according to the second embodiment. 
         FIG.  23    is a perspective view of each lens group in the interchangeable lens (during transition) according to the second embodiment. 
         FIG.  24    is a perspective view of each lens group in the interchangeable lens (first focal length range) according to the second embodiment. 
         FIG.  25    is an external view of each lens group in an interchangeable lens (second focal length range) according to a third embodiment. 
         FIG.  26    is an external view of each lens group in the interchangeable lens (during transition) according to the third embodiment. 
         FIG.  27    is an external view of each lens group in the interchangeable lens (during transition) according to the third embodiment. 
         FIG.  28    is an external view of each lens group in the interchangeable lens (during transition) according to the third embodiment. 
         FIG.  29    is an external view of each lens group in the interchangeable lens (during transition) according to the third embodiment. 
         FIG.  30    is an external view of each lens group in the interchangeable lens (during transition) according to the third embodiment. 
         FIG.  31    is an external view of each lens group in the interchangeable lens (during transition) according to the third embodiment. 
         FIG.  32    is an external view of each lens group in the interchangeable lens (first focal length range) according to the third embodiment. 
         FIG.  33    is an external view of each lens group in the interchangeable lens (second focal length range) according to the third embodiment. 
         FIG.  34    is an external view of each lens group in the interchangeable lens (during transition) according to the third embodiment. 
         FIG.  35    is an external view of each lens group in the interchangeable lens (first focal length range) according to the third embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, embodiments of the present disclosure will be described with reference to the drawings. Throughout the drawings, the same or corresponding components are denoted by the same reference numerals. Although an interchangeable lens, which is an example of an optical device, will be described in embodiments, the present disclosure is also applicable, for example, to lens-integrated cameras, and may be variously modified and changed within the scope of the gist thereof. 
     Before specific description of how embodiments are implemented, structures common to the embodiments will be described. 
       FIG.  1    and  FIG.  2    are external views of an optical device (hereinafter referred to as an interchangeable lens)  100  and a digital camera (hereinafter referred to as a camera body)  1  serving as an image pickup apparatus to which the interchangeable lens  100  is detachably attached, according to embodiments of the present disclosure.  FIG.  1    is a front perspective view of the interchangeable lens  100  (second focal length range) and the camera body  1  according to embodiments of the present disclosure, and  FIG.  2    is a back perspective view of the interchangeable lens  100  (second focal length range) and the camera body  1  (with the interchangeable lens  100  detached therefrom) according to embodiments of the present disclosure. In embodiments of the present disclosure, as illustrated in  FIG.  1   , an optical axis direction or a direction in which the optical axis of an image pickup optical system housed in the interchangeable lens  100  extends (i.e., a direction along the optical axis) is referred to as an X axis direction, and directions orthogonal to the X axis direction are referred to as a Z axis direction (horizontal direction) and a Y axis direction (vertical direction). The Z axis direction and the Y axis direction may be collectively referred as a Z/Y axis direction. The direction of rotation about the Z axis is referred to as a pitch direction, and the direction of rotation about the Y axis is referred to as a yaw direction. 
     The pitch direction and the yaw direction (which may hereinafter be collectively referred to as a pitch/yaw direction) are the directions of rotation about two axes, the Z axis and the Y axis, which are orthogonal to each other. 
     The camera body  1  illustrated in  FIG.  1    has a grip  2  on the left side as viewed from the front (or on the right side as viewed from the back). The grip  2  allows the user to hold the camera body  1  by hand. The camera body  1  has a power operation portion  3  on the upper surface thereof. When the user turns on the operation portion  3  of the camera body  1  in the power-off state, a current starts to flow and the camera body  1  is powered on. A computer program for, for example, origin detection processing for a focus group including a focus lens is executed, and an image pickup standby state is entered. Conversely, when the user turns off the power operation portion  3  of the camera body  1  in the power-on state, the camera body  1  is powered off. 
     The camera body  1  also has a mode dial  4 , a release button  5 , and an accessory shoe  6  on the upper surface thereof. The user&#39;s turning of the mode dial  4  can switch the image pickup mode. Examples of the image pickup mode include a manual still-image pickup mode in which the user can set image pickup conditions, such as a shutter speed and an f-number, an automatic still-image pickup mode in which a proper amount of exposure is automatically achieved, and a moving-image pickup mode for picking up a moving image. 
     A user&#39;s half-press of the release button  5  can give an instruction to perform an image pickup preparation, such as autofocus or automatic exposure control, and a user&#39;s full-press of the release button  5  can give an instruction to perform an image pickup operation. An illuminating device, such as an external flash, or an accessory (camera accessory) for a light emitting device is detachably attached to the accessory shoe  6 . 
     The interchangeable lens  100  has a lens mount  102  that can be mechanically connected to a camera mount  7  of the camera body  1 . The interchangeable lens  100  also has an electrical connecting member  101 , which is electrically connected to the camera body  1 . As illustrated in  FIG.  2   , the electrical connecting member  101  according to embodiments of the present disclosure is disposed in the lower phase of the lens mount  102  in the circumferential direction. However, the present disclosure is not limited to this, and the electrical connecting member  101  may be disposed in the upper phase. 
     The interchangeable lens  100  includes therein an image pickup optical system that collects light from a subject to form a subject image on the image plane. The outer periphery of the interchangeable lens  100  is provided with a focus operation ring (operation member)  103  that can be rotated about the optical axis by a user&#39;s operation. For example, when the user turns the focus operation ring  103  in manual focus mode, at least one of lens groups (e.g., focus group) constituting the image pickup optical system is moved to a predetermined use position corresponding to the angle of the focus operation ring  103 . This allows the user to perform desired focusing (focus adjustment). 
     As illustrated in  FIG.  2   , the camera body  1  has a backside operation unit  8  and a display unit  9  on the back side thereof. The backside operation unit  8  includes a plurality of buttons and dials to which various functions are assigned. When the camera body  1  is in the power-on state and either the still-image or moving-image pickup mode is set, the display unit  9  displays a live view of a subject image picked up by an image pickup element (described below). The display unit  9  also displays image pickup parameters representing image pickup conditions, such as a shutter speed and an f-number. The user can change the set values of image pickup parameters by operating the backside operation unit  8  while viewing the display. The backside operation unit  8  includes a playback button used to view a recorded picked-up image. By operating the playback button, the user can display the picked-up image in the display unit  9 . The display unit  9  may be of a touch panel type having the same functions as the backside operation unit  8 . 
     With reference to  FIG.  3    and  FIG.  4   , the positional relations of components constituting the interchangeable lens  100  according to embodiments of the present disclosure will be described.  FIG.  3    and  FIG.  4    are cross-sectional views taken along the XZ plane containing a first optical axis  10 . The center line illustrated here is synonymous with the X axis described above, as it substantially coincides with the first optical axis  10  determined by the first lens group  110 . An image plane  16  is synonymous with the YZ plane, as it is orthogonal to the first optical axis  10 .  FIG.  3    is a cross-sectional view of the interchangeable lens  100  (second focal length range) and the camera body  1  according to embodiments of the present disclosure, and  FIG.  4    is a cross-sectional view of the interchangeable lens  100  (first focal length range) and the camera body  1  according to embodiments of the present disclosure. 
       FIG.  3    illustrates a configuration in which the second lens group  210  and the third lens group  310  are disposed on the image plane side of the first lens group  110  to provide a second focal length range.  FIG.  4    illustrates a configuration in which the second lens group  210  and the third lens group  310  are withdrawn from the first optical axis  10  and the first lens group  110  is moved into the vacated space to provide a first focal length range. 
     The overall length of the interchangeable lens  100  according to embodiments of the present disclosure is long in  FIG.  3    and short in  FIG.  4   , and image pickup is possible in both states. 
     The image pickup optical system of the interchangeable lens  100  is constituted by the first lens group  110  serving as a master lens, and the second lens group  210  and the third lens group  310  serving as an extender lens, which is a type of conversion lens. The first lens group  110  has the first focal length range, and the second lens group  210  and the third lens group  310  are configured to change the first focal length range to the second focal length range by being inserted into the first optical axis  10  on the side of the first lens group  110  adjacent to the image plane  16 . The first focal length range corresponds to a wide-angle side (short focus), and the second focal length range corresponds to a telephoto side (long focus). The interchangeable lens  100  includes a first cam cylinder  108  and a second cam cylinder  109  that are configured to move the first lens group  110 , which serves as the master lens, in the direction of the first optical axis  10 . Thus, in both the first and second focal length ranges, the first lens group  110  is movable in the direction of the first optical axis  10  and desired focusing (focus adjustment) can be made. 
     While described in detail below, the interchangeable lens  100  according to embodiments of the present disclosure can switch between the first focal length range and the second focal length range by combining, for example, a user&#39;s operation with an operation by a dedicated actuator.  FIG.  1    to  FIG.  3    illustrate an example where the interchangeable lens  100  provides the second focal length range corresponding to the telephoto side. When, in the state of the second focal length range (telephoto side), the user turns the focus operation ring  103  toward ultra-infinity, the first lens group  110  is moved toward the image plane  16  in conjunction with the rotation of the focus operation ring  103 . At the same time, the second lens group  210  and the third lens group  310  are withdrawn from the first optical axis  10  to respective withdrawal positions. Thus, by moving the first lens group  110  to the vacated space and bringing it further toward the image plane  16 , the overall length of the interchangeable lens  100  is shortened as illustrated in  FIG.  4   . 
     In embodiments of the present disclosure, the master lens is composed of a single group and the extender lens is composed of two groups. However, the present disclosure does not limit the configuration of the image pickup optical system. For example, the master lens may be composed of multiple groups, or may include another independent focus group or lens stabilization group. The extender lens may be composed only of a single group. The conversion lens of the present disclosure may be a wide conversion lens, a macro lens, or a reducer lens, instead of the extender lens described in the embodiments of the present disclosure. 
     The first lens group  110  includes an aperture group  120  for adjusting the amount of light. The aperture group  120  includes an aperture drive unit (not shown), a plurality of aperture blades  121 , and a drive ring  122 . To adjust the amount of light, the aperture drive unit changes the aperture shape of the aperture blades  121  by means of the drive ring  122 . 
     A fixed cylinder  106  is a fixed member secured to the lens mount  102 . The fixed cylinder  106  has a straight guiding groove (not shown) divided into three equal parts in the circumferential direction. The straight guiding groove in the fixed cylinder  106  is fitted to a straight guiding key (not shown) on a straight guiding cylinder  107 . This regulates the movement of the straight guiding cylinder  107  in the rotational direction and guides the straight guiding cylinder  107  in the direction of the first optical axis  10 . The first cam cylinder  108  is held by a bayonet (not shown) on the outer periphery of the fixed cylinder  106  in such a way as to be rotatable about the first optical axis  10 . The first cam cylinder  108  is coupled through a coupling key (not shown) to the focus operation ring  103 . Like the fixed cylinder  106 , the straight guiding cylinder  107  has a straight guiding groove (not shown) divided into three equal parts in the circumferential direction. The straight guiding groove in the straight guiding cylinder  107  is fitted to a straight guiding key (not shown) on the first lens group  110 . This regulates the movement of the first lens group  110  in the rotational direction and guides the first lens group  110  in the direction of the first optical axis  10 . The second cam cylinder  109  is held by a bayonet (not shown) on the outer periphery of the straight guiding cylinder  107  in such a way as to be rotatable about the first optical axis  10 . 
     The first cam cylinder  108  and the second cam cylinder  109  are internally provided with first and second cam grooves (not shown), respectively, each divided into three equal parts in the circumferential direction. The first and second cam grooves are fitted to respective cam followers (not shown) on the straight guiding cylinder  107  and the first lens group  110 . The second cam cylinder  109  is configured to move integrally with the straight guiding cylinder  107  in the direction of the first optical axis  10 . The first cam cylinder  108  and the second cam cylinder  109  are rotationally regulated by a coupling key (not shown) and configured to rotate in conjunction with each other in the circumferential direction while relatively moving in the direction of the first optical axis  10 . Therefore, when the focus operation ring  103  is turned by the user, the first lens group  110  moves through the straight guiding cylinder  107  and the second cam cylinder  108  in the direction of the first optical axis  10  while its movement in the rotational direction is regulated. 
     In embodiments of the present disclosure, the configuration of a so-called two-stage collapsible lens barrel allows the first lens group  110  to move into the space created by withdrawal of the second lens group  210  and the third lens group  310 . In particular, when the interchangeable lens  100  provides the first focal length range (wide-angle side) as illustrated in  FIG.  4   , bringing the first lens group  110  toward the image plane  16  can shorten the overall length of the interchangeable lens  100  and make it possible to achieve high portability. The configuration of such a lens barrel will not be described in detail here, as it is a known technique that has been adopted in many optical devices. 
     As described above, the present disclosure is characterized in that a space created after withdrawal of a lens group by switching from a focal length range (telephoto side) to another focal length range (wide-angle side) is used to shorten the overall lens length. There have been related techniques in which the overall lens length in the optical axis direction is shortened by withdrawing a retractable lens group from the optical axis of an image pickup optical system, reducing the distance between lens groups, and moving the lens groups to respective positions close to each other. However, these techniques are ones that adopt a collapsible mechanism for switching from an image-pickup state to a non-image-pickup state, and do not allow image pickup in a collapsed state where the overall lens length is shortened. This means that although high portability is achieved, it takes extra time for transition from a collapsed state where image pickup is not allowed to a state where image pickup is possible. 
     Unlike the related techniques, the first lens group  110  according to embodiments of the present disclosure has the first focal length range which allows image pickup to be performed by the first lens group  110  alone; that is, image pickup is possible even in the state of  FIG.  4    where the overall lens length is shortened. As compared to optical devices that adopt a typical collapsible mechanism, the interchangeable lens  100  requires less time before start of image pickup and can reduce loss of image pickup opportunities while achieving high portability. 
     The description of the structures common to embodiments of the present disclosure ends here. 
     First Embodiment 
     With reference to  FIG.  5    to  FIG.  12   , movement of each lens group of the interchangeable lens  100  according to a first embodiment will be described in detail.  FIG.  5    to  FIG.  12    are cross-sectional views of the first lens group  110 , the second lens group  210 , and the third lens group  310  taken along the XZ plane containing the first optical axis  10 .  FIG.  5    to  FIG.  12    illustrate a transition from the second focal length range to the first focal length range.  FIG.  5    is a cross-sectional view of each lens group in the interchangeable lens  100  (second focal length range) according to the present embodiment.  FIG.  6    to  FIG.  11    are cross-sectional views of each lens group in the interchangeable lens  100  (during transition) according to the present embodiment.  FIG.  12    is a cross-sectional view of each lens group in the interchangeable lens  100  (first focal length range) according to the present embodiment. 
       FIG.  5    illustrates the interchangeable lens  100  that provides the second focal length range. As illustrated, the first lens group  110 , the second lens group  210 , and the third lens group  310  are arranged in this order from the subject side, at given positions on the first optical axis  10 . When the interchangeable lens  100  provides the second focal length range, desired focusing (focus adjustment) can be performed by moving the first lens group  110  along the first optical axis  10 . This does not involve positional movement of the second lens group  210  and the third lens group  310 . 
     When the interchangeable lens  100  makes a transition from the second focal length range to the first focal length range, first, the first lens group  110  starts to move in a first direction  115  substantially parallel to the first optical axis  10  ( FIG.  6   ). As the first lens group  110  further moves toward the image plane  16  in the first direction  115 , the second lens group  210  and the third lens group  310  start to withdraw in a second direction  215  and a third direction  315 , respectively ( FIG.  7   ). As a driving source (not shown) for withdrawal of the second lens group  210  and the third lens group  310 , the present embodiment assumes an actuator corresponding to each lens. However, the present disclosure is not limited to this. For example, a configuration of an optical device that adopts a collapsible mechanism, such as that described above, is disclosed in which a retractable lens is moved by driving force of a zoom motor that shortens the overall lens length. The present disclosure may be implemented by combining the techniques described above. 
     As for the directions of withdrawal of the second lens group  210  and the third lens group  310 , the second direction  215  and the third direction  315  are opposite each other, with the first optical axis  10  therebetween. This can reduce vibration and changes in the center of gravity that occur as the second lens group  210  moves in the second direction  215  and the third lens group  310  moves in the third direction  315 . 
       FIG.  5    to  FIG.  12    are cross-sectional views taken along the XZ plane as described above.  FIG.  2    shows that the electrical connecting member  101  is located on the Y axis. The phases in which the second lens group  210  and the third lens group  310  withdraw thus differ from the phase of the electrical connecting member  101 . This allows efficient use of space around the lens mount  102  and enables size reduction of the interchangeable lens  100 . 
     When the second lens group  210  withdraws further in the second direction  215  and the third lens group  310  withdraws further in the third direction  315 , the first lens group  110  moves into the space created by the withdrawal of the second lens group  210  and the third lens group  310  ( FIG.  8    to  FIG.  10   ). A second optical axis  20  is the optical center of the second lens group  210 , and a third optical axis  30  is the optical center of the third lens group  310 . As the withdrawal proceeds, the angles of the second optical axis  20  and the third optical axis  30  with respect to the first optical axis  10  both increase. The second lens group  210  and the third lens group  310  are both larger in lens diameter than in lens thickness. Therefore, as compared to withdrawing each lens group parallel to the radial direction, withdrawing it at an angle can save more space in the radial direction and can more effectively prevent size increase of the interchangeable lens  100 . 
       FIG.  11    illustrates the second lens group  210  and the third lens group  310  that have completed the withdrawal to given positions. Even after completion of the withdrawal of the second lens group  210  and the third lens group  310 , the first lens group  110  continues to move in the first direction  115 . Then, when the first lens group  110  further moves in the first direction  115  and completes the movement to a given position, the transition from the second focal length range to the first focal length range ends ( FIG.  12   ). 
     The first lens group  110  illustrated in  FIG.  12    is closer to the image plane  16  than that illustrated in any of  FIG.  5    to  FIG.  11    is. The transition from the second focal length range to the first focal length range can thus shorten the overall length of the interchangeable lens  100 . Since the first lens group  110  has the first focal length range, image pickup is possible even when the overall lens length is minimized by completion of the withdrawal of the second lens group  210  and the third lens group  310  and the movement of the first lens group  110  toward the image plane  16 . Even when the interchangeable lens  100  provides the first focal length range, desired focusing (focus adjustment) can be performed by moving the first lens group  110  along the first optical axis  10 . 
     A transition from the second focal length range to the first focal length range has been described. Conversely, for a transition from the first focal length range to the second focal length range, the process illustrated in  FIG.  5    to  FIG.  12    is carried out in reverse order. For example, when the first lens group  110  is moved from the image plane side toward the subject side by a user&#39;s operation, the second lens group  210  rotates to move from the withdrawal position illustrated in  FIG.  11    and  FIG.  12    to the position on the first optical axis  10  illustrated in  FIG.  6   . The driving source for rotationally moving the second lens group  210  is a dedicated actuator (not shown). When the second focal length range is provided, the second lens group  210  is rotationally regulated by holding force of the actuator and secured in place on the first optical axis  10 . 
     When the interchangeable lens  100  makes a transition again from the second focal length range to the first focal length range, the dedicated actuator (not shown) moves the second lens group  210  to the withdrawal position. The interchangeable lens  100  according to the present embodiment is thus configured to be capable of switching between the first focal length range and the second focal length range by combining a user&#39;s operation with an operation by the dedicated actuator. 
       FIG.  13 A  is a graph showing a distance between each lens group and the image plane  16  of the interchangeable lens  100  (during transition) in the optical axis direction, according to the present embodiment. Specifically,  FIG.  13 A  shows the distance from the center of gravity of each of the first lens group  110 , the second lens group  210 , and the third lens group  310  to the image plane  16  in the direction of the first optical axis  10  during transition of the interchangeable lens  100  from the second focal length range to the first focal length range. In  FIG.  13 A , the horizontal axis represents the number of steps, and the vertical axis represents the distance to the image plane  16 . Note that the number of steps represents a degree of transition from the second focal length range to the first focal length range. 
     As the transition from the second focal length range to the first focal length range proceeds, the distance between the image plane  16  and the first lens group  110  decreases and is minimized in the first focal length range. On the other hand, the distance between the image plane  16  and the second lens group  210  is minimized in the second focal length range. As the transition from the second focal length range proceeds, the distance between the image plane  16  and the second lens group  210  gradually increases up to the middle and then stays virtually unchanged. This indicates that as the first lens group  110  approaches the second lens group  210 , the second lens group  210  moves toward the subject side in the direction of the first optical axis  10 . 
     Also, in the transition from the second focal length range to the first focal length range, the distance between the image plane  16  and the third lens group  310  is minimized in the second focal length range. As the transition from the second focal length range proceeds, the distance between the image plane  16  and the third lens group  310  gradually increases. This indicates that as the first lens group  110  approaches the third lens group  310 , the third lens group  310  moves toward the subject side in the direction of the first optical axis  10 . 
     As a reference,  FIG.  13 A  also shows a distance from the connection surface (mount surface) of the camera mount  7  and the lens mount  102  to the image plane  16 . In the direction of the first optical axis  10 , the first lens group  110  and the second lens group  210  are always closer to the subject than the mount surface is. On the other hand, when the second focal length range is provided, the third lens group  310  at least partially overlaps the mount surface. When the first focal length range is provided, the third lens group  310  withdraws, like the second lens group  210 , to a position not overlapping the lens mount  102  in the direction of the first optical axis  10 . 
       FIG.  13 B  is a graph showing a distance from the first optical axis  10  to the center of gravity of each of the first lens group  110 , the second lens group  210 , and the third lens group  310  in the radial direction during transition of the interchangeable lens  100  from the second focal length range to the first focal length range. In  FIG.  13 B , the horizontal axis represents the number of steps, and the vertical axis represents the distance to the first optical axis  10 . As in  FIG.  13 A , the number of steps represents a degree of transition from the second focal length range to the first focal length range. 
     As described above, the first lens group  110  moves in the first direction  115  substantially parallel to the first optical axis  10 . Therefore, even when a transition from the second focal length range to the first focal length range takes place, the distance from first optical axis  10  to the first lens group  110  in the radial direction remains unchanged. As the transition from the second focal length range to the first focal length range proceeds, however, the second lens group  210  becomes distant from the first optical axis  10  as it withdraws in the second direction  215 . 
     Also, as the transition from the second focal length range to the first focal length range proceeds, the third lens group  310  withdraws in the third direction  315  opposite the second direction  215 . This means that as the third lens group  310  moves away from the first optical axis  10 , it also becomes distant from the second lens group  210 . In the present embodiment, as the center of gravity of the third lens group  310  moves in the third direction  315  toward the grip  2  of the camera body  1 , the center of gravity of the second lens group  210  moves in the second direction  215  opposite the third direction  315 , with the first optical axis  10  therebetween. By thus cancelling out changes in the center of gravity, it is possible to reduce vibration and allow the user to perform image pickup by holding the camera body  1  by hand without a feeling of strangeness. 
     As a reference,  FIG.  13 B  also shows a distance from the fitting diameter (mount diameter) of the camera mount  7  and the lens mount  102  to the first optical axis  10 . The first lens group  110  is always disposed on the first optical axis  10  in a plane substantially parallel to the image plane  16 , that is, as viewed in the direction of the first optical axis  10 . On the other hand, while the second lens group  210  and the third lens group  310  are disposed on the first optical axis  10  when the second focal length range is provided, they are withdrawn from the first optical axis  10  when the first focal length range is provided. As shown in  FIG.  13 B , the second lens group  210  and the third lens group  310  are each withdrawn to a position where it is partially disposed radially outside the fitting diameter (mount diameter) of the camera mount  7  and the lens mount  102  in a plane substantially parallel to the image plane  16 , that is, as viewed in the direction of the first optical axis  10 . 
     As described above, the first lens group  110  according to the present embodiment moves toward the image plane  16  in the first direction  115  substantially parallel to the first optical axis  10 . At the same time, by moving in the second direction  215 , the second lens group  210  according to the present embodiment moves toward the subject in the direction of the first optical axis  10  and moves in a direction away from the first optical axis  10  in the radial direction. Also, by moving in the third direction  315 , the third lens group  310  according to the present embodiment moves toward the subject in the direction of the first optical axis  10  and moves in a direction away from the second lens group  210  in the radial direction. The transition from the second focal length range to the first focal length range is thus completed. 
     In the present embodiment, the overall lens length can be shortened by withdrawing the second lens group  210  and the third lens group  310  to change the focal length range and moving the first lens group  110  into the space created by the withdrawal. 
     Although the second lens group  210  and the third lens group  310  are combined to form the internal conversion lens in the present embodiment, the present disclosure is not limited to this. For example, a switching between the first focal length range and the second focal length range may be achieved by the second lens group  210  alone. In this case, the third lens group  310  may be a neutral density filter, a protective filter, or a polarizing filter. 
     Second Embodiment 
     A second embodiment of the present disclosure will now be described. 
     With reference to  FIG.  14    to  FIG.  21   , movement of each lens group of the interchangeable lens  100  according to the present embodiment will be described in detail.  FIG.  14    to  FIG.  21    are external views of the first lens group  110  and the second lens group  210 .  FIG.  14    to  FIG.  21    illustrate the XZ plane, as viewed in the Y axis direction, and illustrate a transition from the second focal length range to the first focal length range.  FIG.  14    is an external view of each lens group in the interchangeable lens  100  (second focal length range) according to the present embodiment.  FIG.  15    to  FIG.  20    are external views of each lens group in the interchangeable lens  100  (during transition) according to the present embodiment.  FIG.  21    is an external view of each lens group in the interchangeable lens  100  (first focal length range) according to the present embodiment. 
       FIG.  14    illustrates the interchangeable lens  100  that provides the second focal length range. As illustrated, the first lens group  110  and the second lens group  210  are arranged in this order from the subject side, at given positions on the first optical axis  10 . When the interchangeable lens  100  provides the second focal length range, desired focusing (focus adjustment) can be performed by moving the first lens group  110  along the first optical axis  10 . This does not involve positional movement of the second lens group  210 . 
     The first lens group  110  is provided with a first contact portion  120  disposed closer to the image plane  16  than a lens of the first lens group  110  closest to the subject is. The second lens group  210  is provided with a second contact portion  220  disposed closer to the subject than a lens of the second lens group  210  closest to the subject is. Although the first contact portion  120  is formed integrally with a first retaining frame  111  in the present embodiment, the first contact portion  120  may be formed as a separate component and secured to the first retaining frame  111 . Similarly, although the second contact portion  210  is formed integrally with a second retaining frame  211 , the second contact portion  210  may be formed as a separate component and secured to the second retaining frame  211 . 
     As illustrated in  FIG.  14    to  FIG.  21   , the first contact portion  120  has a first contact surface  120   a  and a first sliding surface  120   b.  Similarly, the second contact portion  220  has a second contact surface  220   a  and a second sliding surface  220   b.  When the interchangeable lens  100  provides the second focal length range as illustrated in  FIG.  14   , the first contact surface  120   a  and the second contact surface  220   a  may be brought closer to each other by moving the first lens group  110  for desired focusing (focus adjustment), but are not brought into contact with each other. The second lens group  210  starts to withdraw when, as illustrated in  FIG.  15    and  FIG.  16   , the first contact surface  120   a  and the second contact surface  220   a  are brought into contact. The second lens group  210  completes the withdrawal when, as illustrated in  FIG.  19    and  FIG.  20   , the first sliding surface  120   b  and the second sliding surface  220   b  slide with respect to each other. 
     When the interchangeable lens  100  makes a transition from the second focal length range to the first focal length range, first, the first lens group  110  starts to move in the first direction  115  substantially parallel to the first optical axis  10  ( FIG.  15   ). This brings the first contact surface  120   a  into contact with the second contact surface  220   a.  In the present embodiment, the second contact surface  220   a  and the second sliding surface  220   b  constitute a continuous plane slightly inclined from a plane orthogonal to the first optical axis  10  (i.e., plane parallel to the image plane  16 ). 
     As the first lens group  110  further moves toward the image plane  16  in the first direction  115 , the second lens group  210  starts to withdraw in the second direction  215  ( FIG.  16   ). The second contact surface  220   a  and the second sliding surface  220   b  rotate integrally with the second lens group  210  while increasing the inclination from the plane orthogonal to the first optical axis  10  (i.e., plane parallel to the image plane  16 ). 
     When the second lens group  210  withdraws further in the second direction  215 , the first lens group  110  moves into the space created by the withdrawal ( FIG.  17    to  FIG.  19   ). The second optical axis  20 , which is the optical center of the second lens group  210 , increases its angle with the first optical axis  10  as the withdrawal of the second lens group  210  proceeds. The second lens group  210  is greater in lens diameter than in lens thickness. Therefore, as compared to withdrawing the second lens group  210  in the direction parallel to the radial direction, withdrawing it at an angle while rotating it can save more space in the radial direction and can more effectively prevent size increase of the interchangeable lens  100 . 
       FIG.  20    illustrates the second lens group  210  that has completed the withdrawal to a given position. Even after completion of the withdrawal of the second lens group  210 , the first lens group  110  continues to move in the first direction  115 . The first sliding surface  120   b  moves toward the image plane  16  while sliding with respect to the second sliding surface  220   b  and maintaining contact therewith. Then, when the first lens group  110  further moves in the first direction  115  and completes the movement to a given position, the transition from the second focal length range to the first focal length range ends ( FIG.  21   ). 
     The first lens group  110  illustrated in  FIG.  21    is closer to the image plane  16  than that illustrated in any of  FIG.  14    to  FIG.  20    is. The transition from the second focal length range to the first focal length range can thus shorten the overall length of the interchangeable lens  100 . Since the first lens group  110  has the first focal length range, image pickup is possible even when the overall lens length is minimized by completion of the withdrawal of the lens group  210  and the movement of the first lens group  110  toward the image plane  16 . 
     Even when the interchangeable lens  100  provides the first focal length range, desired focusing (focus adjustment) can be performed by moving the first lens group  110  along the first optical axis  10 . At this point, the length of the first sliding surface  120   b  in the direction of the first optical axis  10  is longer than the distance traveled by the lens of the first lens group  110  closest to the subject after completion of the withdrawal of the second lens group  210 . Therefore, the second sliding surface  220   b  is unlikely to fall off the first sliding surface  120   b  even when the first lens group  110  moves along the first optical axis  10 . 
     A transition from the second focal length range to the first focal length range has been described. Conversely, for a transition from the first focal length range to the second focal length range, the process illustrated in  FIG.  14    to  FIG.  21    is carried out in reverse order. In the present embodiment, the second lens group  210  is constantly biased by a biasing member (not shown) in the direction opposite the second direction  215 . When the first lens group  110  moves from the image plane side toward the subject side, the second lens group  210  rotates to move from the withdrawal position illustrated in  FIG.  20    and  FIG.  21    to the position on the first optical axis  10  illustrated in  FIG.  15    while the first sliding surface  120   b  and the second sliding surface  220   b  slide with respect to each other. 
     When the second focal length range is provided, the second lens group  210  is rotationally regulated by a regulating member (not shown) and aligned with and secured in place on the first optical axis  10 . The first lens group  110  and the second lens group  210  are thus arranged as illustrated in  FIG.  14   , with the first contact surface  120   a  and the second contact surface  220   a  being spaced apart. 
     When the interchangeable lens  100  makes a transition again from the second focal length range to the first focal length range, the first lens group  110  moves the second lens group  210  toward the withdrawal position against biasing force of the biasing member (not shown). The interchangeable lens  100  according to the present embodiment is thus configured to be capable of switching between the first focal length range and the second focal length range without using a dedicated actuator. 
       FIG.  22    is a perspective view that illustrates, like  FIG.  14   , the interchangeable lens  100  that provides the second focal length range. As illustrated, the first lens group  110  and the second lens group  210  are arranged in this order from the subject side, at given positions on the first optical axis  10 . At this point, the first contact portion  120  and the second contact portion  220  are spaced apart. 
       FIG.  23    is a perspective view that illustrates, like  FIG.  17   , a process of transition from the second focal length range to the first focal length range. The second lens group  210  has a rotary shaft  225 , on which the second lens group  210  rotates to withdraw along an arc path. 
       FIG.  24    is a perspective view that illustrates, like  FIG.  21   , the interchangeable lens  100  that provides the first focal length range. At this point, the transition from the second focal length range to the first focal length range has been completed and the second lens group  210  stays at the withdrawal position. 
     When a transition from the second focal length range to the first focal length range takes place in the present embodiment, the lens of the second lens group  210  closest to the subject is once separated from the lens of the first lens group  110  closest to the image plane  16 . After the separation, the lens of the second lens group  210  closest to the subject completes the withdrawal at a position close to a side face of the first retaining frame  111 . Thus, as compared to the case where the second lens group  210  completes the withdrawal at a distance from the first lens group  110 , it is possible to save more space in the radial direction and more effectively prevent size increase of the interchangeable lens  100 . 
     As illustrated in  FIG.  3    and  FIG.  4   , the interchangeable lens  100  may include the third lens group  310  on the side of the second lens group  210  adjacent to the image plane  16 . When the second focal length range is provided, the first lens group  110 , the second lens group  210 , and the third lens group  310  are arranged at given positions on the first optical axis  10 . When a transition from the second focal length range to the first focal length range takes place, the third lens group  310  may withdraw in a direction different from the second direction  215 , as the second lens group  210  withdraws in the second direction  215 . 
     As described above, the first lens group  110  according to the present embodiment moves toward the image plane  16  in the first direction  115  substantially parallel to the first optical axis  10 , and the second lens group  210  moves in the second direction  215 . The second lens group  210  moves toward the subject in the direction of the first optical axis  10 , and moves away from the first optical axis  10  in the radial direction. When the second lens group  210  completes the withdrawal and the first lens group  110  completes the movement in the first direction  115  at a given position on the image plane side, the transition from the second focal length range to the first focal length range ends. 
     As described above, in the present embodiment, the configuration for withdrawing the internal conversion lens is made more efficient to prevent size increase of the lens. 
     Although the internal conversion lens is constituted by the second lens group  210  alone in the present embodiment, the present disclosure is not limited to this. For example, a switching between the first focal length range and the second focal length range may be achieved by a combination of the second lens group  210  and the third lens group  310 . In this case, the third lens group  310  may be a neutral density filter, a protective filter, or a polarizing filter. 
     Third Embodiment 
     A third embodiment of the present disclosure will now be described. 
     With reference to  FIG.  25    to  FIG.  32   , movement of each lens group of the interchangeable lens  100  according to the present embodiment will be described in detail.  FIG.  25    to  FIG.  32    are external views of the first lens group  110 , the second lens group  210 , and the third lens group  310 .  FIG.  25    to  FIG.  32    illustrate the XZ plane, as viewed in the Y axis direction, and illustrate a transition from the second focal length range to the first focal length range.  FIG.  25    is an external view of each lens group in the interchangeable lens  100  (second focal length range) according to the present embodiment.  FIG.  26    to  FIG.  31    are external views of each lens group in the interchangeable lens  100  (during transition) according to the present embodiment.  FIG.  32    is an external view of each lens group in the interchangeable lens  100  (first focal length range) according to the present embodiment. 
       FIG.  25    illustrates the optical system that provides the second focal length range.  FIG.  25    shows that the first lens group  110 , the second lens group  210 , and the third lens group  310  are arranged in this order from the subject side, at given positions on the first optical axis  10 . When the interchangeable lens  100  provides the second focal length range, desired focusing (focus adjustment) can be performed by moving the first lens group  110  along the first optical axis  10 . This does not involve positional movement of the second lens group  210  and the third lens group  310 . 
     The second lens group  210  has a first rotary shaft  225  whose center is substantially orthogonal to the first optical axis  10 . The third lens group  310  has a second rotary shaft  325  whose center is substantially orthogonal to the first optical axis  10 . If the first rotary shaft  225  is long enough to penetrate the first lens group  110 , the first rotary shaft  225  interferes with the first lens group  110  when the first lens group  110  moves toward the image plane  16 . Similarly, if the second rotary shaft  325  is long enough to penetrate the first lens group  110 , the second rotary shaft  325  interferes with the first lens group  110  when the first lens group  110  moves toward the image plane  16 . Accordingly, in the present embodiment, the first rotary shaft  225  and the second rotary shaft  325  are each divided into two parts that are opposite each other, with a plane orthogonal to the rotation center therebetween. The first rotary shaft  225  can thus be disposed at a position overlapping the first lens group  110  in the direction of the first optical axis  10 , and this makes space saving possible. Similarly, the second rotary shaft  325  can be disposed at a position overlapping the second lens group  210  in the direction of the first optical axis  10 . If the first rotary shaft  225  and the second rotary shaft  325  are not long enough to penetrate the first lens group  110 , they both may not be divided and may be disposed on only one side of the plane orthogonal to the rotation center. 
     When the interchangeable lens  100  makes a transition from the second focal length range to the first focal length range, first, the first lens group  110  starts to move in the first direction  115  substantially parallel to the first optical axis  10  ( FIG.  26   ). 
     As the first lens group  110  further moves toward the image plane  16  in the first direction  115 , the second lens group  210  and the third lens group  310  start to withdraw in the second direction  215  and the third direction  315 , respectively ( FIG.  27   ). 
     At this point, in a plane substantially parallel to the image plane  16 , that is, as viewed in the direction of the first optical axis  10 , the first rotary shaft  225  is disposed in the same phase as the second direction  215  in which the second lens group  210  withdraws. On the other hand, in a plane substantially parallel to the image plane  16 , that is, as viewed in the direction of the first optical axis  10 , the second rotary shaft  325  is disposed in the phase opposite that of the third direction  315  in which the third lens group  310  withdraws. 
     As a driving source (not shown) for withdrawing each of the second lens group  210  and the third lens group  310 , the present embodiment assumes a dedicated actuator, such as that described as related art in Japanese Patent Laid-Open No. 11-311828. The present disclosure is not limited to this. For example, a configuration of an optical device that adopts a collapsible mechanism, such as that described above, is disclosed in which a retractable lens is moved by driving force of a zoom motor that shortens the overall lens length. The present disclosure may be implemented by combining the known techniques described above. 
     As for the directions of withdrawal of the second lens group  210  and the third lens group  310 , the second direction  215  and the third direction  315  are opposite each other, with the first optical axis  10  therebetween. This can reduce vibration and changes in the center of gravity that occur as the second lens group  210  moves in the second direction  215  and the third lens group  310  moves in the third direction  315 . 
       FIG.  25    to  FIG.  32    are external views including the first optical axis  10 , as viewed in the Y axis direction.  FIG.  2    shows that the electrical connecting member  101  is located on the Y axis. The phases in which the second lens group  210  and the third lens group  310  withdraw thus differ from the phase of the electrical connecting member  101 . This allows efficient use of space around the lens mount  102  and enables size reduction of the interchangeable lens  100 . 
     The rotation centers of the first rotary shaft  225  and the second rotary shaft  325  are disposed to extend in the direction parallel to the Y axis. That is, the direction of the rotation centers of the first rotary shaft  225  and the second rotary shaft  325  coincides with the Y axis direction in which the camera body  1  with the interchangeable lens  100  attached thereto is placed by the user. Therefore, when the camera body  1  is placed, the second lens group  210  and the third lens group  310  are withdrawn in directions different from the Y axis direction in which impact is applied to the camera body  1 . Accordingly, when the first rotary shaft  225  and the second rotary shaft  325  are disposed with the rotation centers thereof parallel to the Y axis direction, the interchangeable lens  100  has more rigidity against impact applied thereto in the Y axis direction and is less likely to be affected by the impact of a user&#39;s operation. 
     When the second lens group  210  withdraws further in the second direction  215  and the third lens group  310  withdraws further in the third direction  315 , the first lens group  110  moves into the space created by the withdrawal of the second lens group  210  and the third lens group  310  ( FIG.  28    to  FIG.  30   ). 
     In the present embodiment, the third lens group  310  is heavier in weight and longer in withdrawal distance than the second lens group  210 . With this configuration, in a plane substantially parallel to the image plane  16 , that is, as viewed in the direction of the first optical axis  10 , the second rotary shaft  325  is disposed in a phase opposite that of the third direction  315  in which the third lens group  310  withdraws. This arrangement of the second rotary shaft  325  and the third direction  315  allows the third lens group  310  to withdraw in the third direction  315  in which the withdrawal distance is longer than that in the second direction  215 . 
       FIG.  31    illustrates the second lens group  210  and the third lens group  310  that have completed the withdrawal to given positions. Even after completion of the withdrawal of the second lens group  210  and the third lens group  310 , the first lens group  110  continues to move in the first direction  115 . Then, when the first lens group  110  further moves in the first direction  115  and completes the movement to a given position, the transition from the second focal length range to the first focal length range ends ( FIG.  32   ). 
     The first lens group  110  illustrated in  FIG.  32    is closer to the image plane  16  than that illustrated in any of  FIG.  25    to  FIG.  31    is. The transition from the second focal length range to the first focal length range can thus shorten the overall length of the interchangeable lens  100 . Since the first lens group  110  has the first focal length range, image pickup is possible even when the overall lens length is minimized by completion of the withdrawal of the second lens group  210  and the third lens group  310  and the movement of the first lens group  110  toward the image plane  16 . Even when the interchangeable lens  100  provides the first focal length range, desired focusing (focus adjustment) can be performed by moving the first lens group  110  along the first optical axis  10 . 
     A transition from the second focal length range to the first focal length range has been described. Conversely, for a transition from the first focal length range to the second focal length range, the process illustrated in  FIG.  25    to  FIG.  32    is carried out in reverse order. For example, when the first lens group  110  is moved from the image plane side toward the subject by a user&#39;s operation, the second lens group  210  and the third lens group  310  rotate to move from the withdrawal positions illustrated in  FIG.  31    and  FIG.  32    to the positions on the first optical axis  10  illustrated in  FIG.  6   . The driving source for rotationally moving each of the second lens group  210  and the third lens group  310  is a dedicated actuator (not shown). When the second focal length range is provided, the second lens group  210  and the third lens group  310  are rotationally regulated by holding force of the actuators and secured in place on the first optical axis  10 . 
     When the interchangeable lens  100  makes a transition again from the second focal length range to the first focal length range, the dedicated actuators (not shown) move the second lens group  210  and the third lens group  310  to the respective withdrawal positions. The interchangeable lens  100  according to the present embodiment is thus configured to be capable of switching between the first focal length range and the second focal length range by combining a user&#39;s operation with an operation by the dedicated actuators. 
     When the focal length range of the optical system is the first focal length range, the second rotary shaft  325  is disposed to overlap some components of the first lens group  110  in the direction of the first optical axis  10 . In a plane substantially parallel to the image plane  16 , that is, as viewed in the direction of the first optical axis  10 , the second rotary shaft  325  is disposed outside the lens of the first lens group  110  closest to the image plane  16 . 
       FIG.  33    to  FIG.  35    are external views of the first lens group  110 , the second lens group  210 , and the third lens group  310  and illustrate the XY plane as viewed in the Z axis direction.  FIG.  33    is an external view of each lens group in the interchangeable lens  100  (second focal length range) according to the present embodiment. The first lens group  110 , the second lens group  210 , and the third lens group  310  are arranged in this order from the subject side. The first rotary shaft  225  may be divided and arranged at positions opposite each other, with a plane orthogonal to the rotation center thereof therebetween. In this case, as viewed in the direction of the first optical axis  10 , the first rotary shaft  225  is disposed outside the lens of the first lens group  110  closest to the image plane  16 . The second rotary shaft  325  may also be divided and arranged at positions opposite each other, with a plane orthogonal to the rotation center thereof therebetween. 
       FIG.  34    is an external view of each lens group in the interchangeable lens  100  (during transition) according to the present embodiment. As viewed in the direction of the first optical axis  10 , when the first rotary shaft  225  is disposed outside the lens of the first lens group  110  closest to the image plane  16 , the first lens group  110  can be moved closer to the image plane  16  than when the second focal length range is provided. 
       FIG.  35    is an external view of each lens group in the interchangeable lens  100  (first focal length range) according to the present embodiment. At this point, the transition from the second focal length range to the first focal length range has been completed, and the second lens group  210  and the third lens group  310  stay at the withdrawal positions. In a plane substantially parallel to the image plane  16 , that is, as viewed in the direction of the first optical axis  10 , the second rotary shaft  325  is disposed outside the lens of the first lens group  110  closest to the image plane  16 . Therefore, when the first focal length range is provided, the first rotary shaft  225  and the second rotary shaft  325  are disposed at positions that overlap the first lens group  110  in the direction of the first optical axis  10 . This allows the first lens group  110 , the second lens group  210 , and the third lens group  310  to be disposed at overlapping positions in the direction of the first optical axis  10  and thus can shorten the overall length of the interchangeable lens  100 . 
     As described above, the first lens group  110  according to the present embodiment moves toward the image plane  16  in the first direction  115  substantially parallel to the first optical axis  10 , and the second lens group  210  moves in the second direction  215 . The second lens group  210  moves toward the subject in the direction of the first optical axis  10 , and moves away from the first optical axis  10  in the radial direction. By moving in the third direction  315 , the third lens group  310  moves toward the subject in the direction of the first optical axis  10 , and moves away from the second lens group  210  in the radial direction. The transition from the second focal length range to the first focal length range is thus completed. 
     In the configuration of the related art, the conversion lens is withdrawn into the space between the prism and the strobe light to change the focal length and reduce an increase in the overall size of the camera. However, this configuration is applicable only to a type of lens-integrated camera that includes a prism and a strobe light. Therefore, for interchangeable lenses or cameras that do not include at least one of a prism and a strobe light, it has been difficult to prevent a size increase. The present disclosure can prevent a size increase of the lens by making the withdrawal space of the internal conversion lens more efficient. 
     Although the second lens group  210  and the third lens group  310  are combined to form the internal conversion lens in the present embodiment, the present disclosure is not limited to this. For example, a switching between the first focal length range and the second focal length range may be achieved by the second lens group  210  alone. In this case, the third lens group  310  may be a neutral density filter, a protective filter, or a polarizing filter. 
     Other Embodiments 
     The present disclosure can provide an optical device that can change the focal length range by withdrawing the internal conversion lens and can shorten the overall lens length by moving the master lens into the space created by the withdrawal. The present disclosure can also provide an optical device that can reduce an increase in lens size by making the configuration for withdrawing the internal conversion lens more efficient. The present disclosure can also provide an optical device that can reduce an increase in lens size by making the withdrawal space of the internal conversion lens more efficient. 
     While the present disclosure has been described with reference to exemplary embodiments, it is to be understood that the disclosure is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of priority from Japanese Patent Application No. 2021-176784 filed Oct. 28, 2021, No. 2021-176785 filed Oct. 28, 2021, and No. 2021-176786 filed Oct. 28, 2021, which are hereby incorporated by reference herein in their entirety.