Patent Publication Number: US-9854179-B2

Title: Imaging apparatus

Description:
TECHNICAL FIELD 
     The present invention relates to an imaging apparatus. 
     BACKGROUND ART 
     PTL 1 discloses a shutter device where two shutter-blades open and close an opening by a stepping motor rotationally driving a drive ring. 
     The shutter device disclosed in PTL 1 has formed an acceleration region where rotating the drive ring does not cause the two shutter blades to open and close the opening, and an exposure region where rotating the drive ring causes the two shutter blades to open and close the opening. The shutter device disclosed in PTL 1 accelerates the stepping motor in the acceleration region, and thereafter the two shutter blades open and close the opening in the exposure region. 
     CITATION LIST 
     Patent Literature 
     PTL 1 Japanese Patent Laid-Open No. 7-56211 
     The present applicant has proposed a shutter device that charges a biasing member at the time of starting running operations of the shutter device, and uses the biasing force of the biasing member in the acceleration region, to raise the speed of the shutter blades in the exposure region. 
     However, when performing bulb exposure or long exposure, a state where the biasing member is kept charged has to be maintained for a long time, which increases electric power consumption of the imaging apparatus. 
     It is an aim of the present invention, in light of this point, to reduce electric power consumption of the imaging apparatus. 
     SUMMARY OF INVENTION 
     In order to solve the above scenarios, the imaging apparatus according to the present invention includes: a motor; a control unit to control driving of the motor; a cam member on which a cam portion is formed, and driven by the motor; a light-shielding member on which an engaging portion that engages the cam portion is formed, and is movable between a closed state where an aperture is closed and an opened state where the aperture is opened in conjunction with the cam member being driven; and a biasing member to bias the cam member; and wherein an exposure operation is started based on a first operation, and the light-shielding member is moved from the opened state to the closed state based on a second operation performed after the first operation has been performed, wherein the cam portion is provided with a first zone where the light-shielding member maintains the closed state or the opened state even if the cam member is driven by the motor, and a second zone where the light-shielding member moves from the closed state to the opened state or from the opened state to the closed state if the cam member is driven by the motor, wherein the first zone and the second zone are provided to the cam portion such that, at the time of the cam member being driven in one direction, the engaging portion follows through the first zone, and thereafter the engaging portion follows through the second zone, wherein the control unit drives the motor in the first direction based on the first operation, whereby the cam member charges the biasing member, and thereafter the control unit controls driving of the motor so as to stop the cam member in the state where the biasing member is charged, wherein in a case where the second operation is performed within a predetermined amount of time after the first operation has been performed, the control unit drives the motor in a second direction that is the opposite direction to the first direction based on the second operation, whereby the cam member is driven by biasing force of the biasing member and driving force of the motor, the engaging portion follows through the first zone, and thereafter the engaging portion follows through the second zone by the control unit driving the motor in the second direction, and wherein, in a case where the second operation is not performed even if a predetermined amount of time elapses after the first operation has been performed, the control unit drives the motor in the second direction, whereby the cam member is driven by biasing force of the biasing member and driving force of the motor until the charge of the biasing member is disengaged, the driving of the motor by the control unit is stopped, and the control unit drives the motor in the second direction based on the second operation, whereby the cam member is driven by the driving force of the motor, the engaging portion follows through the first zone, and thereafter the control unit drives the motor in the second direction, whereby the engaging member follows through the second zone. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIGS. 1A and 1B  are external views of a shutter unit. 
         FIG. 2  is a disassembled perspective view of the shutter unit as viewed from an imaging device side. 
         FIG. 3  is a disassembled perspective view of the shutter unit as viewed from a photography lens side. 
         FIGS. 4A and 4B  are diagrams describing a cam gear. 
         FIG. 5  is a diagram describing a stepping motor. 
         FIGS. 6A through 6C  are diagrams describing the shutter unit in a stopped state. 
         FIGS. 7A through 7C  are diagrams describing the shutter unit in a running standby state. 
         FIGS. 8A through 8C  are diagrams describing the shutter unit in a free-running state. 
         FIGS. 9A through 9C  are diagrams describing the shutter unit in a state of having started running. 
         FIGS. 10A through 10C  are diagrams describing the shutter unit in a state immediately before ending running. 
         FIGS. 11A through 11C  are diagrams describing the shutter unit in a state immediately after ending running. 
         FIGS. 12A through 12C  are diagrams describing the shutter unit in a state after having ended running. 
         FIG. 13  is a timing chart in a case where a live-view mode has been selected. 
         FIG. 14  is a timing chart in a case where a quiet mirror driving mode has been selected. 
         FIG. 15  is a timing chart in a case where a high-speed mirror driving mode has been selected. 
         FIG. 16  is a timing chart in a case where a bulb exposure mode is selected, and bulb exposure has been performed with an exposure time of 30 seconds or less. 
         FIG. 17  is a timing chart in a case where a bulb exposure mode is selected, and bulb exposure has been performed with an exposure time of exceeding 30 seconds. 
         FIG. 18  is a timing chart in a case where a long exposure mode is selected, and an exposure time exceeding 30 seconds has been set. 
         FIGS. 19A and 19B  are tables for correcting operation characteristics of the shutter unit. 
         FIG. 20  is a cross-sectional diagram of a digital single-lens reflex camera body and an interchangeable lens. 
         FIG. 21  is a functional block diagram for describing the configuration of the cross-sectional diagram of a digital single-lens reflex camera body. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     An embodiment of the present invention will be described below with reference to  FIGS. 1 through 21 . 
     Digital Single-Reflex Camera Body  101  and Interchangeable Lens  201   
       FIG. 20  is a cross-sectional diagram of a digital single-reflex camera body  101  and an interchangeable lens  201  serving as an imaging apparatus to carry out the present invention. 
     In  FIG. 20 , the interchangeable lens  201  is detachably attached to the camera body  101 . The interchangeable lens  201  is mounted to the camera body  101  by a camera-side mount portion  102  and an interchangeable-lens-side mount portion  202  being joined. Upon the interchangeable lens  201  being mounted to the camera body  101 , a contact portion  103  of the camera body  101  and a contact portion  203  of the interchangeable lens  201  are electrically connected. Electric power is supplied form the camera body  101  to the interchangeable lens  201  via the contact portion  103  and contact portion  203 . Communication is also performed between the camera body  101  and the interchangeable lens  201  via the contact portion  103  and contact portion  203 . 
     The interchangeable lens  201  has multiple photography lenses  204  and a diaphragm  205 . A light flux that has passed through the photography lenses  204  is cast into a main mirror  106  of the camera body  101 . The main mirror  106  is a mirror that is capable of entering and being retracted from the photography optical path. The main mirror  106  is a half mirror. The light flux reflected at the main mirror  106  is guided to a viewfinder optical system  120 . 
     On the other hand, the light flux that has passed through the main mirror  106  is reflected downwards at a sub-mirror  105  and guided to a focal point detecting unit  121 . The focal point detecting unit  121  detects the amount of defocus, and computes the lens driving amount by which to move the focusing lenses included in the photography lenses  204 , so that a focused state is achieved. The computed lens driving amount is transmitted to the interchangeable lens  201 . The interchangeable lens  201  controls a motor based on the received lens driving amount and moves the focusing lenses. 
     The main mirror  106  is held by a main mirror holding frame  107 , and is axially borne by a rotating shaft  106   b  so as to be capable of turning. The sub-mirror  105  is held by a sub-mirror holding frame  109 . The sub-mirror holding frame  109  is axially borne by the main mirror holding frame  107 . 
     The viewfinder optical system  120  includes a focusing screen  110 , a pentaprism  111 , and an ocular lens  112 . The light flux reflected at the main mirror  106  casts an image of the subject on the focusing screen  110 . The user can observe the subject image on the focusing screen  110  via the pentaprism  111  and ocular lens  112 . 
     A shutter unit  100  is disposed behind the sub-mirror  105 . The shutter unit  100  is a single-blade type focal plane shutter that travels from an open state where an aperture is opened, to a closed state where the aperture is closed, at the time of ending an exposure action. 
     Behind the shutter unit  100  in  FIG. 20  is disposed an optical low-pass filter  114 . Behind the optical low-pass filter  114  is disposed an imaging device  116  that is held by an imaging device holder  115  fixed to the housing, and a cover member  117  that covers the imaging device  116 . A rubber member  118  holds the optical low-pass filter  114  and also seals off between the optical low-pass filter  114  and the imaging device  116 . The configuration is such that light that has passed through the optical low-pass filter  114  is input to the imaging device  116 . 
     In the present embodiment, the exposure operation of the imaging device  116  is started by performing a reset scan (hereinafter referred to as electronic first curtain run). After the imaging device  116  has started the electronic first curtain run, and after a time interval corresponding to a set shutter speed, the shutter unit  100  runs to a close state where the aperture is closed. 
       FIG. 21  is a functional block diagram describing the configuration of the control system of the camera body  101 . 
     An A/D conversion unit  150  convers analog image signals from the imaging device  116  into digital image data. The data output from the A/D conversion unit  150  is written to image display memory  155  or memory  157  via an image processing unit  154  and a memory control unit  152 . 
     A timing generating circuit  151  supplies clock signals and control signals to the imaging device  116  and A/D conversion unit  150 , and is controlled by the memory control unit  152  and a system control unit  153 . 
     The memory control unit  152  controls the A/D conversion unit  150 , the timing generating circuit  151 , the image processing unit  154 , the image display memory  155 , a display control unit  156 , the memory  157 , and a compression/decompression unit  158 . 
     The system control unit  153  is configured of a microcomputer unit including a CPU, and controls the overall camera by executing programs stored in memory  166 . 
     The image processing unit  154  performs predetermined image processing such as pixel interpolation processing, color conversion processing, and so forth, on image data from the A/D conversion unit  150  or the memory control unit  152 . 
     The memory  157  has a sufficient storage capacity for storing a predetermined amount of image data. 
     The compression/decompression unit  158  compresses and decompresses image data, read out from the memory  157 , according to a predetermined image compression format (e.g., adaptive discrete cosine transform or the like). The image data regarding which processing has ended is written to the memory  157 , and also recorded in a detachable recording medium  159  configured using non-volatile memory such as flash memory or the like. 
     The compression/decompression unit  158  reads out image data in the recording medium  159  to the memory  157 , and writes the image data to the image display memory  155  via the image processing unit  154  and memory control unit  152 . The data written to the image display memory  155  is also used in a case of display on an image display unit  160  by the display control unit  156 . 
     A mirror control unit  161  controls the operations of a mirror unit including the main mirror  106 . A control circuit  312  controls operations of the shutter unit  100  via a drive circuit  313 . A diaphragm control unit  163  controls the operations of the diaphragm  205 . The focal point detecting unit  121  detects defocus amount, and computes the lens drive amount to move the focusing lenses included in the photography lenses  204 , so that a focused state is achieved. The computed lens drive amount is transmitted to the interchangeable lens  201 . 
     The memory  166  stores constants, variables, programs, and so forth, for the system control unit  153  to operate, and has recorded therein various types of programs relating to processing that accompanies photography. 
     A power control unit  167  is configured of a power source detecting circuit, a DC-DC converter, a switching circuit that switches circuit blocks to which power is to be supplied, and so forth. The power control unit  167  performs detection of whether or not a power source unit has been mounted, the type of power source, the remaining charge in a battery, and so forth, controls the DC-DC converter based on the detection results and instructions from the system control unit  153 , and supplies electric power to various parts, as much voltage as necessary for as long as necessary. 
     A release button  168  is an operating member to instruct a recording operation of a still image. The release button  168  has a two-stage switch structure. When the release button  168  is pressed to the first stage, a first switch (SW 1 ) turns on. When the first switch turns on, photometry operations and focal point detection operations are executed. When the release button  168  is pressed to the second state, a second switch (SW 2 ) turns on. When the second switch turns on, still image recording operations are started. The release button  168  is equivalent to an example of a signal output unit in the present invention. 
     A mode dial  169  can select an optical viewfinder mode and a live view mode. When the optical viewfinder mode is selected, still image recording operations can be performed in a state of observing an optical image of the subject using the viewfinder optical system  120 . On the other hand, when the live view mode is selected, still image recording operations can be performed in a state of observing a subject image on the image display unit  160 . 
     In a case where the optical viewfinder mode is selected, the mode dial  169  can be used to select a high-speed mirror drive mode and a quiet mirror drive mode. When the high-speed mirror drive mode is selected, the mirror unit including the main mirror  106  is driven at a high speed, thereby reducing release time lag. When the quiet mirror drive mode is selected, the mirror unit including the main mirror  106  is driven at a low speed, and the mirror drive sound can be made smaller. The live view mode and high-speed mirror drive mode are equivalent to an example of a first photography mode in the present invention. The quiet mirror drive mode is equivalent to an example of a second photography mode in the present invention. 
     The mode dial  169  can be used to select a bulb exposure mode and a long exposure mode. In a case where the bulb exposure mode is selected, the release button  168  is pressed down far, the exposure operation starts at the timing where the second switch (SW 2 ) turns on, and the exposure operation ends at the timing where the second switch (SW 2 ) turns off. Note that an arrangement may be made where the exposure operation starts at a timing where the release button  168  is pressed down far and the second switch (SW 2 ) turns on, and the exposure operation ends at a timing where the release button  168  is pressed down far again and the second switch (SW 2 ) turns on. When the long exposure mode is selected, the exposure operation starts at a timing where the release button  168  is pressed down far and the second switch (SW 2 ) turns on, and exposure operations are performed for an exposure time set by a settings dial  170 . 
     A temperature sensor  171  can detect the ambient temperature around the shutter unit  100 . The temperature sensor  171  outputs the detected temperature information to the system control unit  153 . The temperature sensor  171  is disposed in the neighborhood of the shutter unit  100 . The temperature sensor  171  detects the ambient temperature around the shutter unit  100  at a predetermined cycle, as long as the power of the camera body  101  is on. 
     An orientation sensor  172  detects the direction of gravity acting on the camera body  101 . Based on the direction of gravity acting on the camera body  101 , the orientation sensor  172  can determine whether the camera body  101  is in a normal position (horizontal position) or a vertical position. The orientation sensor  172  outputs the determined orientation information to the system control unit  153 . The orientation sensor  172  detects the direction of gravity acting on the camera body  101  at a predetermined cycle, as long as the power of the camera body  101  is on. 
     About the Shutter Unit  100   
     The shutter unit  100  will be described with reference to  FIGS. 1A through 11C . 
       FIG. 1A  is a diagram illustrating the shutter unit  100  as viewed from the imaging device  116  side.  FIG. 1B  is a diagram illustrating the shutter unit  100  as viewed from the photography lenses  204  side. 
       FIG. 2  is a disassembled perspective view of the shutter unit  100  as viewed from the imaging device  116  side.  FIG. 3  is a disassembled perspective view of the shutter unit  100  as viewed from the photography lenses  204  side. 
     A cover plate  8  is fixed to the imaging device  116  side of a shutter base plate  1  by screws  14 . A blade unit serving as a light-shielding member is disposed between the shutter base plate  1  and the cover plate  8 . The blade unit has shutter blades  4 ,  5 , and  6  that serve as blade members, blade arms  2  and  3  that serve as connecting members, and a driving member  11 . 
     An aperture  1   a  is formed in the shutter base plate  1 , and an aperture  8   a  is formed in the cover plate  8 . The shutter blades  4 ,  5 , and  6  are capable of moving between a closed state where the apertures  1   a  and  8   a  are closed, and an opened state where the apertures  1   a  and  8   a  are opened. When the shutter blades  4 ,  5 , and  6  are in the opened state, the photography light flux passes through the apertures  1   a  and  8   a  of the shutter unit  100 . 
     Shafts  1   b,    1   c,    1   d,  and  1   e  are erected on the imaging device  116  side of the shutter base plate  1 , as illustrated in  FIG. 2 . A hole  2   a  and a hole  2   b  are formed in the blade arm  2 . The shaft  1   b  is inserted into the hole  2   a  of the blade arm  2 , whereby the blade arm  2  is axially borne by the shaft  1   b.    
     A hole  3   a,  a hole  3   b,  and a hole  3   c  are formed in the blade arm  3 . The shaft  1   d  is inserted into the hole  3   a  of the blade arm  3 , whereby the blade arm  3  is axially borne by the shaft  1   d.  A balancer  9  is attached to the hole  3   c  of the blade arm  3 . 
     The tip of the blade arm  2  and the shutter blades  4 ,  5 , and  6  are each connected by connecting shafts  7 . The tip of the blade arm  3  and the shutter blades  4 ,  5 , and  6  are each connected by connecting shafts  7 . 
     A biasing spring  10  has a coil portion. The shaft  1   c  is inserted into the coil portion of the biasing spring  10 . One end of the biasing spring  10  engages the hole  3   b  of the blade arm  3 , and the other end of the biasing spring  10  engages the shaft  1   d.  The biasing spring  10  biases the blade arm  3  in the direction of the shutter blades  4 ,  5 , and  6  opening the apertures  1   a  and  8   a.    
     Formed in and on the driving member  11  a hole  11   a,  light-shielding pieces  11   b   1  and  11   b   2 , a follower pin  11   c,  a bearing  11   d,  and a driving pin  11   e.  The follower pin  11   c  is equivalent to an example of an engaging member in the present invention. 
     The shaft  1   b  of the shutter base plate  1  is inserted into the hole  11   a  of the driving member  11 , whereby the driving member  11  is axially borne by the shaft  1   b.  The driving pin  11   e  is inserted into the hole  2   b  of the blade arm  2 , so the blade arm  2  and driving member  11  are integral. Accordingly, the blade arm  2  and the driving member  11  rotate with the shaft  1   b  as the center of rotation. 
     The blade arm  2  rotates on the shaft  1   b  and the blade arm  3  rotates centered on the shaft  1   c,  whereby the shutter blades  4 ,  5 , and  6  move between the closed state where the apertures  1   a  and  8   a  are closed, and an opened state where the apertures  1   a  and  8   a  are opened. 
     When the driving member  11  rotates with the shaft  1   b  as the center of rotation, the light-shielding piece  11   b   1  or light-shielding piece  11   b   2  passes through a slit of a photointerrupter  22 . This switches between a shielded state where the photointerrupter  22  is shielded by the light-shielding piece  11   b   1  or light-shielding piece  11   b   2 , and a photoreception state where the photointerrupter  22  is shielded by neither the light-shielding piece  11   b   1  nor the light-shielding piece  11   b   2 . The photointerrupter  22  can optically detect the position of the driving member  11 . The output of the photointerrupter  22  is input to the control circuit (control unit)  312  of a stepping motor  19 . Note that an L level signal is output when the photointerrupter  22  is in the shielded state, and an H level signal is output when the photointerrupter  22  is in the photoreception state in the present embodiment. 
     The driving member  11  rotates integrally with the blade arm  2  with the shaft  1   b  as the center of rotation. Accordingly, when the shutter blades  4 ,  5 , and  6  move between the closed state and the opened state, the output of the photointerrupter  22  changes between the L level and H level. 
     The light-shielding piece  11   b   1  and  11   b   2  are configured such that when the shutter blades  4 ,  5 , and  6  are in the opened state, the photointerrupter  22  outputs the L level, and when the shutter blades  4 ,  5 , and  6  are in the closed state, the photointerrupter  22  outputs the H level. 
     A coil spring  12  is disposed on the imaging device  116  side of the driving member  11 , so that the bearing  11   d  is inserted in the inner circumferential portion of the coil spring  12 . 
     After attaching the coil spring  12  to the bearing  11   d,  a cover member  13  is fixed to the cover plate  8  by screws  14 . A bearing  13   a  is formed on the cover member  13 . The cover member  13  is fixed to the cover plate  8  so that the shaft  1   b  is inserted into the bearing  13   a.  Thus, the coil spring  12  is compressed between the driving member  11  and the cover member  13 , and the driving member  11  rotates in the optical axis direction without any rattling. 
     A hole  23   a  is formed in a blade tip rubber member  23 . The shaft  1   e  is inserted into the hole  23   a  of the blade tip rubber member  23 , thereby attaching the blade tip rubber member  23  to the shutter base plate  1 . At least the tip of the shutter blade  4  comes into contact with the blade tip rubber member  23  when the shutter blades  4 ,  5 , and  6  close the apertures  1   a  and  8   a  so as to be in the closed state. 
     A shaft  1   f  is erected on the photography lenses  204  side of the shutter base plate  1 , as illustrated in  FIG. 3 . 
     A cam gear  15  is axially borne by the shaft  1   f,  as illustrated in  FIGS. 2 and 3 . The cam gear  15  has formed thereupon a cam groove  15   a,  a gear portion  15   b,  a protrusion  15   c,  a notch  15   d,  and a cylindrical portion  15   e.  The cam gear  15  is equivalent to an example of a cam member in the present invention. The cam groove  15   a  is equivalent to an example of a cam portion in the present invention. 
     The protrusion  15   c  is formed protruding from the base of the cam gear  15  toward a holder member  17  side, as illustrated in  FIG. 3 . The notch  15   d  is formed on both side faces of the protrusion  15   c.  The cylindrical portion  15   e  is formed protruding toward the photography lenses  204  side. The shaft  1   f  of the shutter base plate  1  is inserted into the cylindrical portion  15   e,  whereby the cam gear  15  is axially borne by the shaft  1   f.  The gear portion  15   b  is formed on the perimeter of the cylindrical portion  15   e.    
     The cam groove  15   a  is formed on the side of the cam gear  15  toward the shutter base plate  1 , as illustrated in  FIG. 2 . The follower pin  11   c  of the driving member  11  engages the cam groove  15   a  of the cam gear  15 . Accordingly, the driving member  11  moves in conjunction with rotation of the cam gear  15 . The cam groove  15   a  has provided therein a first elastic member  24  and a second elastic member  25 . 
     A weight  16  is fixed by screws  14  on the base of the cam gear  15 , at the holder member  17  side, as illustrated in  FIGS. 2 and 3 . The weight  16  has a notch  16   a  formed therein so that the protrusion  15   c  is inserted into the notch  16   a.  The weight  16  is fixed to the base of the cam gear  15  by screws  14 . The weight  16  has a sufficiently large mass as compared to the cam gear  15 . The cam gear  15  functions as a flywheel by the weight  16  being fixed to the cam gear  15 . 
     After the cam gear  15  to which the weight  16  has been fixed is axially borne by the shaft  1   f,  the holder member  17  is fixed to the photography lenses  204  side of the shutter base plate  1  by screws  14 , as illustrated in  FIGS. 2 and 3 . 
     The holder member  17  has formed therein and thereon a retaining portion  17   a,  a retaining portion  17   b,  a hole  17   c,  a bearing  17   d,  an abutting portion  17   e,  and an opening  17   f,  as illustrated in  FIGS. 2 and 3 . Fixing the holder member  17  to the photography lenses  204  of the shutter base plate  1  inserts the shaft  1   f  into the bearing  17   d.  The cam gear  15  and weight  16  are rotate held between the shutter base plate  1  and the holder member  17 . 
     A driving spring  18  is attached to the face of the holder member  17  in the side toward the photography lenses  204 , as illustrated in  FIGS. 2 and 3 . The driving spring  18  has arms  18   a  and  18   b  and a coil  18   c  formed. The driving spring  18  is attached to the holder member  17  such that the bearing  17   d  is inserted into the coil  18   c,  the arm  18   a  is retained by the retaining portion  17   a,  and the arm  18   b  is retained by the retaining portion  17   b.  The driving spring  18  is equivalent to an example of a biasing member in the present invention. 
     Fixing the holder member  17  to the shutter base plate  1  inserts the protrusion  15   c  of the cam gear  15  into the opening  17   f.  Rotating the cam gear  15  moves the protrusion  15   c  within the opening  17   f.  When the protrusion  15   c  moves within the opening  17   f  and the protrusion  15   c  abuts against the arm  18   a  of the driving spring  18 , the arm  18   a  of the driving spring  18  engages the notch  15   d.  In the same way, when the protrusion  15   c  abuts against the arm  18   b  of the driving spring  18 , the arm  18   b  of the driving spring  18  engages the notch  15   d.    
     The stepping motor  19  is fixed by screws  14  to the photography lens  204  side of the holder member  17  via an attaching plate  20 , as illustrated in  FIGS. 2 and 3 . A pinion gear  21  is press-fit to the output shaft of the stepping motor  19 . Fixing the stepping motor  19  to the holder member  17  inserts the output shaft of the stepping motor  19  into the hole  17   c,  and the pinion gear  21  meshes with the gear portion  15   b  of the cam gear  15 . Accordingly, driving the stepping motor  19  rotates the cam gear  15 . 
     When the cam gear  15  rotates, the follower pin  11   c  of the driving member  11  follows through the cam groove  15   a  and the driving member  11  rotates. The driving member  11  is integrated with the blade arm  2 , so the blade arm  2  rotates. The shutter blades  4 ,  5 , and  6  are capable of parallel link motion by the blade arms  2  and  3 . The shutter blades  4 ,  5 , and  6  can move to the closed state where the apertures  1   a  and  8   a  are closed and the opened state where the apertures  1   a  and  8   a  are opened. 
     Regarding the Cam Gear  15   
       FIG. 4A  is a plan view of the cam gear  15  to which the weight  16  has been fixed, as viewed from the shutter base plate  1  side.  FIG. 4B  is a plan view of the cam gear  15  to which the weight  16  has been fixed, as viewed from the holder member  17  side. 
     Five zones, zone A through zone E, are formed in the cam groove  15   a,  as illustrated in  FIG. 4A . The cam groove  15   a  has a recess  15   a - 1 , and cam regions  15   a - 2  through  15   a - 6  formed therein. When the follower pin  11   c  of the driving member  11  is situated in zone A of the cam groove  15   a,  and the cam gear  15  rotates in one direction, the follower pin  11   c  follows through in the order of zone A to zone E. 
     The cam region  15   a - 2  is formed in zone A of the cam groove  15   a.  The cam region  15   a - 3  is formed in zone B of the cam groove  15   a.  The cam region  15   a - 4  is formed in zone C of the cam groove  15   a.  The cam region  15   a - 5  is formed in zone D of the cam groove  15   a.  The cam region  15   a - 6  is formed in zone E of the cam groove  15   a.    
     The recess  15   a - 1  is formed between zone A and zone B where the shutter blades  4 ,  5 , and  6  are in the opened state where the apertures  1   a  and  8   a  are opened, the follower pin  11   c  of the driving member  11  enters the recess  15   a - 1 . By the follower pin  11   c  of the driving member  11  entering the recess  15   a - 1  when the shutter unit  100  is in a standby state, the follower pin  11   c  of the driving member  11  is held between zone A and zone B of the cam groove  15   a  in a stable manner. 
     When the cam gear  15  is rotated in the clock-wise direction from the state of the follower pin  11   c  having entered the recess  15   a - 1  in  FIG. 4A , the follower pin  11   c  of the driving member  11  comes into contact with the cam region  15   a - 2  of the cam groove  15   a,  and follows through zone A of the cam groove  15   a.  The cam region  15   a - 2  is formed so that there is almost zero cam lift, so the driving member  11  hardly rotates at all while the follower pin  11   c  is following through zone A of the cam groove  15   a.  Accordingly, the shutter blades  4 ,  5 , and  6  maintain the opened state where the apertures  1   a  and  8   a  are opened while the follower pin  11   c  is following through zone A of the cam groove  15   a.    
     When the cam gear  15  is rotated in the counterclockwise direction from the state of the follower pin  11   c  having entered the recess  15   a - 1  in  FIG. 4A , the follower pin  11   c  of the driving member  11  comes into contact with the cam region  15   a - 3  of the cam groove  15   a,  and follows through zone B of the cam groove  15   a.  The cam region  15   a - 3  is formed so that there is almost zero cam lift, so the driving member  11  hardly rotates at all while the follower pin  11   c  is following through zone B of the cam groove  15   a.  Accordingly, the shutter blades  4 ,  5 , and  6  maintain the opened state where the apertures  1   a  and  8   a  are opened while the follower pin  11   c  is following through zone B of the cam groove  15   a.    
     When the cam gear  15  is rotated in the counterclockwise direction from the state of the follower pin  11   c  following through zone B of the cam groove  15   a,  the follower pin  11   c  of the driving member  11  comes into contact with the cam region  15   a - 4  of the cam groove  15   a,  and follows through zone C of the cam groove  15   a.  When the follower pin  11   c  follows through zone C of the cam groove  15   a,  the driving member  11  rotates and the shutter blades  4 ,  5 , and  6  move from the opened state where the apertures  1   a  and  8   a  are opened to a state immediately before closing the apertures  1   a  and  8   a.    
     When the cam gear  15  is rotated in the counterclockwise direction from the state of the follower pin  11   c  following through zone C of the cam groove  15   a,  the follower pin  11   c  of the driving member  11  comes into contact with the cam region  15   a - 5  of the cam groove  15   a,  and follows through zone D of the cam groove  15   a.  When the follower pin  11   c  follows through zone D of the cam groove  15   a,  the driving member  11  further rotates, and the shutter blades  4 ,  5 , and  6  move to a state where the apertures  1   a  and  8   a  are completely closed. 
     When the cam gear  15  is rotated in the counterclockwise direction from the state of the follower pin  11   c  following through zone D of the cam groove  15   a,  the follower pin  11   c  of the driving member  11  comes into contact with the cam region  15   a - 6  of the cam groove  15   a,  and follows through zone E of the cam groove  15   a.  The cam region  15   a - 6  is formed so that there is almost zero cam lift, so the driving member  11  hardly rotates at all while the follower pin  11   c  is following through zone E of the cam groove  15   a.  Accordingly, the shutter blades  4 ,  5 , and  6  maintain the closed state where the apertures  1   a  and  8   a  are completely closed while the follower pin  11   c  is following through zone E of the cam groove  15   a.    
     The first elastic member  24  and second elastic member  25  are provided in zone E of the cam groove  15   a,  as illustrated in  FIG. 4A . More specifically, the width of the groove is formed larger in zone E of the cam groove  15   a.  The first elastic member  24  is applied on the inner side of the zone E of the cam groove  15   a,  and the second elastic member  25  is applied on the outer side of the zone E of the cam groove  15   a.  The width between the first elastic member  24  and the second elastic member  25  is approximately the same as the width of the groove at other places than the zone E of the cam groove  15   a  as a result of having provided the first elastic member  24  and second elastic member  25  in the zone E of the cam groove  15   a.    
     When the shutter blades  4 ,  5 , and  6  go to the state of completely closing the apertures  1   a  and  8   a,  the tip of the shutter blade  4  comes into contact with the blade tip rubber member  23 , and the shutter blades  4 ,  5 , and  6  bounce. When the shutter blades  4 ,  5 , and  6  bounce, the follower pin  11   c  alternatingly collides with the first elastic member  24  and second elastic member  25  in zone E of the cam groove  15   a.  The first elastic member  24  and second elastic member  25  are formed using a material having elasticity, so even if the follower pin  11   c  collides the first elastic member  24  and second elastic member  25  can absorb the shock. 
     The protrusion  15   c  is formed to protrude from the base of the cam gear  15  toward the holder member  17  side, as illustrated in  FIG. 4B . The notch  15   d  is formed on both side faces of the protrusion  15   c.  The bearing  15   e  is formed protruding toward the holder member  17  side. The gear portion  15   b  is formed on the perimeter of the cylindrical portion  15   e.    
     The weight  16  is fixed on the base of the cam gear  15  toward the holder member  17  side, as illustrated in  FIG. 4B . The notch  16   a  is formed in the weight  16 . The weight  16  is fixed by screws  14  to the base of the cam gear  15  toward the holder member  17  side, so that the protrusion  15   c  is inserted into the notch  16   a.    
     Regarding the Stepping Motor  19   
       FIG. 5  is a diagram describing the aforementioned stepping motor  19 . Some of the parts are illustrated cut away, for description. 
     The stepping motor  19  is a stepping motor that is capable of step driving where the conduction state of the coil is switched according to set time intervals and driven (open-loop driving), and two types of feedback driving with different advance angles. 
     In a case of driving the stepping motor  19  in the step driving mode (open-loop driving mode), driving is performed where the conduction state of the coil is switched in accordance with set time intervals. When driving the stepping motor  19  in the feedback driving mode, driving is performed where the conduction state of the coil is switched in accordance with output of a position sensor that detects the rotational position of the rotor. 
     A rotor  301  has a magnet  302 , as illustrated in  FIG. 5 . The stepping motor  19  is rotatably controlled by the control circuit (control unit)  312  and drive circuit  313 . The magnet  302  is formed having a cylinder shape, the outer peripheral face being divided in the circumferential direction, so that opposite poles are formed in alternation. The magnet  302  is divided into eight in the circumferential direction in the present embodiment, and eight magnetic poles are formed. 
     A first coil  303  is disposed at one end of the magnet  302  in the axial direction. 
     A first yoke  305  is formed from a soft magnetic material. The first yoke  305  has a plurality of first magnetic portions  305   a  that face the outer peripheral face of the magnet  302  across a gap. The first magnetic portions  305   a  are subjected to excitation by electricity being supplied to the first coil  303 . 
     The first coil  303 , the first yoke  305 , and the magnet  302  facing the multiple first magnetic portions  305   a  make up a first stator unit. 
     A second coil  304  is disposed at the other end of the magnet  302  in the axial direction from the end to which the first coil  303  is attached. 
     A second yoke  306  is formed from a soft magnetic material. The second yoke  306  has a plurality of second magnetic portions  306   a  that face the outer peripheral face of the magnet  302  across a gap. The second magnetic portions  306   a  are subjected to excitation by electricity being supplied to the second coil  304 . 
     The second coil  304 , the second yoke  306 , and the magnet  302  facing the multiple second magnetic portions  306   a  make up a second stator unit. 
     The rotor  301  can be rotated by switching the poles (N pole and S pole) that are excited by the first magnetic portions  305   a  and second magnetic portions  306   a.    
     A first magnetism sensor (first detecting element)  307 , a second magnetism sensor (second detecting element)  308 , a third magnetism sensor (third detecting element)  309 , and a fourth magnetism sensor (fourth detecting element)  310 , make up a detecting unit. The magnetism sensors are each Hall elements that detect magnetic flux of the magnet  302 , and are fixed to a motor cover  311 . 
     The motor cover  311  fixedly holds the first yoke  305  and the second yoke  306  so that the first magnetic portions  305   a  and the second magnetic portions  306   a  are disposed shifted generally 90 degrees in electrical angle as to the magnetizing phase of the magnet  302 . 
     Note that the electrical angle here is one cycle of the magnetic force of a magnet represented in the form of 360°, and the electrical angle θ can be expressed by the following Expression where the number of poles of the rotor is M and the mechanical angle is θ 0 .
 
θ=θ0× M/ 2
 
     The number of magnetic poles of the magnet  302  is eight poles in the present embodiment, so 90 degrees in electrical angle is 22.5 degrees in mechanical angle. 
     The control circuit  312  can perform driving switching between step driving and two types of feedback driving having different advance angles. When performing step driving, the control circuit  312  controls the drive circuit  313  so as to switch the conduction state of the first coil  303  and the second coil  304  at predetermined time intervals. 
     In a case of performing step driving, the outputs of the first magnetism sensor  307 , second magnetism sensor  308 , third magnetism sensor  309 , and fourth magnetism sensor  310  are not used, regardless of the direction of rotation of the stepping motor  19 . 
     In a case of driving the stepping motor  19  in a first direction, and feedback driving of which the advance angle is larger is to be performed, the control circuit  312  controls the drive circuit  313  as follows. The conduction state of the first coil  303  is switched by the output of the first magnetism sensor  307 , and the conduction state of the second coil  304  is switched by the output of the second magnetism sensor  308 . 
     In a case of driving the stepping motor  19  in the first direction, and feedback driving of which the advance angle is larger is to be performed, the control circuit  312  controls the drive circuit  313  as follows. The conduction state of the first coil  303  is switched by the output of the third magnetism sensor  309 , and the conduction state of the second coil  304  is switched by the output of the fourth magnetism sensor  310 . 
     In a case of driving the stepping motor  19  in a second direction the opposite to the first direction, and feedback driving of which the advance angle is smaller is to be performed, the control circuit  312  controls the drive circuit  313  as follows. The conduction state of the first coil  303  is switched by the output of the third magnetism sensor  309 , and the conduction state of the second coil  304  is switched by the output of the fourth magnetism sensor  310 . 
     In a case of driving the stepping motor  19  in the second direction, and feedback driving of which the advance angle is larger is to be performed, the control circuit  312  controls the drive circuit  313  as follows. The conduction state of the first coil  303  is switched by the output of the first magnetism sensor  307 , and the conduction state of the second coil  304  is switched by the output of the second magnetism sensor  308 . 
     Operations of Shutter Unit  100   
       FIGS. 6A through 12C  are diagrams for describing the operations of the shutter unit  100 . 
     First, the running operations of the shutter unit  100  will be described. 
       FIGS. 6A through 6C  are diagrams describing the shutter unit  100  in a stopped state.  FIG. 6A  is a diagram of the shutter unit  100  as viewed from the imaging device  116  side. In  FIG. 6A , the shutter base plate  1 , cover plate  8 , and cover member  13  are omitted from illustration.  FIG. 6B  is a diagram of the shutter unit  100  as viewed from the photography lenses  204  side. In  FIG. 6B , the shutter base plate  1 , cover plate  8 , and stepping motor  19  are omitted from illustration.  FIG. 6C  is a diagram describing the relationship of engaging between the follower pin  11   c  of the driving member  11  and the cam groove  15   a.    
     When the shutter unit  100  is in a stopped state, the shutter blades  4 ,  5 , and  6  are in the opened state where the apertures  1   a  and  8   a  are opened, as illustrated in  FIG. 6A . The biasing spring  10  biases the blade arm  3  in the counterclockwise direction in  FIG. 6A . This biasing force is transmitted to the blade arm  2  via the shutter blades  4 ,  5 , and  6 , so the blade arm  2  also is biased in the counterclockwise direction in  FIG. 6A . Accordingly, the driving member  11  also is biased in the counterclockwise direction in  FIG. 6A . Thus, the biasing force of the biasing spring  10  presses the follower pin  11   c  against the recess  15   a - 1 . At this time, the light-shielding piece  11   b   1  is positioned within the slit of the photointerrupter  22 , and the output of the photointerrupter  22  is L level. The photointerrupter  22  outputs the L level when the shutter blades  4 ,  5 , and  6  have opened the apertures  1   a  and  8   a,  and outputs the H level when the shutter blades  4 ,  5 , and  6  have closed the apertures  1   a  and  8   a.    
     When the shutter unit  100  is in a stopped state, the arm  18   a  of the driving spring  18  is retained at the retaining portion  17   a,  and the arm  18   b  of the driving spring  18  is retained at the retaining portion  17   b,  as illustrated in  FIG. 6B . That is to say, the driving spring  18  is not charged by the notch  15   d  of the cam gear  15 . 
     When the shutter unit  100  is in a stopped state, the follower pin  11   c  has entered into the recess  15   a - 1  as illustrated in  FIG. 6C . The biasing force of the biasing spring  10  acts on the driving member  11  so that the follower pin  11   c  is pressed against the recess  15   a - 1 . Accordingly, the follower pin  11   c  of the driving member  11  can beheld between zone A and zone B of the cam groove  15   a  in a stable manner, even without applying holding electricity to the stepping motor  19 . 
     The control circuit  312  drives the stepping motor  19  in the first direction by feedback driving of which the advance angle is smaller from the stopped state illustrated in  FIGS. 6A through 6C , and rotates the cam gear  15  in the clockwise direction. Accordingly, the shutter unit  100  goes from the stopped state illustrated in  FIGS. 6A through 6C  to a running standby state illustrated in  FIGS. 7A through 7C . 
       FIGS. 7A through 7C  are diagrams describing the running standby state of the shutter unit  100 .  FIG. 7A  is a diagram of the shutter unit  100  as viewed from the imaging device  116  side. In  FIG. 7A , the shutter base plate  1 , cover plate  8 , and cover member  13  are omitted from illustration.  FIG. 7B  is a diagram of the shutter unit  100  as viewed from the photography lenses  204  side. In  FIG. 7B , the shutter base plate  1 , cover plate  8 , and stepping motor  19  are omitted from illustration.  FIG. 7C  is a diagram describing the relationship of engaging between the follower pin  11   c  of the driving member  11  and the cam groove  15   a.    
     When the shutter unit  100  is in the running standby state, the follower pin  11   c  of the driving member  11  comes into contact with the cam region  15   a - 2  of the cam groove  15   a,  and follows through zone A of the cam groove  15   a,  as illustrated in  FIG. 7C . The cam region  15   a - 2  is formed so that the cam lift is almost zero. When the shutter unit  100  goes from the stopped state to the running standby state, the driving member  11  rotates slightly when the follower pin  11   c  departs from the recess  15   a - 1 . However, the shutter blades  4 ,  5 , and  6  maintain the opened state where the apertures  1   a  and  8   a  are opened, as illustrated in  FIG. 7A . When the shutter unit  100  is in the running standby state, the output of the photointerrupter  22  is also maintained at L level. 
     When the shutter unit  100  goes from the stopped state to the running standby state, the cam gear  15  rotates in the counterclockwise direction, as illustrated in  FIG. 7B . At this time, the protrusion  15   c  of the cam gear  15  comes into contact with the arm  18   a  of the driving spring  18 . The cam gear  15  rotates in the counterclockwise direction against the biasing force of the driving spring  18  until the protrusion  15   c  abuts the abutting portion  17   e  of the holder member  17 . When the protrusion  15   c  of the cam gear  15  comes into contact with the arm  18   a  of the driving spring  18 , the arm  18   a  is held in a stable manner by one side of the notch  15   d  formed in both side faces of the protrusion  15   c.    
     After the running standby state of the shutter unit  100  illustrated in  FIGS. 7A through 7C , the control circuit  312  controls the drive circuit  313  so that the cam gear  15  is stopped in a state where the driving spring  18  is charged. The drive circuit  313  applies holding electricity to the stepping motor  19  at this time. 
     The control circuit  312  drives the stepping motor  19  in the second direction from the running standby state illustrated in  FIGS. 7A through 7C  by step driving, and rotates the cam gear  15  in the counterclockwise direction. Accordingly, the shutter unit  100  goes from the running standby state illustrated in  FIGS. 7A through 7C  to the free-running state illustrated in  FIGS. 8A through 8C . At this time, the second driving direction of the stepping motor  19  is the opposite direction as the first driving direction of the stepping motor  19 . 
       FIGS. 8A through 8C  are diagrams describing the free-running state of the shutter unit  100 .  FIG. 8A  is a diagram of the shutter unit  100  as viewed from the imaging device  116  side. In  FIG. 8A , the shutter base plate  1 , cover plate  8 , and cover member  13  are omitted from illustration.  FIG. 8B  is a diagram of the shutter unit  100  as viewed from the photography lenses  204  side. In  FIG. 8B , the shutter base plate  1 , cover plate  8 , and stepping motor  19  are omitted from illustration.  FIG. 8C  is a diagram describing the relationship of engaging between the follower pin  11   c  of the driving member  11  and the cam groove  15   a.    
     When the shutter unit  100  is in the free-running state, the follower pin  11   c  of the driving member  11  comes into contact with the cam region  15   a - 3  of the cam groove  15   a,  and follows through zone B of the cam groove  15   a,  as illustrated in  FIG. 8C . The cam region  15   a - 3  is formed so that the cam lift is almost zero. Accordingly, the shutter blades  4 ,  5 , and  6  maintain the opened state where the apertures  1   a  and  8   a  are opened, as illustrated in  FIG. 8A . When the shutter unit  100  is in the free-running state, the output of the photointerrupter  22  is also maintained at L level. 
     When the shutter unit  100  goes from the running standby state to the free-running state, the driving member  11  hardly rotates at all. Until the shutter unit  100  goes from the running standby state to the free-running state, the cam gear  15  is rotated in the counterclockwise direction by the combined force of the driving force of the stepping motor  19  and the biasing force of the driving spring  18 . When the follower pin  11   c  passes the recess  15   a - 1 , a large inertial force is acting on the follower pin  11   c.  This inertial force is larger than the force of the biasing spring  10  pressing the follower pin  11   c  against the recess  15   a - 1 . Accordingly, when the shutter unit  100  goes from the running standby state to the free-running state, the follower pin  11   c  does not enter the recess  15   a - 1 . 
     After the arm  18   a  of the driving spring  18  is retained by the retaining portion  17   a  as illustrated in  FIG. 8B , the cam gear  15  rotates in the counterclockwise direction by driving force of the stepping motor  19 . 
     The control circuit  312  drives the stepping motor  19  in the second direction from the free-running state illustrated in  FIGS. 8A through 8C  by step driving, and rotates the cam gear  15  in the counterclockwise direction. Accordingly, the shutter unit  100  goes from the free-running state illustrated in  FIGS. 8A through 8C  to a state of having started running illustrated in  FIGS. 9A through 9C . 
       FIGS. 9A through 9C  are diagrams describing the state of having started running of the shutter unit  100 .  FIG. 9A  is a diagram of the shutter unit  100  as viewed from the imaging device  116  side. In  FIG. 9A , the shutter base plate  1 , cover plate  8 , and cover member  13  are omitted from illustration.  FIG. 9B  is a diagram of the shutter unit  100  as viewed from the photography lenses  204  side. In  FIG. 9B , the shutter base plate  1 , cover plate  8 , and stepping motor  19  are omitted from illustration.  FIG. 9C  is a diagram describing the relationship of engaging between the follower pin  11   c  of the driving member  11  and the cam groove  15   a.    
     When the shutter unit  100  is in the state of having started running, the follower pin  11   c  of the driving member  11  comes into contact with the cam region  15   a - 4  of the cam groove  15   a,  and follows through zone C of the cam groove  15   a,  as illustrated in  FIG. 9C . When the follower pin  11   c  follows through zone C of the cam groove  15   a,  the driving member  11  rotates in the clockwise direction in  FIG. 9A , and the shutter blades  4 ,  5 , and  6  begin to close the apertures  1   a  and  8   a.    
     When the driving member  11  begins to slightly rotate in the clockwise direction in  FIG. 9A  from the state of having started running illustrated in  FIGS. 9A through 9C , the light-shielding piece  11   b   1  departs from within the slit of the photointerrupter  22 . At this time, the light-shielding piece  11   b   2  is not in the slit of the photointerrupter  22  either, so the output of the photointerrupter  22  changes from L to H. The output of the photointerrupter  22  changing from L to H is equivalent to an example of output of a first detection signal in the present invention. 
     The control circuit  312  measures the elapsed time tp 1  from switching to feedback driving of which the advance angle is larger till the output of the photointerrupter  22  changes from L to H ( FIGS. 13 through 18 ). A reference time tp 1 ref held in the control circuit  312  and the measured elapsed time tp 1  are compared. The reference time tp 1 ref is set at the time of manufacturing the shutter unit  100 . 
     When the shutter unit  100  is in the state of having started running, the arm  18   a  of the driving spring  18  is retained at the retaining portion  17   a,  and the arm  18   b  of the driving spring  18  retained at the retaining portion  17   b,  as illustrated in  FIG. 9B . In the state of having started running, the cam gear  15  rotates in the counterclockwise direction by the driving force of the stepping motor  19  alone. 
     The control circuit  312  drives the stepping motor  19  in the second direction by feedback driving of which the advance angle is larger, from the state of having started running illustrated in  FIGS. 9A through 9C , and rotates the cam gear  15  in the counterclockwise direction. Accordingly, the shutter unit  100  goes from the state of having started running in  FIGS. 9A through 9C  to the state immediately before ending running illustrated in  FIGS. 10A through 10C . 
       FIGS. 10A through 10C  is a diagram describing the state immediately before ending running of the shutter unit  100 .  FIG. 10A  is a diagram of the shutter unit  100  as viewed from the imaging device  116  side. In  FIG. 10A , the shutter base plate  1 , cover plate  8 , and cover member  13  are omitted from illustration.  FIG. 10B  is a diagram of the shutter unit  100  as viewed from the photography lenses  204  side. In  FIG. 10B , the shutter base plate  1 , cover plate  8 , and stepping motor  19  are omitted from illustration.  FIG. 10C  is a diagram describing the relationship of engaging between the follower pin  11   c  of the driving member  11  and the cam groove  15   a.    
     When shutter unit  100  is in the state immediately before ending running, the follower pin  11   c  of the driving member  11  comes into contact with the cam region  15   a - 5  of the cam groove  15   a,  and follows through zone D of the cam groove  15   a,  as illustrated in  FIG. 10C . The cam region  15   a - 5  is formed to gradually reduce the rotational speed of the driving member  11 . 
     The driving member  11  gradually decelerates when the follower pin  11   c  follows through zone D of the cam groove  15   a,  even without the control circuit  312  decelerating the driving speed of the stepping motor  19 . Accordingly, when the follower pin  11   c  follows through zone D of the cam groove  15   a,  the driving member  11  rotates with a reduced rotation speed, and the shutter blades  4 ,  5 , and  6  are in the state immediately before closing the apertures  1   a  and  8   a,  as illustrated in  FIG. 10A . 
     When the shutter blades  4 ,  5 , and  6  are in the state immediately before closing the apertures  1   a  and  8   a,  the shutter blades  4 ,  5 , and  6  are braked in the present embodiment, accordingly, the shutter blades  4 ,  5 , and  6  are braked before the timing of the connecting shaft  7  passing the edge of the aperture  1   a.  Generally, when timing of the connecting shaft  7  passing the edge of the aperture  1   a  and the timing of starting braking coincide, trouble may occur where the connecting shaft  7  is caught on the edge of the aperture  1   a.  In the present embodiment, the timing of the shutter blades  4 ,  5 , and  6  being braked is before the timing of the connecting shaft  7  passing the edge of the aperture  1   a,  so the risk of such trouble can be avoided. 
     When shutter unit  100  is in the state immediately before ending running, illustrated in  FIGS. 10A through 10C , the light-shielding piece  11   b   2  enters the slit of the photointerrupter  22  and the output of the photointerrupter  22  changes from H to L. The output of the photointerrupter  22  changing from H to L is equivalent to an example of output of a second detection signal in the present invention. 
     The control circuit  312  measures the elapsed time tp 2  from the output of the photointerrupter  22  changing from L to H till the output of the photointerrupter  22  changes from H to L (see  FIGS. 13 through 18 ). The elapsed time tp 2  is measured for each running operation of the shutter unit  100 , and a reference time tp 2 ref held in the control circuit  312  and the measured elapsed time tp 2  are compared. The reference time tp 2 ref is set at the time of manufacturing the shutter unit  100 . 
     When the shutter unit  100  is in the state immediately before ending running, the arm  18   a  of the driving spring  18  is retained at the retaining portion  17   a,  and the arm  18   b  of the driving spring  18  retained at the retaining portion  17   b,  as illustrated in  FIG. 10B . In the state immediately before ending running, the cam gear  15  rotates in the counterclockwise direction by the driving force of the stepping motor  19  alone. 
     The control circuit  312  drives the stepping motor  19  in the second direction by feedback driving of which the advance angle is larger, continuing from the state of immediately before ending running illustrated in  FIGS. 10A through 10C , and rotates the cam gear  15  in the counterclockwise direction. Accordingly, the shutter unit  100  goes from the state of immediately before ending running in  FIGS. 10A through 10C  to the state immediately after ending running illustrated in  FIGS. 11A through 11C . 
       FIGS. 11A through 11C  are diagrams describing the state immediately after ending running of the shutter unit  100 .  FIG. 11A  is a diagram of the shutter unit  100  as viewed from the imaging device  116  side. In  FIG. 11A , the shutter base plate  1 , cover plate  8 , and cover member  13  are omitted from illustration.  FIG. 11B  is a diagram of the shutter unit  100  as viewed from the photography lenses  204  side. In  FIG. 11B , the shutter base plate  1 , cover plate  8 , and stepping motor  19  are omitted from illustration.  FIG. 11C  is a diagram describing the relationship of engaging between the follower pin  11   c  of the driving member  11  and the cam groove  15   a.    
     When shutter unit  100  is in the state immediately after ending running, the tip of the shutter blade  4  comes into contact with the blade tip rubber member  23 , as illustrated in  FIG. 11A . At this time, the light-shielding piece  11   b   2  departs from within the slit of the photointerrupter  22 , and the output of the photointerrupter  22  changes from L to H again. When shutter unit  100  is in the state immediately after ending running illustrated in  FIGS. 11A through 11C , the output of the photointerrupter  22  is H. 
     When the shutter blades  4 ,  5 , and  6  are in the opened state, the photointerrupter  22  outputs L, and when the shutter blades  4 ,  5 , and  6  are in the closed state, outputs H. 
     When shutter unit  100  is in the state immediately after ending running as illustrated in  FIG. 11C , the follower pin  11   c  of the driving member  11  comes into contact with the cam region  15   a - 6  of the cam groove  15   a,  and follows through zone E of the cam groove  15   a.  The cam region  15   a - 6  is formed so that there is almost zero cam lift, so the driving member  11  hardly rotates at all while the follower pin  11   c  is following through zone E of the cam groove  15   a.    
     The first elastic member  24  is applied on the inner side of the zone E of the cam groove  15   a,  and the second elastic member  25  is applied on the outer side of the zone E of the cam groove  15   a,  as illustrated in  FIG. 11C . Accordingly, while the follower pin  11   c  is following through zone E of the cam groove  15   a,  the follower pin  11   c  is sandwiched between the first elastic member  24  and second elastic member  25 . 
     When the shutter unit  100  is in the state immediately after ending running, the arm  18   a  of the driving spring  18  is retained at the retaining portion  17   a,  and the arm  18   b  of the driving spring  18  retained at the retaining portion  17   b,  as illustrated in  FIG. 11B . In the state immediately before ending running, the cam gear  15  rotates in the counterclockwise direction by the driving force of the stepping motor  19  alone. 
     The control circuit  312  drives the stepping motor  19  in the first direction from the state immediately after ending running illustrated in  FIGS. 11A through 11C . Driving the stepping motor  19  in the first direction rotates the cam gear  15  in the clockwise direction, but the inertial force to rotate the cam gear  15  in the counterclockwise direction is large, so the cam gear  15  rotates in the counterclockwise direction while being gradually decelerated. 
     Accordingly, the shutter unit  100  goes from the state immediately after ending running, illustrated in  FIGS. 11A through 11C , to the state after having ended running, illustrated in  FIGS. 12A through 12C . 
       FIGS. 12A through 12C  are diagrams describing the state after having ended running of the shutter unit  100 .  FIG. 12A  is a diagram of the shutter unit  100  as viewed from the imaging device  116  side. In  FIG. 12A , the shutter base plate  1 , cover plate  8 , and cover member  13  are omitted from illustration.  FIG. 12B  is a diagram of the shutter unit  100  as viewed from the photography lenses  204  side. In  FIG. 12B , the shutter base plate  1 , cover plate  8 , and stepping motor  19  are omitted from illustration.  FIG. 12C  is a diagram describing the relationship of engaging between the follower pin  11   c  of the driving member  11  and the cam groove  15   a.    
     When shutter unit  100  is in the state after having ended running, the follower pin  11   c  of the driving member  11  comes into contact with the cam region  15   a - 6  of the cam groove  15   a,  and follows through zone E of the cam groove  15   a,  as illustrated in  FIG. 12C . 
     As illustrated in  FIG. 12A , the tip of the shutter blade  4  comes into contact with the blade tip rubber member  23 , and the shutter blades  4 ,  5 , and  6  bounce. When the shutter blades  4 ,  5 , and  6  bounce, the follower pin  11   c  alternatingly collides with the first elastic member  24  and second elastic member  25  in zone E of the cam groove  15   a,  as illustrated in  FIG. 12C . The first elastic member  24  and second elastic member  25  are formed using a material having elasticity, so even if the follower pin  11   c  collides the first elastic member  24  and second elastic member  25  can absorb the shock. Thus, the bouncing of the shutter blades  4 ,  5 , and  6  in the state after having ended running is reduced. 
     When shutter unit  100  is in the state after having ended running, the arm  18   a  of the driving spring  18  is retained at the retaining portion  17   a,  and the arm  18   b  of the driving spring  18  is retained at the retaining portion  17   b,  as illustrated in  FIG. 12B . That is to say, the driving spring  18  is not charged by the notch  15   d  of the cam gear  15 . 
     When shutter unit  100  is in the state after having ended running as illustrated in  FIG. 12A , the output of the photointerrupter  22  maintains the H level. That is to say, when the shutter blades  4 ,  5 , and  6  are in the closed state, the photointerrupter  22  continues to output the H level. 
     When shutter unit  100  is in the state after having ended running illustrated in  FIGS. 12A through 12C , the control circuit  312  controls the drive circuit  313  and stops the stepping motor  19 . 
     Even when shutter unit  100  is in the state after having ended running, the follower pin  11   c  is situated around the middle of zone E OF THE cam groove  15   a,  as illustrated in  FIG. 12C . It is conceivable that the cam gear  15  may rotate in the counterclockwise direction from the state after having ended running due to inertial force after having stopped the stepping motor  19 . In this case, the protrusion  15   c  of the cam gear  15  comes into contact with the arm  18   b  of the driving spring  18  as illustrated in  FIG. 12B , so the counterclockwise rotation of the cam gear  15  can be stopped using the biasing force of the driving spring  18 . 
     Next, returning operations of the shutter unit  100  will be described. 
     In the returning operations of the shutter unit  100 , the state after having ended running illustrated in  FIGS. 12A through 12C  is returned to the stopped state illustrated in  FIGS. 6A through 6C , by driving the stepping motor  19  in the opposite direction from the running operations. 
     The control circuit  312  drives the stepping motor  19  in the first direction from the state after having ended running illustrated in  FIGS. 12A through 12C  to the state immediately after ending running illustrated in  FIGS. 11A through 11C  by step driving, and rotates the cam gear  15  in the clockwise direction. 
     Thereafter, the control circuit  312  drives the stepping motor  19  in the first direction from the state immediately after ending running illustrated in  FIGS. 11A through 11C  to the state of having started running illustrated in  FIGS. 9A through 9C  by feedback driving of which the advance angle is larger, and rotates the cam gear  15  in the clockwise direction. 
     At this time, the shutter blades  4 ,  5 , and  6  move from the closed state to the opened state. The output of the photointerrupter  22  changes from H to L, and subsequently changes from L to H, and further changes from H to L. 
     In the returning operations of the shutter unit  100 , when the stepping motor  19  is driving in the first direction by feedback driving of which the advance angle is larger, The control circuit  312  starts deceleration of the stepping motor  19 . Specifically, when the stepping motor  19  is driving in the first direction by feedback driving of which the advance angle is larger, The driving direction of the stepping motor  19  is reversed at the timing of the output of the photointerrupter  22  going from H to L the second time. That is to say, when the output of the photointerrupter  22  changes form H to L the second time, the control circuit  312  drives the stepping motor  19  in the second direction by feedback driving of which the advance angle is larger. Driving the stepping motor  19  in the second direction means that the cam gear  15  is rotated in the counterclockwise direction, but the inertial force of rotating the cam gear  15  in the clockwise direction is large, so the cam gear  15  rotates in the clockwise direction as it is gradually decelerated. 
     In the present embodiment, the speed of the follower pin  11   c  sliding through the cam region  15   a - 5  of the cam groove  15   a  is reduced. This enables wear to be reduced in the cam region  15   a - 5  that affects the running precision. 
     Thereafter, the control circuit  312  drives the stepping motor  19  in the first direction by step driving while decelerating and rotates the cam gear  15  in the clockwise direction, from the state of having started running, illustrated in  FIGS. 9A through 9C , to the stopped state illustrated in  FIGS. 6A through 6C . 
     In the returning operations of the shutter unit  100 , the stepping motor  19  is driven in the first direction from the state of having started running, illustrated in  FIGS. 9A through 9C , by step driving, and when the follower pin  11   c  enters the recess  15   a - 1 , control is performed to stop the stepping motor  19 . That is to say, in the returning operations of the shutter unit  100 , the running standby state illustrated in  FIGS. 7A through 7C  does not occur. 
     The shutter unit  100  is returned to the stopped state illustrated in  FIGS. 6A through 6C  by these returning operations. 
     Still Image Recording Operations of Camera Body  101   
       FIGS. 13 through 18  are timing charts for describing still image recording operations of the camera body  101 . 
       FIG. 13  is a timing chart illustrating still image recording operations in a case where a live-view mode has been selected by the mode dial  169 . 
     Upon the live-view mode having been selected by the mode dial  169 , the system control unit  153  controls the mirror control unit  161  to bring the mirror unit, that was in a mirror-down state, to a mirror-up state. Subsequently, the system control unit  153  causes the imaging device  116  to start sequential readout operations, and performs sequential display of subject images on the image display unit  160 . 
     At timing A 1  in  FIG. 13 , when the release button  168  is lightly pressed and the first switch (SW 1 ) turns on, the system control unit  153  controls the control circuit  312 . The control circuit  312  drives the stepping motor  19  in the first direction by feedback driving of which the advance angle is smaller via the drive circuit  313 . Accordingly, the stepping motor  19  rotates the cam gear  15  in the clockwise direction, and the shutter unit  100  is made to operate from the stopped state illustrated in  FIGS. 6A through 6C  to the running standby state illustrated in  FIGS. 7A through 7C . 
     When the shutter unit  100  is in the running standby state illustrated in  FIGS. 7A through 7C , at timing B 1  in  FIG. 13  the control circuit  312  applies holding electricity to the stepping motor  19  via the drive circuit  313 . Accordingly, the cam gear  15  can be stopped in a state with the driving spring  18  charged. 
     When the release button  168  is pressed deeply and the second switch (SW 2 ) turns on, the charges of the entire face of the imaging device  116  are reset. Thereafter, the imaging device  116  starts the electronic first curtain run from the timing D 1  in  FIG. 13 , where charges are accumulated one line at a time. 
     When the set exposure time elapses from starting of the electronic first curtain run, at timing C 1  in  FIG. 13  the control circuit  312  drives the stepping motor  19  in the second direction by step driving via the drive circuit  313 . Accordingly, the stepping motor  19  rotates the cam gear  15  in the counterclockwise direction, and the shutter unit  100  is made to operate from the running standby state illustrated in  FIGS. 7A through 7C  to the free-running state illustrated in  FIGS. 8A through 8C . 
     During the time from the shutter unit  100  going from the running standby state illustrated in  FIGS. 7A through 7C  to the free-running state illustrated in  FIGS. 8A through 8C , the cam gear  15  rotates in the counterclockwise direction due to the combined force of the driving force of the stepping motor  19  and the biasing force of the driving spring  18 . 
     Step driving of the stepping motor  19  is performed until the shutter unit  100  goes to the state of having started running, illustrated in  FIGS. 9A through 9C . During the time from the shutter unit  100  going from the free-running state illustrated in  FIGS. 8A through 8C  to the state of having started running, illustrated in  FIGS. 9A through 9C , the cam gear  15  rotates in the counterclockwise direction by the driving force of the stepping motor  19 . The shutter blades  4 ,  5 , and  6  maintain the opened state where the apertures  1   a  and  8   a  are opened, until immediate prior to the state of having started running, illustrated in  FIGS. 9A through 9C . 
     The stepping motor  19  is driven in the second direction by step driving by a predetermined number of driving pulses from the timing C 1  in  FIG. 13 . Thereafter, at timing E 1  in  FIG. 13 , the control circuit  312  drives the stepping motor  19  in the second direction by feedback driving of which the advance angle is larger, via the drive circuit  313 . 
     Accordingly, the stepping motor  19  rotates the cam gear  15  in the counterclockwise direction, and the shutter unit  100  is made to operate from the state of having started running, illustrated in  FIGS. 9A through 9C , to the state immediately before ending running, illustrated in  FIGS. 10A through 10C . The shutter blades  4 ,  5 , and  6  begin to close the apertures  1   a  and  8   a  from the state of having started running illustrated in  FIGS. 9A through 9C , and the shutter blades  4 ,  5 , and  6  are in a state of immediately prior to closing the apertures  1   a  and  8   a  at the state immediately before ending running illustrated in  FIGS. 10A through 10C . 
     When the cam gear  15  is rotated in the counterclockwise direction after the shutter unit  100  going to the state of having started running, illustrated in  FIGS. 9A through 9C , the output of the photointerrupter  22  goes from L to H. The output of the photointerrupter  22  is input to the control circuit  312  of the stepping motor  19 . 
     The control circuit  312  obtains the elapsed time tp 1  (see  FIG. 13 ) from having switched to the feedback driving of which the advance angle is larger till the output of the photointerrupter  22  changes from L to H. 
     The elapsed time tp 1  of the shutter unit  100  is measured for each running operation in the present embodiment, regardless of the mode that has been set, and the measured elapsed time tp 1  is compared with the reference time tp 1 ref held at the control circuit  312 . The reference time tp 1 ref is set at the time of manufacturing the shutter unit  100 . The timing C 1  in  FIG. 13  is adjusted based on the difference between the measured elapsed time tp 1  and the reference time tp 1 ref. The timing C 1  in  FIG. 13  is equivalent to an example of a driving start timing in the present invention. 
     The time T illustrated in  FIG. 13  is the time from the stepping motor  19  starting to drive in the second direction by step driving till the shutter blades  4 ,  5 , and  6  start to close the apertures  1   a    8   a.  The time T is set at the time of manufacturing the shutter unit  100 , but may change due to reasons such as wear of the cam groove  15   a  after prolonged use, or the like. In the present embodiment, the timing C 1  in  FIG. 13  is adjusted in the next running operation, based on the difference between the elapsed time tp 1  and the reference time tp 1 ref. Accordingly, change in the time T can be corrected. For example, in a case where the measured elapsed time tp 1  is 2 ms longer than the reference time tp 1 ref, adjustment is performed in the next running operation to make the timing C 1  in  FIG. 13  2 ms earlier. 
     Thereafter, when the shutter unit  100  is in the state immediately before ending running, illustrated in  FIGS. 10A through 10C , the output of the photointerrupter  22  changes from H to L at a timing F 1  in  FIG. 13 . 
     The control circuit  312  obtains the elapsed time tp 2  (see  FIG. 13 ) from the output of the photointerrupter  22  changing from L to H, till the output of the photointerrupter  22  changes from H to L. 
     The elapsed time tp 2  of the shutter unit  100  is measured for each running operation in the present embodiment, regardless of the mode that has been set, and the measured elapsed time tp 2  is compared with the reference time tp 2 ref held at the control circuit  312 . The reference time tp 2 ref is set at the time of manufacturing the shutter unit  100 . The driving speed of the stepping motor  19  from timing E 1  to timing G 1  in  FIG. 13  is adjusted based on the difference between the measured elapsed time tp 2  and the reference time tp 2 ref. 
     The driving speed of the stepping motor  19  from timing E 1  to timing G 1  in  FIG. 13  is set at the time of manufacturing the shutter unit  100 , but may change due to reasons such as wear of the cam groove  15   a  after prolonged use, or the like. In the present embodiment, the driving pulse frequency for the stepping motor  19  from timing E 1  to timing G 1  in  FIG. 13  is adjusted in the next running operation, based on the difference between the measured elapsed time tp 2  and the reference time tp 2 ref. Accordingly, the driving speed of the stepping motor  19  from timing E 1  to timing G 1  in  FIG. 13  can be corrected. For example, in a case where the measured elapsed time tp 2  is 2 ms longer than the reference time tp 2 ref, adjustment is performed in the next running operation to raise the driving pulse frequency for the stepping motor  19  from timing E 1  to timing G 1  in  FIG. 13 . Accordingly, the driving speed of the stepping motor  19  is raised. 
     When the stepping motor  19  is driven in the second direction by feedback driving of which the advance angle is larger, by a predetermined number of pulses from the timing E 1  in  FIG. 13 , the shutter unit  100  is in the state immediately after ending running, illustrated in  FIGS. 11A through 11C . When the shutter unit  100  goes to the state immediately after ending running, the output of the photointerrupter  22  changes from L to H. 
     When the shutter unit  100  goes to the state immediately after ending running, at timing G 1  in  FIG. 13  the control circuit  312  drives the stepping motor  19  in the first direction by step driving via the drive circuit  313 . Driving the stepping motor  19  in the first direction means that the cam gear  15  is rotated in the clockwise direction, but the inertial force of rotating the cam gear  15  in the counterclockwise direction is large, so the cam gear  15  rotates in the counterclockwise direction as it is gradually decelerated. The control circuit  312  causing reverse driving of the stepping motor  19  in this way is equivalent to an example of deceleration control in the present invention. 
     When the stepping motor  19  is driven in the first direction by step driving, by a predetermined number of driving pulses from the timing G 1  in  FIG. 13 , the shutter unit  100  is in the state after having ended running, illustrated in  FIGS. 12A through 12C . When the stepping motor  19  is driven in the first direction by step driving, by a predetermined number of driving pulses from the timing G 1  in  FIG. 13 , at timing H 1  in  FIG. 13  the control circuit  312  controls the drive circuit  313  and stops the stepping motor  19 . 
     At timing I 1  in  FIG. 13 , the control circuit  312  drives the stepping motor  19  in the first direction by step driving via the drive circuit  313 . Accordingly, the shutter unit  100  is made to operate from the state after having ended running, illustrated in  FIGS. 12A through 12C  to the state immediately after ending running, illustrated in  FIGS. 11A through 11C . 
     When the stepping motor  19  is driven in the first direction by step driving, by a predetermined number of driving pulses from the timing I 1  in  FIG. 13 , the shutter unit  100  is in the state immediately after ending running, illustrated in  FIGS. 11A through 11C . At timing J 1  in FIG.  13 , the control circuit  312  drives the stepping motor  19  in the first direction by the feedback driving of which the advance angle is larger, via the drive circuit  313 . Accordingly, the shutter unit  100  is made to operate from the state immediately after ending running, illustrated in  FIGS. 11A through 11C , to the state of having started running, illustrated in  FIGS. 9A through 9C . At timing J 1  in  FIG. 13 , the output of the photointerrupter  22  changes from H to L, and at timing K 1  in  FIG. 13 , the output of the photointerrupter  22  changes from L to H. 
     When the stepping motor  19  is driven in the first direction by feedback driving of which the advance angle is larger, by a predetermined number of driving pulses from the timing J 1  in  FIG. 13 , the shutter unit  100  is in the state of having started running, illustrated in  FIGS. 9A through 9C . At timing L 1  in  FIG. 13 , the control circuit  312  drives the stepping motor  19  in the first direction by step driving, via the drive circuit  313 , and at timing M 1  in  FIG. 13  controls the stepping motor  19  to stop. Accordingly, the shutter unit  100  is made to operate from the state of having started running, illustrated in  FIGS. 9A through 9C , to the stopped state illustrated in  FIGS. 6A through 6C . In the returning operations of the shutter unit  100 , the stepping motor  19  is controlled to stop when the follower pin  11   c  is in a state of entering the recess  15   a - 1 , without charging the driving spring  18 . 
     Thus, in a case where the live view mode has been selected, the shutter unit  100  is controlled to operate from the stopped state illustrated in  FIGS. 6A through 6C  to the running standby state illustrated in  FIGS. 7A through 7C  at the timing of the first switch (SW 1 ) turning on. At the timing of second switch (SW 2 ) turning on, the driving spring  18  is already charged, so the release time lag can be reduced by the amount of time necessary to charge the driving spring  18 . 
       FIG. 14  is a timing chart illustrating still image recording operations in a case where an optical viewfinder mode has been selected by the mode dial  169 , and where a quiet mirror driving mode has also been selected. 
     Upon the mode being changed by the mode dial  169  from the live-view mode to the optical viewfinder mode, the system control unit  153  ends sequential readout operations of the imaging device  116 . Thereafter, the system control unit  153  controls the mirror control unit  161  bring the mirror unit, that was in the mirror-up state, to the mirror-down state. 
     At timing A 2  in  FIG. 14 , when the release button  168  is deeply pressed and the second switch (SW 2 ) turns on, the system control unit  153  controls the control circuit  312 . The control circuit  312  drives the stepping motor  19  in the first direction by feedback driving of which the advance angle is smaller via the drive circuit  313 . Accordingly, the stepping motor  19  rotates the cam gear  15  in the clockwise direction, and the shutter unit  100  is made to operate from the stopped state illustrated in  FIGS. 6A through 6C  to the running standby state illustrated in  FIGS. 7A through 7C . 
     When the shutter unit  100  is in the running standby state illustrated in  FIGS. 7A through 7C , at timing B 2  in  FIG. 14  the control circuit  312  applies holding electricity to the stepping motor  19  via the drive circuit  313 . Accordingly, the cam gear  15  can be stopped in a state with the driving spring  18  charged. At this time, the system control unit  153  controls the mirror control unit  161  to bring the bring the mirror unit, that was in the mirror-down state, to the mirror-up state. 
     When the second switch (SW 2 ) turns on, the charges of the entire face of the imaging device  116  are reset at timing A 2  in  FIG. 14 . Thereafter, the imaging device  116  starts the electronic first curtain run from the timing D 2  in  FIG. 14 , where charges are accumulated one line at a time. 
     When the set exposure time elapses from starting of the electronic first curtain run, at timing C 2  in  FIG. 14  the control circuit  312  drives the stepping motor  19  in the second direction by step driving, via the drive circuit  313 . Accordingly, the stepping motor  19  rotates the cam gear  15  in the counterclockwise direction, and the shutter unit  100  is made to operate from the running standby state illustrated in  FIGS. 7A through 7C  to the free-running state illustrated in  FIGS. 8A through 8C . 
     The stepping motor  19  is driven in the second direction by step driving by a predetermined number of driving pulses from the timing C 2  in  FIG. 14 . Thereafter, at timing E 2  in  FIG. 14 , the control circuit  312  drives the stepping motor  19  in the second direction by feedback driving of which the advance angle is larger, via the drive circuit  313 . 
     Accordingly, the stepping motor  19  rotates the cam gear  15  in the counterclockwise direction, and the shutter unit  100  is made to operate from immediately before the state of having started running, illustrated in  FIGS. 9A through 9C , to the state immediately before ending running, illustrated in  FIGS. 10A through 10C . The shutter blades  4 ,  5 , and  6  begin to close the apertures  1   a  and  8   a  from the state of having started running illustrated in  FIGS. 9A through 9C , and the shutter blades  4 ,  5 , and  6  are in a state of immediately prior to closing the apertures  1   a  and  8   a  at the state immediately before ending running illustrated in  FIGS. 10A through 10C . 
     In a case where the quiet mirror driving mode has been selected, the driving pulse frequency for driving the stepping motor  19  from the state of having started running, illustrated in  FIGS. 9A through 9C , to the state immediately after ending running, illustrated in  FIGS. 11A through 11C , is set lower than a case where the high-speed mirror driving mode has been selected. Accordingly, the speed of the shutter blades  4 ,  5 , and  6  closing the apertures  1   a  and  8   a  is lower, and the operating sound of the shutter unit  100  can be made to be smaller. 
     When the cam gear  15  is rotated in the counterclockwise direction after the shutter unit  100  going to the state of having started running, illustrated in  FIGS. 9A through 9C , the output of the photointerrupter  22  changes from L to H. The output of the photointerrupter  22  is input to the control circuit  312  of the stepping motor  19 . 
     The control circuit  312  obtains the elapsed time tp 1  (see  FIG. 14 ) from having switched to the feedback driving of which the advance angle is larger till the output of the photointerrupter  22  changes from L to H. The timing C 1  in  FIG. 14  is adjusted based on the difference between the measured elapsed time tp 1  and the reference time tp 1 ref. The detailed adjustment method is as described above. 
     Thereafter, when the shutter unit  100  is in the state immediately before ending running, illustrated in  FIGS. 10A through 10C , the output of the photointerrupter  22  changes from H to L at timing F 2  in  FIG. 14 . 
     The control circuit  312  obtains the elapsed time tp 2  (see  FIG. 14 ) from the output of the photointerrupter  22  changing from L to H, till the output of the photointerrupter  22  changes from H to L. The driving speed of the stepping motor  19  from timing E 2  to timing G 2  in  FIG. 14  is adjusted based on the difference between the measured elapsed time tp 2  and the reference time tp 2 ref. 
     When the stepping motor  19  is driven in the second direction by feedback driving of which the advance angle is larger, by a predetermined number of driving pulses from the timing E 2  in  FIG. 14 , the shutter unit  100  is in the state immediately after ending running, illustrated in  FIGS. 11A through 11C . When the shutter unit  100  goes to the state immediately after ending running, the output of the photointerrupter  22  changes from L to H. 
     When the shutter unit  100  goes to the state immediately after ending running, at timing G 2  in  FIG. 14  the control circuit  312  drives the stepping motor  19  in the first direction by step driving via the drive circuit  313 . Driving the stepping motor  19  in the first direction means that the cam gear  15  is rotated in the clockwise direction, but the inertial force of rotating the cam gear  15  in the counterclockwise direction is large, so the cam gear  15  rotates in the counterclockwise direction as it is gradually decelerated. 
     When the stepping motor  19  is driven in the first direction by step driving, by a predetermined number of driving pulses from the timing G 2  in  FIG. 14 , the shutter unit  100  is in the state after having ended running, illustrated in  FIGS. 12A through 12C . When the stepping motor  19  is driven in the first direction by step driving, by a predetermined number of driving pulses from the timing G 2  in  FIG. 14 , at timing H 2  in  FIG. 14  the control circuit  312  controls the drive circuit  313  and stops the stepping motor  19 . At this time, the system control unit  153  controls the mirror control unit  161  to bring the mirror unit, in the mirror-up state, to the mirror-down state. 
     At timing  12  in  FIG. 14 , the control circuit  312  drives the stepping motor  19  in the first direction by step driving via the drive circuit  313 . Accordingly, the shutter unit  100  is made to operate from the state after having ended running, illustrated in  FIGS. 12A through 12C  to the state immediately after ending running, illustrated in  FIGS. 11A through 11C . 
     When the stepping motor  19  is driven in the first direction by step driving, by a predetermined number of driving pulses from the timing I 2  in  FIG. 14 , the shutter unit  100  is in the state immediately after ending running, illustrated in  FIGS. 11A through 11C . At timing J 2  in FIG.  14 , the control circuit  312  drives the stepping motor  19  in the first direction by the feedback driving of which the advance angle is larger, via the drive circuit  313 . Accordingly, the shutter unit  100  is made to operate from the state immediately after ending running, illustrated in  FIGS. 11A through 11C , to the state of having started running, illustrated in  FIGS. 9A through 9C . At timing J 2  in  FIG. 14 , the output of the photointerrupter  22  changes from H to L, and at timing K 2  in  FIG. 14 , the output of the photointerrupter  22  changes from L to H. 
     When the stepping motor  19  is driven in the first direction by feedback driving of which the advance angle is larger, by a predetermined number of driving pulses from the timing J 2  in  FIG. 14 , the shutter unit  100  is in the state of having started running, illustrated in  FIGS. 9A through 9C . At timing L 2  in  FIG. 14 , the control circuit  312  drives the stepping motor  19  in the first direction by step driving via the drive circuit  313 , and at timing M 2  in  FIG. 14  controls the stepping motor  19  to stop. Accordingly, the shutter unit  100  is made to operate from the state of having started running, illustrated in  FIGS. 9A through 9C , to the stopped state illustrated in  FIGS. 6A through 6C . In the returning operations of the shutter unit  100 , the stepping motor  19  is controlled to stop when the follower pin  11   c  is in a state of entering the recess  15   a - 1 , without charging the driving spring  18 . 
     Thus, in a case where the quiet mirror driving mode has been selected, the shutter unit  100  is controlled to operate from the stopped state illustrated in  FIGS. 6A through 6C  to the running standby state illustrated in  FIGS. 7A through 7C  at the timing of the second switch (SW 2 ) turning on. The driving spring  18  is charged after the second switch (SW 2 ) turns on, so the release time lag is longer by the amount of time necessary to charge the driving spring  18 . However, the amount of time of applying holding electricity to the stepping motor  19  in the state of the driving spring  18  being charged can be reduced, so the electric power consumption of the camera body  101  can be reduced. 
       FIG. 15  is a timing chart illustrating still image recording operations in a case where an optical viewfinder mode has been selected by the mode dial  169 , and where a high-speed mirror driving mode has also been selected. 
     Upon the mode being changed by the mode dial  169  from the live-view mode to the optical viewfinder mode, the system control unit  153  ends sequential readout operations of the imaging device  116 . Thereafter, the system control unit  153  controls the mirror control unit  161  bring the mirror unit, that was in the mirror-up state, to the mirror-down state. 
     At timing A 3  in  FIG. 15 , when the release button  168  is lightly pressed and the first switch (SW 1 ) turns on, the system control unit  153  controls the control circuit  312 . The control circuit  312  drives the stepping motor  19  in the first direction by feedback driving of which the advance angle is smaller via the drive circuit  313 . Accordingly, the stepping motor  19  rotates the cam gear  15  in the clockwise direction, and the shutter unit  100  is made to operate from the stopped state illustrated in  FIGS. 6A through 6C  to the running standby state illustrated in  FIGS. 7A through 7C . 
     When the shutter unit  100  is in the running standby state illustrated in  FIGS. 7A through 7C , at timing B 3  in  FIG. 15  the control circuit  312  applies holding electricity to the stepping motor  19  via the drive circuit  313 . Accordingly, the cam gear  15  can be stopped in a state with the driving spring  18  charged. 
     When the release button  168  is deeply pressed and the second switch (SW 2 ) turns on, the charges of the entire face of the imaging device  116  are reset. Thereafter, the imaging device  116  starts the electronic first curtain run from the timing D 3  in  FIG. 15 , where charges are accumulated one line at a time. When the second switch (SW 2 ) turns on, the system control unit  153  controls the mirror control unit  161  to bring the mirror unit, in the mirror-down state, to the mirror-up state. 
     The operations at timing C 3  through timing M 3  in  FIG. 15  are the same as the operations at timing C 2  through timing M 2  in  FIG. 14 , so description will be omitted. 
     Thus, in a case where the high-speed mirror driving mode has been selected, the shutter unit  100  is controlled to operate from the stopped state illustrated in  FIGS. 6A through 6C  to the running standby state illustrated in  FIGS. 7A through 7C  at the timing of the first switch (SW 1 ) turning on. At the timing of second switch (SW 2 ) turning on, the driving spring  18  is already charged, so the release time lag can be reduced by the amount of time necessary to charge the driving spring  18 . 
       FIG. 16  is a timing chart illustrating still image recording operations in a case where bulb exposure mode has been selected by the mode dial  169 .  FIG. 16  illustrates an example of bulb exposure operations in the optical viewfinder mode, regarding bulb exposure where the exposure time is 30 seconds or shorter. 
     At timing A 4  in  FIG. 16 , when the release button  168  is deeply pressed and the second switch (SW 2 ) turns on, the system control unit  153  controls the control circuit  312 . The control circuit  312  drives the stepping motor  19  in the first direction by feedback driving of which the advance angle is smaller via the drive circuit  313 . Accordingly, the stepping motor  19  rotates the cam gear  15  in the clockwise direction, and the shutter unit  100  is made to operate from the stopped state illustrated in  FIGS. 6A through 6C  to the running standby state illustrated in  FIGS. 7A through 7C . 
     When the shutter unit  100  is in the running standby state illustrated in  FIGS. 7A through 7C , at timing B 4  in  FIG. 16  the control circuit  312  applies holding electricity to the stepping motor  19  via the drive circuit  313 . Accordingly, the cam gear  15  can be stopped in a state with the driving spring  18  charged. At this time, the system control unit  153  controls the mirror control unit  161  to bring the mirror unit, that was in the mirror-down state, to the mirror-upstate. 
     When the second switch (SW 2 ) turns on, the charges of the entire face of the imaging device  116  are reset at timing A 4  in  FIG. 16 . Thereafter, the imaging device  116  starts the electronic first curtain run from the timing D 4  in  FIG. 16 , where charges are accumulated one line at a time. 
     The system control unit  153  measures the time elapsed after the second switch (SW 2 ) turns on, and determines whether or not the elapsed time has exceeded a predetermined amount of time after the second switch (SW 2 ) has turned on. The predetermined time here is set so that the bulb exposure time is 30 seconds. The predetermined time is set based on the exposure time, and the amount of time necessary for operations of the shutter unit  100  and imaging device  116 . In a case where determination is made that the elapsed time has exceeded a predetermined amount of time after the second switch (SW 2 ) has turned on, the bulb exposure time exceeds 30 seconds. 
     In a case where the second switch (SW 2 ) turns off within a predetermined amount of time of elapsed time after the second switch (SW 2 ) has turned on, at timing C 4  in  FIG. 16  the control circuit  312  drives the stepping motor  19  in the second direction by step driving, via the drive circuit  313 . That is to say, in a case where the second switch (SW 2 ) turns off at a time where the bulb exposure time is 30 seconds or shorter, at timing C 4  in  FIG. 16  the control circuit  312  drives the stepping motor  19  in the second direction by step driving. Accordingly, the stepping motor  19  rotates the cam gear  15  in the counterclockwise direction, and the shutter unit  100  is made to operate from the running standby state illustrated in  FIGS. 7A through 7C  to the free-running state illustrated in  FIGS. 8A through 8C . 
     The operations at timing C 4  through timing M 4  in  FIG. 16  are the same as the operations at timing C 2  through timing M 2  in  FIG. 14 , so description will be omitted. 
     As described above, when performing bulb exposure where the exposure time is 30 seconds or shorter, the drive circuit  313  continues to apply holding electricity to the stepping motor  19  until the second switch (SW 2 ) turns off. 
       FIG. 17  is a timing chart illustrating still image recording operations in a case where bulb exposure mode has been selected by the mode dial  169 .  FIG. 17  illustrates an example of bulb exposure operations in the optical viewfinder mode, regarding bulb exposure where the exposure time exceeds 30 seconds. 
     At timing A 5  in  FIG. 17 , when the release button  168  is deeply pressed and the second switch (SW 2 ) turns on, the system control unit  153  controls the control circuit  312 . The control circuit  312  drives the stepping motor  19  in the first direction by feedback driving of which the advance angle is smaller via the drive circuit  313 . Accordingly, the stepping motor  19  rotates the cam gear  15  in the clockwise direction, and the shutter unit  100  is made to operate from the stopped state illustrated in  FIGS. 6A through 6C  to the running standby state illustrated in  FIGS. 7A through 7C . 
     When the shutter unit  100  is in the running standby state illustrated in  FIGS. 7A through 7C , at timing B 5  in  FIG. 17  the control circuit  312  applies holding electricity to the stepping motor  19  via the drive circuit  313 . Accordingly, the cam gear  15  can be stopped in a state with the driving spring  18  charged. At this time, the system control unit  153  controls the mirror control unit  161  to bring the mirror unit, that was in the mirror-down state, to the mirror-up state. 
     When the second switch (SW 2 ) turns on, the charges of the entire face of the imaging device  116  are reset at timing A 5  in  FIG. 17 . Thereafter, the imaging device  116  starts the electronic first curtain run from the timing D 5  in  FIG. 17 , where charges are accumulated one line at a time. 
     When the system control unit  153  determines that the amount of elapsed time after the second switch (SW 2 ) has turned on has exceeded the predetermined time, at timing N 5  in  FIG. 17 , the control circuit  312  drives the stepping motor  19  in the second direction by step driving, via the drive circuit  313 . Accordingly, the stepping motor  19  rotates the cam gear  15  in the counterclockwise direction, and the shutter unit  100  is made to operate from the running standby state illustrated in  FIGS. 7A through 7C  to the stopped state illustrated in  FIGS. 6A through 6C . That is to say, the charge of the driving spring  18  is disengaged, and the stepping motor  19  is stopped. 
     When the second switch (SW 2 ) turns off thereafter, at timing C 5  in  FIG. 17  the control circuit  312  drives the stepping motor  19  in the second direction by step driving, via the drive circuit  313 . Accordingly, the stepping motor  19  rotates the cam gear  15  in the counterclockwise direction, and the shutter unit  100  is made to operate from the stopped state illustrated in  FIGS. 6A through 6C  to the running standby state illustrated in  FIGS. 8A through 8C . 
     The operations at timing E 5  through timing M 5  in  FIG. 17  are the same as the operations at timing C 2  through timing M 2  in  FIG. 14 , so description will be omitted. 
     As described above, when performing bulb exposure where the exposure time exceeds 30 seconds, charging of the driving spring  18  is disengaged while exposing. After the charging of the driving spring  18  is disengaged, the drive circuit  313  does not apply holding electricity to the stepping motor  19 , so the power consumption of the camera body  101  can be reduced. In bulb exposure where the exposure time exceeds 30 seconds, the biasing force of the driving spring  18  is not used at the time of the shutter blades  4 ,  5 , and  6  starting to close the apertures  1   a  and  8   a.  However, in a case where the exposure time exceeds 30 seconds, lower running speed and running stability of the shutter blades  4 ,  5 , and  6  do not affect the image quality. 
       FIG. 18  is a timing chart illustrating still image recording operations in a case where a long exposure mode has been selected by the mode dial  169 , and also an exposure time exceeding 30 seconds has been set by the settings dial  170 . Note that a timing chart describing still image recording operations in a case where an exposure time of 30 seconds or shorter has been set (predetermined exposure time or shorter) is the same as the timing charts described with reference to  FIGS. 13 through 15 . When the long exposure mode is selected, the shutter unit  100  is moved from the opened state to the closed state, after a predetermined amount of time has elapsed from the second switch (SW 2 ) turning on. The predetermined time is set based on the exposure time, and the amount of time necessary for operations of the shutter unit  100  and imaging device  116 . 
     At timing A 6  in  FIG. 18 , when the release button  168  is deeply pressed and the second switch (SW 2 ) turns on, the charges of the entire face of the imaging device  116  are reset. Thereafter, the imaging device  116  starts the electronic first curtain run from the timing D 6  in  FIG. 18 , where charges are accumulated one line at a time. When the second switch (SW 2 ) turns on, the system control unit  153  controls the mirror control unit  161  to bring the mirror unit, in the mirror-down state, to the mirror-up state. 
     When the set exposure time has elapsed from the start of the electronic first curtain run, at timing C 6  in  FIG. 18  the control circuit  312  drives the stepping motor  19  in the second direction by step driving, via the drive circuit  313 . Accordingly, the stepping motor  19  rotates the cam gear  15  in the counterclockwise direction, and the shutter unit  100  is made to operate from the stopped state illustrated in  FIGS. 6A through 6C  to the free-running state illustrated in  FIGS. 8A through 8C . 
     The operations at timing E 6  through timing M 6  in  FIG. 18  are the same as the operations at timing E 2  through timing M 2  in  FIG. 14 , so description will be omitted. 
     As described above, when long exposure where the exposure time exceeds 30 seconds, biasing force of the driving spring  18  is not used at the time of the shutter blades  4 ,  5 , and  6  starting to close the apertures  1   a  and  8   a.  Accordingly, the drive circuit  313  does not apply holding electricity to the stepping motor  19 , so electric power consumption of the camera body  101  can be reduced. In a case where the exposure time exceeds 30 seconds, lower running speed and running stability of the shutter blades  4 ,  5 , and  6  do not affect the image quality. 
     Environmental Correction of Shutter Unit  100   
     The operation characteristics of the shutter unit  100  performing running operations change depending on the orientation of the camera body  101  and the ambient temperature around the shutter unit  100 . The control circuit  312  according to the present embodiment acquires information relating to the orientation of the camera body  101  and the environment in which the shutter unit  100  is used, such as the ambient temperature around the shutter unit  100 . The control circuit  312  then corrects the operation characteristics of the shutter unit  100  based on the acquired information. 
     First, operation characteristics correction of the shutter unit  100  according to the orientation of the camera body  101  will be described. 
     When the orientation of the camera body  101  changes, the direction of gravity acting on the camera body  101  changes, and the direction of gravity acting on the shutter unit  100  also changes. Depending on the direction of gravity acting on the shutter unit  100 , the gravity acting on the shutter unit  100  impedes the shutter blades  4 ,  5 , and  6  from moving from the opened state to the closed state. When the shutter unit  100  performs running operations, the shutter blades  4 ,  5 , and  6  move from up to down in the present embodiment, as illustrated in  FIGS. 6 through 12C . Even in a state where the shutter unit  100  is attached to the camera body  101 , the shutter blades  4 ,  5 , and  6  still move from up to down when the shutter unit  100  performs running operations. 
     If the camera body  101  is in the normal position (horizontal position), the direction in which the center of gravity of the shutter blades  4 ,  5 , and  6  and blade arms  2  and  3  moves generally matches the direction of gravity acting on the camera body  101  when the shutter unit  100  performs running operations. Accordingly, in this orientation, the gravity acting on the shutter unit  100  does not impede the running operations of the shutter unit  100 . 
     If the camera body  101  is in an inverse position where the camera body  101  is upside-down, the direction in which the center of gravity of the shutter blades  4 ,  5 , and  6  and blade arms  2  and  3  moves generally opposes the direction of gravity acting on the camera body  101 . Accordingly, in this orientation, the gravity acting on the shutter unit  100  impedes the running operations of the shutter unit  100 . 
     Driving members of the shutter unit  100  such as the stepping motor  19  and cam gear  15  and so forth are attached to the camera body  101  so as to be situated at a grip portion side. 
     In a case where the camera body  101  is put in the vertical position so that the grip portion of the camera body  101  is above, the driving members such as the stepping motor  19  and cam gear  15  and so forth are situated above the apertures  1   a  and  8   a.    
     In this orientation, the blade arms  2  and  3  are above the shutter blades  4 ,  5 , and  6 . Accordingly, in the initial running operations of the shutter blades  4 ,  5 , and  6  and blade arms  2  and  3 , the direction in which the center of gravity of the shutter blades  4 ,  5 , and  6  and blade arms  2  and  3  moves generally matches the direction of gravity acting on the camera body  101 . Accordingly, in this orientation, the gravity acting on the shutter unit  100  does not impede the running operations of the shutter unit  100 . 
     In a case where the camera body  101  is put in the vertical position so that the grip portion of the camera body  101  is below, the driving members such as the stepping motor  19  and cam gear  15  and so forth are situated below the apertures  1   a  and  8   a.  In this orientation, the blade arms  2  and  3  are below the shutter blades  4 ,  5 , and  6 . Accordingly, in the initial running operations of the shutter blades  4 ,  5 , and  6  and blade arms  2  and  3 , the direction in which the center of gravity of the shutter blades  4 ,  5 , and  6  and blade arms  2  and  3  moves generally opposes the direction of gravity acting on the camera body  101 . Accordingly, in this orientation, the gravity acting on the shutter unit  100  impedes the running operations of the shutter unit  100 . 
     In an orientation where the interchangeable lens  201  mounted to the camera body  101  faces upwards or downwards, the sliding resistance between the shutter blades  4 ,  5 , and  6  and blade arms  2  and  3 , and the shutter base plate  1  and cover plate  8  increase due to the gravity acting on the camera body  101 . Accordingly, in this orientation, the gravity acting on the shutter unit  100  impedes the running operations of the shutter unit  100 . 
     These points are taken into consideration in the present embodiment to correct the operation characteristics of the shutter unit  100  according to the orientation of the camera body  101 . 
     The orientation sensor  172  according to the present embodiment detects the direction of gravity acting on the camera body  101  at a predetermined cycle, and outputs to the control circuit  312 . The control circuit  312  determines the orientation of the camera body  101  based on the information regarding direction of gravity. Each time the orientation of the camera body  101  is determined, the control circuit  312  executes correction of operation characteristics of the shutter unit  100 , based on the table illustrated in  FIG. 19A . 
       FIG. 19A  is an example of a table for correcting operation characteristics of the shutter unit  100  depending on the orientation of the camera body  101 . 
     The timings (C 1  through C 6 ) of driving the stepping motor  19  from the running standby state illustrated in  FIGS. 7A through 7C  is adjusted depending on the orientation of the camera body  101 , as illustrated in  FIG. 19A . The timings (C 1  through C 6 ) of driving the stepping motor  19  from the running standby state illustrated in  FIGS. 7A through 7C  are equivalent to examples of a driving start timing in the present invention. 
     The driving pulses for driving the stepping motor  19  from the state of having started running, illustrated in  FIGS. 9A through 9C , to the state immediately after ending running, illustrated in  FIGS. 11A through 11C , are adjusted according to the orientation of the camera body  101 , as illustrated in  FIG. 19A . 
     In a case where determination is made that the camera body  101  is in the normal position, the gravity acting on the shutter unit  100  does not impede the running operations of the shutter unit  100 . Accordingly, the timing for driving the stepping motor  19  from the running standby state illustrated in  FIGS. 7A through 7C  is not adjusted, and neither is the frequency of driving pulses for driving the stepping motor  19  from the state of having started running illustrated in  FIGS. 9A through 9C , to the state immediately after ending running illustrated in  FIGS. 11A through 11C , adjusted. 
     In a case where determination is made that the camera body  101  is in the inverse position, the timing to start running is delayed for the shutter blades  4 ,  5 , and  6  and blade arms  2  and  3  by the gravity acting on the camera body  101 , and the running speed of the shutter blades  4 ,  5 , and  6  and blade arms  2  and  3  falls. Accordingly, the timing for driving the stepping motor  19  from the running standby state illustrated in  FIGS. 7A through 7C  is quickened by a time T 11 , and the frequency of the driving pulses for driving the stepping motor  19  from the state of having started running illustrated in  FIGS. 9A through 9C , to the state immediately after ending running illustrated in  FIGS. 11A through 11C , are raised by a frequency F 11 . 
     In a case where determination is made that the orientation of the grip portion of the camera body  101  is up, the gravity acting on the shutter unit  100  does not impede the running operations of the shutter unit  100 . Accordingly, the timing for driving the stepping motor  19  from the running standby state illustrated in  FIGS. 7A through 7C  is not adjusted, and neither is the frequency of the driving pulses for driving the stepping motor  19  from the state of having started running illustrated in  FIGS. 9A through 9C , to the state immediately after ending running illustrated in  FIGS. 11A through 11C , adjusted. 
     In a case where determination is made that the orientation of the grip portion of the camera body  101  is down, the timing to start running is delayed for the shutter blades  4 ,  5 , and  6  and blade arms  2  and  3  by the gravity acting on the camera body  101 . However, in this case, the running speed of the shutter blades  4 ,  5 , and  6  and blade arms  2  and  3  does not fall. Accordingly, the timing for driving the stepping motor  19  from the running standby state illustrated in  FIGS. 7A through 7C  is quickened by a time T 13 , but the frequency of the driving pulses for driving the stepping motor  19  from the state of having started running illustrated in  FIGS. 9A through 9C , to the state immediately after ending running illustrated in  FIGS. 11A through 11C , is not adjusted. 
     In a case where determination is made that orientation is such that the mounted interchangeable lens  201  is facing upwards, the timing to start running is delayed for the shutter blades  4 ,  5 , and  6  and blade arms  2  and  3  by the gravity acting on camera body  101 . In this case, the running speed of the shutter blades  4 ,  5 , and  6  and blade arms  2  and  3  falls. The timing for driving the stepping motor  19  from the running standby state illustrated in  FIGS. 7A through 7C  is quickened by a time T 14 , and the frequency of the driving pulses for driving the stepping motor  19  from the state of having started running illustrated in  FIGS. 9A through 9C , to the state immediately after ending running illustrated in  FIGS. 11A through 11C , is raised by a frequency F 14 . 
     In a case where determination is made that orientation is such that the mounted interchangeable lens  201  is facing upwards, the timing to start running is delayed for the shutter blades  4 ,  5 , and  6  and blade arms  2  and  3  by the gravity acting on the camera body  101 . Moreover, in this case, the running speed of the shutter blades  4 ,  5 , and  6  and blade arms  2  and  3  falls. Accordingly, the timing for driving the stepping motor  19  from the running standby state illustrated in  FIGS. 7A through 7C  is quickened by a time T 15 , and the frequency of the driving pulses for driving the stepping motor  19  from the state of having started running illustrated in  FIGS. 9A through 9C , to the state immediately after ending running illustrated in  FIGS. 11A through 11C , is raised by a frequency F 15 . 
     Next, correction of the operation characteristics of the shutter unit  100  according to the ambient temperature around the shutter unit  100  will be described. 
     When the ambient temperature around the shutter unit  100  is a low temperature, the lubricant such a grease used for the sliding portions of the shutter unit  100  hardens, and resistance due to the lubricant increases. Accordingly, the timing to start running is delayed for the shutter blades  4 ,  5 , and  6  and blade arms  2  and  3  by the gravity acting on the shutter unit  100 , and the running speed of the shutter blades  4 ,  5 , and  6  and blade arms  2  and  3  falls. 
     On the other hand, when the ambient temperature around the shutter unit  100  is a high temperature, the lubricant such a grease used for the sliding portions of the shutter unit  100  softens, and resistance due to the lubricant decreases, but precision of the shape of parts formed of synthetic resin deteriorates due to thermal expansion. Accordingly, the timing to start running is delayed for the shutter blades  4 ,  5 , and  6  and blade arms  2  and  3 , but the running speed of the shutter blades  4 ,  5 , and  6  and blade arms  2  and  3  increases due to the softening of the lubricant. 
     These points are taken into consideration in the present embodiment to correct the operation characteristics of the shutter unit  100  according to the ambient temperature around the shutter unit  100 . 
     The temperature sensor  171  detects the ambient temperature around the shutter unit  100  at a predetermined cycle and outputs to the control circuit  312 , in the present embodiment. The control circuit  312  corrects the operation characteristics of the shutter unit  100  based on the table illustrated in  FIG. 19B , each time the ambient temperature around the shutter unit  100  is detected. 
       FIG. 19B  is an example of a table for correcting operation characteristics of the shutter unit  100  depending on the ambient temperature around the shutter unit  100 . 
     In a case where the ambient temperature around the shutter unit  100 , detected by the temperature sensor  171  is in a range of 0° or higher but lower than 40°, the ambient temperature around the shutter unit  100  is within a designed standard temperature range. Accordingly, the timing for driving the stepping motor  19  from the running standby state illustrated in  FIGS. 7A through 7C  is not adjusted, and neither is the frequency of the driving pulses for driving the stepping motor  19  from the state of having started running illustrated in  FIGS. 9A through 9C , to the state immediately after ending running illustrated in  FIGS. 11A through 11C , adjusted. 
     In a case where the ambient temperature around the shutter unit  100 , detected by the temperature sensor  171  is below 0°, the shutter unit  100  is in a low temperature environment below the predetermined temperature range. Accordingly, the timing for driving the stepping motor  19  from the running standby state illustrated in  FIGS. 7A through 7C  is quickened by a time T 21 , and the frequency of the driving pulses for driving the stepping motor  19  from the state of having started running illustrated in  FIGS. 9A through 9C , to the state immediately after ending running illustrated in  FIGS. 11A through 11C , is raised by a frequency F 21 . 
     In a case where the ambient temperature around the shutter unit  100 , detected by the temperature sensor  171  exceeds 40°, the shutter unit  100  is in a high temperature environment exceeding the predetermined temperature range. Accordingly, the timing for driving the stepping motor  19  from the running standby state illustrated in  FIGS. 7A through 7C  is quickened by a time T 22 , and the frequency of the driving pulses for driving the stepping motor  19  from the state of having started running illustrated in  FIGS. 9A through 9C , to the state immediately after ending running illustrated in  FIGS. 11A through 11C , is reduced by a frequency F 22 . 
     Although a preferred embodiment of the present invention has been described, the present invention is not restricted to these embodiments, and various modifications and alterations may be made within the scope of the essence thereof. 
     According to the present invention, electric power consumption of the imaging apparatus can be reduced. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     This application claims the benefit of International Patent Application No. PCT/JP2015/057514, filed Mar. 13, 2015, which is hereby incorporated by reference herein in its entirety.