Patent Publication Number: US-6707992-B2

Title: Camera system having a communication system between a camera body and a photographing lens

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a camera system having a camera body and a photographing lens which is detachably attached to the camera body, and having a communication system between the camera body and the photographing lens, wherein a rear converter can be mounted between the camera body and the photographing lens. 
     2. Description of the Related Art 
     In conventional interchangeable lens cameras, the camera body obtains fundamental information on the photographing lens via predetermined data communication performed between the camera body and the photographing lens. However, if a rear converter is mounted between the camera body and the photographing lens, the data communication cannot be performed, so that it is impossible to use any useful features that the photographing lens may possess. 
     Even if the rear converter is simply provided with relay channels for connecting each communication channel of the camera body with a corresponding connecting channel of the photographing lens, the camera body cannot recognize the existence of such rear converter, so that the camera body cannot control operations of the photographing lens properly with only data received from the photographing lens. In addition, if the camera body is provided with additional electrical contacts for data communications between the camera body and the rear converter, the camera body needs to be provided with one or more additional components for the additional electrical contacts, and also switching between the communication channels becomes necessary, complicating the structure of the camera system. 
     SUMMARY OF THE INVENTION 
     The present invention provides a communication system between a camera body and a photographing lens of a camera system, wherein a rear converter can be mounted between the camera body and the photographing lens, and data on the rear converter can be used without any complicated structure. 
     For example, in an embodiment, an interchangeable lens camera system having a camera body, a photographing lens, and a rear converter which can be mounted between the camera body and the photographing lens, is provided, the camera body having a first group of contacts, the photographing lens having a second group of contacts, the camera body and the photographing lens communicating with each other via the first group of contacts and the second group of contacts with the first group of contacts being electrically connected with the second group of contacts, respectively, wherein the rear converter includes a group of relay channels via which the first group of contacts of the camera body are electrically connected with the second group of contacts of the photographing lens, respectively, in a state where the rear converter is mounted between the camera body and the photographing lens; a rear converter memory in which rear converter data on the rear converter is stored, the rear converter memory including at least one port electrically connected to corresponding at least one relay channel of the group of relay channels; and a rear converter controller which controls a reading operation of the rear converter data from the rear converter memory, the rear converter controller including at least one port electrically connected to corresponding at least one relay channel of the group of relay channels. The rear converter memory and the rear converter controller have a function to send the rear converter data to the camera body while the camera body and the photographing lens communicate with each other via the first group of contacts, the second group of contacts, and the group of relay channels. 
     It is desirable for the photographing lens to include a lens memory in which photographing lens data is stored; wherein the camera body includes a body controller which communicates with the lens memory to read the photographing lens data from the lens memory; wherein a portion of the photographing lens data serves as dummy data for the rear converter; and wherein the rear converter data is read out of the lens memory to be transmitted to the body controller in synchronization with an operation of the body controller in which the body controller receives the dummy data. 
     The body controller can be electrically connected to the rear converter controller via a first communication/control contact of each of the first group of contacts and the second group of contacts, and a data I/O contact of each of the first group of contacts and the second group of contacts. The photographing lens can include a lens controller which communicates with the body controller. The body controller is electrically connected to the lens controller via the first communication/control contact, a second communication/control contact of each of the first group of contacts and the second group of contacts, and at least one relay channel of the group of relay channels, wherein a handshake operation is performed between the body controller and the lens controller via the second communication/control contact. The lens controller sends out dummy data to enable the data I/O contact if inputting a command for the rear converter, which is issued by the body controller, via the data I/O contact, while the lens controller communicates with the body controller. The rear converter sends out the rear converter data to the data I/O contact in the case where the command is input via the data I/O contact. 
     In an embodiment, the rear converter receives the dummy data from the lens controller in the case where the lens controller receives the command; and the rear converter sends the rear converter data to the body controller in synchronization with an operation of the body controller in which the body controller receives the dummy data. 
     The body controller can be set to recognize one of a last one byte and a last few types of the photographing lens data as the dummy data for the rear converter. 
     In another embodiment, a rear converter which can be mounted between a camera body and a photographing lens of an interchangeable lens camera system, is provided, the camera body having a first group of contacts, the photographing lens having a second group of contacts, the camera body and the photographing lens communicating with each other via the first group of contacts and the second group of contacts with the first group of contacts being electrically connected to the second group of contacts, respectively, wherein the rear converter includes a group of relay channels via which the first group of contacts of the camera body are electrically connected with the second group of contacts of the photographing lens, respectively, in a state where the rear converter is mounted between the camera body and the photographing lens; a rear converter memory in which rear converter data is stored, the rear converter memory including ports electrically connected to at least one relay channel of the group of relay channels; and a rear converter controller which controls a reading operation of the rear converter data from the rear converter memory, the rear converter controller including ports electrically connected to at least one relay channel of the group of relay channels. The rear converter memory and the rear converter controller have a function to send the rear converter data to the camera body while the camera body and the photographing lens communicate with each other via the first group of contacts, the second group of contacts, and the group of relay channels. 
     Each of the first group of contacts and the second group of contacts can include a first communication/control contact via which the body controller sends a control signal to the lens controller; a second communication/control contact via which the lens controller sends a control signal to the body controller; and a data I/O contact for data communication. The first communication/control contact, the second communication/control contact, and the data I/O contact of the first group of contacts are electrically connected to the first communication/control contact, the second communication/control contact and the data I/O contact of the second group of contacts, respectively, via the group of relay channels. The rear converter memory and the rear converter controller are electrically connected to relay channels of the group of relay channels which correspond to the first communication/control contact and the data I/O contact. The rear converter memory and the rear converter controller have a function to send the rear converter data to the camera body after a commencement of a handshake operation between the body controller and the lens controller via the second communication/control contact in the case where the camera body commands the rear converter controller to send the rear converter data via the data I/O contact. 
     The present disclosure relates to subject matter contained in Japanese Patent Application No.2001-54543 (filed on Feb. 28, 2001) which is expressly incorporated herein by reference in its entirety. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be described below in detail with reference to the accompanying drawings in which: 
     FIG. 1 is a block diagram of fundamental elements of control systems of a camera body and a photographing lens of an SLR camera system having a communication system between the camera body and the photographing lens according to the present invention; 
     FIG. 2 is a block diagram of fundamental elements of the control system of the camera body; 
     FIG. 3 is a block diagram of fundamental elements of a communication/control system of the photographing lens; 
     FIG. 4 is a block diagram of fundamental components of a photographing lens which is provided with a lens controller which operates with a first power, and a peripheral circuit which operates with a second power; 
     FIG. 5 is a block diagram of fundamental components of a photographing lens which is provided with a lens controller and a peripheral circuit both of which operate with the first power; 
     FIGS. 6A and 6B show a flow charts for the first portion of a main process of the camera body, to which the present invention is applied; 
     FIG. 7 is a flow chart for the remaining portion of the main process of the camera body, to which the present invention is applied; 
     FIG. 8A is a flow chart for a communication identification process including of an old-type communication process and a new-type communication setting request process of the camera body; 
     FIG. 8B is a flow chart for operations of a photographing lens which are performed in accordance with operations of the new-type communication setting request process of the camera body; 
     FIG. 9 is a flow chart for the new-type communication setting request process of the camera body; 
     FIG. 10 is a flow chart for a camera state information setting process of the camera body; 
     FIG. 11 is a flow chart for an image-shake compensation data setting process of the camera body; 
     FIG. 12A is a block diagram of fundamental elements of a control system of the first embodiment of the photographing lens which incorporates an image-shake compensation device; 
     FIG. 12B is a conceptual diagram of a compensation lens (an image-stabilizing optical system) LC of the image-shake compensation device; 
     FIG. 13 is a flow chart for a main process of the first embodiment of the photographing lens; 
     FIG. 14 is a flow chart for a new-type communication setting process of the photographing lens; 
     FIG. 15 is a flow chart for a 1 ms-timer interrupt process of the first embodiment of the photographing lens; 
     FIG. 16 is a flow chart for the first half of an inverse-INT interrupt process of the first embodiment of the photographing lens; 
     FIG. 17 is a flow chart for the remaining half of the inverse-INT interrupt process of the first embodiment of the photographing lens; 
     FIG. 18 is a timing chart for the communication identification process from the moment the main switch of the camera body is turned ON to the moment immediately after the commencement of the new-type communication process; 
     FIG. 19A is a timing chart for a handshake operation performed between the camera body and the photographing lens at the commencement of the new-type communication process; 
     FIG. 19B is a timing chart for a handshake operation performed between the camera body and the photographing lens at the commencement of the new-type communication process; 
     FIG. 20 is a timing chart for an old-type communication process that is performed between the camera body and the photographing lens; 
     FIG. 21A is a timing chart for communication in the new-type communication process that is performed between the camera body and the photographing lens; 
     FIG. 21B is a timing chart for communication in the new-type communication process that is performed between the camera body and the photographing lens; 
     FIG. 22 is a block diagram of fundamental elements of a communication/control system of a second embodiment of the photographing lens  200  which incorporates a lens AF system; 
     FIG. 23 is a flow chart for a main process of the second embodiment of the photographing lens; 
     FIG. 24 is a flow chart for a 1 ms-timer interrupt process of the second embodiment of the photographing lens; 
     FIG. 25 is a flow chart for the first half of an inverse-INT interrupt process of the second embodiment of the photographing lens; 
     FIG. 26 is a flow chart for the remaining half of the inverse-INT interrupt process of the second embodiment of the photographing lens; 
     FIG. 27 is a schematic block diagram of fundamental elements of control systems of a photographing lens, a rear converter, and a camera body of an embodiment of an SLR camera system, wherein the rear converter is mounted between the camera body and the photographing lens; 
     FIG. 28 is a timing chart for the communication identification process, from the moment the main switch of the camera body is turned ON to the moment immediately after the commencement of the new-type communication process in the embodiment of the SLR camera system shown in FIG. 27; 
     FIG. 29 is a timing chart for communications in the new-type communication process that is performed between the camera body and the new type of photographing lens, and between the rear converter and the camera body in the embodiment of the SLR camera system shown in FIG. 27; 
     FIG. 30 is a flow chart for the main process of the rear converter; 
     FIG. 31 is a flow chart for the new-type communication setting process of the rear converter; and 
     FIG. 32 is a flow chart for the inverse-INT interrupt process of the rear converter. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows fundamental elements of control systems of a camera body and an interchangeable photographing lens of an embodiment of an SLR camera system to which the present invention is applied. The camera body  100  is provided with a body CPU (body controller)  111  serving as a controller which comprehensively controls the overall operations of the SLR camera system. The camera body  100  is provided with a body mount  103  to which the photographing lens  200  is mounted. A group of communication/control contacts (body communication line)  104  are provided on the body mount  103 . The group of communication/control contacts  104  consists of six contacts in this particular embodiment. One of the six contacts serves as a power contact (constant-voltage contact) for supplying a first power from the camera body  100  to low power elements (e.g., a ROM) provided in the photographing lens  200  to drive the low power elements, while another one of the six contacts serves as a control terminal via which a ROM provided in the photographing lens  200  is enabled or disabled (i.e., turned ON or OFF). A power contact  105  (VPZ) via which a second power is supplied from the camera body  100  to the photographing lens  200  is provided on the body mount  103 . The power capacity of the second power that is supplied from the power contact  105  (VPZ) to the photographing lens  200  is substantially greater than that of the first power that is supplied from the aforementioned constant-voltage contact of the group of communication/control contacts  104 . Although the supply voltage of the second power is greater than the supply voltage of the first power, the supply voltage of the second power can be identical to the supply voltage of the first power or even smaller than the supply voltage of the first power as long as the power capacity of the second power is substantially greater than the power capacity of the first power. 
     Although it is desirable that the group of communication/control contacts  104  and the power contact  105  (VPZ) be provided on the body mount  103 , the group of communication/control contacts  104  and the power contact  105  (VPZ) can be provided behind the body mount  103  in a mirror box of the camera body  100 , in which a quick-return mirror is positioned. Alternatively, it is possible that the group of communication/control contacts  104  be provided on the body mount  103  and the power contact  105  (VPZ) be provided behind the body mount  103  in the mirror box of the camera body  100 . 
     FIG. 2 shows fundamental elements of the control system of the camera body  100 . A photometering switch SWS, a release switch SWR, a main switch SWMAIN, an image-shake compensation switch SW 1  and an AF switch SWAF are connected to the body CPU  111 , which serves as a controller that comprehensively controls the overall operations of the SLR camera system. 
     The power to peripheral circuits of the camera body  100  is turned ON and OFF when the main switch SWMAIN is turned ON and OFF, respectively. The power from a battery  113  accommodated in the camera body  100  is supplied to each peripheral circuit of the camera body  100  via a regulator (DC/DC converter)  116  when the main switch SWMAIN is turned ON, and the power from the battery  113  to each peripheral circuit of the camera body  100  is cut off when the main switch SWMAIN is turned OFF. The body CPU  111  is always supplied with power from the battery  113  via the regulator  116 , so that the body CPU  111  is in operation at all times. 
     The camera body  100  is provided with a strobe circuit  121 , a mirror circuit  123 , a shutter circuit  125 , a film-winding circuit  127 , a photometering circuit  129  and a distance measuring circuit  131 , which are all connected to the body CPU  111 . The photometering switch SWS is turned ON when a release button (not shown) is the camera body is depressed by half a step, and the release switch SWR is turned ON when the release button is fully depressed. Immediately after the photometering switch SWS is turned ON, the body CPU  111  actuates the photometering circuit  129  to perform a photometering operation. At the same time, the body CPU  111  calculates and sets an optimum shutter speed and an optimum aperture value (f-number), and actuates the strobe circuit  121  to perform a strobe charging process as needed. Furthermore, the body CPU  111  actuates the distance measuring circuit  131  to determine an amount of defocus, to perform an autofocus process if an autofocus mode has been set via the AF switch SWAF. Immediately after the release switch SWR is turned ON, the body CPU  111  actuates the shutter circuit  125  to drive a focal plane shutter mechanism (not shown) to expose a film frame. Upon completion of an exposure, the body CPU  111  actuates the film-winding circuit  127  to wind up film by one frame and at the same time to charge the focal plane shutter mechanism. 
     When the new-type photographing lens (e.g., a KAF III type photographing lens having a lens CPU, a lens ROM, and all of the communication functions which correspond with those of the camera body  100 )  200  is mounted to the camera body  100 , during the time the main switch SWMAIN is ON, the body CPU  111  turns ON a switch circuit  115  to supply the power from the battery  113  as the aforementioned second power to the photographing lens  200  via the power contact  105  (VPZ) of the camera body  100  and associated power contact  205  (VPZ) of the photographing lens  200 , which is in contact with the power contact  105  (VPZ). In addition, if an image-shake compensation mode has been set via the image-shake compensation switch SW 1 , and if the photographing lens  200  is provided with an image-shake compensation device, the body CPU  111  outputs an image-shake compensation command to the photographing lens  200  via lens communication to make the photographing lens  200  perform an image-shake compensation operation. If the photographing lens  200  mounted to the camera body  100  is further provided therein with a lens AF system, the body CPU  111  outputs defocus data (e.g., the amount of driving of an AF motor  261  (see FIG. 12A) and the direction of driving of the AF motor in the photographing lens  200 ) to the photographing lens  200  via lens communication to make the photographing lens  200  perform a lens autofocus process. 
     As shown in FIG. 12A, an encoder  231 , the AF motor (focusing lens driving device)  261 , an AF lens group (focusing lens group) Lf, and the lens CPU  211  constitute a focus adjusting system (electrical component). 
     The photographing lens  200  is provided on a lens mount  203  thereof with a group of communication/control contacts (lens communication line)  204  and the power contact  205  (VPZ). The group of communication/control contacts  204  and the power contact  205  (VPZ) come into contact with the group of communication/control contacts  104  and the power contact  105  (VPZ) of the camera body  100 , respectively, when the photographing lens  200  is mounted to the body mount  103  of the camera body  100  via the lens mount  203 . The photographing lens  200  is provided therein with a lens CPU (LCPU/lens controller/electronic device)  211 , a lens ROM (LROM/lens memory/nonvolatile lens memory)  221 , the encoder  231  and a peripheral circuit  241 . Various modes and parameters are stored in the lens ROM  221 . A current focal length (zoom code) and a photographic distance are detected via the encoder  231 . The peripheral circuit  241  includes, for example, as shown in FIG. 12A, image-shake compensation motors (X-motor  254  and Y-motor  257 ), the AF motor  261 , and a power zoom motor (power zoom driving device)  264 , which are all provided in the photographing lens  200 . Note that the power zoom motor  264  is connected to a lens group Lz, wherein the lens group Lf and the lens group Lz constitute at least part of a zoom lens system of the photographing lens  200 . 
     The group of communication/control contacts  104  of the camera body  100  consists of six contacts: a first contact  104   a  (Fmin 1 /Inverse-SCKL), a second contact  104   b  (Fmin 2 /DATAL), a third contact  104   c  (Fmin 3 /RESL), a fourth contact  104   d  (CONTL), a fifth contact  104   e  (Fmax 1 /Inverse-FBL) and a sixth contact  104   f  (Fmax 2 /Inverse-FLB). Likewise, the group of communication/control contacts  204  of the photographing lens  200  consists of six contacts: a first contact  204   a  (Fmin 1 /Inverse-SCKL), a second contact  204   b  (Fmin 2 /DATAL), a third contact  204   c  (Fmin 3 /RESL), a fourth contact  204   d  (CONTL), a fifth contact  204   e  (Fmax 1 /Inverse-FBL) and a sixth contact  204   f  (Fmax 2 /Inverse-FLB) which come into contact with the first through sixth contacts  104   a  through  104   f  respectively, when the photographing lens  200  is mounted to the camera body  100 . 
     The power line from port P 13  of the body CPU  111  to the fourth contact  104   d  constitutes a first body power line for supplying the first power to the photographing lens  200 . The power line from the battery  113  to the power contact  105  (via the switch circuit  115 ) constitutes a second body power line for supplying the second power to the photographing lens  200 . The power line from the fourth contact  204   d  to a port CONT of the lens ROM  221  constitutes a first lens power line for supplying power from the camera body  100  to the photographing lens  200 . The power line from the power contact  205  to a regulator  243  and to a switching circuit  242  constitutes a second lens power line for supplying power from the camera body  100  to the lens CPU  211 . As shown in FIG. 1, the second power that is output from the camera body  100  to be input to the photographing lens  200  via the power contacts  105  and  205  (VPZ) is supplied to the lens CPU  211  via the regulator  243  of the photographing lens  200  and also to the peripheral circuit  241  via a switching circuit  242  of the photographing lens  200 . The lens ROM  221  of the photographing lens  200  operates with constant voltage power (the first power) supplied from the fourth contact  204   d  (CONTL), whereas the lens CPU  211  operates with the second power having a large power capacity supplied from the power contact (VPZ)  205 . The processing speed and the throughput of a CPU is generally proportional to the power consumption of the CPU. Accordingly, in the present embodiment of the SLR camera system to which the present invention is applied, providing the second power having a large power capacity to the photographing lens  200  makes it possible for the photographing lens  200  be provided therein with not only a CPU which achieves a high throughput, but also high power components (i.e., components which require a large current) such as a lens motor and an image-shake compensation device. 
     FIG. 3 is a block diagram of fundamental elements of a communication/control system of the photographing lens  200 . The first contact  204   a  (Fmin 1 /Inverse-SCKL), the second contact  204   b  (Fmin 2 /DATAL), the third contact  204   c  (Fmin 3 /RESL), and the fourth contact  204   d  (CONTL) of the group of communication/control contacts  204 , of the photographing lens  200 , are connected to four ports RES, SIO, Inverse-SCK, and CONT of the lens ROM  221 , respectively. 
     The port RES of the lens ROM  221  serves as an input port via which the lens ROM  221  inputs a reset signal that changes the state of the lens ROM  221  from a disabled state to an enabled state. The port SIO of the lens ROM  221  serves as an I/O port for serial communication. The port Inverse-SCK of the lens ROM  221  serves as an input port via which the lens ROM  221  inputs a clock signal for communication from the camera body  100 . The port CONT of the lens ROM  221  serves an input port via which the lens ROM  221  inputs a constant voltage power (the first power) from the camera body  100 . 
     The lens ROM  221  operates in accordance with the first power (constant voltage power), which is supplied from the camera body  100  to be applied to the port CONT of the lens ROM  221 . The lens ROM  221  is set to change the state of the lens ROM  221  from a disabled state to an enabled state by a reset signal, which is input via the port RES of the lens ROM  221  to enter the enabled state. Lens data written in the lens ROM  221  is read out therefrom to be output to the camera body  100  via the port SIO of the lens ROM  221 , in synchronization with the clock signal input, via the port Inverse-SCK. The port RES of the lens ROM  221  and the third contact  204   c  (Fmin 3 /RESL), which is connected to the port RES, also serve as a control line for changing the state of the lens ROM  221  between an enabled state and a disabled state. Namely, the lens ROM  221  operates while the first power is being supplied to the fourth contact  204   d  (CONTL), and the lens ROM  221  is set to change the state thereof from a disabled state to an enabled state if the level of the third contact  204   c  (Fmin 3 /RESL) falls to a low level, and the lens ROM  221  is set to change the state of the lens ROM  221  from an enabled state to a disabled state if the level of the third contact  204   c  (Fmin 3 /RESL) rises to a high level. The timing chart thereof is shown in FIG.  20 . 
     As shown in FIG. 3, the lens CPU  211  is provided with eight ports RXD, TXD, TXDEN, Inverse-SCK, P 00 , P 01 , INT and VCC, and the photographing lens  200  is provided with first through fourth high input voltage proof Schmitt inverters VCC1, VCC2, VCC3 and VCC4. The first contact  204   a  (Fmin 1 /Inverse-SCKL) is connected to the port Inverse-SCK of the lens CPU  211  via the second and third Schmitt inverters VCC2 and VCC3, and the second contact  204   b  (Fmin 2 /DATAL) is connected to the port RXD of the lens CPU  211  and also to each of the two ports TXD and TXDEN of the lens CPU  211  via a first I/O protection circuit  212 . 
     The port RXD of the lens CPU  211  serves as a data input port. The port TXD of the lens CPU  211  serves as a data output port. The port TXDEN of the lens CPU  211  serves as a control port via which the lens CPU  211  determines whether data can be output from the port TXD of the lens CPU  211 . The port Inverse-SCK of the lens CPU  211  serves as an input port via which the lens CPU  211  inputs a clock signal for communication from the camera body  100 . 
     When the control port TXDEN of the lens CPU  211  is at a high level, if the level of a data output port TXD of the lens CPU  211  rises to a high level, a field effect transistor (FET) of the first I/O protection circuit  212  is turned OFF while a transistor of the first I/O protection circuit  212  is turned ON to thereby cause the level of port  212   a  to rise to a high level. On the other hand, if the level of the data output port TXD of the lens CPU  211  falls to a low level when the control port TXDEN of the lens CPU  211  is at a high level, the field effect transistor (FET) of the first I/O protection circuit  212  is turned ON while the transistor of the first I/O protection circuit  212  is turned OFF to thereby cause the level of port  212   a  to fall to a low level. Therefore, when the control port TXDEN of the lens CPU  211  is at a high level, the level of the data output port TXD of the lens CPU  211  is output from the first I/O protection circuit  212  via port  212   a  to be input to the second contact  204   b  (Fmin 2 /DATAL). 
     Because each of the field effect transistor (FET) and the transistor of the first I/O protection circuit  212  is OFF when the control port TXDEN is at a low level, port  212   a  is in a high impedance state regardless of the level of the data output port TXD of the lens CPU  211 . 
     The sixth contact  204   f  (Fmax 2 /Inverse-FLB) is connected to each of the two ports P 00  and P 01  of the lens CPU  211  via a second I/O protection circuit  213 , while the fifth contact  204   e  (Fmax 1 /Inverse-FBL) is connected to the port INT of the lens CPU  211  via the fourth high input voltage proof Schmitt inverter VCC4. The port P 00  of the lens CPU  211  serves as an output port while the port P 01  of the lens CPU  211  serves as a control port via which the lens CPU  211  determines whether data can be output from the port P 00 . The port INT of the lens CPU  211  serves as an input port via which the lens CPU  211  inputs an interrupt signal. 
     When the control port P 01  of the lens CPU  211  is at a high level, if the level of the output port P 00  of the lens CPU  211  rises to a high level, a field effect transistor (FET) of the second I/O protection circuit  213  is turned OFF while a transistor of the second I/O protection circuit  213  is turned ON to thereby cause the level of port  213   a  to rise to a high level. On the other hand, if the level of the output port P 00  of the lens CPU  211  falls to a low level when the control port P 01  of the lens CPU  211  is at a high level, the field effect transistor (FET) of the second I/O protection circuit  213  is turned ON while the transistor of the second I/O protection circuit  213  is turned OFF to thereby cause the level of port  213   a  to fall to a low level. Therefore, when the output port P 00  of the lens CPU  211  is at a high level, the level of the output port P 00  of the lens CPU  211  is output from the second I/O protection circuit  213  via port  213   a  to be input to the sixth contact  204   f  (Fmax 2 /Inverse-FLB). 
     Because each of the field effect transistor (FET) and the transistor of the second I/O protection circuit  213  is OFF when the control port P 01  is at a low level, port  213   a  is in a high impedance state regardless of the level of the output port P 00  of the lens CPU  211 . 
     The power contact  205  (VPZ) is connected to the power port VCC of the lens CPU  211  via a regulator  243 . The lens CPU  211  operates with constant voltage supplied from the regulator  243  to the power port VCC. 
     Selection between the communication channel for communication of the body CPU  111  with the lens ROM  221  (i.e., lens ROM communication/old-type communication) and the communication channel for communication of the body CPU  111  with the lens CPU  211  (i.e., new-type communication) depends on a reset signal input to the third contact  204   c  (Fmin 3 /RESL). If the level of the input port RES of the lens ROM  221  rises to a high level, the lens ROM  221  enters a disabled state and the SIO port of the lens ROM  221  enters a high impedance state. This makes the aforementioned new-type lens communication between the body CPU  111  and the lens CPU  211  possible. 
     The first contact  204   a  (Fmin 1 /Inverse-SCKL), the second contact  204   b  (Fmin 2 /DATAL), the third contact  204   c  (Fmin 3 /RESL), the fifth contact  204   e  (Fmax 1 /Inverse-FBL) and the sixth contact  204   f  (Fmax 2 /Inverse-FLB) maintain compatibility with conventional camera systems using interchangeable lenses in which serial communication between camera body and interchangeable lens is performed without using a ROM (lens ROM) provided in an interchangeable lens. For instance, in order to maintain compatibility with a camera body which can obtain the minimum f-number and the maximum f-number from the photographing lens mounted to the camera body, diodes for making the first, second, third, fifth and sixth contacts  204   a ,  204   b ,  204   c ,  204   e  and  204   f  serve as aperture information contacts so that the camera body can input data on the minimum f-number (the f-number at maximum aperture) via the first, second and third contacts  204   a ,  204   b  and  204   c  and so that the camera body can input data on the maximum f-number (the f-number at minimum aperture) via the fifth and sixth contacts  204   e  and  204   f  are selectively provided in a manner such that the camera body can distinguish between the maximum f-number and the minimum f-number by checking continuity of each contact via the diodes. 
     FIG. 4 is a block diagram of fundamental components of a photographing lens  200   a  which is provided with a lens CPU  211   a  and a peripheral circuit  241   a . The lens CPU  211   a  operates with the first power supplied from the fourth contact  204   d  (CONTL), while the peripheral circuit  241   a  operates with power supplied from the power contacts  105  and  205  (VPZ). In the photographing lens  200   a  shown in FIG. 4, the power supplied from the power contacts  105  and  205  (VPZ) is supplied to the peripheral circuit  241   a  via the switching circuit  242 . 
     FIG. 5 is a block diagram of fundamental components of a photographing lens  200   b  which is provided with a lens CPU  211   b  and a peripheral circuit  241   b . The lens CPU  211   b  operates with the first power supplied from the fourth contact  204   d  (CONTL). The photographing lens  200   b  shown in FIG. 5 is not provided with either a power contact or a regulator corresponding to the power contact  205  (VPZ) or the regulator  243 , respectively. Each of the lens CPU  211   b  and the peripheral circuit  241   b  operates with the first power supplied from the fourth contact  204   d  (CONTL). 
     In the photographing lens  200   a  shown in FIG. 4, the camera body  100  supplies the first power and the second power to the fourth contacts  104   d  and  204   d  (CONTL) and the power contacts  105  and  205  (VPZ), respectively. On the other hand, in the photographing lens  200   b  shown in FIG. 5, the camera body  100  supplies only the first power to the fourth contacts  104   d  and  204   d  (CONTL). 
     Fundamental operations of the camera body  100  and the photographing lens  200  will be hereinafter discussed in detail with reference to the flow charts shown in FIGS. 6 through 11 and the timing charts shown in FIGS. 18 through 21B. FIG. 6 shows a flow chart for the main process of the camera body  100  which is performed by the body CPU  111 . Control enters the main process immediately after the battery  113  is loaded into the camera body  100 . The camera body  100  performs both old-type communication (lens ROM communication) and new-type communication between the camera body  100  and the photographing lens  200 , whereas the camera body  100  performs only the old-type communication (lens ROM communication) between the camera body  100  and the photographing lens  200  if the photographing lens  200  is of any other type which is not provided with any CPU corresponding to the lens CPU  211  of the photographing lens  200  but provided with only a lens ROM, and which accordingly does not have any communication capability of the photographing lens  200 . It should be noted that operations or processes having step numbers bearing a prefix “CS” are related to control/operation of the camera body  100  and that operations or processes having step numbers bearing a prefix “LS” are related to control/operation of the photographing lens  200 . 
     Fundamental commands for discussion of the present embodiment of the SLR camera system are listed below. All the commands listed below are those which are transmitted from the camera body  100  to the photographing lens  200 . 
     COMMANDS TRANSMITTED FROM CAMERA BODY TO LENS IN ORDER TO COMMAND LENS TO TRANSMIT DATA TO CAMERA BODY 
       70 : Command for making the photographing lens send a lens status thereof to the camera body. 
       71 : Command for making the photographing lens send a lens status thereof to the camera body and for making the lens CPU enter a sleep mode together with the body CPU. 
       72 : Command for making the photographing lens send information on functions that the photographing lens possesses, such as an image-shake compensation function and a lens autofocus function, to the camera body. 
       7 F: Command for a rear converter. 
     COMMANDS FOR DATA TRANSMISSION FROM CAMERA BODY TO LENS 
     B 0 : Command for sending data to the photographing lens. 
     B 1 : Command for sending data to the photographing lens and for making the lens CPU enter a sleep mode. 
     B 2 : Command for sending data on a driving-amount for the AF motor provided in the photographing lens to the photographing lens. 
     INSTRUCTION COMMANDS TRANSMITTED FROM CAMERA BODY TO LENS 
     D 0 : Command for making the lens CPU enter the sleep mode. 
     D 1 : Command for turning OFF an image-shake compensation function. 
     D 2 : Command for turning ON the image-shake compensation function. 
     D 3 : Command for stopping the driving of the AF motor provided in the photographing lens. 
     D 4 : Command for resuming the driving of the AF motor provided in the photographing lens. 
     In the main process shown in FIG. 6, firstly it is determined whether the main switch SWMAIN is ON (step CS 101 ). The operation at step CS 101  is repeated until the main switch SWMAIN is turned ON. If the main switch SWMAIN is turned ON (if YES at step CS 101 ), a communication identification process (i.e., an old-type communication process at step CS 103  and a new-type communication setting request process at step CS 105 ) is performed. Command  72  is transmitted to the photographing lens to receive data therefrom (step CS 107 ). Command  72  commands the lens CPU  211  to output information on the functions that the photographing lens possesses to the body CPU  111 . The functions of the photographing lens can include, e.g., an image-shake compensation function, a lens autofocus function and other functions which operate with power (the second power) supplied from the power contacts VPZ. In the present embodiment of the SLR camera system, such information on functions that the photographing lens has is represented by 1-byte data (8-bit data), wherein the sixth bit represents the presence or absence of the autofocus function while the fourth bit represents the present or absence of the image-shake compensation function. Upon receiving command  72 , the lens CPU  211  of the (new-type) photographing lens  200  outputs information on functions that the photographing lens  200  possesses to the body CPU  111 . FIG. 18 shows a timing chart for the aforementioned communication identification process from the moment the main switch SWMAIN is turned ON to the moment immediately after the commencement of the new-type communication process. FIGS. 19A and 19B each show a timing chart for a handshake operation performed between the camera body  100  and the photographing lens  200  at the commencement of the communication process. FIG. 20 shows a timing chart for the old-type communication process. FIGS. 21A and 21B show timing charts for the new-type communication process. 
     After the operation at step CS 107 , the body CPU  111  sets a lens sleep flag SLP to “0” (step CS 109 ). The lens sleep flag SLP “1” or “0” indicates that the lens CPU  211  is in the sleep mode (low power operation mode) or not in the sleep mode, respectively. The operations or processes at steps CS 103  through CS 109  are performed when the main switch SWMAIN is turned from OFF to ON. Thereafter, the operations at and after step CS 111  are repeated. 
     At step CS 111 , ON/OFF states of all the switch ports are input. Subsequently, a camera state information setting process is performed (step CS 113 ). In the camera state information setting process, the information on the current states of some specific switches and a flash charging system which is to be transmitted to the lens CPU  211  via the new-type communication is prepared. Subsequently, the old-type communication process is performed (step CS 115 ), and it is determined whether a photographing lens is mounted to the camera body  100  (step CS 117 ). If no photographing lens is mounted (if YES at step CS 117 ), each of the fourth contact  104   d  (CONTL) and the power contact  105  (VPZ) is set to a low level (step CS 119 ), and control returns to step CS 101 . If it is determined at step CS 117  that a photographing lens is mounted (if NO at step CS 117 ), it is determined whether a new-type flag is “1”, i.e., whether the photographing lens currently mounted to the camera body  100  is the (new-type) photographing lens  200  (step CS 121 ). The new-type flag “1” indicates that the photographing lens currently mounted to the camera body  100  is the (new-type) photographing lens  200 . If the new-type flag is “1” (if YES at step CS 121 ), it is determined whether a power hold flag PH is “0”, i.e., whether the camera body  100  is not in a power hold state (step CS 123 ). If the power hold flag PH is “0” (if YES at step CS 123 ), it is determined whether the lens sleep flag SLP is “1” (step CS 125 ). If the lens sleep flag SLP is “1” (if YES at step CS 125 ), control returns to step CS 111  since the photographing lens  200  is already in a sleep mode. If it is determined at step CS 125  the lens sleep flag SLP is not “1”, command B 1  is transmitted to the lens CPU  211  to make the photographing lens  200  enter the sleep mode (step CS 127 ). Subsequently, the lens sleep flag SLP is set to “1” (step CS 129 ), and control returns to step CS 111 . 
     If it is determined at step CS 123  that the power hold flag PH is not “0” (if NO at step CS 123 ), command B 0  is transmitted to the lens CPU  211  to start the lens CPU  211  (step CS 131 ), and the lens sleep flag SLP is set to “0” (step CS 133 ). 
     Subsequently, it is determined whether a rear converter  300  (see FIG. 27) is mounted between the camera body and the photographing lens via the result of the old-type communication process at step CS 115  (step CS 134   a ). If the rear converter  300  is mounted between the camera body and the photographing lens  200  (if YES at step CS 134   a ), command  7 F, which commands the rear converter  300  to send information (data) thereon to the camera body, is transmitted to the camera body  100  (step CS 134   b ), and control proceeds to step CS 135 . If no rear converter is mounted between the camera body and the photographing lens (if NO at step CS 134   a ), control proceeds straight from step CS 134   a  to step CS 135 . At step CS 135  it is determined whether an image-shake compensating type lens flag is “1”, i.e., whether the photographing lens  200  mounted to the camera body  100  is provided with an image-shake compensation device. If the image-shake compensating type lens flag is “1” (if YES at step CS 135 ), an image-shake compensation data setting process, in which predetermined flags and data on image-shake compensation are set, is performed (step CS 137 ), and control proceeds to step CS 139 . If the image-shake compensating type lens flag is not “1” (if NO at step CS 135 ), control skips step CS 137  to proceed straight from step CS 135  to step CS 139 . If it is determined at step CS 121  that the new-type flag is not “1”, control proceeds straight from step CS 121  to step CS 139 . 
     At step CS 139  it is determined whether a SWMAIN flag is “0”, i.e., whether the main switch SWMAIN has been turned from ON to OFF. If it is determined at step CS 139  that the SWMAIN flag is not “1” (if NO at step CS 139 ), it is determined whether the photometering switch SWS is ON (step CS 141 ). If the photometering switch SWS is not ON (if NO at step CS 141 ), control returns to step CS 111 . If the photometering switch SWS is ON (if YES at step CS 141 ), control proceeds to step CS 151 . If it is determined at step CS 139  that the SWMAIN flag is “1”, it is determined whether the new-type flag is “1” (step CS 143 ). If it is determined at step CS 143  that the new-type flag is not “1”, control returns to step CS 101 . If it is determined at step CS 143  that the new-type flag is “1” (i.e., that the (new-type) photographing lens  200  is currently mounted to the camera body  100 ), it is determined at step CS 145  whether a second power flag VpzONCPU is “1”, i.e., whether the photographing lens  200  mounted to the camera body  100  is of a type which operates with power supplied from the power contact  105  (VPZ). If it is determined at step CS 145  that the second power flag VpzONCPU is “1” (if YES at step CS 145 ), the port VPZ is turned OFF, i.e., power supplied to the power contact  105  (VPZ) is cut off (step CS 147 ), and control returns to step CS 101 . If it is determined at step CS 145  that the second power flag VpzONCPU is not “1” (if NO at step CS 145 ), control returns to step CS 101  since the photographing lens mounted to the camera body  100  does not operate with power supplied from the power contact  105  (VPZ). 
     Operations which are performed after it is determined at step CS 141  that the photometering switch SWS is ON will be hereinafter discussed with reference to the flow chart shown in FIG.  7 . 
     If it is determined at step CS 141  that the photometering switch SWS is ON (if YES at step CS 141 ), a photometering operation in which photometric data is input from a photometering sensor and an exposure arithmetic operation are performed in accordance with a currently-selected photometering mode and a currently-selected exposure mode, respectively (step CS 151 ). Subsequently, AF sensor data is input from an AF sensor in accordance with a currently-selected AF mode, while a predetermined AF arithmetic operation necessary for attaining an in-focus state is performed in accordance with the input AF sensor data (step CS 153 ). 
     Subsequently, it is determined whether the new-type flag is “1” (step CS 155 ). If the new-type flag is “1” (if YES at step CS 155 ), it is determined whether a lens AF flag is “1”, i.e., whether the photographing lens  200  mounted to the camera body  100  has a lens autofocus function (step CS 157 ). If the lens AF flag is “1” (if YES at step CS 157 ), it is determined whether an AFON flag is “1” (step CS 159 ). The AFON flag “1” indicates that the AF function is ON, i.e., the AF function is in operation. If the AFON flag is “1” (if YES at step CS 159 ), data on a driving-amount of an AF lens (focusing lens group) of the photographing lens is transmitted to the lens CPU  211  (step CS 161 ), and subsequently control proceeds to step CS 163 . If at least one of the new-type flag, the lens AF flag and the AFON flag is not “1”, control skips the operation at step CS 161  and proceeds to step CS 163 . 
     At step CS 163  it is determined whether an in-focus state has been obtained. If an in-focus state has not been obtained (if NO at step CS 163 ), control returns to step CS 111  shown in FIG.  6 . Accordingly, in the present embodiment of the SLR camera system, an in-focus priority control in which the shutter cannot be released unless an in-focus state is obtained is adopted. A release priority control in which the shutter can be released even in an out-of-focus state can be adopted. In this case, the operation at step CS 163  is omitted. 
     If it is determined at step CS 163  that an in-focus state has been obtained (if YES at step CS 165 ), it is determined whether the release switch SWR is ON (step CS 165 ). If the release switch SWR is OFF (if NO at step CS 165 ), control returns to step CS 111 . 
     If the release switch SWR is ON (if YES at step CS 165 ), it is determined whether the new-type flag is 1 (step CS 167 ). If the new-type flag is 1 (if YES at step CS 167 ), a release stage indicator RLS is set to “1”, and information on the indicator RLS “1” is transmitted to the lens CPU  211  (step CS 169 ). Subsequently control proceeds to step CS 171 . If the new-type flag is not 1 (if NO at step CS 167 ), control skips step CS 169  to proceed straight from step CS 167  to step CS 171 , so that the information on the indicator RLS “1” is not transmitted to the lens CPU  211 . The release stage indicator RLS “1” informs the photographing lens  200  of a stage at which the quick return mirror is moving toward the retracted position thereof after the release switch SWR has been turned ON. 
     At step CS 171  the mirror circuit  123  is actuated to drive a mirror drive motor so that the quick return mirror of the camera body  100  moves up to a retracted position. Subsequently, it is determined whether the new-type flag is 1 (step CS 173 ). If the new-type flag is 1 (if YES at step CS 173 ), the release stage indicator RLS is set to “2”, and information on the stage indicator RLS “2” is transmitted to the lens CPU  211  (step CS 175 ). Subsequently, control proceeds to step CS 177 . If the new-type flag is not 1 (if NO at step CS 173 ), control skips step CS 175  to proceed straight from step CS 173  to step CS 177 , so that the information on the indicator RLS “2” is not transmitted to the lens CPU  211 . The release stage indicator RLS “2” informs the photographing lens  200  of a stage at which a film frame is under exposure after the quick return mirror has moved up to the retracted position thereof. 
     At step CS 177  the shutter circuit  125  is actuated to drive the focal plane shutter mechanism to perform an exposure operation. Upon completion of the exposure operation, it is determined whether the new-type flag is 1 (step CS 179 ). If the new-type flag is 1 (if YES at step CS 179 ), the release stage indicator RLS is set to “3”, and information on this indicator RLS “3” is transmitted to the lens CPU  211  (step CS 181 ). Subsequently control proceeds to step CS 183 . If the new-type flag is not 1 (if NO at step CS 179 ), control skips step CS 181  to proceed straight from step CS 179  to step CS 183 , so that the information on the indicator RLS “3” is not transmitted to the lens CPU  211 . The release stage indicator RLS “3” informs the photographing lens  200  of a stage at which film is wound after the exposure operation has been completed. 
     At step CS 183  a film-winding operation in which the film-winding circuit  127  is actuated to drive a film motor (shutter charge motor) to wind film by one frame is performed while a shutter charge operation is performed (step CS 183 ). Subsequently, it is determined whether the new-type flag is “1” (step CS 185 ). If the new-type flag is 1 (if YES at step CS 185 ), the release stage indicator RLS is set to “0”, and information on this indicator RLS “0” is transmitted to the lens CPU  211  (step CS 187 ). Subsequently control returns to step CS 111 . If the new-type flag is not 1 (if NO at step CS 185 ), control skips step CS 187  to return straight from step CS 185  to step CS 111 , so that the information on the indicator RLS “0” is not transmitted to the lens CPU  211 . The release stage indicator RLS “0” informs the photographing lens of a stage at which the aforementioned film-winding operation has been completed, i.e., a state at which the shutter can be released. 
     In the above described release process at and after step CS 151 , the release stage indicator RLS that indicates a stage in the release process is transmitted to the lens CPU  211  each time each stage in the release process is completed, if the (new-type) photographing lens  200  is mounted to the camera body  100 . This makes it possible for the photographing lens  200  to perform operations which correspond to operational state and stage of the camera body  100 . 
     The communication identification process, which is composed of the old-type communication process at step CS 103  and the new-type communication setting request process at step CS 105 , will be hereinafter discussed in detail with reference to the flow charts shown in FIGS. 8A and 8B. FIG. 8A shows operations of the communication identification process, while FIG. 8B shows operations of the photographing lens  200  which are performed by the lens CPU  211  in accordance with operations of the new-type communication setting request process at step CS 105 . The new-type communication setting request process at step CS 105  includes operations at steps CS 203  through CS 215  shown in FIG.  8 A. 
     Control enters the communication identification process immediately after the power of the camera body  100  is turned ON. The communication identification process is performed to identify the type of photographing lens  200  and communication protocols used therefor. Immediately after the power of the camera body  100  is turned ON (i.e., immediately after it is determined that the main switch SWMAIN is ON at step CS 101 ), control enters the old-type communication process at step CS 103 . In the old-type communication process at step CS 103 , it is determined whether the photographing lens currently mounted to the camera body  100  is provided with a lens ROM from which the body CPU  111  can read out any predetermined lens data, and subsequently the old-type communication (lens ROM communication) is performed in accordance with communication protocols used for the photographing lens having such a lens ROM, if it is determined that the photographing lens currently mounted to the camera body  100  is provided with such a lens ROM. In the lens ROM communication, predetermined lens data written in the lens ROM  221  are read therefrom. This lens data includes data on the lens type of the currently mounted photographing lens. 
     Upon completion of the lens ROM communication, it is determined, from the result of the lens ROM communication, whether the photographing lens  200  currently mounted to the camera body  100  is a new type of photographing lens (step CS 203 ). If it is determined that a new type of photographing lens is not mounted to the camera body  100  (if NO at step CS 203 ), control exits the communication identification process, and from this time on only the old-type communication (lens ROM communication) is performed between the photographing lens  200  and the camera body  100 . 
     If it is determined at step CS 203  that the photographing lens  200  mounted to the camera body  100  is a new type of photographing lens (if YES at step CS 203 ), it is determined whether the currently-mounted (new-type) photographing lens  200  is of a type (VpzON type) which operates with power supplied from the power contact  105  (VPZ) (step CS 205 ). If the currently-mounted photographing lens  200  is a VpzON type lens (if YES at step CS 205 ), the power contact  105  (VPZ) is turned ON; namely, power is supplied to the power contact  105  (VPZ) (step CS 207 ). Subsequently, control proceeds to step CS 209 . On the other hand, if the currently-mounted photographing lens  200  is not a VpzON type lens (if NO at step CS 205 ), control skips step CS 207  to proceed straight from step CS 205  to step CS 209 , so that no power is supplied to the power contact  105  (VPZ). 
     At step CS 209  the level of the fifth contact  104   e  (Fmax 1 /Inverse-FBL) is made to fall to a low level (“Lo” or “L” level), and subsequently it is determined whether the level of the sixth contact  104   f  (Fmax 2 /Inverse-FLB) is a low level (step CS 211 ). The operation at step CS 211  is repeated as long as the level of the sixth contact  104   f  (Fmax 2 /Inverse-FLB) is a high level. If it is determined at step CS 211  that the level of the sixth contact  104   f  (Fmax 2 /Inverse-FLB) is a low level (if YES at step CS 211 ), the level of the fifth contact  104   e  (Fmax 1 /Inverse-FBL) is raised to a high level (“Hi” or “H” level) (step CS 213 ), and subsequently it is determined whether the level of the sixth contact  104   f  (Fmax 2 /Inverse-FLB) is a high level (step CS 215 ). The operation at step CS 215  is repeated as long as the level of the sixth contact  104   f  (Fmax 2 /Inverse-FLB) is a low level. If it is determined at step CS 215  that the level of the sixth contact  104   f  (Fmax 2 /Inverse-FLB) is a high level (if YES at step CS 215 ), this means that the (new type of) photographing lens  200  mounted to the camera body  100  operates normally, so that control comes out of the communication identification process, and from this time on new-type communication is performed between the photographing lens  200  (the lens CPU  211 ) and the camera body  100  (the body CPU  111 ). 
     On the other hand, while the camera body  100  performs the operations at steps CS 207  through CS 215 , the (new-type) photographing lens  200  performs the operations represented by the flow chart shown in FIG.  8 B. If the power contact  105  (VPZ) is supplied with power at step CS 207 , this power is supplied to the photographing lens  200  via the power contact  205  (VPZ). This causes the regulator  243  to supply a constant voltage to the lens CPU  211 , which in turn causes the lens CPU  211  to initialize internal RAM thereof (step LS 201 ). Subsequently, it is determined whether the level of the fifth contact  204   e  (Fmax 1 /Inverse-FBL) is a low level (step LS 203 ). The operation at step LS 203  is repeated as long as the level of the fifth contact  204   e  (Fmax 1 /Inverse-FBL) is a high level. If it is determined, via the fifth contact  204   e  (Fmax 1 /Inverse-FBL) and the port INT of the lens CPU  211 , that the level of the fifth contact  104   e  (Fmax 1 /Inverse-FBL) falls to a low level due to the operation at step CS 209  (if YES at step LS 203 ), the level of the sixth contact  204   f  (Fmax 2 /Inverse-FLB) is made to fall to a low level via the port P 00  of the lens CPU  211  (step LS 205 ). Thereafter, it is determined whether the level of the fifth contact  204   e  (Fmax 1 /Inverse-FBL) is a high level (step LS 207 ). The operation at step LS 207  is repeated as long as the level of the fifth contact  204   e  (Fmax 1 /Inverse-FBL) is a low level. If it is determined that the level of the fifth contact  104   e  (Fmax 1 /Inverse-FBL) rises to a high level due to the operation at step CS 213  (if YES at step LS 207 ), the level of the sixth contact  204   f  (Fmax 2 /Inverse-FLB) is raised to a high level (step LS 209 ). Subsequently, control comes out of the communication identification process, and from this time on the new-type communication is performed between the (new-type) photographing lens  200  (the lens CPU  211 ) and the camera body  100  (the body CPU  111 ). 
     FIG. 18 shows a timing chart for the communication identification process that is performed between the body CPU  111  of the camera body  100  and the lens CPU  211  of the photographing lens  200 . In the communication identification process, the fifth contacts  104   e  and  204   e  (Fmax 1 /Inverse-FBL) and the sixth contacts  104   f  and  204   f  (Fmax 2 /Inverse-FLB) are used to serve as handshake connectors/lines (see FIGS.  19 A and  19 B). Immediately after the power of the camera body  100  is turned ON, the body CPU  111  makes the level of the fourth contact  204   d  (CONTL) rise to a high level to perform the old-type communication (lens ROM communication). 
     OLD-TYPE COMMUNICATION (LENS ROM COMMUNICATION) 
     FIG. 20 shows a timing chart for the old-type communication process between the camera body  100  and the photographing lens  200 , i.e., between the body CPU  111  and the lens ROM  221 . In the lens ROM communication, predetermined lens data written in the lens ROM  221  are read therefrom. The levels of the first contact  104   a  (Fmin 1 /Inverse-SCKL), the third contact  104   c  (Fmin 3 /RESL) and the fourth contact  104   d  (CONTL) of the group of communication/control contacts  104  of the camera body  100  before the commencement of the lens ROM communication are a high level, a high level and a low level, respectively. The second contact  104   b  (Fmin 2 /DATAL) before the commencement of the lens ROM communication is in a high impedance (floating) state. 
     The body CPU  111  makes the level of the fourth contact  104   d  (CONTL) rise to a high level to actuate the lens ROM  221  when starting the lens ROM communication. Subsequently, after waiting a predetermined period of time necessary for the lens ROM to operate with stability, the body CPU  111  makes the level of the third contact  104   c  (Fmin 3 /RESL) fall to a low level to change a state of the lens ROM  221  from a disabled state to an enabled state. Thereafter, if the body CPU  111  outputs a clock signal from the first contact  104   a  (Fmin 1 /Inverse-SCKL), the lens ROM  221  reads out predetermined data from an internal ROM thereof to output the predetermined data to the second contact  204   b  (Fmin 2 /DATAL), so that the body CPU  111  inputs the predetermined data via the second contact  104   b  (Fmin 2 /DATAL). The body CPU  111  makes the level of the third contact  104   c  (Fmin 3 /RESL) rise to a high level upon having input a predetermined number of bytes of lens data. In the present embodiment of the SLR camera system, the last one or few bytes of the lens data are spare bytes. These spare bytes can receive data (rear converter data) output from a ROM (memory/rear converter memory)  321  provided in the rear converter  300  when the rear converter  300  is mounted between the camera body and the photographing lens. More specifically, when the lens ROM communication (the old-type communication) is performed with the rear converter  300  being mounted between the camera body  100  and the photographing lens  200 , as shown in FIG. 27, a predetermined number of bytes serving as the aforementioned spare bytes of the lens data stored in the lens ROM  221  are in a floating state with dummy data so that the spare bytes are transmitted to the camera body  100  with the data output from the ROM  321  of the rear converter  300  being added to the spare bytes. The body CPU  111  can determine whether the rear converter  300  is connected between the camera body  100  and the photographing lens  200  in accordance with the input data of the spare bytes. 
     Information on the lens type is included in data obtained via the above described lens ROM communication, and includes data (new-type lens bit=“1”) for identification of the new-type photographing lens (i.e., a lens which can perform the new-type communication) and data (VpzONCPU bit=“1”) for identification of the necessity for power supply. The body CPU  111  of the camera body  100  identifies whether or not the photographing lens  200  mounted to the camera body  100  is a new type of photographing lens from such data. 
     NEW-TYPE COMMUNICATION 
     Upon completion of the old-type communication, the body CPU  111  starts supplying power to the power contacts  105  and  205  (VPZ). Subsequently, the body CPU  111  makes the level of the fifth contact  104   e  ( 204   e ) (Fmax 1 /Inverse-FBL) fall to a low level to interrupt the lens CPU  211 , and waits for the level of the sixth contact  104   f  ( 204   f ) (Fmax 2 /Inverse-FLB) to fall to a low level, i.e., waits for the lens CPU  211  to make the level of the sixth contact  204   f  (Fmax 2 /Inverse-FLB) fall to a low level. The fifth contact  104   e  ( 204   e ) (Fmax 1 /Inverse-FBL), the sixth contact  104   f  ( 204   f ) (Fmax 2 /Inverse-FLB), and the second contact  104   b  ( 204   b ) (Fmin 2 /DATAL) correspond to a first communication/control contact, a second communication/control contact and an data I/O contact, respectively. 
     Upon the interrupt by the body CPU  111 , the lens CPU  211  “wakes up” and operates normally if in the sleep mode, and initializes the internal RAM thereof. Subsequently, upon completion of the initializing operation, the lens CPU  211  makes the level of the sixth contact  204   f  (Fmax 2 /Inverse-FLB) fall to a low level, and waits for the level of the fifth contact  204   e  ( 104   e ) (Fmax 1 /Inverse-FBL) to rise to a high level. 
     Immediately after the level of the sixth contact  104   f  ( 204   f ) (Fmax 2 /Inverse-FLB) falls to a low level, the body CPU  111  makes the level of the fifth contact  104   e  ( 204   e ) (Fmax 1 /Inverse-FBL) rise to a high level, and waits for the level of the sixth contact  104   f  ( 204   f ) (Fmax 2 /Inverse-FLB) to rise to a high level. 
     Immediately after the level of the fifth contact  204   e  ( 104   e ) (Fmax 1 /Inverse-FBL) rises to a high level, the lens CPU  211  makes the sixth contact  204   f  ( 104   f ) (Fmax 2 /Inverse-FLB) rise to a high level to complete the communication identification process. 
     Upon identifying that the level of the sixth contact  104   f  ( 204   f ) (Fmax 2 /Inverse-FLB) has risen to a high level, the body CPU  111  completes the communication identification process. 
     From this time on, data and commands are transmitted between the camera body  100  and the photographing lens  200  via the new-type communication. 
     The camera state information setting process performed at step CS 113  will be hereinafter discussed in detail with reference to the flow chart shown in FIG.  10 . In the camera state information setting process, the information on the current states of specific switches and a flash charging system which is to be transmitted to the lens CPU  211  via the new-type communication is prepared. Specifically, in the present embodiment of the SLR camera system, it is determined whether the autofocus system of the camera body  100  is in operation, whether an electronic flash (strobe) is in the middle of charging, whether a power hold timer has expired since the photometering switch SWS is turned OFF, and whether the main switch SWMAIN is ON, wherein flags which indicate these states are set as state information. 
     In the camera state information setting process, it is determined whether the photometering switch SWS is ON (step CS 301 ). If the photometering switch SWS is ON (if YES at CS 301 ), it is determined whether the AF switch SWAF is ON, i.e., whether the autofocus mode has been set via the AF switch SWAF (step CS 303 ). If the AF switch SWAF is ON (if YES at step CS 303 ), the AFON flag is set to “1” (step CS 305 ) and subsequently control proceeds to step CS 309 . If the AF switch SWAF is not ON (if NO at step CS 303 ), the AFON flag is set to “0” (step CS 307 ), and subsequently control proceeds to step CS 309 . If the AF switch SWAF is not ON (if NO at step CS 301 ), the AFON flag is set to “0” (step CS 307 ), and subsequently control proceeds to step CS 309 . 
     At step CS 309  it is determined whether the electronic flash is in the middle of charging. If the electronic flash is in the middle of charging (if YES at step CS 309 ), a flag PAUSE is set to “1” (step CS 311 ), and subsequently control proceeds to step CS 315 . The flag PAUSE is set to “1” when any high power operation which requires a large current is performed at present. The electric flash charging operation corresponds to a high power operation in the present embodiment of the SLR camera system. Therefore, the flag PAUSE is set to “1” when the electronic flash is in the middle of charging. When the flag PAUSE is “1”, the photographing lens  200  suspends all high power operations thereof. The film-winding operation and the shutter charge operation are also high power operations performed in the present embodiment of the SLR camera system. 
     At step CS 315  it is determined whether the photometering switch SWS is ON. If the photometering switch SWS is ON (if YES at CS 315 ), the power hold flag PH is set to “1” (step CS 321 ), and subsequently control proceeds to step CS 323 . If the photometering switch SWS is not ON (if NO at CS 315 ), it is determined whether the power hold timer has expired (step CS 317 ). If the power hold timer has expired (if YES at step CS 317 ), the power hold flag PH is set to “0” (step CS 319 ), and subsequently control proceeds to step CS 323 . If the power hold timer has not expired (if NO at step CS 317 ), the power hold flag PH is set to “1” (step CS 321 ), and subsequently control proceeds to step CS 323 . The power hold timer measures the time from the moment the photometering switch SWS is turned OFF to the moment the body CPU  111  enters a sleep mode, and the power hold flag PH “1” or “0” indicates that the camera body  100  is in operation or in a sleep mode (a power saving mode), respectively. 
     At step CS 323 , it is determined whether the main switch SWMAIN is ON. If the main switch SWMAIN is ON (if YES at step CS 323 ), the SWMAIN flag is set to “1” (step CS 325 ), and subsequently control returns. If the main switch SWMAIN is not ON (if NO at step CS 323 ), the SWMAIN flag is set to “0” (step CS 327 ), and subsequently control returns. 
     NEW-TYPE COMMUNICATION (LENS CPU COMMUNICATION) 
     Timing charts in the new-type communication between the lens CPU  211  and the body CPU  111  are shown in FIGS. 18,  19 A,  19 B,  21 A and  21 B. In the new-type communication, the fifth contacts  104   e  and  204   e  (Fmax 1 /Inverse-FBL), and the sixth contacts  104   f  and  204   f  (Fmax 2 /Inverse-FLB), are used to serve as handshake connectors/lines (see FIGS.  19 A and  19 B). The level of each of the fifth contact  104   e  (Fmax 1 /Inverse-FBL) and the sixth contact  104   f  (Fmax 2 /Inverse-FLB) is pulled up by the body CPU  111  so that the fifth contact  104   e  (Fmax 1 /Inverse-FBL) and the sixth contact  104   f  (Fmax 2 /Inverse-FLB) cannot short circuit when the new type of photographing lens  200  is mounted to or dismounted from the camera body  100  (see FIGS.  19 A and  19 B). 
     NEW-TYPE COMMUNICATION SETTING REQUEST PROCESS 
     The new-type communication setting request process performed at step CS 105  will be hereinafter discussed in detail with reference to the flow chart shown in FIG.  9 . 
     In the new-type communication setting request process, firstly it is determined whether the new-type flag is “1”, i.e., whether the photographing lens  200  currently mounted to the camera body  100  is a new type of photographing lens (step CS 221 ). If the new-type flag is not “1” (if NO at step CS 221 ), control returns since the currently mounted photographing lens  200  is not a new type of photographing lens. If the new-type flag is “1” (if YES at step CS 221 ), operations at and after steps CS 223  in the new-type communication setting request process are performed since the photographing lens  200  currently mounted to the camera body  100  is a new type of photographing lens  200  which allows new-type communication. 
     At step CS 223  it is determined whether the second power flag VpzONCPU is “1”. If the second power flag VpzONCPU is “1” (if YES at step CS 223 ), the power contact  105  (VPZ) is turned ON, namely, power is supplied to the power contact  105  (VPZ) (step CS 225 ). Subsequently, control proceeds to step CS 227 . On the other hand, if the second power flag VpzONCPU is not “1” (if NO at step CS 223 ), control skips step CS 225  to proceed straight from step CS 221  to step CS 225 , so that no power is supplied to the power contact  105  (VPZ). 
     At step CS 227 , the level of the fifth contact  104   e  (Fmax 1 /Inverse-FBL) is made to fall to a low level, and subsequently it is determined whether the level of the sixth contact  104   f  (Fmax 2 /Inverse-FLB) is a low level (step CS 229 ). The operation at step CS 229  is repeated as long as the level of the sixth contact  104   f  (Fmax 2 /Inverse-FLB) is a high level. If it is determined at step CS 229  that the level of the sixth contact  104   f  (Fmax 2 /Inverse-FLB) is a low level (if YES at step CS 229 ), the level of the fifth contact  104   e  (Fmax 1 /Inverse-FBL) is raised to a high level (step CS 231 ), and subsequently it is determined whether the level of the sixth contact  104   f  (Fmax 2 /Inverse-FLB) is a high level (step CS 233 ). The operation at step CS 233  is repeated as long as the level of the sixth contact  104   f  (Fmax 2 /Inverse-FLB) is a low level. If it is determined at step CS 233  that the level of the sixth contact  104   f  (Fmax 2 /Inverse-FLB) is a high level (if YES at step CS 233 ), control returns, i.e., control proceeds to step CS 107 . 
     IMAGE-SHAKE COMPENSATION DATA SETTING PROCESS 
     The image-shake compensation data setting process, which is performed at step CS 137  on condition that the photographing lens  200  mounted to the camera body  100  is of a type which incorporates an image-shake compensation device, will be hereinafter discussed in detail with reference to the flow chart shown in FIG.  11 . FIG. 12A shows fundamental elements of a control system of an embodiment (first embodiment) of the photographing lens  200  which incorporates an image-shake compensation device. FIG. 12B shows a conceptual diagram of a compensation lens (an image-stabilizing optical system) LC of the image-shake compensation device. The image-shake compensation device includes a pair of sensors, i.e., an X-direction angular speed sensor (horizontal-vibration sensor)  251  and a Y-direction angular speed sensor (vertical-vibration sensor)  252 , for determining magnitude and direction of the vibration of the photographing lens  200  due to hand movement. If a state where the photographing lens  200  is properly mounted to the camera body  100  and normally held in a horizontal position is considered as a reference state, the X-direction angular speed sensor  251  senses the angular speed of the photographing lens  200  in the horizontal direction of the optical axis thereof (in the X-direction about the Y-axis), while the Y-direction angular speed sensor senses the angular speed of the photographing lens  200  in the horizontal direction of the optical axis thereof (in the Y-direction about the X-axis) wherein an intersection point of the optical axis of the photographing lens  200  and the picture plane defines the intersection point of the X-axis and the Y-axis. Each of the vertical and horizontal vibration sensors can be a conventional gyro sensor. The vertical-vibration sensor exclusively senses the shake of the photographing lens  200  in the vertical direction, while the horizontal-vibration sensor exclusively senses the shake of the photographing lens  200  in the horizontal direction. 
     The image-shake compensation device of the photographing lens  200  is provided with the compensation lens LC (see FIG.  12 B), and operates to compensate the shaking of the object image on the picture plane by driving the compensation lens LC in the X-direction and the Y-direction with an X-motor  254  and a Y-motor  257 , respectively, in a plane perpendicular to the optical axis of the photographing lens  200 . The position of the compensation lens LC is sensed by the number of pulses output from each of an X-direction photo-interrupter  255  and a Y-direction photo-interrupter  258  when the compensation lens LC is driven, wherein a position where the optical axis of the compensation lens LC coincides with the optical axis of the photographing lens  200  is regarded as a reference position. Rotation of each of the X-motor  254  and the Y-motor  257  is controlled by the lens CPU  211  via an X-motor driver  253  and a Y-motor driver  256 , respectively. 
     Note that the X-direction angular speed sensor  251 , the Y-direction angular speed sensor  252 , the X-motor driver  253 , the Y-motor driver  256 , the X-motor  254 , the Y-motor  257 , X-direction photo-interrupter  255 , the Y-direction photo-interrupter  258 , and the compensation lens LC collectively constitute the image-shake compensation device. 
     The lens CPU  211  serves as a controller and an arithmetic processing unit for the image-shake compensation device. The lens CPU  211  starts operating immediately after the image-shake compensation switch SW 1  is turned ON to determine the direction of driving of the compensation lens LC and the amount of movement (speed) thereof to drive the X-motor  254  and the Y-motor  257 . 
     In the image-shake compensation data setting process shown in FIG. 11, firstly, it is determined whether the main switch flag SWMAIN has changed from “0” to “1” (step CS 401 ). If the main switch flag SWMAIN has changed from “0” to “1” (if YES at step CS 401 ), command  70  is transmitted to the photographing lens  200  to receive data therefrom (step CS 403 ). Subsequently, the lens CPU  211  waits for an initialize flag Init “0” to be transmitted from the camera body  100  (step CS 405 ). Namely, it is determined at step CS 405  whether the initialize flag Init is “0”. 
     Command  70  is data which is transmitted from the camera body  100  to the photographing lens  200  to make the photographing lens  200  send the status thereof (status data) to the camera body  100 . In the present embodiment of the SLR camera system, the status data which is transmitted from the photographing lens  200  to the camera body  100 , immediately after the photographing lens  200  receives command  70 , is represented by one-byte data, wherein the 7th bit thereof is defined as the initialize flag Init. The 0th bit of the one-byte data is defined as an identification bit which indicates whether an AF switch is ON or OFF. The 1st bit of the one-byte data is defined as an identification bit which indicates whether the diaphragm is set automatically or manually. The 6th bit of the one-byte data is defined as an identification bit which indicates whether any function of the photographing lens  200  is in operation or not. Each of the second through fifth bits is undefined. Therefore, each of the second through fifth bits can be defined as a specific identification bit if any new function is added to the photographing lens  200 . It should be noted that 0 bit or no data indicates negation. 
     The initialize flag Init is changed from “1” to “0” and output from the photographing lens  200  to the camera body  100  when an operation at step LS 117  or LS 125 , in which the compensation lens LC is driven to return to the initial position thereof where the optical axis of the compensation lens coincides with the optical axis of the photographing lens  200 , is completed. If it is determined at step CS 405  that the initialize flag Init is “0”, control proceeds to step CS 407 . If it is determined at step CS 401  that the main switch flag SWMAIN has not changed from “0” to “1” (if NO at step CS 401 ), control proceeds straight from step CS 401  to CS 407 . 
     At step CS 407 , it is determined whether the main switch flag SWMAIN has changed from “1” to “0”. If the main switch flag SWMAIN has changed from “1” to “0” (if YES at step CS 407 ), this means that the main switch SWMAIN has turned from ON to OFF, so that subsequently command  70  is transmitted to the photographing lens  200  to receive data therefrom (step CS 409 ). Subsequently, the lens CPU  211  waits for the initialize flag Init “0” to be transmitted from the camera body  100  (step CS 411 ). Namely, it is determined at step CS 411  whether the initialize flag Init is “0”. Control returns to step CS 409  if the initialize flag Init is not “0”. 
     If it is determined at step CS 411  that the initialize flag Init is “0”, control proceeds to step CS 413 . If it is determined at step CS 407  that the main switch flag SWMAIN has not changed from “1” to “0” (if NO at step CS 407 ), control proceeds straight from step CS 407  to CS 413 . 
     If it is determined at step CS 413  that the power hold flag PH has changed from “1” to “0” (if YES at step CS 413 ), command  70  is transmitted to the photographing lens  200  to receive data therefrom (step CS 415 ). Subsequently, the lens CPU  211  waits for the initialize flag Init “0” to be transmitted from the camera body  100  (step CS 417 ). Namely, it is determined at step CS 417  whether the initialize flag Init is “0”. Control returns to step CS 415  if the initialize flag Init is not “0”. If it is determined at step CS 417  that the initialize flag Init is “0”, control proceeds to step CS 419 . If it is determined at step CS 413  that the power hold flag PH has not changed from “1” to “0” (if NO at step CS 413 ), control proceeds straight from step CS 413  to CS 419 . 
     At step CS 419  it is determined whether the image-shake compensation switch SW 1  has been turned from ON to OFF. If the image-shake compensation switch SW 1  has been turned from ON to OFF (if YES at step CS 419 ), command D 1  (individual function data) for turning OFF the image-shake compensation function of the photographing lens  200  is transmitted thereto (step CS 421 ), and subsequently control proceeds to step CS 423 . Upon receiving command D 1 , the photographing lens  200  completes the image-shake compensation operation. If the image-shake compensation switch SW 1  has not been turned from ON to OFF (if NO at step CS 419 ), control skips CS 421  to proceed straight from step CS 419  to step CS 423 . At step CS 423  it is determined whether the image-shake compensation switch SW 1  has been turned from OFF to ON. If the image-shake compensation switch SW 1  has been turned from OFF to ON (if YES at step CS 423 ), command D 2  (individual function data) for turning ON the image-shake compensation function of the photographing lens  200  is transmitted thereto (step CS 425 ), and subsequently control returns. If the image-shake compensation switch SW 1  has not been turned from OFF to ON (if NO at step CS 423 ), control skips CS 425  and returns. Upon receiving command D 2 , the photographing lens  200  starts the image-shake compensation operation. 
     Fundamental operations and processes performed by the lens CPU  211  of the photographing lens  200  that incorporates the image-shake compensation device will be hereinafter discussed in detail with reference to the flow charts shown in FIGS. 13 through 17. FIG. 13 shows a flow chart for the main process of the photographing lens  200  which is performed by the lens CPU  211 . Control enters the main process immediately after the lens CPU  211  is supplied with power via the operation at step CS 225 , at which power is supplied to the power contact  105  (VPZ). 
     In the main process shown in FIG. 13, firstly the lens CPU  211  initializes internal RAM and ports thereof (step LS 101 ). Subsequently, a new-type communication setting process (“new-type communication setting process” shown in FIG. 14) is performed (step LS 103 ). In this process, a 1 ms-timer interrupt (see FIG. 15) and an interrupt via the port (inverse) INT of the lens CPU  211  (see FIG. 16) are enabled to receive an interrupt from the camera body  100  to thereby make the new-type communication possible between the new type of photographing lens (photographing lens  200 ) and the camera body  100 . 
     Subsequently, it is determined whether a sleep flag which is set to “1” at step LS 433  or LS  437  is “1” (step LS 105 ). If the sleep flag is “1” (if YES at step LS 105 ), the lens CPU  211  stops operations of internal devices of the photographing lens  200  such as the lens motor (step LS 107 ), the sleep flag is set to “0” (step LS 109 ), and the lens CPU  211  enters the sleep mode (step LS 111 ). The lens CPU  211  “wakes up” upon receiving an interrupt signal via the port (inverse) INT thereof. 
     If it is determined at step CS 105  that the sleep flag is not “1” (if NO at step LS 105 ), it is determined whether a compensation lens reset flag is “1” (step LS 113 ). If the compensation lens reset flag is “1” (if YES at step LS 113 ), the initialize flag Init is set to “1” (step LS 115 ). Subsequently, a resetting operation is performed (step LS 117 ). In the resetting operation, the X-motor  254  and Y-motor  257  are driven to move the compensation lens LC to firstly a predetermined mechanical extremity (reference point) in the range of movement of the compensation lens LC, and subsequently the initial position (central position) thereof where the optical axis of the compensation lens LC coincides with the optical axis of the photographing lens  200 . After the resetting operation is performed, the compensation lens reset flag and the initialize flag are set to “0” (step LS 119 ), and control proceeds to step LS 121 . According to this resetting operation, the absolute position of the compensation lens LC is secured, and accordingly the compensation lens LC can be positioned precisely at the initial position (central position) thereof. 
     If it is determined at step LS 113  that the compensation lens reset flag is not “1”, it is determined whether a compensation lens center flag is “1” (step LS 121 ). If the compensation lens center flag is not “1” (if NO at step LS 121 ), control returns to step LS 105 . If the compensation lens center flag is “1” (if YES at step LS 121 ), the initialize flag Init is set to “1” (step LS 123 ). Subsequently, a centering operation is performed in which the X-motor  254  and Y-motor  257  are driven to move the compensation lens LC to the initial position (central position) where the optical axis of the compensation lens LC coincides with the optical axis of the photographing lens  200  (step LS 125 ). Subsequently, the compensation lens center flag and the initialize flag are set to “0” (step LS 127 ), and control returns to step LS 105 . 
     The new-type communication setting process performed at step LS 103  will be hereinafter discussed in detail with reference to the flow chart shown in FIG.  14 . In the new-type communication setting process, firstly it is determined whether the level of the fifth contact  204   e  (Fmax 1 /Inverse-FBL) is a low level (step LS 221 ). If the level of the fifth contact  204   e  (Fmax 1 /Inverse-FBL) is not a low level (if NO step LS 221 ), the operation at step LS 221  is performed again, so that the operation at step LS 221  is repeated until the level of the fifth contact  204   e  (Fmax 1 /Inverse-FBL) falls to a low level. If the level of the fifth contact  204   e  (Fmax 1 /Inverse-FBL) is a low level (if YES step LS 221 ), the sixth contact  204   f  (Fmax 2 /Inverse-FLB) is made to fall to a low level (step LS 223 ), and subsequently a communication setting process is performed (step LS 225 ). The communication setting process includes a setting process for serial communication, and an interrupt enabling process via the port (inverse) INT of the lens CPU  211 . 
     Upon completion of the communication setting process at step LS 225 , it is determined whether the level of the fifth contact  204   e  (Fmax 1 /Inverse-FBL) is a high level (step LS 227 ). If the level of the fifth contact  204   e  (Fmax 1 /Inverse-FBL) is not a high level (if NO step LS 227 ), the operation at step LS 227  is performed again, so that the operation at step LS 227  is repeated until the level of the fifth contact  204   e  (Fmax 1 /Inverse-FBL) rises to a high level. If the level of the fifth contact  204   e  (Fmax 1 /Inverse-FBL) is a high level (if YES step LS 227 ), the sixth contact  204   f  (Fmax 2 /Inverse-FLB) is raised to a high level (step LS 229 ), and subsequently control returns. 
     A 1 ms-timer interrupt process for the image-shake compensation operation will be hereinafter discussed in detail with reference to the flow chart shown in FIG.  15 . The 1 ms-timer interrupt process starts each time a 1 ms hard timer expires during operation of the lens CPU  211 . In the 1 ms-timer interrupt process, the lens CPU  211  inputs an angular speed signal from each of the X-direction angular speed sensor  251  and the Y-direction angular speed sensor  252  to detect the vibration of the photographing lens  200  due to hand movement, and subsequently determines the direction of driving of the compensation lens LC and the amount of movement (speed) thereof to drive the X-motor  254  and the Y-motor  257  to move the compensation lens LC by the determined amount of movement in the determined driving direction. 
     In the 1 ms-timer interrupt process, firstly it is determined whether a compensation function OFF flag is “1” (step LS 301 ). If the compensation function OFF flag is “1” (if YES step LS 301 ), a compensation work flag is set to “0” (step LS 303 ) and control returns. The compensation work flag “1” or “0” indicates that the image-shake compensation device operates or does not operate, respectively. 
     If the compensation function OFF flag is “0” (if NO step LS 301 ), it is determined whether a compensation ON flag is “0” (step LS 305 ). If the compensation ON flag is “0” (if YES step LS 305 ), this means that the image-shake compensation operation is not performed, so that the compensation work flag is set to “0” (step LS 303 ), and control returns. 
     If the compensation ON flag is “1” (if NO step LS 305 ), the compensation work flag is set to “1”, and subsequently a vibration detection process is performed (step LS 309 ). In the vibration detection process, the lens CPU inputs an angular speed signal from each of the X-direction angular speed sensor  251  and the Y-direction angular speed sensor  252  to detect the vibration of the photographing lens  200 , and subsequently determines the direction of driving of the compensation lens LC and the amount of movement thereof. 
     After the vibration detection process at step LS 309  is performed, it is determined whether a drive ON flag is “0” (step LS 311 ). If the drive ON flag is not “0” (if NO at step LS 311 ), the X-motor  254  and the Y-motor  257  are driven to move the compensation lens LC by the amount of movement in the determined driving direction that are determined at step LS 309  (step LS 315 ), and subsequently control returns. If the drive ON flag is “0” (if YES at step LS 311 ), the driving of each of the X-motor  254  and the Y-motor  257  is stopped forcefully (step LS 313 ), and control returns. 
     An inverse-INT interrupt process will be hereinafter discussed with reference to the flow chart shown in FIGS. 16 and 17. The inverse-INT interrupt process starts immediately after the level of the fifth contact  204   e  (Fmax 1 /Inverse-FBL) falls to a low level to thereby cause the port (inverse) INT of the lens CPU  211  to fall to a low level. 
     In the inverse-INT interrupt process, firstly at least one command is received from the camera body  100  via the new-type communication (step LS 401 ). Subsequently, it is determined whether at least one of commands  70 ,  71  and  72  was received at step LS 401  (step LS 403 ). If at least one of commands  70 ,  71  and  72  was received at step LS 401  (if YES at step LS 403 ), a lens data transmitting process (8-bit data transmitting process) is performed via the new-type communication (step LS 405 ), and control proceeds to step LS 407 . If none of commands  70 ,  71  and  72  was received at step LS 401  (if NO at step LS 403 ), control proceeds straight from step LS 403  to step LS 407 . 
     At step LS 407 , it is determined whether at least one of commands B 0  and B 1  was received at step LS 401 . If neither of commands B 0  and B 1  was received at step LS 401  (if NO at step LS 407 ), control proceeds to step LS 431 . If at least one of commands B 0  and B 1  was received at step LS 401  (if YES at step LS 407 ), a body data receiving process is performed via the new-type communication (step LS 409 ). Subsequently, it is determined whether the main switch flag SWMAIN has changed from “0” to “1” (step LS 411 ), whether the main switch flag SWMAIN has changed from “1” to “0” (step LS 415 ), whether the power hold flag PH is “1” (step LS 419 ), and whether the power hold flag PH has changed from “1” to “0” (step LS 423 ). 
     If it is determined at step LS 411  that the main switch flag SWMAIN has changed from “0” to “1” (if YES at step LS 411 ), the compensation lens reset flag is set to “1” (step LS 413 ), and control proceeds to step LS 415 . If it is determined at step LS 415  the main switch flag SWMAIN has changed from “1” to “0” (if YES at step LS 415 ), the compensation lens center flag is set to “1” (step LS 417 ), and control proceeds to step LS 419 . If it is determined at step LS 419  that the power hold flag PH is “1” (if YES at step LS 419 ), the compensation ON flag is set to “1” (step LS 421 ), and control proceeds to step LS 423 . If it is determined at step LS 423  that the power hold flag PH has changed from “1” to “0” (if YES at step LS 423 ), the compensation ON flag is set to “0” and the compensation lens center flag is set to “1” (step LS 424 ), and control proceeds to step LS 425 . If it is determined “NO” at all of steps LS 411 , LS 415 , LS 419  and LS 423 , control proceeds from step LS 411  to step LS 425  with none of the operations at steps LS 413 , LS 417 , LS 421  and LS 424  being performed. 
     At step LS 425 , it is determined whether the flag PAUSE is “1”. If the flag PAUSE is “1” (if YES at step LS 425 ), the drive ON flag is set to “0” (step LS 427 ), and control proceeds to step LS 431 . If the flag PAUSE is “0” (if NO at step LS 425 ), the drive ON flag is set to “1” (step LS 429 ), and control proceeds to step LS 431 . The flag PAUSE is set to “1” when any high power operation which requires a large current is currently performed. In the present embodiment of the SLR camera system, the flag PAUSE is set to “1” when the electronic flash is in the middle of charging (step CS 311 ). Subsequently, the lens CPU  211  sets the drive ON flag to “0” upon receipt of the flag PAUSE “1” (step LS 427 ), and control proceeds from step LS 311  to step LS 313  to stop the driving of each of the X-motor  254  and the Y-motor  257  forcefully in the 1 ms-timer interrupt process shown in FIG.  15 . However, the X-direction angular speed sensor  251  and the Y-direction angular speed sensor  252  continue to operate. 
     It is determined at step LS 431  whether at least one of commands  71  and B 1  was received at step LS 401 . If at least one of commands  71  and B 1  was received at step LS 401  (if YES at step LS 431 ), the sleep flag is set to “1” (step LS 433 ), and control proceeds to step LS 435 . If neither of commands  71  and B 1  was received at step LS 401  (if NO at step LS 431 ), control proceeds from step LS 431  to step LS 435 . If the sleep flag is set to “1”, control proceeds from step LS 105  to step LS 107  so that the lens CPU  211  enters the sleep mode in the main process shown in FIG.  13 . 
     Command  71  is data which is transmitted from the camera body  100  to the photographing lens  200  to make the photographing lens  200  send the status thereof to the camera body  100 , and also to make the lens CPU  211  enter a sleep mode together with the body CPU  111 . 
     At step LS 435 , it is determined whether command D 0  was received at step LS 401 . If command D 0  was received at step LS 401  (if YES at step LS 435 ), the sleep flag is set to “1” (step LS 437 ), and control proceeds to step LS 439 . If command D 0  was not received at step LS 401  (if NO at step LS 435 ), control proceeds straight from step LS 435  to step LS 439 . 
     At step LS 439 , it is determined whether command D 1  was received at step LS 401 . If command D 1  was received at step LS 401  (if YES at step LS 439 ), the compensation function OFF flag is set to “1” (step LS 441 ), and control proceeds to step LS 443 . If command D 1  was not received at step LS 401  (if NO at step LS 439 ), control proceeds straight from step LS 439  to step LS 443 . 
     At step LS 443  it is determined whether command D 2  was received at step LS 401 . If command D 2  was received at step LS 401  (if YES at step LS 443 ), the compensation function OFF flag is set to “0” (step LS 445 ), and control proceeds to step LS 447 . If command D 2  was not received at step LS 401  (if NO at step LS 443 ), control proceeds straight from step LS 443  to step LS 447 . 
     At step LS 447  it is determined whether command was received at step LS 401 . If command  7 F was received at step LS 401  (if YES at step LS 447 ), the lens CPU  211  performs a dummy data communication process (step LS 449 ) and control returns. If command  7 F was not received at step LS 401  (if NO at step LS 447 ), control returns. 
     Command  7 F is data which is transmitted from the camera body  100  to the photographing lens  200  to make the rear converter  300  output data therefrom, if the rear converter  300  is mounted between the camera body  100  and the photographing lens  200 . The dummy data communication process at step LS 449  is performed to allocate communication channel for the body CPU  111  so that the body CPU  111  can receive data output from the rear converter  300 . 
     Fundamental structures and processes of an embodiment of the photographing lens  200  which incorporates an image-shake compensation device have been described above. Another embodiment (second embodiment) of the photographing lens  200  which incorporates a lens AF system will be hereinafter discussed with reference to FIGS. 22 through 26. It should be noted that elements and processes/processes in the second embodiment of the photographing lens  200  which are similar to those in the first embodiment of the photographing lens  200  shown in FIGS. 12 through 17 are respectively designated by similar reference numerals and step numbers. 
     FIG. 22 is a block diagram of fundamental elements of a communication/control system of the second embodiment of the photographing lens  200  which incorporates a lens AF system. The second embodiment of the photographing lens  200  is provided with an AF motor driver  261 , an AF motor (lens motor)  262  and a photo-interrupter  263 . The lens CPU  211  drives the AF motor  262  via the AF motor driver  261  in accordance with data on the driving-amount of the AF motor  262  and the driving direction thereof that is received from the body CPU  111  to move a focusing lens group Lf along the optical axis thereof to an axial position thereon at which an in-focus state is obtained. The amount of movement of the focusing lens group Lf is detected by counting the number of pulses output from the photo-interrupter  263 . 
     FIG. 23 shows a flow chart for the main process of the second embodiment of the photographing lens  200  which incorporates a lens AF system. Control enters the main process immediately after the lens CPU  211  is supplied with power via the operation at step CS 225 , at which power is supplied to the power contact  105  (VPZ). 
     In the main process shown in FIG. 23, firstly the lens CPU  211  initializes internal RAM and ports thereof (step LS 101 ). Subsequently, the new-type communication setting process (“new-type communication setting process” shown in FIG. 14) is performed (step LS 103 ). In this process, a 1 ms-timer interrupt (see FIG. 24) and an interrupt via the port (inverse) INT of the lens CPU  211  (see FIG. 25) are enabled to receive an interrupt from the camera body  100  to thereby make the new-type communication possible between the photographing lens  200  and the camera body  100 . 
     Subsequently, it is determined whether a sleep flag which is set to “1” at step LS 433  or LS 437  is “1” (step LS 105 ). If the sleep flag is “1” (if YES at step LS 105 ), the lens CPU  211  stops internal devices of the photographing lens  200  such as the AF motor  262  and the photo-interrupter  263  (step LS 107 ), the sleep flag is set to “0” (step LS 109 ), and the lens CPU  211  enters the sleep mode (step LS 111 ). The lens CPU  211  wakes up on receiving an interrupt signal via the port (inverse) INT thereof. 
     If it is determined at step CS 105  that the sleep flag is not “1” (if NO at step LS 105 ), the operation at step LS 105  is repeated. The new-type communication setting process shown in FIG. 14, a 1 ms-timer interrupt process shown in FIG. 24, and an inverse-INT interrupt process shown in FIG. 25 are performed during the time the operation at step LS 105  is repeated. 
     The new-type communication setting process performed at step LS 103  shown in FIG. 23 is identical to that shown in FIG. 14, and accordingly further description of the new-type communication setting process performed at step LS 103  shown in FIG. 23 is omitted. 
     The 1 ms-timer interrupt process which is repeated at regular intervals when the lens CPU  211  is in operation, in the second embodiment of the photographing lens  200 , will be hereinafter discussed with reference to the flow chart shown in FIG.  24 . This 1 ms-timer interrupt process starts each time a 1 ms hard timer expires during operation of the lens CPU  211  to control operation of the AF motor  262 . 
     In the 1 ms-timer interrupt process, firstly it is determined whether an AF function ON flag is “0” (step LS 331 ). If the AF function ON flag is “0” (if YES step LS 331 ), a lens AF process is not performed, wherein an AF work flag is set to “0” (step LS 333 ), and control returns. The AF work flag “1” or “0” indicates that the lens AF process operates or does not operate, respectively. 
     If the AF function ON flag is not “0” (if NO step LS 331 ), it is determined whether a drive end flag is “1” (step LS 335 ). If the drive end flag is “1” (if YES at step LS 335 ), this means that the driving of the AF motor  262  has been completed, so that the AF work flag is set to “0” (step LS 333 ) and control returns. 
     If the drive end flag is not “1” (if NO at step LS 335 ), it is determined whether a drive ON flag is “0” (step LS 337 ). If the drive ON flag is “0” (if YES at step LS 337 ), the AF motor  262  is stopped forcefully (step LS 339 ), and control returns. 
     If the drive ON flag is not “0” (if NO at step LS 337 ), the AF work flag is set to “1” (step LS 341 ), and subsequently the AF motor  343  is started (driven) (step LS 343 ). Subsequently, it is determined whether the driving of the AF motor  343  is completed (step LS 345 ). If the driving of the AF motor  343  is completed (if YES at step LS 345 ), the drive end flag is set to “1” (step LS 347 ), and control returns. If the driving of the AF motor  343  has not been completed (if NO at step LS 345 ), control returns. 
     An inverse-INT interrupt process in the second embodiment of the photographing lens  200  will be hereinafter discussed with reference to the flow chart shown in FIGS. 25 and 26. The inverse-INT interrupt process starts immediately after the level of the fifth contact  204   e  (Fmax 1 /Inverse-FBL) falls to a low level to thereby cause the port (inverse) INT of the lens CPU  211  to fall to a low level. 
     In the inverse-INT interrupt process, firstly at least one command is received from the camera body  100  via the new-type communication (step LS 401 ). Subsequently, it is determined whether at least one of commands  70 ,  71  and  72  was received at step LS 401  (step LS 403 ). If at least one of commands  70 ,  71  and  72  was received at step LS 401  (if YES at step LS 403 ), a lens data transmitting process (8-bit data transmitting process) is performed via the new-type communication, and control proceeds to step LS 407 . If none of commands  70 ,  71  and  72  was received at step LS 401  (if NO at step LS 403 ), control proceeds straight from step LS 403  to step LS 407 . 
     At step LS 407 , it is determined whether at least one of commands B 0  and B 1  was received at step LS 401 . If neither of commands B 0  and B 1  was received at step LS 401  (if NO at step LS 407 ), control proceeds to step LS 461 . If at least one of commands B 0  and B 1  was received at step LS 401  (if YES at step LS 407 ), a body data receiving process is performed via the new-type communication (step LS 409 ). Subsequently, it is determined whether the AF ON flag is “1” (step LS 451 ). If the AF ON flag is “1”, (if YES at step LS 451 ), the AF function ON flag is set to “1” (step LS 453 ), and control proceeds to step LS 455 . If the AFON flag is not “1”, (if NO at step LS 451 ), the AF function ON flag is set to “0” (step LS 454 ), and control proceeds to step LS 455 . 
     At step LS 455  it is determined whether the release stage indicator RLS is “2”. The release stage indicator RLS is a two-bit data which is set to “0”, “1”, “2” or “3” by the body CPU  111 . The release stage indicator RLS “1” indicates a stage at which the quick return mirror is moving toward the retracted position thereof after the release switch SWR has been turned ON. The release stage indicator RLS “2” indicates a stage at which a film frame is under exposure after the quick return mirror has moved up to the retracted position thereof. The release stage indicator RLS “3” indicates a stage at which the camera body  100  is in a stage at which film is advanced after the exposure operation has been completed. The release stage indicator RLS “0” indicates any other stage of the camera body  100 . If the release stage indicator RLS is “2” (if YES at step LS 455 ), this means that a film frame is under exposure after the quick return mirror has moved up to the retracted position thereof, so that the drive ON flag is set to “0” (step LS 457 ), and control proceeds to step LS 461 . If the release stage indicator RLS is not “2” (if NO at step LS 455 ), the drive ON flag is set to “1” (step LS 459 ) and control proceeds to step LS 461 . 
     At step LS 461 , it is determined whether command B 2  was received at step LS 401 . If command B 2  was received at step LS 401  (if YES at step LS 461 ), lens driving amount data is received from the body CPU  111  (step LS 463 ). Subsequently, this received lens driving amount data is set (step LS 465 ), and the drive end flag is set to “0” (step LS 467 ). Subsequently, control proceeds to step LS 431 . If command B 2  was not received at step LS 401  (if NO at step LS 461 ), control proceeds to step LS 431 . 
     It is determined at step LS 431  whether at least one of commands  71  and B 1  was received at step LS 401 . If at least one of commands  71  and B 1  was received at step LS 401  (if YES at step LS 431 ), the sleep flag is set to “1” (step LS 433 ) and control proceeds to step LS 435 . If neither of commands  71  and B 1  was received at step LS 401  (if NO at step LS 431 ), control proceeds from step LS 431  to step LS 435 . If the sleep flag is set to “1”, control proceeds from step LS 105  to step LS 107 , in the main process shown in FIG. 13, so that the lens CPU  211  enters the sleep mode. 
     At step LS 435 , it is determined whether command D 0  was received at step LS 401 . If command D 0  was received at step LS 401  (if YES at step LS 435 ), the sleep flag is set to “1” (step LS 437 ) and control proceeds to step LS 469 . If command D 0  was not received at step LS 401  (if NO at step LS 435 ), control proceeds straight from step LS 435  to step LS 469 . 
     At step LS 469 , it is determined whether command D 3  was received at step LS 401 . If command D 3  was received at step LS 401  (if YES at step LS 469 ), the drive ON flag is set to “0” (step LS 471 ), and control proceeds to step LS 473 . If command D 3  was not received at step LS 401  (if NO at step LS 469 ), control proceeds straight from step LS 469  to step LS 473 . 
     At step LS 473 , it is determined whether command D 4  was received at step LS 401 . If command D 4  was received at step LS 401  (if YES at step LS 473 ), the drive ON flag is set to “1” (step LS 475 ), and control proceeds to step LS 477 . If command D 4  was not received at step LS 401  (if NO at step LS 473 ), control proceeds straight from step LS 473  to step LS 477 . 
     At step LS 477  it is determined whether command  7 F was received at step LS 401 . If command  7 F was received at step LS 401  (if YES at step LS 447 ), the lens CPU  211  performs the dummy data communication process (step LS 479 ), and control returns. If command  7 F was not received at step LS 401  (if NO at step LS 477 ), control returns. At this point, command  7 F is issued for data communication between the lens CPU  211  and a CPU (controller/rear converter controller)  311  of the rear converter  300 . In a state where the rear converter  300  is mounted between the camera body  100  and the photographing lens  200 , the CPU  311  of the rear converter  300  recognizes command  7 F as a command for the rear converter  300  upon receipt of command  7 F, and subsequently sends rear converter communication data (new-type communication data) to the body CPU  111 . 
     FIG. 27 is a schematic block diagram of fundamental elements of control systems of the photographing lens  200 , the rear converter  300 , and the camera body  100  of an embodiment of the SLR camera system according to the present invention, wherein the rear converter  300  is mounted between the camera body  100  and the photographing lens  200 . The rear converter  300  is provided with the CPU  311  serving as a controller which controls functions of the rear converter  300 , and the ROM  321  serving as a storing device in which fundamental data on the rear converter  300  are stored. As shown in FIG. 27, each of the CPU  311  and the ROM  321  of the rear converter  300  is provided with I/O ports similar to those of the lens CPU  211  and the lens ROM  221 . The rear converter  300  can either serve as a teleconverter or wide converter, being provided with a variable power lens group (not shown). 
     The rear converter  300  is provided with a rear mount  303  which is mounted to the mount  103  of the camera body  100 , and a front mount  3031  to which the lens mount  203  of the photographing lens  200  is mounted. The rear mount  303  is provided thereon with six contacts (relay/communication contacts) which come in contact with the six contacts  104   a  through  104   f  provided on the mount  103  of the camera body  100 , respectively, while the front mount  3031  is provided thereon with another six contacts (relay/communication contacts) which come in contact with the six contacts  204   a  through  204   f  provided on the lens mount  203  of the photographing lens  200 . 
     The six contacts formed on the rear mount  303  of the rear converter  300  include a first contact  304   a  (Fmin 1 /Inverse-SCKL), a second contact  304   b  (Fmin 2 /DATAL), a third contact  304   c  (Fmin 3 /RESL), a fourth contact  304   d  (CONTL), a fifth contact  304   e  (Fmax 1 /Inverse-FBL), and a sixth contact  304   f  (Fmax 2 /Inverse-FLB). The six contacts formed on the front mount  3031  of the rear converter  300  include a first contact  304   a   1  (Fmin 1 /Inverse-SCKL), a second contact  304   b   1  (Fmin 2 /DATAL), a third contact  304   c   1  (Fmin 3 /RESL), a fourth contact  304   d   1  (CONTL), a fifth contact  304   e   1  (Fmax 1 /Inverse-FBL), and a sixth contact  304   f   1  (Fmax 2 /Inverse-FLB) which are connected with the first contact  304   a  (Fmin 1 /Inverse-SCKL), the second contact  304   b  (Fmin 2 /DATAL), the third contact  304   c  (Fmin 3 /RESL), the fourth contact  304   d  (CONTL), the fifth contact  304   e  (Fmax 1 /Inverse-FBL), and the sixth contact  304   f  (Fmax 2 /Inverse-FLB) on the rear mount  303 , respectively. Accordingly, the rear six contacts  304   a  through  304   f  and the front six contacts  304   a   1  through  304   f   1  of the rear converter  300  serve as a group of relay channels via which the group of communication/control contacts  104  ( 104   a  through  104   f ) on the mount  103  of the camera body  100  are electrically connected with the group of communication/control contacts  204  ( 204   a  through  204   f ) on the lens mount  203  of the photographing lens  200 , respectively, in a state where the rear converter  300  is properly mounted between the camera body  100  and the photographing lens  200 . 
     The first contact  304   a  (Fmin 1 /Inverse-SCKL) on the rear mount  303  and the first contact  304   a   1  (Fmin 1 /Inverse-SCKL) on the front mount  3031  are connected to a port Inverse-SCK of each of the CPU  311  and the lens ROM  321 . The second contact  304   b  (Fmin 2 /DATAL) on the rear mount  303  and the second contact  304   b   1  (Fmin 2 /DATAL) on the front mount  3031  are connected to a port DATA of each of the CPU  311  and the lens ROM  321 . The third contact  304   c  (Fmin 3 /RESL) on the rear mount  303  and the third contact  304   c   1  (Fmin 3 /RESL) on the front mount  3031  are connected to a port RES of each of the CPU  311  and the lens ROM  321 . The fourth contact  304   d  (CONTL) on the rear mount  303  and the fourth contact  304   d   1  (CONTL) on the front mount  3031  are connected to a port CONT of each of the CPU  311  and the lens ROM  321 . The fifth contact  304   e  (Fmax 1 /Inverse-FBL) on the rear mount  303  and the fifth contact  304   e   1  (Fmax 1 /Inverse-FBL) on the front mount  3031  are connected to a port (Fmax/Inverse-FBL) of each of the CPU  311  and the lens ROM  321 . The sixth contact  304   f  (Fmax 2 /Inverse-FLB) on the rear mount  303  and the sixth contact  304   f   1  (Fmax 2 /Inverse-FLB) on the front mount  3031  are not connected to any ports of each of the CPU  311  and the lens ROM  321 . 
     The CPU  311  of the rear converter  300  is not provided with any port which corresponds to a connection port of the lens CPU  211  that is connected to the sixth contact  204   f  (Fmax 2 /Inverse-FLB) on the lens mount  203 . The lens CPU  211  starts communicating with the body CPU  111  immediately after the level of the fifth contacts  104   e  and  204   e  (Fmax 1 /Inverse-FBL) fall to a low level, and a handshake operation is performed between the body CPU  111  and the lens CPU  211  via the sixth contacts  104   f  and  204   f  (Fmax 2 /Inverse-FLB). While the handshake operation is performed, the CPU  311  sends out data (rear converter data) on the rear converter  300  via a port Fmax 1  of the CPU  311  in synchronization with signals transmitted through the fifth contacts  104   e  and  204   e  (Fmax 1 /Inverse-FBL). For this reason, the CPU  311  is provided with no port which is connected to the sixth contacts  104   f  and  204   f  (Fmax 2 /Inverse-FLB) which are used for the handshake performed between the body CPU  111  and the lens CPU  211 . The fifth contact  304   e  (Fmax 1 /Inverse-FBL) on the rear mount  303  is connected to a first communication/control contact. The first communication/control contact is defined by the fifth contacts  104   e  and  204   e.    
     The rear converter  300  is provided on the rear mount  303  thereof with a power contact  305 , and is provided on the front mount  3031  thereof with a power contact  3051 . The power contact  105  of the camera body  100  is connected with the power contact  205  of the photographing lens  200  via the two power contacts  305  and  3051  when the rear converter  300  is mounted between the camera body  100  and the photographing lens  200 . Battery power can be supplied to the CPU  311  from the battery  113  via the power contacts  105  and  205 . Likewise, battery power can be supplied to the lens CPU  211  from the battery  113  via the power contacts  305  and  3051 . 
     The rear converter  300  is characterized in that the CPU  311  thereof sends out data on the rear converter  300  on demand of the body CPU  111  while the handshake operation is performed between the body CPU  111  and the lens CPU  211 . 
     Fundamental operations of the embodiment of the SLR camera system with the rear converter  300  will be hereinafter discussed in detail with reference to the timing charts shown in FIGS. 28 and 29 in combination with the flow charts shown in FIGS. 30,  31  and  32 . Operations for communications between the camera body  100  and the photographing lens  200  are to the same as those in the above-described embodiment of the SLR camera system wherein the rear converter  300  is not mounted between the camera body  100  and the photographing lens  200 . 
     Immediately after the main switch SWMAIN is turned ON in a state where the rear converter  300  is properly mounted between the camera body  100  and the photographing lens  200 , as shown in FIG. 27, the body CPU  111  supplies the first power to the fourth contact  104   d  (CONTL), and makes the level of the third contact  104   c  (Fmin 3 /RESL) fall to a low level to communicate with the lens ROM  221 , i.e., to perform the lens ROM communication (the old-type communication). At this time, the first power is supplied to each of the CPU  311  and the ROM  321  of the rear converter  300  via the fourth contact  304   d  (CONTL), while the lens ROM  221  is set to change from a disable state to an enable state if the level of the third contact  304   c  (Fmin 3 /RESL) falls to a low level. 
     Although this old-type communication is similar to the old-type communication performed with no rear converter being mounted between the camera body  100  and the photographing lens  200 , the lens ROM  221  does not output any data for the last few bytes when sending out the lens data on the photographing lens  200 , rather, the ROM  321  of the rear converter  300  outputs data on the rear converter  300  (rear converter data) instead. The rear converter data that is output from the ROM  321  of the rear converter  300  is, e.g., data on the type of the rear converter  300 , so that the body CPU  111  recognizes the existence of the rear converter  300  upon receiving the rear converter data. Subsequently, if the body CPU  111  recognizes the rear converter  300  as a new type which is compatible with the new-type lens communication, the body CPU  111  issues command  7 F to the rear converter  300  to communicate with the CPU  311  of the rear converter  300  to receive the aforementioned rear converter communication data (new-type communication data) from the CPU  311 . Since the rear converter communication data is transmitted to the body CPU  111  under control of the CPU  311  of the rear converter  300 , data values in the rear converter communication data can be varied in accordance with a variation in power of the rear converter  300 , and/or the rear converter communication data can be sent out with additional information. This increases the degree of freedom in the development of the rear converter  300 . 
     FIG. 30 shows a flow chart for the main process of the rear converter  300  which is performed by the CPU  311  thereof. Control enters the main process shown in FIG. 30 immediately after the level of the fifth contact  304   e  (Fmax 1 /Inverse-FBL) falls to a low level and the level of the third contact  304   c  (Fmin 3 /RESL) rises to a high level when the body CPU  111  supplies the first power to the fourth contact  304   d  (CONTL). It should be noted that operations or processes having step numbers bearing a prefix “RS” are related to control/operation of the rear converter  300 . 
     In the main process shown in FIG. 30, firstly the CPU  311  of the rear converter  300  initializes internal RAM and ports thereof (step RS 101 ). Subsequently, a new-type communication setting process (“new-type communication setting process” shown in FIG. 31) is performed (step RS 103 ). In this process, an interrupt via an interrupt port Fmax 1  (inverse-INT) of the CPU  311  is enabled to receive an interrupt from the camera body  100  to thereby make the new-type communication possible between the camera body  100  and the rear converter  300 . 
     Subsequently, it is determined whether a sleep flag which is set to “1” by a command issued by the body CPU  111  is “1” (step RS 105 ). If the sleep flag is “1” (if YES at step RS 105 ), the CPU  311  performs a CPU stop operation to enter a power saving mode (step RS 107 ), the sleep flag is set to “0” (step RS 109 ), and the CPU  311  enters sleep mode (step RS 111 ). The CPU  311  wakes upon receiving an interrupt signal via the interrupt port Fmax 1  (inverse-INT) of the CPU  311 . 
     If it is determined at step RS 105  that the sleep flag is not “1” (if NO at step RS 105 ), the operation at step RS 105  is repeated. The new-type communication setting process shown in FIG. 31 is performed during the time the sleep flag (which is checked at step RS 105 ) is “0”. 
     The new-type communication setting process performed at step RS 103  will be hereinafter discussed in detail with reference to the flow chart shown in FIG.  31 . In the new-type communication setting process, firstly it is determined whether the level of the interrupt port Fmax 1  (inverse-INT) is a low level (step RS 201 ). If the level of the interrupt port Fmax 1  (inverse-INT) is not a low level (if NO step RS 201 ), the operation at step RS 201  is performed again, so that the operation at step RS 201  is repeated until the level of the interrupt port Fmax 1  (inverse-INT) falls to a low level. If the level of the interrupt port Fmax 1  (inverse-INT) falls to a low level (if YES step RS 201 ), a communication setting process is performed (step RS 203 ). The communication setting process includes a setting process for serial communication, and an interrupt enabling process via the interrupt port Fmax 1  (inverse-INT). Upon completion of the communication setting process at step RS 203 , it is determined whether the level of the interrupt port Fmax 1  (inverse-INT) is a high level (step RS 205 ). If the level of the interrupt port Fmax 1  (inverse-INT) is not a high level (if NO step RS 205 ), the operation at step RS 205  is performed again, so that the operation at step RS 205  is repeated until the level of interrupt port Fmax 1  (inverse-INT) rises to a high level. Control returns if the level of interrupt port Fmax 1  (inverse-INT) rises to a high level (if YES step RS 205 ). 
     The inverse-INT interrupt process performed by the CPU  311  of the rear converter  300  will be hereinafter discussed with reference to the flow chart shown in FIG.  32 . The inverse-INT interrupt process shown in FIG. 32 starts immediately after the level of the fifth contact  304   e  (Fmax 1 /Inverse-FBL) falls to a low level to thereby cause the interrupt port Fmax 1  (inverse-INT) of the CPU  311  to fall to a low level. In the inverse-INT interrupt process shown in FIG. 32, the CPU  311  sends the rear converter data to the camera body  100  upon receipt of command  7 F. 
     In the inverse-INT interrupt process shown in FIG. 32, firstly at least one command (8-bit data) is received from the camera body  100  via the new-type communication (step RS 301 ). Subsequently, it is determined whether at least one of commands  70 ,  71 ,  72 , B 0 , B 1 , B 2 , D 1 , D 2 , D 3  and D 4  was received at step RS 301  (step RS 303 ). If at least one of these commands was received at step RS 301  (if YES at step RS 303 ), such a command or commands are those which have been issued for the photographing lens  200 , so that a dummy data communication process in which the CPU  311  receives unnecessary communication data (dummy data) for the rear converter  300  is performed (step RS 305 ), and subsequently control proceeds to step RS 307 . If none of commands  70 ,  71 ,  72 , B 0 , B 1 , B 2 , D 1 , D 2 , D 3  and D 4  is received at step RS 301  (if NO at step RS 303 ), control proceeds from step RS 303  to step RS 307 . 
     At step RS 307 , it is determined whether at least one of commands D 0 ,  71  and B 1  was received at step RS 301 . If at least one of commands D 0 ,  71  and B 1  was received at step RS 301  (if YES at step RS 307 ), the sleep flag is set to “1” (step RS 309 ), and control proceeds to step RS 311 . If none of commands D 0 ,  71  and B 1  was received at step RS 301  (if NO at step RS 307 ), control proceeds from step RS 307  to step RS 311 . Accordingly, when the photographing lens  200  enters sleep mode, the rear converter  300  also enters sleep mode. 
     At step RS 311  it is determined whether command  7 F was received at step RS 301 . If command  7 F was received at step RS 301  (if YES at step RS 311 ), the rear converter data is transmitted to the body CPU  311  (step RS 313 ) and subsequently control returns. If it is determined at step RS 311  that command  7 F was not received at step RS 301  (if NO at step RS 311 ), control returns. Command  7 F is issued for the rear converter  300 . The photographing lens  200  performs the dummy data communication process (step LS 449  or LS 479 ) upon receiving command  7 F issued by the body CPU  111 , and the CPU  311  of the rear converter  300  sends the rear converter data to the body CPU  111  in synchronization with the dummy data communication process. The body CPU  111  performs operations/processes in accordance with the rear converter data upon receiving the rear converter data. 
     As can be understood from the above descriptions, according to the present embodiment of the SLR camera system to which the present invention is applied, a data area for the rear converter  300  is secured in advance so that the rear converter  300  can send the rear converter data to the camera body during data communication between the camera body  100  and the photographing lens  200 . This makes it possible for the camera body  100  to communicate with each of the photographing lens  200  and the rear converter  300 , and to control operations of the photographing lens  200  and the rear converter  300  without the need for switching data communications therebetween. 
     The rear converter can be provided with one or more additional functions/capabilities, e.g., a variable diaphragm function and a swing/tilt function. If the rear converter is provided with such one or more additional functions/capabilities, data on such additional functions/capabilities can be transmitted to the camera body as the rear converter data. 
     As can be understood from the foregoing, according to the present embodiment of the SLR camera system to which the present invention is applied, since the rear converter includes a group of relay channels via which the first group of contacts of the camera body are electrically connected with the second group of contacts of the photographing lens, respectively, in a state where the rear converter is properly mounted between the camera body and the photographing lens; a memory in which rear converter data on the rear converter is stored, the memory including at least one port electrically connected to corresponding at least one relay channel of the group of relay channels; and a controller which controls a reading operation of the rear converter data from the memory, the controller including at least one port electrically connected to corresponding at least one relay channel of the group of relay channels; wherein the memory and the controller have a function to send the rear converter data to the camera body while the camera body and the photographing lens communicate with each other via the first group of contacts, the second group of contacts, and the group of relay channels; neither the camera body nor the photographing lens needs to be provided with any additional contacts for data communications. In addition, data on the rear converter can be transmitted to the camera body without the need for switching in data communications between the photographing lens and the rear converter. 
     Obvious changes may be made in the specific embodiments of the present invention described herein, such modifications being within the spirit and scope of the invention claimed. It is indicated that all matter contained herein is illustrative and does not limit the scope of the present invention.