Abstract:
An image pickup apparatus, comprising:
       a lens unit,   a grip unit which can be attached and detached to/from the lens unit and forms all or a part of a grip when photographing,   a guiding member which, being set on the lens unit, guides the grip unit in a direction approximately orthogonal to an optical axis of the lens unit; and   a guided member which is set on the grip unit and engaged with the guiding member.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an image pickup apparatus, and more particularly to an image pickup apparatus such as an interchangeable-lens camera in which a lens unit is removable from a camera body. 
     2. Description of the Related Art 
     Conventionally, interchangeable-lens cameras which allow a lens unit to be removed from a camera body for replacement is known in the field of film cameras. Recently, cameras which allow lens units to be changed have been proposed in the field of digital cameras as in the case of film cameras. 
     Generally, in such interchangeable-lens cameras, a lens unit is attached to the camera body using a bayonet mount. That is, the lens unit is mounted on the camera body by turning the lens unit on an optical axis with respect to the camera body. 
     Incidentally, some digital cameras have an image pickup element such as a CCD incorporated in the lens unit (see, for example, Japanese Patent Application Laid-Open No. 2004-350047). In such digital cameras, however, if the lens unit is attached to the camera body using a bayonet mount, it is not possible to provide a sufficient number of electrical contacts. 
     To deal with this problem, Japanese Patent Application Laid-Open No. 2003-156790 proposes an interchangeable-lens camera in which engaging members and fastening members of the lens unit and camera body are installed on opposite sides of the optical axis. In this camera, the lens unit is engaged with the camera body via the engaging members, tilted toward the camera body, and then fastened to the camera body via the fastening members. This makes it possible to mount the lens unit on the camera body without rotating it on the optical axis. 
     However, with the camera described in Japanese Patent Application Laid-Open No. 2003-156790, when mounting the lens unit on the camera body, an operator must hold the lens unit and camera body in different hands, having both hands full and interrupting other operations. 
     SUMMARY OF THE INVENTION 
     The present invention has been made in view of the above circumstances and has an object to provide an image pickup apparatus which allows a lens unit to be attached and detached to/from a camera body with one hand. 
     To achieve the above object, according to a first aspect of the present invention, there is provided an image pickup apparatus, comprising: 
     a lens unit, 
     a grip unit which can be attached and detached to/from the lens unit and forms all or a part of a grip when photographing, 
     a guiding member which, being set on the lens unit, guides the grip unit in a direction approximately orthogonal to an optical axis of the lens unit; and 
     a guided member which is set on the grip unit and engaged with the guiding member. 
     According to the first aspect, the grip unit can be attached and detached to/from the lens unit by holding the grip unit with one hand. Specifically, with the grip unit held in one hand, the guided member on the grip unit can be engaged with and guided by the guiding member on the lens unit and then the grip unit can be attached to the lens unit. Also, with the grip unit held in one hand, the grip unit can be detached from the lens unit by disengaging the guided member from the guiding member on the lens unit. In the first aspect, it is preferable that the grip unit can be attached and detached laterally to/from the lens unit. 
     According to a second aspect of the present invention, the image pickup apparatus according to the first aspect further comprises a lock which, being disposed on the grip unit, restrains relative movement of the lens unit and the grip unit in the direction approximately orthogonal to the optical axis when the lens unit is mounted on the grip unit. 
     According to the second aspect of the present invention, since the lock is provided, it is possible to restrain relative movement of the lens unit and the grip unit in the direction approximately orthogonal to the optical axis. Since movements in directions other than the direction approximately orthogonal to the optical axis are restrained by the guided member and guiding member, the lock, when activated, can fasten the lens unit and the grip unit securely. 
     Also, according to the second aspect of the present invention, since the lock is installed on the grip unit, the lock can be operated with the hand which is gripping the grip unit. 
     According to a third aspect of the present invention, in the image pickup apparatus according to the second aspect, the lens unit is equipped with an image pickup element. The lens unit, which has the image pickup element as well as lenses, does not need a high positioning accuracy with respect to the grip unit. This makes it possible to simplify an attach/detach mechanism. 
     According to a fourth aspect of the present invention, in the image pickup apparatus according to the second or third aspect, the lock is disposed pivotally on the grip unit. This makes it possible to operate the lock using a simpler configuration. 
     According to a fifth aspect of the present invention, in the image pickup apparatus according to the second, third, or fourth aspect, the grip unit has a front member and rear member coupled pivotally, the guided member is set on the front member, the lock is disposed on the rear member, and the rear member is urged in a turning direction in which the lock operates. 
     According to the fifth aspect of the present invention, the grip unit is attached to the lens unit when the rear member is turned with the guided member on the front member engaged with the guiding member on the lens unit. Also, according to the fifth aspect, since the rear member is urged in the locking direction, the lock can be operated more easily. 
     According to a sixth aspect of the present invention, in the image pickup apparatus according to the fifth aspect, a display screen which displays images obtained through the lens unit is installed on the rear member. 
     The sixth aspect of the present invention, according to which the display screen is installed on the rear member, makes it possible to simplify the configuration and reduce the size of the apparatus compared to when the display screen is installed on the front member. Also, it makes it possible to adjust the attitude of the display screen by turning the rear member. 
     According to a seventh aspect of the present invention, in the image pickup apparatus according to any of the first to sixth aspects, the lens unit and the grip unit are equipped with electrical contacts which are connected when the lens unit and the grip unit are coupled. According to the seventh aspect, the electrical contacts are connected automatically when the lens unit and the grip unit are coupled. 
     According to an eighth aspect of the present invention, in the image pickup apparatus according to the second, third, fourth, fifth, sixth, or seventh aspect, the lock restrains the movement near the guided member. The eighth aspect, according to which the movement is restrained near the guided member, provides a reliable mechanical configuration. 
     According to a ninth aspect of the present invention, in the image pickup apparatus according to the second, third, fourth, fifth, sixth, seventh, or eighth aspect, the lock comprises a first lock and second lock, the first lock holding the lens unit to the grip unit and the second lock restraining the relative movement of the lens unit and the grip unit in the direction approximately orthogonal to the optical axis. 
     According to the ninth aspect of the present invention, since the lens unit is held to the grip unit by the first lock, locking operation can be performed easily by the second lock. Also, the use of two locks makes it possible to fasten the lens unit and the grip unit more securely. 
     The present invention, which allows the grip unit to be attached and detached to/from the lens unit by holding the grip unit with one hand, makes it possible to change lens units with one hand. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of a digital camera according to a first embodiment as viewed from the front; 
         FIG. 2  is a perspective view of the digital camera according to the first embodiment as viewed from the rear; 
         FIG. 3  is an assembly diagram of the digital camera according to the first embodiment; 
         FIG. 4  is an assembly diagram of the digital camera according to the first embodiment; 
         FIG. 5  is a block diagram showing an overall configuration of the digital camera according to the first embodiment; 
         FIGS. 6A to 6D  are explanatory diagrams illustrating operation of the digital camera according to the first embodiment 
         FIGS. 7A to 7C  are explanatory diagrams illustrating a digital camera with a lock of a different shape; 
         FIG. 8  is a perspective view showing the back side of a digital camera according to a second embodiment; 
         FIG. 9  is an assembly diagram of the digital camera according to the second embodiment; 
         FIGS. 10A and 10B  are diagrams showing an internal configuration of the digital camera according to the second embodiment; 
         FIG. 11  is an assembly diagram of a digital camera according to a third embodiment; 
         FIG. 12  is an assembly diagram of a digital camera according to a fourth embodiment; and 
         FIG. 13  is an assembly diagram of a digital camera according to a fifth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention will be described below with reference to the drawings. Incidentally, although in examples described below, the image pickup apparatus according to the present invention is applied to interchangeable-lens digital cameras, the present invention is not limited to this and can be applied to camera-equipped cell phones, film cameras, and the like. 
       FIG. 1  is a perspective view of a digital camera  10  according to a first embodiment as viewed from the front while  FIG. 2  is a perspective view of the digital camera  10  as viewed from the rear.  FIGS. 3 and 4  are assembly diagrams of the digital camera  10 . 
     As shown in the figures, the digital camera  10  comprises a lens unit  11  and a camera body  12 , where the camera body  12  is removably attached to the rear end of the lens unit  11 . 
     The lens unit  11  is approximately cylindrical in shape with a flat surface  11 A cut on its flank to form a D shape as shown in  FIG. 1 . The flat surface  11 A is formed on the side opposite the mounting side of the camera body  12  (indicated by an arrow in  FIG. 3 ). By placing the lens unit  11  with the flat surface  11 A down, it is possible to prevent the lens unit  11  from rolling. 
     A taking lens  18  is installed at the front end of the lens unit  11 . Also, control rings  33  such as a focus ring and zoom ring are turnably supported around the periphery of the lens unit  11 . Incidentally, it is preferable that the control rings  33  do not protrude beyond the flat surface  11 A, but this is not absolutely necessary. 
     As shown in  FIG. 3 , a CCD housing  13  protrudes from the rear face of the lens unit  11 . A CCD  54  (see  FIG. 5 ) and substrate (not shown) are housed in the CCD housing  13  and a female connector  15  which serves as an electrical contact is installed on a flank of the CCD housing  13 . The female connector  15  is coupled with a male connector  25  (described later) on the camera body  12  to transmit photographic image and other data. 
     Groove-like guiding members  17  are formed on top and bottom faces of the CCD housing  13 . The groove-like guiding members  17  are designed to engage with guided members  19  on the camera body  12  (described later). The guiding members  17  are formed in a direction orthogonal to an optical axis P of the lens unit  11 . 
     On the other hand, the camera body  12  has a grip  14  which bulges out cylindrically and a shutter button  16  is provided on the top face of the grip  14 . A flash unit  22  is installed in an upper right front part of the camera body  12  as shown in  FIG. 1 . A liquid crystal monitor  24 , mode selector switch  26 , and cross-key pad  27  are disposed in predetermined positions on the rear face of the camera body  12  as shown in  FIG. 2 . 
     The camera body  12  has a plate-like front part  20  extending from the grip  14  and a plate-like rear part  21  coupled with the front part  20  pivotally on the grip  14 . The rear part  21  is pivotally coupled with the grip  14  via pivot hinges  29  with which a lever  23  is formed integrally. By turning the rear part  21  away from the front part  20 , it is possible to open the rear part  21  away from the front part  20  with the lever  23  as shown in  FIGS. 3 and 4 . By turning the rear part  21  in the opposite direction, it is possible to close the rear part  21  over the front part  20  (i.e., fold the rear part  21  over the front part  20 ) as shown in  FIGS. 1 and 2 . 
     The grip  14  contains an urging device (not shown), which urges the rear part  21  in such a direction as to close over the front part  20 . Thus, the rear part  21  is closed over the front part  20  if nothing is done. When the rear part  21  is turned by operating the lever  23  against an urging force of the urging device, the rear part  21  is opened away from the front part  20 . 
     The base end of the front part  20  is coupled with the grip  14  as shown in  FIG. 3 . The front part  20  has an approximate U shape with a recess  28  formed on the front side of the front part  20  to accept the CCD housing  13  on the lens unit  11 . The recess  28  is formed in such a way as to conform to the shape of the CCD housing  13  on the lens unit  11 , and the guided members  19  convex in shape are formed on internal surfaces of the recess  28 . The guided members  19  are formed in such a way as to engage with the guiding members  17  on the lens unit  11 , and the CCD housing  13  is inserted in the recess  28  and guided to a predetermined mounting location as the guided members  19  are engaged with the guiding members  17 . The connector  25  is disposed in the bottom of the recess  28  so as to be coupled with the connector  15  when the CCD housing  13  on the lens unit  11  is fully inserted in the recess  28 . 
     The rear part  21  has a lock  31  at its tip. The lock  31  protrudes toward the front part  20 . The lock  31  is placed to the left of the CCD housing  13  on the lens unit  11  as indicated by a two-dot chain line in  FIG. 4  when the rear part  21  is closed over the front part  20 . This prevents the front part  20  from moving relative to the lens unit  11  in the direction orthogonal to the optical axis, and thereby restrains the CCD housing  13  from coming off the recess  28 . 
     Incidentally, it is advisable that a gap be formed around the CCD housing  13  when the camera body  12  is attached to the lens unit  11 . For example, the lock  31  should be a little thicker than the CCD housing  13 . Then, a little gap will be formed between the rear part  21  and front part  20  when the rear part  21  is closed over the front part  20 . This will improve heat dissipation characteristics of the CCD housing  13 , making it possible to prevent the CCD housing  13  from becoming hot. 
       FIG. 5  is a block diagram showing an internal configuration of the digital camera  10 . It shows a configuration in which the camera body  12  is attached to the lens unit  11 . Of the components shown in  FIG. 5 , at least the taking lens  18 , the CCD  54 , an iris/mechanical shutter  56 , a lens drive  58 , and an iris drive  60  are installed in the lens unit  11 . They are electrically connected to components installed in the camera body  12  via the connectors  15  and  25  (see  FIG. 3 ). 
     As shown in  FIG. 5 , the digital camera  10  has its entire operation totally controlled by a central processing unit (CPU)  30 . The CPU  30  functions as a control device which controls the camera system based on a predetermined program and as a computation device which performs various computations including automatic exposure (AE) computations, autofocus (AF) computations, and white balance (WB) computations. 
     A ROM  34  connected to the CPU  30  via a bus  32  contains programs executed by the CPU  30  as well as various data and the like needed for control. An EEPROM  36  contains CCD pixel defect information, various constants/information related to camera operation, etc. 
     A memory (SDRAM)  38  is used as a program load area, a work area for the CPU  30 , and a temporary storage area for image data or voice data. An HDD (hard disk drive unit)  40 , which is erasable, is a temporary storage memory used exclusively to store image data. It incorporates a three-axis acceleration sensor  42  for use to detect free fall and vibration (dynamic acceleration). When free fall of the digital camera  10  is detected by the three-axis acceleration sensor  42 , a head is retracted from a hard disk of the HDD  40  by a head retraction device (not shown) incorporated in the HDD  40 . 
     The three-axis acceleration sensor  42  detects vibrations of the camera body  12  in three axis directions (X, Y, and Z axes orthogonal to each other) when the shutter button  16  is pressed (released) and outputs a voltage signal which represents the vibration detected in each axis direction to the CPU  30 . The CPU  30  calculates a variation (which corresponds to velocity of deflection) in the voltage signal outputted for each axis, compares the calculated variations with prestored variations which represent allowable vibrations, displays a warning on the liquid crystal monitor if the calculated variations exceed the variations which represent allowable vibrations, and then prompts the user to take a photograph again by informing the user about a mode change. 
     The mode selector switch  26  is a control device used to switch between Shoot mode and Playback mode. When a movable contact strip  26 A is connected to a contact a by manipulation of the mode selector switch  26 , a signal about that is inputted in the CPU  30 , the digital camera  10  is set to the Shoot mode. When the movable contact strip  26 A is connected to a contact b, the digital camera  10  is set to the Playback mode to play back recorded images. 
     The shutter button  16  is an operation button used to give a command to start shooting. It has a two-stage configuration consisting of a switch S 1  which is turned on when the shutter button  16  is half-pressed and a switch S 2  which is turned on when the shutter button  16  is full-pressed. 
     A Menu/OK key (not shown in  FIG. 2 ) is an operation key which combines functions of a menu button used to display a menu on a screen of the liquid crystal monitor  24  and an OK button used to confirm and apply a selection. The cross-key pad  27  (see  FIG. 2 ) is a control used to give four types of direction command (Up, Down, Left, and Right). It functions as a button used to select an item on the menu screen or select various settings from individual menus. A Cancel key (not shown in  FIG. 2 ) is used to erase a desired object such as a selected item, cancel a command, or return to the previous state. 
     The liquid crystal monitor  24 , which is also used as a user interface screen, displays menu information, selected items, settings, or other information as required. The liquid crystal monitor  24  is a liquid crystal display, but an organic EL or other display units may be used alternatively. 
     The digital camera  10  has a media socket  46  into which a recording medium  48  may be inserted. There is no restriction on the type of recording medium and various media may be used including semiconductor memory cards typified by Smart Media (trademark), small portable hard disks, magnetic disks, optical disks, and magneto-optical disks. 
     A media controller  50  performs necessary signal conversion to exchange input and output signals compatible with the recording medium  48  inserted in the media socket  46 . 
     Also, the digital camera  10  is equipped with a USB interface  52  as a communications device for connection with external devices such as personal computers. By connecting the digital camera  10  with external devices via a USB cable, it is possible to exchange data with the external devices. Of course, communications systems other than USB are also available. 
     Next, photo-taking functions of the digital camera  10  will be described. 
     When the Shoot mode is selected by the mode selector switch  26 , power is supplied to an image pickup portion which includes a color CCD solid-state image pickup element (hereinafter abbreviated to CCD)  54 , making the digital camera  10  ready to shoot. 
     The lens unit  11  is an optical unit consisting of the taking lens  18  which includes a focus lens and the iris/mechanical shutter  56 . The lens unit  11  is motor-driven by the lens drive  58  and iris drive  60  which in turn are controlled by the CPU  30 . It performs zoom control, focus control, and iris control. 
     Light passing through the taking lens  18  forms an image on a light-sensitive surface. A large number of photodiodes (light-sensitive elements) are arranged two-dimensionally on the light-sensitive surface of the CCD  54 . Primary color filters of red (R), green (G), and blue (B) are arranged in a certain structure for each photodiode. The CCD  54  has an electronic shutter function for controlling a charging time (shutter speed) of each photodiode. The charging time on the CCD  54  is controlled by the CPU  30  via a timing generator  62 . Incidentally, an image pickup element of another type such as an MOS may be used instead of the CCD  54 . 
     A subject image formed on the light-sensitive surface of the CCD  54  is converted by the photodiodes into signal charges corresponding to the amount of incident light. The signal charges accumulated in the photodiodes are read out in sequence as a voltage signal (image signal) based on drive pulses supplied from the timing generator  62  on instructions from the CPU  30 . 
     The signal outputted from the CCD  54  is sent to an analog processor (CDS/AMP)  64 , in which R, G, B signals of each pixel are sampled and held (correlated double sampling), amplified, and then sent to an A/D converter  66 . Dot-sequential R, G, B signals converted into digital signals by the A/D converter  66  are stored in the memory  38  via an image input controller  68 . 
     An image signal processing circuit  70  processes the R, G, B signals stored in the memory  38  on instructions from the CPU  30 . Specifically, the image signal processing circuit  70  functions as an image processing device including a simultaneous excitation circuit (a processing circuit which interpolates spatial displacement of color signals resulting from color filter arrangement of a single-panel CCD, and thereby converts the color signals into simultaneous color signals), white balance correction circuit, gamma correction circuit, profile correction circuit, and luminance and color difference signal generation circuit, and thereby performs predetermined signal processing using the memory  38  on command from the CPU  30 . 
     R, G, B image data inputted in the image signal processing circuit  70  are converted into a luminance signal and color difference signal and subjected to predetermined processing such as gamma correction by the image signal processing circuit  70 . After being processed by the image signal processing circuit  70 , the image data are stored in the HDD  40 . 
     When displaying photographic images on the liquid crystal monitor  24 , image data are read out of the HDD  40  and sent to a video encoder  72  via the bus  32 . The video encoder  72  converts the inputted image data into a signal in a predetermined display format (e.g., a composite color video signal in the NTSC format) and outputs the signal to the liquid crystal monitor  24 . 
     When the shutter button  16  is half-pressed, turning on S 1 , the digital camera  10  starts AE and AF processes. That is, the image signal outputted from the CCD  54  is inputted in an AF detection circuit  74  and AE/AWB detection circuit  76  via the image input controller  68 . 
     The AE/AWB detection circuit  76  includes a circuit which divides a screen into multiple areas (e.g., 16×16) and integrates R, G, B signals from the resulting areas. The AE/AWB detection circuit  76  supplies the integrated values to the CPU  30 . The CPU  30  detects brightness of a subject (subject luminance) based on the integrated values from the AE/AWB detection circuit  76  and calculates an exposure value (photographic EV value) suitable for photography. An f-stop number and shutter speed are determined based on the calculated exposure value and a predetermined program chart. Then, the CPU  30  obtains a proper amount of exposure by controlling the electronic shutter and iris of the CCD  54  based on the f-stop number and shutter speed. 
     During automatic white balance adjustment, the AE/AWB detection circuit  76  calculates an average integrated value of each color in the R, G, B signals for each of the divided areas and provides the calculation results to the CPU  30 . Upon receiving the respective integrated values of R, B, and G, the CPU  30  finds ratios of R/G and B/G for each of the divided areas, determines the type of light source based on distribution of the R/G and B/G values in R/G and B/G color spaces, and corrects signals on each color channel by controlling gain values (white balance correction values) for R, G, B signals of a white balance adjustment circuit such that, for example, the values of the R/G and B/G ratios will be approximately 1 according to a white balance adjustment value suitable for the determined type of light source. If the gain values of the white balance adjustment circuit are adjusted such that the values of the R/G and B/G ratios will be other than 1, it is possible to generate an image with a certain tinge. 
     AF control in the digital camera  10  employs, for example, contrast AF which involves moving a focusing lens (movable lenses, in a lens optical system of the taking lens  18 , which contribute to focus adjustment) in such a way as to maximize a high-frequency component of a G signal of video signals. That is, the AF detection circuit  74  consists of a high-pass filter which passes only the high-frequency component of the G signal, absolute-value calculator, AF area extractor which cuts signals in a predetermined focus area (e.g., central part of the screen) out of the screen, and integrator which integrates absolute value data in the AF area. 
     The data of the integrated values obtained by the AF detection circuit  74  are passed to the CPU  30 . The CPU  30  calculates focus evaluation values (AF evaluation values) at a plurality of AF detection points while moving the focusing lens by controlling the lens drive  58  and determines a lens position which maximizes the evaluated focus value to be an in-focus position. Then, it makes the lens drive  58  move the focusing lens to the determined in-focus position. Incidentally, the focus evaluation values may be calculated using the luminance signal (Y signal) instead of the G signal. 
     After the AE/AF processes which is started when SI is turned on at a half-press of the shutter button  16 , when the shutter button  16  is full pressed, turning on S 2 , a shooting operation for recording is started. Image data acquired in response to the activation of S 2  is converted into a luminance/color difference signal (Y/C signal) and subjected to predetermined processing including gamma correction by the image signal processing circuit  70 , and then they are stored in the memory  38 . 
     The Y/C signal stored in the memory  38  is compressed in a predetermined format by a compression/decompression circuit  78  and recorded on a recording medium  48  via a media controller  50 . Still images, for example, are stored in JPEG format. 
     When the Playback mode is selected by the mode selector switch  26 , compressed data are read from the last file (file last recorded) on the recording medium  48 . If the last file recorded is a still-image file, the compressed image data read out is decompressed into an uncompressed YC signal by the compression/decompression circuit  78 , converted into a signal for display by the image signal processing circuit  70  and video encoder  72 , and outputted to the liquid crystal monitor  24 . Consequently, the image from the file is displayed on the screen of the liquid crystal monitor  24 . 
     During frame-by-frame playback of still images (including playback of the first frame of moving images), the file to be played back (forward/backward frame advance) can be changed using the Right key or Left key of the cross-key pad. The image file corresponding to the given frame is read out of the recording medium  48  and the still image or moving image is displayed on the screen of the liquid crystal monitor  24  in a manner similar to that described above. Incidentally, the digital camera  10  is driven by power supplied from a battery  82  via a power circuit  80 . 
     Next, operation of the digital camera  10  configured as described above will be described with reference to  FIGS. 6A to 6D , which are explanatory diagrams illustrating how the camera body  12  is attached to the lens unit  11  placed with the flat surface  11 A down. 
     First, by gripping the camera body  12  with one hand as shown in  FIG. 6A , the user opens the rear part  21  away from the front part  20  as shown in  FIG. 6B  by rotating the lever  23 . 
     Next, the CCD housing  13  on the lens unit  11  is inserted in the recess  28  in the front part  20 . In so doing, the guided members  19  (see  FIG. 3 ) in the front part  20  is engaged with the guiding members  17 . Consequently, the CCD housing  13  on the lens unit  11  can be inserted securely in the recess  28  in the front part  20 . 
     As shown in  FIG. 6C , when the CCD housing  13  on the lens unit  11  is fully inserted in the recess  28 , the connector  15  on the lens unit  11  is coupled with the connector  25  on the camera body  12 . In this state, if the user takes his/her hand off the lever  23  (or relaxes the pressure on the lever  23 ), the rear part  21  turns toward the front part  20  as shown in  FIG. 6D  by the urging force of the urging device (not shown) and is closed over the front part  20 . Consequently, the lock  31  is placed under the lens unit  11  (the other side in the attaching direction). This prevents the CCD housing  13  on the lens unit  11  from moving relative to the camera body  12  in the direction orthogonal to the optical axis P. At the same time, movements other than in the direction orthogonal to the optical axis P are restrained by the guiding members  17  and guided members  19 , and thus the lens unit  11  is fastened to the camera body  12 . 
     In this way, the camera body  12  is attached to the lens unit  11 . In so doing, the photographer only needs to operate the camera body  12  with one hand without the need to grip the lens unit  11 . Thus, the digital camera  10  according to this embodiment allows the camera body  12  to be attached to the lens unit  11  with one hand. 
     The camera body  12  is removed from the lens unit  11  in an order opposite to how it is attached. Specifically, with the camera body  12  held with one hand as shown in  FIG. 6D , the user opens the rear part  21  away from the front part  20  by turning the lever  23  as shown in  FIG. 6C . This releases the lock  31 . 
     The user picks up the camera body  12  in an open state as shown in  FIG. 6B . Consequently, the CCD housing  13  on the lens unit  11  falls off the recess  28  in the camera body  12 , disengaging the camera body  12  from the lens unit  11 . 
     Then, as shown in  FIG. 6A , the user closes the front part  20  and rear part  21  of the camera body  12 . This completes the operation of removing the camera body  12  from the lens unit  11 . Again, in the removal operation, the photographer only needs to hold the camera body  12  with one hand without the need to grip the lens unit  11 . Thus, the digital camera  10  according to this embodiment allows the camera body  12  to be attached and detached to/from the lens unit  11  with one hand, thus allowing the lens unit  11  to be changed with one hand. Therefore, the photographer can change the lens unit  11  easily even if he/she has one of his/her hands occupied. 
     In the first embodiment described above, there is no particular limit to the shape of the lock  31 , and any shape may be used as long as the lock  31  is engaged securely with the CCD housing  13  on the lens unit  11 . Thus, for example, a taper  31 A may be provided at the tip of the lock  31  as shown in  FIG. 7A . In that case, if the CCD housing  13  is inserted in the recess  28  with the rear part  21  closed over the front part  20 , the CCD housing  13  slides over the taper  31  A of the lock  31  as shown in  FIG. 7B , pushing the rear part  21  away from the front part  20 . This makes it possible to insert the CCD housing  13  in the recess  28  in the front part  20 . When the CCD housing  13  is fully inserted in the recess  28  in the front part  20 , the rear part  21  is closed over the front part  20  by an urging force as shown in  FIG. 7C , causing the lock  31  to restrain the movement of the CCD housing  13  and front part  20 . In this way, the taper  31 A provided at the tip of the lock  31  makes it easier to attach the camera body  12  to the lens unit  11 . Incidentally, a taper may be provided on the CCD housing  13  on the side where the CCD housing  13  is inserted in the front part  20 . This produces the same effect as the configuration described above. Also, the lock  31  may be semicircular in cross section. 
     Next, a second embodiment will be described with reference to  FIGS. 8 to 10 .  FIG. 8  is a perspective view showing the back side of a digital camera  100  according to the second embodiment.  FIG. 9  is an assembly diagram of the digital camera  100 .  FIG. 10  is a diagram showing an internal structure of a camera body  102 . Incidentally, components with the same configuration and operation as those of the first embodiment are designated by the same reference numerals as the corresponding components of the first embodiment, and description thereof will be omitted. 
     The camera body  102  of the digital camera  100  according to the second embodiment shown in  FIGS. 8 to 10  differs from that of the digital camera  10  according to the first embodiment. Specifically, it has a casing  104  formed integrally with a grip  14 , and a liquid crystal monitor  24  and various switches (not shown) are installed on the back of the casing  104 . 
     As shown in  FIG. 9 , a recess  106  is formed at the tip of the casing  104  to accept a CCD housing  13  on a lens unit  11 . A connector  25  is installed in the bottom of the recess  106 . Levers  108  are installed on inner surfaces of the recess  106 . 
     The levers  108  have guided members  108 A convex in shape to engage with guiding members  17  on the lens unit  11 . Also, they have locks  108 B which are installed at the tips of the guided members  108 A, protruding inward. When the CCD housing  13  is inserted in the recess  106 , the locks  108 B are engaged with the CCD housing  13 , preventing the CCD housing  13  from coming off the recess  106 . Also, tapers  108 C are formed at the tips of the locks  108 B so that when the CCD housing  13  is inserted in the recess  106 , the CCD housing  13  will slide over the tapers  108 C to expand the locks  108 B outward. 
     As shown in  FIG. 10 , the levers  108  are approximately L-shaped. The levers  108  are supported at bends swingably around axes  114  by the casing  104 . Incidentally, the levers  108  have been installed with the guided members  108 A and locks  108 B protruding in the recess  106  in the casing  104 . Consequently, the amount of protrusion changes when the levers  108  swing. 
     At the other ends of the levers  108 , slots  108 D are formed in the direction orthogonal to the guided members  108 A. An unlock pin  110  is passed through the slots  108 D. It is linked to an unlock button  112  shown in  FIG. 9 . The unlock button  112  is installed swingably in the direction of an arrow in  FIG. 9 . When the unlock button  112  is moved left in  FIG. 9 , the levers  108  engaged with the unlock pin  110  swings, causing the locks  108 B at the tips of the levers  108  to retract outward (in such a direction as to increase spacing). Consequently, the CCD housing  13  on the lens unit  11  is disengaged from the locks  108 B, releasing the lock. 
     A spring  116  is installed in the casing  104  with its ends attached to the respective levers  108 , urging the levers  108  inward (in such a direction as to decrease the spacing). 
     Also, stopper pins  118  are installed in the casing  104 . They are disposed on the inner sides of the respective levers  108  to restrain inward swing of the levers  108  by engaging with the levers  108 . Incidentally, the stopper pins  118  are placed in such a way as to restrain the levers  108  at locations where the guided members  108 A on the levers  108  will be parallel to each other. 
     With the digital camera  100  according to the second embodiment configured as described above, to attach the camera body  102  to the lens unit  11 , the user inserts the CCD housing  13  on the lens unit  11  in the recess  106  in the camera body  102  by gripping the camera body  102 . In so doing, it is advisable to place the lens unit  11  on a flat surface as in the case of  FIG. 6 . 
     As the CCD housing  13  on the lens unit  11  is inserted in the recess  106  in the camera body  102 , the CCD housing  13  expands the spacing between the levers  108  by sliding over the tapers  108 C of the locks  108 B. As the user further inserts the CCD housing  13  in the recess  106 , the guided members  108 A on the levers  108  engage with the guiding members  17  on the lens unit  11 , guiding the CCD housing  13  reliably into the recess  106 . 
     When the CCD housing  13  is fully inserted in the recess  106 , the connector  15  on the lens unit  11  is coupled with the connector  25  on the camera body  12  and the levers  108  swing inward by the urging force of a spring  120 , causing the locks  108 B at their tips to be engaged with the CCD housing  13 . This restrains the movement of the lens unit  11  in the direction of the optical axis P, thereby fastening the lens unit  11  to the camera body  102 . Thus, the second embodiment makes it possible to attach the camera body  102  to the lens unit  11  by holding the camera body  102  with one hand. In particular, it allows the lens unit  11  to be mounted on the camera body  102  by simply inserting the CCD housing  13  on the lens unit  11  in the recess  106  in the camera body  102 . This makes the mounting operation easier. 
     When detaching the lens unit  11  and camera body  102  from each other, the user grips the grip  14  of the camera body  102  and moves the unlock button  112  leftward in  FIG. 8  with the gripping hand. Consequently, the pair of levers  108  swing against the urging force of the spring  120 , expanding the spacing between the locks  108 B and thereby disengaging the locks  108 B from the CCD housing  13 . In this state, the user can remove the camera body  102  from the lens unit  11  by moving the camera body  102  in such a direction as to pull the CCD housing  13  out of the recess  106 . Thus, the second embodiment makes it possible to remove the camera body  102  from the lens unit  11  by griping the camera body  102  with one hand and operating the unlock button  112  with the gripping hand. 
     In this way, the second embodiment allows the camera body  102  to be attached and detached easily to/from the lens unit  11  with one hand. 
     Also, the second embodiment provides highly reliable locking because the locks  108 B on the camera body  102  comes into operation by being engaged with the guiding members  17 . 
     Next, a third embodiment will be described with reference to  FIG. 11 .  FIG. 11  is an assembly diagram of a digital camera according to the third embodiment. 
     The digital camera  130  according to the third embodiment shown in  FIG. 11  differs from the digital camera  10  according to the first embodiment in configuration of a front part  134  of a camera body  132 . Specifically, according to the third embodiment, a pair of protrusions (which corresponds to a first lock)  136  are provided in the front part  134  of the camera body  132 . The pair of protrusions  136  are formed in the recess  28  protruding inward so as to engage with the CCD housing  13  when the CCD housing  13  is inserted in the recess  28 . Thus, the protrusions  136  make it possible to restrain the lens unit  11  from moving in the direction orthogonal to the optical axis P and hold the lens unit  11  to the camera body  132 . Incidentally, it is advisable that the CCD housing  13  is configured to snap into engagement with the pair of protrusions  136 , for example, with a click when it is inserted in the recess  28  in the front part. 
     The rear part  21  of the camera body  132  is configured in a manner similar to the first embodiment and has a lock  31  (which corresponds to a second lock) installed at its tip. Thus, the lock can be effected when the rear part  21  is closed over the front part  134  by turning. 
     With the digital camera  130  according to the third embodiment configured as described above, when the CCD housing  13  on the lens unit  11  is inserted in the recess  28  in the front part  134  of the camera body  132 , the protrusions  136  of the front part  134  engage with the CCD housing  13 , locking the CCD housing  13 . Thus, after the CCD housing  13  is inserted in the recess  28 , the user can lift the lens unit  11  by holding the camera body  132 . In this state, the user activates the lock  31  by turning the rear part  21 . Consequently, the lens unit  11  and camera body  132  are locked by the two types of locking device (i.e., the protrusions  136  and lock  31 ), ensuring more reliable coupling of the lens unit  11  and camera body  132 . 
     Next, a fourth embodiment will be described with reference to  FIG. 12 .  FIG. 12  is an assembly diagram of a digital camera according to the fourth embodiment. 
     The digital camera  140  according to the fourth embodiment shown in  FIG. 12  differs from the digital camera  10  according to the first embodiment in configuration of a camera body  142 . Specifically, in the camera body  142  according to the fourth embodiment, a rear part  146  is supported pivotally on a shaft  148  placed above a front part  144 . The rear part  146  is designed to turn maintaining an appropriate frictional resistance. Also, it is designed to be able to stop and maintain its attitude at a desired pivotal position. 
     The liquid crystal monitor  24  is installed on the inner side of the rear part  146  (i.e., that side of the rear part  146  which faces the front part  144  when the rear part  146  is folded over the front part  144 ). Thus, when the rear part  146  is closed over the front part  144 , the liquid crystal monitor  24  is hidden in the camera body  142 . This protects the liquid crystal monitor  24 . 
     With the digital camera  140  according to the fourth embodiment configured as described above, by stopping the rear part  146  of the camera body  142  at a desired pivotal position, it is possible to put the liquid crystal monitor  24  in a desired attitude. Thus, even if the digital camera  140  is held above or below the visual point of the photographer, by adjusting the attitude of the rear part  146 , it is possible to adjust the attitude of the liquid crystal monitor  24  as desired so that it will be easily viewable. 
     Also, according to the fourth embodiment, since a space is provided around the CCD housing  13  when the rear part  146  is opened away from the front part  144 , it is possible to efficiently dissipate heat generated in the CCD housing  13 , and thereby prevent temperature rises in the CCD housing  13 . 
     Furthermore, according to the fourth embodiment, since the liquid crystal monitor  24  is installed on the inner side of the rear part  146 , the liquid crystal monitor  24  can be housed in the camera body  142  when the rear part  146  is closed over the front part  144 . This protects the liquid crystal monitor  24 . 
     Next, a digital camera according to a fifth embodiment will be described with reference to  FIG. 13 .  FIG. 13  is an assembly diagram of the digital camera according to the fifth embodiment. 
     The digital camera  150  according to the fifth embodiment differs from the digital camera  10  according to the first embodiment in that a connector  25  is installed in the place of the lock  31  according to the first embodiment. Specifically, in the digital camera  150  according to the fifth embodiment, the connector  25  is installed, facing inward, near the inner front edge of the rear part  21  of a camera body  152 . On the other hand, the lens unit  11  has a connector  15  installed adjacent to the CCD housing  13 , where the connector  15  is intended to fit over the connector  25 . 
     With the fifth embodiment configured as described above, after inserting the CCD housing  13  in the recess  28  in the camera body  152 , the connector  25  is coupled with the connector  15  when a rear part  154  is closed by turning. This restrains the lens unit  11  from moving relative to the camera body  152  in the direction orthogonal to the optical axis P, thereby fastening the lens unit  11  to the camera body  152 . Thus, according to the fifth embodiment, the connectors  15  and  25  combine locking devices which restrain movement of the camera body  152 , eliminating the need to provide a separate locking device. 
     Incidentally, although in the first to fifth embodiments described above, the flat surface  11 A is provided in lateral part of the lens unit  11  to prevent the lens unit  11  from rolling, this is not restrictive. For example, the lens unit  11  may be equipped with anti-rolling protrusions in lateral part or formed into a polygonal prism. Alternatively, the lens unit  11  may be attached and detached using a camera bag, clothing, or the like for holding the lens unit  11  in a predetermined attitude. 
     Also, although in the first to fifth embodiments described above, the CCD  54  is installed in the lens unit  11 , this is not restrictive and the CCD  54  may be installed in the camera body  12 . 
     Also, although in the first to fifth embodiments described above, the lens unit  11  and camera body  12  are fastened to each other by having their relative movement restrained by locking devices, they may be fastened by a fastening device such as an electromagnet installed separately.