Patent Publication Number: US-2017351163-A1

Title: Shutter device and image-capturing apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to a shutter device and an image-capturing apparatus. 
     BACKGROUND ART 
     So-called normally open type shutter devices having a front curtain light-shielding blade and a rear curtain light-shielding blade are known. In an electronic camera equipped with such a shutter device, a front curtain light-shielding blade is withdrawn from a photographic opening of the shutter device to one side in a direction of movement of light-shielding blades, while a rear curtain light-shielding blade is withdrawn to the other side in order to display a preview image in a photographing preparation state before an actual exposure (see PTL1, for example). 
     CITATION LIST 
     Patent Literature 
     PTL1: Japanese Laid-Open Patent Publication No. 2008-164804 
     SUMMARY OF INVENTION 
     Technical Problem 
     In the electronic camera equipped with the shutter device described in PTL1, the front curtain light-shielding blade which has been withdrawn from the photographic opening to one side is moved toward the other side to shield the photographic opening, so that a reset operation of the image sensor is performed before the actual exposure. Then, the front curtain light-shielding blade and the rear curtain light-shielding blade are moved toward the one side with a predetermined time difference to expose an image sensor. A release time lag is thus increased. 
     However, no specific configuration of a shutter device that can further reduce the release time lag has been proposed. 
     Solution to Problem 
     According to the  1 st aspect of the present invention, a shutter device comprises: a substrate having an opening; a first light-shielding member that has a light-shielding region having a length in a first direction larger than a length of the opening in the first direction and a length in a second direction smaller than a length of the opening in the second direction, and partly shields the opening while moving from a first position outside the opening of the substrate to a second position outside the opening, the second position being different from the first position; and a second light-shielding member that has a light-shielding region having a length in the first direction smaller than the length of the opening in the first direction and a length in the second direction smaller than the length of the opening in the second direction, and shields the opening between an end in the first direction of the first light-shielding member and the substrate while moving in the second direction. 
     According to the 2nd aspect of the present invention, it is preferred that in the shutter device according to the 1st aspect, the second light-shielding member is located outside the opening while the first light-shielding member is located in the first position, and the second light-shielding member partly shield the opening in the end in the first direction of the light-shielding region along with the movement of the first light-shielding member in the second direction. 
     According to the 3rd aspect of the present invention, it is preferred that the shutter device according to the 1st or 2nd aspect further comprises: a first driving member that is provided for the first light-shielding member and drives the first light-shielding member in the second direction, wherein: the second light-shielding member is driven in the second direction by the first driving member. 
     According to the 4th aspect of the present invention, the shutter device according to any one of the 1st to 3rd aspects may further comprise: a third light-shielding member that moves from the first position in the second direction to shield the opening; and a second driving member that moves the third light-shielding member. 
     According to the 5th aspect of the present invention, it is preferred that in the shutter device according to the 4th aspect, the end in the first direction of the light-shielding region of the first light-shielding member has a shape that extends around the movement range of the second driving member. 
     According to the 6th aspect of the present invention, it is preferred that in the shutter device according to any one of the 1st to 5th aspects, the first light-shielding member and the second light-shielding member move to different positions outside the opening of the substrate. 
     According to the 7th aspect of the present invention, an image-capturing apparatus comprises: the shutter device according to any one of the 1st to 6th aspects; and an image sensor that receives luminous flux from a subject through the shutter device. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a view illustrating a configuration of main components of a digital camera according to an embodiment. 
         FIG. 2  is a view illustrating an internal configuration of a shutter device according to a first embodiment. 
         FIG. 3  is a view illustrating an internal configuration of the shutter device according to the first embodiment. 
         FIG. 4  is a view illustrating an internal configuration of the shutter device according to the first embodiment. 
         FIG. 5  is a view illustrating an internal configuration of the shutter device according to the first embodiment. 
         FIG. 6  is a view illustrating a light-shielding region of a front curtain light-shielding blade of the shutter device according to the embodiment. 
         FIG. 7  is a view illustrating an internal configuration of a shutter device according to a second embodiment. 
         FIG. 8  is a view illustrating an internal configuration of the shutter device according to the second embodiment. 
         FIG. 9  is a view illustrating an internal configuration of the shutter device according to the second embodiment. 
         FIG. 10  is a view illustrating an internal configuration of the shutter device according to the second embodiment. 
         FIG. 11  is a view illustrating an internal configuration of a shutter device according to a third embodiment. 
         FIG. 12  is a view illustrating an internal configuration of the shutter device according to the third embodiment. 
         FIG. 13  is a view illustrating an internal configuration of the shutter device according to the third embodiment. 
         FIG. 14  is a view illustrating an internal configuration of the shutter device according to the third embodiment. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     First Embodiment 
     An image-capturing apparatus including a shutter device according to an embodiment will be described with reference to the drawings. 
       FIG. 1  is a view illustrating a configuration of main components of a digital camera  1  which is an image-capturing apparatus according to an embodiment. As illustrated in  FIG. 1 , the digital camera  1  is a so-called mirrorless camera including a camera body  20  and a lens barrel  10  that is removably attached to the camera body  20  with a lens mount  9  therebetween. The digital camera  1  may be a single lens reflex camera, instead of a mirrorless camera. 
     The lens barrel  10  includes an image-forming optical system  11  and a diaphragm  12 . The image-forming optical system  11  is an optical system constituted by a plurality of lenses including a focus adjusting lens, for forming a subject image on a predetermined image-forming plane. The focus adjusting lens is moved back and forth in an optical axis L direction by an operation of a lens driving motor (not shown).  FIG. 1  schematically illustrates the image-forming optical system  11  as a single lens, for convenience of illustration. The diaphragm  12  limits light flux passing through the image-forming optical system  11 , that is, an amount of incident light. 
     The camera body  20  has a shutter device  21 , an image sensor  22 , and a controller  26  provided therein. The camera body  20  also has a rear side monitor  30 , which includes a display device such as a liquid display, provided on its rear side. The camera body  20  further has an operating unit  40  provided thereon. 
     The image sensor  22  is an image sensor having a number of pixels arranged in a matrix, such as a CMOS image sensor. The image sensor  22  is arranged so that its image-capturing plane is positioned on the image-forming plane of the image-forming optical system  11 . The image sensor  22  captures the subject image formed on the image-capturing plane by the image-forming optical system  11  through the shutter device  21  and outputs image-capturing signals to the controller  26 . Furthermore, various optical filters including an infrared cut filter are provided on the image-capturing plane of the image sensor  22 , although not illustrated in  FIG. 1 . The plurality of pixels constituting the image sensor  22  are two-dimensionally arranged in a pixel row direction (the X axis direction in  FIG. 2  described later) and in a pixel column direction (the Y axis direction in  FIG. 2  described later) that is orthogonal to the pixel row direction. The pixels are reset and the image-capturing signals are read out for each of pixel rows at different positions in the pixel column direction at different timings. 
     The shutter device  21  is provided on a front side (a subject side) of the image sensor  22 . The shutter device  21  is a so-called focal plane shutter that is driven by a front curtain actuator and a rear curtain actuator (not shown) in accordance with driving signals from a power control unit (not shown) of a controller  26  described later, to shield light flux which would be incident onto the image sensor  22  from the subject. Details of the shutter device  21  will be described later. 
     The controller  26 , which is constituted by a microprocessor, its peripheral circuits, and other circuits, controls components of the digital camera  1  by reading and executing control programs stored in advance in a storage medium (not shown) such as a flash memory. The controller  26  performs various image processing operations on the image-capturing signals output from the image sensor  22  to generate image data of the subject image and record the generated image data in a portable storage medium (not shown) such as a memory card. The controller  26  controls operations of the shutter device  21  and the image sensor  22 , as described later. The controller  26  has the power control unit (not shown) that functions to control the operation of the shutter device  21 . The controller  26  may be made of electronic circuits having functions equivalent to functions of the control programs. 
     The operating unit  40  includes various switches allocated to various operating members operated by a user, and outputs operation signals corresponding to operations of the operating members to the controller  26 . The operating members include, for example, a release button, a menu button for displaying a menu screen on the rear side monitor  30 , a cross key that is operated for selecting various settings and the like, a determination button for determining the settings and the like selected with the cross key, and a mode switching button for switching an operation mode of the digital camera  1  between a photographing mode and a reproduction mode. 
     Details of the shutter device  21  according to this embodiment will now be described. 
       FIGS. 2 to 5  are views illustrating an internal configuration of the shutter device  21  as seen from the image sensor  22  side, that is, the rear side of the digital camera  1 . For convenience of explanation, a coordinate system having the X axis and the Y axis will be defined as illustrated in the figures.  FIG. 2  is a view illustrating a state of the shutter device  21  before a start of photographing is instructed by the user operating the release button. In  FIG. 2 , both a front curtain light-shielding blade  220  and a rear curtain light-shielding blade  250  described later have been withdrawn in a first withdrawn position  201  above (or on the negative Y axis side of) an opening  215 .  FIG. 3  illustrates a state of the shutter device  21  after the user operates the release button to instruct the start of photographing, where the front curtain light-shielding blade  220  has started moving downward (in the positive Y axis direction) to traverse the opening  215 . In  FIG. 3 , however, the rear curtain light-shielding blade  250  has not yet started to move.  FIG. 4  is a view illustrating a state of the shutter device  21  wherein the front curtain light-shielding blade  220  further moves in the positive Y axis direction from the state illustrated in  FIG. 3  and the auxiliary light-shielding blade  300  is now moving across the opening  215  downward (in the positive Y axis direction), in coordination with the front curtain light-shielding blade  220 .  FIG. 5  is a view illustrating a state where the front curtain light-shielding blade  220  and the auxiliary light-shielding blade  300  have moved further downward (in the positive Y axis direction) from the state illustrated in  FIG. 4  to withdraw into a second withdrawn position  202  below (or on the positive Y axis side of) the opening  215  and into a fourth withdrawn position  204  on the right side of (or on the positive X axis side of) the opening  215 , respectively, while the rear curtain light-shielding blade  250  has not yet started to move. 
     The shutter device  21  includes the substrate  210 , the front curtain light-shielding blade  220 , the rear curtain light-shielding blade  250 , the auxiliary light-shielding blade  300 , a front curtain driving arm  221 , a front curtain driven arm  231 , a rear curtain driving arm  251 , a rear curtain driven arm  261 , the front curtain actuator (not shown), and the rear curtain actuator (not shown). In this embodiment, each of the front curtain actuator and the rear curtain actuator is made of an electric motor or the like. 
     The substrate  210  is fixed in the camera body  20  and has an opening  215  to expose the image sensor  22  with light flux from the subject. The opening  215  is formed into a rectangular shape having two sides extending in the X axis direction and two sides extending along the Y axis direction. In the following description, a side of the opening  215  on the negative Y axis side will be referred to as an upper end  215 U, a side on the positive Y axis side will be referred to as a bottom end  215 B, and the length in the Y axis direction between the upper end  215 U and the bottom end  215 B will be denoted by L 0 . 
     Rear Curtain 
     As illustrated in  FIGS. 3 to 5 , for example, the rear curtain driving arm  251  has a substrate-side coupling part  252  in one end. The rear curtain driving arm  251  is rotatably pivoted at the substrate-side coupling part  252  by the substrate  210  on the rear side (the image sensor  22  side) of the substrate  210 . The rear curtain driven arm  261  has a substrate-side coupling part  262  in one end. The rear curtain driven arm  261  is rotatably pivoted at the substrate-side coupling part  262  by the substrate  210  on the rear side (the image sensor  22  side) of the substrate  210 , on the positive Y axis side of (or below in the figures) the rear curtain driving arm  251 . The rear curtain driving arm  251  has a light-shielding member-side coupling part  253  at the other end. A plurality of rear curtain light-shielding blades  250  are rotatably coupled to the rear curtain driving arm  251  at the light-shielding member-side coupling part  253  with a caulking pin. The rear curtain driven arm  261  has a light-shielding member-side coupling part  263  at the other end. A plurality of rear curtain light-shielding blades  250  are rotatably coupled to the rear curtain driven arm  261  at the light-shielding member-side coupling part  263  with a caulking pin. The rear curtain driving arm  251  and the rear curtain driven arm  261  constitute a known parallel link mechanism for moving the rear curtain light-shielding blade  250 . 
     The rear curtain driving arm  251  and the rear curtain driven arm  261  are provided above (or on the negative Y axis side of) the front curtain driving arm  221  and the front curtain driven arm  231  in the figures. Specifically, the substrate-side coupling part  252  of the rear curtain driving arm  251  and the substrate-side coupling part  262  of the rear curtain driven arm  261  are coupled to the substrate  210  below (or on the negative Y axis side of) the substrate-side coupling part  222  of the front curtain driving arm  221  described later and the substrate-side coupling part  232  of the front curtain driven arm  231  described later. 
     The rear curtain light-shielding blade  250  is a light-shielding member constituted by a plurality of blades extending in the X axis direction, each blade being pivoted at its right end by the rear curtain driving arm  251  and the rear curtain driven arm  261  in the figures. 
     The rear curtain driving arm  251  has a hole  254 , into which a rear curtain driving pin  282  penetrating through an arcuate elongated hole  270  of the substrate  210  is inserted from the depth side of the paper plane, that is, from the front side of the digital camera  1 . The rear curtain driving pin  282  is driven by the rear curtain actuator (not shown). The rear curtain actuator is made of an electric motor, as described above. The rear curtain actuator is driven by a driving current or power supply from a power supply unit (not shown) of the controller  26 . When the rear curtain driving pin  282  is driven along the elongated hole  270  by the rear curtain actuator, the rear curtain driving arm  251  and the rear curtain driven arm  261  rotate about the substrate-side coupling part  252  and the substrate-side coupling part  262 , respectively. 
     When the rear curtain driving arm  251  is driven to rotate about the substrate-side coupling portion  252 , the rear curtain light-shielding blade  250  is driven by the known parallel link mechanism constituted by the rear curtain driving arm  251 , the rear curtain driven arm  261 , and the rear curtain light-shielding blade  250  to move across the opening  215  of the substrate  210  in the Y axis direction. In this embodiment, the rear curtain light-shielding blade  250  can move to the first withdrawn position  201  outside the opening  215  and to a light-shielding position where the rear curtain light-shielding blade  250  entirely covers the opening  215 . As illustrated in  FIGS. 2 to 5 , the plurality of blades of the rear curtain light-shielding blade  250  overlap one another in the first withdrawn position  201 . Although not illustrated, the plurality of blades of the rear curtain light-shielding blade  250  are unfolded to shield the opening  215  in the light-shielding position. 
     Although this embodiment describes the rear curtain light-shielding blade  250  moving on the rear side (the image sensor  22  side) of the opening  215 , a variation of the embodiment contemplates the rear curtain light-shielding blade  250  moving on the front side (the subject side) of the opening  215 . Furthermore, although the rear curtain light-shielding blade  250  entirely shields the opening  215  in this embodiment, the rear curtain light-shielding blade  250  may partly shield the opening  215  in the same manner as the front curtain light-shielding blade  220  described later. In this case, the rear curtain light-shielding blade  250  may be made of a single blade or may be constituted by a plurality of blades so as to not entirely cover the opening  215 . 
     Front Curtain 
     As well illustrated in  FIG. 3 , the front curtain driving arm  221  has a substrate-side coupling part  222  in one end. The front curtain driving arm  221  is rotatably pivoted at the substrate-side coupling part  222  by the substrate  210  on the rear side (the image sensor  22  side) of the substrate  210 . The front curtain driven arm  231  has a substrate-side coupling part  232  in one end. The front curtain driven arm  231  is rotatably pivoted at the substrate-side coupling part  232  by the substrate  210  on the rear side (the image sensor  22  side) of the substrate  210 , above (or on the negative Y axis side) the front curtain driving arm  221  in the figures. The front curtain driving arm  221  has a light-shielding part-side coupling part  223  at the other end. The front curtain light-shielding blade  220  is rotatably coupled to the front curtain driving arm  221  at the light-shielding member-side coupling part  223  with a caulking pin. The front curtain driven arm  231  has a light-shielding part-side coupling part  233  at the other end. The front curtain light-shielding blade  220  is rotatably coupled to the front curtain driven arm  231  at the light-shielding member-side coupling part  233  with a caulking pin. The front curtain driving arm  221  and the front curtain driven arm  231  constitute a known parallel link mechanism for moving the front curtain light-shielding blade  220 . 
     As described above, the front curtain driving arm  221  and the front curtain driven arm  231  are provided below (or on the positive Y axis side of) the rear curtain driving arm  251  and the rear curtain driven arm  261  in the figures. Specifically, the substrate-side coupling part  222  of the front curtain driving arm  221  and the substrate-side coupling part  232  of the front curtain driven arm  231  are coupled to the substrate  210  below (or on the positive Y axis side of) the substrate-side coupling part  252  of the rear curtain driving arm  251  and the substrate-side coupling part  262  of the rear curtain driven arm  261  in the figures. 
     The front curtain light-shielding blade  220  is a light-shielding member that extends in the X axis direction and is pivoted at its right end by the front curtain driving arm  221  and the front curtain driven arm  231 . In this embodiment, the front curtain light-shielding blade  220  is made of a single blade in the figures. 
     The front curtain driving arm  221  has a hole  224 , into which a front curtain driving pin  281  penetrating through an elongated hole  240  of the substrate  210  is inserted from the depth side of the paper plane, that is, from the front side of the digital camera  1 . The front curtain driving pin  281  is driven by the front curtain actuator (not shown). The front curtain actuator is driven by a driving current or power supply from a power supply unit (not shown) of the controller  26 . When the front curtain driving pin  281  is driven along the elongated hole  240  by the front curtain actuator, the front curtain driving arm  221  and the front curtain driven arm  231  rotate about the substrate-side coupling part  222  and the substrate-side coupling part  232 , respectively. 
     When the front curtain driving arm  221  is driven to rotate about the substrate-side coupling portion  222 , the front curtain light-shielding blade  220  is driven by the known parallel link mechanism, which is constituted by the front curtain driving arm  221 , the front curtain driven arm  231 , and the front curtain light-shielding blade  220 , to move across the opening  215  of the substrate  210  in the Y axis direction, as described above. In this embodiment, the front curtain light-shielding blade  220  can move between the first withdrawn position  201  outside the opening  215  and the second withdrawn position  202  outside the opening  215 , the second withdrawn position  202  being opposite to the first withdrawn position  201 . The front curtain light-shielding blade  220  has moved to the first withdrawn position  201  in  FIG. 2  and in the second withdrawn position  202  in  FIG. 5 . 
     As described above, the front curtain light-shielding blade  220  is made of a single blade. The upper edge  220 U ( FIG. 3 ) which is a side extending in the X axis direction on the negative Y axis side of the front curtain light-shielding blade  220  has a length larger than the width of the opening  215  in the X axis direction. Furthermore, a length (a light-shielding width) L 1  in the Y axis direction (a direction of movement of the front curtain light-shielding blade  220  and the rear curtain light-shielding blade  250 ) between the upper edge  220 U of the front blade light-shielding blade  220  and a bottom edge  220 B ( FIG. 3 ), which is a side extending in the X axis direction on the positive Y axis side, is shorter (smaller) than the length L 0  of the opening  215  in the Y axis direction. The front curtain light-shielding blade  220  can therefore only partly cover the opening  215 , in terms of structure. In other words, the front curtain light-shielding blade  220  has a light-shielding range in its direction of movement that is smaller than the length of the opening  215  in the direction of movement, in terms of structure. Details of the light-shielding region of the front curtain light-shielding blade  220  will be described later. 
     The length L 1  of the front curtain light-shielding blade  220  in the Y axis direction is determined so that no subject light flux from the subject is irradiated at least onto pixel rows that are being subjected to the pixel reset in the image sensor  22 . The minimal possible length can be designed to be a pixel pitch by matching a speed of movement of the front curtain light-shielding blade  220  with a pixel reset speed determined by a time required for the image sensor  22  to reset pixels for each entire image row. The time for the pixel reset may usually be set as desired. For an actual movement of the front curtain light-shielding blade  220 , however, it is difficult to perfectly match the speed of movement of the front curtain light-shielding blade  220  with the pixel rest speed. Also considering other error factors, the length L 1  of the front curtain light-shielding blade  220  in the Y axis direction is determined so that the following inequality (1) is satisfied: 
         L 0&gt; L 1≧Δ L 11   (1)
 
     where ΔL 11  is a constant which is determined from experiments or the like as a margin for a manufacturing error of the front curtain light-shielding blade  220  or deformation during the movement of the front curtain light-shielding blade  220  due to a material strength thereof, a margin for preventing an influence of light passing around the ends in the Y axis direction of the front curtain light-shielding blade  220  onto the image sensor, and a margin of synchronous error between the pixel reset speed and the speed of movement of the front curtain light-shielding blade  220 . 
     Although this embodiment describes the front curtain light-shielding blade  220  moving on the rear side (the image sensor  22  side) of the opening  215 , a variation of the embodiment contemplates a front curtain light-shielding blade  220  moving on the front side (the subject side) of the opening  215 . Furthermore, the front curtain light-shielding blade  220  is not limited to the configuration made of a single blade. Alternatively, the front curtain light-shielding blade  220  may be constituted by a plurality of blades and a light-shielding region formed by the plurality of blades may have a shorter (smaller) length in the Y axis direction than the length LO of the opening  215  in the Y axis direction so as to not entirely cover the opening  215 . 
     The Light-Shielding Region of the Front Curtain Light-Shielding Blade 
       FIG. 6( a )  illustrates a state where the front curtain light-shielding blade  220  is located in the first withdrawn position  201 .  FIG. 6( b )  illustrates a state where the front curtain light-shielding blade  220  is moving across the opening  215 . In  FIG. 6( a ) , the rear curtain light-shielding blade  250 , the rear curtain driving arm  251 , and the rear curtain driven arm  261  are omitted for convenience of explanation. In  FIGS. 6( a ) and ( b ) , an illustration of the auxiliary light-shielding blade  300  is omitted. 
     In this embodiment, a light-shielding region end on the positive X axis side (the right end side of the front curtain light-shielding blade) of the light-shielding region of the front curtain light-shielding blade  220  has an upper edge  220 U, an arcuate edge  220 A, and a side edge  220 C connecting the upper edge  220 U and the arcuate edge  220 A, as illustrated in  FIG. 6( a ) . The arcuate edge  220 A is formed along an arc  270   a  of the arcuate elongated hole  270  and has a shape that is recessed in the negative X axis direction, on the positive Y axis side of the upper edge  220 U. In other words, the arcuate edge  220 A has a shape corresponding to the shape of the arcuate elongated hole  270 . The side edge  220 C extends from a positive X axis-side end point of the upper edge  220 U in the positive Y axis direction to couple to the arcuate edge  220 A. The light-shielding region end of the front curtain light-shielding blade  220  extends around the elongated hole  270  which is the movement range of the rear curtain driving pin  282 . The length of the light-shielding region end on the positive X axis side of the front curtain light-shielding blade  220  in the positive Y axis direction from the upper edge  220 U is thus smaller than L 1 . 
     As illustrated in  FIG. 6( b ) , when the front curtain light-shielding blade  220  moves across the opening  215 , the arcuate edge  220 A also moves across the opening  215 . As described above, the length of the light-shielding region end on the positive X axis side of the front curtain light-shielding blade  220  is smaller than L 1  in the Y axis direction, since the arcuate edge  220 A is provided in this light-shielding end. This makes it unable to shield a region R in the opening  215 , which is denoted by hatching, below (or on the positive Y axis side of) the arcuate edge  220 A of the front curtain light-shielding blade  220  when the front curtain light-shielding blade  220  moves across the opening  215 . As described above, the length L 1  of the front curtain light-shielding blade  220  is determined based on the time required for the pixel reset. Subject light that has passed through the region R can thus be incident onto the image sensor  22  during the pixel reset, which can cause an insufficient exposure. The shutter device  21  in this embodiment has the auxiliary light-shielding blade  300  to shield the region R. 
     Auxiliary Light-Shielding Blade 
     The auxiliary light-shielding blade  300  will be described with reference to  FIGS. 2 to 5 . The auxiliary light-shielding blade  300  is rotatably attached to an auxiliary light-shielding blade coupling part  301  in the middle of the substrate-side coupling part  222  and the light-shielding part-side coupling part  223  of the front curtain driving arm  221  and to an auxiliary light-shielding blade coupling part  302  in the middle of the substrate-side coupling part  232  and the light-shielding part-side coupling part  233  of the front curtain driven arm  231 , to constitute a parallel link mechanism, together with the front curtain light-shielding blade  220 . 
     The above-described configuration allows the front curtain driven arm  231  and the front curtain light-shielding blade  220  to move across the opening  215  in the positive Y axis direction in coordination with each other, when the front curtain driving arm  221  is driven to rotate about the substrate-side coupling part  222 . 
     In this embodiment, the auxiliary light-shielding blade  300  can move across the opening  215  in the positive Y axis direction from a third withdrawn position  203  to a fourth withdrawn position  204 . The third withdrawn position  203  is a position outside the opening  215  on the positive X axis side and on the upper side (or on the negative Y axis side). The fourth withdrawn position  204  is a position outside the opening  215  on the positive X axis side and on the lower side (or on the positive Y axis side). It should be noted that the auxiliary light-shielding blade  300  is located in the third withdrawn position  203  in  FIG. 2  and in the fourth withdrawn position  204  in  FIG. 5 . 
     The auxiliary light-shielding blade  300  is made of a single blade. The blade constituting the auxiliary light-shielding blade  300  has a first edge  303  which is a side on the negative X axis side extending in the Y axis direction, a second edge  304  which is a side on the positive X axis side extending in the Y axis direction, a third edge  305  which is a side on the negative Y axis side, and a fourth edge  306  which is a side on the positive Y axis side extending in the X axis direction. A length L 3  in the X axis direction between the first edge  303  and the second edge  304  is smaller than the length of the opening  215  in the X axis direction. A length L 4  in the Y axis direction between the third edge  305  and the fourth edge  306  is smaller than the length of the opening  215  in the Y axis direction. In other words, the auxiliary light-shielding blade  300  can partly shield the opening  215 . The auxiliary light-shielding blade  300  is coupled with the front curtain driving arm  221  and the front curtain driven arm  231  in the vicinity of the second edge  304 . It should be noted that the first edge  303  of the auxiliary light-shielding blade  300  is located on the positive X axis side of the opening  215 , when the auxiliary light-shielding blade  300  is located in the third withdrawn position  203 . 
     The light-shielding region of the auxiliary light-shielding blade  300  shields a region of the opening  215  below (or on the positive Y axis side of) the light-shielding region end on the positive X axis side of the front curtain light-shielding blade  220  described above, while the auxiliary light-shielding blade  300  moves in the positive Y axis direction. As described above with reference to  FIG. 6( b ) , the region R of the opening  215  that cannot be shielded by the front curtain light-shielding blade  220  is left below the light-shielding region end on the positive X axis side of the front curtain light-shielding blade  220 . The region R is a region caused by the fact that the light-shielding region end of the front curtain light-shielding blade  220  is formed to extend around the movement range of the rear curtain driving pin  282  so that the length of the light-shielding region end in the Y axis direction is smaller than the length L 1 . The auxiliary light-shielding blade  300  shields the region R while moving across the opening  215  in the positive Y axis direction. In other words, the lengths L 3  and L 4  of the auxiliary light-shielding blade  300  are larger than the lengths of the region R in the X axis and Y axis directions, respectively. 
     Operation of the Shutter Device  21   
     The shutter device  21  configured as described above operates as follows. Before the user operates the release button, the front curtain light-shielding blade  220  and the rear curtain light-shielding blade  250  are located in the first withdrawn position  201  as illustrated in  FIG. 2 , while the auxiliary light-shielding blade  300  is located in the third withdrawn position  203 . In this state, subject light having passed through the photographic lens  11  is incident onto the image sensor  22  through the opening  215 . Image-capturing signals are repeatedly read out from the image sensor  22  and images (preview images) corresponding to the image-capturing signals are displayed on the rear side monitor  30 . This process is referred to as a live view display. 
     When the user operates the release button, the power supply unit (not shown) of the controller  26  starts to supply an electric power to the front curtain actuator (not shown) for shifting the front curtain light-shielding blade  220 . When being supplied with the electric power, the front curtain actuator rotates the front curtain driving pin  281  along the elongated hole  240  in the counterclockwise direction. As a result, the front curtain driving arm  221  is driven to rotate about the substrate-side coupling part  222  in a plane parallel to the XY plane. Accordingly, the front curtain light-shielding blade  220 , the front curtain driven arm  231 , and the auxiliary light-shielding blade  300  are driven in a linked manner so that the front curtain light-shielding blade  220  moves from the first withdrawn position  201  in the positive Y axis direction and the auxiliary light-shielding blade  300  moves from the third withdrawn position  203  in the counterclockwise direction. The front curtain light-shielding blade  220  starts to enter the opening  215  from the upper end  215 U of the opening  215 , and the auxiliary light-shielding blade  300  starts to enter the opening  215  from the positive X axis-side edge of the opening  215  (see  FIG. 3 ). 
     When the front curtain driving arm  221  is further driven to rotate, the front curtain light-shielding blade  220  and the auxiliary light-shielding blade  300  move in the positive Y axis direction and also the front curtain driven arm  231  rotates (see  FIG. 4 ). In this point in time, the light-shielding region end on the positive X axis side of the light-shielding region of the front curtain light-shielding blade  220  also moves across the opening  215 . Since the light-shielding region on the positive X axis side of the front curtain light-shielding blade  220  has a smaller length in the Y axis direction than L 1  as described above, the region R of the opening  215  that cannot be shielded by the front curtain light-shielding blade  220  is left below (or on the positive Y axis side of) the light-shielding region end. The auxiliary light-shielding blade  300  moves in the positive Y axis direction with shielding the region R. As described above, the auxiliary light-shielding blade  300  constitutes the parallel link mechanism, together with the front curtain light-shielding blade  220  as well as the front curtain driving arm  221  and the front curtain driven arm  231 . The auxiliary light-shielding blade  300  thus moves in the Y axis direction with the first edge  303  of the auxiliary light-shielding blade  300  being oriented in the Y axis direction. 
     The bottom edge  220 B of the front curtain light-shielding blade  220  and the negative X axis-side end of the auxiliary light-shielding blade  300  start to move across the opening  215  and start to shield the image-capturing plane of the image sensor  22  behind the shutter. The image sensor  22  resets stored charge for pixels in the shielded region. When the upper edge  220 U of the front curtain light-shielding blade  220  passes through the region of the image sensor  22  that has been shielded by the front curtain light-shielding blade  220  as illustrated in  FIGS. 3 and 4 , an exposure is started in the image-capturing plane of the image sensor  22  to store electric charges for pixels included in the image-capturing region through which the upper edge  200 U has passed. 
     The upper edge  220 U of the front curtain light-shielding blade  220  moves in the positive Y axis direction beyond the bottom end  215 B of the opening  215  so that the front curtain light-shielding blade  220  moves into the second withdrawn position  202  below the opening  215  (see  FIG. 5 ). The auxiliary light-shielding blade  300  moves in a direction further away from the opening  215 , along with the rotational movement of the front curtain driving arm  221 , into the fourth withdrawn position  204  (see  FIG. 5 ). When the front curtain light-shielding blade  220  moves to the second withdrawn position  202  and the auxiliary light-shielding blade  300  moves to the fourth withdrawn position  204 , the pixel reset and the exposure (i.e., the charge storage) are performed for the entire image-capturing plane of the image sensor  22 . 
     In this context, the controller  26  controls the timing of pixel reset for each of pixel rows extending in the X axis direction that constitute the image sensor  22 , in accordance with the shift of the front curtain light-shielding blade  220  and the auxiliary light-shielding blade  300  in the positive Y axis direction. In other words, the controller  26  resets pixels for pixel rows included in a region that is shielded from light flux from the subject by the shift of the front curtain light-shielding blade  220  and the auxiliary light-shielding blade  300 . 
     Once a time equivalent to the exposure time has elapsed since the front curtain light-shielding blade  220  started to move, the power control unit (not shown) of the controller  26  supplies an electric power to the rear curtain actuator (not shown) for moving the rear curtain light-shielding blade  250 . When being supplied with the electric power, the rear curtain actuator rotates the rear curtain driving pin  282  along the elongated hole  270  in the counterclockwise direction. As a result, the rear curtain driving arm  251  is driven to rotate about the substrate-side coupling part  252  in a plane parallel to the XY plane so that the rear curtain light-shielding blade  250  moves from the withdrawn position above the opening  215  in the positive Y axis direction by the action of the parallel link mechanism constituted by the rear curtain driving arm  251  and the rear curtain driven arm  261 . 
     In this way, the front curtain light-shielding blade  220  first starts to move in the positive Y axis direction and, after a time equivalent to the exposure time has elapsed, the rear curtain light-shielding blade  250  then starts to move in the positive Y axis direction. Consequently, subject light is incident onto the image sensor  22  after the reset, only during the exposure time, from a space between the upper edge  220 U ( FIG. 3 ) of the front curtain light-shielding blade  220  and the lower end of the lowermost blade of the rear curtain light-shielding blade  250 . The image sensor  22  is exposed with the subject light. 
     Thereafter, the rear curtain light-shielding blade  250  moves to the light-shielding position where it entirely covers the opening  215 . 
     The controller  26  controls the image sensor  22  to start to sequentially read pixels from the outermost pixel row on the negative Y axis side. Upon completion of reading the image-capturing signals from all the pixel rows, the controller  26  outputs driving signals from the power supply unit (not shown) to cause the front curtain light-shielding blade  220 , the rear curtain light-shielding blade  250 , and the auxiliary light-shielding blade  300  to be moved in the negative Y axis direction with the driving force of the electric motor (not shown). The front curtain light-shielding blade  220  and the rear curtain light-shielding blade  250  are stored in the first withdrawn position  201  above the opening  215 , while the auxiliary light-shielding blade  300  is stored in the third withdrawn position  203 . The operational control of the shutter device  21  during the exposure is then ended. 
     In this embodiment, the front curtain light-shielding blade  220  and the rear curtain light-shielding blade  250  are stored in the first withdrawn position  201  above the opening  215  until the exposure starts, as described above. In contrast to the case where the front curtain light-shielding blade  220  and the rear curtain light-shielding blade  250  are stored in positions that are opposite to each other with the opening  215  therebetween, it is thus not necessary to move the front curtain light-shielding blade  220  to a stored position at the start of the exposure. As a result, a release time lag is eliminated or minimized. 
     The embodiment described above provides the following operational advantages. 
     (1) In the shutter device  21 , both the front curtain light-shielding blade  220  and the rear curtain light-shielding blade  250  are withdrawn to the other side in the photographing preparation state before the actual exposure. In the actual exposure, the front curtain light-shielding blade  220  is moved in the positive Y axis direction to reset pixels in a range of the image sensor  22  that is shielded by the front curtain light-shielding blade  220 , and then the rear curtain light-shielding blade  250  is moved in the positive Y axis direction with a predetermined time difference with respect to the front curtain light-shielding blade  220  to end the exposure of the image sensor  22 . 
     In the shutter device  21  configured so that both the front curtain light-shielding blade  220  and the rear curtain light-shielding blade  250  are stored in the first withdrawn position, the movement range of the front curtain light-shielding blade  220  is made wider than that of the known shutter device  21 . This can cause the front curtain light-shielding blade  220  during its withdrawal movement to interfere with the rear curtain driving pin  282  driving the rear curtain light-shielding blade  250 . In this case, if the front curtain light-shielding blade  220  is shaped to extend around the movement range of the rear curtain driving pin  282  in order to avoid to interfere with the rear curtain driving pin  282  during the withdrawal movement, the light-shielding region end of the front curtain light-shielding blade  220  can fail to shield the opening  215  while moving in the positive Y axis direction. 
     Thus, the shutter device  21  according to this embodiment includes the auxiliary light-shielding blade  300  that has a light-shielding region having lengths in the X axis and Y axis directions smaller than the those of the opening  215  and can move in the Y axis direction in coordination with the front curtain light-shielding blade  220 . The auxiliary light-shielding blade  300  partly shields the opening  215  in the light-shielding region end of the front curtain light-shielding blade  220 , while moving in the Y axis direction. The front curtain light-shielding blade  220  and the rear curtain light-shielding blade  250  can therefore be stored in the first withdrawn position  201  until the start of photographing. This can reduce the release time lag and also shield the opening  215  so that the reduced light-shielding region in the light-shielding region end on the positive X axis side of the front curtain light-shielding blade  220  is compensated for. In other words, leakage light in the light-shielding region end on the positive X axis side of the front curtain light-shielding blade  220  is prevented from being incident onto the image sensor  22  during the pixel reset, which can prevent the insufficient exposure. 
     Furthermore, the light-shielding region of the auxiliary light-shielding blade  300  has lengths in the X axis and Y axis directions smaller than those of the opening  215 . In other words, the auxiliary light-shielding blade  300  has a smaller light-shielding region than that of the front curtain light-shielding blade  220 . This minimizes an increase in mass caused by providing the auxiliary light-shielding blade  300 , which contributes to a weight reduction. Additionally, a noticeable increase in power supplied to the front curtain actuator can be restrained. 
     (2) The auxiliary light-shielding blade  300  withdraws outside the opening  215  while the front curtain light-shielding blade  220  is stored in the position outside the opening  215  of the substrate  210 . Furthermore, the auxiliary light-shielding blade  300  partly shields the opening  215  in the light-shielding region end on the positive X axis side of the front curtain light-shielding blade  220 , along with the movement of the front curtain light-shielding blade  220  in the Y axis direction. This can thus prevent a deterioration in image quality of the photographed image due to an insufficient exposure. 
     (3) The auxiliary light-shielding blade  300  is coupled to the front curtain driving arm  221  and the front curtain driven arm  231  and moved in the Y axis direction by the front curtain driving arm  221  and the front curtain driven arm  231 . It is thus not necessary to use special members for moving the auxiliary light-shielding blade  300 , which prevents an increase in number of components and contributes to a reduction in weight of the shutter device  21 . Furthermore, it is possible that the auxiliary light-shielding blade  300  can be moved in the Y axis direction in firm coordination with the front curtain light-shielding blade  220  and shield the region R, since the auxiliary light-shielding blade  300  moves in the Y axis direction along with the rotational movement of the front curtain driving arm  221  and the front curtain driven arm  231 . 
     Second Embodiment 
     A second embodiment according to the present invention will be described with reference to the drawings. In the following description, the same components as those in the first embodiment are denoted by the same reference symbols and only differences between the embodiments will be mainly described. Configurations and functions not particularly described are the same as those in the first embodiment. This embodiment differs from the first embodiment in that the auxiliary light-shielding blade is differently shaped and attached. Thus, the following description mainly refers to how the auxiliary light-shielding blade is shaped and attached. 
       FIGS. 7 to 10  are views illustrating an internal configuration of the shutter device  21  according to the second embodiment as seen from the image sensor  22  side, that is, the rear side of the digital camera  1 . For convenience of explanation, a coordinate system having the X axis and the Y axis will be defined as illustrated in the figures.  FIG. 7  is a view illustrating a state of the shutter device  21  before a user operates the release button to instruct the start of photographing. In  FIG. 7 , the front curtain light-shielding blade  220  and the rear curtain light-shielding blade  250  are withdrawn in the first withdrawn position  201 , while the auxiliary light-shielding blade  310  is withdrawn in the third withdrawn position  203 .  FIG. 8  illustrates a state of the shutter device  21  after the user operates the release button to instruct the start of photographing, where the front curtain light-shielding blade  220  has started moving downward (in the positive Y axis direction) to traverse the opening  215 . It should be noted that the rear curtain light-shielding blade  250  has not yet started to move in  FIG. 8 .  FIG. 9  is a view illustrating a state of the shutter device  21  wherein the front curtain light-shielding blade  220  further moves in the negative Y axis direction from the state illustrated in  FIG. 8  and the auxiliary light-shielding blade  310  is now moving across the opening  215  downward (in the positive Y axis direction), in coordination with the front curtain light-shielding blade  220 .  FIG. 10  is a view illustrating a state where the front curtain light-shielding blade  220  and the auxiliary light-shielding blade  300  have moved further downward (in the positive Y axis direction) from the state illustrated in  FIG. 9  to withdraw into a second withdrawn position  202  below (or on the positive Y axis side of) the opening  215 , while the rear curtain light-shielding blade  250  has not yet started to move. 
     The auxiliary light-shielding blade  310  is fixed in the vicinity of the light-shielding part-side coupling part  223  of the front curtain driving arm  221  and moves together along with the rotational movement of the front curtain driving arm  221 . When the front curtain light-shielding blade  220  is driven by the known parallel link mechanism constituted by the front curtain driving arm  221  and the front curtain driven arm  231 , the auxiliary light-shielding blade  310  moves across the opening  215  in the positive Y axis direction in coordination with the movement of the front curtain light-shielding blade  220 . 
     It should be noted that the front curtain driving arm  221  does not include the auxiliary light-shielding blade coupling part  301  and also the front curtain driven arm  231  does not include the auxiliary light-shielding blade coupling part  302  in this embodiment, since the auxiliary light-shielding blade  310  is fixed to the front curtain driving arm  221 . 
     In this embodiment, the auxiliary light-shielding blade  310  starts to enter the opening  215  from the positive X axis-side edge of the opening  215  and can move across the opening  215  in the positive Y axis direction to the second withdrawn position  202 . It should be noted that the auxiliary light-shielding blade  310  is located in the third withdrawn position  203  in  FIG. 7  and in the second withdrawn position  202  in  FIG. 10 . 
     The auxiliary light-shielding blade  310  is made of a single planar blade. The blade constituting the auxiliary light-shielding blade  300  has a first edge  311 , a second edge  312 , a third edge  313 , and a fourth edge  314 . The first edge  311  is a side extending in the Y axis direction on the negative X axis side while the auxiliary light-shielding blade  310  moves in the Y axis direction (see  FIG. 9 ). The second edge  312  is a side extending in the Y axis direction on the positive X axis side while the auxiliary light-shielding blade  310  moves in the Y axis direction (see  FIG. 9 ). The third edge  313  is a side extending in the X axis direction on the negative Y axis side while the auxiliary light-shielding blade  310  moves in the Y axis direction (see  FIG. 9 ). The fourth edge  314  is a side extending in the X axis direction on the positive Y axis side while the auxiliary light-shielding blade  310  moves in the Y axis direction (see  FIG. 9 ). 
     A length L 31  in the X axis direction between the first edge  311  and the second edge  314  is smaller than the length of the opening  215  in the X axis direction (see  FIG. 9 ). A length L 41  in the Y axis direction between the third edge  315  and the fourth edge  316  is larger than a spacing between the front curtain driving arm  221  and the front curtain driven arm  231  during the rotational movement and smaller than the length of the opening  215  in the Y axis direction (see  FIG. 9 ). The auxiliary light-shielding blade  310  can thus partly shield the opening  215 . The light-shielding region of the auxiliary light-shielding blade  310  shields a region R of the opening  215  that is left in the light-shielding region end on the positive X axis side of the front curtain light-shielding blade  220  described above, while the auxiliary light-shielding blade  310  moves in the positive Y axis direction (see  FIG. 9 ). In other words, the lengths L 3  and L 4  of the auxiliary light-shielding blade  310  are larger than the lengths of the region R in the X axis and Y axis directions, respectively. 
     When the shutter device  21  starts to operate, the auxiliary light-shielding blade  310  starts to move from the third withdrawn position  203  (see  FIG. 7 ) and enter the opening  215  from the positive X axis-side edge of the opening  215  (see  FIG. 8 ). In accordance with the rotational movement of the front curtain driving arm  221  and the front curtain driven arm  231 , the front curtain light-shielding blade  220  and the auxiliary light-shielding blade  310  move in the positive Y axis direction (see  FIG. 9 ). The auxiliary light-shielding blade  310  moves in the positive Y axis direction to shield the region R. Eventually, the front curtain light-shielding blade  220  and the auxiliary light-shielding blade  310  move to the second withdrawn position  202  below the opening  215  (see  FIG. 10 ). 
     The second embodiment described above provides the same operational advantages as the operational advantages (1) to (3) achieved by the first embodiment. 
     Additionally, the auxiliary light-shielding blade  310  is fixed in the vicinity of the light-shielding part-side coupling part  223  of the front curtain driving arm  221 . In comparison to the case where the auxiliary light-shielding blade  310  is rotatably coupled to the front curtain driving arm  221  and the front curtain driven arm  231 , the auxiliary light-shielding blade  310  is easy to attach, which contributes to an improvement in productivity. 
     Although the auxiliary light-shielding blade  310  and the front curtain driving arm  221  are separate members, a region of the auxiliary light-shielding blade  310  may be integrally formed with the front curtain driving arm  221 . 
     Third Embodiment 
     A third embodiment according to the present invention will be described with reference to the drawings. In the following description, the same components as those in the first embodiment are denoted by the same reference symbols and only differences between the embodiments will be mainly described. Configurations not specifically described are the same as those in the first embodiment. This embodiment differs from the first embodiment in that the auxiliary light-shielding blade is differently shaped and attached. Thus, the following description mainly refers to how the auxiliary light-shielding blade is shaped and attached. 
       FIGS. 11 to 14  are views illustrating an internal configuration of the shutter device  21  according to the third embodiment as seen from the image sensor  22  side, that is, the rear side of the digital camera  1 . For convenience of explanation, a coordinate system having the X axis and the Y axis will be defined as illustrated in the figures.  FIG. 11  is a view illustrating a state of the shutter device  21  before the user operates the release button to instruct the start of photographing. In  FIG. 11 , the front curtain light-shielding blade  220 , the rear curtain light-shielding blade  250 , and the auxiliary light-shielding blade  320  are withdrawn in the first withdrawn position  201 .  FIG. 12  illustrates a state of the shutter device  21  after the user operates the release button to instruct the start of photographing, where the front curtain light-shielding blade  220  has started moving downward (in the positive Y axis direction) to traverse the opening  215 . In  FIG. 12 , however, the rear curtain light-shielding blade  250  has not yet started to move.  FIG. 13  is a view illustrating a state of the shutter device  21  wherein the front curtain light-shielding blade  220  further moves in the positive Y axis direction from the state illustrated in  FIG. 12  and the auxiliary light-shielding blade  320  is now moving across the opening  215  downward (in the positive Y axis direction), in coordination with the front curtain light-shielding blade  220 .  FIG. 14  is a view illustrating a state where the front curtain light-shielding blade  220  and the auxiliary light-shielding blade  310  have moved further downward (in the positive Y axis direction) from the state illustrated in  FIG. 13  to withdraw into a second withdrawn position  202  below (or on the positive Y axis side of) the opening  215 , while the rear curtain light-shielding blade  250  has not yet started to move. 
     The auxiliary light-shielding blade  320  is fixed in the vicinity of the light-shielding part-side coupling part  233  of the front curtain driven arm  231  and moves together along with the rotational movement of the front curtain driven arm  231 . When the front curtain light-shielding blade  220  is driven by the known parallel link mechanism constituted by the front curtain driving arm  221  and the front curtain driven arm  231 , the auxiliary light-shielding blade  320  moves across the opening  215  in the positive Y axis direction in coordination with the movement of the front curtain light-shielding blade  220 . 
     It should be noted that the front curtain driving arm  221  does not include the auxiliary light-shielding blade coupling part  301  and also the front curtain driven arm  231  does not include the auxiliary light-shielding blade coupling part  302  in this embodiment, since the auxiliary light-shielding blade  320  is fixed on the front curtain driven arm  231 . 
     In this embodiment, the auxiliary light-shielding blade  320  starts to enter the opening  215  from the first withdrawn position  201  to the upper end  215 U of the opening  215  and can move across the opening  215  in the positive Y axis direction to the second withdrawn position  202 . It should be noted that the auxiliary light-shielding blade  320  is located in the first withdrawn position  201  in  FIG. 11  and in the second withdrawn position  202  in  FIG. 14 . 
     The auxiliary light-shielding blade  320  is made of a single planar blade. The blade constituting the auxiliary light-shielding blade  300  has a first edge  321 , a second edge  322 , and a third edge  323  so that the light-shielding region is formed into a sector shape. The first edge  321  is a side extending in the X axis direction when the auxiliary light-shielding blade  320  is located in the first withdrawn position  201  (see  FIG. 11 ). The second edge  322  is a side extending in the same direction as that the front curtain driven arm  231  extends (see  FIGS. 11 to 14 ). The auxiliary light-shielding blade  320  is fixed to the front curtain driven arm  231  in the vicinity of the second edge  322 . The third edge  323  is formed into an arcuate shape connecting the first edge  321  and the second edge  322  (see  FIGS. 11 to 14 ). The first edge  321  and the second edge  322  have the substantially same length since the auxiliary light-shielding blade  320  has a sector shape as described above. 
     A length L 32  between a connecting point of the first edge  321  and the third edge  323  and a connecting point of the second edge  322  and the third edge  323  is smaller than the length of the opening  215  in the X axis direction (see  FIG. 12 ). A length L 42  of the first edge  321  or the second edge  322 , that is, a diameter of the sector forming the light-shielding region of the auxiliary light-shielding blade  320  is smaller than the length L 0  of the opening  215  (see  FIG. 12 ). The auxiliary light-shielding blade  310  can thus partly shield the opening  215 . The light-shielding region of the auxiliary light-shielding blade  320  shields the region R in the light-shielding region end on the positive X axis side of the front curtain light-shielding blade  220  described above, while the auxiliary light-shielding blade  320  moves in the positive Y axis direction (see  FIG. 13 ). In other words, the lengths L 32  and L 42  of the auxiliary light-shielding blade  320  are larger than the lengths of the region R in the X axis and Y axis directions, respectively. 
     When the shutter device  21  starts to operate, the auxiliary light-shielding blade  320  starts to move together with the front curtain light-shielding blade  220  from the first withdrawn position  201  (see  FIG. 11 ) and enter the opening  215  from the upper edge  220 U of the opening  215  (see  FIG. 12 ). In accordance with the rotational movement of the front curtain driving arm  221  and the front curtain driven arm  231 , the front curtain light-shielding blade  220  and the auxiliary light-shielding blade  320  move in the positive Y axis direction (see  FIG. 13 ). The auxiliary light-shielding blade  320  then moves in the positive Y axis direction with shielding the region R. Eventually, the front curtain light-shielding blade  220  and the auxiliary light-shielding blade  320  move to the second withdrawn position  202  below the opening  215  (see  FIG. 14 ). 
     The third embodiment described above provides the same operational advantages as the operational advantages ( 1 ) to ( 3 ) achieved by the first embodiment. 
     Additionally, since the auxiliary light-shielding blade  320  is fixed in the vicinity of the light-shielding part-side coupling part  223  of the front curtain driven arm  231 , the auxiliary light-shielding blade  320  is easy to attach, which contributes to an improvement in productivity as in the case of the second embodiment. 
     Although the auxiliary light-shielding blade  320  and the front curtain driven arm  231  are separate members, a region of the auxiliary light-shielding blade  320  may be integrally formed with the front curtain driven arm  231 . 
     Variations 
     Instead of coupling or fixing the front curtain driving arm  221  and/or the front curtain driven arm  231  to the auxiliary light-shielding blade as in the shutter device  21  according to the first to third embodiments described above, the shutter device  21  may include a special auxiliary light-shielding blade driving arm for driving an auxiliary light-shielding blade. In this case, the auxiliary light-shielding blade driving arm has a substrate-side coupling part on one end and an auxiliary light-shielding blade coupling part on the other end. The auxiliary light-shielding blade driving arm is rotatably pivoted at the substrate-side coupling part by the substrate  210  on the rear side (the image sensor  22  side) of the substrate  210 . The auxiliary light-shielding blade is rotatably coupled to the auxiliary light-shielding blade driving arm at the auxiliary light-shielding blade coupling part with a caulking pin. 
     The auxiliary light-shielding blade driving arm has a coupling part which is a planar member, for example. The auxiliary light-shielding blade driving arm is coupled to the front curtain driving arm  221  with this coupling part. When the front curtain driving arm  221  is driven to rotate about the substrate-side coupling part  222  as described above, the auxiliary light-shielding blade driving arm, which is coupled to the front curtain driving arm  221  via the coupling part, is also driven to rotate about the substrate-side coupling part. Consequently, the auxiliary light-shielding blade moves in the Y axis direction, in coordination with the front curtain light-shielding blade  220  which moves in the Y axis direction along with the rotational movement of the front curtain driving arm  221 . 
     The auxiliary light-shielding blade driving arm may not be coupled to the front curtain driving arm  221  with the coupling part. In this case, the auxiliary light-shielding blade driving arm is configured to be driven to rotate about the substrate-side coupling part by the auxiliary light-shielding blade actuator which is constituted by an electric motor or the like. The power supply unit of the controller  26  controls a timing at which the front curtain actuator is supplied with an electric power and a timing at which the auxiliary light-shielding blade actuator is supplied with an electric power. The auxiliary light-shielding blade thus can move in the Y axis direction to shield the region R while the front curtain light-shielding blade  220  moves in the Y axis direction. Consequently, the auxiliary light-shielding blade moves in the Y axis direction in coordination with the movement of the front curtain light-shielding blade  220 . 
     In the above description, the front curtain actuator is made of an electric motor or the like. Alternatively, the front curtain actuator may be configured to shift the front curtain light-shielding blade  220  toward the second withdrawn position  202  by a biasing force of a spring and to urge the front curtain light-shielding blade  220  into the first withdrawn position  201  by a power of the electric motor. The same also applies to the rear curtain actuator. Furthermore, the front curtain actuator may be made of an electric motor or the like, while the rear curtain actuator may be constituted by a spring and an electric motor. Still further, the front curtain actuator may be constituted by a spring and an electric motor, while the rear curtain actuator may be made of an electric motor or the like. 
     The above-described embodiments and variations may be combined. 
     The present invention is not limited to the embodiments described above and other embodiments that are conceivable within the technical idea of the present invention are also included within the scope of the present invention, as long as they do not impair the features of the present invention. 
     The disclosure of the following priority application is herein incorporated by reference: 
     Japanese Patent Application No. 2014-223429 (filed Oct. 31, 2014) 
     REFERENCE SIGNS LIST 
       1  . . . digital camera,  21  . . . shutter device,  22  . . . image sensor,  201  . . . first withdrawn position,  202  . . . second withdrawn position,  203  . . . third withdrawn position,  204  . . . fourth withdrawn position,  210  . . . substrate,  215  . . . opening,  220  . . . front curtain light-shielding blade,  221  . . . front curtain driving arm,  222  . . . substrate-side coupling part,  223  . . . light-shielding member-side coupling part,  231  . . . front curtain driven arm,  232  . . . substrate-side coupling part,  233  . . . light-shielding member-side coupling part,  240 ,  270  . . . elongated hole,  250  . . . rear curtain light-shielding blade,  251  . . . rear curtain driving arm,  261  . . . rear curtain driven arm,  281  . . . front curtain driving pin,  282  . . . rear curtain driving pin,  300 ,  310 ,  320  . . . auxiliary light-shielding blade