Patent Publication Number: US-9411124-B2

Title: Imaging apparatus and controlling method therefor, and lens unit and controlling method therefor, and imaging system

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is a divisional of application Ser. No. 13/729,990, filed Dec. 28, 2012, the entire disclosure of which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the automatic focus adjustment of a lens unit and an imaging apparatus that is mountable to the lens unit. 
     2. Description of the Related Art 
     In recent years, AF (auto focus) devices for cameras that determine an AF evaluation value by detecting the sharpness of an image from an imaging signal and shift a focus lens to a position where the AF evaluation value is the highest to thereby perform focus adjustment have been prevailing. Hereinafter, the above method is referred to as the “TVAF method”. As an AF evaluation value, the high frequency component level of an image signal extracted by a band pass filter with a predetermined band is typically used. When an object is captured, an AF evaluation value increases as the focus lens is being focused and is maximized at an in-focus point as shown in  FIG. 2A . In other words, in the example, the degree of focusing decreases with distance from the in-focus position.  FIG. 2B  shows an operation (hereinafter referred to as “wobbling operation”) for determining a focusing direction based on the change in the AF evaluation value obtained when the focus lens is driven at micro intervals. In the wobbling operation, the influence of the movement of the lens on a capturing screen is not noticeable, and thus, the wobbling operation is used particularly for capturing moving images. On the other hand, the drive amount of the focus lens and the image plane shift amount are not always the same as shown in  FIG. 2C , the ratio (sensitivity) between both amounts is different for each lens unit and may vary depending on the positions of the focus lens and the zoom lens. 
     Japanese Patent Laid-Open No. 2008-242442 discloses an automatic focus adjustment device for adapting the AF method of this type to a video camera having an interchangeable lens unit. The wobbling operation is enabled by an interchangeable lens system by passing a wobbling operation signal to the lens unit and thus causing the lens unit to perform wobbling operation control. 
     However, in the case of controlling the focus lens by use of a conventional interchangeable lens system, it is difficult for a camera body to change the movement of the focus lens when the improvement in wobbling operation is desired in the future. Also, it is an undesirable necessity that different drive commands be prepared when it is desired that a camera realize the drive control of the focus lens for each lens unit, resulting in a complication of control. As described above, the image plane shift amount relative to the drive amount of the focus lens is different for each lens unit and may also vary depending on a focus lens position and a zoom lens position. For this reason, even if the control unit provided in the camera body of the interchangeable lens system can provide an instruction about a desired image plane shift amount to the lens unit, the control unit is unaware of the actual drive amount of the focus lens relative to the image plane shift amount. In other words, it is difficult for the control unit of the camera body to acquire detailed information about lens configuration, lens specification, and the like in order to provide an instruction about a specific drive amount of the focus lens to the lens unit. 
     SUMMARY OF THE INVENTION 
     The present invention provides an interchangeable lens system that an imaging apparatus transmits integrated information of a focus lens to a lens apparatus so as to control the various shifts of the focus lens including a wobbling operation. 
     According to an aspect of the present invention, an imaging apparatus is provided that is mountable to a lens unit provided with an imaging optical system including a focus lens. The imaging apparatus includes an imaging unit configured to generate an imaging signal by photoelectrically converting an object image; a signal processing unit configured to generate an evaluation signal for focus adjustment using the imaging signal; and control unit configured to generate drive information about a focus lens based on the evaluation signal and to transmit the drive information to the lens unit when mounted. When micro vibration of the focus lens is performed, the control unit is configured to transmit to the lens unit first information about the position of the focus lens serve as a reference for micro vibration and second information about an amount of movement of the focus lens indicated as a shift amount of an image plane with reference to the position of the focus lens when the first information was transmitted, as drive information about the focus lens. 
     According to the present invention, an imaging apparatus that transmits drive information including information about the shift amount of an image plane from the imaging apparatus body to a lens unit so as to control the movement of the focus lens may be provided. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram illustrating an example of the configuration of an imaging system including a lens unit and an imaging apparatus in order to describe embodiments of the present invention in conjunction with  FIGS. 2 to 17 . 
         FIG. 2A  is a diagram illustrating a TVAF signal. 
         FIG. 2B  is a diagram illustrating a wobbling operation. 
         FIG. 2C  is a schematic diagram illustrating a focus lens drive amount and an image plane shift amount. 
         FIG. 3  is an explanatory diagram illustrating a phase difference AF-enabled imaging element on an image capturing plane. 
         FIG. 4  is a flowchart (former half) illustrating TVAF processing in conjunction with  FIG. 5 . 
         FIG. 5  is a flowchart (latter half) illustrating the continuation of  FIG. 4 . 
         FIG. 6  is a flowchart (former half) illustrating wobbling operation in conjunction with  FIG. 7 . 
         FIG. 7  is a flowchart (latter half) illustrating the continuation of  FIG. 6 . 
         FIG. 8A  is a diagram illustrating micro-driving. 
         FIG. 8B  is a diagram illustrating an accumulation timing of an imaging element. 
         FIG. 9  is a diagram illustrating processing performed by a camera control unit and a lens control unit. 
         FIGS. 10A and 10B  are diagrams illustrating an example of communication data. 
         FIG. 10C  is a diagram illustrating a variant example of a focus lens during a wobbling operation. 
         FIG. 11A  is a diagram illustrating an example of control of a focus lens position. 
         FIG. 11B  is a diagram illustrating processing performed when a focus lens reaches an end of a movable region during wobbling operation. 
         FIG. 12  is a flowchart (former half) illustrating mountain-climbing driving in conjunction with  FIG. 13 . 
         FIG. 13  is a flowchart (latter half) illustrating the continuation of  FIG. 12 . 
         FIG. 14  is a diagram illustrating mountain-climbing driving. 
         FIG. 15A  is a plan view illustrating an image capturing pixel of an imaging element. 
         FIG. 15B  is a cross-sectional view illustrating an image capturing pixel of an imaging element. 
         FIG. 16A  is a plan view illustrating a focus detection pixel of an imaging element. 
         FIG. 16B  is a cross-sectional view illustrating a focus detection pixel of an imaging element. 
         FIG. 17  is a pixel layout diagram illustrating an arrangement of image capturing pixels and focus detection pixels. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.  FIG. 1  is a block diagram illustrating an example of the configuration of an imaging system including a lens unit and an imaging apparatus according to an embodiment of the present invention. The imaging apparatus includes a mountable lens unit  117  and a camera unit  118  served as a body which is used by being mounted with the lens unit  117 . In other words, the lens unit  117  is mountable on the camera unit  118  and a so-called interchangeable lens system is constituted. 
     Light reflected from an object passes through an imaging optical system consisting of a fixed first group lens  101 , a movable second lens group  102 , an aperture  103 , a fixed third lens group  104 , and a movable fourth lens group  105 , all of which are provided in the lens unit  117 , to thereby be focused on an imaging element  106  provided within the camera unit  118 . The second lens group  102  performs a zooming operation. The fourth lens group (hereinafter referred to as “focus lens”)  105  includes both a focus adjustment function and a compensation function for compensating the shift of a focal plane due to the zooming operation. 
     The imaging element  106  is a photoelectric conversion element constituted by a CMOS (Complementary Metal Oxide Semiconductor) image sensor or the like and generates an imaging signal by photoelectrically converting an object image. The imaging signal photoelectrically converted by the imaging element  106  is amplified to an optimum level by an amplifier  107 , and then is output to a camera signal processing unit  108 . Hereinafter, a description will be given of an exemplary configuration of the imaging element  106  with reference to  FIGS. 15 to 17 .  FIG. 15A  and  FIG. 16A  are diagrams illustrating the structures of an image capturing pixel and a focus detection pixel included in the imaging element  106 . In the present embodiment, focus detection pixels having a structure to be described below are distributed and arranged in an image capturing pixel group of the Bayer array in accordance with a predetermined rule. 
       FIG. 15A  and  FIG. 15B  show an example of the arrangement and structure of the image capturing pixel.  FIG. 15A  is a plan view illustrating 2 by 2 image capturing pixels. As is generally known, in the Bayer array, a plurality of G (green) pixels are diagonally arranged, and an R (red) pixel and a B (blue) pixel are arranged as the two remaining pixels. This 2 by 2 structure is repeatedly arranged in a two-dimensional array. 
       FIG. 15B  is a cut-away cross-sectional view taken along the line A-A of the image capturing pixel shown in  FIG. 15A . An on-chip microlens ML is arranged in the front-most surface of each pixel, and an R (Red) color filter CF R  and a G (Green) color filter CF G  are arranged on back of the on-chip microlens ML. Reference symbol PD (PhotoDiode) denotes a schematic photoelectric conversion unit of the imaging element  106 . A signal line for transmitting various signals within the CMOS image sensor is formed in a wiring layer CL (Contact Layer). An imaging optical system TL (Taking Lens) and its exit pupil EP (Exit Pupil) are schematically shown. The on-chip microlens ML and photoelectric conversion unit PD of the image capturing pixel are configured to capture a light flux having passed through the imaging optical system TL as effectively as possible. A signal generated by the image capturing pixel is output to the camera signal processing unit  108 .  FIG. 15B  shows only the incident beam of the R pixel, but the G pixel and the B pixel also have the same structure. 
       FIG. 16A  and  FIG. 16B  show an example of the arrangement and structure of focus detection pixels for carrying out pupil splitting in the horizontal direction of the imaging optical system. By performing pupil splitting in the horizontal direction, the focus of an object, e.g., a vertical line having a luminance distribution in the horizontal direction can be detected. The horizontal direction is defined as a direction along a straight line perpendicular to the optical axis and the vertical axis when the user or photographer holds the camera in the state in which the optical axis of the imaging optical system is horizontal. The vertical direction is defined as a direction perpendicular to the defined horizontal direction. 
     In the present embodiment, from among light transmitted through different regions of the exit pupil of the imaging optical system, a part of light is shielded and remaining non-shielded light is received by focus detection pixels.  FIG. 16A  is a plan view illustrating 2 by 2 pixels including focus detection pixels. When obtaining an imaging signal, the main component of luminance information is acquired by a G pixel. The image recognition feature of a person is sensitive to luminance information. Thus, if a G pixel is lost, degradation of the image quality is readily perceived. On the other hand, an R pixel or a B pixel is used to acquire color information (color difference information), but the visual feature of a person is not sensitive to color information as compared with luminance information. Hence, if only a few pixels for acquiring color information are lost, degradation of the image quality is hardly recognized. Thus, in the present embodiment, among the 2 by 2 pixels, the G pixels are left to serve as image capturing pixels, and the R and B pixels are replaced with focus detection pixels SA and SB. 
       FIG. 16B  is a cut-away cross-sectional view taken along the line A-A shown in  FIG. 16A . The microlens ML and the photoelectric conversion element PD have the same structures as those of the image capturing pixel shown in  FIG. 15B . In the present embodiment, a signal obtained from the focus detection pixel is not used to generate an image, and thus, a transparent film CF W  (white) is arranged in place of the color filter for separating color. To carry out pupil splitting using a photoelectric conversion unit as a unit, the opening of the wiring layer CL is offset in one direction from the center line of the microlens ML. More specifically, the opening OPHA of the focus detection pixel SA is offset in the horizontal direction (to the right side in  FIG. 16 ) and receives a light flux having passed through the left side of the exit pupil EPHA of the imaging optical system TL. The opening OPHB of the focus detection pixel SB is offset to the left in a direction opposite to that of the pixel SA and receives a light flux having passed through the right side of the exit pupil EPHB of the imaging optical system TL. The focus detection pixels SA having the above configuration are arrayed regularly in the horizontal direction, and an object image obtained by these pixel groups is defined as an image A. The focus detection pixels SB are also arrayed regularly in the horizontal direction, and an object image obtained by these pixel groups is defined as an image B. The signals for the image A and the image B are output to a phase difference AF signal processing unit  119  (see  FIG. 1 ). The phase difference AF signal processing unit  119  detects the defocus amount of an image plane of the object image by detecting the relative position (phase difference) of the images A and B. The detection result is output to a camera control unit to be described below. 
     When the defocus amount of an object, e.g., a horizontal line having a luminance distribution in the vertical direction is detected, the configuration shown in  FIG. 16B  is rotated through 90 degrees such that the opening OPHA of the pixel SA is offset downward and the opening OPHB of the pixel SB is offset upward. Alternatively, the opening OPHA of the pixel SA may be offset upward and the opening OPHB of the pixel SB may be offset downward. 
       FIG. 17  shows an example of the arrangement of the image capturing pixels SA and the focus detection pixels SB described with reference to  FIG. 15A ,  FIG. 15B ,  FIG. 16A , and  FIG. 16B . In consideration of the fact that the focus detection pixels cannot be used for the image capturing pixels, in the present embodiment, the focus detection pixels are discretely arranged at predetermined intervals along the horizontal direction and the vertical direction. Also, the focus detection pixels are not arranged at positions of the G pixels so as to make image degradation less apparent. In the present embodiment, as shown in  FIG. 17 , two pairs of the pixels SA and the pixels SB are arranged within a block consisting of 12 by 24 pixels so as to complete the pixel arrangement pattern in one block. 
     As the configuration of the imaging element  106  that is capable of performing AF (auto focus) using a phase difference detection method, a pixel may also be divided into two pixels in one microlens as shown in  FIG. 3A  and  FIG. 3B .  FIG. 3A  shows an example of the sensor arrangement for focus state detection provided in the imaging element  106  and  FIG. 3B  shows an enlarged portion of the sensor arrangement shown in  FIG. 3A . Each microlens is represented by a circular frame and each sensor for each pixel is represented by a rectangular frame. In a location (e.g., see second row in third column) where a pixel is divided into two pixels at the left and right sides with respect to one microlens, the outputs of these pixels are added and the resulting output is output to the camera signal processing unit  108  (see  FIG. 1 ). On the other hand, the output of a pixel at the left side and the output of a pixel at the right side are independently output to the phase difference AF signal processing unit  119 . Among the paired sensors shown in  FIG. 3B , an image A is formed by a left side sensor group and an image B is formed by a right side sensor group. The phase difference AF signal processing unit  119  determines the defocus amount of an image plane from the phase difference between the paired left and right image signals. 
     The camera signal processing unit  108  applies various image processing to an output signal obtained from the amplifier  107  to thereby generate an image. A display unit  109  is constituted by a liquid crystal display device (LCD) or the like and displays an image in accordance with an image obtained from the camera signal processing unit  108 . A recording unit  110  records an image obtained from the camera signal processing unit  108  in a recording medium such as a semiconductor memory or the like. A TVAF gate  113  serves to pass a signal in a region for use in focus detection only from among the output signals of all pixels obtained from the amplifier  107 . A TVAF signal processing unit  114  extracts a high frequency component from the signals passed through the TVAF gate  113  and generates a TVAF evaluation value signal (evaluation signal) to thereby output the generated TVAF evaluation value signal to a camera control unit  116 . The TVAF evaluation value signal represents the sharpness (contrast state) of an image generated on the basis of the image signal obtained from the imaging element  106 . Since sharpness may vary depending on the focus state of an imaging optical system, the value (AF evaluation value) indicated by the TVAF evaluation value signal is focus adjustment information indicating the focus state of the imaging optical system.  FIG. 2A  is a graph illustrating an example of the relationship between a focus lens position and an AF evaluation value where focus lens position is plotted on the horizontal axis and AF evaluation value is plotted on the vertical axis. The peak position of the focus lens  105  when the AF evaluation value reaches its peak value (extreme value) corresponds to the in-focus point. 
     As described above, the phase difference AF signal processing unit  119  calculates the defocus amount (image plane displacement amount) of an image plane based on the phase difference between the image A and the image B obtained from the output of the imaging element  106  and outputs the calculated defocus amount to the camera control unit  116 . The camera control unit  116  that controls the operation of the entire imaging apparatus controls the TVAF gate  113  so as to set a TVAF frame at a predetermined percentage of an image. The camera control unit  116  performs AF control based on the TVAF evaluation value signal acquired from the TVAF signal processing unit  114  and the image plane displacement amount acquired from the phase difference AF signal processing unit  119  to thereby transmit a focus lens drive command to a lens control unit  115 . Here, it is assumed that the focus lens drive amount to be set by the camera control unit  116  is an image plane shift amount (the shift amount of the image forming position of an object image). The reason for this is that a different lens unit is used for the interchangeable lens system and that the actual focus lens drive amount relative to the image plane shift amount is different depending on type of the lens unit and the lens position (the focus position or the zoom position) even if the same lens unit is used. The sign of the image plane shift amount to be set is different depending on the drive direction. For example, the image plane shift amount on the close side is plus and that on the infinity side is minus. 
       FIG. 2C  is a schematic diagram illustrating a lens drive amount and an image plane shift amount. The change in lens position is represented by an arrow A and the change in image plane position is represented by an arrow B. The ratio between the lens drive amount and the image plane shift amount is sensitivity that is different for each lens unit to be used and changes depending on the positions of the focus lens and the zoom lens. Sensitivity (hereinafter abbreviated as “S”) is determined with reference to the data table prepared in advance in a storage unit within the lens unit  117 . 
     Next, a description will be given of a drive unit and its control unit within the lens unit  117 . A zoom drive unit  111  drives the second lens group  102 , and a focus drive unit  112  drives the focus lens  105 . Each of the zoom drive unit  111  and the focus drive unit  112  is constituted by an actuator such as a stepping motor, a DC motor, a vibrating motor, a voice coil motor, or the like. The lens control unit  115  receives a focus lens drive command from the camera control unit  116 , controls the focus drive unit  112  in accordance with the command, and shifts the focus lens  105  in the optical axis direction to thereby perform focusing. At this time, the lens control unit  115  acquires an image plane shift amount as a lens drive amount from the camera control unit  116 . The lens control unit  115  computes the actual focus lens drive amount (lens position coordinate value) from the instructed image plane shift amount to thereby perform focus control. Also, the lens control unit  115  transmits position information about the focus lens  105  to the camera control unit  116 . 
     Next, a description will be given of a focus lens drive command to be transmitted from the camera control unit  116  to the lens control unit  115 . In the present embodiment, communication is performed two times during  1 V ( 1 V is the length of one period of a vertical synchronization signal VD and the length of n periods is hereinafter represented by “nV”). In a first communication, the lens control unit  115  transmits information on the lens position and the reference position to the camera control unit  116 . In a second communication, the camera control unit  116  transmits a focus lens drive command to the lens control unit  115 . Each of the first communication and the second communication is fixed length packet communication. Note that the camera control unit  116  performs AF control using information received by the first communication and transmits the focus lens drive command generated by the AF control to the lens control unit  115  in the subsequent second communication. 
       FIGS. 10A to 10C  show a drive command and the movement of the lens in accordance therewith.  FIG. 10A  illustrates information about drive of the focus lens  105 , which is included in communication from the camera control unit  116  to the lens control unit  115 . The information about drive of the focus lens is included in a drive command in the second communication and includes first information about a lens position served as a reference for a focus lens drive and second information about the shift amount of an image plane.
         Reference position α: (lens position coordinate)   Amplitude β: (image plane shift amount coordinate)   Reference position shift amount γ: (image plane shift amount coordinate)       

     Here, the focus lens drive amount set by the camera control unit  116  is an image plane shift amount. In other words, the amplitude β and the reference position shift amount γ are information about the shift amount of the image forming position of an object image. The reference position α is a position in a lens position coordinate system set in the focus lens  105 . The reference position is a position served as a reference for a drive command to be transmitted from the camera control unit  116  and is normally the vibration center position of wobbling (micro vibration). 
     The lens control unit  115  acquires the above information about drive of the focus lens and calculates a target position and a new reference position with the aid of the following arithmetic expression using the sensitivities S 1  and S 2  obtained with reference to table data. Here, the symbol S 1  represents sensitivity at a current reference position and the symbol S 2  represents sensitivity at a new reference position. When there is a shift from the reference position (γ≠0),
 
Focus lens drive target position=α+β/ S 2+γ/ S 1   (Formula 1)
 
New Reference position=α+γ/ S 1  (Formula 2)
     When there is no shift from the reference position (γ=0),
 
Focus lens drive target position=α+β/ S 1+γ/ S 1   (Formula 1)
 
New Reference position=α+γ/ S 1  (Formula 2)
   

     Each of the amplitude β and the reference position shift amount γ is converted to a lens position by dividing them by sensitivity described in  FIG. 2C . In other words, the lens control unit  115  computes the actual drive amount for actually driving the focus lens  105  with respect to the instructed image plane shift amount to thereby control the position of the focus lens  105 . Then, the lens control unit  115  transmits information about position of the focus lens  105  to the camera control unit  116 . 
       FIG. 10B  illustrates information about the position of the focus lens  105 , which is included in information to be transmitted from the lens control unit  115  back to the camera control unit  116 . Communication of the information is performed in the first communication.
         Focus lens position: (lens position coordinate)   New reference position: (lens position coordinate)       

     These positions are position information in a lens position coordinate system. As described above, information about the position of the focus lens  105  includes a plurality of position information, i.e., third information about the position of the focus lens  105  served as a new reference for micro vibration and fourth information about a focus lens position corresponding to a communication timing from the lens control unit  115  to the camera control unit  116 . Note that fourth information may also be information about a focus lens position at a predetermined timing. For example, information about a predetermined timing (notification timing) may be transmitted from the camera control unit  116  in the second communication, and information about a focus lens position at the predetermined timing may be transmitted from the lens control unit  115  in the subsequent first communication. Here, when the predetermined timing received by the second communication is timing after the subsequent first communication, the lens control unit  115  may predict a focus lens position at the predetermined timing to thereby transmit the predicted focus lens position in the first communication. 
       FIG. 10C  illustrates the movement of the focus lens  105  during the wobbling operation. In the example, the initial reference position is represented by α and a new reference position is represented by α′.  FIG. 11A  is a diagram illustrating a drive command during the wobbling operation using specific numerical values, where time is plotted on the horizontal axis and timing at which a vertical synchronization signal (VD) is output is shown in the upper part of  FIG. 11A . Note that the output timing of the vertical synchronization signal is synchronized with the electric charge accumulation timing of the imaging element  106 . As shown in  FIGS. 11A and 11B , communication from lens to camera is included in the first communication and communication from camera to lens is included in the second communication. Note that information communicated in the first communication and the second communication is not limited to those shown in  FIGS. 11A and 11B .  FIGS. 11A and 11B  show how the focus lens  105  is driven. The following values are shown in the lower part of  FIGS. 11A and 11B , respectively.
         Lens→camera communication data: focus lens position, and new reference position   Camera→lens communication data: reference position α, amplitude β, and reference position shift amount γ       

     The term “lens→camera” means transmission from the lens control unit  115  to the camera control unit  116 , whereas the term “camera→lens” means transmission from the camera control unit  116  to the lens control unit  115 . 
     The content of communication performed during the vertical synchronization periods (1), (3), and (5) is as follows. For ease of explanation, it is assumed that S1=S2=0.5.
         Vertical synchronization period (1): time T1 “camera →lens” α=100, β=5, γ=0       

     The lens control unit  115  calculates a target position and a new reference position based on the received drive command. 
     Focus lens drive target position=100+5/0.5+0/0.5=110 
     New Reference position=100+0/0.5=100
         Vertical synchronization period (3): time T3 “camera→lens” α=100, β=5, γ=0       

     The lens control unit  115  calculates a target position and a new reference position based on the received drive command. 
     Focus lens drive target position=100+5/0.5+0/0.5=90 
     New Reference position=100+0/0.5=100
         Vertical synchronization period (5): time T5 “camera →lens” α=100, β=5, γ=10       

     The lens control unit  115  calculates a target position and a new reference position based on the received drive command. 
     Focus lens drive target position=100+5/0.5+10/0.5=130 
     New Reference position=100+10/0.5=120 
     In the example shown in  FIG. 11A , by communicating the information, the wobbling operation centered on a reference position “120” is carried out after the wobbling operation centered on a reference position “100”. In the above example, after the focus lens drive is performed by the transmitted drive command, the camera control unit  116  performs AF control based on the AF evaluation value acquired from electric charges accumulated in the imaging element  106  while the focus lens is stopped at the close side/infinity side. For example, after the focus lens is driven in the close direction by the drive command transmitted at the time T1 by the camera control unit  116 , the camera control unit  116  generates a drive command to be transmitted at the time T3 based on the AF evaluation value acquired from electric charges accumulated while the focus lens is stopped at the close side. 
     Although no description has been given above, a focus lens position and a new reference position are also transmitted from the lens control unit  115  to the camera control unit  116  in the vertical synchronization periods (2), (4), and (6). Also, the reference position α, the amplitude β, and the reference position shift amount γ are transmitted from the camera control unit  116  to the lens control unit  115 . Since the AF evaluation values acquired in the vertical synchronization periods (2), (4), and (6) are values generated from electric charges accumulated in the imaging element  106  while the focus lens is driven, the AF evaluation values are not used for AF control. Thus, the reference position α and the amplitude β are the same as those used previously and the reference position shift amount γ is transmitted as zero. However, the above condition is no longer applicable if the focus lens reaches an end of a movable region. 
     Next,  FIG. 11B  shows a state in which the focus lens reaches an end of a set movable region during the wobbling operation. When the focus lens reaches an end of a movable region, the lens control unit  115  transmits a command (including end information) indicating that the focus lens position is at an end of a movable region to the camera control unit  116 . End information is included in data transmitted from the lens control unit  115  to the camera control unit  116  in the first communication for each 1V. In  FIG. 11B , the camera is informed of whether or not the focus lens position is at an end of a movable region by setting a bit corresponding to end information to 0 or 1. In the present embodiment, when the focus lens position does not reach an end of a movable region, the bit is set to “0”, whereas the focus lens position reaches an end of a movable region, the bit is set to “1”.
         Lens→camera communication data: focus lens position, new reference position, and end information   Camera→lens communication data: reference position α, amplitude β, and reference position shift amount γ       

     The term “lens→camera” means transmission from the lens control unit  115  to the camera control unit  116 , whereas the term “camera→lens” means transmission from the camera control unit  116  to the lens control unit  115 . 
     The content of communication performed during the vertical synchronization periods (1), (3), and (5) is as follows. For ease of explanation, it is assumed that S1=S2=0.5 and the focus end position is “115”.
         Vertical synchronization period (1): time T1 “camera→lens” α=100, β=5, γ=10       

     The lens control unit  115  calculates a target position and a new reference position based on the received drive command. 
     Focus lens drive target position=100+5/0.5+10/0.5=130 
     New Reference position=100+10/0.5=120 
     Although the drive target position of the focus lens is “130”, the lens control unit  115  stops the focus lens at position “115” because the focus end position is “115”.Furthermore, the focus lens position “115” (the position of the focus end), a new reference position “120”, and end information “1” are transmitted in a communication cycle after 2V (corresponds to the vertical synchronization period (3)). 
     Next, the camera control unit  116  sets the reference position α to the focus end position. At this time, the camera control unit  116  sets a double value of the amplitude β to the reference position shift amount γ.
         Vertical synchronization period (3): time T3 “camera →lens”α=115, β=−5, γ=−10       

     The lens control unit  115  calculates a target position and a new reference position based on the received drive command. 
     Focus lens drive target position=115−5/0.5−10/0.5=85 
     New Reference position=115−10/0.5=95 
     The lens control unit  115  transmits the calculated target position and new reference position to the camera control unit  116  in a communication cycle after 2V (corresponds to the vertical synchronization period (5)).
         Vertical synchronization period (5): time T5 “camera →lens”α=95, β=5, γ=0       

     The lens control unit  115  calculates a target position and a new reference position based on the received drive command. 
     Focus lens drive target position=95+5/0.5+0/0.5 =105 
     New Reference position=95+0/0.5=95 
     The lens control unit  115  transmits the calculated target position and new reference position to the camera control unit  116  in a communication cycle after 2V (corresponds to the vertical synchronization period (7)). In the example, after the focus lens reaches an end of a movable region during the wobbling operation centered on the reference position “100”, the wobbling operation centered on a reference position “95” is performed. 
     Next, a description will be given of AF control performed by the camera control unit  116  with reference to the flowcharts shown in  FIG. 4  and  FIG. 5 . The control is executed in accordance with a computer program stored in a memory provided in the camera control unit  116 . 
     In step S 601 , the process starts. In step S 602 , wobbling operation for driving the focus lens  105  at micro intervals is performed. In the operation, focus determination of whether or not the focus lens  105  is in a focused state and direction determination as to a direction of a focal point exists if the focus lens  105  is in a non-focused state can be made. The detailed description will be given below of the operation with reference to  FIG. 6  and  FIG. 7 . In step S 603 , whether or not focus determination was successfully made is determined. If focus determination was successfully made, the process advances to step S 612 , and focus stop and reactivation determination processing is performed. If focus determination was not successfully made, the process advances to step S 604 . In step S 604 , whether or not direction determination was successfully made is determined. If direction determination was successfully made, the process advances to step S 605  shown in  FIG. 5  and mountain-climbing driving is performed. If direction determination was not successfully made, the process advances to step S 608 . 
     In step S 605 , the mountain-climbing driving for the focus lens  105  is executed at a predetermined speed along the determined direction. The mountain-climbing driving controls the focus lens  105  to drive in a direction of increasing a TVAF evaluation value. The processing for searching the position of the focus lens  105  where the TVAF evaluation value becomes its peak value (hereinafter referred to as “peak position”) by associating the TVAF evaluation value with the focus lens position acquired from the lens unit  117  is performed. The detailed description will be given below of the search processing with reference to  FIG. 12  and  FIG. 13 . In step S 606 , the camera control unit  116  sets the following drive information in order to return the focus lens  105  to the peak position during the mountain-climbing driving operation.
         Reference position=peak position   Amplitude=0   Reference position shift amount=0       

     The drive information is transmitted to the lens control unit  115 . As a result, the focus lens  105  can be shifted to the peak position. 
     In step S 607 , determination processing whether or not the focus lens  105  has returned to the peak position is performed. If the focus lens  105  has returned to the peak position, the process returns to step S 602  shown in  FIG. 4  and the wobbling operation is performed again. If the focus lens  105  has not returned to the peak position, the process returns to step S 606  and the mountain-climbing driving operation is continued. 
     If direction determination was not successfully made in step S 604  shown in  FIG. 4 , the process advances to step S 608  and processing for determining whether or not the image plane displacement amount was successfully detected by phase difference detection is performed. If the image plane displacement amount was successfully detected in step S 608 , the process advances to step S 609  and it is determined whether or not the image plane displacement amount is equal to or greater than a predetermined amount (threshold value). If the image plane displacement amount is equal to or greater than a predetermined amount, the process advances to step S 610  shown in  FIG. 5  and the focus lens  105  is driven by an amount corresponding to the image plane displacement amount. The drive information to be set in this case is as follows:
         Reference position=focus lens position at a time point corresponding to the center of the period for accumulation in electric charges for focus detection pixels during phase difference detection   Amplitude=value corresponding to the image plane displacement amount detected by phase difference AF   Reference position shift amount=0       

     The drive information is transmitted to the lens control unit  115 . In the case of phase difference detection, electric charges may be accumulated across a few frames to thereby generate an image signal. Thus, the camera control unit  116  calculates a focus lens position at a time point corresponding to the center of the period for accumulation in electric charges upon detection of the image plane displacement amount based on the focus lens position received by the lens control unit  115  in the first communication during electric charge accumulation for phase difference detection. The calculated position is transmitted as information about the reference position to the lens control unit  115 . In the next step S 611 , it is determined whether or not the focus lens  105  has shifted from the current focus lens position by an amount corresponding to the image plane displacement amount detected by phase difference AF. If lens driving was performed by an amount corresponding to the image plane displacement amount, the process returns to step S 602  shown in  FIG. 4 , whereas if lens driving was not performed, the process returns to step S 610 . On the other hand, if the image plane displacement amount was not successfully detected in step S 608  or if the image plane displacement amount is less than a predetermined amount in step S 609 , the process returns to step S 602 . 
     Next, a description will be given of focus stop and reactivation determination processing from step S 612  shown in  FIG. 4 . In step S 612 , the camera control unit  116  acquires a TVAF evaluation value. In step S 613 , the following drive information is set so as to shift the focus lens  105  to the position determined to be in-focus, i.e., the peak position.
         Reference position=peak position   Amplitude=0   Reference position shift amount=0       

     The drive information is transmitted to the lens control unit  115 . As a result, the focus lens  105  can be driven to the position determined to be in-focus. 
     In step S 614 , processing for determining whether or not the focus lens  105  has shifted to the peak position is performed. If the focus lens  105  has shifted to the peak position, the process advances to step S 615  shown in  FIG. 5 , whereas if otherwise, the process returns to step S 612 . In step S 615 , the camera control unit  116  stores a TVAF evaluation value at a focal point in a memory. In step S 616 , the camera control unit  116  acquires a TVAF evaluation value at present time from the TVAF signal processing unit  114 . In step S 617 , processing for determining whether or not the fluctuation width of the TVAF evaluation value is large is performed by comparing the TVAF evaluation value stored in step S 615  with the latest TVAF evaluation value acquired in step S 616 . It is determined whether the fluctuation width is small or large by comparing the fluctuation width with a threshold value. When the TVAF evaluation value fluctuates largely, the camera control unit  116  determines that an object has been changed and the process returns to step S 602  shown in  FIG. 4  and then the camera control unit  116  resumes the wobbling operation. If the fluctuation width of the TVAF evaluation value is equal to or less than a threshold value, the process returns to step S 616 . 
     Next, a description will be given of the micro-driving operation with reference to  FIG. 6  and  FIG. 7 . In step S 701 , the process starts. In step S 702 , a wait (wait processing) is executed at the timing of the vertical synchronization signal (VD) such that the following processing is performed at a predetermined cycle. 
     In step S 703 , the camera control unit  116  communicates with the lens control unit  115  to thereby acquire information about the current position, the reference position, and the like of the focus lens  105 . In step S 704 , processing for determining a drive cycle and a drive delay time is performed. In the example, the drive cycle is 2V and the drive delay time is ½V. In step S 705 , the camera control unit  116  determines whether or not the value of the current variable Mode is zero. The Mode is an internal variable representing a difference in state from zero to three. If the value is zero, the process advances to step S 706 , whereas if the value is other than zero, the process advances to step S 711 . 
     In step S 706 , the camera control unit  116  stores the TVAF evaluation value as the infinity-side TVAF evaluation value in a memory. This is an evaluation value based on the output of the imaging element  106  accumulated while the focus lens  105  remains stayed at the infinity side. In the next step S 707  (see  FIG. 7 ), a value for Mode increments by one, and the process advances to step S 708 . If a value for Mode is equal to or greater than four, the value returns to zero. 
     In step S 708 , it is determined whether or not directions determined as the focusing direction are the same successively for a preset number of times (hereinafter referred to as “NA”). If it is determined that directions determined as the focusing direction are the same successively for a number of NA times, the process advances to step S 725 , whereas if otherwise, the process advances to step S 709 . In step S 709 , it is determined whether or not the focus lens  105  has been reciprocated repeatedly within the same area for a preset number of times (hereinafter referred to as “NB”). If the focus lens  105  has been reciprocated repeatedly within the same area for a number of NB times, the process advances to step S 726 , whereas if otherwise, the process advances to step S 710  and the camera control unit  116  transmits the drive command for the focus lens  105  to the lens control unit  115 . 
     In step S 725 , the camera control unit  116  determines that direction determination was successfully made, and the process advances to step S 728 . The series of processes are ended and the process shifts to mountain-climbing driving. In step S 726 , a focus position is computed based on past lens position information. In step S 727 , the camera control unit  116  determines that focus determination was successfully made, and the process advances to step S 728 . The series of processes are ended and the process shifts to focus stop and reactivation determination. 
     In step S 711  shown in  FIG. 6 , it is determined whether or not a value for Mode at present time is one. If the value for Mode is one, the process advances to step S 712  shown in  FIG. 7 , whereas if the value for Mode is other than one, the process advances to step S 717 . In step S 712 , an amplitude value indicating how much an image plane should be vibrated from the reference position and a reference position shift amount indicating how much the vibration center should be shifted on an image plane are computed. Here, the drive amount is an image plane shift amount. For amplitude, although no detailed description will be given, processing for setting a small amplitude value when the depth of focus is shallow and for setting a large amplitude value when the depth of focus is deep is performed on the basis of the depth of focus. In step S 713 , the infinity-side TVAF evaluation value (see step S 706 ) obtained when the value for Mode is zero is compared with the close-side TVAF evaluation value (see step S 718 ) obtained when the value for Mode is two (to be described below). If the infinity-side TVAF evaluation value is greater than the close-side TVAF evaluation value, the process advances to step S 714 . If the infinity-side TVAF evaluation value is not greater than the close-side TVAF evaluation value, the process advances to step S 715 . 
     In step S 714 , the camera control unit  116  sets the following drive information.
         Reference position=reference position acquired from previous lens position information   Amplitude=the amount of vibrating an image plane   Reference position shift amount=the amount of shifting the vibration center of an image plane       

     The drive information is transmitted to the lens control unit  115 . As a result, the reference position of the focus lens  105  is shifted by an amount corresponding to the reference position shift amount so that the focus lens  105  can be shifted from a new reference position by the drive amount corresponding to amplitude. 
     In step S 715 , the camera control unit  116  sets the following drive information.
         Reference position=reference position acquired from previous lens position information   Amplitude=the amount of vibrating an image plane   Reference position shift amount=0       

     The drive information is transmitted to the lens control unit  115 . As a result, the focus lens  105  can be shifted from the reference position by the drive amount corresponding to amplitude. After step S 714  or step S 715 , the process advances to step S 707 . 
     In step S 717  shown in  FIG. 6 , it is determined whether or not the value for Mode at present time is two. If the value for Mode is two, the process advances to step S 718  shown in  FIG. 7 , whereas if the value for Mode is other than two, the process advances to step S 720  shown in  FIG. 7 . 
     In step S 718 , the camera control unit  116  stores the TVAF evaluation value as the close-side TVAF evaluation value in a memory. The TVAF evaluation value is based on the sensor output accumulated while the focus lens  105  remains stayed at the close side. Then, the process advances to step S 707 . Step S 708  and subsequent steps are the same as described above. 
     In step S 720 , processing for driving the focus lens  105  to the close side is performed and the camera control unit  116  computes the amplitude and the reference position shift amount. These are the image plane shift amount. In the next step S 721 , the infinity-side TVAF evaluation value (see step S 706 ) obtained when the value for Mode is zero is compared with the close-side TVAF evaluation value (see step S 718 ) obtained when the value for Mode is two. If the close-side TVAF evaluation value is greater than the infinity-side TVAF evaluation value, the process advances to step S 722 . If the close-side TVAF evaluation value is not greater than the infinity-side TVAF evaluation value, the process advances to step S 723 . 
     In step S 722 , the camera control unit  116  sets the following drive information.
         Reference position=reference position acquired from previous lens position information   Amplitude=the amount of vibrating an image plane   Reference position shift amount=the amount of shifting the vibration center on an image plane       

     The drive information is transmitted to the lens control unit  115 . In step S 723 , the camera control unit  116  sets the following drive information.
         Reference position=reference position acquired from previous lens position information   Amplitude=the amount of vibrating an image plane   Reference position shift amount=0       

     The drive information is transmitted to the lens control unit  115 . After step S 722  or step S 723 , the process advances to step S 707 . 
       FIG. 8A  shows an example of the time profile of the focus lens operation, where time is plotted on the horizontal axis and vertical synchronization signal VD of the image signal is plotted on the uppermost part of  FIG. 8A . The parallelogram frame shown beneath the vertical synchronization signal VD represents the accumulation time of an imaging element (CMOS sensor) (see first to eleventh accumulation periods), and EVx (x=1 to 10) shown beneath the parallelogram frame represents an TVAF evaluation value obtained at the timing. Furthermore, the change in position of the focus lens  105  is shown beneath the TVAF evaluation value. Tx (x=3, 5, 6) represents a time at which the TVAF evaluation value is taken into the camera control unit  116 . 
       FIG. 8B  is a diagram illustrating the driving of a CMOS sensor.  FIG. 8B  shows an image capturing plane and scanning lines on the left side thereof and an accumulation time and a transfer time for each scanning line on the right side thereof. The CMOS sensor employs a rolling shutter system for performing a shutter operation for each scanning line. Thus, an accumulation time and a transfer time are different in the upper part and the lower part of the screen as shown in  FIG. 8B . In other words, the delay occurs in an accumulation period and a transfer period attached to the tail thereof for each scanning line. The parallelogram frame shown in  FIG. 8A  represents the entire accumulation period. 
     During the wobbling operation (see  FIG. 2B ), the TVAF evaluation value is monitored while moving the focus lens  105  between the close side and the infinity side to thereby drive the focus lens  105  in the focusing direction. At this time, while the focus lens  105  is located on the close side or the infinity side, the TVAF evaluation value needs to be acquired from the image signal accumulated in the imaging element  106 . For this purpose, the driving timing of the focus lens  105  needs to be matched with the accumulation period of the imaging element  106 . Although the focus lens  105  is not located on the close side or the infinity side across the entire accumulation period, the TVAF frame (focus state detecting frame) is set to a small range with respect to the image capturing screen, which is sufficient for accumulation of scanning lines within the TVAF frame. For example, for electric charges accumulated in the imaging element  106  during the third accumulation period shown in  FIG. 8A , a TVAF evaluation value EV 3  is acquired by the camera control unit  116  at a time T 3 . For electric charges accumulated in the imaging element  106  during the fifth accumulation period, a TVAF evaluation value EV 5  is acquired by the camera control unit  116  at a time T 5 . At a time T 6 , the TVAF evaluation values EV 3  and EV 5  are compared to each other. If EV 5 &gt;EV 3 , the vibration center shifts, whereas if EV 3 ≧EV 5 , the vibration center does not shift. In this manner, the focusing direction and the focused state are determined. 
       FIG. 9  is a diagram illustrating processing performed by the camera control unit  116  and the lens control unit  115  in  1 V, where time is plotted on the horizontal axis. Firstly, immediately after obtaining the vertical synchronization signal (VD), the camera control unit  116  acquires information about a lens position and a reference position from the lens control unit  115 . Next, the camera control unit  116  performs AF control by acquiring a TVAF evaluation value and phase difference AF information to thereby create a focus lens drive command. After receiving the focus lens drive command from the camera control unit  116 , the lens control unit  115  computes a focus drive target position as described above. After the wait processing for a drive delay time, lens driving processing is performed to thereby actually shift the focus lens  105 . 
     Next, a description will be given of the mountain-climbing driving operation with reference to  FIG. 12  and  FIG. 13 . In step S 1301 , the process starts. In step S 1302 , wait processing is executed such that the following processing is performed at a predetermined cycle and the following processing starts at the timing of VD. In step S 1303 , the camera control unit  116  communicates with the lens control unit  115  to thereby acquire information about the focus lens position, the reference position, and the like. In step S 1304 , the camera control unit  116  sets a mountain-climbing driving speed. Here, the mountain-climbing driving speed is an image plane shift amount per unit time (e.g., per one second). Although no detailed description will be given, processing for setting a low speed at which the image plane changes when the depth of focus is shallow and for setting a high speed when the depth of focus is deep is performed on the basis of the depth of focus. As a result, the change amount of blurr is substantially constant without providing a sense of unnatural impression. 
     In step S 1305 , the TVAF evaluation value acquired in step S 1303  is compared with the previous TVAF evaluation value. It is determined in step S 1305  whether or not the difference between the current and previous TVAF evaluation values is smaller than a predetermined amount (threshold value). If the difference is smaller than a predetermined amount, the process advances to step S 1306 , whereas if the difference is not smaller than a predetermined amount, the process advances to step S 1312  shown in  FIG. 12 . Here, the predetermined amount is a determination reference value which is determined in consideration of the S/N (signal-to-noise) ratio of the TVAF evaluation value and is set to be equal to or greater than the fluctuation width of the TVAF evaluation value under the condition that the focus lens position is constant by fixing the object. If such settings are not made, the focus lens position may be affected by the fluctuation of the TVAF evaluation value, whereby the mountain-climbing driving cannot be made in the correct direction. 
     In step S 1306 , processing for determining whether or not the focus lens  105  has reached the infinity end is performed. The infinity end is the end position closest to the infinity side in the movable range of the focus lens  105  by design. If the focus lens  105  has reached the infinity end, the process advances to step S 1307 , whereas if the focus lens  105  has not reached the infinity end, the process advances to step S 1308 . In step S 1308 , processing for determining whether or not the focus lens  105  has reached the close end is performed. The close end is the end position closest to the close side in the movable range of the focus lens  105  by design. If the focus lens  105  has reached the close end, the process advances to step S 1309 , whereas if the focus lens  105  has not reached the close end, the process advances to step S 1310  shown in  FIG. 13 . In steps S 1307  and S 1309 , a flag for storing an end in which the drive direction is reversed is set. In step S 1307 , an infinity end flag is set. In step S 1309 , a close end flag is set. Then, the process advances to step S 1314  shown in  FIG. 13 . The focus lens  105  continues mountain-climbing driving by reversing the drive direction to the backward direction. 
     In step S 1310  shown in  FIG. 13 , the camera control unit  116  sets the following drive information in order to perform the mountain-climbing driving operation for the focus lens  105  at the speed determined in step S 1304  along the same forward direction as the previous direction.
         Reference position=focus lens position acquired in first communication   Amplitude=value corresponding to direction (e.g., represented by +1 or −1)   Reference position shift amount=0       

     After step S 1310  or step S 1314 , the process advances to step S 1311 , and the set drive information is transmitted to the lens control unit  115 . In addition to the above information, the lens control unit  115  also receives information about an image plane shift amount per unit time. Then, the lens control unit  115  calculates the shift amount of the focus lens  105  in  1 V using the received image plane shift amount per unit time. The lens control unit  115  can shift the actual position of the focus lens  105  by an amount corresponding to the desired image plane shift amount based on information received from the camera control unit  116 . Then, the process returns to step S 1302 , and the current processing ends. 
     In step S 1312 , processing for determining whether or not the TVAF evaluation value decreases after passing its peak position is performed. If the TVAF evaluation value does not decrease, the process advances to step S 1313 . If the focus lens  105  passes over the peak position and the TVAF evaluation value decreases, the process advances to step S 1315  to thereby end mountain-climbing driving. Then, the process advances to step S 1316 . The series of processes are ended and the process shifts to the wobbling operation. In step S 1313 , it is determined whether or not the TVAF evaluation value decreases successively for a predetermined number of times. If it is determined that the TVAF evaluation value decreases successively for a predetermined number of times, the process advances to step S 1314 , whereas if otherwise, the process advances to step S 1310 . 
     In step S 1314 , the camera control unit  116  sets the following drive information in order to perform the mountain-climbing driving operation for the focus lens  105  at the speed determined in step S 1304  in a direction opposite to the previous direction.
         Reference position=focus lens position acquired in first communication   Amplitude=value corresponding to direction (e.g., represented by +1 or −1, which is the opposite sign of the previous one)   Reference position shift amount=0       

     The process advances to step S 1311 , the drive information determined in step S 1314  is transmitted to the lens control unit  115 . 
       FIG. 14  illustrates the movement of the focus lens  105  during the mountain-climbing driving operation. In the symbol A shown in  FIG. 14 , the TVAF evaluation value decreases after passing the peak value. Thus, the camera control unit  116  determines that the focus lens  105  has passed the focal point and ends the mountain-climbing driving operation. The process shifts to the wobbling operation. On the other hand, in the symbol B shown in  FIG. 14 , the TVAF evaluation value decreases without finding the peak value, the camera control unit  116  reverses the drive direction to thereby continue the mountain-climbing driving operation. 
     As described above, the focus lens  105  shifts while repeating the sequence of “reactivation determination→wobbling→mountain-climbing driving→wobbling→reactivation determination”. The imaging apparatus maintains the focused state by performing focus adjustment control such that the TVAF evaluation value always becomes the maximum value. 
     According to the present embodiment, an integrated drive command can be provided from an imaging apparatus body to a lens apparatus in an interchangeable lens system so that the various focus lens operations including a wobbling operation are controlled. More specifically, the “reference position, amplitude, and reference position shift amount” are transmitted as drive information from an imaging apparatus body to a lens apparatus. As a result, the necessity of switching a drive command in response to an operation state such as a wobbling operation, a mountain-climbing driving operation, or the like is eliminated. Thus, the movement of the focus lens can be controlled in accordance with a drive command given by the control unit provided in an imaging apparatus body without complicating a control system. Also, an image plane shift amount is set by a drive command issued by an imaging apparatus body and thus a lens apparatus that has received the drive command can perform lens driving by calculating the actual drive amount of the focus lens corresponding to the image plane shift amount. 
     In the embodiments, a description has been given mainly to an example in which a drive command for a wobbling operation is transmitted from the camera control unit  116  to the lens control unit  115 . The present invention is not limited thereto, but the camera control unit  116  can transmit drive information regarding the shift operation of a specific image plane shift amount and the shift operation to a specific lens position to the lens control unit  115 . The drive control method of the embodiments may also be applicable to the driving of a movable optical member other than a focus lens, such as a zoom lens, an image shape correcting lens, or the like. 
     Aspects of the present invention can also be realized by a computer of a system or apparatus (or devices such as a CPU or MPU) that reads out and executes a program recorded on a memory device to perform the functions of the above-described embodiments, and by a method, the steps of which are performed by a computer of a system or apparatus by, for example, reading out and executing a program recorded on a memory device to perform the functions of the above-described embodiments. For this purpose, the program is provided to the computer for example via a network or from a recording medium of various types serving as the memory device (e.g., computer-readable medium). 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of Japanese Patent Application No. 2012-004560 filed on Jan. 13, 2012, and Japanese Patent Application No. 2012-238265 filed on Oct. 29, 2012 which are hereby incorporated by reference herein in their entirety.