Patent Publication Number: US-2007097219-A1

Title: Image stabilizer, and image shake correction method for imaging device

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an image stabilizer, and further relates to a method of correcting image shake in an imaging device by moving a part of an imaging optical system in a plane orthogonal to an optical axis of the imaging optical system.  
      2. Description of the Prior Art  
      Optical image stabilizers (shake reduction systems) prevent (reduce) image shake of an object image formed on an imaging surface by moving a part of an optical system relative to an optical axis thereof so that the part of the optical system shifts from the optical axis in accordance with the direction and the magnitude of vibration (shake) applied to the optical device in which the image stabilizer is incorporated. Since the operating range of the movable part of the optical system must be made to remain within a range in which image quality does not deteriorate (in which a sufficient amount of marginal rays is collected to prevent vignetting from occurring), the effective aperture of the lens must be increased to achieve a wide operating range, which undesirably increases the size of the optical device. Additionally, since a long focal-length optical system has a large magnification, the amount of shake correction per unit of shake angle becomes great, which makes it difficult to miniaturize the image stabilizer.  
     SUMMARY OF THE INVENTION  
      The present invention provides a compact image stabilizer which is configured to be capable of reliably correcting image shake even if the magnification is large. The present invention further provides a method of correcting image shake by which image shake can be corrected reliably using a compact image stabilizer even if the magnification of the optical system thereof is large.  
      According to an aspect of the present invention, an image stabilizer is provided, including an imaging device including an object coverage area changing device for changing an object coverage area for an object which is to be photographed through an imaging optical system; an image shake correction device which moves a shake correction optical element of the imaging optical system in a plane orthogonal to an optical axis in accordance with a direction and magnitude of vibration applied to the imaging device; a memory, in which area data is prestored, the area data designating changes in relative sizes between an image circle of the imaging optical system and an effective picture area of an imaging surface of the imaging device when the object coverage area changing device changes the object coverage area; and a moving range controller which changes a moving range of the shake correction optical element that corresponds to a change of the object coverage area in accordance with an operating state of the object coverage area changing device based on the area data prestored in the memory.  
      It is desirable for the moving range controller to change the moving range of the shake correction optical element within a range so that no part of the effective picture area deviates outside from the image circle.  
      It is desirable for the object coverage area changing device to include an optical zoom device which changes distances in the optical axis direction between optical elements of the imaging optical system that are positioned on the optical axis to vary an optical focal length.  
      It is desirable for the moving range controller to operate so as to increase the moving range of the shake correction optical element as the optical focal length of the optical zoom device increases.  
      It is desirable for the imaging optical system to include an image sensor which produces an electronic image of the object, and for the object coverage area changing device to trim a part of the electronic image to change the effective picture area.  
      It is desirable for the moving range controller to operates so as to increase the moving range of the shake correction optical element as an area of a remaining part of the electronic image, that remains after the trimming, decreases.  
      It is desirable for the imaging optical system to include an image sensor which produces an electronic image of the object. The object coverage area changing device includes an optical zoom device which changes distances in the optical axis direction between optical elements of the imaging optical system that are positioned on the optical axis to vary an optical focal length; and an electronic zoom device which trims a part of an image formed on the image sensor to change the effective picture area.  
      It is desirable for the shake correction optical element to be an image sensor.  
      It is desirable for the imaging optical system to be a zoom lens system and an image sensor.  
      In an embodiment, an image stabilizer is provided, including an imaging optical system including an image sensor and an optical zoom device for changing a focal length; an image shake correction device which moves a shake correction optical element of the imaging optical system in a plane orthogonal to an optical axis in accordance with a direction and magnitude of vibration applied to the imaging optical system; a memory in which area data is prestored, the area data designating changes in size of an image circle of the imaging optical system when the optical zoom device changes the focal length; and a moving range controller which changes a moving range of the shake correction optical element that corresponds to a change of the object coverage area in accordance with an operating state of the optical zoom device based on the area data prestored in the memory.  
      It is desirable for the moving range controller to change the moving range of the shake correction optical element within a range so that no part of an effective picture area of an imaging surface of the image sensor deviates outside from the image circle.  
      In an embodiment, an image stabilizer is provided, including an imaging optical system including an image sensor; an electronic zoom device which trims a part of an image formed on the image sensor to change an object coverage area for an object which is formed through the imaging optical system; an image shake correction device which moves a shake correction optical element of the imaging optical system in a plane orthogonal to an optical axis in accordance with a direction and magnitude of vibration applied to the imaging optical system; a memory in which area data is prestored, the area data indicating changes in size of an effective picture area of an imaging surface of the image sensor that corresponds to the object coverage area when the electronic zoom device changes the object coverage area; and a moving range controller which changes a moving range of the shake correction optical element that corresponds to a change of the effective picture area in accordance with an operating state of the electronic zoom device based on the area data prestored in the memory.  
      It is desirable for the moving range controller to change the moving range of the shake correction optical element within a range so that no part of the effective picture area deviates outside from the image circle.  
      In an embodiment, a method of correcting image shake in an imaging device is provided, wherein the imaging device includes an object coverage area changing device for changing an object coverage area for an object which is to be photographed through an imaging optical system, and an image shake correction device which moves a shake correction optical element of the imaging optical system in a plane orthogonal to an optical axis, the method including prestoring area data in a memory, the area data designating changes in  10  relative sizes between an image circle of the imaging optical system and an effective picture area of an imaging surface when the object coverage area changing device changes the object coverage area; reading the area data from the memory in accordance with an operating state of the object coverage area changing device to calculate a moving range of the shake correction optical element that corresponds to a change of the object coverage area based on the area data read out from the memory; and moving the shake correction optical element in the plane within the calculated moving range thereof in accordance with a direction and magnitude of vibration applied to the imaging optical system.  
      It is desirable for the moving range of the shake correction optical element, which is calculated based on the area data read out from the memory, to be determined within a range so that no part of the effective picture area deviates outside from the image circle.  
      According to the image stabilizer and the method of correcting image shake to which the present invention is applied, a compact image stabilizer can reliably correct image shake even if the magnification of the optical system thereof is large.  
      The present disclosure relates to subject matter contained in Japanese Patent Application No. 2005-303465 (filed on Oct. 18, 2005) which is expressly incorporated herein in its entirety. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The present invention will be discussed below in detail with reference to the accompanying drawings, in which:  
       FIG. 1  is a front elevational view of an embodiment of a digital camera equipped with an image stabilizer according to the present invention;  
       FIG. 2  is a schematic diagram of major elements of the digital camera shown in  FIG. 1 ;  
       FIG. 3  is a conceptual illustration showing the relative positional relationship between the image sensor and the image circle of the imaging optical system of the digital camera before an electronic zoom operation is performed, and the moving range of the image sensor;  
       FIG. 4  is a view similar to that of  FIG. 3 , showing a shifted state of the moving range of the image sensor when an electronic zoom operation has been performed from the state shown in  FIG. 3 ;  
       FIG. 5  is a conceptual illustration showing the relative positional relationship between the image sensor and the image circle of the imaging optical system of the digital camera at the wide-angle extremity, and the moving range of the image sensor;  
       FIG. 6  is a view similar to that of  FIG. 5 , showing the relative positional relationship between the image sensor and the image circle of the imaging optical system of the digital camera at the telephoto extremity, and the moving range of the image sensor;  
       FIG. 7  is a flow chart showing operations of an image-sensor moving range shifting control which are performed by the main CPU shown in  FIG. 2 ; and  
       FIG. 8  is a flow chart showing operations of the image-sensor moving range shifting control which are performed by the shake correction control CPU shown in  FIG. 2 .  
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       FIG. 1  shows a first embodiment of a digital camera (imaging device)  10  equipped with an optical axis correction apparatus according to the present invention. The digital camera  10  is provided on the front of a camera body  11  with a zoom lens (zoom lens barrel)  12 , an optical viewfinder  13  and a flash  14 . The digital camera  10  is provided on the top of the camera body  11  with a shutter release button  15 . The digital camera  10  is provided on the back thereof with a zoom switch  16  and an LCD  28  which indicates the picture area (object coverage area).  
      As shown in  FIG. 2 , the zoom lens  12  is provided with a zoom lens system (photographing optical system)  20  including a plurality of lens groups (first, second and third lens groups) L 1 , L 2  and L 3 , and an image sensor (shake correction optical element)  21  which is located at a focal point of the zoom lens system  20 . The optical axis of the zoom lens system  20  is shown by the letters “OZ” in  FIG. 2 . The digital camera  10  is provided therein with a main CPU (an element of a moving range controller/an element of an image shake correction controller)  22 , a shake correction control CPU (an element of the moving range controller/an element of the image shake correction controller)  23 , an EEPROM (memory)  24 , an X gyro sensor  25  and a Y gyro sensor  26 .  
      The first, second and third lens groups L 1 , L 2  and L 3 , which are elements of the zoom lens system  20 , are driven by a zoom mechanism (an element of an object coverage area changing device/an element of an optical zoom device)  31  including a zoom motor (an element of the object coverage area changing device/an element of the optical zoom device)  30  as a driving source of the zoom mechanism. The second lens group L 2  is moved along the optical axis OZ by the zoom mechanism  31  to vary focal length of the zoom lens system  20 . The zoom lens system  20 , the image sensor  21  and the optical zoom device ( 30  and  31 ) constitute an imaging optical system. The zoom switch  16  is a momentary switch which can be selectively operated between the telephoto side (Tele) and wide-angle side (Wide). Operating the zoom switch  16  to telephoto side and wide-angle side causes the zoom lens system  20  to change to the long focal length side (telephoto extremity) and the short focal length side (wide-angle extremity), respectively.  
      In addition to the optical zoom function of the zoom lens system  20 , the digital camera  10  includes an electronic zoom (digital zoom) function. As well known in the art, a digital zoom function is a digital image process in which a part (central part) of an electronic image (digital image) captured by an image sensor (e.g., CCD or CMOS sensor) is trimmed to change the object coverage area to thereby raise the scaling factor (display magnification) of an object image relative to the object viewed by the photographer. The digital camera  10  is provided with an image processing circuit (an element of the object coverage area changing device/an electronic zoom device)  27  which performs digital imaging processing (electronic zoom). When the zoom lens system  20  is at the telephoto extremity, further operating the zoom switch  16  to telephoto side causes the digital camera  10  to enter an electronic zoom mode in which an electronically image magnifying process is performed by the image processing circuit  27  under control of the main CPU  22 .  
      The digital camera  10  is provided with an image stabilizer (anti-shake system/image shake correction device) including an X-direction drive mechanism (an element of the image shake correction device)  34  and a Y-direction moving device (an element of the image shake correction device)  35 . The X-direction drive mechanism  34  and the Y-direction drive mechanism  35  are provided with an X-direction motor (an element of the image shake correction device)  32  and a Y-direction motor (an element of the image shake correction device)  33 , respectively. The image sensor  21  can be moved by the X-direction drive mechanism  34  and the Y-direction drive mechanism  35  in a plane orthogonal to the optical axis OZ. Specifically, the X-direction drive mechanism  34  moves the image sensor  21  linearly in the horizontal direction (X-direction; see  FIG. 2 ) in a plane orthogonal to the optical axis OZ, and the Y-direction drive mechanism  35  moves the image sensor  21  linearly in the vertical direction (Y-direction; see  FIG. 2 ) in a common plane orthogonal to the optical axis OZ.  
      Note that if the K-direction drive mechanism  34  and the Y-direction drive mechanism  35  are driven at the same time independently, the image sensor  21  can be linearly moved or moved in a curved line as desired.  
      Deviations of an object image (image shake) on the imaging surface of the image sensor  21  can be corrected (offset) by moving the image sensor  21  in accordance with the direction and magnitude of vibration (shake) applied to the digital camera (the zoom lens system  20 ) by the X-direction drive mechanism  34  (which includes the X-direction motor  32 ) and the Y-direction drive mechanism  35  (which includes the Y-direction motor  33 ).  
      More specifically, the X gyro sensor  25  detects the angular velocity about the X-axis while the Y gyro sensor  26  detects the angular velocity about the Y-axis. The angular velocity detected by the X gyro sensor  25  and the angular velocity detected by the Y gyro sensor  26  are time-integrated to obtain an angle of movement, and subsequently, an X-direction deviation amount and a Y-direction deviation amount of an object image are calculated from an angle of movement thus obtained, and the amount of driving (moving) of the image sensor  21  and the direction of driving (moving) of the image sensor  21  (i.e., the amount of driving of the X-direction motor  32  and the amount of driving of the Y-direction motor  33 ) which are necessary for canceling the image shake of the object image are calculated. Subsequently, based on these calculated values, the shake correction control CPU  23  controls driving operations of the X-direction motor  32  and the Y-direction motor  33 . This control suppresses (corrects) image shake of an object image picked up by the image sensor  21 .  
      When an optical zoom operation or an electronic zoom operation is performed, the size relationship between the area of an image circle formed on the imaging surface of the image sensor  21  via the zoom lens system  20  and the effective picture area on the imaging surface of the image sensor  21  (the area trom which image data is actually captured) varies. The present invention directed toward this size change between the image circle and the effective picture area; i.e., the moving range of the image sensor  21  for image-shake correction is shifted appropriately within a range so that no part of the effective picture area deviates outside from the image circle when the object coverage area is changed by an optical zoom operation or an electronic zoom operation.  
      The concept of such a shifting operation of the moving range of the image sensor  21  for image-shake correction when an electronic zoom operation is performed will be hereinafter discussed with reference to  FIGS. 3 and 4 .  FIG. 3  shows a state where the zoom lens system  20  is at the telephoto extremity without an electronic zoom operation being additionally performed. In  FIG. 3 , K 1  represents the outside shape of the image sensor  21 , K 2  designates the mechanical moving range (mechanical moving limit) of the imaging surface of the Image sensor  21  (by the X-direction moving device  34  and the Y-direction moving device  35 ), K 3  designates the effective picture area on the imaging surface of the image sensor  21 , which is actually used for capturing image data, KC designates the center of the effective picture area, and G designates the image circle projected by the zoom lens system  20 .  
      If the image sensor  21  is freely moved over the entire mechanical moving range K 2  of the imaging surface of the image sensor  21  to correct image shake, there is a possibility of a part of the effective picture area K 3  deviating outside from the image circle G, thus causing a part of the rectangular image to be cropped out in the final image. In addition, if the image sensor  21  is moved to a mechanical moving limit thereof, there is a possibility of a moving part hitting another part within the camera body  11 , thus causing damage to occur. Therefore, the moving range of the image sensor  21  is electronically controlled so that the outer edge of the effective picture area K 3  and the center KC of the effective picture area K 3  remain within a range MP and a range MC shown in  FIG. 3 , respectively. The range MP and the range MC represent the electronic moving range of the outer edge of the effective picture area K 3  and the electronic moving range of the center KC of the effective picture area K 3 , respectively, within the boundaries of a region where no part of the entire effective picture area K 3  deviates outside from the image circle G (where no part of the entire rectangular image is cropped out in the final image). In other words, image quality is maintained by electronically limiting the moving range of the image sensor  21  in an image shake correction control.  
       FIG. 4  shows a state where the zoom lens system  20  is at the telephoto extremity with an electronic zoom operation being additionally performed. The size of the image circle G, the outside shape K 1  of the imaging surface of the image sensor  21  and the mechanical moving range K 2  of the imaging surface of the image sensor  21  in  FIG. 4  are the same as those shown in  FIG. 3 . However, in preparation for an electronic zoom operation, the effective picture area K 3  is reduced (trimmed) to an effective picture area (reduced effective picture area) K 3 ′ which is smaller than the effective picture area K 3 . Thereupon, the moving range of the image sensor  21  is electronically controlled so that the outer edge of the effective picture area K 3 ′ and the center KC of the effective picture area K 3 ′ remain within a range MP′ and a range MC′ shown in  FIG. 4  which are wider than the range MP and MC shown in  FIG. 3 , respectively. The range MP′ and the range MC′ represent the electronic moving range of the outer edge of the effective picture area K 3 ′ and the electronic moving range of the center KC of the effective picture area K 3 ′, respectively, within the boundaries of a region where no part of the entire effective picture area K 3 ′ deviates outside from the image circle G (where no part of the entire rectangular image is cropped out in the final image).  
      Accordingly, when the digital camera  10  moves from the state shown in  FIG. 3  in which the electronic zoom is not activated to the state shown in  FIG. 4  in which the electronic zoom has been activated, the amount of driving of the image sensor  21  for image-shake correction can be increased by shifting the electronic moving range of the outer edge of the effective picture area K 3  and the electronic moving range of the center KC of the effective picture area K 3  from the narrow electronic moving range MP of the outer edge of the effective picture area K 3  and the narrow electronic moving range MC of the center KC of the effective picture area K 3  to the wide electronic moving range MP′ of the outer edge of the effective picture area K 3 ′ and the wide electronic moving range MC′ of the center KC of the effective picture area K 3 ′, respectively. In the case shown in  FIG. 4 , the outside shape K 1  of the image sensor  21  reaches the mechanical moving range (mechanical moving limit) K 2  of the imaging surface of the image sensor  21  before reaching the aforementioned boundaries of the region where no part of the entire effective picture area K 3  deviates outside from the image circle s, and a further movement of the image sensor  21  is prevented. In any case, the mechanical moving range of the image sensor  21  can be effectively used, and the image stabilizer of the digital camera  10  can deal with image shake with no increase in size of the optical system or the image stabilizer of the digital camera  10  even if the amount of image-shake correction becomes great. Specifically when the object coverage area is reduced by an electronic zoom operation, enlarging the electronic moving range of the image sensor  21  is effective because the amount of image-shake correction per unit of shake angle increases as the scaling factor (display magnification) of an object image indicated on the LCD  20  (located on the back of the camera body  11 ) relative to the object increases.  
      Although the shifting operation of the moving range of the image sensor  21  for image-shake correction when an electronic zoom operation is performed has been discussed above only in two stages wherein the electronic zoom of the digital camera  10  is activated and not activated, respectively, it is possible that a desired object coverage area be selected from among different object coverage areas in an electronic zoom operation. Even in the case where the zoom range of the electronic zoom is provided as a stepwise zoom range, the effective picture area (K 3 ′) used on the image sensor  21  becomes narrower as the display magnification increases, and therefore, according to this variation in the effective picture area, the moving range of the image sensor  21  only needs to be increased stepwise.  
      The concept of the shifting operation of the moving range of the image sensor  21  for image-shake correction when an optical zoom operation is performed will be hereinafter discussed with reference to  FIGS. 5 and 6 . In  FIGS. 5 and 6 , the outside shape K 1  of the image sensor  21 , the mechanical moving range K 2  of the image sensor  21  and the effective picture area K 3  on the imaging surface of the image sensor  21  are identical to those shown in  FIG. 3 . In regard to the image circle of the zoom lens system  20 , although an image circle G-T shown in  FIG. 6  when the zoom lens system  20  is at the telephoto extremity is greater than the image circle G shown in  FIGS. 3 and 4  when the zoom lens system  20  is set at the telephoto extremity, this is only for the purpose of illustrating the difference in size between the image circle G-T and an image circle G-W shown in  FIG. 5  when the zoom lens system  20  is at the wide-angle extremity, rather than for the purpose of obtaining the size of the image circle itself when the zoom lens system  20  is at the telephoto extremity.  
       FIG. 5  shows a state where the zoom lens system  20  is set at the wide-angle extremity. A range MP-W and a range MC-W shown in  FIG. 5  represent the electronic moving range of the outer edge of the effective picture area K 3  and the electronic moving range of the center KC of the effective picture area K 3 , respectively, within the boundaries of a region where no part of the entire effective picture area K 3  deviates outside from the image circle G-W (no part of the entire rectangular image is cropped out in the final image).  
       FIG. 6  shows a state where the zoom lens system  20  is at the telephoto extremity. The image circle G-T shown in  FIG. 6  when the zoom lens system  20  is at the telephoto extremity is larger than the image circle G-W when the zoom lens system  20  is at the wide-angle extremity. Therefore, an electronic moving range MP-T of the outer edge of the effective picture area K 3  and an electronic moving range MC-T of the center KC of the effective picture area K 3  within the boundaries of a region where no part of the entire effective picture area K 3  deviates outside from the image circle G-T (no part of the entire rectangular image is cropped out in the final image) are wider than the aforementioned electronic moving range MP-W and the aforementioned electronic moving range MC-W, respectively.  
      Accordingly, when the zoom lens system  20  changes the angle of view from the wide-angle extremity ( FIG. 5 ) to the telephoto extremity ( FIG. 6 ), the amount of driving of the image sensor  21  for image-shake correction can be increased by shifting the aforementioned narrow electronic moving ranges MP-W and MC-W shown in  FIG. 5  to the aforementioned wide electronic moving ranges MP-T and MC-T shown in  FIG. 6 , respectively. Consequently, the mechanical moving range of the image sensor  21  can be effectively used, and the image stabilizer of the digital camera  10  can deal with image shake with no increase in size of the optical system or the image stabilizer of the digital camera  10  even if the amount of image-shake correction becomes great. Specifically, when the scaling factor of an object image is increased (the object coverage area is reduced) by an optical zoom operation, enlarging the electronic moving range of the image sensor  21  is effective because the amount of image-shake correction per unit of shake angle increases.  
      Although the shifting operation of the moving range of the image sensor  21  for image-shake correction when an optical zoom operation is performed has been discussed above only in two stages wherein the digital camera  10  is set at the wide-angle extremity and the telephoto extremity, respectively, it is possible for a desired focal length to be selected from among different steps of focal lengths in an optical zoom operation. Even in the case where the zoom range of the optical zoom is a stepped zoom range, the electronic moving range of the image sensor  21  only needs to be widened stepwise according to the image circle obtained at each of the different steps of focal lengths.  
      Control flow of the above described shifting operation of the moving range of the image sensor  21  for image-shake correction when an optical zoom operation or an electronic zoom operation is performed will be hereinafter discussed with reference to flow charts shown in  FIGS. 7 and 8 . As a precondition of this control, the zoom range of the optical zoom that is performed by operation of the optical zoom lens system  20  is configured to be a stepwise zoom range including four focal length steps in total from the wide-angle extremity to the telephoto extremity. In  FIG. 7 , four focal length data of these four focal length steps are shown as zoom data  1 ,  2 ,  3  and  4 , respectively. Zoom data  1  and  4  correspond to the wide-angle extremity and the telephoto extremity, respectively, and zoom data  2  and  3  correspond to two intermediate focal lengths between the wide-angle extremity and the telephoto extremity, respectively. Additionally, in the electronic zoom operation, the scaling factor (display magnification/zoom) can be varied in three steps. In  FIG. 7 , the three scaling factor data are shown as zoom data  5 ,  6  and  7 , respectively. Zoom data  5  designates the smallest scaling factor of the electronic zoom, zoom data  7  designates the greatest scaling factor of the electronic zoom, and zoom data  6  designates an intermediate scaling factor of the electronic zoom therebetween.  
      The range (size) of the image circle is measured beforehand at each of the four focal length steps in the zoom range of the optical zoom, and area data  1 ,  2 ,  3  and  4  which represent the four electronic moving ranges of the image sensor  21  that correspond to the four image circles at the four focal length steps, respectively, are written in the EEPROM  24 . Additionally, the range (size) of the image circle is measured beforehand at each of the three steps of the stepwise electronic zoom range, and area data  5 ,  6  and  7  which represent the three electronic moving ranges of the image sensor  21  that correspond to the three effective picture areas at the three steps of the stepwise electronic zoom range, respectively, are written in the EEPROM  24 . Each of area data  1  through  7  consists of X-direction area data and Y-direction area data which indicate an amount of driving of the X-direction motor  32  and an amount of driving of the Y-direction motor  33 , respectively. Fourteen items of data in total: X-shift data  1  and Y-shift data  1  which correspond to zoom data  1  (the wide-angle extremity of the optical zoom) through X-shift data  7  and Y-shift data  7  which correspond to zoom data  7  (the maximum scaling factor of the electronic zoom) are stored in the EEPROM  24 . Although the zoom range of the optical zoom is configured to have a stepwise optical zoom range of the four steps and the zoom range of the electronic zoom is configured to have a stepwise electronic zoom range of the three steps in the above illustrated embodiment, the number of the steps in each of the optical zoom and the electronic zoom is not limited solely to these particular number of steps.  
      The flow chart shown in  FIG. 7  shows operations of an image-sensor moving range shifting control which are performed by the main CPU  22 . Upon the zoom switch  16  being operated (step S 10 ), it is determined whether the state of the zoom switch  16  has changed (step S 11 ) If it is determined that the state of the zoom switch  16  has not changed (if NO at step S 11 ), the relative positional relationship between the image circle and the effective picture area of the image sensor  21  has not varied, so that control ends without performing any operation for shifting the moving range of the image sensor  21  for image-shake correction. If it is determined that the state of the zoom switch  16  has changed (if YES at step S 11 ), it is determined which of the seven steps from the wide-angle extremity of the optical zoom to the maximum scaling factor of the optical zoom has been selected by the operation of the zoom switch  16  (steps S 12  through S 11 ). Subsequently, X-direction area data and Y-direction area data of one of the seven zoom data  1  through  7  which corresponds to the selected zoom position are read out from the EEPROM  24  (steps S 19  through S 25 ), and zoom data n, X-direction area data n and Y-direction area data n are sent to the shake correction control CPU  23  (steps S 26  and  27 ), wherein “n” corresponds to the selected zoom position number among the zoom positions  1  through  7 . For instance, if the zoom switch  16  is operated to select the second zoom position (zoom data  6 ) of the electronic zoom (if YES at step S 17 ), X-shift data  6  and Y-shift data  6  are read out from the EEPROM  24  (step S 24 ).  
      Subsequently, control proceeds to the process shown in  FIG. 8 . The shake correction control CPU  23  inputs zoom data n, X-direction area data n and Y-direction area data n which are output from the main CPU  22  (steps S 30  and S 31 ). Subsequently, the shake correction control CPU  23  drives the zoom motor  30  according to the input zoom data n to change the focal length of the zoom lens system  20  (step S 32 ). Thereupon, the second lens group L 2  moves in the optical axis direction to vary the focal length of the zoom lens system  20 . Immediately after it is determined that the focal length of the zoom lens system  20  has reached the set focal length, the zoom motor  30  is stopped.  
      If the input zoom data n is one of zoom data  5  through  7  of the electronic zoom, the zoom motor  30  is driven to the telephoto extremity. When the focal length of the zoom lens system  20  has reached the telephoto extremity, the zoom motor  30  is stopped.  
      If the zoom motor  30  driving operation is completed (if YES at step S 33 ), the electronic moving range of the image sensor  21  in the X-direction is calculated (step S 34 ). This electronic moving range is obtained by subtracting the input X-direction area data n from the mechanical moving range of the image sensor  21  in the X-direction (X limit). Subsequently, the electronic moving range of the image sensor  21  in the Y-direction is calculated (step S 35 ). This electronic moving range is obtained by subtracting the input Y-direction area data n from the mechanical moving range of the image sensor  21  in the Y-direction (Y limit). Thereafter, the X-direction motor  32  and the Y-direction motor  33  are driven so that the image sensor  21  moves within the electronic moving ranges of the image sensor  21  in the X-direction and the Y-direction that are obtained at steps S 34  and S 35 , respectively.  
      As can be understood from the foregoing, the mechanical moving range of the image sensor  21  can be used most effectively by determining an electronic moving range of the image sensor  21  by utilizing (adding) data of the mutual size relationship between the effective picture area and the image circle, the size relationship between which varies in accordance with the selected object coverage area. Therefore, even if the amount of movement of the image sensor  21  per unit of time for image-shake correction becomes great by increasing the scaling factor, the follow-up ability of the image stabilizer can be enhanced, which makes it possible to achieve a high image-correction capability within a compact structure.  
      Although the present invention has been discussed above with reference to the specific illustrated embodiment described above, the present invention is not limited solely thereto. For instance, although the above illustrated embodiment of the digital camera  10  is equipped with both an optical zoom function and an electronic zoom function, the present invention can also be applied to an imaging device equipped with only one of an optical zoom function and an electronic zoom function.  
      Obvious changes may be made in the specific embodiment of the present invention described herein, such modifications being within the spirit and scope of the invention claimed. It is indicated that all matter contained herein is illustrative and does not limit the scope of the present invention.