Patent Publication Number: US-2007098398-A1

Title: Image taking apparatus

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to an image taking apparatus. The image taking apparatus includes an imaging device which reads an object image formed on an imaging area to generate image data, and an image taking optical system which images an object on the imaging area to generate image data responding to an operation.  
      2. Description of the Related Art  
      So-called digital cameras have come into wide use recent years. A digital camera captures object light entering through an image taking lens, with an imaging device to generate an image signal. A digital camera is provided with components such as a diaphragm to control object light quantity responding to conditions such as brightness of a place to be shot, and a shutter to limit time period while the imaging area is exposed to object light. A driving source such as a motor is used to drive a diaphragm or a shutter (for example, Japanese patent Laid-open No. H07-191378, FIG. 1, pp. 7.)  
      According to the technique disclosed in Japanese patent Laid-open No. H07-191378, the blade-shaped member used for the shutter is so devised as to suppress power consumption by the motor as a driving source.  
      Some digital cameras have motion picture taking function. Those cameras generally records motion picture data together with audio data.  
      Mechanical operation noises of a driving source to drive a shutter or diaphragm may be recorded through a microphone mounted on the camera while taking a motion picture.  
      For example, when the shutter disclosed in Japanese patent Laid-open No. H07-191378 is applied to a digital camera having motion picture taking function, motor operation noises may be recorded through the microphone even though power consumption of the motor as a driving source is saved.  
      In other words, because mechanical operation noises of a driving source are unnecessary for a user, it is desirable to reduce noises.  
      In addition, digital camera miniaturization has been progressed recent years. In this situation, there is a problem that driving sources such as a motor to drive a diaphragm and a shutter generally require large space.  
     SUMMARY OF THE INVENTION  
      The present invention has been made in view of the above-mentioned circumstances and provides an image taking apparatus which includes a light quantity controlling capability with noise reducing capability installed, and which is simultaneously miniaturized.  
      A first image taking apparatus according to the invention is exemplified as follows. An image taking apparatus which includes an imaging device reading an object image formed on an imaging area to generate image data and an image taking optical system imaging an object on the imaging area, and generates image data responding to an image taking operation, the image taking apparatus including:  
      a light quantity control mechanism which regulates quantity of object light to transmit to the imaging area, the object light entering into the image taking optical system,  
      the light quantity control mechanism further comprising:  
      a base plate which has an aperture on an optical axis of the image taking optical system; and  
      a light quantity control plate which is arranged to overlap the base plate, and which expands and contracts responding to an electrical field formed by an applied voltage, thereby varying an area covering the aperture of the base plate.  
      According to the first image taking apparatus, because the light quantity control mechanism, in which the light quantity control plate expands and contracts responding to an electrical field to control object light quantity, is applied, an image taking apparatus which includes capabilities such as a diaphragm and shutter is provided without using a mechanism which is driven by driving source such as a motor used for driving a diaphragm and shutter. Therefore, because this light quantity control mechanism does not include a mechanism which produces noises by a driving source such as a motor which is used for a diaphragm and shutter, diaphragm and shutter which does not produce noises are provided. In addition, because space for a driving source such as a motor used for a diaphragm and shutter is saved, a miniaturized image taking apparatus is provided.  
      It is preferable that in the first image taking apparatus among the image taking apparatus according to the invention, the light quantity control plate is composed of a plurality of diaphragm blades which jointly form an aperture overlapping the aperture of the base plate, and which expand and contract responding to an electrical field, thereby varying an area of the aperture overlapping the aperture of the base plate.  
      In the first image taking apparatus, because the plural diaphragm blades expand and contract responding to an electrical field, it is not necessary to use an existing component which drives a diaphragm blade and it is possible to reduce number of parts to be used. Therefore, the image taking apparatus is miniaturized.  
      It is desirable that in the first image taking apparatus among the image taking apparatus according to the invention, the light quantity control plate further comprising:  
      a member made of a liquid crystal elastomer which expands and contracts responding to an electrical field; and  
      a pair of electrodes which are arranged to sandwich the member made of the liquid crystal elastomer, and which form an electrical field in the member made of the liquid crystal elastomer with a voltage applied, thereby expanding and contracting the member made of the liquid crystal elastomer.  
      In the first image taking apparatus, because a liquid crystal elastomer is used as the light quantity control plate which expands and contracts quickly responding to an electrical field, it is possible to control efficiently object light quantity.  
      It is desirable that in the first image taking apparatus among the image taking apparatus according to the invention, the light quantity control plates further comprising:  
      a member made of an electrostrictive polymer which expands and contracts responding to an electrical field; and a pair of electrodes which are arranged to sandwich the member made of the electrostrictive polymer, and which form an electrical field in the member made of the electrostrictive polymer with a voltage applied, thereby expanding and contracting the member made of the electrosrictive polymer.  
      In the first image taking apparatus, because an electrostrictive polymer is also used as the light quantity control plate which expands and contracts quickly responding to an electrical field, it is possible to control efficiently object light quantity.  
      A second image taking apparatus is exemplified as follows. An image taking apparatus which includes an imaging device reading an object image formed on an imaging area to generate image data and an image taking optical system imaging an object on the imaging area, and generates taken image data responding to an image taking operation, the image taking apparatus comprising:  
      a light quantity control mechanism which regulates quantity of object light to transmit to the imaging area, the object light entering into the image taking optical system, wherein  
      the light quantity control mechanism further comprising:  
      a base plate which has an aperture on an optical axis of the image taking optical system;  
      a light quantity control plate which moves to vary an area covering the aperture of the base plate; and  
      a driving plate which expands and contracts responding to an electrical field formed by an applied voltage, thereby moving the light quantity control plate.  
      In the second image taking apparatus, because a light quantity control mechanism, in which a driving plate expands and contracts responding to an electrical field to move a light quantity control plate to control object light quantity, is applied, an image taking apparatus which includes capabilities such as a diaphragm and shutter is provided without using a mechanism which is driven by a driving source such as a motor used for driving a diaphragm and shutter, similarly to the first image taking apparatus. Therefore, because the light quantity control mechanism does not include a mechanism which produces noises by a driving source such as a motor which is used for a diaphragm and shutter, a diaphragm and a shutter which does not produce noises are provided. In addition, because space for a driving source such as a motor used for a diaphragm and shutter is saved, a miniaturized image taking apparatus is provided.  
      It is preferable that in the second image taking apparatus, the light quantity control plate is a diaphragm member which has an aperture and is driven by the driving plate to move between a small aperture position where the aperture overlaps the aperture of the base plate and a saved position where the light quantity control plate is saved from the aperture of the base plate.  
      In the second image taking apparatus, it is possible to adjust precisely light quantity going through the aperture of the base plate.  
      It is desirable that in the second image taking apparatus among the image taking apparatus according to the invention, the light quantity control plate is a diaphragm member which is arranged to overlap the base plate and which is driven by the driving plate, thereby moving to vary an area covering the aperture of the base plate.  
      In the second image taking apparatus, by applying such a diaphragm member, it is possible to control light quantity without using plural diaphragm blades.  
      It is desirable that in the second image taking apparatus among the image taking apparatus according to the invention, the light quantity control plate is composed of a plurality of diaphragm blades which jointly form an aperture overlapping the aperture of the base plate, and which is driven by the driving plate, thereby varying an area of the aperture overlapping the aperture of the base plate.  
      In the second image taking apparatus, because plural diaphragm blades are used to allow adjusting a diaphragm aperture at plural levels, it is possible to enhance the degree of freedom to control light quantity.  
      It is desirable that in the second image taking apparatus among the image taking apparatus according to the invention, the driving plate further including:  
      a member made of a liquid crystal elastomer which expands and contracts responding to an electrical field; and  
      a pair of electrodes which are arranged to sandwich the member made of the liquid crystal elastomer, and which form an electrical field in the member made of the liquid crystal elastomer with a voltage applied, thereby expanding and contracting the member made of the liquid crystal elastomer.  
      In the second image taking apparatus, because a liquid crystal polymer is used to expand and contract quickly responding to an electrical field, it is possible to control efficiently object light quantity.  
      It is desirable that in the second image taking apparatus among the image taking apparatus according to the invention, the driving plate further including:  
      a member made of an electrostrictive polymer which expands and contracts responding to an electrical field, and which form an electrical field in the member made of the electrostrictive polymer with a voltage applied, thereby expanding and contracting the member made of the electrostrictive polymer.  
      With the second image taking apparatus, because an electrostrictive polymer is also used as the driving plate to expand and contract quickly responding to an electrical field, it is possible to control efficiently object light quantity.  
      According to the invention, an image taking apparatus which includes a light quantity controlling capability as well as noise reducing capability, and which is simultaneously miniaturized, is provided. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a diagram showing a fundamental principle of a light quantity control mechanism applied to an image taking apparatus according to the invention.  
       FIG. 2  is an external perspective diagram of a digital camera as a first embodiment of a first image taking apparatus.  
       FIG. 3  is an external perspective diagram of a digital camera of the first embodiment of the first image taking apparatus.  
       FIG. 4  is a perspective view a digital camera shown in  FIG. 2  viewed from the above of its back.  
       FIG. 5  is a cross section showing a lens barrel collapsed in the digital camera of the first embodiment of the first image taking apparatus, when cut along an optical axis.  
       FIG. 6  is a cross section showing the lens barrel of the digital camera of the first embodiment of the first image taking apparatus with a back lens group in a wide-angled zoom, when cut along an optical axis.  
       FIG. 7  is a cross section showing the lens barrel of the digital camera of the first embodiment of the first image taking apparatus with the back lens group in a telephoto zoom, when cut along an optical axis.  
       FIG. 8  is a diagram showing a configuration of a light quantity control mechanism of the digital camera which is the first embodiment of the first image taking apparatus.  
       FIG. 9  is a schematic diagram showing an inner configuration of the digital camera shown in  FIG. 2 .  
       FIG. 10  is a diagram showing a light quantity control mechanism of a digital camera which is a second embodiment of the first image taking apparatus.  
       FIG. 11  is a diagram showing a light quantity control mechanism of a digital camera which is a first embodiment of a second image taking apparatus.  
       FIG. 12  is a diagram showing a light quantity control mechanism of a digital camera which is a second embodiment of the second image taking apparatus.  
       FIG. 13  is a diagram showing a light quantity control mechanism of a digital camera which is a third embodiment of the second image taking apparatus. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Exemplary embodiments of the invention will be described with reference to the accompanying drawings.  
       FIG. 1  is a diagram showing a fundamental principle of a light quantity control mechanism applied to an image taking apparatus according to the invention.  
      A light quantity control plate  100  shown in  FIG. 1  has an elastic layer  101  which expands and contracts responding to an electrical field formed inside. An electrostrictive polymer is applied to the electrical layer  101 .  
      The electrostrictive polymer is a polymer having a rubber elasticity to expand and contract responding to an electrical field. The elastic polymer  101  has shading quality.  
      The light quantity control plate  100  includes a pair of electrodes  102   a  and  102   b  which are affixed to the elastic layer  101  to expand and contract together with the elastic layer  101 . The light quantity control plate  100  is processed for insulation to prevent a short circuit when they are overlaid each other.  
      As shown in part (a) of  FIG. 1 , the elastic layer  101  has a predetermined thickness at an initial state when a power switch  103  for applying an electrical field is turned off. As shown in part (c) of  FIG. 1 , when the power switch  103  is turned on, the light quantity control plate  100  is electrically connected to a power source  104 _ 2 . Then, an electrical field is formed between the electrode  102   a  and the electrode  102   b . With an electrical field formed, the elastic layer  101  expands and the electrodes  102   a  and  102   b  also expand. In addition, when the power switch  103  is turned off after it is turned on, the light quantity control plate  100  returns to the initial state, as shown in part (a) of  FIG. 1 . Further, with the voltage controlled variably, the light quantity control plate  100  expands and contracts responding to an electrical field formed inside.  
      As described above, the electrostrictive polymer is applied to the elastic layer  101 . However, a liquid crystal elastomer is also applied to obtain the same effect. The liquid crystal elastomer is also a polymer having rubber elasticity to expand and contract responding to an electrical field.  
      Next, a digital camera which is a first embodiment of a first image taking apparatus according to the invention will be described.  
       FIGS. 2 and 3  are both perspective views of the digital camera which is the first embodiment of the first image taking apparatus, as obliquely viewed from the above of its front.  
      FIGS.  2  shows a state where the lens barrel  10  including an image taking lens is collapsed in the digital camera  1 .  FIG. 3  shows a state where the lens barrel is extended.  
      On a front  11  of the digital camera  1  shown in  FIGS. 2 and 3  are provided a flash window  12  through which a flash is transmitted toward an object, a finder object window  13  through which a user looks at an object, and a microphone  14  for recording sounds. On a top  15  is provided a release button  16 .  
       FIG. 4  is a perspective view of a digital camera shown in  FIG. 2  as obliquely viewed from the above of its back.  
      As shown in  FIG. 2 , an a back  21  of the digital camera  1  is provided a power source button  22  and a mode switch  23 . The power source button  22  is used for turning on and off power for the digital camera  1 . The mode switch  23  is used for switching mode between an image taking mode and a replay mode.  
      On a back  21  of the digital camera  1  are provided a menu selection and execution key  24 . The menu selection and execution key  24  is a key for changing menus freely to select a setting condition, the menus of still picture taking and motion picture taking in the image taking mode, and still picture replaying and motion picture replaying in the replay mode.  
      Further, on the back  21  of the digital camera  1  are provided a wide-angle zoom key  25 , a telephoto zoom key  26 , an LCD panel  27 , an optical finder eyepiece window  28  and a speaker  29 . The wide-angle zoom key  25  is a key for setting a focal length to a wide angle. The telephoto zoom key  26  is a key for setting a focal length to a telephoto angle. The LCD panel  27  is for displaying a picture of an object, the menus of the menus election and execution key  24  and others. The optical finder eyepiece window  28  is a window through which a user looks at an object to be taken an image of. The speaker  29  is for playing back sounds recorded by the microphone  14 .  
       FIG. 5  is across section showing a lens barrel collapsed in the digital camera of the first embodiment of the first image taking apparatus, when cut along an optical axis.  
      In a space inside the lens barrel  10  is included a shooting lens in which three group lenses of a front group lens  301 , a back group lens  302  and a focusing lens  303  are located in an order from the front to the back such that their optical axes are aligned. Behind the focusing lens  303  is provided a CCD  304  which reads object light to generate image data. The CCD  304  corresponds to an example of the imaging device according to the invention.  
       FIG. 6  is a cross section showing the lens barrel of the digital camera according to the embodiment of the first image taking apparatus, with a back group lens in a wide-angled zoom, when cut along an optical axis.  FIG. 7  is a cross section showing the lens barrel of the digital camera of the embodiment of the first image taking apparatus with the back lens group in a telephoto zoom, when cut along an optical axis.  
      The shooting lens described above is configured such that the back group lens  302  moves along the optical axis between a wide angle end shown in  FIG. 6  and a telephoto angle end shown in  FIG. 7  to vary focal length, and the focusing lens  303  moves along the optical axis to adjust focus. Between the front group lens  301  and the back group lens  302  is provided a light quantity control mechanism  500 . The light quantity control mechanism  500  will be described later in detail.  
      A fixed tube  50  and a driving tube  52  which rotates freely on the fixed tube  50  are provided in the lens barrel  10 . Because a ridge  50   a  formed circumferentially on an outer wall of the fixed tube  50  is engaged in a groove formed on an inner circumferential surface of the driving tube  52 , the driving tube  52  is restricted in moving in the direction of the optical axis against the fixed tube  50 . A gear  51  is provided on an outer circumferential surface of the driving tube  52 . Rotation driving force is transmitted to the gear  51  from a motor (not shown) to rotate the driving tube  52 .  
      A keyway  52   a  extending in the direction of the optical axis is formed in the driving tube  52 . A pin-shaped cam follower  54  fixed to a rotationally moving tube  53  goes through a spiral cam groove formed in the fixed tube  50  and is engaged in the keyway  52   a . Accordingly, as the driving tube  52  rotates, the rotationally moving tube  53  rotates to move along the cam groove in the direction of the optical axis.  
      Inside the rotationally moving tube  53  is provided a rectilinear frame  55 . The rectilinear frame  55  is engaged with the rotationally moving tube  53  so as to be rotatable on the rotationally moving tube  53 , and in also engaged in the keyway  50   b  of the fixed tube  50  to be limited in rotation. Accordingly, as the rotationally moving tube  53  rotates to move in the direction of the optical axis according to rotation of the driving tube  52 , the rectilinear frame  55  moves linearly in the direction of the optical axis according to movement of the rotationally moving tube  53 .  
      A pin-shaped cam follower  63  is fixed to a back group lens holding frame  302   a  holding the back group lens  302  described above. Because the cam follower  63  is engaged in both a keyway of the rotationally moving tube  53  and a keyway  55   a  extending in the direction of the optical axis of the rectilinear frame  55 , a back group lens  305  moves linearly along the keyway of the rotationally moving tube  53  as the rotationally moving tube  53  rotates to move in the direction of the optical axis according to rotation of the driving tube  52 .  
      In addition, a rectilinear tube  56  holding the front group lens  301  is provided in the lens barrel  10 . In the rectilinear tube  56 , acam follower  57  fixed to the rectilinear tube  56  is engaged in both a cam groove of the rotationally moving tube  53  and the keyway  55   a  of the rectilinear frame  55 . The keyway  55   a  extends in the direction of the optical axis. Accordingly, as the rotationally moving tube  53  rotates to move in the direction of the optical axis according to rotation of the driving tube  52 , the rectilinear tube  56  moves linearly in the direction of the optical axis along the form of the cam groove of the rotationally moving tube  53 , in which the cam follower  57  is engaged, according to rotation of the driving tube  52 .  
      As described above, the lens barrel  10  is extended and the lens barrel  10  is collapsed as the driving tube  52  rotates in the opposite direction.  
      The rotationally moving tube  53  further rotates with a position of the front group lens  301  being maintained after the lens barrel  10  is finished extended. At this point, the back group lens unit  305  moves in the direction of the optical axis along the cam groove of the rotationally moving tube  53 , and in this manner, view angle (that is, focal length) adjustment is performed.  
      Further, of the shooting lenses, the focusing lens  303  is adjusted to be focused as follows. As a lead screw  61  is rotated by a motor (not shown), the focusing lens  303  moves in the direction of the optical axis according to rotation of the lead screw  6  because a focusing lens holding frame  62  holding the focusing lens  303  is engaged in threads of the lead screw  61 . Thereby focusing is performed.  
      Next, a light quantity control mechanism of the digital camera  1  which is the embodiment of the first image taking apparatus will be described.  
       FIG. 8  is a diagram showing a configuration of a light quantity control mechanism of the digital camera which is the first embodiment of the first image taking apparatus.  
      Part (a) of  FIG. 8  is a diagram showing a configuration of a first diaphragm blade and a second diaphragm blade.  
      Part (b) of  FIG. 8  shows a front view and a cross section of the light quantity control mechanism.  
      The light quantity control mechanism  500  is composed of a base plate  502  having an aperture, a first diaphragm blade  501   a  and a second diaphragm blade  501   b . The first diaphragm blade  501   a  and the second diaphragm blade  501   b  correspond to the light quantity control plate having shading quality shown in  FIG. 1 . The first diaphragm blade  501   a  is provided with electrodes  102   a _ 2  and  102   b _ 2  both sandwiching an elastic layer  101 _ 2 . The second diaphragm blade  501   b  is provided with electrodes  102   a _ 3  and  102   b _ 3  both sandwiching an elastic layer  101 _ 3 . Electrostrictive polymer is applied to the elastic layers  101 _ 2  and  101 _ 3 . Thickness for each section of the first diaphragm blade  501   a  and the second diaphragm blade  501   b  appears large in the drawing for the sake of convenience, however, thickness of the blades is practically thin as shown in part (b) of  FIG. 8 .  
      Both of the first diaphragm blade  501   a  and the second diaphragm blade  501   b  are located on the base plate  502 . The first diaphragm blade  501   a  is provided with an (diaphragm blade) aperture  501   c  and an aperture  501   e , and is pinned on the base plate  502  with a fixing pin member  502   b . The second diaphragm blade  501   b  is also provided with a diaphragm blade aperture  501   d  and an aperture  501   f  and is pinned on the base plate  502  with a fixing pin member  502   c . The blades are fixed only with the fixing pin members  502   b  and  502   c , so that the first diaphragm blades  501   a  and the second diaphragm blade  501   b  are able to expand and contract.  
      The first diaphragm blade  501   a  and the second diaphragm blade  501   b  overlay the aperture  502   a  of the base plate  502  and the diaphragm blade apertures  501   c  and  501   d  together form an aperture which overlays the aperture  502   a  of the base plate  502  to vary an area of the aperture which overlays the aperture  502   a  of the base plate  502  responding to an electrical field.  
      Part (b) of  FIG. 8  is a diaphragm showing the position relation between the first diaphragm blade  501   a  and the second diaphragm blade  501   b  in an initial state. In part (b) of  FIG. 8 , any voltage is not applied and the aperture  502   a  of the base plate  502  is closed wholly.  
      Part (c) of  FIG. 8  is a diaphragm showing the position relation between the first diaphragm blade  501   a  and the second diaphragm blade  501   b  after a predetermined voltage is applied with the power on.  
      The first diaphragm blade  501   a  and the second diaphragm blade  501   b  expand responding to an applied voltage and vary the area of the aperture overlaying the aperture  502   a  of the base plate. In part (c) of  FIG. 8 , the first diaphragm blade  501   a  and the second diaphragm blade  501   b  cover a portion of the aperture  502   a.    
      Part (d) of  FIG. 8  shows the position relation between the first diaphragm blade  501   a  and the second diaphragm blade  501   b  after a predetermined voltage is added further in the state shown in part (c) of  FIG. 8 .  
      The first diaphragm blade  501   a  and the second diaphragm blade  501   b  expand with a voltage applied, allowing the aperture  502   a  of the base plate to open wholly.  
      In the light quantity control mechanism  500 , when the power is off, the aperture  502   a  of the base plate is closed by the first diaphragm blade  501   a  and the second diaphragm blade  501   b . When the power is turned on, the aperture  502   a  of the base plate allows light to go through. Therefore, if the first light quantity control mechanism  500  is used for a diaphragm or a shutter, power consumption is saved.  
      Returning to  FIG. 6 , the description will be continued.  
      The light quantity control mechanism  500  is held by a holding frame  302   b  such that the light quantity control mechanism  500  can move along the optical axis together with the back group lens unit  305  composed of the back group lens  302  and the back group lens holding frame  302   a.    
      Next, an internal configuration of the digital camera  1 , which is the first embodiment of the first image taking apparatus according to the invention, will be described.  
       FIG. 9  is a diagram showing an internal configuration outline of the digital camera  1  shown in  FIG. 2 .  
      The digital camera  1  is provided with a main CPU  110 , which controls all processes of the digital camera  1 .  
      The main CPU  110  includes an EEPROM  110 _ 1 . The EEP ROM  110 _ 1  is composed of rewritable nonvolatile memories. The main CPU  110  also includes a ROM, in which programs are stored. Operations of the digital camera  1  are controlled by the main CPU  110  in accordance with procedures of the programs.  
      The digital camera  1  includes an operation section  20  and a power supply  104 . The operation section  20  gives the main CPU  110  instructions for processing responding to operations of operation members provided on the back  21  on the top  14  of the digital camera  1  described in  FIGS. 2 and 4 . The power supply  104  provides power to each block when the power is turned on.  
      The digital camera  1  includes an image taking section  30  constituting an image taking optical system. As described above, the image taking section  30  includes the lens barrel  10  and the CCD  304 . The light quantity control mechanism  500  is provided in the lens barrel  10 . Operations of the light quantity control mechanism  500  will be described later.  
      The digital camera  1  includes a CDS AMP  120 , an A/D conversion section  121 , a white balance/gamma processing section  122 , an optical control CPU  123  and a clock generator  124 . The CDS AMP  120  performs processes such as reducing noises of an analogue image signal output from the CCD  304 . The A/D conversion section converts an analogue image signal to a digital image signal. The white balance/gamma processing section  122  adjusts white balance and performs a gamma correction for an object image responding to the instructions from the main CPU  110 . The optical control CPU  123  extends the lens main barrel  10  and moves the shooting lens in the lens main body barrel  10  by controlling a motor (not shown) in accordance with the instruction from the main CPU  110 . The clock generator  124  outputs a timing signal through the optical control CPU  123  in accordance with the instruction from the main CPU  110 . In the CCD  304 , the A/D conversion section  121  and the white balance/gamma processing section  122 , an image signal is systematically processed synchronously with the timing signal output from the clock generator  124 .  
      The digital camera  1  includes an AF detecting section  111  and an AE detecting section  112 . The AF detecting section  111  detects focusing information on an image, and the AE detecting section  112  detects luminance information of an image.  
      The digital camera  1  includes a buffer memory  125 , a YC processing section  126 , a YC→RGB conversion section  127 , a driver  128  and a data bus  130 . The buffer memory  125  temporarily stores RGB image data processed in the white balance/gamma processing section  122 . The YC processing section  126  converts an image signal input through the data bus  130  to a YC signal represented by luminance (Y) and color (C). Low-resolution through image data stored in the buffer memory  125  is supplied to the YC→RGB conversion section  127  through the bus  130  on a first-in-first-out basis. The through image data is in RGB form and is not processed in the YC→RGB conversion section  127 . Accordingly, the through image data is transferred to the LCD panel  27  to be displayed through the driver  128  which quickly processes the through image data.  
      The digital camera  1  includes a compression and decompression section  131 , an interface (I/F) section  132 , a memory card  133  and a flash control section  134 . The compression and decompression section  131  compresses image data converted to YC format data. The interface (I/F) section  132  provides communication interface complied with various communication standards to record compressed image data in the memory card  133 . The flash control section  134  flashes through a flash window  12 .  
      The digital camera  1  includes an audio processing section  141  and an audio replaying section  142 . The audio processing section  141  converts sounds picked up with a microphone to audio data. The audio replaying section  142  replays appropriate audio data with a speaker  29 .  
      Next, image-taking operation of the digital camera  1  will be described.  
      The description will show a case where a user takes a motion picture.  
      First, the user presses the power button  22  to perform a power-on operation, and then the operation section  20  accepts the operation. Accordingly, the main CPU  110  starts programs stored in the ROM to display an image on the LCD panel  27  and goes to a state to accept a setting operation for an image taking condition.  
      When the user selects a motion picture mode using the menu selection and execution key after turning the mode switch  23  to the motion picture mode, the main CPU  110  causes the CCD  304  at predetermined intervals to output image data representing an object image focused on the CCD  304 , to the CDS AMP  120 . The output image data is processed through the A/D conversion section and the subsequent processing sections to obtain a through image to be displayed on the LCD panel  27 . Then, the object images captured by the shooting lens are displayed on the LCD panel  27  as if the images were a motion picture.  
      When the user designates a view angle using the wide-angle zoom key  25  or the telephoto zoom key  26  arranged on the back  21  of the digital camera  1 , the designated view angle is passed on to the optical control CPU  110 , and then to the optical control CPU  123 . The optical control CPU  123  controls the motor and etc. (not shown), and extend the lens barrel  10  to move the back group lens  302  to a position corresponding to the view angle. In addition, the optical control CPU  123  controls the motor and etc. (not shown) to move the focusing lens  302  shown in FIGS.  5  to  7  along the optical axis.  
      The user takes an image on a through image displayed on the LCD panel  27 . Therefore, the AF detecting section  111  continuously senses a focusing position and a focusing mechanism moves the focusing lens  303  to the focusing position such that a through image representing an object at which the user points the digital camera  1  is promptly displayed.  
      The user sets the image taking condition to recording start using the menu selection and execution key  24 , then the AE detecting section  112  consequently detects luminance of field.  
      Receiving an instruction from the main CPU, the optical control CPU  123  causes electrodes of the first diaphragm blade  501   a  and the second diaphragm blade  501   b  to apply electrical field, based on the luminance of field. The first diaphragm blade  501   a  and the second diaphragm blade  501   b  expand and contract responding to the electrical field formed inside, and the electrodes adhered on the expansion and contraction layers  101 _ 2  and  101 _ 3  simultaneously expand and contract. As the first diaphragm blade  501   b  and the second diaphragm blade  501   b  expand, an area of an aperture overlaying the aperture  502   a  of the base plate varies. As a result, light quantity of the object is controlled most appropriately based on the luminance of field to adjust the diaphragm.  
      Subsequently, the image data representing the object focused on the CCD  304  is output at the predetermined intervals to the CDS AMP  120 . The CDS AMP  120  reduces noises of the image data output from the CCD  304  and provides the noise reduced image data to the A/D conversion section  121 . The A/D conversion section  121  generates image data composed of RGB digital signals converted from analogue signals. The generated image data is image-processed in the white balance/gamma processing section  122  and then is stored in the buffer memory  125 . The image data stored in the buffer memory  125  is provided to the YC conversion section  126  to be converted to a YC signal from the RGB signal. The compression and decompression section  131  performs a compression process on the taken image data converted to the YC signal. Further, the main CPU  110  stores the motion picture data associated with the audio data both taken together in the memory card  133  through the I/F  132 .  
      In addition, the motion picture data stored in the memory card  133  is expanded in the compression and decompression section  131  and is converted to a RGB signal in the YC/RGB conversion section  127  and then the motion picture data is transferred to the LCD panel  27  through the driver  128 . A motion picture represented by the motion picture data is displayed on the LCD panel  27 .  
      As the user sets an image taking condition to “the image taking finished” using the menu selection and execution key  24 , recording a motion picture and sounds is finished.  
      In the description above, the light quantity control mechanism  500  is explained as a diaphragm controlling the aperture, and also performs well as a shutter which mechanically controls an area of the aperture and a shutter speed.  
      Next, a digital camera of a second embodiment of the first image taking apparatus will be described.  
      A difference of the digital camera between the second embodiment of the first image taking apparatus and the digital camera  1  will only be described. The difference lies in a configuration of the light quantity control mechanism.  
       FIG. 10  is a diagram showing a light quantity control mechanism of the digital camera which is the second embodiment of the first image taking apparatus.  
      Part (a) of  FIG. 10  is a diagram showing a configuration of a first diaphragm blade and a second diaphragm blade.  
      Part (b) of  FIG. 10  shows a front view and a cross section of the light quantity control mechanism.  
      This light quantity control mechanism  600  includes a base plate  602  having an aperture, the first diaphragm blade  601   a  and the second diaphragm blade  601   b . The first diaphragm blade  601   a  and the second diaphragm blade  601   b  are the light quantity control plate having shading quality described in  FIG. 1 .  
      The first diaphragm blade  601   a  is provided with electrodes  102   a _ 4  and  102   b _ 4  both sandwiching an expansion and contraction layer  101 _ 4 . The second diaphragm blade  601   b  is provided with electrodes  102   a _ 5  and  102   b _ 5  both sandwiching an expansion and contraction layer  101 _ 5 . Electrostrictive polymer is used in the expansion and contraction layers  101   — 4 and  101 _ 5 . Thickness for each section of the first diaphragm blade  601   a  and the second diaphragm blade  601   b  appears large in the drawing for the sake of convenience, however, the thickness of the blades is practically thin as shown in part (b) of  FIG. 10 .  
      Both of the first diaphragm blade  601   a  and the second diaphragm blade  501   b  are located on the base plate  602 . The first diaphragm blade  601   a  is provided with an aperture  601   c  and is pinned on the base plate  602  with a fixing pin member  602   b . The second diaphragm blade  601   b  is provided with an aperture  601   d  and is pinned on the base plate  602  with fixing pin member  602   c.    
      Part (b) of  FIG. 10  is a diagram showing positions of the first diaphragm blade  601   a  and the second diaphragm blade  601   b  in an initial state.  
      The shapes of the diaphragm blades  601   a  and  601   b  are different from those of the diaphragm blades  501   a  and  501   b  shown in part (c) of  FIG. 8  such that the aperture  602   a  of the base plate  602  is wholly open by the diaphragm blades  601   a  and  601   b  when the power is off. Accordingly, the electric power consumption is reduced when the diaphragm blades  601   a  and  601   b  are used as a shutter for reading image data of the CCD  304 .  
      Part (c) of  FIG. 10  shows the position relation between the first diaphragm blade  601   a  and the second diaphragm blade  601   b  after the power is turned on to apply a predetermined voltage.  
      The first diaphragm blade  601   a  and the second diaphragm blade  601   b  expand to vary an area of the aperture, which is formed by themselves, overlapping the aperture  602   a  of the base plate. In part (c) of  FIG. 10 , a portion of the aperture  602   a  of the base plate is overlapped with the first diaphragm blade  601   a  and the second diaphragm blade  601   b.    
      Part (d) of  FIG. 10  shows the position relation between the first diaphragm blade  601   a  and the second diaphragm blade  601   b  after a predetermined voltage is added further to the state shown in part (c) of  FIG. 10 .  
      The first diaphragm blade  601   a  and the second diaphragm blade  601   b  both expand responding to an applied voltage to close wholly the aperture  602   a  of the base plate.  
      As the light quantity control mechanism  600  applied in the second embodiment of the first image taking apparatus is used to replace the light quantity control mechanism  500  shown in FIGS.  6  to  8 , a user may take a motion picture with noises reduced, similarly to the digital camera  1  described above.  
      Next, a light quantity control mechanism of a digital camera, which is a first embodiment of a second image taking apparatus, will be described.  
      Differences between the light quantity control mechanism of the second image taking apparatus and the light quantity control mechanism of the first image taking apparatus are described as follows. In the light quantity control mechanism of the first image taking apparatus, the light quantity control plate is configured to expand and contract responding to an applied voltage. On the other hand, in the light quantity control plate of the second image taking apparatus is configured not to expand and contract but to move to vary an area of an aperture overlapping an aperture of a base plate. In addition, a driving plate, which expands and contracts to move light quantity control plates responding to an applied voltage, is newly added.  
       FIG. 11  is a diagram showing the light quantity control mechanism of the digital camera which is the first embodiment of the second image taking apparatus.  
      Part (a) of  FIG. 11  is a diagram showing a configuration of the driving plate which expands and contracts, responding to an electrical field, to move the light quantity control plates.  
      Part (b) of  FIG. 11  is a front view showing a first diaphragm blade as the light quantity control plate. Part (c) of  FIG. 11  is a front view showing a second diaphragm blade as the light quantity control plate.  
      Based on the same principle described using  FIG. 1 , a driving plate  704  shown in part (a) of  FIG. 11  expands and contracts responding to an electrical field formed by an applied voltage. The driving blade  704  has shading quality and is provided with electrodes  102   a _ 6  and  102   b _ 6  both sandwiching an elastic layer  101 _ 6  which expands and contracts responding to an electrical field. In addition, the driving plate  704  includes apertures  705   a ,  705   b  and  705   c . These apertures will be described later.  
      Electrostrictive polymer is used in the elastic layer  101 _ 6 .  
      The electrodes  102   a _ 6  and  102   b 6 are made of an expanding and contracting polymer and are adhered to the elastic layer  101   — 6 to expand and contract together with the elastic layer  101 _ 6 .  
      The thickness of the section of the driving plate  704  appears large in the drawing for the sake of convenience, however, the driving plate  704  is practically made thin.  
      The first diaphragm blade  701  is provided with guide apertures  701   a ,  701   b  and  701   c  for moving on the base plate  701 . The second diaphragm blade  702  is also provided with guide apertures  702   a ,  702   b  and  702   c  for moving on the base plate  701 .  
      Part (d) of  FIG. 11  shows a front view of the light quantity control mechanism  700 .  
      The first diaphragm blade  701  and the second diaphragm blade  702  are arranged such that they are overlapping with each other on the base plate  703 .  
      A first pin  703   e  goes through an aperture  705   a  of the driving plate  704  and the guide aperture  702   c  of the first diaphragm blade  702 . A second pin  703   f  goes through an aperture  705   c  of the driving plate  704  and the guide aperture  701   c  of the second diaphragm blade  701 . The first pin  703   e  and the second pin  703   f  slide on a driving plate guide groove  703   d  formed on the base plate  703 .  
      The driving plate  704  is pinned with a third pin  704   a  through an aperture  705   b  on the base plate  703 . A fourth pin  703   b  goes through the guide apertures  701   a  and  702   a , and a fifth pin  703   c  goes through the guide apertures  701   b  and  702   b.    
      Part (d) of  FIG. 11  is a diagram showing the position relation between the first diaphragm blade  701  and the second diaphragm blade  702  after a predetermined voltage is applied with the power on.  
      The first diaphragm blade  701  and the second diaphragm blade  702  expand with a voltage applied, to vary an area of the aperture overlapping the aperture  703   a  of the base plate. In part (d) of  FIG. 11 , a portion of the aperture  703   a  of the base plate is covered by the first diaphragm blade  701  and the second diaphragm blade  702 .  
      Part (e) of  FIG. 11  shows the position relation between the first diaphragm blade  701  and the second diaphragm blade  702  after a predetermined voltage is added further to the state shown in part (d) of  FIG. 11 .  
      The first diaphragm blade  701  and the second diaphragm blade  702  both expand with a voltage applied to uncover wholly the aperture  703   a  of the base plate. Part (g) of  FIG. 11  shows a cross section of the drawing shown in part (f) of  FIG. 11 .  
      As the light quantity control mechanism  700  applied in the first embodiment of the second image taking apparatus is used to replace the light quantity control mechanism  500  shown in FIGS.  6  to  8 , a user may take a motion picture with noises reduced, similarly to the digital camera described above.  
      Next, a light quantity control mechanism of a digital camera, which is a second embodiment of the second image taking apparatus, will be described.  
       FIG. 12  is a diagram showing a light quantity control mechanism of a digital camera which is the second embodiment of the second image taking apparatus.  
      Part (a) of  FIG. 12  is a front view showing a first diaphragm blade  802 .  
      The first diaphragm blade  802  includes guide apertures  802   a ,  802   b  and  802   c  for sliding on a baseplate  801  by expansion and contraction of the driving plate  805 . The driving plate  805  will be described later.  
      Part (b) of  FIG. 12  is a front view showing the second diaphragm blade  803 . The second diaphragm blade  803  includes guide apertures  803   a ,  803   b  and  803   c  for sliding on the base plate  801  by expansion and contraction of the driving plate  805 .  
      Part (c) of  FIG. 12  is a front view showing the light quantity mechanism  800 .  
      The first diaphragm blade  802  and the second diaphragm blade  803  are arranged such that they are overlapping with each other on the base plate  801 . The guide aperture  802   a  of the first diaphragm blade  802  and the guide aperture  803   a  of the second diaphragm blade  803  are overlapped each other such that a guide pin  801   b  goes through these apertures on the base plate  801 . The guide aperture  802   b  of the first diaphragm blade  802  and the guide aperture  803   b  of the second diaphragm blade  803  are overlapped each other such that a guide pin  801   c  goes through these apertures on the base plate  801 .  
      One end of the driving plate  805  of the light quantity control mechanism  800  is fixed to a part  807  of the digital camera main body. The driving plate  805  expands and contracts responding to an electrical field formed by an applied voltage, similarly to the driving plate  704 .  
      An end of a guide member  804  for sliding the diaphragm blade is connected through a guide pin  806  to a tip of the driving plate  805 . A guide pin  804   b  goes through the guide aperture  801   c  of the first diaphragm blade  802 , the guide aperture  802   c  of the second diaphragm blade  803  and the base plate  801  to be connected to the other end of the guide member  804 . The guide member  804  is rotationally supported by a rotation axis  804   a.    
      As the driving plate  805  expands with a voltage applied, the guide member rotates counterclockwise about the rotation axis  804   a . As a result, the first diaphragm blade  802  and the second diaphragm blade  803  slide in different directions each other, covering the aperture  801   a  of the base plate  801 . Accordingly, an area of the aperture  801   a  of the base plate can be varied by applying variably a voltage to the driving plate  805 .  
      As the light quantity control mechanism  800  applied in the second embodiment of the second image taking apparatus is used to replace the light quantity control mechanism  500  shown in FIGS.  6  to  8 , a user may take a motion picture with noises reduced, similarly to the digital camera  1  described above.  
      Next, a light quantity control mechanism of a digital camera, which is a third embodiment of the second image taking apparatus, will be described.  
       FIG. 13  is a diagram showing a light quantity control mechanism of a digital camera which is the third embodiment of the second image taking apparatus.  
      In the light quantity control mechanism  900 , a driving plate  901  is attached to a part  904  of a digital camera. The driving plate  901  expands and contracts responding to an electrical field formed by an applied voltage, similarly to the driving plate  704 . A light quantity control plate  902 , which varies an area covering an aperture  905   a  of a base plate  905 , is connected to the driving plate  901  at a connecting section  903 . The light quantity control plate  902  is provided with an aperture  902   a  smaller than the aperture  905   a . The light quantity control plate  902  is rotationally supported by a rotation axis  902   a . The light quantity control plate  902  is a diaphragm member driven by the driving plate  901  to move between a small aperture position where the aperture  902   b  overlaps with the aperture  905   a  of the base plate and a saved position where the light quantity control plate  902  is saved from the aperture  905   a  of the base plate.  
      The base plate  905  is arranged such that the aperture  905   a  is set on an optical axis of an image taking optical system. As the light quantity control mechanism  900  applied in the third embodiment of the second image taking apparatus is used to replace the light quantity control mechanism  500  shown in FIGS.  6  to  8 , a user may take a motion picture with noises reduced, similarly to the digital camera  1 .  
      An electrostrictive polymer is used for the expansion and contraction layer of the light quantity control plate applied in the embodiments of the first image taking apparatus and the expansion and contraction layers of the driving plates applied in the embodiments of the second image taking apparatus. However, an liquid crystal elastomer which expands and contracts responding to an electrical field may be used to obtain same results.  
      As described above, according to the invention, an image taking apparatus which is miniaturized and includes a mechanism to control light quantity with noises reduced can be obtained.  
      In the embodiments, an electrostrictive polymer or a liquid crystal elastomer are exemplified as the expansion and contraction layer. However, polymers such as a polymer gel, an ionic conductive polymer and a piezo polymer may be used as a polymer which expands and contracts responding to an electrical field.