Abstract:
A digital camera includes: a mirror box that defines a space in which a light flux from a photographic lens is guided to an imaging unit; a mirror unit that is arranged inside the mirror box and is configured to rotate between a viewing position in which the mirror unit is inserted in a photographic light path from the photographic lens to the imaging unit to reflect the light flux and a photographing position in which the mirror unit is retracted from the photographic light path; and an opening section that discharges from the mirror box air that is moved when the mirror unit is rotated.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation application of U.S. patent application Ser. No. 12/068,236, filed Feb. 4, 2008, the disclosure of which is herein incorporated in its entirety by reference. The disclosure of the following priority applications are herein incorporated by reference: 
         [0002]    Japanese Patent Application No. 2007-025614 (filed Feb. 5, 2007); and 
         [0003]    Japanese Patent Application No. 2007-026805 (filed Feb. 6, 2007). 
         [0004]    Also, the disclosure of the following application is herein incorporated by reference: 
         [0005]    Japanese Patent Application No. 2001-102253 (filed Mar. 30, 2001). 
     
    
     BACKGROUND 
       [0006]    1. Field 
         [0007]    The present invention relates to a digital camera and to an interchangeable lens. 
         [0008]    2. Description of the Related Art 
         [0009]    Japanese Laid-open Patent Publication No. 2002-300442 discloses a camera in which an illumination means such as an LED provided below a mirror box illuminates an imaging unit through an opening provided on the lower surface of the mirror box to detect dust (foreign matter) adherent to an optical filter. 
         [0010]    The construction described in the above-mentioned publication is simply contemplated to detect the dust adherent to the imaging unit but can not remove the adherent dust. 
       SUMMARY 
       [0011]    A digital camera according to a 1st aspect of the present invention includes: a mirror box that defines a space in which a light flux from a photographic lens is guided to an imaging unit; a mirror unit that is arranged inside the mirror box and is configured to rotate between a viewing position in which the mirror unit is inserted in a photographic light path from the photographic lens to the imaging unit to reflect the light flux and a photographing position in which the mirror unit is retracted from the photographic light path; and an opening section that discharges from the mirror box air that is moved when the mirror unit is rotated. 
         [0012]    According to a 2nd aspect of the present invention, in the digital camera according to the 1st aspect, it is preferable that the opening section is provided in the mirror box closer to the photographic lens than a point of intersection between the mirror unit in the viewing position and an optical axis of the photographic lens. 
         [0013]    According to a 3rd aspect of the present invention, in the digital camera according to the 1st aspect, at least a part of the opening section may be provided in the mirror box in an area closer to the photographic lens than an edge, on a side to the photographic lens, of the mirror unit in the viewing position. 
         [0014]    According to a 4th aspect of the present invention, in the digital camera according to the 1st aspect, a flash-sensor unit arranged in a vicinity of the mirror box may be further included, wherein the opening section may be provided in an area of the mirror box closer to the photographic lens than the flash-sensor unit. 
         [0015]    According to a 5th aspect of the present invention, in the digital camera according to the 1st aspect, the opening section may be provided in an area of the mirror box in a direction in which the mirror unit moves from the photographing position to the viewing position. 
         [0016]    According to a 6th aspect of the present invention, in the digital camera according to the 5th aspect of the present invention, it is preferable that the opening section is provided in an area close to an optical axis of the photographic lens. 
         [0017]    According to a 7th aspect of the present invention, in the digital camera according to the 1st aspect, the opening section may be provided only in a part of the mirror box closer to the photographic lens than an edge, on a side to the photographic lens, of the mirror unit in the viewing position. 
         [0018]    According to a 8th aspect of the present invention, in the digital camera according to the 1st aspect, the opening section may be provided in a plane of the mirror box, which plane intersects neither an optical axis of the photographic lens nor an axis of rotation of the mirror unit. 
         [0019]    According to a 9th aspect of the present invention, in the digital camera according to the 1st aspect, the opening section may be provided in a plane of the mirror box, which plane is near the mirror unit in the photographing position. 
         [0020]    According to a 10th aspect of the present invention, in the digital camera according to the 1st aspect, the opening section may be provided in a plane of the mirror box, which is on a side of the mirror box opposite to a plane near the mirror unit in the photographing position. 
         [0021]    According to a 11th aspect of the present invention, in the digital camera according to the 1st aspect, the opening section may be provided in a plane of the mirror box, which plane intersects an axis of rotation of the mirror unit. 
         [0022]    According to a 12th aspect of the present invention, in the digital camera according to the 1st aspect, a shutter arranged between the mirror unit and the imaging unit may be further provided, and the mirror unit may be rotated when the shutter is in a closed state. 
         [0023]    According to a 13th aspect of the present invention, in the digital camera according to the 1st aspect, a shutter arranged between the mirror unit and the imaging unit may be further provided, and the mirror unit may be rotated from the photographing position to the viewing position when the shutter is in an opened state. 
         [0024]    According to a 14th aspect of the present invention, in the digital camera according to the 1st aspect, a shutter arranged between the mirror unit and the imaging unit may be further provided, the mirror unit may be rotated from the photographing position to the viewing position when the shutter is in an opened state, and the mirror unit may be rotated from the viewing position to the photographing position when the shutter is in a closed state. 
         [0025]    An interchangeable lens for a camera according to a 15th aspect of the present invention includes an opening section adapted to discharge air that is moved when a mirror unit arranged in the camera is rotated. 
         [0026]    A digital camera according to a 16th aspect of the present invention includes the interchangeable lens for a camera according to the 15th aspect. 
         [0027]    According to a 17th aspect of the present invention, in the digital camera according to the 1st aspect, it is preferable that a lid member that is adapted to open and close the opening section. 
         [0028]    According to a 18th aspect of the present invention, in the digital camera according to the 17th aspect, the photographic lens may be detachably attached to a camera body of the digital camera, and the lid member may be adapted to be in an open state when the photographic lens is attached to the camera body of the digital camera and to be in a closed state when the photographic lens is detached from the camera body of the digital camera. 
         [0029]    According to a 19th aspect of the present invention, in the digital camera according to the 17th aspect, the lid member may be adapted to be in an open state when the mirror unit is being rotated and to be in a closed state when the mirror unit is not being rotated. 
         [0030]    According to a 20th aspect of the present invention, in the digital camera according to the 17th aspect, the lid member may be adapted to be in an open state when power of the digital camera is ON and to be in a closed state when the power of the digital camera is OFF. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0031]      FIG. 1  is an elevational view showing a single-lens reflex digital camera according to an embodiment of the present invention; 
           [0032]      FIG. 2  is a cross-sectional view along the A-A line in  FIG. 1 ; 
           [0033]      FIG. 3  is an enlarged view of the vicinity of a mirror box in  FIG. 2 ; 
           [0034]      FIG. 4  is an enlarged view of the vicinity of the mirror box in a state in which an interchangeable lens is detached; 
           [0035]      FIG. 5  is a schematic view of the mirror box as seen from above; 
           [0036]      FIG. 6  is a view illustrating the flow of air while the mirror unit is being raised; 
           [0037]      FIG. 7  is a view illustrating the mirror unit in a state in which it has been raised to a photographing position; 
           [0038]      FIG. 8  is a view of a conventional camera illustrating the flow of air when the mirror unit is in a viewing position; 
           [0039]      FIG. 9  is a view similar to  FIG. 8 , illustrating the state in which the mirror unit is being raised; 
           [0040]      FIG. 10  is a view similar to  FIG. 8 , illustrating the state in which the mirror unit is in the photographing position; 
           [0041]      FIGS. 11A and 11B  are each a view showing an example of the camera provided with a large air hole; 
           [0042]      FIG. 12  is a view showing an example in which an air hole is provided at a corner portion defined by the bottom plate of the mirror box and a lens mount; 
           [0043]      FIG. 13  is a view showing an example in which a side wall of the mirror box is provided with an air hole; 
           [0044]      FIG. 14  is a view showing an example in which the interchangeable lens is provided with an air hole; and 
           [0045]      FIG. 15  is a block diagram illustrating control of the camera. 
       
    
    
     DETAILED DESCRIPTION 
       [0046]    Referring to  FIGS. 1 to 7 , one embodiment of the present invention is explained. 
         [0047]      FIG. 1  is an elevational view showing a single-lens reflex digital camera according to an embodiment of the present invention and  FIG. 2  is a cross-sectional view along the A-A line in  FIG. 1 . A camera body  100  includes a lens mount  11  and behind the lens mount  11  a mirror box  20  that provides a photographic light path. Behind the mirror box  20  is arranged a shutter  12 , and behind the shutter  12  is provided an imaging unit  13 . Above the mirror box  20  is arranged a finder optical system  60 . 
         [0048]    On the lens mount  11  an interchangeable lens (photographic lens)  200  is to be mounted. A light flux from a photographic subject that passes through the interchangeable lens  200  is incident into the mirror box  20  through an opening of the lens mount  11 . In the mirror box  20 , there is arranged a mirror unit  30 . 
         [0049]      FIG. 15  is a schematic block diagram illustrating the construction of the digital camera of the present embodiment. 
         [0050]    The light flux from the photographic subject input through the photographic lens  200 , when the mirror unit  30  is in a viewing position as detailed hereinbelow, is reflected by the mirror unit  30  and incident into the finder optical system  60 . On the other hand, when the mirror unit  30  is in a photographic position, the light flux is incident into the imaging unit  13 , so that an image of the photographic subject is captured. The image unit  13  outputs an image signal, which is temporarily stored in a buffer memory not shown. Then, the image signal is sent to a control circuit  71 , in which the image signal is subjected to well-known image processing such as white balance processing, color conversion processing or gradation correction processing. The image data obtained by the processing in the control circuit  71  is compressed by a well-known method such as a JPEG method and the compressed image data is recorded in a memory card  73  loaded in a memory card slot  72 . The memory card  73  is detachably attached to the camera body  100 . Note that the destination of recording of the image data may be the memory card  73  that is detachably attached to the camera body  100  or a memory  79  incorporated in the camera body  100 . 
         [0051]    An operation unit  74  includes various operation members to be operated by a user in order to operate the digital camera. The operation unit  74  includes, for example, a release button  1  and an operation member that instructs a dust removing operation detailed hereinbelow. A lid member  41  is a lid that opens and closes an air hole detailed hereinbelow. Opening and closing of the lid member  41  is controlled by the control circuit  71  through an opening/closing mechanism  75 . Note that the opening/closing of the lid member  41  may be controlled not only by the control circuit  71  but also by a mechanical mechanism alone depending on whether or not the photographic lens  200  is loaded on the lens mount. 
         [0052]    A photographic lens detection unit  76  detects whether the photographic lens  200  is attached to or detached from the camera body  100 . A signal indicating whether the photographic lens  200  is attached to or detached from the camera body  100  detected by the photographic lens detection unit  76  may be sent to the control circuit  71  and a dust removal operation may be performed depending on whether the photographic lens  200  is attached or detached. Alternatively, a power source unit  77  may send a signal on ON/OFF of a power source to the control circuit  71  to make the dust removal operation be performed depending on ON/OFF of the power source of the digital camera. The mirror unit  30  is controlled by the control circuit  71  through a mirror drive circuit  78  and is driven not only when photographing but also when performing dust removal. The dust removal operation is detailed later on. 
         [0053]      FIGS. 3 and 4  are enlarged views of the vicinity of the mirror box  20 .  FIG. 5  is a schematic view of the mirror box  20  as seen from above (from the side of a viewfinder). The mirror unit  30  includes a main mirror unit  31  which in turn includes a main mirror, which is a half mirror, and a support member therefor as well as a submirror unit  32  that includes a submirror and a support member therefor. 
         [0054]    The main mirror unit  31  is rotatably supported on one end thereof around an X-axis along a lateral direction of the camera in a rear part of the mirror box  20  (see  FIG. 3 ). The submirror unit  32  is supported on the main mirror unit  31  such that the submirror  32  is rotatable around the X-axis along the lateral direction of the camera. The mirror unit  30  is driven by the control circuit  71  through the mirror drive circuit  78  and is rotatable between a viewing position in which the mirror unit  30  is inserted in a photographing light path as shown in  FIG. 3  and a photographic position in which the mirror unit  30  is retracted from the photographic light path as shown in  FIG. 7 .  FIG. 6  shows a state in which the mirror is on the way of being rotated. 
         [0055]    In a lower space  50  of the mirror box  20 , there is provided a flash-sensor unit  80  (see  FIG. 7 ). At the back of the flash-sensor unit  80  is arranged a focus detection unit (not shown) and in the front of the flash-sensor unit  80  is arranged a lens drive mechanism (not shown). The flash-sensor unit  80  includes an element that receives light reflected on a screen of the shutter  12  and performs photoelectric conversion of the received light to output a photoelectric conversion signal, which is utilized in flash control. 
         [0056]    A bottom plate  21  of the mirror box  20  is bored to form a slit-like air hole  21   a  that communicates a space in the mirror box  20  with the lower space  50 . The function and effect of the air hole  21   a  is detailed later on. The air hole  21   a  is provided closer to the photographic lens  200  than the flash-sensor unit  80  is (see  FIG. 7 ), preferably closer to the photographic lens  200  than an edge of the mirror unit  30  on the side to the photographic lens  200  in the viewing position is (see  FIG. 3 ). The width of the air hole  21   a  in the direction to front and rear of the camera is, for example, about 1 to about 2 mm in the present embodiment. However, the width may be smaller or larger than this. 
         [0057]    The air hole  21   a  can be opened and closed by the lid member  41 . The lid member  41  is supported on a base plate  42 . The base plate  42  is supported so as to be movable in the direction to front and rear (in the direction of an optical axis of the photographic lens  200 ). A tension spring  43  urges the base plate  42  toward the photographic lens  200 . In a slot provided in the base plate  42  is fitted a pin that protrudes from the camera body  100 . The movement of the base plate  42  is guided with this construction. A protrusion  42   a  provided in the base plate  42  runs through the camera body  100  and abuts a rear wall  201  of the interchangeable lens  200  to be restricted of the movement of the base plate  42  as shown in  FIG. 3 . In this state, the lid member  41  is retracted at the back of the air hole  21   a  and the air hole  21   a  is open. 
         [0058]    On the other hand, as shown in  FIG. 4 , when the interchangeable lens  200  is detached from the mount  11 , the pressing force on the protrusion  42   a  is released. On this occasion, the base plate  42  is moved toward the lens mount  11  by the force urged thereon by the spring  43 , and interlocked with the movement of the base plate  42 , the air hole  21   a  is closed by the lid member  41 . 
         [0059]    Note that in  FIGS. 6 and 7 , the lid member  41  and its drive mechanism (the base plate  42  and the tension spring  43 ) are not shown. Further, it would be also acceptable to configure the digital camera such that the air hole  21   a  is opened due to retraction of the lid member  41  by the opening/closing mechanism  75  controlled by the control circuit  71  (see  FIG. 15 ) while the mirror unit  30  is being rotated and when the mirror unit  30  is not being rotated, the air hole  21   a  is closed by the lid member  41 . Also, it would be acceptable to configure the digital camera such that when the power of the digital camera is turned ON, the opening/closing mechanism  75  controlled by the control circuit  71  (see  FIG. 15 ) causes the lid member  41  to be retracted to open the air hole  21   a  whereas when the power of the digital camera is turned OFF, the opening/closing mechanism  75  causes the lid member  41  to close the air hole  21   a.    
         [0060]    The imaging unit  13  is an integral structure of an image sensor  13   a  such as a CCD and an optical filter (such as an optical low pass filter or an infrared cut filter)  13   b.  Light flux that has passed through the opening of the shutter  12  transmits the optical filter  13   b  and is received by the image sensor  13   a.  The imaging sensor  13   a  converts the received light to a photoelectrically converted output, from which an image data is generated and stored. 
         [0061]    In the digital camera thus constructed, when photography is not performed, the mirror unit  30  is in the viewing position shown in  FIG. 3  and is inserted in the photographic light path. For this reason, part of the light flux from the photographic subject that is incident into the mirror box  20  is reflected upward by the main mirror unit  31  and enters the finder optical system  60  and viewed by the user through an eyepiece unit  61  ( FIG. 2 ). Part of the light flux that has transmitted through the main mirror unit  31  is reflected downward by the submirror unit  32  and enters a focus detection unit (not shown) provided in the lower space  50  to contribute to focus detection. 
         [0062]    When the release button  1  (see  FIG. 1 ) is pressed all the way down, the control circuit  71  controls to flip up the mirror unit  30  to the photographing position as shown in  FIG. 7  and to retract it from the photographic light path through the mirror drive circuit  75 . Then, the shutter  12  is opened and the light flux incident into the mirror box  20  passes through the opening of the shutter  12  without being interrupted by the mirror unit  30  and is guided to the imaging unit  13 . 
         [0063]    When neither the photographic lens  200  nor a cap is mounted on the lens mount  11 , the mirror box  20  communicates with an external space through the lens mount  11  and hence minute dust floating in the atmosphere could come into the mirror box  20  from the lens mount  11 . Further, the dust generated in the camera, for example, when the shutter  12  or the like is driven floats in the mirror box  20 . When the dust in the mirror box  20  adheres to the imaging unit  13 , in particular the front of the optical filter  13   b,  the dust may appear on the photographed image to decrease the visual quality of the image. 
         [0064]    Explanation is made on the mechanism in which dust adheres to the optical filter  13   a.    
         [0065]      FIGS. 8 to 10  show an example of a conventional camera that is provided with no air hole  21   a.  In  FIGS. 8 to 10 , parts that have similar functions as those in the present embodiment described above are assigned the same reference numerals. 
         [0066]    When the mirror unit  30  is in the viewing position as shown  FIG. 8 , the space in the mirror box  20  is air-tightly closed by the interchangeable lens  200  and the shutter  12  in the direction to front and rear, by the finder optical system  60  and the bottom plate  21  (see  FIG. 11B ) in the direction of top and bottom, and by the side walls  22  in the direction of right and left. However, the space in the mirror box  20  is not completely closed. Since the mirror unit  30  is flipped up as shown in  FIG. 9  when the release button is pressed, an upper space above the mirror unit  30  is abruptly narrowed, most of the air in the upper space flows down as a relatively rapid stream in the front of the mirror unit  30 , that is, a space between the mirror unit  30  and the interchangeable lens  200  (arrow C). On this occasion, the dust in the air moves to the same direction (direction indicated by the arrow C) as entrained in the flow of air. 
         [0067]    The air that has flown down collides with the bottom plate  21  of the mirror box  20  to be turned to a different direction to form a flow of air toward the side of the shutter  12  (arrow D). Thereafter, as shown in  FIG. 10 , the mirror unit  30  reaches the photographing position and when the shutter  12  is opened, the air directed toward the side of the shutter  12  passes through an opening S of the shutter  12  (slit opening) to reach the imaging unit  13 . The dust carried by the air adheres to the front surface of the optical filter  13   b.    
         [0068]    Next, explanation is made on dust controlling effect provided by the air hole  21   a.    
         [0069]    In the present embodiment, the bottom plate  21  of the mirror box  20  is provided with the air hole  21   a  on its part in the front of the mirror unit  30  (on the side of the photographic lens  200 ) and when the interchangeable lens is mounted, the air hole  21   a  is opened. The position of the air hole  21   a  is just below the flow of the air that flows down due to the flipping of the mirror unit  30  as shown in  FIG. 6 , so that most of the air that flows down passes through the air hole  21   a  and goes straight forward (arrow F) to be discharged into the lower space  50 . As a result, most of the dust entrained in the air is also discharged in the lower space  50 . Therefore, the amount of the air (dust) that goes in the direction of D on the bottom plate  21  of the mirror box  20  is much more decreased than conventionally and the amount of the dust that adheres on the optical filter  13   b  after the shutter  12  is opened as shown in  FIG. 7  is decreased. 
         [0070]    In order to discharge the dust to the outside of the mirror box  20  by utilizing the flow of air generated by the mirror unit  30  to decrease the flow of the air toward the direction D in  FIG. 9 , the position of the air hole  21   a  to be formed may be determined as follows. 
         [0071]    The air hole  21   a  is formed only in an area of the bottom plate  21  that is closer to the photographic lens  200  than the edge of the mirror unit  30  on the side of the photographic lens  200 . 
         [0072]    The air hole  21   a  may be provided such that at least a part of the air hole  21   a  is arranged in an area of the bottom plate  21  that is closer to the photographic lens  200  than the edge of the mirror unit  30  on the side of the photographic lens  200 . 
         [0073]    The air hole  21   a  may be provided in an area in the direction of rotation of the mirror unit  30  (in the direction of C or in a reverse direction thereto in  FIG. 9 ) of the bottom plate  21  or of a top plate of the mirror box  20 . 
         [0074]    The position of the air hole  21   a  in the bottom plate  21  in a direction perpendicular to an optical axis of the photographic lens  200  is preferably in a central part near the optical axis of the photographic lens  200 . Although the length of the air hole  21   a  to its long side (in the longitudinal direction in  FIG. 5 ) is preferably the same as or smaller than the width of the mirror unit  30 , it may be larger than the width of the mirror unit  30 . 
         [0075]    The air hole  21   a  may be provided in an area closer to the photographic lens  200  than the intersection of the mirror unit  30  in the viewing position and the optical axis of the photographic lens  200 . 
         [0076]    In this manner, in the present embodiment, by a simple operation such that a part of the mirror box  20  is provided with the air hole  21   a  without addition of any members, the amount of dust that adheres to the imaging unit  13  can be decreased. The inventors of the present embodiment have conducted experimentation comparing the state in which dust adheres to the optical filter  13   b  between the structure of the present embodiment and the conventional structure shown in  FIGS. 8 to 10 . The results confirm that the amount of adherent dust after repeating the photographing operation with the camera body  100  10,000 times can be reduced according to the structure of the present embodiment to about half that of the conventional structure. 
         [0077]    When the interchangeable lens  200  is detached from the lens mount  11 , the part where the air hole  21   a  is provided is exposed to the outside. On this occasion, since the air hole  21   a  is closed by the lid member  41 , the members arranged in the lower space  50  are not viewed, so that the appearance of the camera is not deteriorated. 
         [0078]    As mentioned above, the operation of discharging dust accompanying driving of the mirror upon photographing has been explained. Next, the operation of discharging dust in time other than photographing is explained. 
         [0079]    For example, upon interchanging lenses, there is a possibility that dust outside comes into the inside of the mirror box  20 . After the interchange of the lenses, the control circuit  71  detects that the interchangeable lens  200  is attached and controls to flip the mirror unit  30  from the viewing position to the photographing position and then to return it to the viewing position. The driving of the mirror is performed in a state in which the shutter  12  is closed. This enables much of the dust that has come into the mirror box  20  to be discharged to the lower space  50  through the air hole  21   a.  Thereafter, the dust is discharged also by driving of the mirror upon photographing, so that the amount of the dust that is adherent to the optical filter  13  can be further decreased. 
         [0080]    Also, the driving of the mirror may be performed in the same manner as that at the time of interchanging lenses in order to discharge dust in other opportunities than when the lenses are interchanged, for example, when the power to the digital camera is turned ON or OFF. Alternatively, the driving of the mirror may be performed similarly in order to discharge dust in accordance with a specified operation, that is, dust discharge operation, by the user. In both cases, it is preferred that the driving of the mirror is permitted only in a state in which the incoming of dust from outside is blocked, that is, only when the interchangeable lens  200  or the cap is attached to the lens mount  11 . Further, the driving of the mirror in the timing other than the photographing is effective even when performed only once but repeating it in a plurality of times enables more dust to be discharged. 
         [0081]    Further, the driving of the mirror may be performed in order to remove the dust that has adhered to the optical filter  13   b.  The driving of the mirror to remove this dust is performed in a state in which the shutter  12  is open. In contrast to the above-mentioned dust discharge action, when the mirror unit  30  is flipped down from the photographing position to the viewing position, the air below the mirror unit  30  flows through the shutter opening against the front surface of the optical filter  13   b  to blow off the dust thereon. Since the space below the mirror unit  30  is abruptly narrowed according to the flip down of the mirror unit  30 , most of the air below the lower space flows in the lower space below the mirror unit  30  in the direction of front and moves to the space in front of the mirror unit  30 . This flow causes the dust to move to the space in front of the mirror unit  30  and the dust is discharged to the lower space  50  through the air hole  21   a  by the next and subsequent actions of the mirror unit  30 . 
         [0082]    Also, it would be acceptable that the mirror unit  30  is rotated from the photographing position to the viewing position in a state in which the shutter  12  is open, and the mirror unit  30  is rotated from the viewing position to the photographing position in as state in which the shutter  12  is closed. When the mirror unit  30  is rotated from the photographing position to the viewing position, the shutter  12  is open, so that the air below the mirror unit  30  flows through the opening of the shutter  12  against the front surface of the optical filter  13   b  to blow off the dust thereon. Next, when the mirror unit  30  is rotated from the viewing position to the photographing position, the shutter is in a closed state, and the dust in the mirror box  20  is discharged through the air hole  21   a.  This operation is performed at least once, preferably a plurality of times to enable the dust adherent to the optical filter  13   b  to be removed. The driving of the mirror in this case too is preferably permitted only when the interchangeable lens  200  or the cap is attached to the lens mount  11 . This operation may be performed at the time of turning ON or OFF the power of the digital camera, or in response to a specified operation by the user. Further, the removal of the dust may be performed as follows. That is, the user judges whether or not dust is adherent to the optical filter  13   b  based on the photographed image and when it is judged that the dust is adherent, the driving of the mirror is performed in response to the dust discharge operation by the user to discharge the dust. In this case, in order to make it easy to judge whether or not dust is adherent, it would be acceptable to photograph a white object by the digital camera and judge whether or not dust is adherent based on the photographed image. Further, it would be acceptable to perform the judgment whether or not dust is adherent by the control circuit  71  and to automatically perform the driving of the mirror to remove the dust. 
         [0083]    Further, the conventional method in which the imaging unit is vibrated to shake off dust and the above-mentioned dust discharge method according to the present embodiment may be used in combination. In this case, by performing the driving of the mirror for the removal of the dust while vibrating the imaging unit  13 , the efficiency of dust removal is increased due to synergism between the vibration and the flow of air. Hereinafter, the operation in this case is explained. 
         [0084]    First, in a state in which the shutter  12  is open, vibration of the optical filter  13   b  is started in order to remove the dust adherent to the optical filter  13   b.  Then, the mirror unit  30  is driven a plurality of times to discharge from the air hole  21   c . When the driving of the mirror unit  30  is completed, the shutter  12  is closed and the vibration of the optical filter  13   b  is stopped. The adherent dust is removed by vibrating the optical filter  13   b  and the removed dust is discharged through the air hole  21   c  by driving the mirror unit  30 . Also, by driving the mirror unit  30 , the dust remaining on the surface of the optical filter  13   b  can be removed. Note that the direction of driving the mirror unit  30  is not particularly limited. It is preferred to arrange the mirror unit  30  in the photographing position and then perform an operation to drive it to the viewing position. 
         [0085]    Note that it would also be acceptable to vibrate the optical filter  13   b  in a state in which the shutter  12  is open to remove the dust, and to close the shutter  12  before the mirror unit  30  is driven and to stop the vibration of the optical filter  13   b.  Also, the vibration of the optical filter  13   b  may be performed only for the first time. It is preferred that the dust removal operation is permitted only when the interchangeable lens  200  or the cap is attached to the lens mount  11 . 
         [0086]    Further, the dust detection may be performed as follows. That is, an illumination means (not shown) such as an LED is provided below the mirror box  20  and the imaging unit  13  is illuminated through an opening (not shown) in the lower surface of the mirror box  20  to detect dust adherent to the optical filter  13   b.  Then, based on the result of the dust detection, it is judged whether or not it is necessary to remove the dust, and when the result is affirmative, the driving of the mirror is performed in order to remove the dust. 
         [0087]    Note that the number and shape of the air holes  21   a  may be optional. In the above-mentioned embodiment, the air hole  21   a  is provided in a part of the bottom plate  21  that is closer to the photographic lens  200  than the edge of the mirror unit  30  on the side of the photographic lens  200 . However, for example, as shown in  FIGS. 11A and 11B , the air hole  21   a  may be provided as extending to the rearward of the edge of the mirror unit  30  on the side of the photographic lens  200 . Further, as shown in  FIG. 12 , the air hole  21   c  may be extended on the side of the photographic lens  200 . 
         [0088]    Further, it is expected that the air hole  21   c  provides the dust removal effect when it is provided in a surface other than the bottom plate  21  of the mirror box  20  as far as the condition is satisfied that the air hole  21   c  includes a part that is further closer to the photographic lens  200  than the edge of the mirror unit  30  in the viewing position on the side of the photographic lens  200 .  FIG. 13  shows an example in which in addition to the air hole  21   a  in the bottom plate  21  of the mirror box  20 , the air holes  22   a  are provided on both side walls  22  of the mirror box  20 , respectively. An air hole may be provided on an upper plate of the mirror box  20 . 
         [0089]    Further, instead of providing an air hole in the mirror box  20 , an air hole  201   a  may be provided for example, in a rear wall surface  201  (a surface opposing the mirror unit  30 ; see  FIG. 3 ) of the interchangeable lens  200 , as shown in  FIG. 14 . In this case, by the flip up of the mirror unit  30 , air containing dust in the mirror box  20  is discharged through the air hole  201   a  to a space in the interchangeable lens  200  to provide an effect similar to that mentioned above. 
         [0090]    Further, in the above-mentioned embodiment, explanation has been made on the example in which the mirror unit  30  is rotated about the axis X in the lateral direction of the digital camera. However, the present invention may be applied to a camera in which the mirror unit  30  is rotated about an axis in the direction of front and rear of the camera. 
         [0091]    Note that in the above-mentioned embodiment, the camera is constructed such that the lid member  41  is opened/closed as interlocked with attachment/detachment of the interchangeable lens  200 . However, when the driving of the mirror at the time other than the time of photographing (discharge of the dust) does not have to be taken into consideration, it would also be acceptable to construct the digital camera such that accompanying the pressing of the release button  1  all the way down, the lid member  41  is moved to the opened position before the driving of the mirror unit  30  is started and after the mirror unit  30  has reached the photographing position, the lid member  41  moves to the closed position. This construction can be realized by constructing the lid member  41  as being of the electric motor-driven type. Further, since the interchange of lenses is usually performed when the power of the digital camera is turned OFF, it would be acceptable to move the lid member  41  to the opened position accompanying the turning ON of the power of the digital camera and to the closed position accompanying to the turning OFF of the power of the digital camera. 
         [0092]    Note that the lid member  41  may be omitted. 
         [0093]    As detailed above, according to one embodiment of the present invention, adherence of dust to the imaging unit  13  can be effectively suppressed. 
         [0094]    The above-described embodiments are examples, and various modifications can be made without departing from the scope of the invention.