Patent Publication Number: US-6910814-B2

Title: Digital camera system

Description:
This application claims benefits of Japanese Application No. 2003-168383 filed in Japan on Jun. 12, 2003, the contents of which are incorporated by this reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a digital camera system having an interchangeable lens and a camera body to which the interchangeable lens can be attached. 
   2. Related Art Statement 
   An image pickup device in a recent digital camera has a narrow dynamic range. Furthermore, it is difficult to receive and performs photoelectric conversion on light emitted diagonally at a predetermined angle or larger. Therefore, the influence of the decrease in amount of peripheral light is more significant than a silver halide camera. In order to solve the problem, Japanese Unexamined Patent Application Publication No. 6-37289 discloses a technology for increasing an opening diameter of a micro-lens on the periphery of an image pickup device. According to the disclosed technology, the opening diameter of a micro-lens of an image pickup device is increased continuously toward the periphery. 
   In order to reduce the influence of the decrease in amount of peripheral light, Japanese Unexamined Patent Application Publication No. 5-130469 discloses a technology for forming a light path of an image pickup device such that the vignetting of a light beam can be prevented in a light path from a photographic lens to the image pickup device. A video camera disclosed in the patent document has a larger opening in an image frame plate so as to prevent vignetting, and the strength of the image frame plate in a diagonal direction of the opening is reinforced by a projection. 
   On the other hand, a lens interchangeable, single-lens reflex type digital camera system has been disclosed. For example, an electronic camera disclosed in Japanese Unexamined Patent Application Publication No. 11-88783 relates to a single-lens reflex type electronic camera having a solid-state imaging device such as a CCD in a film opening by using the body of a conventional silver halide camera. 
   SUMMARY OF THE INVENTION 
   A digital camera system according to the present invention has a predetermined image circle. The digital camera system includes an interchangeable lens having a lens side mount portion for attaching the interchangeable lens to a camera body and a lens side opening portion provided in the lens mount portion through which luminous flux can pass for forming an image in the image circle and allowing the forming of an image in the image circle, and a camera body having an image pickup device having an imaging range with the aspect ratio of 4:3 on an imaging surface within the image circle, a body side mount portion located at a position apart from the imaging surface by a predetermined distance and a body side opening portion provided in the body side mount portion for allowing luminous flux from the interchangeable lens to pass through. In this case, the size of the body side opening portion is equal to or larger than the square formed by connecting ends of segments tilted by an angle θ with respect to an optical axis diagonally from four corners of the imaging range and extended to the body side opening portion, and the angle θ satisfies:
 
12 degrees≦0. 
 
   A camera body according to the present invention of a digital camera to which an interchangeable lens is removably mounted, includes an image pickup device having an imaging surface of an imaging range with a predetermined aspect ratio, and a mount portion to which the interchangeable lens is mounted, the mount portion having an opening portion for allowing luminous flux from the interchangeable lens to pass through, being located at a position apart from the imaging surface by a predetermined distance. In this case, the size of the opening portion is equal to or larger than the square formed by connecting ends of segments tilted by an angle θ with respect to an optical axis diagonally from four corners of the imaging range and extended to the opening portion, and the angle θ satisfies:
 
12 degrees≦0. 
 
   Another digital camera system according to the present invention has a predetermined image circle. The digital camera system includes an interchangeable lens, which can form an image within the image circle, the lens having a lens side mount portion for mounting the interchangeable lens to a camera body and a lens side opening portion provided in the lens side mount portion for allowing luminous flux for forming an image in the image circle to pass through, and a camera body having an image pickup device having an imaging surface, a body side mount portion provided at a position apart from the imaging surface by a predetermined distance, and a body side opening portion provided in the body side mount portion, for allowing luminous flux from the interchangeable lens to pass through. In this case, the body side opening portion satisfies:
 
 Dm/Di≧ 1.8 
         where the minimum circle diameter including the opening portion is Dm and the diameter of the image circle is Di.       

   A digital camera body according to the invention to which an interchangeable lens having a predetermined image circle can be removably mounted, the digital camera body including an image pickup device having an imaging surface of an imaging range with a predetermined aspect ratio, a mount portion to which the interchangeable lens is mounted, the mount portion being located at a position apart from the imaging surface by a predetermined distance, and an opening portion provided in the mount portion, for allowing luminous flux from the interchangeable lens to pass through. In this case, the size of the opening portion is equal to or larger than the circumscribed circle of the square formed by connecting ends of segments tilted by a predetermined angle with respect to an optical axis diagonally from four corners of the imaging range and extended to the opening portion and satisfies:
 
 Dm/Di≧ 1.8 
 
where the minimum circle diameter including the opening portion is Dm and the diameter of the image circle is Di.
 
   An interchangeable lens according to the present invention is removably mounted to a digital camera body. The interchangeable lens includes a mount portion for mounting to the digital camera body, and an opening portion provided in the mount portion, for allowing luminous flux to pass through. In this case,
 
 Dm 1/ Dc≧ 1.8 
 
is satisfied where the diameter of the circumscribed diameter of the imaging range of the digital camera body is Dc and the minimum circle diameter including the opening portion is Dm1.
 
   Another digital camera system according to the present invention has a predetermined image circle. The digital camera system includes interchangeable lenses, which can form an image within the image circle, each of the lenses having a lens side mount portion for mounting the interchangeable lens to a camera body, and a lens side opening portion provided in the lens side mount portion for allowing luminous flux for forming an image within the image circle to pass through, and a camera body having an image pickup device having an imaging range with the aspect ratio of 4:3 on an imaging surface within the image circle, a body side mount portion provided at a position apart from the imaging surface by a predetermined distance and a body side opening portion provided in the mount portion for allowing luminous flux from the interchangeable lens to pass through. In this case, the lens side opening portion of an interchangeable lens having the widest outermost light beam of an exit luminous flux among the interchangeable lenses has a size equal to or larger than the size of the square formed by connecting ends of a first plane formed by tilting the long side of the imaging range by a predetermined angle θ 1  apart with respect to an optical axis and extending the long side to the lens side opening portion and a second plane formed by tilting the short side of the imaging range by a predetermined angle θ 2  apart with respect to the optical axis and extending the short side to the lens side opening portion. In this case, the angles θ 1  and θ 2  satisfy:
 
10 degrees  23  θ1 and 8 degrees≦θ2. 
 
   Another digital camera system according to the present invention has a predetermined image circle. The digital camera system includes an interchangeable lens, which can form an image within the image circle, the lens having a lens side mount portion for mounting the interchangeable lens to the camera body, and a lens side opening portion provided in the lens side mount portion for allowing luminous flux for forming an image in the image circle to pass through, and a camera body having an image pickup device having an imaging range with the aspect ratio of 4:3 on the imaging surface within the image circle, a body side mount portion provided at a position apart from the imaging surface by a predetermined distance and a body side opening portion provided in the mount portion for allowing luminous flux from the interchangeable lens to pass through. In this case, the body side opening portion has a size equal to or larger than the size of the square formed by connecting ends of a first plane formed by tilting the long side of the imaging range by a predetermined angle apart with respect to an optical axis and extending the long side to the body side opening portion and a second plane formed by tilting the short side of the imaging range by a predetermined angle apart with respect to the optical axis and extending the short side to the body side opening portion, wherein, when luminous flux of a main light beam parallel to the optical axis enters to the periphery of the imaging range, the luminous flux equal to F No. 3 can be guided. 
   The other features and advantages of the present invention will be apparent from descriptions below. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective diagram (including a partial section view) of a lens replaceable single-lens reflex type digital camera in a digital camera system according to a first embodiment of the invention; 
       FIG. 2  is a perspective diagram of a digital camera body of the digital camera in  FIG. 1 ; 
       FIG. 3  is a vertical section diagram of a mount portion, mirror box portion and imaging unit where an interchangeable lens is attached to the camera body of the digital camera in  FIG. 1 ; 
       FIG. 4  is an exploded perspective diagram around the mount portion of the camera body in  FIG. 1 ; 
       FIG. 5  is a light beam diagram showing the emission of an object luminous flux captured from an interchangeable lens barrel to an image pickup device in the digital camera in  FIG. 1 ; 
       FIG. 6  is a graph showing a relationship of a luminous flux angle θ incident on a photoelectric conversion surface of an image pickup device and F number of an interchangeable lens in the digital camera in  FIG. 1 ; 
       FIG. 7  is a graph showing mount diameters Dn for F numbers of an interchangeable lens in the digital camera in  FIG. 1  by using FBs as parameters; 
       FIG. 8A  is a diagram showing a longitudinal section (section in X-direction) of a photoelectric conversion surface where a center luminous flux and peripheral luminous flux through a wide angle interchangeable lens barrel attached to the digital camera in  FIG. 1  are emitted to the photoelectric conversion surface (image forming surface); 
       FIG. 8B  shows a latitudinal section (section in Y-direction) of a photoelectric conversion surface where a center luminous flux and peripheral luminous flux through a wide angle interchangeable lens barrel attached to the digital camera in  FIG. 1  are emitted to the photoelectric conversion surface (image forming surface); 
       FIG. 9A  is a diagram showing a longitudinal section (section in XZ-direction) of a photoelectric conversion surface where a center luminous flux and peripheral luminous flux through a replacement telephoto lens barrel attached to the digital camera in  FIG. 1  are emitted to the photoelectric conversion surface (image forming surface); 
       FIG. 9B  is a diagram showing a latitudinal section (section in YZ-direction) of a photoelectric conversion surface where a center luminous flux and peripheral luminous flux through a replacement telephoto lens barrel attached to the digital camera in  FIG. 1  are emitted to the photoelectric conversion surface (image forming surface); 
       FIG. 10  is a diagram showing an effective screen range (effective imaging range) and recording screen range (imaging and recording screen) of a photoelectric conversion surface of an image pickup device in the digital camera in FIG.  1  and image circles corresponding to the ranges; 
       FIG. 11  is a light beam diagram showing a relationship of a mount opening and the circumscribed circle with respect to an imaging range inscribing a reference image circle of the image pickup device in the digital camera in  FIG. 1 ; 
       FIG. 12  is a light beam diagram showing a relationship between an image circle circumscribing an imaging range of an image pickup device applied in a digital camera according to a second embodiment of the invention and a circumscribed circle of a mount opening; 
       FIG. 13A  shows a light beam diagram of a section along a ZX surface (horizontal surface) between a photoelectric conversion surface of the image pickup device and the mount opening portion in the digital camera in  FIG. 12 ; 
       FIG. 13B  shows a light beam diagram of a section along a ZY surface (vertical surface) between a photoelectric conversion surface of the image pickup device and the mount opening portion in the digital camera in  FIG. 12 ; and 
       FIG. 14  is a diagram showing an imaging range of a 4/3 type image pickup device and the image circle on an imaging range of a square type image pickup device applied in a digital camera according to a third embodiment of the invention. 
   

   DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
   Embodiments of the invention will be described with reference to drawings. 
     FIG. 1  is a perspective diagram (including a partial section view) of a lens replaceable single-lens reflex type digital camera in a digital camera system according to a first embodiment of the invention.  FIG. 2  is a perspective diagram of a digital camera body of the digital camera.  FIG. 3  is a vertical section diagram of a mount portion, mirror box portion and imaging unit where an interchangeable lens is attached to the camera body of the digital camera.  FIG. 4  is an exploded perspective diagram around the mount portion of the camera body. 
   A digital camera  1  of a digital camera system according to this embodiment includes a digital camera body and multiple kinds of interchangeable lens, which can be attached to the camera body and has unique opening shapes of a mount portion and mirror box portion corresponding to a contained image pickup device. Before the description of the opening shape, internal constructions of a digital camera body (called camera body hereinafter)  11  and interchangeable lens barrel  12  as an interchangeable lens will be described with reference to  FIGS. 1  to  4 . 
   The interchangeable lens barrel  12  is a lens barrel containing multiple kinds of photographic optical system  12   a  having various kinds of focal distances as shown in  FIGS. 5 and 6 , which will be described later. The interchangeable lens barrel  12  has a lens side mount portion  37 , which can be attached to the body side mount portion  47 , which will be described later, of the camera body  11 . 
   The camera body  11  is a so-called single-lens reflex type camera body including various components provided inside the camera body portion  11   a  and having a body side mount portion in the front of the surface such that the lens barrel  12  for holding a photographic optical system  12   a  can be removably attached. In other words, the substantial center portion of the front side of the camera body portion  11   a  has an exposure opening of a predetermined size, which can guide object luminous flux into the camera body portion  11   a . A body side mount portion  47  is provided on the periphery of the exposure opening. 
   A more detailed construction of the camera body  11  will be described. First of all, various operation members for operating the camera body portion  11   a , such as a release button  17  for generating instruction signals for starting a photographic operation, are provided at a predetermined position of the upper surface portion or back surface portion of the camera body  11   a.    
   The camera body portion  11   a  has, at predetermined positions, a front plate  41 , a body side mount portion  47 , a mirror box  42 , a finder  13 , a shutter portion  14 , an imaging unit  15  and multiple circuit substrates including a main circuit substrate  16 . The front plane  41  has a body side opening portion  41   a  in the front of the surface side of the camera body portion  11   a . The body side mount portion  47  is located on the front surface portion  41   b  of the front plane  41 . The mirror box  42  is fixed behind the mount portion of the front plane  41 . The finder  13  is provided for forming a desired object image, which is formed by the photographic optical system  12   a , at a predetermined position different from the position on the photoelectric conversion surface  27   a , which is an imaging surface of the image pickup device  27 . The finder  13  is a so-called observation optical system. The shutter portion  14  is supported by a projection  42   f  behind the mirror box  42  and includes a shutter mechanism for controlling the time for irradiating object luminous flux to a photoelectric conversion surface of the image pickup device  27 . The imaging unit  15  is a unit fixed and held behind the shutter portion  14  by the projection  41   f  of the front plane  41 . The imaging unit  15  includes the image pickup device  27  for obtaining object imaging signals from object light through the imaging optical system  12   a . Various electric members of electric circuits such as an image signal processing circuit for performing various kinds of signal processing on the image signals obtained by the image pickup device  27  are implemented on the multiple circuit substrates such as main circuit substrate  16 . A dust-preventive filter  21  is provided in the front of the surface of the imaging unit  15 . The dust-preventive filter  21  prevents adherence of dust to the photoelectric conversion surface of the image pickup device. 
   The mirror box  42  has a mirror box opening portion  42   a  and a space behind the mirror box opening portion  42   a . The mirror box opening portion  42   a  pivotally supports a reflector  13   b  and allows the passage of object luminous flux from the photographic optical system  12   a  without vignetting of the luminous flux for forming an image on the photoelectric conversion surface  27   a  of the image pickup device  27 . 
   The reflector  13   b  lies in the space behind opening portion  42   a  and can pivotably move between a reflecting (dotted-line) position for reflecting incident luminous flux to the finder  13  side and a turnout (solid-line) position turning out from the reflecting position. 
   The finder  13  has the reflector  13   b , a pentaprism  13   a  and an eyepiece  13   c . The reflector  13   b  is arranged to guide am object luminous flux through the photographic optical system  12   a  by bending the optical axis of the object luminous flux to the observation optical system side. The pentaprism  13   a  receives luminous flux emitted from the reflector  13   b  and forms an erect image. The eyepiece  13   c  forms an image best suitable for enlarging and observing an image formed by the pentaprism  13   a.    
   The reflector  13   b , as set forth above, moves between the turnout position away from an optical axis O of the photographic optical system  12   a  and a predetermined position on the optical axis. Normally, the reflector  13   b  is located at a predetermined angle, such as 45 degrees, with respect to the halo on the optical axis of the photographic optical system  12   a . Thus, when the camera  1  is at the normal state, the optical axis of the object luminous flux having passed through the photographic optical system  12   a  is bent by the reflector  13   b  and is reflected to the pentaprism  13   a  side above the reflector  13   b.    
   On the other hand, while the camera is performing a photographic operation and during the actual exposure operation, the reflector  13   b  moves from the optical path of the photographic optical system  12   a  to the aforesaid predetermined turnout position. Thus, the object luminous flux is guided to the image pickup device side and forms an image on the photoelectric conversion surface. 
   The shutter portion  14  is similar to those generally used in a conventional camera, such as a focal plane type shutter mechanism and a driving circuit for controlling operations of the shutter mechanism. 
   The imaging unit  15  includes the image pickup device  27 , an image pickup device fixing plate  28 , an optical low-pass filter (called LPF hereinafter)  25 , a low-pass filter receiving member  26 , an image pickup device storage case member  24  (called CCD case  24  hereinafter), a dust-preventive filter receiving member  23 , the dust-preventive filter  21 , a piezoelectric element  22  and a press member  20 . The image pickup device  27  constituted by a CCD for obtaining image signals corresponding to the light irradiated onto the photoelectric conversion surface of the image pickup device  27  through the photographic optical system  12   a  as shown in FIG.  3  and so on. The image pickup device fixing plate  28  is constituted by a: thin-plate like member for fixing and supporting the image pickup device  27 . The optical LPF  25  is an optical element on the photoelectric conversion surface of the image pickup device  27 , for removing high frequency components from an object luminous flux irradiated through the photographic optical system  12   a . The low-pass filter receiving member  26  is constituted by an elastic member substantially in a frame shape and is provided on the periphery between the optical LPF  25  and the image pickup device  27 . The CCD case  24  stores, fixes and holds the image pickup device  27  and supports the optical LPF  25  by closely abutting to the periphery and the vicinity. A predetermined position of the CCD case  24  is closely in close contact with the dust-preventive filter receiving member  23 . The dust-preventive filter receiving member  23  is provided in the front of the surface side of the CCD case  24  and is in close contact with the periphery or the vicinity. The dust-preventive filter  21  is a dust-preventive member supported by the dust-preventive filter receiving member  23  and faces toward the optical LPF  25  at a position spaced apart from the optical LPF  25  by a predetermined distance in the front of the surface side of the optical LPF  25  on the photoelectric conversion surface side of the image pickup device  27 . The piezoelectric element  22  is provided on the periphery of the dust-preventive filter  21  and removes dust by giving a predetermined amount of vibration to the dust-preventive filter  21 . The press member  20  is constituted by an elastic body for connecting, fixing and holding the dust-preventive filter  21  to the dust-preventive filter receiving member  23  in an air-tight manner. 
   The image pickup device  27  performs photoelectric conversion processing on object luminous flux received by the photoelectric conversion surface  27   a  of the image pickup device  27  through the photographic optical system  12   a . Thus, the image pickup device  27  can obtain image signals corresponding to the object image on the photoelectric conversion surface. The image pickup device  27  may be a 4/3 type charge-coupled device or the like. In this case, the term “4/3 type” refers to the size of the image pickup device, and a 4/3 type image pickup device has an image circle with the diameter of about 21.2 to 25 mm. 
   The image pickup device  27  is implemented at a predetermined position on the main circuit substrate  16  through the image pickup device fixing plate  28 . An image signal processing circuit and work memory, not shown, are implemented together on the main circuit substrate  16 . Thus, output signals from the image pickup device  27 , that is, image signals obtained through optoelectric processing are transmitted to the image signal processing circuit. A protection glass (not shown for simplicity) is attached in front of the photoelectric conversion surface of the image pickup device  27 . 
   The signal processing performed in the image signal processing circuit includes various kinds of signal processing such as processing for converting image signals obtained from the image pickup device  27  to signals suitable for recording. In this case, the image signals correspond to the image formed on the optoelectric surface of the image pickup device  27  by the photographic optical system  12   a  held within the lens barrel  12  attached to the body side mount portion  47 . These kinds of signal processing are the same as processing normally performed in a general digital camera for handling electronic image signals. 
   The optical LPF  25  is provided in the front of the surface side of the image pickup device  27  through the low-pass filter receiving member  26 . The optical LPF  25  is constituted by crystal, which is an optical element having a double refraction characteristic. The optical LPF  25  further contains an infrared absorbing glass. 
   The CCD case  24  covers the optical LPF  25 . The CCD case  24  has a rectangular opening substantially at the center. The optical LPF  25  and image pickup device  27  are provided in the opening from the back. A step  24   a  having a substantial L-shaped section is provided on the internal periphery on the back side of the opening. 
   As described above, the low-pass filter receiving member  26  constituted by an elastic member is provided between the optical LPF  25  and the image pickup device  27 . The low-pass filter receiving member  26  is provided at a position avoiding an effective range of the photoelectric conversion surface on the periphery of the front surface side of the image pickup device  27 . Furthermore, the low-pass filter receiving member  26  is abutted to the vicinity of the periphery of the back side of the optical LPF  25 . The optical LPF  25  and the image pickup device  27  are in constant contact with each other substantially in an air-tight manner. Thus, elastic force toward the optical axis by the low-pass filter receiving member  26  acts on the optical LPF  25 . 
   Then, the periphery of the front surface side of the optical LPF  25  is located so as to be in contact with the step  24   a  of the CCD case  24  substantially in an air-tight manner. Thus, the position in the optical axis direction of the optical LPF  25  is controlled against the elastic force by the low-pass filter receiving member  26  for attempting to move the optical LPF  25  toward the optical axis. 
   In other words, the optical LPF  25  laid within the opening of the CCD case  24  from the back surface side is positionally controlled by the step  24   a  in the optical axis direction. Thus, the optical LPF  25  is prevented from coming out from the inside of the CCD case  24  toward the front surface side. 
   In this way, after the optical LPF  25  is inserted from the back surface side into the opening of the CCD case  24 , the image pickup device  27  is located on the back surface side of the optical LPF  25 . In this case, the low-pass filter receiving member  26  is held at its periphery between the optical LPF  25  and the image pickup device  27 . 
   As described above, the image pickup device  27  is implemented on the main circuit substrate  16  through the image pickup device fixing plate  28 . The image pickup device fixing plate  28  is fixed through a spacer  28   a  with a screw into a screw hole from the back surface side of the CCD case  24 . The main circuit substrate  16  is fixed to the image pickup device fixing plate  28  with a screw through a spacer  16   a.    
   The dust-preventive filter receiving member  23  is fixed to the screw hole of the CCD case  24  in the front of the surface side of the CCD case  24  with a screw. A peripheral slot in a substantial ring shape is provided at a predetermined position in the front of the surface side on the periphery side of the CCD case  24 . On the other hand, a ring-shape projection to fit to the peripheral slot of the CCD case  24  is provided in a substantial-ring form at a predetermined position on the back surface side of the periphery side of the dust-preventive filter receiving member  23 . Therefore, when the ring-shape projection fits into the peripheral slot, the CCD case  24  and the dust-preventive filter receiving member  23  fit into each other substantially in an air-tight manner in a ring-shaped area, that is, in an area having the peripheral slot and the ring-shaped projection. 
   The dust-preventive filter  21  contains glass and has a circular or polygonal plate as a whole. An area extending at least from the center of the dust-preventive filter  21  to the edge is transparent. The transparent area faces toward the front surface side of the optical LPF  25  through a predetermined space. The dust-preventive filter  21  is fixed and is held by a press member such that the dust-preventive filter  21  can be associated with the dust-preventive filter receiving member  23  in an air-tight manner. The press member is constituted by an elastic body such as a flat spring. 
   The dust-preventive filter receiving member  23  has a circular or polygonal opening in the vicinity of the substantial center of the dust-preventive filter receiving member  23 . The opening is designed to be large enough for object luminous flux through the photographic optical system  12   a  to illuminate the photoelectric conversion surface of the image pickup device  27  at the back. 
   The body side mount portion  47  has a square body side mount opening portion  41   a , a body side mount plate  45 , a mount spring  46 , a contact spring holder  51 , a contact spring  53 , a mount contact frame  52 , and a mount contact pin  54 . The body side mount opening portion  41   a  is provided within the front surface portion  41   b  of the front plate  41 , as shown in  FIGS. 3 and 4 . The body side mount plate  45  and the mount spring  46  are fixed to the front surface portion  41   b . A mount flexible substrate (called FPC hereinafter)  55  is attached to the contact spring  53 . The mount contact spring  54  is a camera body side connecting terminal. The end of the mount FPC  55  is connected to a lens drive control portion and/or a power supply portion within the camera body  11 . 
   The body side mount plate  45  has a bayonet  45   a  on the internal periphery of the opening. The mount spring  46  has a spring portion  46   d . The body side mount plate  45  is fixed to the front plate  41  with the mount spring  46  being inserted on the back of the body side mount plate  45 , by screwing a screw  61  through a screw inserting hole  45   c  into an opening portion screw portion  41   c . A mount lock pin  44  is provided on the periphery of the front surface portion  41   b  of the front plate  41 . 
   Nine mount contact pins  54  are inserted to pin holes  52   c  of the mount contact frame  52 . The contact spring holder  51  is fixed to and is supported by the mount contact frame  52  by screwing the screw  62  into the screw hole  52   b  through a screw inserting hole  51   a . The fixed and supported mount contact pins  54  are forced, extended and held toward the front of the mount contact frame  52  by nine contact springs  53  attached to the contact spring holder  51 . 
   The mount contact frame  52  having the contact spring holder  51  is fixed outward under the square body side opening portion  41   a  by screwing screw  63  to the screw hole  41   d  through the screw inserting hole  52   a . Thus, the bottom part of the body side mount opening portion  41   a  can be obtained. When the mount contact frame  52  is attached, the mount contact pins  54  are provided in the form of a circular arc inside of the opening portion  45   a  of the body side mount plate  45  and under the body side opening portion  41   a.    
   On the other hand, as shown in  FIG. 3 , the lens side mount portion  37  of the interchangeable lens barrel  12  has a lens side mount opening portion  31   a  and a bayonet nails  31   b , which can associate with the bayonet  45   a  of the body side mount plate  45 . Furthermore, nine mount contacts  33  are provided in the form of a circular arc at the bottom of the lens side mount opening portion  31   a . The nine mount contacts  33  are lens side connecting terminals held by the terminal holder  32 . The mount contacts  33  are connected to the lens side FPC  34 . The lens side FPC  34  has a power supply line and/or an electric drive control line and is connected to a focus driving portion, for example, within the interchangeable lens barrel  12 . 
   In order to attach the interchangeable lens barrel  12  to the camera body  11  having the above-described construction, the lens side mount portion  37  of the interchangeable lens barrel  12  is rotationally fitted into the mount plate  45  of the body side mount portion  47 . Then, the bayonet nails  31   b  are associated therewith such that the lens can be attached. Under the lens-attached condition, the interchangeable lens barrel  12  is electrically connected to the drive control portion of the camera body  11  through the connecting terminal portion so as to allow the control for focus, zoom and iris driving. An object luminous flux enters to the finder  13  or the image pickup device  27  through the lens side mount opening portion  31   a  and the body side mount opening portion  41   a , and the object can be observed or be shot. 
   Here, the form of the mount opening of the lens mount portion  37  and/or the body side mount portion  47  for passing luminous flux and the form of luminous flux passing portion of the mirror box  42  will be described. 
   In the description below and the drawings, the direction along the optical axis O is the Z-direction. The object side (lens side) of the Z-direction is the front while the image pickup device side (image-forming side) is the back. The direction orthogonal to the optical axis O and along the longer side in the imaging range (photoelectric conversion surface) of the image pickup device is an X-direction (horizontal direction). The left and right are determined from the object viewpoint. The direction orthogonal to the optical axis O and along the shorter side of the imaging range (photoelectric conversion surface) of the image pickup device is a Y-direction (vertical direction). 
   In a digital camera system according to this embodiment, in order for object luminous flux captured by the interchangeable lens barrel  12  to enter to the periphery of the imaging range of the image pickup device  27 , the mount portion and the member, such as a mirror box, between the image pickup device and the lens must have openings. In other words, in order to guide light uniformly to the center and periphery of the image pickup device, the openings must have a form allowing the same luminous flux angle as the luminous flux angle of the luminous flux from the end to the center of the imaging range. In this case, as the degrees of the tilt of the main light beam of a luminous flux incident on the periphery to the optical axis increases, the size of the openings can be reduced. 
     FIG. 5  is a light beam diagram showing an entering state of an object luminous flux captured from the interchangeable lens barrel  12  to the image pickup device  27 . 
   As shown in  FIG. 5 , the object luminous flux entering from the exit pupil diameter D0 of the interchangeable lens barrel  12  and the center and peripheral luminous flux entering to the center and periphery of the optical axis O of the photoelectric conversion surface  27   a  on the imaging range of the image pickup device  27  have a luminous flux angle θ about the respective main light beams, where the luminous flux angle θ refers to an angle of one side of a luminous flux (that is, half angle). 
   In order to prevent a shortage in light amount of the periphery in the imaging range, the vignetting of the peripheral luminous flux must be prevented at the lens side mount opening portion  31   a  (having at least an opening range Rm mentioned later), the body side mount opening portion  41   a  (opening having the opening range equal to the opening range Rm mentioned later for preventing the vignetting of luminous flux passing therethrough) and a light passing portion of the mirror box  42 . At the limit of the longer focal distance side (Tele side), the photographic optical system  12   a  requires a shown lens side opening portion  31   a  because the main light beam of the peripheral luminous flux is parallel to the optical axis O. On the other hand, on the short focal distance side (Wide side) shorter than the long focal distance, the photographic optical system  12   a  requires an opening  31   a ′ narrower than the lens side opening portion  31   a  because the main light beam of the peripheral luminous flux is a light beam tilting toward the optical axis O. 
   In the photographic optical system  12   a , when an object distance is at infinity, the exit pupil position  12   a   0  of the exit pupil diameter D0 is spaced from the photoelectric conversion surface  27   a , which is at an image-forming position), by a focal distance f. The luminous flux angle θ is expressed by:
 
tan (θ)= D 0/(2× f )  EQ1 
 
The relationship of the exit pupil diameter D0, the focal distance f and F No. (the F-number) is:
 
 F No.=f/D 0 
 
Based on EQ1, the relationship between the luminous flux angle θ and the F-number is:
 
θ=tan −1 (1/(2 ×F No .))  EQ2 
 
     FIG. 6  is a graph showing a relationship between the luminous flux angle θ and the F-number (or Av value). In  FIG. 6 , when the slope of the main light beam is 5 degrees or 10 degrees, the luminous flux angle θ is an angle of the outer light beam of a peripheral luminous flux with respect to the optical axis O. The angle of the slope of the main light beam is plus in the counterclockwise direction in FIG.  5 . 
   The mount diameter Dm ( FIG. 11 ) of the mount portion (such as lens side opening portion  31   a  or the body side opening portion  41   a ) required at the position spaced from the imaging surface by a predetermined distance (flange back) FB with respect to an image circle (having a diameter Di, see  FIG. 11 ) including the imaging range of the photoelectric conversion surface  27   a  is expressed by:
 
 Dm=Di+ 2×FB×tan θ  EQ3 
 
or 
 
 Dm=Di+FB/F No.   EQ4 
 
   As described above, the image pickup device  27  is a 4/3 type CCD and has an imaging range of the photoelectric conversion surface  27   a  of 17.8 mm (long side)×13.4 mm (short side) with an aspect ratio of about 4:3 (where the imaging range corresponds to an effective pixel range L-w2×L-h2 mentioned later, see FIG.  10 ). The diameter Di2 of the image circle I-ce circumscribing the square imaging range is 22.28 mm. 
     FIG. 7  is a graph indicating mount diameters for F-numbers by using FBs as parameters when the value of the diameter Di2 is applied to the diameter Di of the image circle of the image pickup device  27  based on EQ4. 
   The luminous flux angle θ required for capturing an object bundle from an interchangeable lens depends on the intensity of the used lens in principle. In other words, as the intensity of the used lens increases (that is, as the F number decreases), the luminous flux angle θ must be increased. For example, in order to guide a luminous flux having the F No. 2.8 to the end of the image circle, the luminous flux angle θ is about 10 degrees. In order to guide a luminous flux having F No. 1.4, the luminous flux angle θ is about 20 degrees (FIG.  6 ). In this way, by increasing the luminous flux angle θ, the lens having larger intensity can be used. However, as shown in the graph, the relationship of the applicable F-numbers and luminous flux angles θ is not linear. Then, when a lens having a small F No. is used, the luminous flux angle θ must be rapidly increased. 
   Generally, the F No. of a wide angle lens is smaller while the F No. of a telephoto lens is larger. Generally, when a focal distance is about 50 mm, the F No. is about 1.4. When the focal distance is about 300 mm, the F No. is about 2 to 2.8. This is because, a telephoto lens is no longer practical when the F No. is small. 
   As described above, the main light beam of a peripheral luminous flux is not always parallel to the optical axis. Especially, when a wide-angle lens is used, the amount of the slope is increased. For example,  FIGS. 8 and 9  show a light beam diagrams of a wide-angle lens and a telephoto lens, respectively. 
     FIGS. 8A ,  8 B and  9 A,  9 B are diagrams showing states where the center luminous flux and peripheral luminous flux enter to the photoelectric conversion surface (Image-forming surface)  27   a  of an image pickup device.  FIGS. 8A ,  8 B is show a case where a wide angle interchangeable lens barrel (with f 12.55 mm and F No. 1.4) is attached.  FIGS. 9A ,  9 B show a case where a telephoto interchangeable lens barrel (with f 300 mm and F No. 2.8).  FIGS. 8A and 9A  show sections in a longer side direction (XY section) of the photoelectric conversion surface  27   a .  FIGS. 8B and 9B  show sections in a shorter side direction (YZ section) of the photoelectric conversion surface  27   a.    
   The angles α-w 1  and α-w 2  of inclination of the main light beam of a peripheral luminous flux by a wide-angle photographic optical system  12   a W shown in  FIGS. 8A and 8B  are about 5 degrees. The angles α-t 1  and α-t 2  of the main light beam of the peripheral luminous flux by a telephoto photographic optical system  12   a T shown in  FIGS. 9A and 9B  are smaller than the angles of inclination of the main light beam of the wide-angle photographic optical system  12   a W. 
   Based on this fact, no problems occur if the luminous flux angle θ is set to be compliant with the lens having an F No. 3 to 4 or below when the amount of inclination of the main light beam is zero. More preferably, the luminous flux angle θ is set to be compliant with the lens having the F No. 2 to 2.8 or below. 
   In order to satisfy the optical characteristic, the proper size of the camera body must be practically obtained while in consideration of the proper F-number. Therefore, the compliant F-number is applied from the viewpoint of the size of the camera body as described below. 
   In other words, the height of a camera body of a lens replaceable silver halide camera system is about 90 to 120 mm. The thickness is about 60 to 80 mm. That is, a size which is extremely larger than the height and the thickness is not practical. In order to obtain a height of about 90 to 100 mm, the mount opening diameter must be about 50 mm or below and preferably smaller than 45 mm. The diameter is desirably about 40 mm. In order to achieve the thickness of about 60 to 80 mm as described above, the flange back FB must be about 35 to 50 mm. 
   Apparently from the relationship between the mount opening diameter and the F number of the image pickup device  27  shown in  FIG. 7 , which is a 4/3 type CCD, when the size of the opening diameter is limited, the luminous flux angle θ must be set so as to have the compliant F number larger than F numbers 1.4 to 1.8 and more preferably F numbers 1.6 to 2.2. 
   In order to achieve the optical limitation and a practical body size, the luminous flux angle θ is preferably set to be compliant with the lens having F-numbers 1.4 to 4. More preferably, the luminous flux angle θ is set to be compliant with the lens having F-numbers 1.6 to 2.8. 
   Therefore, when the circle of the reference opening is a circle obtained by extending a predetermined image circle to the opening portion in a direction away from the optical axis O by a predetermined angle in accordance with the compliant F number as described above, the desired compliant F number can be obtained. 
   Since the real imaging range of the image pickup device  27  is rectangular, the required shape of the opening does not have to be circular. At least a square inscribing the reference opening is only required. Therefore, an opening is required having a size larger than the square formed by connecting ends of a segment extending to the opening portion in a direction away from the optical axis by a predetermined angle in accordance with the proper F number diagonally from the square of the imaging range. 
   According to this embodiment, the diameter Di of the image circle corresponding to the recording screen range is 21 to 23 mm or 21.6 to 22.7. The diagonal length of the recording range inscribing the image circle is about half (21.6 mm) of the diagonal line of a 135-format screen. In other words, when a lens having the focal distance of 50 mm is used in a digital camera according to this embodiment, the angle of view can be the same as the angle obtained when a lens having the focal distance of about 100 mm is used in a 135-format camera. Therefore, the correlation of the angle of view with respect to the 135-format camera can be realized only by doubling the focal distance of the lens. 
   The imaging range on the photoelectric conversion surface  27   a  of the image pickup device  27  is a screen with the aspect ratio of 4:3 inscribing the image circle. No practical problems occur when luminous flux from the lens can reach onto the recording screen range within the imaging range. However, an image circle larger than the image circle corresponding to the recording screen range to some extent is desirably set in consideration of errors occurring in pa manufacture and in assembly. 
     FIG. 10  is a diagram showing a valid screen range (valid imaging range) and recording screen range (imaging and recording range) in the photoelectric conversion surface  27   a  of the image pickup device  27  (see  FIG. 3 ) and image circles corresponding to the ranges. 
   In the image pickup device  27 , as shown in  FIG. 10 , a recording screen range L-w1×L-h1 must be smaller than a valid screen range L-w2×L-h2. The recording screen range L-w1×L-h1 is a range to be actually converted to electric signals as image information during image processing and to be captured. The valid screen range L-w2×L-h2 is an entirely shootable range of the image pickup device  27 . This is because the outer area around a required recording pixel (called peripheral pixel area hereinafter) is required for creating the recording pixel by the image pickup device  27 . Furthermore, due to the precision limits in dimension of the image pickup device  27  itself and positional errors in assembly of the image pickup device  27  to the camera body  11  through the image pickup device fixing plate  28  and the front plate  41 , the position of the optical axis O is displaced from the center of the valid screen range L-w2×L-h2 of the image pickup device  27 . In order to absorb the displaced amount, the valid screen range L-w2×L-h2 is taken larger than the recording screen range L-w1×L-h1 as described above. 
   The form of the opening must be determined so as to prevent vignetting of the object luminous flux in a range entering to the valid screen range L-w2×L-h2 as the imaging range, which is passing through the interchangeable lens barrel  12  and the camera body  11 . The decrease in light amount of peripheral light in the valid screen range L-w2×L-h2 must be prevented. 
   The circumscribed circle of the recording screen range L-w1×L-h1 is the recording screen image circle I-cr, and the diameter is Di1. The circumscribed circle of the valid screen range (imaging range) L-w2×L-h2 including the peripheral pixel area is a valid screen image circle (imaging range image circle) I-ce of the valid screen range (imaging range), and the diameter is Di2. In the real design, the valid screen image circle I-ce is slightly larger. The increased amount Δd is added to the diameter Di2 of the valid screen image circle I-ce, and the valid screen image circle I-ce is added to the recording screen image circle I-cr. Then, an image circle I-c 0  having a diameter Di3 can be obtained. By applying the imaging range of the image circle I-c 0 , the form of the openings can be set. More specifically, the image circle I-co having the increased amount Δd of about 1 mm is handled as a reference image circle corresponding to the recording screen range. However, in the description below, the form of openings are set by using the valid screen image circle I-ce as an imaging range image circle (which is a reference image circle I-c having the diameter Di mentioned below) and by using the valid screen range L-w2×L-h2 as an imaging range (imaging range Ri mentioned below). The size of the valid screen range (imaging range) L-w2×L-h2 is 17.8 mm×13.4 mm according to this embodiment. 
   The diameter Dm of the circumscribed circle Im for the square mount opening range Rm, which is a reference opening guided by a luminous flux angle θ of a predetermined half angle diagonally from the end of the imaging range Ri inscribing the reference image circle I-c is determined as follows. 
   In this case, the mount opening range Rm minimizes the size of the form of the lens side mount opening portion  31   a . In other words, the lens side mount opening portion  31   a  of the interchangeable lens having the maximum mount opening portion among interchangeable lenses of the camera system is set to be sufficient to cover at least the square of the mount opening range Rm (where the minimum mount opening range of the lens side mount opening portion  31   a  is Rm). The body side mount opening  41   a  is also set to at least the size of the square opening range Rm. Thus, the form of the opening prevents the vignetting of object luminous flux passing through the mount opening range Rm. 
   In order to guide a desired luminous flux to the periphery of the image pickup device, nothing should block the luminous flux from the exit pupil position of the optical system to the image pickup device. Therefore, the members provided between the exit pupil position to and the image pickup device also needs need openings. In other words, members, such as a mirror box, a body side mount, a lens side mount and a flare iris, provided between the exit pupil position and the image pickup device must have the opening range Rm in order to prevent the vignetting of object luminous flux. Since the camera system is lens-interchangeableable, the range of the opening on the camera body side must be set so as to handle the attachment of an interchangeable lens (called the maximum light beam interchangeable lens hereinafter) having the outermost light beam in exit light beams is the farthest from the optical axis among interchangeable lenses of the camera system. On the other hand, the opening range of the interchangeable lens side can be set in accordance with the outermost light beam of the exit light beams of each lens. In other words, the opening range can be smaller with an interchangeable lens having a narrower outermost light beam than that of the maximum light beam interchangeable lens. In this case, in the lens side mount portion, the forms of fitting portions of the mount, such as bayonet nails, relating to the mount to the camera body are common in all interchangeable lenses. 
     FIG. 11  is a light beam diagram showing a relationship between the mount opening range Rm and the circumscribed circle Im and the imaging range Ri inscribed in the reference image circle Ic. 
   As shown in  FIG. 11 , the mount opening range Rm giving the minimum opening of the lens side mount opening portion  31   a  is a square range obtained by connecting ends of four segments Sd extending to the position of the mount opening portion tilting outward and being spaced by a flange back FB with respect to the optical axis O diagonally from the square of the imaging range Ri. The predetermined luminous flux angle θd may be 12 to 14 degrees in order to satisfy the flange back FB and/or F number. 
   The body side opening  41   a  also has at least the size of the mount opening range Rm. Furthermore, in shooting, those elements blocking the object luminous flux (such as the reflector  13   b  and the shutter opening frame) are not positioned in the space enclosed by four planes of the four segments within the mirror box  42 . 
   In the camera body shown in  FIG. 2 , as shown in the section diagram in  FIG. 3 , the mirror box  42 , the front plate  41  and the body side mount portion  47  are located between the image pickup device  27  and the interchangeable lens  12 . Therefore, the opening portion of these members is formed so as to satisfy the mount opening range Rm at the position in the optical axis direction where the opening is located. 
   By setting the mount opening range Rm as described above, the interchangeable lens with the AV value of 2.5 to 2 becomes compliant even when the luminous flux having a main light beam parallel to the optical axis enters the end of the imaging surface. In other words, even when F No. 1.4 (AV value: 1) is used, the difference in light amount for the AV value of 1.5 to 1 only occurs between the center and the periphery. 
   As described above, the lens having a small F No. as described above is a wider angle lens. Therefore, the main light beam of peripheral luminous flux tilts by some degrees with respect to the optical axis. Therefore, the above-described difference in light amount does not actually occur. Like the lens shown in  FIGS. 8A ,  8 B, when the main light beam of the peripheral luminous flux tilts by about 5 degrees, the luminous flux of 1.4 to 1 in AV value can be guided to the periphery. In other words, with the interchangeable lens having F No. 1.4 only causes 0.4 or below in AV value between the center and the periphery, which is not a significant problem. On the other hand, even a brighter telephoto lens causing the main light beam of the peripheral luminous flux to be substantially parallel to the optical axis has F No. 2 to 2.8 (2 to 3 in AV value), which is not a practical problem. 
   The diameter Dm of the circumscribed circle Im having the mount opening range Rm, which is a reference opening here depends on the distance from the imaging surface to the opening. The diameter Di of the image circle Ic in view of the placement of the mirror box  42  having the reflector  13   b  between the image pickup device and the body mount desirably satisfies:
 
 Dm/Di≧ 1.8 
 
Thus, the turnout reflector  13   b  can be located outside of the inclined plane formed by facing segments Sd ( FIG. 11 ) connecting the imaging range between the body mount and the image pickup device and the mount opening. Furthermore, the inserted reflector  13   b , shutter  14  and various filters may be located between the body mount and the image pickup device.
 
   Furthermore, as described above, a body side mount contact pin  54  and lens side mount contact  33 , which are terminals for connecting the power supply line and the drive control signal line are provided in the body side mount portion  47  of the camera body  11  and the lens mount portion  37  of the interchangeable lens barrel  12 . The area for locating the connection terminal portions can be reduced in size by locating the connection terminal portions in a comb-shaped space area Tm ( FIG. 11 ) established between the square-shaped mount opening range Rm and the circumscribed circle Im. 
   The area for locating the connection terminal portions is not limited to the comb-shaped space area Tm shown in  FIG. 11  but may be an upper or left or right side horizontal comb space area. 
   As an example of a real typical value of the imaging portion and mount portion in the digital camera  1  according to the first embodiment, the image circle diameter Di in the range of 21.6 to 22.6 mm. The flange back (distance from the photoelectric conversion surface to the mount opening portion) FB is 40.2 mm. The imaging range (which is a valid pixel range with an aspect ration of about 4:3 on the photoelectric conversion surface) Lw×Lh (=the above-described Lw2×Lh2) is 17.8 mm×13.4 mm. 
   Next, a digital camera system according to a second embodiment of the invention will be described with reference to  FIGS. 12 and 13A  and  13 B. 
     FIG. 12  is a light beam diagram showing a relationship between an image circle circumscribing an imaging range of an image pickup device of a camera body applied in this embodiment and a circumscribed circle of a mount opening.  FIGS. 13A and 13B  are light beam diagrams between the photoelectric conversion surface of the image pickup device according to this embodiment and a mount opening portion.  FIG. 13A  shows a light beam diagram of a section along a ZX surface (horizontal surface).  FIG. 13B  is a light beam diagram of a section along a ZY surface (vertical surface). 
   An interchangeable lens type digital camera according to this embodiment is a digital camera having compliant F No. of a short side and long side of an imaging range different from those of the digital camera  1  according to the first embodiment. In the digital camera, a compliant F No. is set at the ends in the short and long side directions of the imaging range. The opening having a size equal to or larger than the size of the square is obtained by extending the ends in the short and long side directions from the short and long sides of the imaging range to the mount opening portion position in a direction away from the optical axis by a predetermined angle corresponding to the compliant F No. 
   The other constructions are similar to that of the digital camera  1  according to the first embodiment, and the same reference numerals are given to the same components hereinafter. 
   In the digital camera according to this embodiment, for setting a form of the mount opening, four segments extended to the opening portion position spaced by the flange back FB so as to be away from the optical axis O by the angle θh of inclination of about 10 degrees in a direction (Y-direction) along the short side and the angle θw of inclination of about 8 degrees in a direction (X-direction) along the long side from four corners of the imaging range Ri of the photoelectric conversion surface  27   a  of the image pickup device inscribing an image circle Ic as shown in  FIGS. 12 ,  13 A and  13 B, that is, a an upper left segment, a an upper right segment, a lower left segment and a lower right segment are Sd 1 , Sd 2 , Sd 3  and Sd 4 , respectively. A square obtained by connecting the lens side front ends of the segments is a minimum mount opening range Rm′. 
   The mount opening of the camera body side may be set so as to satisfy the minimum mount opening range Rm′. The minimum mount opening range Rm′ is set in accordance with the maximum light beam interchangeable lens having the widest outmost light beam of an exit luminous flux among interchangeable lenses of the camera system. 
   On the other hand, the minimum mount opening range of the interchangeable lens side may be set in order not to block the outermost light beam of the exit luminous flux of each interchangeable lens. However, the mount must have a predetermined form to be mounted to the camera body in order to be compliant as a camera system. The lens side mount opening portion will be described with reference to the maximum light beam interchangeable lens, for example. 
   In other words, a first plane obtained by tilting the long side of the imaging range Ri by 10 degrees in a direction (Y-direction) away from the optical axis O and extending the long side to the position of the opening portion is called plane H 1 . A second plane obtained by tilting the short side of the imaging range Ri by 8 degrees in a direction (X-direction) away from the optical axis O and extending the short side to the position of the opening portion is called plane H 2 . The plane H 1  is a plane (boundary plane shown in  FIG. 13B ) provided between the segment Sd 1  and the segment Sd 2  or between the segment Sd 3  and the segment Sd 4 . The plane H 2  is a plane (boundary plane shown in  FIG. 13A ) provided between the segment Sd 1  and the segment Sd 3  or between the segment Sd 2  and the segment Sd 4 . The square established by the lens-side front four sides of the planes H 1  and H 2  is called minimum mount opening range Rm′. 
   The square Rm 1  is within a circumscribed circle of the square formed by connecting ends of the segments tilted by a predetermined angle θ 3  (see  FIG. 12 ) in direction away from the four corners of the imaging range Ri with respect to the optical axis and extended to the opening portion. Thus, the imaging range Ri is within the valid pixel range with the aspect ratio of 4:3. Therefore, the angle θ 3  can be equal to the tilting angle θ according to the first embodiment and can be set so as to satisfy the condition below:
 
12 degrees≧θ 3 ≦14 degrees 
 
   The circumscribed circle of the mount opening range Rm′ is Im′, and the lens side mount opening portion  31   a  of the maximum light beam interchangeable lens can have the minimum opening portion. The body side mount opening portion  41   a  has a size equal to the size of the mount opening range Rm′ or larger. The space within the mirror box  42  and surrounded by the four planes H 1  and H 2  formed by four segments Sd 1 , Sd 2 , Sd 3  and Sd 4  contains nothing (reflector  13   b  and shutter frames) to block object luminous flux in shooting. 
   A main light beam of a peripheral light beam parallel to the optical axis can be adapted up to AV 3.6 (equal to adaptive F No. 3.5) at the end of the mount opening range Rm′ in the long side direction and up to AV  3  (equal to adaptive F No. 2.8) at the end in the short side direction. Therefore, when a lens with F No. 1.4 is used as an interchangeable lens barrel, the amount of light falls by 2.6 levels at the end in the long side direction and by 2 levels at the end in the short side direction. However, as described above, the lens barrel with F No. 1.4 may be a wide angle lens barrel, and the main light beam of a peripheral ray beam tilts with respect to the optical axis O. When the above illustrated lens barrel is used, the amount of light falls by about 1.2 levels at the end in the long side direction and by about 0.8 levels at the end in the short side direction, which are practically not a problem. On the other hand, when a telephoto lens barrel causing a peripheral luminous flux with a main light beam substantially parallel to the optical axis is used, the F No. is 2 to 2.8 (equal to AV 2 to 3). Therefore, the telephoto lens barrel can be used with no problems. 
   When a digital camera according to this embodiment is used, the reference mount diameter Dm of the circumscribed circle Im of the minimum mount opening range Rm′ depends on the distance (flange back FB) from the imaging surface to the opening portion. However, in consideration of the existence of the mirror box  42  between the image pickup device  27  and the body side mount portion  47 , the relationship between the reference opening diameter Dm and the image circle Di is desirably set so as to satisfy:
 
 Dm/Di≧ 1.8 
 
   In a digital camera according to this embodiment, a connecting terminal for electric connection between the camera body and the interchangeable lens barrel may be provided outside of the square of the mount opening range Rm′ and is desirably provided outside of the square and inside of the circumscribed circle Im′ of the square. 
   The mirror box  42 , the front panel  41 , and the body side mount portion  47  and so on are provided between the image pickup device  27  and the interchangeable lens  12 , as shown in the section diagram in  FIG. 3 , in the camera body shown in FIG.  2 . Therefore, in order to apply this embodiment to the camera body shown in  FIG. 2 , the opening portions of these members must satisfy the mount opening range Rm′ in the positions in the optical axis direction where the openings are provided. 
   Next, a digital camera system according to a third embodiment of the invention will be described with reference to FIG.  14  and so on. 
     FIG. 14  is a diagram showing an imaging range of a 4/3 type image pickup device and the image circle on the imaging range of a square image pickup device applied to this embodiment. 
   In an interchangeable lens type digital camera according to this embodiment, a square image pickup device having an imaging range with the aspect ratio of 1:1 is applied. The mount opening portion of the camera adopts the same shape as the mount opening shape adopted to the digital camera according to the second embodiment. 
   The other construction is similar to that of the digital camera according to the first or second embodiment, and the same reference numerals are given to the same components in the description below. 
   An image pickup device applied to the camera body of the digital camera according to this embodiment is a square image pickup device as described above. The image circle Ic, which is a circumscribed circle of the imaging range Ri′ (an area Lw′×Lh′: valid screen range) of the photoelectric conversion surface has the same diameter as that of the image circle corresponding to the imaging range Ri of the image pickup device  27  with the aspect ratio 4:3 applied to the digital camera according to the second embodiment. Therefore, the mount opening of the camera according to this embodiment is the same as the mount opening range Rm′ ( FIG. 12 ) set based on the imaging range Ri of the image pickup device  27 , like the camera according to the second embodiment. 
   In other words, as shown in  FIGS. 12 ,  13 A and  13 B, the minimum mount opening of the mount opening range Rm′ (the circumscribed circle Im′) is a square formed by connecting lens side ends of four segments Sd 1  extended by a flange back FB dimension from four corners of the imaging range Ri of the photoelectric conversion surface  27   a  of an image pickup device inscribing the image circle Ic in a direction apart from an optical axis by the tilting angle θw of about 10 degrees in a direction (Y-direction) along the short side and by the tilting angle θw of about 8 degrees in a direction (X-direction) along the long side. 
   The 4/3 type image pickup device (image pickup device)  27  is replaced by a square type image pickup device, and the square type image pickup device is mounted to the camera body having the opening portion of the mount opening range Rm′ to which the interchangeable lens barrel  12  according to the second embodiment designed for the 4/3 type image pickup device. Then, differences in amount of enter light by the outputs of the image pickup devices were measured. Table 1 below shows results of the measurement of amounts of reduction in EV value of the amounts of peripheral light with respect to the amount of center light between the 4/3 type image pickup device and the square type image pickup device at peripheral positions (on the short side, long side and diagonal line). 
   
     
       
         
             
             
             
             
           
             
               TABLE 1 
             
             
                 
             
             
                 
               4:3 
               SQUARE 
                 
             
             
               ZOOMING 
               IMAGE PICKUP 
               IMAGE PICKUP 
             
             
               STATE 
               DEVICE 
               DEVICE 
               DIFFERENCE 
             
             
                 
             
           
          
             
                 
             
          
         
         
             
             
          
             
                 
               SHORT SIDE 
             
          
         
         
             
             
             
             
          
             
               WIDE 
               −0.203 
               −0.293 
               −0.09 
             
             
               STANDARD 
               −0.133 
               −0.179 
               −0.046 
             
             
               TELE 
               −0.148 
               −0.174 
               −0.026 
             
          
         
         
             
             
          
             
                 
               LONG SIDE 
             
          
         
         
             
             
             
             
          
             
               WIDE 
               −0.396 
               −0.278 
               −0.118 
             
             
               STANDARD 
               −0.216 
               −0.179 
               −0.037 
             
             
               TELE 
               −0.249 
               −0.174 
               −0.075 
             
          
         
         
             
             
          
             
                 
               DIAGONAL 
             
          
         
         
             
             
             
             
          
             
               WIDE 
               −0.963 
               −0.963 
               0 
             
             
               STANDARD 
               −0.883 
               −0.883 
               0 
             
             
               TELE 
               −1.003 
               −1.003 
               0 
             
             
                 
             
          
         
       
     
   
   As shown in Table 1, the difference in amount of reduction in EV value of the amount of peripheral light with respect to the amount of center light between the 4/3 type image pickup device and the square image pickup device is about ±0.1 EV, which is practically not a problem. Therefore, only by attaching the square type image pickup device to the camera body according to the second embodiment instead, the digital camera body according to this embodiment can be a digital camera body having the aspect ratio of 1:1 compliant with the interchangeable lens barrel having the F number applied in the second embodiment. 
   Cameras having various specifications may be applied in an interchangeable lens type digital camera system. Therefore, cameras can have imaging ranges with different aspect ratios even having the same image circle. Especially, even when an image pickup device with the aspect ratio of 1:1 is mounted to the camera system according to this embodiment, the length-to-width concept of the camera no longer exists. In this case, when a screen with an arbitrary aspect ratio is trimmed and is read from the imaging range, the direction for holding a camera does not have to be changed for vertically long pictures and horizontally long pictures. Thus, the usability can be improved. 
   A connecting terminal for electric connection between the camera body and the interchangeable lens barrel in the digital camera according to this embodiment may be provided outside of the square of the mount opening range Rm′ and is desirably provided outside of the square and inside of the circumscribed circle Im′ of the square. 
   The present invention is not limited to the above-described embodiments, but various changes can be practically implemented without departing from the principle. Furthermore, the above-described embodiments includes various steps of the invention, and various inventions can be extracted by combining disclosed multiple constructional requirements as necessary. 
   For example, even when several constructional requirements are removed from the entire constructional requirements according to the embodiments, so long as the problems described in the section, Problems to be Solved by the Invention, can be solved, and the advantages described in the section, Advantages of the Invention, can be obtained, the construction the constructional requirement of which is removed can be extracted as the invention.