Patent Publication Number: US-2022236628-A1

Title: Camera, interchangeable lens apparatus, adapter apparatus, control method, and storage medium

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of International Patent Application No. PCT/JP2018/020714, filed on May 30, 2018, which claims the benefit of Japanese Patent Applications Nos. 2017-107260, filed on May 31, 2017, and 2018-102897, filed on May 30, 2018, each of which is hereby incorporated by reference herein in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a camera system including a camera, an interchangeable lens apparatus (simply referred to as interchangeable lens hereinafter), and an adapter apparatus (simply referred to as an adapter hereinafter) located between the camera and the interchangeable lens, which can communicate with each other. 
     Description of the Related Art 
     In an interchangeable lens type camera system including a camera to which an interchangeable lens is detachably attachable, a communication is performed for the camera to control the operation of the interchangeable lens and for the interchangeable lens to provide the camera with data necessary for its control and imaging. In particular, in imaging a recording use motion image and a live-view display use motion image with the interchangeable lens, a smooth lens control is required at an imaging cycle, so it is necessary to synchronize the imaging timing of the camera and the control timing of the interchangeable lens with each other. Thus, the camera needs to complete a data reception from the interchangeable lens and a transmission of a command, such as a variety of instructions and requests, to the interchangeable lens within the imaging cycle. However, as a data amount received by the camera from the interchangeable lens becomes larger or the imaging cycle becomes shorter (or the frame rate becomes higher), a communication of a large amount of data at higher speed is required. 
     An adapter such as a wide converter or a teleconverter (extender) may be mounted between the camera and the interchangeable lens. In this case, a command transmission from the camera to the interchangeable lens and a data transmission from the interchangeable lens to the camera are performed via the adapter. Furthermore, for proper AF, AE, etc. in the camera, not only data on the interchangeable lens but also data specific to the adapter is required. A camera system disclosed in Japanese Patent Laid-Open No. 2012-037692 performs the command transmission from the camera to the adapter and the data transmission from the adapter to the camera by a common communication channel as that for the command transmission from the camera to the interchangeable lens and the data transmission from the interchangeable lens to the camera. In other words, a one-to-many communication is achieved among the camera, the interchangeable lens, and the adapter using one communication channel. 
     However, in the one-to-many communication using only a single communication channel, for example, the camera cannot transmit a command to the interchangeable lens or receive data from the interchangeable lens while data is transmitted from the adapter to the camera. As a result, an expedited communication between the camera and the interchangeable lens is hindered. 
     SUMMARY OF THE INVENTION 
     The present invention provides a camera, an interchangeable lens apparatus, and an adapter apparatus, each of which can expedite a communication between the camera and the interchangeable lens apparatus and smooth a communication between the camera and the adapter apparatus. 
     A camera according to one aspect of the present invention to which an interchangeable lens apparatus is connected via at least one adapter apparatus includes a lens-camera communication controller configured to communicate with the interchangeable lens apparatus via a camera-lens communication channel connected from the camera to the interchangeable lens apparatus via the adapter apparatus, and an adapter-camera communication controller configured to communicate with the adapter apparatus via a camera-adapter communication channel provided separately from the camera-lens communication channel with the adapter apparatus. The camera-lens communication channel includes a first data communication channel used during a data communication and a first notification channel used for a notification of a timing of a communication via the first data communication channel, and the camera-adapter communication channel includes a second data communication channel used during the data communication and a second notification channel used for a notification of a timing of a communication via the second data communication channel. 
     A camera system including the above camera, an interchangeable lens connected to the camera, and an adapter apparatus connected to the camera and the adapter apparatus also constitute another aspect of the present invention. 
     An adapter apparatus according to another aspect of the present invention to which the camera and interchangeable lens are connected includes a relay channel for forming part of a camera-lens communication channel used for a communication between the camera and the interchangeable lens, and an adapter-camera communication controller configured to communicate with the camera via a camera-adapter communication channel provided separately from the relay channel with the camera. The camera-lens communication channel includes a first data communication channel used during a data communication and a first notification channel used for a notification of a timing of a communication via the first data communication channel, and the camera-adapter communication channel includes a second data communication channel used during a data communication and a second notification channel used for a notification of a timing of a communication via the second data communication channel. 
     An interchangeable lens apparatus according to another aspect of the present invention connected to an adapter apparatus and a camera via the adapter apparatus includes a first lens-camera communication controller configured to communicate with the camera via a camera-lens communication channel connected to the interchangeable lens from the camera via the adapter apparatus, and a second lens-camera communication controller provided separately from the camera-lens communication channel and configured to communicate with the camera via a communication channel including a camera adapter communication channel connected to the camera and the adapter. The first camera-lens communication channel includes a first data communication channel used during a data communication and a first notification channel used for a notification of a timing of communication via the first data communication channel, and the communication channel includes the camera-adapter communication channel include a second data communication channel used during a data communication and a second notification channel used for a notification of a timing of a communication via the second data communication channel. 
     A control method for a camera connected to an interchangeable lens apparatus via at least one adapter apparatus includes the steps of communicating with the interchangeable lens apparatus via a camera-lens communication channel connected from the camera to the interchangeable lens apparatus via the adapter apparatus, and communicating with the adapter apparatus via a camera-adapter communication channel from a camera-lens communication channel with the adapter apparatus separate, and controlling an operation of the interchangeable lens using data obtained through a communication with the interchangeable lens apparatus, and controlling an operation of the adapter apparatus using data obtained through a communication with the adapter apparatus. The camera-lens communication channel includes a first data communication channel used during a data communication and a first notification channel used for a notification of a timing of a communication via the first data communication channel, and the camera-adapter communication channel includes a second data communication channel used during a data communication and a second notification channel used for a notification of a timing of communication via the second data communication channel. 
     The imaging control program as a computer program that executes the above control method also constitutes another aspect of the present invention. 
     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. 1  is a block diagram showing a configuration of a camera system according to a first embodiment of the present invention. 
         FIG. 2  is a flowchart showing lens control processing according to the first embodiment. 
         FIGS. 3A and 3B  explain a first communication according to the first embodiment. 
         FIG. 4  is a flowchart illustrating adapter information acquisition processing according to the first embodiment. 
         FIGS. 5A and 5B  explain a data occupancy status of each communication according to the first embodiment. 
         FIG. 6  is a block diagram showing a configuration of a camera system according to a second embodiment of the present invention. 
         FIG. 7  is a flowchart showing lens control processing according to the second embodiment. 
         FIG. 8  is a diagram for explaining a first communication when an interchangeable lens is activated from a camera according to the second embodiment. 
         FIG. 9  is a diagram for explaining the first communication when an interchangeable lens is activated from the interchangeable lens according to the second embodiment. 
         FIG. 10  is a flowchart illustrating adapter control processing according to the second embodiment. 
         FIGS. 11A and 11B  explain a second communication according to the first embodiment. 
         FIG. 12  is a diagram for explaining a third communication (one-to-many) according to the first embodiment. 
         FIG. 13  is a diagram for explaining the third communication (one-to-one) according to the first embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Referring now to the accompanying drawings, a description will be given of embodiments according to the present invention. 
     First Embodiment 
       FIG. 1  illustrates a configuration of a camera system according to a first embodiment of the present invention. The camera system includes a camera  20 , an interchangeable lens apparatus (referred to as an interchangeable lens hereinafter)  10 , and two adapter apparatuses (referred to as adapters hereinafter)  30  and  40  disposed between the camera  20  and the interchangeable lens  10 . The camera system has a first communication use camera-lens communication channel  100  (referred to as a first communication channel  100  hereinafter) for transmitting a command for an instruction and a request from the camera  20  to the interchangeable lens  10 . In addition, the camera system includes, separate from the communication channel  100 , a second communication use lens-camera communication channel (referred to as a second communication channel  200  hereinafter) for transmitting data indicating optical data, status, and the like from the interchangeable lens  10  to the camera  20 . The camera system further includes a third communication use camera-adapter communication channel (referred to as a third communication channel  300  hereinafter) for communicating data indicating a command, optical data of each adapter, and the state and the like between the camera  20  and the two adapters  30  and  40 . 
     The interchangeable lens  10  has an imaging optical system including a plurality of movable optical elements such as a lens and an aperture stop or diaphragm (iris). The camera  20  includes an image sensor  204  that captures an object image formed by the imaging optical system, and generates an image signal using an output signal from the image sensor  204 . The adapter  40  is detachably connected (attached) to the mount  201  of the camera  20  at a mount  402 . The adapter  30  is detachably connected to a mount  401  of the adapter  40  at its mount  302 . The adapter  30  includes an extender, a wide converter, or the like, and the adapter  40  includes an ND adapter or the like, and includes adapter optical elements  309  and  409  such as a magnification varying lens and an ND filter, respectively. Further, the interchangeable lens  10  is detachably connected to the mount  301  of the adapter  30  at its mount  101 . 
     When the mounts  101 ,  301 ,  302 ,  401 ,  402 , and  201  are all connected, first communication contacts  102 ,  303 ,  306 ,  403 ,  406 , and  202  provided to the respective mounts are electrically connected to each other, and a camera-lens communication channel is formed for the first communication. The first communication is used for a communication used for the camera  20  to control the operation of the movable optical element of the interchangeable lens  10 . 
     When the mounts  101 ,  301 ,  302 ,  401 ,  402 , and  201  are all connected, second communication contacts  103 ,  304 ,  307 ,  404 ,  407 , and  202  provided to the respective mounts are electrically connected to each other, and a camera-lens communication channel is formed for the second communication. The second communication is used to transmit optical data of the interchangeable lens  10  (referred to as lens optical data hereinafter) and data indicating the state of the interchangeable lens  10  (referred to as lens state data hereinafter) to the camera  20 . Further, by connecting the mounts  101 ,  301 ,  302 ,  401 ,  402 , and  201 , third communication contacts  104 ,  305 ,  308 ,  405 ,  408 , and  203  provided to the respective mounts are electrically connected to each other to form a camera-adapter communication channel for the third communication. The third communication is a one-to-many communication between the camera  20  and the two adapters  30  and  40 . The third communication is used for the camera  20  to transmit a command for controlling their operations to the adapters  30  and  40 . Further, it is used for the adapters  30  and  40  to transmit optical data to the camera  20  of adapter optical elements  309  and  409  and operation data indicating a user operation to the adapters  30  and  40 . The following description will refer to the respective optical data of the adapters  30  and  40  as first adapter optical data and second adapter optical data. The respective operation data of the adapters  30  and  40  will be referred to as first adapter operation data and second adapter operation data. The third communication is also used for a communication between the interchangeable lens  10  and the adapters  30  and  40 . 
     In the interchangeable lens  10 , the movable optical elements in the imaging optical system described above include a focus lens  105 , a magnification varying lens  106 , an iris  107 , and an image stabilization lens  108 . The focus lens  105  moves in the optical axis direction of the imaging optical system to perform focusing. The magnification varying lens  106  moves in the optical axis direction to perform a magnification variation. The iris  107  performs a light amount adjustment. The image stabilization lens  108  moves (shifts) in a direction orthogonal to the optical axis direction to reduce an object image blur caused by a camera shake due to camera shake or the like. 
     A focus controller  109  includes a focus actuator that moves the focus lens  105 , a focus driver that controls driving of the focus lens  105 , and a focus position sensor that detects the position of the focus lens  105 . A zoom controller  110  includes a zoom adapter that moves the magnification varying lens  106 , a zoom driver that controls its driving, and a zoom position sensor that detects the position of the magnification varying lens  106 . An iris controller  111  includes an iris driver that drives an iris motor provided to the iris  107  and an iris position sensor that detects an open/close position (F-number or aperture value) of the iris  107 . An image stabilization controller  112  includes an image stabilization actuator that shifts the image stabilization lens  108 , an image stabilization driver that controls its driving, and a shift position sensor that detects the shift position of the image stabilization lens  108 . 
     A shake detection unit  113  includes a vibration gyro and the like, and detects a camera shake amount that is a shake amount of the interchangeable lens  10  (or a camera system). 
     A lens controller  114  controls the operations of the focus lens  105 , the magnification varying lens  106 , and the iris  107  through the focus, zoom, and iris controllers  109  to  111  in accordance with the lens control command received from a camera controller  205  in the camera  20 . The lens controller  114  controls the operation (shift) of the image stabilization lens  108  through the image stabilization controller  112  in response to receiving the lens control command. The lens controller  114  transmits lens optical data and lens state data to the camera controller  205 . The lens controller  114  communicates with the camera controller  205  through a first lens communicator  115  and a second lens communicator  116 , and communicates with the adapters  30  and  40  through a third lens communicator  117 . 
     The first lens communicator  115  constitutes a camera-lens communication controller together with the lens controller  114 , and performs a first communication with the camera controller  205 . The first communication is used to receive a command, such as a lens control command, from the camera controller  205 . 
     The second lens communicator  116  performs a second communication with the camera controller  205 . The second communication is used to transmit lens optical data and lens state data to the camera controller  205 . The third lens communicator  117  constitutes an adapter-lens communication controller together with the lens controller  114 , and performs a third communication with third adapter communicators  310  and  410  in the adapters  30  and  40 . The third communication between the third adapter communicators  310  and  410  is also used to transmit lens optical data and lens state data from the lens controller  114  to the adapter controllers  311  and  411 . 
     The lens controller  114  and the lens first to third communicators  115  to  117  include a computer such as a CPU provided in the interchangeable lens  10 . A lens operation member  118  is an operation member operated by the user in the interchangeable lens  10 , and includes a switch, an electronic ring, or the like. 
     In the camera  20 , the image sensor  204  includes a CMOS image sensor or the like, and photoelectrically converts (captures) an object image. The camera controller  205  converts the output signal from the image sensor  204  into an image signal and outputs it to an image display unit  206 . 
     In addition, the camera controller  205  transmits a lens control command to the lens controller  114  to control the operation of the interchangeable lens  10  and receives lens optical data and lens state data from the lens controller  114 . The camera controller  205  communicates with the lens controller  114  through the first camera communicator  207  and the camera second communicator  208 , and communicates with the adapters  30  and  40  through the third camera communicator  209 . 
     The first camera communicator  207  constitutes a lens-camera communication controller together with the camera controller  205 , and performs a first communication with the first lens communicator  115 . As described above, the first communication is used to transmit a command such as a lens control command from the camera controller  205  to the lens controller  114 , or to transmit data from the lens controller  114  to the camera controller  205 . The camera second communicator  208  performs a second communication with the first lens communicator  115 . As described above, the second communication is used to receive lens optical data and lens state data from the lens controller  114 . 
     The third camera communicator  209  constitutes an adapter-camera communication controller together with the camera controller  205 , and performs a third communication with the third adapter communicators  310  and  410 . The third communication is used to transmit an adapter control command and an adapter transmission requesting command (a command for requesting a transmission of adapter specific information) to the adapter controllers  311  and  411 . Moreover, the third communication is used to receive the adapter specific information from the adapter controllers  311  and  411 . The adapter specific information includes, for example, first and second adapter optical data and first and second adapter operation data. The camera controller  205  and the camera first to third communicators  207  to  209  include a computer such as a CPU provided in the camera  20 . In the first and third communications, at least one of a communication method, a communication timing, a communication speed (communication rate), and a communication voltage is different from each other. 
     The image display unit  206  includes a liquid crystal monitor or the like, and displays an image signal (captured image) from the camera controller  205 . The camera operation member  210  is an operation member operated by the user in the camera  20  in order to set an imaging condition, and includes a dial, a switch, or the like. 
     In the adapters  30  and  40 , the adapter optical elements  309  and  409  described above are optical elements for adding a specific optical action to the interchangeable lens  10 , and include a magnification varying lens, an ND filter, or the like. In this embodiment, the adapter  30  is an extender having a magnification varying lens as the adapter optical element  309 , and the adapter  40  is an ND adapter having an ND filter as the adapter optical element  409 . The adapter optical element may be an member other than a magnification varying lens or an ND filter. 
     The adapter controllers  311  and  411  control the operations of the adapters  30  and  40  (insertion into and ejection from the imaging optical path of the magnification varying lens and the ND filter) according to the adapter control command received from the camera controller  205 . 
     The adapter controllers  311  and  411  communicate with the camera controller  205  and the lens controller  114  via the third adapter communicators  310  and  410 . The third adapter communicators  310  and  410  together with the adapter controllers  311  and  411  constitute a camera-adapter communication controller and a lens-adapter communication controller, and perform the third communication with the third camera communicator  209  and the third lens communicator  117 . As described above, the third communication with the third camera communicator  209  is a communication used to receive the adapter control command and the adapter request command from the camera controller  205 , and to transmit the first and second adapter optical data to the camera controller  205 . As described above, the third communication with the third lens communicator  117  is used to receive lens optical data and lens state data from the lens controller  114 . 
     The adapter controller  311  and the third adapter communicator  310  include a CPU provided in the adapter  30 . The adapter controller  411  and the third adapter communicator  410  include a computer such as a CPU provided in the adapter  40 . 
     The adapter operation members  312  and  412  are operation members operated by the user in the adapters  30  and  40 , and include switches, electronic rings, and the like. Here, a predetermined function is assigned to the operation of the adapter operation members  312  and  412 . Alternatively, a user&#39;s favorite function is assigned through an unillustrated setting unit of the camera  20 . Illustrative functions for the operation of the adapter operation members  312  and  412  include, for example, the following. When the adapter operation members  312  and  412  are switches, they are at least one of ON/OFF of the image stabilization function, setting of the image stabilization level of the image stabilization function, and switching between the autofocus and the manual focus. When the adapter operation members  312  and  412  are electronic rings, the adapter operation members  312  and  412  are at least one of an adjustment function of an aperture position (aperture diameter), an adjustment function of a focus position, and an adjustment function of a zoom position of the interchangeable lens  10 . At least one of the aperture position, the focus position, and the zoom position is adjusted in the lens  10  by an adjustment amount corresponding to the amount by which the electronic ring is operated. 
     Referring now to a flowchart in  FIG. 2 , a description will be given of processing in which the camera  20  (camera controller  205 ) controls the interchangeable lens  10  (lens controller  114 ). Each of the camera controller  205  and the lens controller  114  executes this processing (and each processing described later) in accordance with an imaging control program that is a computer program. 
     When the camera  20  is activated in S 201 , the camera controller  205  proceeds to S 202 . In the step S 202 , the camera controller  205  supplies the power to the interchangeable lens  10  and the adapters  30  and  40  via an unillustrated power supply mount contact. 
     In the step S 203 , the camera controller  205  causes the first camera communicator  207  to detect the communication voltage used by the interchangeable lens  10 , and sets the communication voltage used by the first camera communicator  207  and the camera second communicator  208  according to the detection result. Thereafter, the first camera communicator  207  and the second camera communicator  208  performs the first communication and the second communication with the first lens communicator  115  and the second lens communicator  116 , respectively, using the set communication voltage. The processing in which the first camera communicator  207  detects the communication voltage of the interchangeable lens  10  will be described later. 
     Next, in S 204 , the lens controller  114  transmits, through the first lens communicator  115  (and the first camera communicator  207 ), ID information of the interchangeable lens  10  such as a lens name and lens specifications (referred to as a lens ID hereinafter) to the camera controller  205 . The camera controller  205  receives the lens ID via the first camera communicator  207 . The lens controller  114  transmits lens state data indicating the current state (lens state) of the interchangeable lens  10  to the camera controller  205  via the second lens communicator  116  (and the camera second communicator  208 ). The camera controller  205  receives the lens state data via the camera second communicator  208 . 
     The lens state data includes the current positions (referred to as an optical element position hereinafter) of the focus lens  105 , the magnification varying lens  106 , the iris  107 , and the image stabilization lens  108  acquired from the focus, zoom and iris controllers  109 ,  110 , and  111  and the image stabilization controller  112  (referred to as the lens image data hereinafter). The lens state data includes a value obtained by normalizing the camera shake amount acquired from the shake detection unit  113 , and lens operation data indicating the operation amount and operation state of the user operation acquired from the lens operation member  118 . When the lens operation member  118  is an electronic ring, the operation amount per unit time of the electronic ring may be included in the lens operation data. If the lens operation member  118  is a switch, the ON/OFF state of the switch may be included in the lens operation data. 
     Next, in S 205 , the camera controller  205  determines lens state data received from the lens controller  114  by the second communication based on the lens state data acquired in S 204 . Then, a command requesting a transmission of the determined lens state data is transmitted to the lens controller  114  via the first camera communicator  207  (and the first lens communicator  115 ). 
     In the step S 206 , the lens controller  114  determines the lens status data indicating the current lens state to be transmitted to the camera controller  205  based on the command received from the camera controller  205  via the first lens communicator  115  in the step S 205 . 
     Next, in S 207 , the lens controller  114  transmits the determined lens state data to the camera controller  205  via the second lens communicator  116  (and the camera second communicator  208 ). 
     In the step S 208 , the camera controller  205  determines an imaging condition based on the lens state data received from the lens controller  114  via the camera second communicator  208 , the magnification varying ratio of the adapter (extender)  30 , and the transmittance of the adapter (ND adapter)  40 . Then, imaging is performed under the imaging conditions. The imaging condition includes an object distance, a focal length, an F-number, a T value, a camera shake amount per unit time, and a shake correction angle for an image stabilization (shift amount of the image stabilization lens  108 ). The camera controller  205  displays on the image display unit  206  the generated captured image as well as a number, a symbol, a mark, an icon, and the like indicating the imaging condition superimposed on the captured image. A method in which the camera controller  205  acquires the magnification ratios and transmittances of the adapters  30  and  40  will be described later. 
     In the step S 209 , the camera controller  205  obtains operation data indicating a user operation on the camera operation member  210  (referred to as camera operation data hereinafter), and acquires the first adapter operation data and the second data from the adapter operation members  312  and  412 . The camera operation data is data indicating exposure (F-number, shutter speed, etc.) and zoom position setting by operating a dial or electronic ring, instructions for AF/image stabilization execution/stop by operating a switch, and the like. The first and second adapter operation data will be described later. Further, processing in which the camera controller  205  acquires the first and second adapter operation data will be described later. 
     In the step S 210 , the camera controller  205  determines lens control data based on the lens state data acquired in the step S 207 , the camera operation data and the first and second adapter operation data acquired in the step S 209 . More specifically, the camera controller  205  acquires a phase difference from a phase difference sensor provided in the image sensor  204  in response to turning on of a switch instructing the execution of AF, and calculates a defocus amount of the imaging optical system using the phase difference. Moreover, it determines a driving amount of the focus lens  105  for obtaining the in-focus state from the calculated defocus amount. The camera controller  205  determines the driving amount of the magnification varying lens  106  based on data indicating the operation amount of the dial or the electronic ring. Further, the camera controller  205  determines the driving amount of the iris  107  based on the exposure setting value set by operating the dial and the luminance level of the image signal generated using the output from the image sensor  204 . Further, the camera controller  205  determines whether or not the image stabilization lens  108  can be driven in accordance with turning on and off of a switch that instructs the execution and stop of the image stabilization. 
     In this way, the camera controller  205  determines the lens control data including the driving amounts of the focus lens  105 , the magnification varying lens  106 , and the iris  107  and whether or not the image stabilization is available. 
     Next, in S 211 , the camera controller  205  transmits a lens control command including lens control data to the lens controller  114  via the first camera communicator  207  (and the first lens communicator  115 ). 
     Next, in S 212 , the lens controller  114  passes the lens control data included in the received lens control command to the focus, zoom and iris controllers  109 ,  110 , and  111 . The focus, zoom, and iris controllers  109 ,  110 , and  111  drive the focus lens  105 , the zoom lens  106 , and the iris  107  according to the lens control data. The lens controller  114  notifies the image stabilization controller  112  of whether or not the image stabilization included in the lens control data is available. When the image stabilization is permitted, the image stabilization controller  112  shifts the image stabilization lens  108  so as to reduce the image shake according to the camera shake amount detected by the shake detection unit  113 . 
     As described above, in the initial communication (when the system is activated) between the camera  20  and the interchangeable lens  10 , the lens specific information, such as the name, specification, and lens correction data of the interchangeable lens  10 , is communicated. During the subsequent activation of the system, the data indicating the state of the imaging optical system of the interchangeable lens  10  including the focal length and the focus position, the data indicating the content of the operation performed on the camera  20  by the user, the above lens control data, and the like are communicated at a predetermined timing. 
     Referring now to  FIGS. 3A and 3B , a description will be given of processing in which the first camera communicator  207  detects the communication voltage of the interchangeable lens  10  and communication processing in the first communication. 
       FIG. 3A  illustrates a configuration of the first communication channel  100  for performing the first communication. In order to form the first communication channel  100  connected from the camera  20  to the interchangeable lens  10  via the adapters  30  and  40 , the first communication contacts  102 ,  303 ,  306 ,  403 ,  406 , and  202  have the following terminals. 
     The first communication contact  303  includes a first communication LCLK terminal  303   a , a first communication DCL terminal  303   b , a first communication DLC terminal  303   c , and a TYPE terminal  303   d . The first communication contact  306  includes a first communication LCLK terminal  306   a , a first communication DCL terminal  306   b , a first communication DLC terminal  306   c , and a TYPE terminal  306   d . The first communication contact  403  includes a first communication LCLK terminal  403   a , a first communication DCL terminal  403   b , a first communication DLC terminal  403   c , and a TYPE terminal  403   d . The first communication contact  406  includes a first communication LCLK terminal  406   a , a first communication DCL terminal  406   b , a first communication DLC terminal  406   c , and a TYPE terminal  406   d.    
     First communication LCLK terminals  102   a ,  303   a ,  306   a ,  403   a ,  406   a , and  202   a  are provided to form a line for a clock signal LCLK output from the first camera communicator  207  (referred to as an LCLK line hereinafter). First communication DCL terminals  102   b ,  303   b ,  306   b ,  403   b ,  406   b , and  202   b  are also provided in order to form a line for the camera data signal DCL output from the first camera communicator  207  (hereinafter referred to as a DCL line). In addition, first communication DLC terminals  102   c ,  303   c ,  306   c ,  403   c ,  406   c , and  202   c  are also provided to form a lens data signal DLC line (hereinafter referred to as a DLC line) output from the first lens communicator  115 . Each of the DLC line and the DCL line corresponds to a first data communication channel used during data communication. The LCLK line corresponds to a first notification channel used for notification of communication timing via the DCL line or the DLC line. The first communication is not limited to clock synchronous communication described later, and may be performed by an asynchronous communication. 
     TYPE terminals  102   d ,  303   d ,  306   d ,  403   d ,  406   d , and  202   d  are also provided for forming an interchangeable lens type detection signal TYPE line (referred to as a TYPE line hereinafter) for detecting the communication voltage of the interchangeable lens  10 . Four lines between the first communication contacts  303 ,  306 ,  403 , and  406  provided in the adapters  30  and  40  constitute a relay channel that forms part of the first communication channel  100 . 
     As illustrated in  FIG. 3A , the LCLK line and the DCL line are pulled up in the interchangeable lens  10 . The LCLK line and the DLC line are pulled up in the camera  20 . 
     The LCLK line, DCL line, DLC line, and TYPE line in the adapters  30  and  40  are short-circuited between the first communication contacts  303  and  306  and between the first communication contacts  403  and  406 , respectively. 
     The TYPE line is pulled down by a predetermined resistance value for each communication voltage in the interchangeable lens  10 , and pulled up by a predetermined resistance value in the camera  20 . The first camera communicator  207  detects the voltage value of the TYPE line, and specifies the communication voltage of the interchangeable lens  10  based on the voltage value determined from the resistance value in the interchangeable lens  10  and the resistance value in the camera  20 . 
       FIG. 3B  illustrates a communication format example of the first communication. This figure illustrates signal waveforms on the LCLK line, the DCL line, and the DLC line. The following description will refer to the clock signal LCLK as an LCLK signal, the camera data signal DCL transmitted and received through the DCL line as a DCL signal, and the lens data signal DLC transmitted and received through the DLC line as a DLC signal. 
     The first camera communicator  207  outputs the LCLK signal to the LCLK line, and outputs eight-bit data B 7  to B 0  as the DCL signal to the DCL line in synchronization with the leading edge of the LCLK signal. The first lens communicator  115  outputs eight-bit data B 7  to B 0  as a DLC signal to the DLC line in synchronization with the leading edge of the LCLK signal. 
     The first camera communicator  207  receives eight-bit (B 7  to B 0 ) data from the DLC line in synchronization with the leading edge of the LCLK signal. The first lens communicator  115  receives eight-bit (B 7  to B 0 ) data from the DCL line in synchronization with the leading edge of the LCLK signal. Thereby, the first camera communicator  207  and the first lens communicator  115  can communicate data with each other. 
     When receiving the eight-bit data from the DCL line, the first lens communicator  115  puts the voltage level of the LCLK line into low for the predetermined time Tbusy, and releases the low level when the predetermined time Tbusy passes. In other words, it puts the voltage level into high. The predetermined time Tbusy is a time for processing the data received by the lens controller  114 , and during this time, the first camera communicator  207  does not transmit data to the first lens communicator  115 . By repeating this communication processing, a data communication of a plurality of bytes is performed between the first camera communicator  207  and the first lens communicator  115  by the first communication. 
     In the second communication, the one-way communication may be performed from the interchangeable lens  10  to the camera  20  by the same clock synchronous communication as the first communication, or may be performed by the asynchronous communication. The third communication may be performed as the clock synchronous communication or the asynchronous communication as the bidirectional communication between the camera  20  and the adapters  30  and  40  and between the interchangeable lens  10  and the adapters  30  and  40 , by a master-slave method or token passing method, etc. 
       FIG. 11A  illustrates a communication format example of the asynchronous communication performed in the second communication on the second communication channel  200 . Herein, one frame is illustrated as the illustrative format of the data to be communicated, which includes ten bits or one-bit start bit, eight-bit data bits, one bit-stop bit. The data bits may be seven or sixteen bits, and may include a parity bit. The stop bits may have two bits. 
       FIG. 11B  illustrates a timing synchronization method of the asynchronous communication in the second communication. The camera controller  205  (and the second camera communicator  208 ) and the lens controller  114  (and the second lens communicator  117 ) send and receive data in synchronization with the internal clock in accordance with a predetermined clock frequency or the clock rate. For example, the internal clock is set to a clock rate 16 times as high as the communication rate between the camera controller  205  and the lens controller  114 . The starting point of data sampling is determined by sampling the trailing edge of the start bit of the received data in synchronization with the internal clock, as shown as the synchronization timing in the figure. As illustrated as a data sampling timing in the figure, the data is latched at a position of eight clocks starting from this synchronization timing. Thereby, the data can be captured at the center of each bit. By performing this data sampling for each bit, the data communication is performed using only one second communication line (lens-camera transmission channel: DLC 2 ). 
     The third communication channel  300  is a communication channel provided to enable the communication between the camera  20  and the adapters  30  and  40 . The third communication channel  300  is used to transmit a command indicating an instruction to transfer to the power saving mode from the camera controller  205  to the adapter controllers  311  and  411  and the lens controller  114 . Herein, the power saving mode is a mode in which the power consumption is lower than that in the normal operation. For example, the power saving mode is a mode that prohibits the data from being transmitted and received, and the movable optical element and the optical elements  309  and  409  in the imaging optical system from being driven. Moreover, the third communication channel  300  is also used to transmit a command indicating a communication counterpart in the one-to-one communication. It is also used to transmit information unique to the adapter controllers  30  and  40  to the camera controller  205 . The information unique to the adapter controllers  30  and  40  will be described later. 
     Referring now to  FIGS. 12 and 13 , a description will be given of the asynchronous communication performed using the third communication channel  300 . The third communication channel  300  includes two signal lines, or a notification channel CS used to communicate the communication timing and a data communication channel DATA used to transmit and receive the data. Herein, the data communication channel DATA corresponds to a second data communication channel used during the data communication. The notification channel CS corresponds to a second notification channel used for the notification of the timing of the communication via the data communication channel DATA. 
       FIG. 12  illustrates communication waveforms of the asynchronous communication performed in the third communication in the third communication channel  300 . In particular, it illustrates the illustrative one-to-many communication in which data can be transmitted simultaneously from an apparatus on the data transmission side to an apparatus on a plurality of data reception sides. More specifically, the camera  20  transmits the data, and then the adapter  30  (or adapter  30 ) transmits the data. The communication performed by such a one-to-many component will be referred to as the broadcast communication hereinafter. 
       FIG. 12  illustrates one integrated signal output from the two adapters  30  and  40  (adapter controllers  311  and  411 ). 
     When all of the camera controller  205 , the adapter controllers  311  and  411 , and the lens controller  114  are configured to output High to the notification channel CS, the signal level of the notification channel CS becomes high. On the other hand, when at least one of the camera controller  205 , the adapter controllers  311  and  411 , and the lens controller  114  outputs Low to the notification channel CS, the signal level of the notification channel CS becomes Low. 
     In the third communication, a communication speed is set in advance on both the data transmission side and the data reception side, and the data communication is performed at a communication bit rate based on this setting. The communication bit rate indicates a data amount transferable per second, and its unit is bps (bit per second). 
     When no data communication is performed, the signal level of the data communication channel DATA is maintained at the high level. Next, in order to notify the data reception side of the start of data transmission, the signal level of the data communication channel DATA is set to be Low for one bit period. This one-bit period will be called a start bit ST, and a data frame starts with the start bit ST. One-byte data is transmitted in an eight-bit period from the second bit to the ninth bit following the start bit ST. 
     The notification channel CS is connected to the camera controller  205 , the adapter controllers  311  and  411 , and the lens controller  114 , and each controller can detect the signal level (voltage level) of the notification channel CS. Further, the notification channel CS is pull-up-connected to an unillustrated power source disposed in the camera  20 . 
     Each controller can set the signal level of the notification channel CS, and all the controllers  205 ,  311 ,  411 , and  114  set the signal level of the notification channel CS to be high so that the signal level of the communication channel CS becomes high. In addition, when one of the controllers sets the signal level of the notification channel CS to low, the signal level of the communication channel CS becomes low. 
     In the third communication, the communication is performed using the camera controller  205  (and the third camera communicator  209 ) as the communication master and the adapter controllers  311  and  411  and the lens controller  114  as the communication slaves. 
     The camera controller  205  that is the communication master notifies the adapters  30  and  40  and the interchangeable lens  10  that are communication slaves of the start of communication by outputting Low to the notification channel CS. Next, the camera controller  205  transmits the data to the adapters  30  and  40  and the interchangeable lens  10  via the data communication channel DATA. On the other hand, the adapter controllers  311  and  411  and the lens controller  114  output Low to the notification channel CS in response to detecting the start bit ST described above via the data communication channel DATA. When the adapter controllers  311  and  411  and the lens controller  114  output Low to the notification channel CS, the signal level of the notification channel CS remains Low because the camera controller  205  outputs Low. 
     The adapter controllers  311  and  411  and the lens controller  114  notify the communication standby request by outputting Low to the notification channel CS. The communication standby request is for temporarily stopping the communication in the camera system, and the presence or absence of the communication standby request is determined based on the signal level of the notification channel CS. 
     The camera controller  205  outputs High to the notification channel CS after transmitting all the data. After receiving the stop bit SP transmitted from the data communication channel DATA, the adapter controllers  311  and  411  and the lens controller  114  execute an analysis of the received data and internal processing corresponding to the received data. Thereafter, after the preparation for executing the next communication is completed, High is output to the notification channel CS. 
     The camera controller  205 , the adapter controllers  311  and  411 , and the lens controller  114  confirm that each controller is ready to perform the next communication when the signal level of the notification channel CS returns to High. 
     In  FIG. 12 , the data transmitted by the camera controller  205  includes a transmission requesting command for the adapter controllers  311  and  411 , and the adapter controllers  311  and  411  provide a data transmission following a data transmission by the adapter controllers  311  and  411 . More specifically, after the signal level of the notification channel CS becomes High, the adapter controllers  311  and  411  output Low to the notification channel CS. This notifies the lens controller  114  and the camera controller  205  of the start of the communication. Next, the adapter controllers  311  and  411  transmit data to the lens controller  114  and the camera controller  205  via the data communication channel DATA. 
     On the other hand, the lens controller  114  and the camera controller  205  output Low to the notification channel CS in response to detecting the above start bit ST via the data communication channel DATA. When the lens controller  114  and the camera controller  205  output Low to the notification channel CS, the adapter controllers  311  and  411  output Low to the notification channel CS, so the signal level of the notification channel CS remains Low. 
     The adapter controllers  311  and  411  output High to the notification channel CS after transmitting all the data. After receiving the stop bit SP transmitted from the data communication channel DATA, the lens controller  114  and the camera controller  205  execute an analysis of the received data and internal processing corresponding to the received data. Then, after the preparation for executing the next communication is completed, High is output to the notification channel CS. 
     When the camera controller  205 , the adapter controllers  311  and  411 , and the lens controller  114  all output High to the notification channel CS, the signal level of the notification channel CS becomes High. The camera controller  205 , the adapter controllers  311  and  411 , and the lens controller  114  can confirm that each controller is ready to perform the next communication when the signal level of the notification channel CS returns to High. 
       FIG. 13  illustrates communication waveforms of the asynchronous communication performed in the third communication in the third communication channel  300 . In particular, an example is illustrated in which communication is individually performed between the camera  20  and one component (one of the interchangeable lens  10  and the adapters  30  and  40 ) selected as the communication counterpart by the camera  20 . Hereinafter, the communication performed by such a one-to-one component will be referred to as a P2P communication. 
     Information indicating a communication slave that is a communication counterpart in the P2P communication is transmitted from the camera controller  205  by the broadcast communication. In the P2P communication, the data transmission side does not output Low to the notification channel CS, and transmits data to the data reception side while maintaining the notification channel CS to be High. In other words, the voltage level of the notification channel CS during the data transmission from the camera  20  to the interchangeable lens  10  and the adapter  30  is made different between the broadcast communication and the P2P communication. 
     When the broadcast communication is switched to P2P communication, the data transmission first starts from the camera controller  205  which is the communication master. 
       FIG. 13  illustrates an example in which a two-byte data transmission is performed from the lens controller  114  to the camera controller  205  after a one-byte data transmission is made from the camera controller  205  to the lens controller  114 . 
     After switching from the broadcast communication to the P2P communication is completed in each component constituting the camera system, the camera controller  205  as the communication master transmits data to the lens controller  114  via the data communication channel DATA. When completing the data transmission, the camera controller  205  notifies the communication standby request by setting the signal level of the notification channel CS to a low output. The camera controller  205  then returns the signal level of the notification channel CS to a high output after the preparation for receiving data is completed for the data receiving side. 
     On the other hand, the lens controller  114  recognizes that the data transmission from the camera controller  205  is completed due to the signal level of the notification channel CS becoming Low, and executes an analysis of the received data and the internal processing corresponding to the received data. In the example of  FIGS. 5A and 5B , the data received from the camera controller  205  includes a data transmission request from the lens controller  114  to the camera controller  205 , and the lens controller  114  generates data to be transmitted to the camera controller  205 . 
     Thereafter, when the signal level of the notification channel CS returns to High, the lens controller  114  that has recognized the cancellation of the communication standby request transmits two-byte data to the camera controller  205 . 
     When the data transmission ends, the lens controller  114  notifies the communication standby request by setting the signal level of the notification channel CS to the low output. Then, the lens controller  114  returns the signal level of the notification channel CS to the high output after the preparation for receiving the data is completed for the data receiving side. The adapter microcomputer  302  that is not selected as the communication counterpart of the P2P communication does not change the output to the notification channel CS or does not participate in the data transmission/reception. 
     The lens controller  114  determines whether the P2P communication continues or is switched to the broadcast communication depending on the data transmission timing from the camera controller  205  after returning the signal level of the notification channel CS to High. 
     The signal level of the notification channel CS while the camera controller  205  is transmitting data is made different between the broadcast communication and the P2P communication. When the data from the camera controller  205  is received while the signal level of the notification channel CS remains high (second voltage level), the lens controller  114  determines that the P2P communication continues. On the other hand, when the data from the camera controller  205  is received after the signal level of the notification channel CS is changed to the low level (first voltage level), the lens controller  114  determines that the P2P communication has been switched to the broadcast communication. 
     As described above, in the P2P communication, the data transmission side changes the signal level of the notification channel CS from the high output to the low output to notify the data reception side that the data transmission by the data transmission side is completed. Therefore, in the P2P communication, a plurality of data frames can be continuously transmitted until the data transmission side changes the signal level of the notification channel CS. Thereby, a high-speed communication can be performed between the camera  20  and the accessory apparatus such as the interchangeable lens  10 , the adapter  30 , and the microcomputer  302 . Then, the data transmission side notifies the communication standby request by maintaining the low signal output level of the notification channel CS until the data reception preparation is completed for the data reception side in the next communication. 
     Referring now to a flowchart in  FIG. 4 , a description will be given of processing in which the camera controller  205  acquires the magnification ratio of the adapter optical element (magnification variable lens)  309 , the transmittance of the adapter optical element (ND filter)  409 , and the first and second adapter operation data. 
     S 401  and S 402  are the same as S 201  and S 202  in  FIG. 2 . The camera controller  205  that has proceeded from S 402  to S 403  transmits a command that requests the adapter controller  311  to transmit the first adapter optical data, which is optical data of the adapter optical element  309 , via the third camera communicator  209  (and the third adapter communicator  310 ). 
     In the step S 404 , the adapter controller  311  transmits the first adapter optical data stored in the internal memory to the camera controller  205  via the third adapter communicator  310  (and the third camera communicator  209 ). The first adapter optical data is data indicating the magnification ratio of the adapter optical element  309 . 
     In the step S 405 , the camera controller  205  transmits a command that requests the adapter controller  411  to transmit the second adapter optical data that is optical data of the adapter optical element  409  to it via the third camera communicator  209  (and the third adapter communicator  410 ). 
     In the step S 406 , the adapter controller  411  transmits the second adapter optical data stored in the internal memory to the camera controller  205  via the third adapter communicator  410  (and the third camera communicator  209 ). The second adapter optical data is data indicating the transmittance of the adapter optical element  409 . 
     Next, in the step S 407 , the camera controller  205  sends a command that requests the adapter controller  311  to transmit the first adapter operation data, which is operation data of the adapter operation member  312 , to it via the third camera communicator  209  (and the third adapter communicator  310 ). 
     Next, in S 408 , the adapter controller  311  acquires an operational amount and an operation state from the adapter operation member  312 . Then, data indicating them is transmitted as first adapter operation data to the camera controller  205  via the third adapter communicator  310  (and the third camera communicator  209 ). When the adapter operation member  312  is an electronic ring, the first adapter operation data is data indicating an operation amount per unit time of the electronic ring. When the adapter operation member  312  is a switch, the data indicates the ON/OFF state of the switch. 
     In the step S 409 , the camera controller  205  sends a command that requests the adapter controller  411  to transmit the second adapter operation data, which is operation data of the adapter operation member  412 , to it via the third camera communicator  209  (and the third adapter communicator  410 ). 
     Next, in S 410 , the adapter controller  411  acquires an operational amount and an operation state from the adapter operation member  412 . Then, data indicating them is transmitted as second adapter operation data to the camera controller  205  via the third adapter communicator  310  (and the third camera communicator  209 ). The second adapter operation data is data similar to the first adapter operation data. By repeating the processing from S 407  to S 410 , the camera controller  205  can periodically acquire the operation data of the adapter operation member  312  and the adapter operation member  412 . 
     For example, when the aperture position adjusting function is assigned to the adapter operation member  312 , the camera  20  instructs the interchangeable lens  10  to change the aperture position via the first communication channel  100  in accordance with the operation amount of the adapter operation member  412  acquired in S 410 . When the ON/OFF function of the image stabilization function is assigned to the adapter operation member  312 , the camera  20  instructs the interchangeable lens  10  to turn on or off the image stabilization control via the first communication channel  100  in accordance with the operation state (ON or OFF) of the adapter operation member  412  acquired in S 410 . This is similarly applied to the adapter operation member  412 . The user can control the state of the imaging optical system of the interchangeable lens  10  through the operations of the adapter operation members  312  and  412 . 
     The above embodiment has described the magnification ratio and transmittance of the adapter optical elements  309  and  409  as the illustrative first and second adapter optical data. 
     Information unique to the adapter  30  or information unique to the adapter  40  other than the first and second adapter optical data may be communicated via the third communication channel  300 . The information unique to the adapter  30  may include, for example, at least one of a name and a specification of the adapter  30 , and correction data of the adapter optical element  309 . Similarly, the information unique to the adapter  40  may include, for example, at least one of the name and specification of the adapter  40 , and correction data of the adapter optical element  409 . For example, at least one of the name, specification, correction data of the adapter optical elements  309  and  409  is transmitted to the camera  20  during the initial communication between the camera  20  and the adapter  30  and between the camera  20  and the adapter  40 . 
     Further, when the state of the imaging optical system of the interchangeable lens  10  or adapter optical element  309  or  409 , etc. changes, and thereby the focal length information, the light transmittance information, etc. changes over time, the adapters  30  and  40  may transmit these update data to the camera  20  in a normal state such as an ongoing imaging standby. Due to the above processing, the camera controller  205  can acquire the magnification ratio and the transmittance of the adapter optical elements  309  and  409  just after starting the power supply, and periodically acquire the operation amount and the operation state of the adapter operation members  312  and  412 , as soon as the start of the power supply. 
     Referring now to  FIGS. 5A and 5B , a description will be given of an occupancy status of communication data in the first communication channel  100 , the second communication channel  200 , and the third communication channel  300 . This description assumes that the lens control command, the lens state data, and the adapter operation data all have the same size. 
       FIG. 5A  illustrates the occupancy state of the communication data in the communication channel in the camera system as a comparative example having only one communication channel. The horizontal axis in the figure indicates time. Ta 1 , Ta 2 , Ta 3 , and Ta 4  indicate transmission times of the lens control command, lens state data, first adapter operation data, and second adapter operation data, respectively. Ca 1  and Ca 2  indicate transmission intervals between the lens control commands and between the lens state data, respectively. 
     The lens transmission requesting command is a command (data) for the camera controller  205  to request the lens controller  114  to transmit the lens state data. The lens controller  114  transmits the lens state data to the camera controller  205  in response to receiving the lens transmission requesting data. The first adapter transmission requesting data and the second adapter transmission requesting command are data for the camera controller  205  to request the adapter controllers  309  and  409  to transmit the first and second adapter operation data, respectively. In response to receiving the first and second adapter transmission requesting data, the adapter controllers  311  and  411  transmit the first and second adapter operation data to the camera controller  205 , respectively. 
     In  FIG. 5A , since the lens control command, the lens state data, and the first and second adapter operation data are sequentially communicated in a single communication channel, the transmission intervals Ca 1  and Ca 2  become longer between the lens control data and between the lens state data. The adapter controllers  311  and  411  need to correspond to the same communication speeds as those of the lens controller  114  and the camera controller  205 . 
     On the other hand,  FIG. 5B  illustrates the occupancy state of the communication data in the camera system according to this embodiment having the first communication, the second communication, and the third communication channel  300 . The horizontal axis in the figure indicates time. Tb 1 , Tb 2 , Tb 3 , and Tb 4  indicate transmission times of the lens control command, the lens state data, the first adapter operation data, and the second adapter operation data, respectively. Cb 1  and Cb 2  indicate transmission intervals between lens control commands and between lens state data, respectively. 
     As illustrated in  FIG. 5B , the lens control command, the lens state data, and the first and second adapter operation data are communicated through communication channels different from each other. Thereby, the camera controller  205  performs the first communication regardless of whether the camera controller  205  and the adapter controllers  30  and  40  are performing the third communication. Further, the lens control command, the lens state data, and the first and second adapter operation data are communicated through communication channels different from each other, so that the transmission interval Cb 1  between the lens control commands is sufficiently shorter than Ca 1  illustrated in  FIG. 5A . Similarly, the transmission interval Cb 2  between the lens state data is also sufficiently shorter than Cb 1 . Thereby, the camera  20  can control the interchangeable lens  10  at a higher speed than the comparative example of  FIG. 5A . 
     This embodiment limits devices connected to the first and second communication channels  200  to the camera  20  and the interchangeable lens  10 . Thereby, compared with a case where another device (adapter) is connected to the communication channel of the camera  20  and the interchangeable lens  10  as in the comparative example, a signal can be prevented from degraded due to the reflection of signals to be communicated. As a result, the communication speed can be made higher between the camera  20  and the interchangeable lens  10  in comparison with the comparative example. Hence, if the communicated data sizes are the same, Tb 1  and Tb 2  are shorter than Ta 1  and Ta 2 . Furthermore, since the devices connected to the second communication channel  200  are limited to the camera  20  and the interchangeable lens  10 , it is unnecessary to transmit the lens transmission requesting command from the camera  20  to the interchangeable lens  10  and the transmission interval between the lens state date can be made shorter. 
     In this embodiment, the transmission times Tb 3  and Tb 4  of the first and second adapter operation data are longer than Tb 3  and Tb 4 . This eliminates the need for the adapters  30  and  40  to support a high-speed communication by setting the communication rate of the third communication slower regardless of the communication rates of the first and second communications. 
     Further, in this embodiment, the lens control command, the lens state data, the first adapter operation data, and the second adapter operation data can be communicated at an arbitrary communication timing without being obstructed by the channel occupancy due to the other data communication. For example, a communication is available not only during the initial communication performed when the interchangeable lens, adapters  30  and  40 , and the like are attached to the camera  20 , but also during the ongoing imaging standby or ongoing imaging operation in the camera  20 . 
     As described above, this embodiment performs a communication of a variety of commands and data performed among the camera  20 , the interchangeable lens  10 , and the adapters  30  and  40  at proper communication timings without being obstructed by another communication. In comparison with a case where there is only one communication channel, various commands and data can be more stably communicated at short intervals, and the stability of the interchangeable lens control, the operability of the adapter, etc. can be improved. 
     Further, since only the camera  20  and the interchangeable lens  10  are connected to the first and second communication channels  200 , the first and second communications can be expedited and enhanced in function, and the controllability of the interchangeable lens can be further improved. In addition, when the camera  20  switches the communication voltage according to the communication voltage of the interchangeable lens  10 , a plurality of interchangeable lenses having different communication voltages can be connected to the camera  20 . Further, by performing the third communication between the camera  20  and the adapters  30  and  40  separately from the first and second communication, it is unnecessary to use an adapter that matches the high communication speed of the camera  20  and the interchangeable lens  10 . As described above, for example, the camera  20  can be realized which can be mounted with both an old interchangeable lens corresponding to the first communication having a high communication voltage and having no contacts with the second communication and the third communication and a new interchangeable lens corresponding to the first communication, the second communication, and the third communication having low communication voltages for the low power consumption. In this case, the cost of the electric circuit can be reduced for the new interchangeable lens since the new interchangeable lens can set a low communication voltage for the first communication, and can communicate at the same voltage as the low communication voltages of the second communication and the third communication. 
     This embodiment has described the adapters  30  and  40  communicating the first and second adapter operation data to the camera  20  through the third communication. However, the interchangeable lens  10  may communicate data relating to the interchangeable lens  10  (such as lens operation data) to the camera  20  via the third lens communicator  117 , the third adapter communicator  310 , and the third camera communicator  209 . 
     In addition, the interchangeable lens that performs the communication with a communication voltage different from the communication voltages of the adapters  30  and  40  may not have the third lens communicator  117  or the third communication contact  104 . This configuration can prevent the third lens communicator  117  and the third adapter communicators  310  and  410  from being connected with the communication voltages different from each other. 
     Second Embodiment 
     Referring now to  FIG. 6 , a description will be given of a second embodiment of the present invention. In this embodiment, those elements, which are corresponding elements in the first embodiment, will be designated by the same reference numerals and a description thereof will be omitted. 
     In this embodiment, the camera individually transfers the interchangeable lens and the adapter between a normal operation state (first state: referred to as a normal state hereinafter) that provides a communication, and a low power consumption state (second state: referred to as a sleep state hereinafter) that does not provide a communication and is lower in power consumption than that in the normal state. When the interchangeable lens is in the sleep state, this embodiment uses the first communication channel  100  as a channel for transmitting a lens activation signal for activating the interchangeable lens. When the adapter is in the sleep state, this embodiment uses the third communication channel  300  as a channel for transmitting an adapter activation signal that starts the adapter. The lens activation signal and the adapter activation signal are transmitted to the interchangeable lens and the adapter by a transmission method different from the first communication and the third communication performed in the normal state. 
     In  FIG. 6 , when an interchangeable lens  10 ′ is in the sleep state, the camera controller  2201  in a camera  20 ′ sends the lens activation signal to a lens controller  2101  via a camera sleep state signal controller  2202  and the first communication channel  100 . The lens controller  2101  in the interchangeable lens  10 ′ receives the lens activation signal from the camera controller  2201  via the first communication channel  100  and the lens sleep state signal controller  2102  when the interchangeable lens  10 ′ is in the sleep state. Furthermore, when the adapters  30 ′ and  40 ′ are in the sleep state, the camera controller  2201  sends the adapter activation signal to adapter controllers  2301  and  2401  in adapters  30 ′ and  40 ′ via the camera sleep state signal controller  2202  and the third communication channel  300 . 
     A flowchart in  FIG. 7  illustrates processing in which the camera  20 ′ transfers the interchangeable lens  10 ′ from the normal operation state (referred to as a normal state hereinafter) to the sleep state, and returns the interchangeable lens  10 ′ to the normal state. The normal state of the interchangeable lens  10 ′ means a state in which the interchangeable lens  10 ′ can perform the first, second, and third communications, and the camera  20 ′ can control driving of the movable optical element in the imaging optical system of the interchangeable lens  10 ′. The sleep state of the interchangeable lens  10 ′ indicates a state in which the interchangeable lens  10 ′ stops the first, second, and third communications and consumes the power lower than the normal state. 
     In the step S 702 , the camera controller  2201  that has started processing in S 701  acquires the camera operation data and the first and second adapter operation data described in the first embodiment. Then, the flow proceeds to S 703 . 
     In S 703 , the camera controller  2201  determines whether the time during which there is no change in the camera operation data or the first and second adapter operation data has exceeded a predetermined time. In other words, it is determined whether or not the non-operation time during which the operation members  207 ,  312 , and  412  of the camera  20 ′ or the adapters  30 ′ and  40 ′ are not operated by the user exceeds the predetermined time. If the non-operation time exceeds the predetermined time, the camera controller  2201  proceeds to S 704 , and if not (if there is an operation), the camera controller  2201  repeats the processing of S 703 . The predetermined time is time enough to determine that the user is not performing an operation for imaging, such as several seconds. 
     In S 704 , the camera controller  2201  transmits a command requesting the lens controller  2101  to transfer to the sleep state via the first camera communicator  207  (and the first lens communicator  115 ). Then, the flow proceeds to S 705 . 
     In S 705 , the lens controller  2101  transfers the interchangeable lens  10 ′ to the sleep state in response to the request to transfer to the sleep state received through the first lens communicator  115 . Only the lens sleep state signal controller  2102  operates in the interchangeable lens  10 ′ in the sleep state. 
     In the step S 706 , the camera controller  2201  acquires the camera operation data and first and second adapter operation data again. Then, the flow proceeds to S 707 . 
     In S 707 , the camera controller  2201  determines whether or not the camera operation data or the first and second adapter operation data acquired in S 702  and S 706  has changed. In other words, it is determined whether or not the operation members  207 ,  312 , and  412  of the camera  20 ′ or the adapters  30 ′ and  40 ′ are operated by the user. The camera controller  2201  proceeds to step S 708  when determining that the operation has been performed, and otherwise (if there is no operation) repeats the determination in the step S 707 . 
     In S 708 , the camera controller  2201  outputs a lens activation signal to the first communication channel  100  via the camera sleep state signal controller  2202 . Processing for outputting the lens activation signal to the first communication channel  100  will be described later. 
     Next, in S 709 , the lens sleep state signal controller  2102  to which the lens activation signal is input activates the lens controller  2101  and transfers the interchangeable lens  10 ′ to the normal state. Then, this flow ends. 
     By this processing, the camera controller  2201  can transfer only the interchangeable lens  10 ′ from the normal state to the sleep state, and can transfer from the sleep state to the normal state. 
     Referring now to  FIG. 8 , a description will be given of processing for outputting the lens activation signal to the first communication channel  100 .  FIG. 8  illustrates signal waveforms on the LCLK line, the DCL line, and the DLC line when the camera sleep state signal controller  2202  outputs the lens activation signal. 
     When the lens activation signal is input from the camera controller  2201  in the step S 708  in  FIG. 7 , the camera sleep state signal controller  2202  outputs the LCLK signal to the LCLK line from time Tc 10 , and outputs a specific data bit string (B 7  to B 0 ). The LCLK signal and a specific data bit string signal are transmitted as a lens activation signal to the lens sleep state signal controller  2102 . 
     The lens sleep state signal controller  2102  activates the lens controller  2101  in response to detecting a change in at least one of the LCLK line and the DCL line in the sleep state. Thereby, the interchangeable lens  10 ′ transfers to the normal state. Thereafter, the first lens communicator  115  outputs Low to the LCLK line for a predetermined time Tbusy, and cancels the Low output at time Tc 11  when the predetermined time Tbusy passes. Thereafter, the first communication illustrated in  FIG. 3B  can be performed between the camera controller  2201  and the lens controller  2101 . 
     This processing can transfer only the interchangeable lens  10 ′ from the sleep state to the normal state using the first communication channel  100 . 
     Referring now to  FIG. 9 , a description will be given of processing for transferring the interchangeable lens  10 ′ from the sleep state to the normal state in accordance with the operation of the lens operation member  118 .  FIG. 9  illustrates signal waveforms on the LCLK line, the DCL line, and the DLC line when the interchangeable lens  10 ′ transfers from the sleep state to the normal state in accordance with the operation of the lens operation member  118 . 
     When the lens sleep state signal controller  2102  detects the operation of the lens operation member  118 , the lens sleep state signal controller  2102  outputs Low as the lens activation request signal to the DLC line from time Tlc 0  illustrated in  FIG. 9 . When the camera sleep state signal controller  2202  detects Low on the DLC line, the first camera communicator  207  outputs the LCLK signal to the LCLK line from time Tlc 1  and outputs a specific data bit string (B 7  to B 0 ) to the DCL line. The LCLK signal and a specific data bit string signal are transmitted as a lens activation signal to the lens sleep state signal controller  2102 . 
     The lens sleep state signal controller  2102  activates the lens controller  2101  in response to detecting a change in at least one of the LCLK line and the DCL line in the sleep state of the interchangeable lens  10 ′. Thereby, the interchangeable lens  10 ′ transfers to the normal state. Thereafter, the first lens communicator  115  cancels the low output on the DLC line at time Tlc 2 . Thereafter, the first lens communicator  115  outputs Low to the LCLK line for the predetermined time Tbusy, and cancels the Low output when the predetermined time Tbusy elapses. Thereafter, the first communication illustrated in  FIG. 3B  can be performed between the camera controller  2201  and the lens controller  2101 . 
     This processing can transfer only the interchangeable lens  10 ′ to the normal state using the first communication channel  100  in response to the operation of the lens operation member  118  of the interchangeable lens  10 ′ in the sleep state. 
     Referring now to a flowchart in  FIG. 10 , a description will be given of processing in which the camera  20 ′ transfers the adapters  30 ′ and  40 ′ from the normal state to the sleep state and again transfers the adapters  30 ′ and  40 ′ to the normal state. The normal state of the adapters  30 ′ and  40 ′ is a state in which the adapters  30 ′ and  40 ′ can perform the third communication and the camera  20 ′ can control driving of the movable optical element of the imaging optical system of the interchangeable lens  10 ′. The sleep state of the adapters  30 ′ and  40 ′ indicates a state where the adapters  30 ′ and  40 ′ stop the third communication and consume the power lower than that in the normal state. 
     In the step S 1002 , the camera controller  2201  that has started the process in S 1001  acquires the camera operation data and the lens operation data described in the first embodiment. Then, the flow proceeds to S 1003 . 
     In S 1003 , the camera controller  2201  determines whether or not the time during which the camera operation data or the lens operation data has not changed exceeds a predetermined time. In other words, it is determined whether or not the non-operation time during which the operation members  207  and  118  of the camera  20 ′ or the interchangeable lens  10 ′ are not operated by the user exceeds the predetermined time. If the non-operation time exceeds the predetermined time, the camera controller  2201  proceeds to S 1004 , and if not (if there is an operation), the camera controller  2201  repeats the processing of S 1003 . The predetermined time is time enough to determine that the user is not performing an operation for imaging, such as several seconds. 
     In S 1004 , the camera controller  2201  transmits a command requesting the adapter controllers  2301  and  2401  to transfer to the sleep state via the third camera communicator  209  (and the third adapter communicators  310  and  410 ). Then, the flow proceeds to S 1005 . 
     In S 1005 , the adapter controllers  2301  and  2401  cause the adapters  30 ′ and  40 ′ to transfer to the sleep state, respectively. Only the adapter sleep state signal controllers  2302  and  2402  operate in the adapters  30  ‘and  40 ’ in the sleep state. 
     In the step S 1006 , the camera controller  2201  acquires the camera operation data and lens operation data again. Then, the flow proceeds to S 1007 . 
     In S 1007 , the camera controller  2201  determines whether there is a change in the camera operation data or the lens operation data acquired in S 1002  and S 1006 . In other words, it is determined whether or not the operation members  207  and  118  of the camera  20 ′ or the interchangeable lens&#39; are operated by the user. If the camera controller  2201  determines that the operation has been performed, the flow proceeds to step S 1008 ; otherwise (if there is no operation), the determination in the step S 1007  is repeated. 
     In S 1008 , the camera controller  2201  outputs an adapter activation signal to the third communication channel  300  via the camera sleep state signal controller  2202 . The processing of outputting the adapter activation signal to the third communication channel  300  is the same as the processing of outputting the lens activation signal to the first communication channel  100  described above. 
     Next, in  51009 , the adapter sleep state signal controllers  2302  and  2402  activate the adapter controllers  2301  and  2401 , respectively, and cause the adapters  30 ′ and  40 ′ to transfer to the normal state. Then, this processing ends. 
     This processing allows the camera controller  2201  to shift only the adapters  30  ‘and  40 ’ from the normal state to the sleep state, and from the sleep state to the normal state. 
     Further, the processing of transferring the adapters  30 ′ and  40 ′ from the sleep state to the normal state according to the operation of the adapter operation members  312  and  412  is similar to the method for transferring the interchangeable lens  10 ′ to the normal state according to the operation of the lens operation member  118  described above. In other words, in response to the operation of the adapter operation members  312  and  412  of the adapters  30 ′ and  40 ′ in the sleep state, the adapter activation request signal is transmitted to the camera  20 ′ using the third communication channel  300 . Then, the adapter activation signal is transmitted from the camera  20 ′ to the adapters  30 ′ and  40 ′ using the third communication channel  300 . Thereby, only the adapters  30 ′ and  40 ′ can be transferred from the sleep state to the normal state. 
     According to this embodiment, the camera  20 ′ can transfer the interchangeable lens  10 ′ and the adapters  30 ′ and  40 ′ to the normal state and the sleep state without depending on their states. Hence, a proper power control can be performed according to the use situations and types of the interchangeable lens and the adapter. For example, when the camera  20 ′ is driven by a battery and the camera  20 ′ detects that the battery power has lowered, only the adapter can be put into a sleep state, thereby making the camera imaging time as long as possible. 
     The embodiment described above has described two adapters arranged between the interchangeable lens  10  and the camera  20 , but the number of adapters is not limited to this embodiment. The present invention is applicable to an interchangeable lens, a camera, and an adapter constituting a camera system in which at least one adapter can be disposed between the interchangeable lens  10  and the camera  20 . 
     Other Embodiments 
     Embodiment(s) of the present invention can also be realized by a computer of a system or apparatus that reads out and executes computer executable instructions (e.g., one or more programs) recorded on a storage medium (which may also be referred to more fully as a ‘non-transitory computer-readable storage medium’) to perform the functions of one or more of the above-described embodiment(s) and/or that includes one or more circuits (e.g., application specific integrated circuit (ASIC)) for performing the functions of one or more of the above-described embodiment(s), and by a method performed by the computer of the system or apparatus by, for example, reading out and executing the computer executable instructions from the storage medium to perform the functions of one or more of the above-described embodiment(s) and/or controlling the one or more circuits to perform the functions of one or more of the above-described embodiment(s). The computer may comprise one or more processors (e.g., central processing unit (CPU), micro processing unit (MPU)) and may include a network of separate computers or separate processors to read out and execute the computer executable instructions. The computer executable instructions may be provided to the computer, for example, from a network or the storage medium. The storage medium may include, for example, one or more of a hard disk, a random-access memory (RAM), a read only memory (ROM), a storage of distributed computing systems, an optical disk (such as a compact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™), a flash memory device, a memory card, and the like. 
     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. 
     The present invention can realize a camera, an interchangeable lens apparatus, and an adapter apparatus, each of which can expedite a communication between the camera and the interchangeable lens apparatus and smooth a communication between the camera and the adapter apparatus. 
     The embodiments described above are merely representative examples, and various modifications and changes may be made to the embodiments when the present invention is implemented.