Abstract:
A lens apparatus, with which compatibility, regarding AF operations, to cameras of a variety of manufacturers can be established more easily, is disclosed. The lens apparatus includes a focus driver which drives a focus lens, a terminal which is a member for communication with the camera. Further, the apparatus includes a signal generating circuit into which an image-pickup signal output from the camera is input via the terminal, and which generates a focus driving signal for the focus driver based on the image-pickup signal.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to lens apparatuses performing AF (autofocus) control. 
   2. Description of the Related Art 
   In recent years, automatic focusing function (referred to in the following as “AF”) has become indispensable in image-pickup apparatuses, such as consumer video cameras, broadcast cameras and professional cameras. The most common approach for AF systems is to extract a signal corresponding to the sharpness of an object based on the image-pickup signal, and to evaluate this signal to detect the focusing state of the optical system. 
   An example of the operation of this AF approach is described with reference to  FIG. 8 . In  FIG. 8 , numerical reference  31  denotes an exchangeable lens apparatus, numerical reference  21  denotes a camera, and numerical reference  34  denotes a camera cable. 
   In the camera  21 , numerical reference  211  denotes an image-pickup device, numerical reference  212  denotes an amplifying circuit that amplifies the output of the image-pickup device  211 , and numerical reference  213  denotes a processing circuit that processes signals that have been amplified by the amplifying circuit  212  and formats them as NTSC or PAL signals or the like. 
   Numerical reference  214  denotes a video output terminal that outputs the video signal that is output from the processing circuit  213 . Numerical reference  216  denotes a sharpness evaluation value generating circuit that receives the output of the amplifying circuit  212 , extracts the sharpness of the video signal from that signal, and generates a sharpness evaluation signal. 
   Numerical reference  215  denotes a camera-side interface (IF) that creates and transmits various kinds of control information that are necessary for the lens control, such as the AF evaluation value that is output by the sharpness evaluation value generating circuit  216 . 
   In the lens apparatus  31 , numerical reference  311  denotes a lens-side IF that receives the control information and the sharpness evaluation value that are output from the camera-side IF  215  via the camera cable  34 . 
   Numerical reference  313  denotes an evaluation value peak searching circuit that generates a signal driving a motor  314  such that the sharpness evaluation value that is successively input from the lens-side IF  311  at the vertical synchronization takes on a peak value. 
   The motor  314  is actuated by a motor driving signal from the evaluation value peak searching circuit  313 , and numerical reference  315  denotes a focus lens that is moved in the optical axis direction by rotating the motor  314 . 
   A light flux that has passed through the focus lens  315  is formed an image on an image-pickup plane of the image-pickup device  211 . A signal that has been photo-electrically converted by the image-pickup device  211  is subjected to a sample-and-hold process and is input into the amplifying circuit  212 . The amplifying circuit  212  amplifies the signal to a suitable level, and inputs it into the processing circuit  213  and the sharpness evaluation value generating circuit  216 . The processing circuit  213  formats the input signal into a video format such as NTSC or PAL, and outputs it to the video output terminal  214 . On the other hand, the sharpness evaluation value generating circuit  216  filters the signal that has been input, generates, at each vertical synchronization period, a digital evaluation signal that indicates the sharpness of the video signal from frequency components included in the video signal, and outputs it as a sharpness evaluation value to the camera-side IF  215 . 
   The camera-side IF  215  transmits to the lens apparatus  31  with this evaluation value and other information necessitated by the lens apparatus  31   
   The lens-side IF  311  outputs the received information to the circuits within the lens apparatus  31 , and outputs for example the sharpness evaluation value to the evaluation value peak searching circuit  313 . The evaluation value peak searching circuit  313  generates a driving signal for the motor  314 , and searches the position of the focus lens  315  at which the sharpness evaluation value takes on a peak, while driving the motor  314  and comparing the sharpness evaluation values that are input into it at each vertical synchronization period. 
   It should be noted that the video AF operation of camera systems employing this structure is discussed in detail in Japanese Patent Laid-Open Nos. H9(1997)-9130, H9(1997)-9131 and H9(1997)-9132 (corresponding to U.S. Pat. No. 6,373,524). 
   On the other hand, ordinary camera systems for broadcasting or professional use are connected with a 12-pin or 36-pin camera cable  34  for serial or parallel communication to exchange the control information that is necessary for the lens control. 
   In order to communicate the sharpness evaluation value between the lens apparatus  31  and the camera  21  by serial transmission, strict compatibility between the lens apparatus  31  and the camera  21  is required. For this reason, in cases in which the lens apparatus  31  and the camera  21  are supplied by different manufacturers, as is often the case with broadcasting or professional camera systems, it has to be ensured that the interfaces of the different manufacturers are compatible with one another. 
   However, it is difficult to promote a uniform standard, because signals necessary for the AF operation, such as the sharpness evaluation value, are what is most characteristic of the autofocus operation of each camera manufacturer. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a lens apparatus and an image-pickup system, with which compatibility, regarding the AF operation, to cameras of a variety of manufacturers can be established more easily. 
   In order to attain this object, a lens apparatus according to one aspect of the present invention includes a focus driver which drives a focus lens, a terminal which is a member for communication with the camera. Further, the apparatus includes and a signal generating circuit into which an image-pickup signal output from the camera is input via the terminal, and which generates a focus driving signal for the focus driver based on the image-pickup signal. 
   A lens apparatus according to another aspect of the present invention includes a focus driver which drives a focus lens, a terminal which is a member for communication with the camera, a signal extraction circuit which extracts the image-pickup signal from the combined signal of the control signal and the image-pickup signal input from the camera via the terminal. Further, the apparatus includes a signal generating circuit which generates a focus driving signal for the focus driver based on the image-pickup signal extracted by the signal extraction circuit. 
   A lens apparatus according to yet another aspect of the present invention includes a driver, a first terminal which is a member for communication with a first camera having communication function according to a first communication format, a second terminal which is a member for communication with a second camera having communication function according to a second communication format. Further, the apparatus includes a circuit which outputs a driving signal to the driver based on a signal received at the second terminal when the lens apparatus is mounted to the first camera. 
   Furthermore, an image-pickup system in accordance with the present invention can be configured by combining any of the above lens apparatuses with a camera. 
   These and further objects and features of the lens apparatus and the image-pickup system of the present invention will become apparent from the following detailed description of preferred embodiments thereof taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows the structure of an image-pickup system in accordance with Embodiment 1 of the present invention. 
       FIG. 2  is a block diagram showing the structure of the communication IFs of a camera and a lens apparatus that constitute an image-pickup system in accordance with Embodiment 1. 
       FIG. 3  is a block diagram showing the structure of the communication IFs of a camera and a lens apparatus that constitute an image-pickup system in accordance with Embodiment 1. 
       FIG. 4  is a block diagram showing the structure of the communication IFs of a camera and a lens apparatus that constitute an image-pickup system in accordance with Embodiment 2 of the present invention. 
       FIG. 5  is a timing chart illustrating the operation timing of Embodiment 2. 
       FIG. 6  is a block diagram showing the structure of the communication IFs of a camera and a lens apparatus that constitute an image-pickup system in accordance with Embodiment 3 of the present invention. 
       FIG. 7  is a timing chart illustrating the operation timing of Embodiment 3. 
       FIG. 8  is a block diagram illustrating the structure of a conventional image-pickup system. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following is a detailed description of embodiments of the present invention, with reference to the accompanying drawings. 
   Embodiment 1 
     FIG. 1  shows the structure of an image-pickup system in accordance with Embodiment 1 of the present invention. In  FIG. 1 , numerical reference  1  denotes an exchangeable lens apparatus in accordance with the present invention, and numerical reference  2  denotes a camera. Numerical reference  4  denotes a camera cable that forms a plurality of transmission paths between the camera  2  and the lens apparatus  1 , and is made of a plurality of core lines (communication lines) that are bundled together. 
   In the camera  2 , numerical reference  201  denotes an image-pickup device made of a CCD or a CMOS sensor. Numerical reference  202  denotes an amplifying circuit that amplifies the output of the image-pickup device  201 . Numerical reference  203  denotes a processing circuit that processes signals that have been amplified by the amplifying circuit  202  and formats them as NTSC or PAL signals or the like. Numerical reference  204  denotes a video output terminal that outputs a video signal (image-pickup signal) that is output from the processing circuit  203 . 
   Numerical reference  205  denotes a camera-side interface (IF) that outputs to the camera cable  4  the video signal that has been output by the amplifying circuit  202  and communicates information by a serial or a parallel communication format to the lens apparatus  1 . 
   In the lens apparatus  1 , numerical reference  101  denotes a lens-side IF that communicates with the camera-side IF  205  via the cable  4 , and into which video signals are input. Numerical reference  102  denotes a sharpness evaluation value generating circuit that generates a sharpness evaluation value indicating the sharpness of the video image, based on the video signal entered through the lens-side IF  101 . Numerical reference  103  denotes an evaluation value peak searching circuit that generates a motor driving signal serving as a focus driving signal, such that the sharpness evaluation value becomes maximal. The sharpness evaluation value generating circuit  102  and the sharpness evaluation value peak searching circuit  103  together constitute a driving signal generating circuit. 
   Numerical reference  104  denotes a motor serving as a focus driving unit (driver) that is actuated by the motor driving signal from the evaluation value peak searching circuit  103 . Numerical reference  105  denotes a focus lens that is moved in an optical axis direction by rotating the motor  104 . 
   Numerical reference  150  is a lens controller, which carries out the various kinds of control of the lens apparatus  1 . Numerical reference  106  denotes an iris (aperture stop), which constitutes an image-taking optical system together with the focus lens  105  and a variator lens that is not shown in the drawings. The aperture diameter of the iris  106  is controlled by the lens controller  150 . 
   A light flux coming from an object that have passed through the image-taking optical system  105  is formed an image on the image-pickup plane of the image-pickup device  201 . The signal that is photo-electrically converted by the image-pickup device  201  is subjected to a sample-and-hold process and is input into the amplifying circuit  202 . The amplifying circuit  202  amplifies the signal to a suitable level, and inputs it into the processing circuit  203  and the camera-side IF  205 . 
   The processing circuit  203  formats the input signal into a video format such as NTSC or PAL, and outputs it to the video output terminal  204 . The camera-side IF  205  communicates various kinds of information, including the video signal, to the lens-side IF  101  of the lens apparatus  1 . 
   Here, it would seem possible to input the image-pickup signal from the camera  2  into the lens apparatus  1  and to generate the signals necessary for the autofocus operation, such as the sharpness evaluation value, with the, circuit inside the lens apparatus  1 . But in prior arts, the core lines within the 12-core or 36-core cables (i.e. cables with 12 or 36 pins) that are used for connecting the camera  2  and the lens apparatus  1  are all defined in order to enable bi-directional serial or parallel communication between the camera  2  and the lens apparatus  1 . Therefore, new definitions for those core lines have to be realigned in order to input the image-pickup signal from the camera  2  to the lens apparatus  1 . 
   Referring to  FIG. 2  and  FIG. 3 , the following is a more detailed description of the communication between the camera  2  and the lens apparatus  1 . It should be noted that  FIG. 2  illustrates the case that the lens apparatus  1  is mounted to a camera provided with a serial communication function, whereas  FIG. 3  illustrates the case that the lens apparatus  1  is mounted to a camera provided with a parallel communication function. 
   In these drawings, numerical references  401 ,  402 ,  404 ,  405 , and  407  to  410  denote communication terminals, numerical reference  406  denotes a power supply terminal, and numerical reference  403  denotes a ground terminal. Furthermore, numerical references  411  and  412  are communication terminals that are mainly used for serial communication. It should be noted, however, that the communication terminal  408  also can be used for serial communication, and the communications  411  and  412  also can be used for parallel communication. The power supply terminal and the communication terminals  401  to  412  are provided on a connector (not shown in the drawings), and the terminals are connected to the core lines of the camera cable  4  that are respectively assigned to each of the terminals. 
   In the lens-side IF  101  of the lens apparatus  1 , numerical reference  110  denotes a serial IF detection circuit that detects a serial communication state. Numerical reference  111  denotes a serial sending circuit that sends information in a serial communication format via the communication terminal  411  to the camera  2 . 
   Numerical reference  112  denotes a serial receiving circuit that receives information in the serial communication format via the communication terminal  412  from the camera  2 . 
   Numerical reference  113  denotes a video buffer B that temporarily stores the video signal that is input from the communication terminal  408 . Numerical reference  114  denotes a video buffer A that temporarily stores a video signal that is input from the communication terminal  412 . 
   Numerical reference  115  denotes a video signal selection circuit (V_SEL) that selects either the output of the video buffer B  113  or the output of the video buffer A  114 , and outputs a video signal to the sharpness evaluation value generating circuit  102 , in accordance with the control by the serial IF detection circuit  110 . 
   Regarding the camera  2 ,  FIG. 2  shows the general structure of the camera-side IF  205  for a camera  2  that is provided with a serial communication function, whereas  FIG. 3  shows the general structure of the camera-side IF  205  for a camera  2  that is provided with a parallel communication function. 
   Numerical reference  206  denotes a video signal output buffer that outputs the video signal which is an output of the amplifying circuit  202  to the communication terminal  408  (in  FIG. 2 ) or to the communication terminal  412  (in  FIG. 3 ). Numerical reference  207  denotes a serial IF control circuit for communicating information in the serial communication format. Numerical reference  208  denotes a parallel IF control circuit for communicating information in the parallel communication format. 
   It should be noted that in the lens apparatus  1  in  FIG. 3 , the circuit for communicating various kinds of information to the parallel IF control circuit  208  has been omitted from the drawings, but such circuit is in fact provided, and handles the transfer of various kinds of information. 
   Referring to  FIG. 2 , the following is a description of the operation of the lens-side IF  101  for the case that the camera  2  is provided with a serial communication function. 
   When electric power is supplied from the camera  2  via the camera cable  4  and the power supply terminal  406  to the lens apparatus  1 , the serial IF detection circuit  110  on the side of the lens apparatus  1  sends a start code (which is a code that has been determined in advance between the lens apparatus  1  and the camera  2 ) via the serial sending circuit  111 , the communication terminal  411  and the camera cable  4  to the serial IF control circuit  207  on the side of the camera  2 . 
   After confirming the start code, the serial IF control circuit  207  sends a response code (which is a code that has been determined in advance between the lens apparatus  1  and the camera  2 ) via the camera cable  4 , the communication terminal  412  and the serial receiving circuit  112  on the side of the lens apparatus  1  to the serial IF detection circuit  110 . 
   By detecting the response code with the serial IF detection circuit  110 , it is determined that the mounted camera  2  has a serial communication function, and communication by the serial communication format with the camera  2  is established. At the same time, the serial IF detection circuit  110  applies a selection control signal for inputting the output from the video buffer B  113  to the sharpness evaluation value generating circuit  102 , to the video signal selection circuit  115 . Thus, the video signal in the video buffer B  113  that has been sent from the camera  2  via the communication terminal  408  is input into the sharpness evaluation value generating circuit  102 . 
   Referring to  FIG. 3 , the following is a description of the operation of the lens-side IF  101  for the case that the camera  2  is provided with a parallel communication function. 
   When electric power is supplied from the camera  2  via the camera cable  4  and the power supply terminal  406  to the lens apparatus  1 , the serial IF detection circuit  110  on the side of the lens apparatus  1  sends a start code (which is a code that has been determined in advance between the lens apparatus  1  and the camera  2 ) via the serial sending circuit  111 , the communication terminal  411  and the camera cable  4  to the parallel IF control circuit  208  on the side of the camera  2 . 
   The parallel IF control circuit  208  cannot confirm this start code at this time, so that no response code is output. The serial IF detection circuit  110  is in a standby state for a predetermined time during which it waits for detection of the response code, and when this predetermined time elapses, the standby state is ended. Thus, the serial IF detection circuit  110  determines that the mounted camera  2  is provided with parallel communication function, and communication by the parallel communication format with the camera  2  is established. 
   At the same time, the parallel IF control circuit  208  applies to the video signal selection circuit  115  with a selection control signal for inputting the output from the video buffer A  114  to the sharpness evaluation value generating circuit  102 . Thus, the video signal in the video buffer A  114  that has been sent from the camera  2  via the communication terminal  412  is input into the sharpness evaluation value generating circuit  102 . 
   In  FIG. 1 , the sharpness evaluation value generating circuit  102  into which the video signal has been input generates, at each vertical synchronization period, a sharpness evaluation value signal, which is obtained by extracting high-frequency components from the video signal by a filtering process, etc., and outputs this sharpness evaluation value signal to the evaluation value peak sending circuit  103 . While driving the motor  104 , the evaluation value peak searching circuit  103  successively compares at each vertical synchronization period a plurality of the sharpness evaluation values that are generated at each vertical synchronization period, and generates such a motor driving signal that the focus lens  105  is moved to a position at which the sharpness evaluation value becomes maximal. Thus, the focus lens  105  is moved to an in-focus position. 
   By configuring the lens apparatus  1  as described above, it is possible to generate a sharpness evaluation value and to achieve an AF operation on the side of the lens apparatus  1  based on the video signal sent from the camera  2  without realigning the details of the definitions for serial communication and parallel communication, by altering the structure of a conventional lens apparatus only slightly. 
   Moreover, even if the camera  2  does not have the function to output video signals to a camera cable  4 , detecting the periodicity of the video synchronization signal and stopping the AF function makes it possible to ensure that no problems occur. 
   Embodiment 2 
     FIG. 4  illustrates the structure of a camera-side IF  205 ′ and a lens-side IF  101 ′ in a camera and lens apparatus configuring an image-pickup system according to Embodiment 2 of the present invention. In this embodiment, structural elements of the camera-side IF  205 ′ and the lens-side IF  101 ′ that are the same as in Embodiment 1 have been given the same numerals, and their further description has been omitted. The basic structure of the camera and the lens apparatus according to the present embodiment is the same as in Embodiment 1. 
   In this embodiment, a video signal that has been obtained by the camera  2  is added (combined) in an analog manner to a control signal with relatively little level fluctuations that has been sent as a parallel communication signal from the camera  2  to the lens apparatus  1 . An example of the control signal with relatively little level fluctuations is a signal for setting the lens apparatus  1  to a mode in which the adjustment of the iris (aperture stop)  106  mounted to the lens apparatus  1  shown in  FIG. 1  is carried out automatically by the lens controller  150 , or to a mode in which the adjustment of the iris  106  is carried out manually by the camera operator, the voltage level of the signal varying in accordance with the mode. 
   In  FIG. 4 , numerical reference  209  in the camera-side IF  205 ′ denotes an adding combination circuit that additionally combines the output of the parallel IF control circuit  208  and of the video signal output buffer  206  in an analog manner. 
   Numerical reference  120  in the lens-side IF  101 ′ denotes a DC component blocking circuit (video signal extracting circuit) that receives the combined signal that is output by the adding combination circuit  209  (i.e. the signal obtained by additionally combining the control signal and the video signal) via the camera cable  4  and the communication terminal  408 , and blocks direct current (DC) components in that received signal. 
   Furthermore, numerical reference  121  denotes an AC component blocking circuit that receives the combined signal that is output by the adding combination circuit  209  via the camera cable  4  and the communication terminal  408 , and blocks frequency (AC) components in that received signal to extract the control signal. 
   Numerical reference  122  denotes a parallel processing circuit that processes the output of the AC component blocking circuit  121  as the control signal, which is a parallel communication signal. Numerical reference  123  denotes a low-pass filter (LPF) that limits the bandwidth of the output of the DC component blocking circuit  120 . 
   The operation of this embodiment is explained using the charts shown in  FIG. 5 , which illustrate signals from the amplifying circuit  202  to the sharpness evaluation value generating circuit  102 . It should be noted that the numerals given next to ( 1 ) to ( 7 ) in  FIG. 5  correspond to the numerals of the structural elements in  FIG. 4 . 
   Here, the camera  2  is provided with a switch (not shown in the drawings) for selecting between the automatic and the manual iris adjustment mode. The parallel IF control circuit  208  generates a control signal (referred to as “level signal” in the following) that is assigned to a high voltage level or a low voltage level in accordance with the information of the switch settings, and sends this level signal by parallel communication via the camera cable  4  and the communication terminal  408  to the lens apparatus  1 . 
   The level signal (shown in  FIG. 5  ( 2 )) generated by the parallel IF control circuit  208  and the video signal that is output from the video signal output buffer  206  (shown in  FIG. 5  ( 1 )) are input into the adding combination circuit  209 . The adding combination circuit  209  additionally combines the two inputs in an analog manner (shown in  FIG. 5  ( 3 )), and sends the result via the camera cable  4  and the communication terminal  408  to the DC component blocking circuit  120  and the AC component blocking circuit  121  on the side of the lens apparatus  1 . 
   The AC component blocking circuit  121  blocks the video signal components (AC components) with a low-pass filter (not shown in the drawings) with large time constant (shown in  FIG. 5  ( 5 ), and inputs the thereby extracted level signal into the parallel processing circuit  122 . The parallel processing circuit  122  sends an instruction signal to the lens controller  150  that switches the iris adjustment mode to automatic or manual, in accordance with the level of the level signal that has been entered. It should be noted that at this time, the level signal is delayed as shown in  FIG. 5  ( 7 ) due to the influence of the AC component blocking circuit  121 , but the setting of the iris adjustment mode does not have to be controlled instantaneously, so that no particular problem occurs. 
   On the other hand, the DC component blocking circuit  120  blocks the level signal component (DC component) within the combined signal that has been sent from the side of the camera  2 , and extracts (restores) the video signal (horizontal component) shown in  FIG. 5  ( 1 ). At this time, the video signal may fluctuate due to the change of the level signal (shown in  FIG. 5  ( 2 )) caused by the parallel IF control circuit  208 . For example, the video signal that is output from the DC component blocking circuit  120  contains an edge component due to the change of the level signal, indicated as “high-frequency noise” in  FIG. 5  ( 4 ). However, this edge component is eliminated by the LPF  123 , which is set up such that it lets only the video band pass as shown in  FIG. 5  ( 6 ). 
   Then, the video signal that has been restored by passing through the DC component blocking circuit  120  and the LPF  123  is entered into the sharpness evaluation value generating circuit  102 . 
   At each vertical synchronization period, the sharpness evaluation value generating circuit  102 , into which the video signal is input, generates a sharpness evaluation value signal, which is obtained by extracting high-frequency components from the video signal by a filtering process, etc. Then, a sharpness evaluation value signal is output to the sharpness evaluation value peak searching circuit  103  (see  FIG. 1 ), as explained for Embodiment 1. Thus, the focus lens  105  can be moved to an in-focus position. 
   By configuring the lens apparatus  1  as described above, it is possible to generate a sharpness evaluation value and to achieve an AF operation on the side of the lens apparatus  1  based on the video signal sent from the camera  2  without realigning the details of the definitions for serial communication and parallel communication. Also in the camera-side IF  205 ′, it is possible to handle the sending of the video signal with a circuit of small size. 
   Embodiment 3 
     FIG. 6  shows the structure of a camera-side IF  205 ″ 0  and a lens-side IF  101 ″ in a camera and a lens apparatus configuring an image-pickup system according to Embodiment 3 of the present invention. In this embodiment, structural elements of the camera-side IF  205 ″ and the lens-side IF  101 ″ that are the same as in Embodiments 1 or 2 have been given the same numerals, and their further description has been omitted. The basic structure of the camera and the lens apparatus according to the present embodiment is the same as in Embodiment 1. 
   In this embodiment, when an edge component is generated in a video signal as a result of a change in the level signal for setting the iris adjustment mode, as described in Embodiment 2, then the sharpness evaluation value based on this video signal is not used for the AF process. 
   In  FIG. 6 , numerical reference  124  denotes an AF process prohibiting signal generating circuit (prohibiting signal output circuit) that detects fluctuations in the level signal that is sent from the AC component blocking circuit  121  by parallel communication, and generates a signal prohibiting the AF calculation process using a synchronization signal that is extracted from the video signal component, which is the output of the DC component blocking circuit  120 . It should be noted that the lens-side IF  101 ″ is not provided with the low-pass filter  123  provided in Embodiment 2. 
   The operation of this embodiment is explained using the charts shown in  FIG. 7 , which illustrate signals in its vertical synchronization periods. It should be noted that the numerals given next to ( 1 ) to ( 5 ) in  FIG. 7  correspond to the numerals of the structural elements in  FIG. 6 . 
   A level signal (shown in  FIG. 7  ( 2 )) that has been restored from the combined signal, which is output from the AC component blocking circuit  121 , and a vertical synchronization signal extracted from the video signal that has been restored with the DC component blocking circuit  120  are input into the AF prohibiting signal generating circuit  124  and converted into a gate signal, as shown in  FIG. 7  ( 5 ). That is to say, using the timing at which the level of the entered level signal changes and the vertical synchronization signal, a prohibiting signal is generated whose level changes at a starting timing A of an effective video area of the video signal (vertical component). 
   This prohibiting signal is input into the evaluation value peak searching circuit  103 . While the prohibiting signal has been input into the evaluation value peak searching circuit  103 , sharpness evaluation values that are generated by the sharpness evaluation value generating circuit  102  are discarded, as shown in  FIG. 7  ( 4 ). Moreover, sharpness evaluation values that are generated while no prohibiting signal is being entered are employed for the AF process following thereafter (as indicated by “process” in  FIG. 7  ( 4 ). 
     FIG. 7  ( 3 ) illustrates an extraction frame signal for specifying the video region (evaluation value extraction frame) within the video signal which is used for the generation of the sharpness evaluation value. 
   The transfer of the sharpness evaluation value signal from the sharpness evaluation value generating circuit  102  to the evaluation value peak searching circuit  103  is performed at the timing of the falling flank of this extraction frame signal (see  FIG. 7  ( 4 )), so that during the period in which the prohibiting signal is at low level, a sharpness evaluation value signal including the influence of the point of the change of the level signal (point B in FIG.  7 ( 2 ))) is transferred. Consequently, the sharpness evaluation value signal that has been transferred during the period in which the prohibiting signal is at low level is discarded by the evaluation value peak searching circuit  103 , and while successively comparing the sharpness evaluation value signal that is unaffected by the change of the level signal (i.e. that has been transferred during the period in which the prohibiting signal is not at low level) at each vertical synchronization period, a motor driving signal is generated such that the focus lens  105  is moved to the position at which the sharpness evaluation value becomes maximal. Thereby, the focus lens  105  is moved to the in-focus position. 
   By configuring the lens apparatus  1  as described above, a correct AF control can be carried out using a more reliable sharpness evaluation value. 
   It should be noted that in this embodiment, if the amplification circuit  202  sets the voltage level of the video signal lower than a low level threshold of the serial communication signal, then, even without the AC component blocking circuit  121 , the parallel processing circuit  122  can perform a proper threshold judgment, and the control signal can be extracted. 
   As explained above, with the above embodiments, it is not necessary anymore to communicate signals that are necessary for AF operation and for which uniform standardization is difficult (such as the sharpness evaluation value) from the camera to the lens apparatus, and compatibility can be easily established between the lens apparatus and the camera. 
   Moreover, using the redundancy in the communication terminal assignment in lens apparatuses that are capable of communication by a serial communication format as well as by a parallel communication format, the image-pickup signal can be input via the communication terminals that are assigned to the communication format that is not the communication format with which the camera complies. Thus, it is possible to input the image-pickup signal from the camera to the lens apparatus without adding new core lines to the cable connecting the camera and the lens apparatus. 
   Moreover, since the image-pickup signal can be sent to the lens apparatus utilizing the communication terminals that are used for communicating a control signal (preferably a control signal whose level does not change frequently during image-pickup) from the camera to the lens apparatus, it is possible to input the image-pickup signal from the camera to the lens apparatus without adding new core lines to the cable connecting the camera and the lens apparatus. 
   It should be noted that when a level change occurs in the control signal included in the combined signal which is generated by combining the image-pickup signal and the control signal sent from the camera, then it is possible to generate a proper focus driving signal unaffected by the noise due to that level change, by restricting the generation of the focus driving signal based on the image-pickup signal in the driving signal generating circuit. 
   While preferred embodiments have been described, it is to be understood that modification and variation of the present invention may be made without departing from the scope of the following claims.