Abstract:
According to the apparatus, the method, the program, and the recording medium of the present invention, the amount of feed of a first zoom lens and the amount of feed of a second zoom lens corresponding to a magnification of the first zoom lens and a magnification of the second zoom lens which are close to each other are associated, and the amounts of feed of the first zoom lens and the second zoom lens corresponding to an arbitrarily designated magnification are set. Accordingly, the magnifications of the first zoom lens and the second zoom lens can be accurately made almost equal over the entire zoom range. Since the magnifications of the first zoom lens and the second zoom lens are made equal on the basis of the amounts of feed, effective pixels do not decrease, unlike magnification correction using an electronic zoom.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to an image pickup apparatus including a plurality of optical systems and, more particularly, to rectification of a discrepancy in zoom factor among the optical systems. 
         [0003]    2.Description of the Related Art 
         [0004]    Various techniques have been developed for rectifying an error between two variable magnification imaging lenses. 
         [0005]    In Japanese Patent Application Laid-Open No. 5-130646, the position of an image pickup apparatus is detected, and misalignment correction control is performed with reference to image pickup condition correction data such that image pickup conditions are optimized. 
         [0006]    In Japanese Patent Application Laid-Open No. 7-111610, drive control is performed based on outputs from zoom encoders such that the magnifications of left and right lenses are always equal. 
         [0007]    In Japanese Patent Application Laid-Open No. 2006-162991, a magnification error between left and right lenses is stored for each of predetermined positions, and the magnifications are controlled by an electronic zoom to be constant. 
         [0008]    In Japanese Patent Application Laid-Open No. 10-307352, a pair of pieces of image data is geometrically transformed, and discrepancies such as a horizontal discrepancy, a vertical discrepancy, a rotational discrepancy, and a discrepancy in magnification are adjusted by the image transformation. The amounts of discrepancy are used in an affine transformation. 
         [0009]    Japanese Patent Application Laid-Open No. 2001-124991 discloses a stereoscopic image pickup apparatus which uses one image pickup element and causes reflection and separation by front lens groups. A lens group closest to a subject of rear lens groups is used for focusing. Variable magnification lenses are located closer to the image pickup element than the lens group. The stereoscopic image pickup apparatus has lens groups for compensating for a tracking lens shift caused by a change of magnification. 
         [0010]    Other conventional techniques related to the present application include Japanese Patent Application Laid-Open Nos. 2003-324113, 2008-3501, and 2002-116366. 
       SUMMARY OF THE INVENTION 
       [0011]    In Japanese Patent Application Laid-Open No. 5-130646, a discrepancy in angle of view between two lenses caused by a manufacturing error is not rectified. In Japanese Patent Application Laid-Open No. 7-111610, zoom drive positions are determined from output signals from the encoders, and the lenses are driven such that the magnifications are kept constant. However, a discrepancy in magnification between two lenses caused by a manufacturing error is not rectified. In Japanese Patent Application Laid-Open No. 2006-162991, a correction amount for a magnification error is stored in advance for each of the predetermined positions, and the magnifications are controlled by an electronic zoom to be constant. Accordingly, effective pixels of one of imaging apparatuses decrease, and a discrepancy in magnification between adjacent ones of the predetermined positions cannot be appropriately rectified. In Japanese Patent Application Laid-Open No. 10-307352, the process of adjusting optical discrepancies by transforming image coordinates is adopted. The process decreases effective pixels. Japanese Patent Application Laid-Open No. 10-307352 makes no disclosure regarding a discrepancy in magnification at the time of a change of magnification. In Japanese Patent Application Laid-Open No. 2001-124991, since two lenses share a variable magnification system, no magnification change error occurs between the two lenses. 
         [0012]    The present invention has as its object to accurately rectify a discrepancy in magnification between different optical systems and ensure the maximum number of effective pixels, over the entire zoom range. 
         [0013]    To achieve the above object, a first aspect of the present invention provides an image pickup apparatus comprising an image pickup section that photoelectrically converts, by an image pickup element, subject images formed through a plurality of image pickup optical systems including a first optical system and a second optical system and outputs a plurality of images corresponding to the image pickup optical systems, a first lens drive section that drives a first zoom lens included in the first optical system, a second lens drive section that drives a second zoom lens included in the second optical system, a control section that controls stepwise driving of the first lens drive section and the second lens drive section, a first counter that counts an amount of stepwise feed of the first zoom lens by the first lens drive section with respect to a predetermined reference position as a start point in accordance with control by the control section, a second counter that counts an amount of stepwise feed of the second zoom lens by the second lens drive section with respect to a predetermined reference position as a start point in accordance with control by the control section, a calculation section that calculates a magnification of the first zoom lens corresponding to the amount of stepwise feed counted by the first counter and a magnification of the second zoom lens corresponding to the amount of stepwise feed counted by the second counter, and a zoom correction information creation section that creates zoom correction information in which the amount of stepwise feed of the first zoom lens and the amount of stepwise feed of the second zoom lens corresponding to one of a plurality of magnifications of the first zoom lens and one of a plurality of magnifications of the second zoom lens close to each other are associated and records the zoom correction information on a predetermined storage medium. 
         [0014]    In the first aspect, it is preferable that the first lens drive section and the second lens drive section each comprise a DC motor, the apparatus further comprises a first encoder which outputs a pulse corresponding to an amount of rotation of the DC motor of the first lens drive section and a second encoder which outputs a pulse corresponding to an amount of rotation of the DC motor of the second lens drive section, the first counter counts, as the amount of feed, the number of pulses outputted by the first encoder to correspond to stepwise driving of the first zoom lens by the first lens drive section, and the second counter counts, as the amount of feed, the number of pulses outputted by the second encoder in response to stepwise driving of the second zoom lens by the second lens drive section. 
         [0015]    In the first aspect, it is preferable that the first lens drive section and the second lens drive section each comprise a stepping motor, the first counter counts, as the amount of feed, the number of drive pulses from the control section to the first lens drive section corresponding to stepwise driving of the first zoom lens by the first lens drive section, and the second counter counts, as the amount of feed, the number of drive pulses from the control section to the second lens drive section corresponding to stepwise driving of the second zoom lens by the second lens drive section. 
         [0016]    In the first aspect, it is preferable that the control section controls the image pickup section to output a first image corresponding to the first optical system and a second image corresponding to the second optical system which are subject images of a predetermined line segment chart each time the control section controls stepwise driving of the first lens drive section and the second lens drive section, and the calculation section calculates a magnification of the first zoom lens on the basis of a first length which is a pixel pitch corresponding to a length of the predetermined line segment chart and a reference pitch which is a pixel pitch corresponding to a length of the predetermined line segment chart when the first zoom lens is located at a predetermined 1× magnification position, from the first image outputted from the image pickup section, and calculates a magnification of the second zoom lens on the basis of a second length which is a pixel pitch corresponding to a length of the predetermined line segment chart and the reference pitch, from the second image. 
         [0017]    In the first aspect, it is preferable that the apparatus further comprises a designation section which designates a zoom factor, the control section identifies a first amount of feed which is the amount of stepwise feed of the first zoom lens and a second amount of feed which is the amount of stepwise feed of the second zoom lens corresponding to the zoom factor designated by the designation section from the zoom correction information and controls the first lens drive section to drive the first zoom lens by the first amount of feed and the second lens drive section to drive the second zoom lens by the second amount of feed. 
         [0018]    In the above aspect, it is preferable that the zoom correction information creation section calculates a difference between the amount of stepwise feed of the first zoom lens and the amount of stepwise feed of the second zoom lens corresponding to each magnification in the zoom correction information and creates differential zoom correction information in which the amount of stepwise feed of the first zoom lens corresponding to each magnification and the difference are associated, and the control section identifies the first amount of feed as the amount of stepwise feed of the first zoom lens and the difference corresponding to the zoom factor designated by the designation section from the differential zoom correction information and controls the first lens drive section to drive the first zoom lens by the first amount of feed and the second lens drive section to drive the second zoom lens by an amount in which the difference is subtracted from the first amount of feed. 
         [0019]    A second aspect of the present invention provides a zoom correction information creation method for an image pickup apparatus having an image pickup section that photoelectrically converts, by an image pickup element, subject images formed through a plurality of image pickup optical systems including a first optical system and a second optical system and outputs a plurality of images corresponding to the image pickup optical systems, a first lens drive section that drives a first zoom lens included in the first optical system, a second lens drive section that drives a second zoom lens included in the second optical system, and a control section that controls stepwise driving of the first lens drive section and the second lens drive section, the method comprising the steps of counting an amount of stepwise feed of the first zoom lens by the first lens drive section with respect to a predetermined reference position as a start point in accordance with control by the control section, counting an amount of stepwise feed of the second zoom lens by the second lens drive section with respect to a predetermined reference position as a start point in accordance with control by the control section, calculating a magnification of the first zoom lens corresponding to the counted amount of stepwise feed of the first zoom lens and a magnification of the second zoom lens corresponding to the counted amount of stepwise feed of the second zoom lens, and creating zoom correction information in which the amount of stepwise feed of the first zoom lens and the amount of stepwise feed of the second zoom lens corresponding to one of a plurality of the magnification of the first zoom lens and one of a plurality of the magnification of the second zoom lens close to each other are associated and recording the zoom correction information on a predetermined storage medium. 
         [0020]    A program for causing an image pickup apparatus to perform the method is also included in the present invention as a third aspect. 
         [0021]    A recording medium in which computer readable code of the program according to the third aspect is stored is also included in the present invention as a fourth aspect. The recording medium includes magnet/optical recording medium like CDs (compact disks), DVD disks, HDDs (hard disk drives) and semiconductor memories like EEPROM or flash memory. 
         [0022]    According to the present invention, the amount of feed of a first zoom lens and the amount of feed of a second zoom lens corresponding to a magnification of the first zoom lens and a magnification of the second zoom lens which are close to each other are associated, and the amounts of feed of the first zoom lens and the second zoom lens corresponding to an arbitrarily designated magnification are set. Accordingly, the magnifications of the first zoom lens and the second zoom lens can be accurately made almost equal over the entire zoom range. Since the magnifications of the first zoom lens and the second zoom lens are made equal on the basis of the amounts of feed, effective pixels do not decrease, unlike magnification correction using an electronic zoom. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0023]      FIG. 1  is a perspective front view of a stereo camera; 
           [0024]      FIG. 2  is a perspective rear view of the stereo camera; 
           [0025]      FIG. 3  is a block diagram of the stereo camera; 
           [0026]      FIG. 4  is a flow chart of a pulse position adjustment table creation process; 
           [0027]      FIG. 5  is a view showing an example of a chart; 
           [0028]      FIG. 6  is a graph showing an example of a tracking curve; 
           [0029]      FIG. 7  is a chart showing an example of a piece of zoom factor information; 
           [0030]      FIG. 8  is a chart showing an example of a pulse position adjustment table; 
           [0031]      FIG. 9  is a flow chart of a pulse position adjustment process when a first variable magnification lens and a second variable magnification lens move in the TELE direction; and 
           [0032]      FIG. 10  is a flow chart of a pulse position adjustment process when the first variable magnification lens and the second variable magnification lens move in the WIDE direction. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First Embodiment  
       [0033]    Referring to  FIG. 1 , a first lens-barrel  4   a  holding a first image pickup section  3   a  and a second lens-barrel  4   b  holding a second image pickup section  3   b  are incorporated in a front surface of a stereo camera  2 . A strobe device  5  and the like are also exposed at the front surface. The first and second lens-barrels  4   a  and  4   b  are spaced horizontally adjacent to each other. The first and second lens-barrels  4   a  and  4   b  extend forward from a camera main body in imaging mode, as indicated by solid lines in  FIG. 1 , and collapse into the camera main body when the power to the stereo camera  2  is OFF or in image reproduction mode, as indicated by dotted lines in  FIG. 1 . A shutter button  6  used for shutter release operation is provided at an upper surface of the stereo camera  2 . 
         [0034]    Referring to  FIG. 2 , an operation section  10  which has zoom buttons  7 , a menu button  8 , a cursor button  9 , and the like and an LCD (Liquid Crystal Display)  11  are provided at a back surface of the stereo camera  2 . Turning on/off of the power, switching among various modes (e.g., imaging mode and reproduction mode), zooming, or the like is performed by appropriate operation of the operation section  10 . The LCD  11  is a parallax barrier type (or lenticular lens type) 3D monitor. The LCD  11  functions as an electronic viewfinder at the time of taking an image and functions as an image reproduction monitor at the time of reproducing an image. 
         [0035]      FIG. 3  shows the electrical configuration of the stereo camera  2 . The first image pickup section  3   a  has a first fixed lens  20 , a first variable magnification lens  21 , a first focus lens  22 , and a first image sensor  23 , all of which are arranged along a lens optical axis L 1 . The first fixed lens  20  is fixedly provided in the first lens-barrel  4   a . The first variable magnification lens  21  is driven by a lens motor  24  which has a DC motor. The first focus lens  22  is driven by a lens motor  26 . The operation of the lens motors  24  and  26  are controlled by a CPU  40 . 
         [0036]    Home position detection sections (HP)  70  and  80  each detect that a corresponding one of the first variable magnification lens  21  and a second variable magnification lens  31  is located at a home position (reference position) and output a detection result to the CPU  40 . For example, in a camera with a two-group type zoom device, a position of a rear group of lenses closest to the position of a front group of lenses is set as a home position. 
         [0037]    The lens motor  24  moves the first variable magnification lens  21  along the lens optical axis L 1  from the home position as a start point to the TELE side/WIDE side (extended side/collapsed side) in response to operation of the zoom buttons  7  (a ring-shaped operation member may be used instead of the buttons) of the operation section  10  to enter information on a TELE or WIDE zoom direction and changes a focal distance (imaging magnification). If the first variable magnification lens  21  is moved to the TELE side, the focal distance becomes longer, and an imaging range becomes narrower. On the other hand, if the first variable magnification lens  21  is moved to the WIDE side, the focal distance becomes shorter, and the imaging range becomes wider. The lens motor  26  moves the first focus lens  22  along the lens optical axis L 1  and performs focusing. The position of the first focus lens  22  is automatically adjusted in keeping with movement of the first variable magnification lens  21  so as to prevent defocusing. Assume that stepwisely-increasing zoom factors (zoom steps Z 1 , Z 2 , . . . , Zn) can be entered through the operation section  10 . A number n of steps is arbitrary. The zoom step Z 1  corresponds to the WIDE end whereas the zoom step Zn corresponds to the TELE end. 
         [0038]    A known encoder as in Japanese Patent Application Laid-Open No. 2008-3501 is attached to the lens motor  24 . Although the details are omitted in  FIG. 3 , an encoder  25  has a pulse disc which is fixed to a main shaft of the lens motor  24  and has a large number of slits formed therein, a light-emitting diode which is arranged at the back surface of the pulse disc, a photosensor which is arranged to face the light-emitting diode across the slits, a pulse generation section which A/D-converts a detection signal from the photosensor and generates a pulse, and a first pulse counter  61  which is capable of counting the number of pulses generated by the pulse generation section and calculating a rotational speed, the number of rotations, and the like. 
         [0039]    When the lens motor  24  is driven, the main shaft and the pulse disc are rotated. If the light-emitting diode is made to emit light at the same time, the photosensor receives a light beam from the light-emitting diode having passed through the slits, photoelectrically converts the light beam, and outputs an electric signal. The pulse generation section A/D-converts the electric signal outputted from the photosensor and outputs a pulse. Since the slits are formed in the pulse disc at regular intervals, the pulse generation section generates a pulse at high level only when the photosensor receives a light beam. The number of pulses counted by the first pulse counter  61  is outputted to the CPU  40 . 
         [0040]    A target zoom direction set through the zoom buttons  7  is outputted to the CPU  40 . The CPU  40  sets a target zoom position according to the target zoom direction. The CPU  40  sets, as the target zoom position, one closest to the current position of the first variable magnification lens  21  of zoom steps on the TELE side if the target zoom direction is the TELE direction and sets, as the target zoom position, one closest to the current position of the first variable magnification lens  21  of zoom steps on the WIDE side if the target zoom direction is the WIDE direction. The CPU  40  converts the target zoom position into the number of pulses needed for the first variable magnification lens  21  to reach a target stop position. Note that a pulse count of 0 corresponds to the home position detected by the home position detection section  70 . 
         [0041]    A focal distance based on a pulse count is stored in an EEPROM  50 . The CPU  40  calculates a current focal distance (zoom position) on the basis of a pulse count from the first pulse counter  61  (or a second pulse counter  71 ) and displays a result of the calculation on the LCD  11 . The CPU  40  drives the lens motor  24  such that a pulse count from the first pulse counter  61  corresponds to a first target stop position. How to determine the first target stop position will be described later. 
         [0042]    The first image sensor  23  receives a light beam formed by the first fixed lens  20 , the first variable magnification lens  21 , and the first focus lens  22  and stores photocharge corresponding to the amount of received light in light-receiving elements. Photocharge storage and transfer operation of the first image sensor  23  is controlled by a timing signal (clock pulse) inputted from a timing generator (not shown). In imaging mode, the first image sensor  23  acquires image signals for one frame at predetermined intervals and sequentially inputs image signals to a correlated double sampling circuit (CDS)  27 . Note that a CCD or MOS solid-state image pickup apparatus is used as the first image sensor  23 . 
         [0043]    The correlated double sampling circuit (CDS)  27  receives picked-up image signals for one frame inputted from the first image sensor  23  and inputs pieces of R, G, and B image data accurately corresponding to the amounts of charge stored in the light-receiving elements to an amplifier (AMP)  28 . The AMP  28  amplifies the inputted pieces of image data and inputs them to an A/D converter  29 . The A/D converter  29  converts the inputted pieces of image data from analog format into digital format. Picked-up image signals from the first image sensor  23  are converted into a piece of first image data (right eye image data) through the CDS  27 , the AMP  28 , and the A/D converter  29 . 
         [0044]    The second image pickup section  3   b  has the same configuration as the first image pickup section  3   a  and has a second fixed lens  30 , the second variable magnification lens  31 , which is driven by a lens motor  34 , a second focus lens  32  which is driven by a lens motor  36 , and a second image sensor  33  which is driven by a timing generator (not shown). The operation of the lens motors  34  and  36  is controlled by the CPU  40 . Pulses generated by an encoder  35  which is attached to the lens motor  34  are detected by the second pulse counter (PC)  71  with the same configuration as the first pulse counter  61 , and the number of pulses is inputted to the CPU  40 . The CPU  40  drives the lens motor  34  such that the pulse count from the second pulse counter  71  corresponds to a second target stop position with respect to the home position serving as a start point detected by the home position detection section  80 . Note that a pulse count of 0 corresponds to the home position detected by the home position detection section  80 . How to determine the second target stop position will be described later. 
         [0045]    Note that the material for each member of the first image pickup section  3   a  is also used as the material for the corresponding member of the second image pickup section  3   b.  The first image pickup section  3   a  and the second image pickup section  3   b  are synchronized and perform the same operation in conjunction with each other. 
         [0046]    A CDS  37 , an AMP  38 , and an A/D converter  39  have the same configurations as the CDS  27 , the AMP  28 , and the A/D converter  29  described above, respectively. Picked-up image signals from the second image sensor  33  are converted into a piece of second image data (left eye image data) through the CDS  37 , the AMP  38 , and the A/D converter  39 . 
         [0047]    The pieces of first and second image data outputted from the A/D converters  29  and  39  are inputted to image signal processing circuits  41  and  42 , respectively. The image signal processing circuits  41  and  42  subject the pieces of image data to various types of image processing such as gradation conversion, white balance correction, and γ correction processing. The piece of first image data outputted from the image signal processing circuit  41  is inputted to a frame memory  43 . The piece of second image data outputted from the image signal processing circuit  42  is inputted to the frame memory  43  through an electronic magnification change circuit  44 . The frame memory  43  is a working memory for temporarily storing the pieces of first and second image data. 
         [0048]    A stereoscopic image processing circuit  45  combines the pieces of first and second image data stored in the frame memory  43  into a piece of stereoscopic image data for stereoscopic display by the LCD  11 . An LCD driver  46  causes the LCD  11  to display the piece of stereoscopic image data obtained through the combination by the stereoscopic image processing circuit  45  as a through image when the LCD  11  is used as an electronic viewfinder in imaging mode. 
         [0049]    A compression/decompression processing circuit  47  compresses the pieces of first and second image data stored in the frame memory  43  in a compression format such as the JPEG format. A media controller  48  records the pieces of image data compressed by the compression/decompression processing circuit  47  on a recording medium  49  such as a memory card. 
         [0050]    When the pieces of first and second image data thus recorded on the recording medium  49  are to be reproduced and displayed on the LCD  11 , the pieces of image data recorded on the recording medium  49  are read out by the media controller  48 . The pieces of image data having undergone decompression by the compression/decompression processing circuit  47  are converted into a piece of stereoscopic image data by the stereoscopic image processing circuit  45 . After that, the piece of stereoscopic image data is reproduced and displayed on the LCD  11  through the LCD driver  46 . 
         [0051]    Although the detailed structure of the LCD  11  is not shown, the LCD  11  has a parallax barrier display layer at the surface. The LCD  11  generates a parallax barrier with a pattern in which alternate light transmissive and light shielding parts are arranged at a predetermined pitch and displays strip-shaped image fragments representing left and right images which are alternately arranged on an image display surface under the parallax barrier display layer. This configuration can provide an observer with a stereoscopic view. 
         [0052]    The CPU  40  controls the overall operation of the stereo camera  2  in a centralized manner. The EEPROM  50  is connected to the CPU  40  in addition to the strobe device  5 , the shutter button  6 , and the operation section  10  described above. The EEPROM  50  is a nonvolatile memory into which data can be electrically rewritten. The EEPROM  50  includes a program storage section  51  and a correction data storage section  52  and can store any data as long as it has free space. 
         [0053]    The program storage section  51  stores a control program for the CPU  40  to perform various types of processing. The correction data storage section  52  stores various pieces of correction data. 
         [0054]    The flow of a pulse position adjustment table creation process according to the preferred embodiment of the present embodiment will be described below with reference to the flow chart in  FIG. 4 . Implementation of the process is controlled by the CPU  40 . A program for causing the CPU  40  to perform the process is stored in the program storage section  51 . Note that since a personal computer or the like with a hardware configuration equivalent to the CPU  40  can control implementation of the process, the CPU  40  need not necessarily be incorporated in the stereo camera  2 . The stereo camera  2  is assumed to be located at a position where it can capture a line segment chart as a subject. 
         [0055]    In S 1 , the CPU  40  drives the lens motor  24  such that the first variable magnification lens  21  of the first image pickup section  3   a  moves to a predetermined drive start position. The predetermined drive start position is stored in the EEPROM  50 , and a position after the lens motor  24  is driven from the home position by an amount corresponding to eight pulses is set as the predetermined drive start position. The predetermined drive start position optically corresponds to a position for which 1× magnification is set (the WIDE end). The CPU  40  then images a line segment chart as in  FIG. 5  by the first image pickup section  3   a.  At this time, the CPU  40  calculates a focusing evaluation value from a piece of first image data and brings the line segment chart into focus by known focusing processing such as AF operation for adjusting the lens position of the first focus lens  22  such that the focusing evaluation value reaches its local maximum. The CPU  40  measures a reference pixel pitch LP 0  corresponding to a length L of the line segment chart (the distance between two points P 1  and P 2  arranged in tandem) on the basis of the piece of first image data outputted from the first image pickup section  3   a  to the frame memory  43 . The reference pixel pitch LP 0  is stored in a RAM  90 . 
         [0056]    The CPU  40  further drives the lens motor  24  to move the first variable magnification lens  21  of the first image pickup section  3   a  in a direction from the drive start position toward a drive end position (e.g., the TELE end) by an amount corresponding to one of detected pulses. After each movement corresponding to one pulse, the CPU  40  drives the lens motor  26  to move the first focus lens  22  to the lens position, performs focusing, and images the line segment chart by the first image pickup section  3   a.  The focusing is performed by determining an adjustment position of the first focus lens  22  corresponding to each position to which the first variable magnification lens  21  is moved using a design curve (tracking curve) as in  FIG. 6  and driving the lens motor  26  to move the first focus lens  22  to the determined position, as well known in the art (e.g., Japanese Patent Application Laid-Open No. 2002-116366). The CPU  40  measures a pixel pitch LP- 1  corresponding to the length L of the line segment chart on the basis of a piece of first image data obtained from the first image pickup section  3   a  and associates the pixel pitch LP- 1  with the number of pulses detected at the time of the measurement. Similar focusing and imaging are performed for the second image pickup section  3   b.  After each movement corresponding to one pulse, the CPU  40  measures a pixel pitch LP- 2  corresponding to the length L of the line segment chart on the basis of a piece of second image data obtained from the second image pickup section  3   b  and associates the pixel pitch LP- 2  with the number of pulses detected at the time of the measurement. The pixel pitches LP- 1  and LP- 2  corresponding to the numbers of detected pulses are stored in the RAM  90 . 
         [0057]    In S 2 , the CPU  40  calculates a zoom factor corresponding to a detected pulse count for the first variable magnification lens  21  on the basis of the reference pixel pitch LP 0  and the pixel pitch LP- 1  corresponding to each of the positions of the first variable magnification lens  21  except for the drive start position. For example, the zoom factor corresponding to each detected pulse count is calculated by dividing the pixel pitch LP- 1  corresponding to the detected pulse count by the reference pixel pitch LP 0 . With this operation, the zoom factor corresponding to each detected pulse count for the first variable magnification lens  21  is obtained. The zoom factors are expressed as a piece I 1  of zoom factor information. Portion (a) of  FIG. 7  shows an example of the piece I 1  of zoom factor information. 
         [0058]    The CPU  40  performs similar processing for the second image pickup section  3   b.  The CPU  40  calculates a zoom factor (e.g., LP- 2 /LP 0 ) corresponding to the detected pulse count at each position from a drive start position of the second variable magnification lens  31  to a drive end position. The zoom factors are expressed as a piece I 2  of zoom factor information. Portion (b) of  FIG. 7  shows an example of the piece I 2  of zoom factor information. The pieces I 1  and I 2  of zoom factor information are stored in the RAM  90 . 
         [0059]    In S 3 , the CPU  40  creates a pulse position adjustment table where a zoom factor of the first variable magnification lens  21  in the piece I 1  of zoom magnification information which coincides with a predefined zoom factor for each zoom step and a zoom factor of the second variable magnification lens  31  in the piece I 2  of zoom magnification information which is closest to the zoom factor of the first variable magnification lens  21  are associated with each other. 
         [0060]    For example, assume that zoom step data defining correspondences between the zoom steps Z 1  to Z 4  and corresponding zoom factors for the first variable magnification lens  21 , such as Z 1  (the WIDE end) and 1.0000, Z 2  and 2.0000, Z 3  and 3.0000, and Z 4  (the TELE end) and 3.9980, are stored in advance in the EEPROM  50 . In this case, a zoom factor of 0.9980 of the second variable magnification lens  31  which is closest to a zoom factor of 1.0000 of the first variable magnification lens  21  for Z 1  is associated with the zoom factor of 1.0000. Similar association is performed for Z 2 , Z 3 , and Z 4 . For example, a zoom factor of 4.0056 of the second variable magnification lens  31  which is closest to a zoom factor of 3.9980 of the first variable magnification lens  21  for Z 4  is associated with the zoom factor of 3.9980. 
         [0061]    As a result of the association, correspondences between detected pulse counts for the first variable magnification lens  21  and detected pulse counts for the second variable magnification lens  31  for the respective zoom steps are determined. The correspondences are stored as the pulse position adjustment table in the EEPROM  50 . 
         [0062]    Portion (a) of  FIG. 8  shows an example (I 3 ) of the pulse position adjustment table. The table I 3  is used to adjust stop pulse positions of the first variable magnification lens  21  and the second variable magnification lens  31  corresponding to a zoom step which is set through the operation section  10  at the time of imaging. 
         [0063]    Portion (b) of  FIG. 8  shows another example ( 14 ) of the pulse position adjustment table. The pulse position adjustment table I 4  is different from the pulse position adjustment table I 3  in  FIG. 8 , in which total pulse counts starting at “0” (the home positions) are associated with each other. In the pulse position adjustment table I 4 , a pulse count for the first variable magnification lens  21  and a difference between the pulse count for the first variable magnification lens  21  and a pulse count for the second variable magnification lens  31  correspond to a single zoom step. The pulse position adjustment table I 4  is created in the manner below. The CPU  40  subtracts the pulse count for the second variable magnification lens  31  corresponding to each magnification in the pulse position adjustment table I 3  from the pulse count for the first variable magnification lens  21 , thereby obtaining a difference. The CPU  40  associates the pulse count for the first variable magnification lens  21  corresponding to each magnification in the pulse position adjustment table I 3  with the difference obtained for the magnification, thereby creating the pulse position adjustment table I 4 . Note that a difference may be obtained by subtracting the pulse count for the first variable magnification lens  21  corresponding to each magnification in the pulse position adjustment table I 3  from the pulse count for the second variable magnification lens  31 . This is because both the methods are essentially the same except for the sign of a difference. 
         [0064]      FIG. 9  shows a flow chart of a pulse position adjustment process when the first variable magnification lens  21  and the second variable magnification lens  31  move in the TELE direction.  FIG. 10  shows a flow chart of a pulse position adjustment process when the first variable magnification lens  21  and the second variable magnification lens  31  move in the WIDE direction. Implementation of the process is controlled by the CPU  40 . A program for causing the CPU  40  to perform the processes is stored in the program storage section  51 . 
         [0065]    Referring to  FIG. 9 , if the zoom buttons  7  are operated to select the TELE direction in S 11  (Yes in S 11 ), the flow advances to S 12  to determine whether pulses, the number of which corresponds to the TELE end (Zn), are detected by the PC  61 . If Yes, the flow advances to S 13 . Otherwise, the flow advances to S 14 . 
         [0066]    In S 13 , the CPU  40  stops driving the lens motor  24 . 
         [0067]    In S 14 , the CPU  40  moves the first variable magnification lens  21  from a current position (Zk) to a position (Zk+1) closer to the TELE side by one step. That is, the CPU  40  identifies a pulse count for the first variable magnification lens  21  corresponding to the position (Zk+1) closer to the TELE side whose zoom step is next to that of the current position (Zk) from the pulse position adjustment table I 3  or I 4  and sets the identified pulse count as a first target stop position. The CPU  40  drives the lens motor  24  such that the number of pulses detected by the PC  61  coincides with the first target stop position. Assume that k ranges from 1 to n−1. 
         [0068]    In S 15 , the CPU  40  determines whether pulses, the number of which corresponds to the TELE end (Zn), are detected by the PC  71 . If Yes, the flow advances to S 16 . Otherwise, the flow advances to S 17 . 
         [0069]    In S 16 , the CPU  40  stops driving the lens motor  24 . 
         [0070]    In S 17 , the CPU  40  moves the second variable magnification lens  31  from a current position (Zk) to a position (Zk+1) closer to the TELE side by one step. That is, the CPU  40  identifies a pulse count for the second variable magnification lens  31  corresponding to the position (Zk+1) closer to the TELE side by one step than the current position (Zk) in the pulse position adjustment table  13  or  14  and sets the identified pulse count as a second target stop position. The CPU  40  drives the lens motor  34  such that the number of pulses detected by the PC  71  coincides with the second target stop position. Note that, when the table I 4  is used, the CPU  40  sets, as the second target stop position, a pulse count obtained by subtracting a difference corresponding to the first target stop position from the first target stop position in the table I 4 . 
         [0071]    In S 18 , the CPU  40  determines whether input operation using the zoom buttons  7  is completed. If Yes, the flow advances to S 19 . Otherwise, the flow returns to S 12 . 
         [0072]    In S 19 , the CPU  40  moves the first variable magnification lens  21  from the current position (Zk+1) to a position (Zk+2) closer to the TELE side by one step. Note that, if the current position is the TELE end, the CPU  40  stops driving the lens motor  24 . 
         [0073]    In S 20 , the CPU  40  moves the second variable magnification lens  31  from the current position (Zk+1) to a position (Zk+2) closer to the TELE side by one step. Note that, if the current position is the TELE end, the CPU  40  stops driving the lens motor  34 . 
         [0074]    Referring to  FIG. 10 , if the zoom buttons  7  are operated to select the WIDE direction in S 31  (Yes in S 31 ), the flow advances to S 32  to determine whether pulses, the number of which corresponds to the WIDE end (Z 1 ), are detected by the PC  61 . If Yes, the flow advances to S 33 . Otherwise, the flow advances to S 34 . 
         [0075]    In S 33 , the CPU  40  stops driving the lens motor  24 . 
         [0076]    In S 34 , the CPU  40  moves the first variable magnification lens  21  from a current position (Zj) to a position (Zj−1) closer to the WIDE side by one step. That is, the CPU  40  identifies a pulse count for the first variable magnification lens  21  corresponding to the position (Zj−1) whose zoom step is previous to that of the current position (Zj) from the pulse position adjustment table  13  and sets the identified pulse count as a first target stop position. The CPU  40  drives the lens motor  24  such that the number of pulses detected by the PC  61  coincides with the first target stop position. Assume that j ranges from 2 to n. 
         [0077]    In S 35 , the CPU  40  determines whether pulses, the number of which corresponds to the WIDE end (Z 1 ), are detected by the PC  71 . If Yes, the flow advances to S 36 . Otherwise, the flow advances to S 37 . 
         [0078]    In S 36 , the CPU  40  stops driving the lens motor  24 . 
         [0079]    In S 37 , the CPU  40  moves the second variable magnification lens  31  from a current position (Zj) to a position (Zj−1) closer to the WIDE side by one step. That is, the CPU  40  identifies a pulse count for the second variable magnification lens  31  corresponding to the position (Zj−1) whose zoom step is previous to that of the current position (Zj) from the pulse position adjustment table  13  and sets the identified pulse count as a second target stop position. The CPU  40  drives the lens motor  34  such that the number of pulses detected by the PC  71  coincides with the second target stop position. 
         [0080]    In S 38 , the CPU  40  determines whether input operation using the zoom buttons  7  is completed. If Yes, the flow advances to S 39 . Otherwise, the flow returns to S 32 . 
         [0081]    In S 39 , the CPU  40  moves the first variable magnification lens  21  from the current position (Zj−1) to a position (Zj−2) closer to the WIDE side by one step. Note that, if the current position is the WIDE end (Z 1 ), the CPU  40  stops driving the lens motor  24 . 
         [0082]    In S 40 , the CPU  40  moves the second variable magnification lens  31  from the current position (Zj−1) to a position (Zj−2) closer to the WIDE side by one step. Note that, if the current position is the WIDE end (Z 1 ), the CPU  40  stops driving the lens motor  34 . 
         [0083]    As described above, a pulse count corresponding to a desired zoom step is identified from the table I 3  or I 4 , and the first variable magnification lens  21  and the second variable magnification lens  31  are driven until pulses, the number of which is equal to the pulse count, are detected. This allows both the optical systems to have almost the same magnifications without losing effective pixels. 
       Second Embodiment  
       [0084]    Lens motors  24  and  34  may each comprise a stepping motor instead of a DC motor. In this case, rotary encoders and pulse counters are unnecessary. In this situation, detected pulse counts in the pulse position adjustment table can be regarded as the numbers of drive pulses to the lens motors  24  and  34 .