Patent Publication Number: US-2021181607-A1

Title: Adapter device, mount apparatus, and accessory

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of International Patent Application No. PCT/JP2018/031995, filed Aug. 29, 2018, which is hereby incorporated by reference herein in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to an adapter device, a mount apparatus, and an accessory. 
     Background Art 
     Conventionally, an accessory (camera accessory), such as an interchangeable lens, which can receive power supply from a digital camera (herein after, referred to as a camera) and communicate commands, data, and so forth with the camera in a state where the accessory is mounted to the camera is known. It is known that multiple contacts (terminals) capable of electric connection, by coming into contact, are provided on both the camera and a mounting portion of the accessory, to enable the power supply and communication. 
     There is also known a mounting system for mounting (coupling) the accessory to the camera employing so-called bayonet coupling. In the bayonet coupling, mounts of both the camera and accessory are relatively rotated, and bayonet claws provided on each of the camera and accessory engage with each other. 
     Corresponding combinations of cameras and accessories employing a mounting system described above are predetermined. For example, corresponding accessories (e.g., interchangeable lenses, etc.) differ depending on the length of the flange focal distance of the camera. In other words, some accessories are not compatible with the flange focal distance of a camera. 
     In a case where an accessory not compatible with a camera is mounted, problems may occur. For example, in a case where an interchangeable lens not compatible with a camera having a certain flange focal distance is mounted to the camera, an optical image of a subject entering via the interchangeable lens may not be focused on the image plane of the camera. Thus, it may be necessary to restrict connection of a camera and an accessory in an incompatible combination. 
     In particular, in a case where a corresponding camera has approximately the same diameter as the diameter a plurality of accessories have, it may be difficult to judge from the external appearance whether the camera and the accessories have a corresponding combination. 
     PTL1 discusses a technique where a protrusion of a lens, which has the same flange focal distance but a short back focus, abuts a wall portion provided to a camera body, thereby preventing erroneous mounting of the lens to a camera body that cannot be mounted with a lens with a short back focus. 
     CITATION LIST 
     Patent Literature 
     
         
         PTL1: Japanese Patent Laid-Open No. 2005-70712 
       
    
     The technique described in PTL1 only discusses a technique that prevents erroneous mounting of a lens to a camera that cannot operate correctly with a lens that uses the same mounting system and has a short back focus. Thus, the technique discussed in PTL1 cannot prevent erroneous mounting of an accessory that has a different flange focal distance to a camera not compatible with the accessory. 
     Further, in the technique discussed in PTL1, a wall portion is provided on the camera body such that a protrusion of the lens is abutted to the camera body. Another configuration is thereby needed, and thus the number of parts or manufacturing cost may be increased. 
     Further, for example, in a case where a conversion lens having substantially the same mount diameter and a long flange focal distance is mounted to a camera having a short flange focal distance, a conversion adapter is necessary to be inserted between the camera and the conversion lens. In this case, the conversion lens has substantially the same diameter on both ends, and thus there is a problem that erroneous mounting may easily occur on the camera and the accessory with respect to the conversion adapter. 
     The present invention is directed to prevent erroneous mounting of an imaging apparatus and an accessory having mounts that can be mutually engaged with each other. 
     SUMMARY OF THE INVENTION 
     The present invention in its first aspect provides an adapter device according to the present invention includes a first mount on one side, and a second mount on another side, the first mount being attachable to and detachable from an imaging apparatus, and the second mount being attachable to and detachable from an accessory, the adapter device being characterized in that the first mount is fastened to the adapter device by a plurality of first screws, and a first mount recess, a first mount claw, a second mount recess, a second mount claw, a third mount recess, and a third mount claw are disposed following a circumferential direction of the first mount, the second mount is fastened to the adapter device by a plurality of second screws, and a fourth mount claw, a fourth mount recess, a fifth mount claw, a fifth mount recess, a sixth mount claw, and a sixth mount recess are disposed following a circumferential direction of the second mount, the first, second, and third mount claws are insertable into mount recesses provided to the imaging apparatus, the fourth, fifth, and sixth mount claws are insertable into mount recesses provided to the accessory, and a smallest angle range out of angle ranges in a circumferential direction of the first mount out of the first, second, and third mount recesses is equal to or smaller than a smallest angle range out of angle ranges in a circumferential direction of the second mount out of the fourth, fifth, and sixth mount claws. 
     The present invention in its second aspect provides an adapter device comprising a first mount on one side and a second mount on another side, a first mount being attachable to and detachable from an imaging apparatus, and the second mount being attachable to and detachable from an accessory, wherein the first mount is fastened to the adapter device by a plurality of first screws, and a first mount recess, a first mount claw, a second mount recess, a second mount claw, a third mount recess, and a third mount claw are disposed following a circumferential direction of the first mount, the second mount is fastened to the adapter device by a plurality of second screws, and a fourth mount claw, a fourth mount recess, a fifth mount claw, a fifth mount recess, a sixth mount claw, and a sixth mount recess are disposed following a circumferential direction of the second mount, the first, second, and third mount claws are insertable into mount recesses provided to the imaging apparatus, the fourth, fifth, and sixth mount claws are insertable to mount recesses provided to the accessory, and a largest angle range out of angle ranges in a circumferential direction of the second mount out of the fourth, fifth, and sixth mount claws is smaller than a largest angle range out of angle ranges in a circumferential direction of the first mount out of the first, second, and third mount recesses. 
     The present invention in its third aspect provides a mount apparatus being attachable to and detachable from an accessory having a first mount, wherein the mount apparatus has a second mount having a plurality of mount claws that can be engaged with a plurality of claws provided to the first mount, the plurality of mount claws includes a first mount claw, and a second mount claw and a third mount claw each having an angle range in a circumferential direction smaller than the angle range of the first mount claw, disposed following a circumferential direction of the second mount, the mount apparatus has a plurality of biasing members biasing the plurality of mount claws provided to the first mount in a center axis direction of the second mount, the first, second and third mount claws respectively have a first, second and third biasing member arrangement portions on which each of the plurality of biasing members is arranged, the second mount is fastened to the imaging apparatus by a plurality of screws, and in a case where a line extending from a center of the second mount in a gravitational direction and a direction opposite to the gravitational direction when viewing the mount apparatus in a normal position from the center axis direction of the second mount is taken as a first mount center line, and a line orthogonal to the first mount center line is taken as a second mount center line, and when viewing the second mount in the center axis direction of the second mount: the first mount claw overlaps the first mount center line, and at least one of the second mount claw and the third mount claw overlap the second mount center line, in a radial direction of the second mount, the first biasing member arrangement portion overlaps the first mount center line in the radial direction of the second mount, and the second biasing member arrangement portion overlaps the second mount center line in the radial direction of the second mount. 
     The present invention in its fourth aspect provides an accessory attachable to and detachable form a mount apparatus having a first mount, wherein the accessory has a second mount having a plurality of mount claws and a plurality of mount recesses that can be engaged with a plurality of claws provided to the first mount, the plurality of mount recesses include a first mount recess, and a second mount recess and a third mount recess that have an angle range in the circumferential direction smaller than the angle range of the first mount recess, disposed following a circumferential direction of the second mount, the second mount is fastened to the imaging apparatus by a plurality of screws, in a state that the accessory is attached to the mount apparatus, the plurality of mount claws are biased in a center axis direction of the second mount by each of a plurality of biasing members arranged in each space of the plurality of claws in the mount apparatus, the plurality of mount claws include a first mount claw, a second mount claw and a third mount claw, and in a case where a line extending from a center of the second mount in a gravitational direction and a direction opposite to the gravitational direction when viewing from the center axis direction of the second mount with the mount apparatus to which the accessory is mounted in a normal position, is taken as a first mount center line, and when viewing the second mount in the center axis direction of the second mount: the first mount center line does not overlap any of the plurality of mount recesses, and at least the biasing member which biases the first mount claw overlaps the first mount center line in a state that the accessory is attached to the mount apparatus. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a block diagram of a camera system including a first lens unit  100  and a camera body  10  as a first imaging apparatus to/from which the first lens  100  can be directly attached/detached according to an embodiment of the present invention. 
         FIG. 1B  is a block diagram illustrating a configuration of a mount portion  1  included in the first lens  100  and the camera body  10  according to an embodiment of the present invention. 
         FIG. 2A  is an external perspective view of a camera body  10  in a state where a first lens unit  100  is mounted to the camera body  10  according to an embodiment of the present invention. 
         FIG. 2B  is an external perspective view of a camera body  10  in a state where the first lens unit  100  is detached from the camera body  10  according to an embodiment of the present invention. 
         FIG. 3A  is a disassembled perspective view of the camera body  10  according to an embodiment of the present invention. 
         FIG. 3B  is a disassembled perspective view of the first lens unit  100  according to an embodiment of the present invention. 
         FIG. 4A  is a diagram exemplarily describing angle ranges that camera mount claws and camera mount recesses having a lock pin  202  as a reference occupy in a case of viewing the camera mount  201  according to an embodiment of the present invention from the photographer side (rear face side of the camera body  10 ) of the camera body  10 . 
         FIG. 4B  is a diagram exemplarily describing angle ranges that a plurality of camera claws  201   a  to  201   c  occupies in a case of viewing the camera mount  201  according to an embodiment of the present invention from the photographer side (rear face side of the camera body  10 ) of the camera body  10 . 
         FIG. 4C  is a cross-sectional diagram taken along a cross-section A-A′ illustrated in  FIG. 4B . 
         FIG. 5A  is a diagram exemplarily describing engagement by camera claws at a normal position of the camera body  10  according to an embodiment of the present invention in a state where the first lens unit  100  is mounted to the camera body  10 . 
         FIG. 5B  is a partial cross-sectional view of the camera body  10  and the first lens  100  taken along a cross-section B-B′ illustrated in  FIG. 5A . 
         FIG. 6A  is a diagram exemplarily describing engagement by lens claws at a vertical position of the camera body  10  according to an embodiment of the present invention in a state where the first lens unit  100  is mounted to the camera body  10 . 
         FIG. 6B  is a partial cross-sectional view of the camera body  10  and first lens  100  taken along a cross-section C-C′ illustrated in  FIG. 6A . 
         FIG. 7A  is a diagram exemplarily describing angles of the claws and recesses in a circumferential direction at a lens mount  301  side in a case of viewing a lens mount  301  according to an embodiment of the present invention from the rear face side (side where the camera body is mounted) in a state where the first lens unit  100  is mounted to the camera body  10 . 
         FIG. 7B  is a cross-sectional view taken along a cross-section D-D′ illustrated in  FIG. 7A . 
         FIG. 8A  is an external perspective view of the camera mount  201  according to an embodiment of the present invention as viewed from the front face side (subject side). 
         FIG. 8B  is an external perspective view of the camera mount  201  according to an embodiment of the present invention as viewed from above. 
         FIG. 9A  is an external perspective view of the lens mount  301  according to an embodiment of the present invention as viewed from the side (rear face side) to which the camera mount  201  is mounted. 
         FIG. 9B  is an external perspective view of the camera mount  301  according to an embodiment of the present invention as viewed from above. 
         FIG. 10A  is a diagram exemplarily describing a contact state between terminals on the camera body  10  and the first lens unit  100  according to an embodiment of the present invention in a mounting start state where mounting of the first lens  100  to the camera body  10  has been started. 
         FIG. 10B  is a diagram exemplarily describing a contact state between terminals on the camera body  10  and the first lens unit  100  according to an embodiment of the present invention in a mounting completed state where mounting of the first lens  100  to the camera body  10  has been completed. 
         FIG. 11A  illustrates an external perspective view of a second lens unit  50  having been mounted to the camera body  10  via a first conversion adapter  40 . 
         FIG. 11B  illustrates an external perspective view of a state where the camera body  10 , first conversion adapter  40 , and second lens unit  50  have each been detached. 
         FIG. 12A  illustrates an external perspective view of a state where the first lens  100  is mounted to a camera body  60  via a second conversion adapter  70 . 
         FIG. 12B  illustrates an external perspective view where the camera body  60 , second conversion adapter  70 , and the first lens  100  have each been detached. 
         FIG. 13A  is a diagram exemplarily illustrating angle ranges that camera claws and camera recesses occupy in the circumferential direction of a camera mount  1401  with a lock pin  1401   z  as a reference, as viewed from the rear face side (camera body  10  side). 
         FIG. 13B  is a diagram exemplarily illustrating angle ranges that multiple camera claws  1401   a  through  1401   c  occupy in the circumferential direction of the camera mount  1401 , as viewed from the rear face side (camera body  10  side). 
         FIG. 13C  is a cross-sectional diagram taken along a cross-section E-E′ illustrated in  FIG. 13B . 
         FIG. 14A  is a diagram exemplarily illustrating angle ranges that lens claws and lens recesses occupy in the circumferential direction of a lens mount  1301  with a lock groove  1301   z  as a reference, as viewed from the rear face side. 
         FIG. 14B  is a diagram exemplarily illustrating angle ranges that multiple lens recesses  1301   a  through  1301   c  occupy in the circumferential direction of the lens mount  1301 , as viewed from the rear face side. 
         FIG. 15A  is a diagram exemplarily describing a frontal view of partway through mounting a predetermined lens unit to a predetermined imaging apparatus that have claws and recesses that interfere with each other. 
         FIG. 15B  is a cross-sectional view taken along a cross-section F-F′ illustrated in  FIG. 15A . 
         FIG. 16A  illustrates a way in which a third lens claw and a first camera claw interfere when the lens mount  301  side is attempted to mount to the camera mount  401  side according to the embodiment of the present invention. 
         FIG. 16B  illustrates a way in which the second lens claw and the second camera claw interfere when the lens mount  301  side is attempted to mount to the camera mount  401  side according to the embodiment of the present invention. 
         FIG. 17A  is a diagram exemplarily describing a way in which the third lens claw and the third camera claw interfere in a case of attempting to insert the first lens claw into the third camera recess, in a case of attempting to insert incompatible claws into recesses at a lens mount  301  side and a camera mount  401  side according to the embodiment of the present invention. 
         FIG. 17B  is a diagram exemplarily describing a way in which the second lens claw and the first camera claw interfere in a case of attempting to insert the first lens claw into the third camera recess, in a case of attempting to insert incompatible claws into recesses at a lens mount  301  side and a camera mount  401  side according to the embodiment of the present invention. 
         FIG. 17C  is a diagram exemplarily describing a way in which the third lens claw and the second camera claw interfere in a case of attempting to insert the first lens claw into the second camera recess, in a case of attempting to insert incompatible claws into recesses at a lens mount  301  side and a camera mount  401  side according to the embodiment of the present invention. 
         FIG. 17D  is a diagram exemplarily describing a way in which the second lens claw and the third camera claw interfere in a case of attempting to insert the first lens claw into the second camera recess, in a case of attempting to insert incompatible claws into recesses at a lens mount  301  side and a camera mount  401  side according to the embodiment of the present invention. 
         FIG. 18A  is a diagram exemplarily illustrating angle ranges that camera claws and camera recesses occupy in the circumferential direction of the camera mount  1201  with a lock pin  1202  as a reference, as viewed from the rear face side. 
         FIG. 18B  is a diagram exemplarily illustrating angle ranges that, regarding multiple camera claws  1201   a  through  1201   c , the claws occupy in the circumferential direction of the camera mount  1201 , as viewed from the rear face side. 
         FIG. 19A  is a diagram exemplarily illustrating angle ranges that lens claws and lens recesses occupy in the circumferential direction of the lens mount  1501  with a lock pin  1501   z  as a reference, as viewed from the rear face side. 
         FIG. 19B  is a diagram exemplarily illustrating angle ranges where recesses are provided regarding the multiple lens recesses  1501   a  through  1501   c  in the circumferential direction of the lens mount  1501 , as viewed from the rear face side. 
         FIG. 19C  is a cross-sectional diagram taken along a cross-section G-G′ illustrated in  FIG. 19B . 
         FIG. 20A  is a diagram exemplarily describing a way in which the third lens claw interfere with the third camera claw, when attempting to mount a reference claw at the lens mount  501  side to a reference recess at the camera mount  201  side according to an embodiment of the present invention. 
         FIG. 20B  is a diagram exemplarily describing a way in which the second lens claw interfere with the third camera claw, when attempting to mount a reference claw at the lens mount  501  side to a reference recess at the camera mount  201  side according to an embodiment of the present invention. 
         FIG. 21A  illustrates a way in which the first lens claw and the third camera claw interfere in a case of attempting to insert the second lens claw into the first camera recess, when attempting to mount a claw other than the reference claw at the lens mount  501  side to a reference recess at the camera mount  201  side according to an embodiment of the present invention. 
         FIG. 21B  illustrates a way in which the third lens claw and the third camera claw interfere in a case of attempting to insert the second lens claw into the first camera recess, when attempting to mount a claw other than the reference claw at the lens mount  501  side to a reference recess at the camera mount  201  side according to an embodiment of the present invention. 
         FIG. 21C  illustrates a way in which the second lens claw and the third camera claw interfere in a case of attempting to insert the third lens claw into the first camera recess, when attempting to mount a claw other than the reference claw at the lens mount  501  side to a reference recess at the camera mount  201  side according to an embodiment of the present invention. 
         FIG. 21D  illustrates a way in which the first lens claw and the third camera claw interfere in a case of attempting to insert the third lens claw into the first camera recess, when attempting to mount a claw other than the reference claw at the lens mount  501  side to a reference recess at the camera mount  201  side according to an embodiment of the present invention. 
         FIG. 22  is a diagram exemplarily describing a state in which claws provided to the camera mount  401  side and lens mount  501  side according to an embodiment of the present invention are engaged. 
         FIG. 23  is a disassembled perspective view of a mount mechanism  5000  according to a modification of the present invention. 
         FIG. 24A  is an external perspective view of a mount mechanism  5000  exemplarily illustrating a non-coupled state of the mount mechanism  5000  according to a modification of the present invention. 
         FIG. 24B  is a frontal view of the mount mechanism  5000  exemplarily illustrating a non-coupled state of the mount mechanism  5000  according to the modification of the present invention. 
         FIG. 24C  is a cross-sectional diagram taken along a cross-section H-H′ illustrated in  FIG. 24B . 
         FIG. 25A  is an external perspective view of a mount mechanism  5000  exemplarily illustrating a coupled state of the mount mechanism  5000  according to a modification of the present invention. 
         FIG. 25B  is a frontal view of the mount mechanism  5000  exemplarily illustrating a coupled state of the mount mechanism  5000  according to the modification of the present invention. 
         FIG. 25C  is a cross-sectional diagram taken along a cross-section I-I′ illustrated in  FIG. 25B . 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
       FIGS. 1A and 1B  are block diagrams of a camera accessory and imaging apparatus according to an embodiment of the present invention.  FIG. 1A  is a diagram exemplarily describing a camera system including a first lens unit (hereinafter referred to as first lens)  100 , serving as an accessory according to the embodiment of the present invention, and a camera body  10  serving as a first imaging apparatus to/from which the first lens  100  can be directly attached/detached.  FIG. 1B  is a diagram describing the configuration of a mount portion  1  included in the first lens  100  and the camera body  10 . That is in  FIG. 1 , the mounts provided on the first lens  100  and the camera body  10  are collectively referred to as the mount portion  1 . Each mount provided to the first lens  100  and camera body  10  will be described below. 
     As illustrated in  FIG. 1A , the camera body  10  has a charge-accumulation type solid-state imaging device (hereinafter referred to simply as sensor)  11 , such as a complementary metal-oxide semiconductor (CMOS) sensor or the like, that performs photoelectric conversion of an optical image of a subject guided by a photography lens group  101  provided on the inner side of the first lens  100  and outputs electric signals. The camera body  10  also has an analogue to digital (A/D) conversion unit  12  that converts analog electric signals output from the imaging sensor  11 , and an image processing unit  13  that generates image signals by performing various types of image processing on the digital signals. The image signals (still image and moving image) generated at the image processing unit  13  can be displayed on a display unit  14 , and recorded in a recording medium  15 . 
     The camera body  10  has memory  16 . This memory  16  serves as a buffer for performing processing on image signals, and also stores operation programs (computer programs) that a below-described camera control unit  18  uses. 
     The camera body  10  has a camera operating input unit  17  including a power source switch for turning the power source on/off, a photography switch (release switch) for starting recording of image signals, and selection/settings switches for performing various types of menu settings. The camera body  10  has the camera control unit  18  including a microprocessor (central processing unit (CPU) serving as a computer) that centrally controls the operations of the camera body  10  and first lens  100 . For example, the camera control unit  18  performs various types of settings based on signals input from the camera operating input unit  17 , or controls communication with a lens control unit  103  provided to the first lens  100  via the mount portion  1 . 
     On the other hand, the first lens  100  has the photography lens group  101  an optical member having multiple lens groups, such as a zoom lens, shift lens, and focus lens, and light amount adjustment members, such as a diaphragm. The first lens  100  has actuators for moving or operating optical members, such as the multiple lens groups and diaphragm, and a lens drive unit  102  that drives the actuators. The first lens  100  includes the lens control unit  103  including a microprocessor (logical CPU (LCPU)) for lenses, which centrally controls operations of the first lens  100 . The lens control unit  103  controls the lens drive unit  102  by communicating with the camera control unit  18  via, for example, the mount portion  1 . 
     (Basic Configuration of Mount Portion  1 ) 
     Next, the configuration of the mount portion  1  including a camera mount face A provided on the camera body  10  side, and an accessory mount face B provided on the first lens  100  side will be described with reference to  FIG. 1B . The camera mount and accessory mount include a locking mechanism, a mount holding mechanism, and multiple electric terminals. The mounts will be described in detail below. 
     The mount portion  1  has multiple terminals that are capable of electrically connecting the camera body  10  and the first lens  100  to each other, as illustrated in  FIG. 1B . The multiple terminals are, at the camera mount face A, exposed to the outside of the camera body  10  as multiple camera-side contact pins provided to a contact holding member  203 . The multiple terminals are, at the accessory mount face B, exposed to the outside of the camera accessory (e.g., first lens  100 ) as multiple accessory-side contact faces provided to a contact face holding member  303 . The contact pins and the contact faces of the camera body  10  side and the camera accessory (e.g., first lens  100 ) side are electrically connected to each other with mutually corresponding contacts in a state where the camera accessory is mounted to the camera body  10 . 
     A camera power source unit  19  generates a communication control power source (VDD) as a power source to be supplied to a mounted camera accessory via a VDD terminal, or power source to be supplied to a first communication I/F unit  21   a  via a power source switching unit  20 . The camera power source unit  19  also generates a driving power source (VBAT) as a power source to be supplied to the mounted camera accessory via a VBAT terminal. 
     The camera power source unit  19  generates a 3.3 V power source as a power source to be supplied to the camera control unit  18 , first communication I/F unit  21   a , and a second/third communication I/F unit  21   b . The camera power source unit  19  also generates 3.0 V power source as a power source to be supplied to the first communication I/F unit  21   a  and second/third communication I/F unit  21   b  via the power source switching unit  20 . 
     The power source switching unit  20  is connected to the camera power source unit  19 . The power source switching unit  20  supplies only one of the VDD and 3.0 V power sources generated at the camera power source unit  19 , to the first communication I/F unit  21   a  as a power source Vs for communication interface. Switching of power source voltage is executed following instructions from the camera control unit  18 . 
     Next, a lens power source  104  generates a 3.0 V power source, as a power source voltage for supply to the lens control unit  103  and a lens-side I/F unit  106 , based on VDD supplied from the camera body  10  side. 
     In a state where the first lens  100  is mounted to the camera body  10 , a driving power source (VBAT) is supplied to a drive circuit unit  105  at the first lens  100  side, via a VBAT terminal from the above-described camera power source unit  19 . 
     Although the power source voltage for the lens control unit  103  and lens-side I/F unit  106  is the same (3.0 V) in the present embodiment, a configuration may be made where the voltage level that the lens control unit  103  exhibits is 3.3 V. In this case, there is the need to supply power source of a voltage level of 3.0 V and 3.3 V to the lens-side I/F unit  106 , the lens power source  104  therefore generates power sources of 3.0 V and 3.3 V. 
     Hereafter, the functions of the terminals common to both the camera mount face A and accessory mount face B will be described. VDD terminals  203   a  and  303   a  are terminals that supply communication control power source (VDD) as communication power primarily used for communication control, to the camera accessory (e.g., the first lens  100 ) from the camera body  10 . Note that while the voltage of power source supplied to the first lens  100  is 5.0 V, the voltage of supplied power source will change depending on the type of accessory mounted to the camera body  10 . 
     VBAT terminals  203   b  and  303   b  are terminals that supply driving voltage source (VBAT), which is driving power used for operating the mechanical driving units of the actuators used for driving the diaphragm and focus lens, from the camera side to the camera accessory side. In other words, the VBAT terminals  203   b  and  303   b  are terminals used to supply power source other than the above-described communication power. Note that the voltage of the power source serving as driving power supplied to the first lens  100  is 4.25 V. The VDD terminals  203   a  and  303   a  and VBAT terminals  203   b  and  303   b  described above are power source terminals for supplying power source from the camera body  10  to the camera accessory, for example. 
     DGND terminals  203   m  and  303   m  are grounding terminals GND terminals) corresponding to the communication control power source VDD. Note that grounding in the present embodiment means to set the voltage level of the grounding terminals to approximately the same level as the negative pole side of the power source, such as a battery. 
     PGND terminals  203   d  and  303   d  are grounding terminals for connecting the camera body  10 , and a mechanical drive system including motors (actuators) provided to a camera accessory (e.g., the first lens  100 ), to ground level. That is to say, the PGND terminals  203   d  and  303   d  are grounding terminals (GND terminals) corresponding to the driving power source VBAT. The DGND terminals  203   m  and  303   m  and PGND terminals  203   d  and  303   d  described above are grounding terminals for grounding various types of power source systems in the camera body  10  and accessory to the ground level. 
     MIF terminals  203   e  and  303   e  are terminals for detecting that the camera accessory (e.g., the first lens  100 ) has been mounted to the camera body  10 . In the present embodiment, the MIF terminals  203   e  and  303   e  detect that the first lens  100  has been mounted to the camera body  10 . 
     The camera control unit  18  detects that the camera accessory has been mounted to or detached from the camera body  10 , by detecting the voltage level that the MIF terminals  203   e  and  303   e  indicated. Based on this detection, the camera control unit  18  starts supply of power source to power source terminals after having detected mounting of, for example, the camera accessory, and effects control to start communication between the camera body  10  and camera accessory. 
     TYPE terminals  203   c  and  303   c  are terminals for distinguishing the type of camera accessory (e.g., the first lens  100 ) mounted to the camera body  10 . The camera control unit  18  detects the value of voltage of signals indicated by the TYPE terminals  203   c  and  303   c , and distinguishes the type of camera accessory mounted to the camera body  10  based on this value. The first lens  100  is pull-down connected to the DGND terminal at a predetermined resistance value. This resistance value differs depending on the type of the camera accessory. 
     Next, description will be made regarding various types of communication terminals between the camera body  10  and the camera accessory. The multiple communication terminals provided to the mount portion  1  are divided into multiple communication systems (groups), and each communication system is capable of performing communication independently. In the present embodiment, LCLK terminals  203   h  and  303   h , DCL terminals  203   f  and  303   f , and DLC terminals  203   g  and  303   g , are a first communication system that performs first communication. DLC 2  terminals  203   i  and  303   i  are a second communication system that performs second communication, which is independent from the first communication. Further, CS terminals  203   k  and  303   k , and DCA terminals  203   j  and  303   j  are a third communication system that performs third communication, which is independent from the first and second communication. In the present embodiment, the camera control unit  18  and lens control unit  103  can perform communication independently with the first through third, via the above-described multiple communication terminals. 
     LCLK terminals  203   h  and  303   h  are terminals of the first communication system, and are terminals for communication clock signals output from the camera body  10  to the camera accessory (e.g., the first lens  100 ), and terminals for the camera body  10  to monitor the busy state of the accessory. 
     DCL terminals  203   f  and  303   f  are terminals of the first communication system, and are communication data terminals for performing bidirectional communication between the camera body  10  and the camera accessory (e.g., the first lens  100 ). 
     DLC terminals  203   g  and  303   g  are terminals of the first communication system, and are terminals for communication data output from the camera accessory (e.g., the first lens  100 ) to the camera body  10 . 
     The above-described LCLK terminals, DCL terminals, and DLC terminals, corresponding to the first communication system, can switch the signal output format between so-called CMOS output type and open type. In the present embodiment, the CMOS output type has switch output of voltage at both H (High) and L (Low). In comparison with this, the open type has switch output at only the L side. Although open type used in the present embodiment is the so-called open drain type, the open type may be the open collector type. 
     DLC 2  terminals  203   i  and  303   i  are terminals of the second communication system, and are terminals for communication data output from the camera accessory (e.g., the first lens  100 ) to the camera body  10 . 
     DCA terminals  203   j  and  303   j  are terminals of the third communication system, and are terminals for communication data for performing bidirectional communication between the camera body  10  and the camera accessory (e.g., the first lens  100 ). 
     CS terminals  203   k  and  303   k  are terminals of the third communication system, and are signal terminals for communication requests between the camera body  10  and camera accessory (e.g., the first lens  100 ). In the present embodiment, in a case where the first lens  100  is mounted to the camera body  10 , the communication voltage at the corresponding terminals in the first through third communication systems is 3.0 V. 
     (Configuration of Camera Mount and Accessory Mount) 
     The configuration of the camera mount  201  and the lens mount (accessory mount)  301  according to the present embodiment will be described with reference to  FIGS. 2A through 3B . In the following description, the mount provided to the imaging apparatus side will be referred to as camera mount, and the mount provided to the lens unit side will be referred to as lens mount. Concerning mounts of the below-described conversion adapter, the side mounted to the imaging apparatus will be referred to as lens mount, and the side mounted to the lens unit will be referred to as camera mount. In the following description, a second conversion adapter  70  has a camera mount  1201  that is the same as the camera mount  201  provided on the camera body  10 . In the following description, a first conversion adapter  40  has a lens mount  1301  that is the same as the lens mount  301  provided on the first lens  100 . 
       FIGS. 2A and 2B  are external perspective views of the camera body  10  and first lens  100  according to the embodiment of the present invention.  FIG. 2A  illustrates a state in which the first lens  100  is mounted to the camera body  10 , and  FIG. 2B  illustrates a state in which the first lens  100  has been removed from the camera body  10 . 
     As illustrated in  FIGS. 2A and 2B , the camera body  10  and first lens  100  have a ring-shaped camera mount  201  and ring-shaped lens mount  301 , which each have contact faces that are parallel in a direction orthogonal to the optical axis. The camera mount  201  and the lens mount  301  do not necessarily have a ring shape, and the shape may be an arc-shape. For example, a part of the ring shaped contact face of the camera mount  201  illustrated in  FIGS. 2A and 2B  may be notched out. In the present embodiment, the center axis of the camera mount  201  and the center axis of the lens mount  301  are same as each optical axis of the camera mount  201  or lens mount  301 . A configuration may be employed where the optical axis is different from the center axis. By rotating the camera body  10  and first lens  100  relative to each other, in a state where the reference faces of each of the camera mount  201  and lens mount  301  are in contact with each other, from an unlocked position to a locked position, the first lens  100  is mounted to the camera body  10 . This will be described in detail below. 
       FIG. 3  illustrates disassembled perspective views of the camera body  10  and first lens  100  according to the embodiment of the present invention.  FIG. 3A  illustrates a disassembled perspective view of the camera body  10 , and  FIG. 3B  illustrates a disassembled perspective view of the first lens  100 . 
     As illustrated in  FIG. 3A , a first optical axis (a first center axis)  3000  indicates a light flux passing through the center of the camera mount  201  of the camera body  10 . As illustrated in  FIG. 3B , an optical axis  3001  is an axis for exemplarily describing a light flux representing an optical image of a subject guided by the first lens  100 . When the first lens  100  is mounted to the camera body  10 , the first optical axis  3000  and optical axis  3001  described above substantially match, and optical fluxes corresponding to these optical axes enter the imaging sensor  11  and are imaged, thereby imaging a subject image. 
     A lock pin  202  is a first restricting member (lock member) for restricting (locking) the mounted state of the camera body  10  and camera accessory as illustrated in  FIG. 3A . The lock pin  202  is capable of advancing and retreating in a direction parallel to the first optical axis  3000 . Specifically, when the first lens  100  is mounted to the camera body  10 , the lock pin  202  enters a lock groove  301   z  a second restricting member provided to the lens mount  301 , and locks the state of the first lens  100  being mounted to the camera body  10 . The lock pin  202  is retracted from the lock groove  301   z  by the user operating a lock disengaging member (not illustrated) connected to the lock pin  202 , thereby the locking of the first lens  100  mounted to the camera body  10  can be disengaged. Even in a case of further rotating the first lens  100  and camera body  10  relative to each other in the mounting direction with the lock disengaging member operated, rotation beyond a lock abutting face  301   y  is restricted (see  FIG. 7A ). 
     The contact holding member  203  is a holding unit for holding below-described (see  FIG. 8 ) multiple contact pins (electrical communication contact group)  203   a  through  203   k  and  203   m , provided on the camera body  10  side. In the present embodiment, the contact pins and contact faces corresponding to the above-described terminals are denoted by the same part numerals as the terminals for the sake of description. 
     A camera body member  204  is a camera housing that holds the members of the camera body  10 . Specifically, the above-described camera mount  201  and contact holding member  203  are fastened to the camera body member  204  by camera mount fastening screws  205   a  through  205   d  and contact holding member fastening screws that are not illustrated. Camera mount fastening screws  205   a  through  205   d  are positioned where none of multiple leaf springs  206   a ,  206   b , and  206   c  are positioned in the camera mount  201 . The camera mount fastening screws  205   a  through  205   d  are exposed at the contact face of the camera mount  201 , the contact face being contacted with the lens mount  301 . Although the camera body member  204  holds an unillustrated imaging unit to which the aforementioned imaging sensor  11  is mounted and an unillustrated shutter unit, description will be omitted. 
     A lens mount biasing member  206  is a biasing unit at the imaging apparatus side to pull lens claws  301   d  and  301   e , which are multiple bayonet claws provided to the below-described lens mount  301 , toward the camera mount  201  side. Specifically, the lens mount biasing member  206  includes multiple leaf springs  206   a ,  206   b , and  206   c , and the bayonet claws provided to the first lens  100  are biased in the optical axis direction by the leaf springs. The lens mount biasing member  206  is held by both the camera mount  201  and camera body member  204  in a space formed therebetween. 
     A front lens  101   a  and rear lens  101   b  are optical members making up the photography lens group  101 , as illustrated in  FIG. 3B . While the photography lens group  101  has multiple lenses, only the front lens  101   a  disposed at the subject-side end and the rear lens  101   b  disposed at the camera body  10  side end are illustrated in the present embodiment to simplify description. 
     A lens barrel  302  is a holding member that holds the photography lens group  101 . The lens mount  301  is fastened to the lens barrel  302  by lens mount fastening screws  304   a  through  304   d . The lens mount fastening screws  304   a  through  304   d  are exposed at the contact face of the lens mount  301 , the contact face being contacted with the camera mount  201 . 
     A contact face holding member  303  is a holding unit for holding multiple contact faces (electrical communication contact group)  303   a  through  303   k  and  303   m  provided to a below-described (see  FIG. 9 ) first lens  100  side. The contact face holding member  303  is fastened to the lens mount  301  by lens contact portion holding portion fastening screws  305   a  and  305   b.    
     (Configuration of Bayonet Claws at Camera Body  10  Side) 
     Next, the multiple bayonet claws provided to the camera mount  201  at the camera body  10  side will be described with reference to  FIGS. 4 through 6 .  FIG. 4  illustrates diagrams exemplarily describing a case of viewing the camera mount  201  according to the embodiment of the present invention from the photographer side (rear face side of the camera body  10 ) of the camera body  10 .  FIG. 4A  is a diagram illustrating angle ranges that camera mount claws (hereinafter referred to simply as camera claws) and camera mount recesses (hereinafter referred to simply as camera recesses) having the lock pin  202  as a reference occupy in the circumferential direction of the camera mount  201 . The camera recesses of the camera mount  201  are notch portions between adjacent claws. Camera recesses of the mount are therefore formed further toward the outside in the radial direction with respect to the center axis of the mount than the claws of the camera mount  201 . Lens recesses of the lens mount  301  are formed further toward the inside in the radial direction with respect to the center axis (parallel to the optical axis) of the mount than the lens claws.  FIG. 4B  is a diagram illustrating angle ranges that multiple camera claws  201   a  through  201   c  occupy in the circumferential direction of the camera mount  201 .  FIG. 4C  is a cross-sectional diagram taken along a cross-section A-A′ illustrated in  FIG. 4B . 
     In the following description, protrusions protruding from recesses in the inner radial direction at the camera mount side will be referred to as camera claws, and protrusions protruding from recesses in the outer diameter direction at the below-described lens mount (accessory mount) side will be referred to as lens mount claws. 
     In the following description, the side of the camera mount  201  as viewed from the side of the photographer (rear face of the camera body  10 ) of the camera body  10  will be referred to as rear face side, and the opposite side will be referred to as front face side (or camera accessory side). It should be noted that in the following description, description will be made with a case of viewing the camera mount  201  from the rear face side as a reference, but in a case of viewing the camera mount  201  from the front face side, angles and directions in the following description stipulating angles (clockwise, etc.) will be reversed. 
     As illustrated in  FIGS. 4A and 4B , a first camera claw  201   a , second camera claw  201   b , and third camera claw  201   c  are provided in order to the camera mount  201  in the circumferential direction (inner radial direction). When viewing the camera mount  201  from the rear face side as illustrated in  FIG. 4 , the camera claw provided at a position farthest from the lock pin  202  is the first camera claw  201   a . The second camera claw  201   b  and third camera claw  201   c  are consecutively provided in order from the first camera claw  201   a  in a clockwise direction. 
     Recesses, which are a first camera recess  201   d , second camera recess  201   e , and third camera recess  201   f , are provided in order to the camera mount  201  in the circumferential direction (inner radial direction). When viewing the camera mount  201  from the rear face side as illustrated in  FIG. 4 , the recess that is provided at a position nearest to the lock pin  202  is the second camera recess  201   e . The third camera recess  201   f  and first camera recess  201   d  are consecutively provided in order from the second camera recess  201   e  in a clockwise direction. 
     As illustrated in  FIG. 4C , a fitting member  201   x , which restricts movement of the camera accessory in a direction parallel to the optical axis when the camera accessory is mounted, is provided to the camera mount  201  side in the circumferential direction. In the present embodiment, the diameter (i.e., the inner diameter of the fitting member  201   x ) in a direction orthogonal to the optical axis (approximately the same as the center axis) of the fitting member  201   x  at the camera mount  201  side is the mount diameter. 
     To mount the first lens  100  to the camera body  10 , the camera claws of the camera body  10  are first inserted into the lens mount recesses of the first lens  100 , and the lens mount claws at the first lens  100  side are inserted into the camera recesses at the camera body  10  side. This state is a mounting start state (first state). In the following description, accessory mount recesses will be referred to simply as accessory recesses, and accessory mount claws will be reference to simply as accessory claws. For example, in the case of the lens mount  301 , this will be lens recesses and lens claws. 
     The camera mount  201  and lens mount  301  are then rotated relative to each other from the mounting start state, whereby the camera claws and lens claws engage in the radial direction orthogonal to the optical axis, and transition to a state where the lens claws are biased by the above-described lens mount biasing member  206 . In this state, relative positional relation between the camera body  10  and the first lens  100  transitions to a locked position where the lock pin  202  has fit into the lock groove  301   z  as described above. This state is a mounting complete state (second state). In the mounting complete state, contact of corresponding terminals at the camera mount  201  and lens mount  301  is complete. 
     As described above, the camera claws and accessory claws are so-called bayonet claws, and as described above, have shapes such that the first lens  100  can be mounted (can be coupled) to the camera body  10  by the so-called bayonet coupling method by engaging of the camera claws and accessory claws. 
     For the description, the end portions of the camera claws  201   a ,  201   b , and  201   c , in the circumferential direction, will be referred to as first end portion  201   a   1 , second end portion  201   a   2 , third end portion  201   b   1 , fourth end portion  201   b   2 , fifth end portion  201   c   1 , and sixth end portion  201   c   2 , respectively. Each of the end portions are denoted with part numerals in order from the first camera claw  201   a  in the clockwise direction, when viewing the camera mount  201  from the rear face side, as described above. The camera claws  201   a ,  201   b , and  201   c  include first, second, and third leaf spring disposition portions  201   a   3 ,  201   b   3 , and  201   c   3  in which the above-described plurality of leaf springs  206   a ,  206   b , and  206   c  of the lens mount biasing member  206  are disposed, respectively. In the present embodiment, the first, second, and third leaf spring disposition portions  201   a   3 ,  201   b   3 , and  201   c   3  each correspond to the notch portions provided between the above-described end portions of each camera claw. The size of the notch portions is a size at which each of the plurality of leaf springs can be arranged For example, the first leaf spring disposition portions  201   a   3  is a notch (separation portion) provided in the camera claw  201   a  between the first end portion  201   a   1  and the second end portion  201   a   2  of the camera claw  201   a.    
     As illustrated in  FIG. 4A , the angles (angle ranges) that the camera claws and camera recesses occupy in the circumferential direction of the camera mount  201  are stipulated as follows in the present embodiment. For the first camera claw  201   a , the angle θa=48°. For the second camera claw  201   b , the angle θb=40°. For the third camera claw  201   c , the angle θc=92°. Further, for the first camera recess  201   d , the angle is 57°. For the second camera recess  201   e , the angle is 66°. For the third camera recess  201   f , the angle is 57°. In here, the angle range of the claw (bayonet claw) and the recess indicates an angle range in which each bayonet claw and the recess (notch portion) the bayonet claw can be inserted occupy in each mount. For example, if the camera mount  201  has a ring shape, the angle range occupied by the first camera claw  201   a  with respect to the entire camera mount  201  (360°) becomes 40°. Even in a case where the mount does not have a complete ring shape, the mount may be considered ring-shaped (360°) to define the angular range of the claws and recesses. 
     When viewing the camera claws from the rear face side of the camera body  10 , the angles in the clockwise direction where the camera claws are disposed in the circumferential direction of the camera mount  201  with the position (referred to as reference position) of the lock pin  202  as a reference are stipulated as follows. The first camera claw  201   a  is disposed between 169° and 217° with the reference position as a start point. The second camera claw  201   b  is disposed between 274° and 314° with the reference position as a start point. The third camera claw  201   c  is disposed between 20° and 112° with the reference position as a start point. 
     When viewing the camera mount  201  from the optical axis direction in the present embodiment, of the multiple bayonet claws, the third camera claw  201   c  overlaps a first camera mount center line  3003  that extends in the vertical direction from the center axis, which is parallel to the optical axis, of the camera mount  201  in the radial direction of the camera mount  201 . The first camera mount center line  3003  is a line that, in a normal position of the camera body  10  where the lock pin  202  is situated at the left side when viewing the camera mount  201  from the front face side, extends in the gravitational direction and the opposite direction from the gravitational direction, from the center (optical axis) of the camera mount  201 . That is to say, the first camera mount center line  3003  is a vertical line that passes through the optical axis in a normal position of the camera. In other words, the first camera mount center line  3003  is a vertical line that passes though the center of the camera mount  201  and orthogonal to the center axis of the camera mount  201  when the camera body  10  is placed on a horizontal plane. 
     In contrast, a line that, in a vertical position of the camera body  10  where the lock pin  202  is situated at the top side when viewing the camera mount  201  from the front face side, extends in the gravitational direction and the opposite direction from the gravitational direction, from the center (optical axis) of the camera mount  201 , is a second camera mount center line  3002 . That is to say, the second lens mount center line  3002  is a horizontal line that passes through the optical axis when the camera body  10  is in the normal position. 
     The second camera mount center line  3002  overlaps the lock pin  202  and first camera claw  201   a  in the radial direction of the camera mount  201 . The first camera mount center line  3003  and the second camera mount center line  3002  are substantially orthogonal. 
       FIG. 5  illustrates diagrams exemplarily describing engagement of the camera body  10  and first lens  100  by camera claws at a normal position of the camera body  10  according to the embodiment of the present invention.  FIG. 5A  is a diagram illustrating a state where the first lens  100  is mounted to the camera body  10 , when viewing from the front face side.  FIG. 5B  is a partial cross-sectional view of the camera body  10  and first lens  100  taken along a cross-section B-B′ illustrated in  FIG. 5A . In  FIG. 5 , the camera body  10  is positioned in the above-described normal position, and, in this state, a camera grip  204   a  provided to the camera body member  204  is situated to the left side when viewing the camera body  10  from the front face side. 
       FIG. 6  illustrates diagrams exemplarily describing engagement of the camera body  10  and first lens  100  by bayonet claws at a vertical position of the camera body  10  according to the embodiment of the present invention.  FIG. 6A  is a diagram illustrating a state where the first lens  100  is mounted to the camera body  10 , when viewing from the front face side.  FIG. 6B  is a partial cross-sectional view of the camera body  10  and first lens  100  taken along a cross-section C-C′ illustrated in  FIG. 6A . In  FIG. 6 , the camera body  10  is positioned in the above-described vertical position, and the camera grip  204   a  in this state is situated to the top side when viewing the camera body  10  from the front face side. 
     In general, in a case of mounting an interchangeable lens to a camera, a gap occurs between the camera and interchangeable lens in a direction orthogonal to the optical axis, due to dimensional tolerance of the two, and looseness of the lens as to the camera increases due to this gap. Particularly, in a case of coupling a camera and interchangeable lens by bayonet coupling, the above-described looseness of the lens becomes greater the farther away from positions where the bayonet claws engage each other in the circumferential direction of the lens. Further, the looseness (bowing) in the gravitational direction of the interchangeable lens as to the camera becomes greater due to the weight of the interchangeable lens itself. Thus, if a subject is imaged in a case where the looseness of the interchangeable lens as to the camera is great, an unnatural image may be obtained, which is unintended by the user, due to the deviation of optical axis of the camera and optical axis of the lens. 
     In the present embodiment, the third camera claw  201   c , which has the widest angle of the camera-side bayonet claws, overlaps the first camera mount center line  3003  in the radial direction of the camera mount  201 , as illustrated in  FIG. 5B . According to this configuration, when the first lens  100  is mounted to the camera body  10 , the first camera mount center line  3003  overlaps the position where the third camera claw  201   c  and a later-described third lens claw  301   f  are engaged. In this case, looseness (bowing) of the camera accessory, such as the first lens  100  mounted to the camera body  10 , in the gravitational direction can be suppressed in the normal position of which the frequency of usage is highest for operating the imaging apparatus, for example. Due to the above-described configuration, the gap  41  illustrated in  FIG. 5B  can be kept from becoming large, so looseness of the first lens  100  as to the camera body  10  in the direction indicated by the arrow illustrated in  FIG. 5B  can be suppressed. 
     In the present embodiment, the first camera claw  201   a  overlaps the second camera mount center line  3002  in the radial direction of the camera mount  201 , as illustrated in  FIG. 6B . According to this configuration, when the first lens  100  is mounted to the camera body  10 , the second camera mount center line  3002  overlaps the position where the first camera claw  201   a  and a later-described first lens claw  301   d  are engaged. In this case, for example, looseness (bowing) of the camera accessory, such as the first lens  100  mounted to the camera body  10 , in the gravitational direction can be suppressed even in the vertical position of the imaging apparatus. Due to the above-described configuration, since the gap  42  illustrated in  FIG. 6B  can be kept from becoming large, looseness of the first lens  100  as to the camera body  10  in the direction indicated by the arrow illustrated in  FIG. 6B  can be suppressed. 
     As illustrated in  FIG. 4B , the angle of the third camera claw  201   c  in the circumferential direction of the camera mount  201 , situated at the top side in a case where the camera body  10  is at the normal position, is greater than the sum of angles of the first claw  201   a  and second claw  201   b  situated at the lower side. More precisely, the total sum of angles in the circumferential direction of the camera claws provided to the camera mount  201  is greater at the upper side of the second camera mount center line as a reference as compared to the lower side. Specifically, the sum of angle θc and the angle θa 1  of the first camera claw  201   a  on the upper side of the second camera mount center line  3002  is larger than the sum of angle θb and the angle θa 2  of the first camera claw  201   a  on the lower side of the second camera mount center line  3002 . That is to say, the layout of the camera claws and recesses is determined to satisfy the two following expressions: 
       θ c≥θa+θb   (1), and
 
       θ a 1+θ c&gt;θa 2+θ b   (2).
 
     According to this configuration, in the normal position of the camera body  10  regarding which the frequency of usage is highest, the strength of camera claws at the upper side (opposite side from the gravitational direction) of the second camera mount center line  3002  that indicates the horizontal direction of the camera mount  201  can be made to be greater than the strength of the camera claws at the lower side (gravitational direction). Thus, in the normal position of the camera body  10  regarding which the frequency of usage is highest in a state where the first lens  100  is mounted, the camera body  10  according to the present embodiment can reduce looseness (bowing) of the first lens  100  as to the camera body  10  in the gravitational direction. According to the camera body  10  of the present embodiment, in the normal position of the camera body  10  regarding which the frequency of usage is highest in a state where the first lens  100  is mounted, deformation of camera claws and lens claws due to the weight of the first lens  100  itself can be suppressed. 
     (Configuration of Bayonet Claws at First Lens  100  Side) 
     Next, multiple lens claws (accessory claws) provided to the lens mount  301  at the first lens  100  side will be described with reference to  FIG. 7 .  FIG. 7  is a diagram exemplarily describing a case of viewing the lens mount  301  according to the embodiment of the present invention from the rear face side (side where the camera body  10  is attached) in a state where the first lens  100  is mounted to the camera body  10 .  FIG. 7A  exemplarily describes angles of the claws and recesses in the circumferential direction at the lens mount  301  side.  FIG. 7B  is a cross-sectional view taken along a cross-section D-D′ illustrated in  FIG. 7A . In the following description, the camera body  10  is positioned in the normal position in the state illustrated in  FIG. 7 . 
     As illustrated in  FIG. 7A , a first lens claw  301   d , second lens claw  301   e , and third lens claw  301   f  are provided in order to the lens mount  301  in the circumferential direction (inner radial direction). When viewing the lens mount  301  from the rear face side as illustrated in  FIG. 7A , the lens claw provided at a position farthest from the lock groove  301   z  is the first lens claw  301   d . The second lens claw  301   e  and third lens claw  301   f  are consecutively provided in order from the first lens claw  301   d  in a clockwise direction. 
     Recesses, which are a first lens recess  301   a , second lens recess  301   b , and third lens recess  301   c , are provided in order, to the lens mount  301  in the circumferential direction (inner radial direction). When viewing the lens mount  301  from the rear face side, the recess provided at a position nearest to the lock groove  301   z  is the third lens recess  301   c  as illustrated in  FIG. 7 . The first lens recess  301   a  and second lens recess  301   b  are then consecutively provided in order from the third lens recess  301   c  in a clockwise direction. 
     As illustrated in  FIG. 7B , a fitting member  301   x , which restricts movement in a direction parallel to the optical axis of the imaging apparatus when mounted on the imaging apparatus, is provided to the lens mount  301  side in the circumferential direction. In the present embodiment, the diameter (i.e., the inner diameter of the fitting member  301   x ) in a direction orthogonal to the optical axis (approximately the same as the center axis) of the fitting member  301   x  at the lens mount  301  side is the mount diameter. 
     For the sake of description, the end portions of the lens claws  301   d ,  301   e , and  301   f , in the circumferential direction, will be referred to as first end portion  301   d   1 , second end portion  301   d   2 , third end portion  301   e   1 , fourth end portion  301   e   2 , fifth end portion  301   f   1 , and sixth end portion  301   f   2 . The end portions are denoted with part numerals in order from the first lens claw  301   d  in the clockwise direction, when viewing the lens mount  301  from the rear face side, as described above. 
     As illustrated in  FIG. 7 , the angles (angle ranges) that the lens claws and lens recesses occupy in the circumferential direction of the lens mount  301  are stipulated as follows in the present embodiment. For the first lens claw  301   d , the angle θd=53°. For the second lens claw  301   e , the angle θe=62°. For the third lens claw  301   f , the angle θf=53°. Further, for the first lens recess  301   a , the angle is 52°. For the second lens recess  301   b , the angle is 44°. For the third lens recess  301   c , the angle is 96°. 
     When viewing the lens claws from the rear face side, the angles where the lens claws are disposed in the circumferential direction of the lens mount  301  with the position (referred to as reference position) of the lock groove  301   z  as a reference in the clockwise direction are stipulated as follows. The first lens claw  301   d  is disposed between 159° and 212° with the reference position as a start point. The second lens claw  301   e  is disposed between 256° and 318° with the reference position as a start point. The third lens claw  301   f  is disposed between 54° and 107° with the reference position as a start point. 
     When viewing the lens mount  301  from the optical axis direction in the present embodiment, of the multiple bayonet claws, the second lens claw  301   e  overlaps a first lens mount center line  3005  that extends in the vertical direction of the lens mount  301 , in the radial direction of the lens mount  301 . When viewing the lens mount  301  from the rear face side and front face side in the present embodiment, of the multiple bayonet claws, the third lens claw  301   f  overlaps the first lens mount center line  3005  in the radial direction of the lens mount  301 . 
     The first lens mount center line  3005  is a line that extends in the gravitational direction and the opposite direction from the gravitational direction, from the center (optical axis) of the camera mount  301 , in a normal position of the camera body  10  to which the first lens  100  has been mounted. In other words, the first lens mount center line  3005  is a vertical line that passes through a center of the lens mount  301  and is orthogonal to the center axis of the lens mount  301  when the camera body  10  to which the first lens  100  is mounted is placed on a horizontal plane. In contrast, in a vertical position of the camera body  10  to which the first lens  100  has been mounted, a line that extends in the gravitational direction and the opposite direction from the gravitational direction, from the center (optical axis) of the camera mount  301 , is a second lens mount center line  3006 . This second lens mount center line  3006  overlaps the lock groove  301   z  and first lens claw  301   d  in the radial direction of the lens mount  301 . The first lens mount center line  3005  and second lens mount center line  3006  are mutually orthogonal. 
     In the present embodiment, when the first lens  100  is mounted to the camera body  10 , the second lens claw  301   e  and third lens claw  301   f  overlap the first lens mount center line  3005  in the radial direction of the lens mount  301 , as illustrated in  FIG. 7 . According to this configuration, the first lens mount center line  3005  overlaps two positions of engaging positions between lens claws and camera claws, when the first lens  100  is mounted to the camera body  10 . In this case, for example, in the normal position of the camera body  10  regarding which the frequency of usage is highest, looseness (bowing) of the first lens  100  mounted to the camera body  10  in the gravitational direction can be reduced. In a case where the first lens  100  is mounted to the camera body  10 , the third leaf spring arrangement portion  201   c   3  described above in  FIGS. 4A and 4B  overlaps with the first lens mount center line  3005  in the radial direction of the lens mount  301 . Specifically, in the case where the first lens  100  is mounted to the camera body  10 , the region where the third lens claw  301   f  is biased by the leaf spring  206   c  overlaps with the first lens mount center line  3005 , and thus the rattling of the first lens  100  can be suppressed more effectively. 
     In the present embodiment, when the first lens  100  is mounted to the camera body  10 , the first lens claw  301   d  overlaps the second lens mount center line  3006  in the radial direction of the lens mount  301 , as illustrated in  FIG. 7A . According to this configuration, when the first lens  100  is mounted to the camera body  10 , the second lens mount center line  3006  overlaps the position where the first lens claw  301   d  and the first camera claw  201   a  engage. In this case for example, even in the vertical position of the imaging apparatus, looseness (bowing) of the first lens  100  mounted to the camera body  10  in the gravitational direction can be reduced. In a case where the first lens  100  is mounted to the camera body  10 , the first leaf spring arrangement portion  201   a   3  described above in  FIGS. 4A and 4B  overlaps with the second lens mount center line  3006  in the radial direction of the lens mount  301 . Specifically, in the case where the first lens  100  is mounted to the camera body  10 , the region where the first lens claw  301   d  is biased by the leaf spring  206   a  overlaps with the first lens mount center line  3006 , and thus the rattling of the first lens  100  can be suppressed more effectively. 
     In a state where the first lens  100  is mounted to the camera body  10 , the second camera mount center line  3002  and second lens mount center line  3006  overlap a lock region where the lock pin  202  and lock groove  301   z  are fit, as described above. According to this configuration, in the vertical position of the camera body  10 , the engaging position of the first camera claw  201   a  and first lens claw  301   d  and the above-described lock region overlap the mount center lines extending in the gravitational direction and the opposite direction thereof. According to this configuration, in the vertical position of the imaging apparatus, for example, looseness (bowing) of the first lens  100  mounted to the camera body  10  in the gravitational direction can be suppressed even more effectively. 
     (Configuration of Contact Pins in Camera Body  10 ) 
     The configuration of the contact pins provided to the camera body  10  side will be described with reference to  FIG. 8  below.  FIG. 8  illustrates external perspective views viewing a camera mount  201  according to the embodiment of the present invention from the front face side (subject side).  FIG. 8A  is an external view of the camera mount  201  from the optical axis direction.  FIG. 8B  is an external perspective view of the camera mount  201  from above. 
     The contact holding member  203 , and contact pins  203   a  through  203   k  and  203   m  held by the contact holding member  203  are disposed following the circumferential direction of the camera mount  201  on the inner side of the camera mount  201 , as illustrated in  FIG. 8A .  FIG. 8A  illustrates an array line on which the contact points are disposed as an array line  3007 . 
     The contact pins  203   a  through  203   k  and  203   m  are movable pins that can advance and retreat (protrude and retract) in a direction parallel to the optical axis  3000 , and are biased from behind toward the first lens  100  side by leaf springs (not illustrated). As described above, the contact pins  203   a  through  203   k  and  203   m  have the functions of the above-described respective terminals, and the part numerals by which the contact pins are denoted are the same as those of the terminals, to facilitate description. 
     As illustrated in  FIG. 8B , out of the contact pins  203   a  through  203   k  and  203   m , the contact pins  203   a ,  203   b ,  203   c , and  203   d  are higher in the direction (toward the front face) parallel to the optical axis  3000  as compared to the other contact pins. The above-described configuration is realized by differing the amount of protrusion from the contact holding member  203  in the optical axis direction in the present embodiment. Alternatively, a configuration may be employed where this is realized by differing the amount of protrusion of the contact pins from the contact holding member  203 . 
     In general, in a case of employing the bayonet coupling method and attaching/detaching an interchangeable lens to/from a camera, the contact pins at the camera side and the contact face on the lens side slide over each other. For example, at the camera side, contact pins other than the contact pin situated at the edge in the rotational direction to complete mounting of the interchangeable lens slide over one or another contact face provided to the lens side. Thus, the more times the camera accessory is attached to and detached from the camera, the more the contact pins and contact faces are worn. 
     The greater the number of terminals there is, the more pronounced this problem is, and the number of times of sliding between contact pins and contact faces increases. Voltage drop increases due to the contact impedance of the terminals rising due to wearing of the contact pins and contact faces, and the interchangeable lens may malfunction, for example, due to the voltage dropping below the allowable voltage range for operation of the electric circuits. 
     To decrease the number of times of sliding of the contact pins, the contact height of the camera-side contact pins and the interchangeable-lens-side contact faces are differed in a direction parallel to the optical axis  3000 , between an upper tier and a lower tier, in the present embodiment. Specifically, the contact holding member  203  has a step in a direction parallel to the optical axis  3000 , with the contact pins  203   a  through  203   d  being provided to the upper tier, and the contact pins  203   e  through  203   k  and  203   m  being provided to the lower tier. The contact face holding member  303  also is stepped in a direction parallel to the optical axis  3001 , with the contact faces  303   a  through  303   d  provided to the lower tier, and the contact faces  303   e  through  303   k  and  303   m  provided to the upper tier. 
     The upper tier of the contact holding member  203  at the camera mount  201  side is a tier protruding toward the front face side (subject side) of the camera body  10  namely the side the lens mount  301  is coupled when the first lens  100  is mounted to the camera body  10 . The lower tier of the contact holding member  203  is a tier recessed toward the rear face side (imaging sensor  11  side) of the camera body  10 . The upper tier of the contact face holding member  303  at the lens mount  301  side is a tier protruding toward the rear face side (imaging sensor  11  side) of the camera body  10  namely the side the camera mount  201  is coupled when the first lens  100  is mounted to the camera body  10 . The lower tier of the contact face holding member  303  is a tier recessed to the front face side (subject side) of the camera body  10 . 
     In a case where the lens mount  301  is mounted to the camera mount  201 , the contact pins provided to the upper tier side of the contact holding member  203  and the contact faces provided to the lower tier side of the contact face holding member  303  are electrically in contact among corresponding terminals. In a case where the lens mount  301  is mounted to the camera mount  201 , the contact pins provided to the lower tier side of the contact holding member  203  and the contact faces provided to the upper tier side of the contact face holding member  303  are electrically in contact among corresponding terminals. Thus, the steps at the camera mount  201  side and lens mount  301  side have a mutually engageable shape, and the contact pins at the camera side and contact faces at the lens side that are provided to different steps do not come into contact when mounting the lens mount  301  to the camera mount face A. 
     According to this configuration, the contact pins  203   e  through  203   k  and  203   m  do not come into contact with the contact faces  303   a  through  303   d , when relatively rotating the first lens  100  as to the camera body  10  from the mounting start state to the mounting completed state. Even when relatively rotating the first lens  100  as to the camera body  10  from the mounting completed state to the mounting start state, the contact pins  203   e  through  203   k  and  203   m  do not come into contact with the contact faces  303   a  through  303   d . That is to say, the number of times of sliding between contact pins and contact faces can be reduced on both the camera mount  201  side and lens mount  301  side. 
     The contact pins at the camera body  10  side and the contact faces at the first lens  100  side are all in a non-contact state in the mounting start state of the first lens  100  as to the camera body  10 , and thereby short-circuiting among terminals before completion of mounting of the first lens  100  can be prevented. 
     (Configuration of Contact Faces in First Lens  100 ) 
     The following is a description regarding the configuration of the contact faces provided to the first lens  100  side, with reference to  FIG. 9 .  FIG. 9  illustrates external perspective views of the lens mount  301  according to the embodiment of the present invention, as viewed from the side (rear face side) to which the camera mount  201  is mounted.  FIG. 9A  is an external view of the lens mount  301  from the optical axis direction.  FIG. 9B  is an external perspective view of the lens mount  301  from above. 
     The contact face holding member  303 , and contact faces  303   a  through  303   k  and  303   m  held by the contact face holding member  303  are disposed on the inner side of the lens mount  301 , following the circumferential direction of the lens mount  301 , as illustrated in  FIG. 9A . An array line on which the contact points are disposed is illustrated in  FIG. 9A  as an array line  3008 . As described above, the contact faces  303   a  through  303   k  and  303   m  have the functions of the above-described respective terminals, and the part numerals by which the contact faces are denoted are the same as those of the terminals, to facilitate description. 
     As illustrated in  FIG. 9B , out of the contact faces  303   a  through  303   k  and  303   m , the contact faces  303   a ,  303   b ,  303   c , and  303   d  are lower in height in the direction parallel to the optical axis  3001  as compared to the other contact faces. In the present embodiment, the above-described configuration is realized by differing the amount of protrusion of the contact face holding member  303  in the optical axis direction. 
     According to the configuration described above, the contact faces  303   a  through  303   d  do not come into contact with the contact pins  203   e  through  203   k  and  203   m , when relatively rotating the first lens  100  as to the camera body  10  from the mounting start state to the mounting completed state. Even when relatively rotating the first lens  100  as to the camera body  10  from the mounting completed state to the mounting start state, the contact faces  303   a  through  303   d  do not come into contact with the contact pins  203   e  through  203   k  and  203   m . That is to say, the number of times of sliding between contact pins and contact faces can be reduced at both the camera mount  201  side and lens mount  301  side. 
     The contact face holding member  303  has a first inclined guiding face  303   n  and a second inclined guiding face  303   p  for drawing corresponding contact pins toward the rear face direction (imaging sensor  11  side) when mounting the first lens  100  to the camera body  10 , as illustrated in  FIG. 9B . According to this configuration, the contact pressure of the contact pins provided to the camera body  10  side as to the contact face holding member  303  gradually changes, whereby deformation and wear of the contact pins provided to the camera body  10  can be reduced. 
     (Operations of Attaching First Lens  100  to Camera Body  10 ) 
     Next, the operations at the time of mounting the first lens  100  to the camera body  10  will be described with reference to  FIG. 10 . 
       FIG. 10  illustrates diagrams exemplarily describing a contact state between terminals on the camera body  10  and first lens  100  according to the embodiment of the present invention.  FIG. 10A  is a diagram for describing the contact state between each terminal in the mounting start state where mounting of the first lens  100  to the camera body  10  has been started.  FIG. 10B  is a diagram for describing the contact state between each terminal in the mounting completed state where mounting of the first lens  100  to the camera body  10  has been completed. In the state illustrated in  FIG. 10A , the contact pins  203   a  and  203   b  at the camera mount  201  side in the optical axis direction overlap the contact faces  303   a  and  303   b  at the lens mount face B side. However, since the height of the contact holding member  203  and the contact face holding member  303  in the direction parallel with the optical axis is made to differ for each region, as described above, none of the contact pins and contact faces come into contact in the state illustrated in  FIG. 10A . 
     The state illustrated in  FIG. 10B  is a state where the first lens  100  has been rotated by approximately 60° as to the camera body  10  from the state illustrated in  FIG. 10A  toward the direction indicated by the arrow (see  FIG. 10A ). That is to say, in the present embodiment, the relative rotational angle of the camera body  10  and first lens  100  from the mounting start state to the mounting completed state is approximately 60°. In the state illustrated in  FIG. 10B , the lock pin  202  is in the state of fitting (locked) the lock groove  301   z.    
     Rotating the first lens  100  by approximately 60° as to the camera body  10  guides the first lens claw  301   d  into the rear face side (imaging sensor  11  side) of the first camera claw  201   a , and these are engaged with each other in the optical axis direction. In this state, the second lens claw  301   e  is guided into the rear face side (imaging sensor  11  side) of the second camera claw  201   b , and these are engaged with each other in the optical axis direction. In the is state, the third lens claw  301   f  is guided into the rear face side (imaging sensor  11  side) of the third camera claw  201   c , and these are engaged with each other in the optical axis direction. Further, the positions of the lens claws provided to the first lens  100  are positioned by being biased toward the rear face side by the lens mount biasing member  206  provided to the camera mount  201  side, thereby coupling the camera body  10  and the first lens  100 . 
     The contact pins at the camera body  10  side are pressed toward the rear face side (imaging sensor  11  side) by the first guiding face  303   n  and second guiding face  303   p . The contact pins of the camera body  10  side come into contact with corresponding places on the contact faces  303   a  through  303   k  and  303   m  at the lens mount  301  side in a state of being pressed, and come into contact with the respectively corresponding contact faces in the mounting completed state. At this time, the contact pin  203   m  provided to the camera mount  201  side and the contact face  303   e  provided to the lens mount  301  firstly start coming into contact. 
     (Basic Configuration of Conversion Adapter) 
     Next, the basic configuration of a conversion adapter (adapter device) a camera accessory mountable to the camera mount  201  of the above-described camera body  10  will be described with reference to  FIGS. 11 through 12 . 
       FIG. 11  illustrates diagrams describing the first conversion adapter  40  mountable to the camera body  10 , and a second lens unit  50 .  FIG. 11A  illustrates an external perspective view of the second lens unit  50  having been mounted to the camera body  10  via the first conversion adapter  40 .  FIG. 11B  illustrates an external perspective view of a state where the camera body  10 , first conversion adapter  40 , and second lens unit  50  have each been detached. The second lens unit (hereinafter referred to as second lens)  50  has a lens mount  501  that is short in flange focal distance, but has the same mount diameter as the camera mount  201 , as to the camera body  10 . That is to say, the second lens  50  has the same mount diameter as the above-described first lens  100 , but unlike the first lens  100 , is a camera accessory not compatible with direct mounting to the camera body  10 . 
       FIG. 12  illustrates diagrams for describing the second conversion adapter  70  mountable to a camera body  60  and the first lens  100 .  FIG. 12A  illustrates an external perspective view of a state where the first lens  100  is mounted to the camera body  60  via the second conversion adapter  70 .  FIG. 12B  illustrates an external perspective view where the camera body  60 , second conversion adapter  70 , and first lens  100  have each been detached. 
     In a case where a lens unit with a long flange focal distance is directly mounted to an imaging apparatus with a short flange focal distance, trouble, such as the focal point not being formed at an accurate position, will occur, and imaging a subject in this way will result in an unnatural image being obtained. For example, the above problem will occur if the second lens unit  50  having a long flange focal distance is mounted to the above-described camera body  10 . 
     In the same way, in a case where a lens unit with a short flange focal distance is directly mounted to an imaging apparatus with a long flange focal distance, trouble, such as the focal point not being formed at an accurate position, will occur, and imaging a subject in this way will result in an unnatural image being obtained. For example, the above problem will occur if the first lens  100  having a short flange focal distance is mounted to the camera body  60  serving as a second imaging apparatus and having a longer flange focal distance than the above-described camera body  10 . 
     Particularly, the camera body  10  and camera body  60 , and the first lens  100  and second lens  50 , have the same mount diameters, and therefore it is difficult for a user to judge which imaging apparatuses and which lens units have flange focal distances that are compatible for direct mounting. 
     It is thereby preferable that only lens units that are compatible can be directly mounted to a certain imaging apparatus, so that imaging apparatuses and lens units that have mutually incompatible flange focal distances are not erroneously directly mounted. 
     In a case of mounting an incompatible lens unit to an imaging apparatus, a conversion adapter needs to be interposed between the two to adjust the flange focal distance. However, in a state where one side of the conversion adapter is mounted to the imaging apparatus, if a lens unit compatible with direct mounting to the imaging apparatus is mounted to the other side of the conversion adapter, the focal point may not be accurately formed, as described above. Thus, the one side and other side of the conversion adapter preferably have configurations to restrict imaging apparatuses and camera accessories that are directly mountable. 
     Specifically, in a case of mounting a lens unit having a long flange focal distance to an imaging apparatus having a short flange focal distance, a conversion adapter is preferable where one end side is only mountable to this imaging apparatus, and the other end side is only mountable to this lens unit. In a case of mounting a lens unit having a short flange focal distance to an imaging apparatus having a long flange focal distance, a conversion adapter is preferable where one end side is only mountable to this imaging apparatus, and the other end side is only mountable to this lens unit. 
     The first conversion adapter  40  has the lens mount  1301  attached to an adapter barrel  40   a  by a plurality of fastening screws (not illustrated), at one end side in the optical axis direction. The plurality of fastening screws are the same as the lens mount fastening screws  304   a  to  304   d  in the lens mount  301  of the first lens unit  100  described above. This lens mount  1301  is an accessory mount attachable to and detachable from the camera mount  201  provided to the camera body  10  described above. 
     A camera mount  1401  is attached to the adapter barrel  40   a  by fastening screws (not illustrated), at the other end side of the first conversion adapter  40  in the optical axis direction. This camera mount  1401  is a camera mount that is attachable to and detachable from the lens mount  501  of the second lens  50 . The camera mount  1401  of the first conversion adapter  40  is attached such that the imaging plane of the imaging sensor  11  of the camera body  10  will be situated at a position corresponding to the flange focal distance of the second lens  50 . 
     The second conversion adapter  70  has the lens mount  1501  attached to an adapter barrel  70   a  by fastening screws (not illustrated), at one end side in the optical axis direction. This lens mount  1501  is an accessory mount that is attachable to and detachable from the camera mount  401  provided to the camera body  60 . 
     The second conversion adapter  70  has the camera mount  1201  attached to the adapter barrel  70   a  by a plurality of fastening screws (not illustrated), at the other end side in the optical axis direction. The plurality of fastening screws are the same as the camera mount fastening screws  205   a  to  205   d  in the camera mount  201  of the camera body  10  described above. This camera mount  1201  is a camera mount that is attachable to and detachable from the lens mount  301  of the first lens  100 , as described above. As described above, the members having the same mount are the camera mount  201  of the camera body  10  and the camera mount  1201  of the second conversion adapter  70 , the lens mount  301  of the first lens  100  and the lens mount  1301  of the first conversion adapter  40 , the camera mount  401  of the camera body  60  and the camera mount  1401  of the first conversion adapter, and the lens mount  501  of the second lens  50  and the lens mount  1501  of the second conversion adapter  70 . In the following description, assume that each mount has the same configuration, and thus duplicated description will be omitted. 
     A first optical member  701   a  and a second optical member  701   b  are provided to the second conversion adapter  70 , between the adapter barrel  70   a  and the lens mount  1501  in the optical axis direction. The first optical member  701   a  and second optical member  701   b  enable the second conversion adapter  70  to extend length of the flange focal distance of the first lens  100  in accordance with the imaging plane of the imaging sensor disposed in the camera body  60 . While the optical members have been illustrated as two lenses for the sake of convenience, this is not restrictive. 
     (Configuration of First Conversion Adapter  40 ) 
     Next, the angles (phases) at which bayonet claws are disposed on the circumferential direction of the camera mount and lens mount of the first conversion adapter  40  will be described with reference to  FIG. 13  through  FIG. 17 . The description of the lens mount  1301  described below is synonymous with the description of the lens mount  301 . Further, the description of the camera mount  1401  described below is synonymous with the description of the camera mount  401 . 
       FIG. 13  illustrates diagrams for exemplarily describing displacement angles of bayonet claws in the camera mount  1401  provided on one end of the first conversion adapter  40 .  FIG. 13A  is a diagram illustrating angle ranges that camera claws and camera recesses occupy in the circumferential direction of the camera mount  1401  with the lock pin  1401   z  as a reference, as viewed from the rear face side (camera body  10  side).  FIG. 13B  is a diagram illustrating angle ranges that multiple camera claws  1401   a  through  1401   c  occupy in the circumferential direction of the camera mount  1401 , as viewed from the rear face side (camera body  10  side).  FIG. 13C  is a cross-sectional diagram taken along a cross-section E-E illustrated in  FIG. 13B . 
     The first conversion adapter  40  is a mount adapter used for mounting the second lens unit  50  having a long flange focal distance to the camera body  10  having a short flange focal distance. Thus, it is preferable for the first conversion adapter  40  to be configured such that the camera body  60  having a long flange focal distance cannot be directly mounted to the lens mount  1301 , and the first lens  100  having a short flange focal distance cannot be directly mounted to the camera mount  1401 . According to this configuration, the positional relation of claws and recesses can be realized such that the lens mount  1301  provided to one end (first end) of the first conversion adapter  40  and the camera mount  1401  provided to the other end (second end) cannot each be directly mounted. 
     A first camera claw  1401   a , second camera claw  1401   b , and third camera claw  1401   c , are provided in order, to the camera mount  1401  in the circumferential direction (inner radial direction). When viewing the camera mount  1401  from the rear face side as illustrated in  FIG. 13A , the camera claw provided at a position farthest from the lock pin  1401   z  is the first camera claw  1401   a . The second camera claw  1401   b  and third camera claw  1401   c  are consecutively provided in order from the first camera claw  1401   a  in a clockwise direction. 
     A first camera recess  1401   d , second camera recess  1401   e , and third camera recess  1401   f  are provided in order, to the camera mount  1401  in the circumferential direction (inner radial direction). When viewing the camera mount  1401  from the rear face side as illustrated in  FIG. 13A , the recess provided at a position nearest to the lock pin  1401   z  is the second camera recess  1401   e . The third camera recess  1401   f  and first camera recess  1401   d  are consecutively provided in order from the second camera recess  1401   e  in a clockwise direction. 
     As illustrated in  FIG. 13C , a fitting member  401   x  that restricts movement of the camera accessory in a direction parallel to the optical axis when the camera accessory is mounted, is provided to the camera mount  1401  side. In the present embodiment, the diameter (i.e., the inner diameter of the fitting member  401   x ) in a direction orthogonal to the optical axis (approximately the same as the center axis) of the fitting member  401   x  at the camera mount  401  side is the mount diameter. 
     The way of bayonet coupling of the first conversion adapter  40  and second lens  50  is approximately the same as the way of bayonet coupling of the camera body  10  and first lens  100  described above, and thus description will be omitted. 
     For the sake of description, each of the end portions of the camera claws  1401   a ,  1401   b , and  1401   c  in the circumferential direction will be referred to as a first end portion  1401   a   1 , second end portion  1401   a   2 , third end portion  1401   b   1 , fourth end portion  1401   b   2 , fifth end portion  1401   c   1 , and end portion  1401   c   2 . Each of the end portions are denoted with part numerals in order from the first camera claw  1401   a  in the clockwise direction, when viewing the camera mount  1401  from the rear face side, as described above. 
     As illustrated in  FIG. 13A , the angles (angle ranges) that the camera claws and camera recesses occupy in the circumferential direction of the camera mount  1401  in the first conversion adapter  40  according to the present embodiment are stipulated as follows. For the first camera claw  1401   a , the angle θ 1 =56°. For the second camera claw  1401   b , the angle θ 2 =62°. For the third camera claw  1401   c , the angle θ 3 =62°. Further, for the first camera recess  1401   d , the angle is 57°. For the second camera recess  1401   e , the angle is 66°. For the third camera recess  1401   f , the angle is 57°. That is to say, the camera mount  1401  has different angles for the camera claws with respect to the above-described camera mount  201  of the camera body  10 , but the angles of the camera recesses are the same. 
     When viewing the camera claws from the rear face side of the first conversion adapter  40 , the angles where the camera claws are disposed on the circumferential direction of the camera mount  1401  with the position (referred to as reference position) of the lock pin  1401   z  as a reference are stipulated as follows. The first camera claw  1401   a  is disposed between 159° and 215° with the reference position as a start point. The second camera claw  1401   b  is disposed between 272° and 334° with the reference position as a start point. The third camera claw  1401   c  is disposed between 40° and 102° with the reference position as a start point. 
       FIG. 14  illustrates diagrams exemplarily describing angles of disposing the bayonet claws on the lens mount  1301  provided to the other end of the first conversion adapter  40 .  FIG. 14A  is a diagram illustrating angle ranges that lens claws and lens recesses occupy in the circumferential direction of the lens mount  1301  with the lock groove  1301   z  as a reference, as viewed from the rear face side.  FIG. 14B  is a diagram illustrating angle ranges that multiple lens recesses  1301   a  through  1301   c  occupy in the circumferential direction of the lens mount  1301 , as viewed from the rear face side. 
     The angles (angle ranges) that the lens recesses occupy in the circumferential direction of the lens mount  1301  are, represented by θ 4  as the angle of the first lens recess  1301   a  and  05  as the angle of the second lens recess  1301   b , as illustrated in  FIG. 14B . The angle of disposing the claws and recesses on the lens mount  1301  of the first conversion adapter  40  is the same as the lens mount  301  of the first lens  100  described above, and therefore description will be omitted. 
     The angles of the claws and recesses in the circumferential direction, on the lens mount  1301  and camera mount  1401  provided to the first conversion adapter  40 , will be compared. For example, at the lens mount  1301  side, the angle θ 5  of the second lens recess  1301   b  having the smallest angle is 44°. Whereas, at the camera mount  1401  side, the angle θ 1  of first camera claw  1401   a  having the smallest angle is 56°. That is to say, the claw having the smallest angle at the camera mount  1401  side is larger than the recess having the smallest angle at the lens mount  1301  side (θ 5 &lt;θ 1 ). In this case, of the recesses on the lens mount  1301  side and the claws on the camera mount  1401  side, at least one or more lens recess and camera claws will interfere with each other. Thus, even if an attempt is made to mount the lens unit to the camera body such that the optical axes at the camera mount  1401  side and lens mount  1301  side are approximately parallel, the claws and recesses interfere, and thereby the lens unit cannot be mounted to the camera body. 
     However, if only one claw and recess are interfering, there may be cases where claws of the camera mount side can be inserted into recesses of the lens mount side.  FIG. 15  illustrates diagrams exemplarily describing a mounting method of a predetermined imaging apparatus  1000  and a predetermined lens unit  2000  having claws and recesses that interfere with each other.  FIG. 15A  is a diagram exemplarily describing a frontal view of partway through mounting a predetermined lens unit to a predetermined imaging apparatus having claws and recesses that interfere with each other.  FIG. 15B  is a cross-sectional view taken along a cross-section F-F′ illustrated in  FIG. 15A . 
     For example, in a state where the optical axis of the lens mount side is obliquely inclined as to the optical axis of the camera mount side, one end of a camera claw is inserted into a lens recess, and from this state, the lens mount and camera mount are rotated relatively to each other, as illustrated in  FIGS. 15A and 15B . In this case, even if the camera claws and lens recesses originally interfere with each other, this interference with each other is resolved during the relative rotation of the lens mount and camera mount, and transition can be made to a state where the camera claw is inserted into this lens recess. In this case, if there are no other camera claws and lens recesses interfering, the lens unit can be mounted to the camera body. 
     In the present embodiment, the claws and recesses on the lens mount  1301  side and camera mount  1401  side are disposed such that the angle of a predetermined lens recess adjacent to a reference lens claw is smaller than the angle of two camera claws adjacent to a reference camera recess. 
     Specifically, in the present embodiment, the angles θ 4  and  05  of the first lens recess  1301   a  and second lens recess  1301   b  adjacent to the first lens claw  1301   d  are smaller than the angles θ 1  and θ 2  of the first camera claw  1401   a  and second claw  1401   b  adjacent to the first camera recess  1401   d . That is to say, θ 4  (52°) is smaller than θ 1  (56°), and θ 5  (44°) is smaller than θ 2  (62°) θ 4 &lt;θ 1 , θ 5 &lt;θ 2 . 
     Thus, even if an attempt is made to insert the first lens claw  1301   d  ( 301   d ) into the first camera recess  401   d  ( 1401   d ), the second lens claw  1301   e  ( 301   e ) interferes with the second camera claw  401   b  ( 1401   b ) in a sure manner, as well does the third lens claw  1301   f  ( 301   f ) with the first camera claw  401   a  ( 1401   a ), as illustrated in  FIG. 16 . 
       FIG. 16  illustrates diagrams exemplarily describing the way in which claws interfere with each other when attempting to mount the lens mount  301  ( 1301 ) side to the camera mount  1401  ( 401 ) side according to the embodiment of the present invention.  FIG. 16A  illustrates the way in which the third lens claw  1301   f  ( 301   f ) and the first camera claw  401   a  ( 1401   a ) interfere.  FIG. 16B  illustrates the way in which the second lens claw  1301   e  ( 301   e ) and the second camera claw  401   b  ( 1401   b ) interfere. 
     As described above, incompatible lens units and imaging apparatuses, and the mount portions of conversion adapters are configured such that two claws of each other out of the claws that an incompatible lens unit and imaging apparatus have interfere with each other, in the present embodiment. According to this configuration, the risk of an incompatible lens unit being erroneously mounted to an imaging apparatus, or an incompatible lens unit and imaging apparatus being erroneously mounted to mount units provided to both ends of a conversion adapter, can be reduced. 
     However, even in a case where the above conditions are satisfied, there may be cases where, when attempting to insert three claws into incompatible recesses, for example, two claws are inserted into recesses depending on the angles of the claws and recesses. 
     In the present embodiment further takes a configuration where the angles of at least two adjacent lens recesses are smaller than the angles of all camera claws. Specifically, in the present embodiment, the angles θ 4  and θ 5  of the first lens recess  1301   a  and second lens recess  1301   b  in the circumferential direction are smaller than the angles θ 1  through θ 3  of the first through third camera claws  1401   a  through  1401   c  in the circumferential direction. That is to say, the relation between the claws and recesses at the lens mount  1301  side and the camera mount  1401  side according to the present embodiment satisfy θ 4 &lt;θ 1 , θ 4 &lt;θ 2 , θ 4 &lt;θ 3 , θ 5 &lt;θ 1 , θ 5 &lt;θ 2 , and θ 5 &lt;θ 3 . 
       FIG. 17  illustrates diagrams exemplarily describing a case of attempting to insert incompatible claws into recesses at the lens mount  1301  side and camera mount  1401  side according to the embodiment of the present invention.  FIG. 17A  illustrates the way in which the third lens claw  1301   f  ( 301   f ) and third camera claw  401   c  ( 1401   c ) interfere in a case of attempting to insert the first lens claw  1301   d  ( 301   d ) into the third camera recess  401   f  ( 1401   f ).  FIG. 17B  illustrates the way in which second lens claw  1301   e  ( 301   e ) and first camera claw  401   a  ( 1401   a ) interfere in a case of attempting to insert the first lens claw  1301   d  ( 301   d ) into the third camera recess  401   f  ( 1401   f ).  FIG. 17C  illustrates the way in which the third lens claw  1301   f  ( 301   f ) and second camera claw  401   b  ( 1401   b ) interfere in a case of attempting to insert the first lens claw  1301   d  ( 301   d ) into the second camera recess  401   e  ( 1401   e ).  FIG. 17D  illustrates the way in which the second lens claw  1301   e  ( 301   e ) and third camera claw  401   c  ( 1401   c ) interfere in a case of attempting to insert the first lens claw  1301   d  ( 301   d ) into the second camera recess  401   e  ( 1401   e ). 
     As illustrated in  FIGS. 17A through 17D , the lens claws and camera claws interfere in at least two places in the present embodiment, regardless of the relative rotational angle of the lens mount  1301  and camera mount  1401 . According to this configuration, erroneous mounting of a lens unit and conversion adapter having the lens mount  301  or the lens mount  1301  to an imaging apparatus and conversion adapter having the camera mount  401  or the camera mount  1401  can be prevented even more effectively. 
     (Configuration of Second Conversion Adapter  70 ) 
     Next, the angles (phases) at which bayonet claws are disposed in the circumferential direction of the camera mount and lens mount of the second conversion adapter  70  will be described with reference to  FIGS. 18 through 21 . The description of the camera mount  1201  described below is synonymous with the description of the camera mount  201 . The description of the lens mount  1501  described below is also synonymous with the description of the lens mount  501 . 
     The second conversion adapter  70  is a mount adapter used for mounting the first lens  100 , which has a short flange focal distance to the camera body  60  having a long flange focal distance. The lens mount  1501  is provided at one end (third end) side of the second conversion adapter  70 , and the camera mount  1201  is provided at the other end (fourth end). The camera mount  1201  of the second conversion adapter  70  has the same configuration as the camera mount  201  of the camera body  10  the first imaging apparatus described above. The lens mount  1501  of the second conversion adapter  70  has the same configuration as the lens mount  501  of the second lens  50  described above. 
     It is therefore preferable for the second conversion adapter  70  to be configured such that the camera body  10  having a short flange focal distance cannot be directly mounted to the lens mount  1501 , and the second lens  50  having a long flange focal distance cannot be directly mounted to the camera mount  1201 . This configuration can be realized by satisfying the positional relation of claws and recesses such that the lens mount  1501  provided to one end (third end) of the second conversion adapter  70  and the camera mount  1201  provided to the other end (fourth end) each cannot be directly mounted. 
       FIG. 18  illustrates diagrams exemplarily describing angles of disposing bayonet claws in the camera mount  1201  provided on one end of the second conversion adapter  70 .  FIG. 18A  is a diagram illustrating angle ranges that camera claws and camera recesses occupy in the circumferential direction of the camera mount  1201  with the lock pin  202  as a reference, as viewed from the rear face side.  FIG. 18B  is a diagram illustrating angle ranges that, regarding multiple camera claws  1201   a  through  1201   c , the claws occupy in the circumferential direction of the camera mount  1201 , as viewed from the rear face side. The angles of disposing the claws and recesses on the camera mount  1201  of the second conversion adapter  70  are the same as the camera mount  1201  of the camera body  10  described earlier, and thus description will be omitted. 
     As illustrated in  FIG. 18B , the angle ranging from the sixth end  1201   c   2  of the third camera claw  1201   c  to the third end  1201   b   1  of the second camera claw  1201   b , in the circumferential direction of the camera mount  1201  including the first camera claw  1201   a , is θ 6  (162°). The angle ranging from the second end  1201   a   2  of the first camera claw  1201   a  to the fifth end  1201   c   1  of the third camera claw  1201   c , in the circumferential direction of the camera mount  1201  including the second camera claw  1201   b , is θ 7  (163°). The angle ranging from the fourth end  1201   b   2  of the second camera claw  1201   b  to the first end  1201   a   1  of the first camera claw  1201   a , in the circumferential direction of the camera mount  1201  including the third camera claw  1201   c , is θ 8  (215°). 
       FIG. 19  illustrates diagrams exemplarily describing angle of disposing bayonet claws in a lens mount  1501  provided on the other end of the second conversion adapter  70 .  FIG. 19A  is a diagram illustrating angle ranges that lens claws and lens recesses occupy in the circumferential direction of the lens mount  1501  with the lock pin  1501   z  as a reference, as viewed from the rear face side.  FIG. 19B  is a diagram illustrating angle ranges where recesses are provided regarding the multiple lens recesses  1501   a  through  1501   c  in the circumferential direction of the lens mount  1501 , as viewed from the rear face side.  FIG. 19C  is a cross-sectional diagram taken along a cross-section G-G′ illustrated in  FIG. 19B . 
     A first lens claw  1501   d , second lens claw  1501   e , and third lens claw  1501   f  are provided in order to the lens mount  1501  in the circumferential direction (inner radial direction). In a case of viewing the lens mount  1501  from the rear face side as illustrated in  FIG. 19A , the lens claw provided at a position farthest from the lock groove  1501   z  is the first lens claw  1501   d . The second lens claw  1501   e  and third lens claw  1501   f  are consecutively provided in order from the first lens claw  1501   d  in a clockwise direction. 
     A first lens recess  1501   a , second lens recess  1501   b , and third lens recess  1501   c  are provided in order, to the lens mount  1501  in the circumferential direction (inner radial direction). In a case of viewing the lens mount  1501  from the rear face side as illustrated in  FIG. 19A , the recess provided at a position nearest to the lock groove  1501   z  is the third lens recess  1501   c . The first lens recess  1501   a  and second lens recess  1501   b  are consecutively provided in order from the third lens recess  1501   c  in a clockwise direction. 
     For the sake of description, the end portions of the lens claws  1501   d ,  1501   e , and  1501   f , in the circumferential direction, will be referred to as first end portion  1501   d   1 , second end portion  1501   d   2 , third end portion  1501   e   1 , fourth end portion  1501   e   2 , fifth end portion  1501   f   1 , and sixth end portion  1501   f   2 . The end portions are denoted with part numerals in order from the first lens claw  1501   d  in the clockwise direction, when viewing the lens mount  1501  from the rear face side, as described above. 
     As illustrated in  FIG. 19A , the angles (angle ranges) that the lens claws and lens recesses occupy in the circumferential direction of the lens mount  1501  are stipulated as follows. The angle of the first lens claw  1501   d  is 53°, the angle of the second lens claw  1501   e  is 62°, and the angle of the third lens claw  1501   f  is 53°. That is to say, the angles of the lens claws on the lens mount  1501  side are the same as the angles of the lens claws on the lens mount  1301  side described above. 
     In contrast, the angles of the lens recesses at the lens mount  1501  side differ from the angles of the lens recesses at the lens mount  1301  ( 301 ) side described above. Specifically, the angle of the first lens recess  1501   a  is 60°, the angle of the second lens recess  1501   b  is 66°, and the angle of the third lens recess  1501   c  is 66°. 
     When viewing the lens claws from the rear face side, the angles in the clockwise direction where the lens claws are disposed on the circumferential direction of the lens mount  1501  with the position (referred to as reference position) of the lock groove  1501   z  as a reference are stipulated as follows. The first lens claw  1501   d  is disposed between 157° and 210° with the reference position as a start point. The second lens claw  1501   e  is disposed between 276° and 338° with the reference position as a start point. The third lens claw  1501   f  is disposed between 44° and 97° with the reference position as a start point. 
     As illustrated in  FIG. 19C , a fitting member  1501   x , which restricts movement of the imaging apparatus in a direction parallel to the optical axis when mounted to the imaging apparatus, is provided to the lens mount  1501  side. In the present embodiment, the diameter (i.e., the inner diameter of the fitting member  1501   x ) in a direction orthogonal to the optical axis (approximately the same as the center axis) of the fitting member  1501   x  at the lens mount  1501  side is the mount diameter. The mount diameters of the camera mounts and lens mounts described above are approximately the same length. 
     As illustrated in  FIG. 19B , the angle ranging from the fifth end  1501   f   1  of the third lens claw  1501   f  to the second end  1501   d   2  of the first lens claw  1501   d , in the circumferential direction of the lens mount  1501  including the first lens recess  1501   a , is θ 9  (166°). The angle ranging from the first end  1501   d   1  of the first lens claw  1501   d  to the fourth end  1501   e   2  of the second lens claw  1501   e , in the circumferential direction of the lens mount  1501  including the second lens recess  1501   b , is θ 10  (181°). The angle ranging from the third end  1501   e   1  of the second lens claw  1501   e  to the sixth end  1501   f   2  of the third lens claw  1501   f , in the circumferential direction of the lens mount  1501  including the third lens recess  1501   c , is θ 11  (181°). 
     The angles of the claws and recesses in the circumferential direction will be compared between the camera mount  1201  and lens mount  1501  provided to the second conversion adapter  70 . For example, the angle (92°) of the third camera claw at the camera mount  1201  side is larger than the angles (66°) of the second and third lens recesses  1501   b  and  1501   c  that are the largest angle of the lens recesses at the lens mount  1501  side. That is to say, the angle of at least one camera claw at the camera mount  1201  side is larger than the angle of the lens recess having the largest angle at the lens mount  1501  side. 
     In this case, of the claws at the camera mount  1201  side and recesses at the lens mount  1501  side, at least one or more camera claws and lens recesses interfere with each other. Thus, even if an attempt is made to mount the lens unit to the camera body such that the optical axis at the camera mount  1201  side and lens mount  1501  side are approximately parallel to each other, the claws and recesses interfere, and therefore the lens unit cannot be mounted to the camera body. 
     However, if only one claw and recess are interfering, there may be cases where claws of the camera mount side can be inserted into recesses of the lens mount side, in the same way as the above description of the first conversion adapter. For example, there are cases where, in a state where the optical axis of the lens mount side is obliquely inclined as to the optical axis of the camera mount side, one end of a camera claw is inserted into a lens recess, and the lens mount and camera mount are rotated relative to each other, and the lens unit can be mounted to the camera body. 
     In the present embodiment, the claws and recesses at the camera mount  1201  side and the lens mount  1501  side are disposed to satisfy θ 6 &lt;θ 9  and θ 7 &lt;θ 10  in the circumferential direction.  FIG. 20  illustrates diagrams exemplarily describing the way in which claws interfere with each other, when attempting to mount a reference claw at the lens mount  1501  ( 501 ) side to a reference recess at the camera mount  201  ( 1201 ) side according to the embodiment of the present invention.  FIG. 20A  illustrates the way in which the third lens claw  1501   f  ( 501   f ) and the third camera claw  201   c  ( 1201   c ) interfere.  FIG. 20B  illustrates the way in which the second lens claw  1501   e  ( 501   e ) and the third camera claw  201   c  ( 1201   c ) interfere. 
     As illustrated in  FIGS. 20A and 20B , in a case where, for example, the reference first lens claw  1501   d  ( 501   d ) is attempted to be inserted into the reference camera recess  201   d  ( 1201   d ), the third camera claw  201   c  ( 1201   c ) interferes with the second lens claw  1501   e  ( 501   e ) and third lens claw  1501   f  ( 501   f ). 
     That is to say, as viewed from the rear face side, the total sum of the angles of one reference lens claw, another lens claw adjacent thereto in the clockwise direction, and a lens recess situated between these lens claws, is taken as a first angle. As viewed from the rear face side, the total sum of the angles of one reference camera recess, another camera recess adjacent thereto in the clockwise direction, and a camera claw portion situated therebetween, is taken as a second angle. As viewed from the rear face side, the total sum of the angles of one reference lens claw, another lens claw adjacent thereto in the counterclockwise direction, and a lens recess situated between these lens claws, is taken as a third angle. As viewed from the rear face side, the total sum of the angles of one reference camera recess, another camera recess adjacent thereto in the counterclockwise direction, and a camera claw portion situated therebetween, is taken as a fourth angle. According to the present embodiment, it is sufficient to layout the claws and recesses at the camera mount  1201  side and lens mount  1501  side such that the first angle described above is larger than the second angle, and the third angle is larger than the fourth angle. 
     According to this configuration, at least two lens claws and one camera claw interfere with each other. Thus, the risk of an incompatible lens unit being erroneously mounted to an imaging apparatus, or an incompatible lens unit and imaging apparatus being erroneously mounted to mount units provided to both ends of a conversion adapter, can be reduced. 
     However, even in a case where, for example, the above conditions are satisfied, there may be cases where, when attempting to insert three claws into incompatible recesses two claws are inserted into recesses depending on the angles of the claws and recesses. 
     The claws and recesses at the camera mount  1201  side and lens mount  1501  side are therefore disposed in the circumferential direction so as to satisfy θ 6 &lt;θ 9 , θ 6 &lt;θ 10 , θ 6 &lt;θ 11 , θ 7 &lt;θ 9 , θ 7 &lt;θ 10 , and θ 7 &lt;θ 11 . That is to say, as viewed from the rear face side, the total sum of the angles of two claws other than the reference lens claw described above, and a lens recess situated therebetween, is taken as a fifth angle. According to the present embodiment, it is sufficient to layout the claws and recesses at the camera mount  1201  side and lens mount  1501  side such that the second angle and fourth angle described above are smaller than any of the first angle, third angle, and fifth angle. 
       FIG. 21  illustrates diagrams exemplarily describing the way in which claws interfere with each other, when attempting to mount a claw other than the reference claw at the lens mount  1501  ( 501 ) side to a reference recess at the camera mount  201  ( 1201 ) side according to the embodiment of the present invention.  FIG. 21A  illustrates the way in which the first lens claw  1501   d  ( 501   d ) and the third camera claw  201   c  ( 1201   c ) interfere in a case of attempting to insert the second lens claw  1501   e  ( 501   e ) into the first camera recess  201   d  ( 1201   d ).  FIG. 21B  illustrates the way in which the third lens claw  1501   f  ( 501   f ) and the third camera claw  201   c  ( 1201   c ) interfere in a case of attempting to insert the second lens claw  1501   e  ( 501   e ) into the first camera recess  201   d  ( 1201   d ).  FIG. 21C  illustrates the way in which the second lens claw  1501   e  ( 501   e ) and the third camera claw  201   c  ( 1201   c ) interfere in a case of attempting to insert the third lens claw  1501   f  ( 501   f ) into the first camera recess  201   d  ( 1201   d ).  FIG. 21D  illustrates the way in which the first lens claw  1501   d  ( 501   d ) and the third camera claw  201   c  ( 1201   c ) interfere in a case of attempting to insert the third lens claw  1501   f  ( 501   f ) into the first camera recess  201   d  ( 1201   d ). 
     As illustrated in  FIGS. 21A through 21D , at least two lens claws and one camera claw interfere, regardless of the relative rotation angle of the lens mount  1501  and camera mount  1201 , according to the present embodiment. According to this configuration, erroneous mounting of a lens unit and conversion adapter having the lens mount  501  and the lens mount  501  to an imaging apparatus and conversion adapter having the camera mount  201  and the camera mount  1201  can be prevented even more effectively. 
       FIG. 22  is a diagram exemplarily describing a state in which claws provided to the camera mount  401  side and lens mount  501  side according to the embodiment of the present invention are engaged.  FIG. 22  illustrates a state in which the camera mount  401  provided to the camera body  60  is engaged to the lens mount  501  provided to the second lens  50 . The first lens claw  501   d  can be inserted into the first camera recess  401   d , as illustrated in  FIG. 22 . The second lens claw  501   e  can be inserted into the second camera recess  401   e . Further, the third lens claw  501   f  can be inserted into the third camera recess  401   f . That is to say, the camera mount  401  side and the lens mount  501  side are a combination compatible with being directly mounted to each other. The camera mount  201  side and the lens mount  301  side are a combination compatible to being directly mounted to each other, as illustrated in  FIG. 10A . 
     As described above, the camera mount  401  ( 1401 ) corresponding to an imaging apparatus (e.g., the camera body  60 ) having a long flange focal distance, and the lens mount  501  ( 1501 ) corresponding to a lens unit (e.g., the second lens  50 ) having a long flange focal distance can be directly mounted to each other. However, the camera mount  201  ( 1201 ) corresponding to an imaging apparatus (e.g., the camera body  10 ) having a short flange focal distance and the lens mount  501  ( 1501 ) corresponding to a lens unit (e.g., the second lens  50 ) having a long flange focal distance cannot be directly mounted to each other. The camera mount  201  ( 1201 ) corresponding to an imaging apparatus (e.g., the camera body  10 ) having a short flange focal distance and the lens mount  301  ( 1301 ) corresponding to a lens unit (e.g., the first lens  100 ) having a short flange focal distance can be directly mounted to each other. However, the camera mount  401  ( 1401 ) corresponding to an imaging apparatus (e.g., the camera body  60 ) having a long flange focal distance and the lens mount  301  ( 1301 ) corresponding to a lens unit (e.g., the first lens  100 ) having a short flange focal distance cannot be directly mounted to each other. 
     An imaging apparatus and camera accessory employing the configuration of the above-described embodiment can therefore prevent erroneous mounting of an imaging apparatus and camera accessory having approximately the same mount diameter but are not mutually compatible. 
     Although a preferable embodiment of the present invention has been described, the present invention is not restricted to this embodiment, and various modifications and alterations can be made within the scope of the essence thereof. For example, a case of employing a digital camera has been described as an example of the imaging apparatus in the above-described embodiment, but imaging apparatuses other than digital cameras, such as digital video cameras, and security cameras, may be employed in the configuration. 
     Although a case of employing an interchangeable lens and an intermediate accessory, such as a conversion adapter, as an example of the camera accessory carrying out the present invention, has been described in the embodiment above, this is not restrictive. Any sort of camera accessory may be employed as long as it is a device having an accessory mount capable of directly connecting (coupling) to a camera mount provided to the above-described imaging apparatuses. 
     Although a configuration has been described in the above embodiment where both of the camera mount and accessory mount corresponding to each other have a pair of electric terminals through which electric connection is established in a mutually mounted state, this is not restrictive. For example, a configuration may be made having electric terminals that do not correspond to each other. For example, a configuration may be made where a terminal that the camera body  10  does not have is provided to a camera accessory mountable to the camera body  10 . 
     Although a configuration has been described in the above embodiment where the electric terminals are disposed in order along a circumferential direction where the diameter from the center of the camera mount and accessory mount is approximately the same, this is not restrictive. For example, a configuration may be made where the electric terminals are disposed along the circumferential direction at different diameters from the center of the camera mount and accessory mount. In this case, the dimensions of the mounts in the radial direction will increase, but friction between terminals can be suppressed. 
     Although a case has been described in the above embodiment where each mount has three claws in the circumferential direction, the number of claws is not restricted to three, as long as the conditions of the above-described embodiment are satisfied. 
     A configuration may be made where each of the three claws provided to the mounts in the above-described embodiment is further divided. That is to say, a configuration may be made where one claw is one claw group made up of multiple claws. A case where a groove is provided to one claw falls under this, for example. In this case, the ranges of angles of claw groups disposed in the circumferential direction of the mounts is the same as those in the embodiment described above. 
     Although a case has been described in the above embodiment where the mount diameter of each mount is the inner diameter of a fitting portion provided to each mount, this is not restrictive. For example, at each mount, an inner diameter of which the radius is the distance from the center (substantially the same as optical axis) of each mount to multiple electronic contacts (terminals) may be used as the mount diameter, or an inner diameter of which the radius is the distance from the center of each mount to a claw or recess may be used as the mount diameter. 
     Although a configuration has been described in the above embodiment where a device having one of a camera mount and an accessory mount is actually rotated as to a device having the other mount, thereby bayonet-coupling the devices to each other, this is not restrictive. For example, a configuration may be employed where a camera mount and accessory mount are relatively rotated, and the camera mount and accessory mount are bayonet-coupled. Specifics of this will be described in detail below. 
       FIG. 23  is a disassembled perspective view of a mount mechanism  5000  according to a modification of the present invention.  FIG. 24  illustrates diagrams for exemplarily describing a non-coupled state of the mount mechanism  5000  according to the modification of the present invention.  FIG. 25  illustrates diagrams for exemplarily describing a coupled state of the mount mechanism  5000  according to the modification of the present invention. In  FIGS. 23 through 25 , the lens mount capable of bayonet-coupling to a movable mount portion  5010  of the mount mechanism  5000  is also illustrated, for the same of description. Members that are the same as those in the above-described embodiment are denoted by the same reference numerals, and description thereof will be omitted. 
     As illustrated in  FIG. 23 , the mount mechanism  5000  according to the present embodiment has, in order from the side to which the lens mount is attached, an operation portion  5030 , a fixed mount portion  5020 , the movable mount portion  5010 , and the contact holding member  203 , centered on the optical axis  3000 . The operation portion  5030  is a ring-shaped operating unit capable of rotating on a center axis, and is fixed to the movable mount portion  5010  by screws, by arm portions  5040 . In the present modification, the operation portion  5030  and movable mount portion  5010  are fixed at two positions, using two arm portions  5040  disposed in an orthogonal direction as to the center axis. According to this configuration, by the operation portion  5030  being rotationally operated, the movable mount portion  5010  also rotates integrally about the center axis as the center. 
     Provided on the movable mount portion  5010  are movable mount claws  5011   a ,  5011   b , and  5011   c , that are each capable of bayonet-coupling with bayonet claws  301   a  through  301   c  provided to the lens mount  301 . Also provided to the movable mount portion  5010  is a screw portion  5012  that has been threaded around the center axis, and the screwed state as to a below-described screw portion  5022  of the fixed mount portion  5020  changes in accordance with the rotation of the movable mount portion  5010  around the center axis. 
     The fixed mount portion  5020  has a camera mount face  5021  that comes into contact with the mount face of the lens mount, and the screw portion  5022  with which the screw portion  5012  of the above-described movable mount portion  5010  is screwed. Unlike the above-described movable mount portion  5010 , the fixed mount portion  5020  does not rotate about the center axis in accordance with rotation operations of the operation portion  5030 . 
     Next, the bayonet coupling method of the mount mechanism  5000  according to the present modification will be described with reference to  FIGS. 24 and 25 . The bayonet claws provided to the lens mount  301  are in a state of being capable to engage the movable mount claws  5011   a  through  5011   c  of the movable mount portion  5010 , in a state of being passed through an opening portion of the operation portion  5030  and an opening portion of the fixed mount portion  5020 . The state illustrated in  FIGS. 24A through 24C  is a state where the operation portion  5030  is situated at an unlocked position. In this state, the lens mount face of the lens mount and the camera mount face  5021  of the fixed mount portion  5020  are in contact, but the claws of each of the lens mount  301  and movable mount portion  5010  do not engage each other, and do not overlap, as viewed from the center axis direction.  FIG. 24C  is a cross-sectional diagram taken along a cross-section H-H′ illustrated in  FIG. 24B .  FIG. 25  exemplifies the mount mechanism  5000  in a state where the operation portion  5030  has been rotationally operated from this state. 
     The state illustrated in  FIGS. 25A through 25C  is a state where the operation portion  5030  is situated in a locked position. In this state, the claws of each of the lens mount  301  and movable mount portion  5010  overlap each other, and thereby are engaged in the center axis direction. In this state, the screwing state of the screw portion  5022  of the fixed mount portion  5020  and the screw portion of the movable mount portion  5010  changes in accordance with rotational operation of the operation portion  5030 , and the movable mount portion  5010  moves toward the imaging device side in the center axis direction.  FIG. 25C  is a cross-sectional diagram taken along a cross-section I-I′ illustrated in  FIG. 25B . As illustrated in  FIGS. 24C and 25C , the movable mount portion  5010  moves away from the fixed mount portion  5020  in a center axis direction in accordance with a non-locked state of the mount mechanism  5000  changing to a locked state of the mount mechanism  5000 . According to this configuration, each of the movable mount claws  5011   a  through  5011   c  in a state of being engaged with the bayonet claws at the lens mount  301  side moves toward the imaging apparatus side. 
     As described above, the mount mechanism  5000  according to the present modification can move the movable mount portion in the center axis direction as to the fixed mount portion, by rotating the movable mount portion that has claws capable of engaging lens-mount-side claws on the center axis. According to this configuration, the mount mechanism  5000  according to the present modification can reduce occurrence of gaps (looseness) occurring between the lens mount and camera-side mount in a coupled state. 
     Although a configuration has been described in the above modification where the mount mechanism  5000  is provided to the imaging apparatus side, this can be applied to a configuration where the mount mechanism  5000  is provided to a camera accessory side, such as an interchangeable lens. 
     According to the present invention, erroneous mounting of an imaging apparatus and an accessory having mounts that can be mutually engaged with each other can be prevented. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention 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.