Patent Publication Number: US-2007121072-A1

Title: Liquid crystal lens, photographing apparatus and flash light emitting unit

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to a liquid crystal lens which uses a liquid crystal and in which a refractive index changes according to an applied voltage, and to an image taking apparatus which has an image taking optical system with a variable focal length, captures an object image which is incident through the image taking optical system, and generates image data, and to a flash light emitting unit.  
      2. Description of the Related Art  
      In a camera which is one of image taking apparatuses, flash light as image taking fill light is radiated toward an object from a light emitting unit in synch with a shutter operation when object brightness is insufficient in image taking. What is known as a light emitting unit is a light emitting unit including an arc tube which emits flash light, and a reflector which reflects the flash light emitted from the arc tube (reflective shade).  
      As such a light emitting unit, a technique which has means which makes a light irradiation direction variable, and which corrects displacement between a shooting lens optical axis and a light emitting unit optical axis by making the shooting lens optical axis and the light emitting unit optical axis always intersect at a position of an object is proposed (see Japanese Patent Laid-Open No. 57-122423).  
      In addition, a technique which makes an irradiation angle variable by changing a form of a reflector from an approximately elliptical to an approximately paraboloid form is proposed (see Japanese Patent Laid-Open No. H2-196228).  
      Furthermore, a technique which changes an irradiation direction of a light emitting section automatically by operating an irradiation direction deflection mechanism on the basis of object information from an image taking screen is proposed (see Japanese Patent Laid-Open No. H4-14029).  
      Moreover, a technique which makes a focal length of the liquid crystal micro lens, using a liquid crystal, variable by dividing an electrode into four parts and applying different voltages to respective four parts which are divided is proposed (see Japanese Patent Laid-Open No. H11-109304).  
      Further, in a diffraction type liquid crystal lens which fills liquid crystal elements between transparent substrates, a technique which has a light distribution film which has two or more concentric regions in which orientation processing is given so that orientation directions of the liquid crystal elements may be different, and makes a focal length variable in an optical axis direction is proposed (see Japanese Patent Laid-Open No. 2002-357804).  
      In addition, in a liquid crystal lens which is provided in an optical pick-up apparatus, a technique which makes a focal length of a light beam variable in an optical axis direction according to a drive signal supplied is proposed (see Japanese Patent Laid-Open No. 2005-18840).  
      Furthermore, as a light emitting unit which emits light, an AF fill light emitting apparatus which assists an auto-focusing (AF) function by emitting distance measurement fill light from a light source (LED) at the time of image taking under low illuminance is also known. The distance measurement fill light which is emitted from the AF fill light emitting apparatus is radiated to an object, and a focusing operation is performed on the basis of the distance measurement fill light which is reflected by the object. In this focusing operation, for example, so-called “hill-climbing type” continuous AF processing is performed. Thus, a focused position is decided by gradually moving a focus lens till a maximal point of an evaluation value while checking directions of increase and decrease of a focal evaluation value with performing minute movement of a focus lens along an optical axis back and forth.  
      Since all the techniques which are proposed in Japanese Patent Laid-Open Nos. 57-122423, H2-196228, and H4-14029 require a mechanism of changing mechanical structure at the time of changing an irradiation direction and an irradiation angle of light variable, there arises a problem of interfering with miniaturization and weight saving of a light emitting unit.  
      In addition, the technique proposed in Japanese Patent Laid-Open No. H11-109304 requires four power sources for applying different voltages to respective four parts of the electrode when making a focal length of the liquid crystal micro lens variable. Hence, there also arise a problem of interfering miniaturization and weight saving of a light emitting unit.  
      Furthermore, since the technique proposed in Japanese Patent Laid-Open Nos. 2002-357804 and 2005-18840 is a technique which makes a focal length variable in an optical axis direction, there is a problem that it is difficult to make a focal length variable except an optical axis direction.  
      Moreover, since an AF fill light emitting apparatus which is a light emitting unit which emits light is arranged generally in a position off an optical axis in terms of layout, a direction of the distance measurement fill light which is emitted from the AF fill light emitting apparatus falls in a direction of intersecting with the optical axis. Hence, it has a defect that a focal length of the lens in which the distance measurement fill light can cover is within a certain limited range, and it does not reach a distant position. Here, although it is conceivable to enlarge a light source which emits distance measurement fill light, there arises a problem of interfering with miniaturization of an AF fill light emitting apparatus.  
      In consideration of the situation mentioned above, the present invention aims at providing a liquid crystal lens which can achieve miniaturization and weight saving of an apparatus, and can transmit light, which is incident, in an optical axis direction and also a direction other than the optical axis direction, and an image taking apparatus which is miniaturized and weight-saved, and can make an irradiation position or an irradiation angle of fill light variable, and a flash light emitting unit incorporating the liquid crystal lens.  
     SUMMARY OF THE INVENTION  
      A liquid crystal lens of the present invention has an optically transparent liquid crystal plate which is composed of two or more liquid crystal pixels divided two-dimensionally, and a liquid crystal drive section which selects only a part of the two or more liquid crystal pixels at the same time and controls voltage application to the liquid crystal pixels which are selected, so as to form, in the liquid crystal plate, a refractive index distribution of light transmitted through the liquid crystal plate, by voltage application control to the liquid crystal pixels which are selected.  
      The liquid crystal lens of the present invention is made with paying attention to that a response speed of a liquid crystal used for the liquid crystal lens is comparatively slow, and hence, it is also possible to keep the refractive index distribution since a state of the liquid crystal is kept even if voltages are applied to only a part at the same time.  
      In addition, it is possible to make also a center and a distribution itself of a refractive index distribution variable by using two or more liquid crystal pixels divided two-dimensionally. For example, it is possible to form in the liquid crystal plate a first refractive index distribution that light is transmitted from a center section of the liquid crystal plate, by selecting only a first part of two or more liquid crystal pixels at the same time to apply a predetermined voltage, or form in the liquid crystal plate a second refractive index distribution that light is transmitted from a left section of the liquid crystal plate by selecting only a second part of the two or more liquid crystal pixels at the same time to apply a predetermined voltage. Hence, it is possible to emit light in an optical axis direction or a direction other than the optical axis direction with a single power source.  
      Here, it is preferable that the voltage application control to the selected liquid crystal pixels in the liquid crystal lens of the present invention is performed to liquid crystal pixels outside an approximate distribution range of the refractive index distribution.  
      Hereby, when the liquid crystal lens of the present invention is used for a flash light emitting unit, or an AF light emitting unit, it is possible to radiate light, which is radiated from one of those light emitting units, toward the front, left side, lower left side, or the like of an object, and hence, it is possible to raise condensing efficiency in the front, left side, lower left side, or the like.  
      In addition, it is a preferable that the voltage application control to the selected liquid crystal pixels in the liquid crystal lens of the present invention is performed to liquid crystal pixels inside an approximate distribution range of the refractive index distribution.  
      Hereby, when the liquid crystal lens of the present invention is used for a flash light emitting unit, or an AF light emitting unit, it is possible to form a refractive index distribution according to a focal length of an image taking optical system. Hence, it is possible to radiate flash light or distance measurement fill light on an object located in a long distance by forming the refractive index distribution so that a refractive index may be little changed, and by making the flash light and the distance measurement fill light from the liquid crystal lens reach up to a long distance. Alternatively it is possible to radiate flash light or distance measurement fill light on an object located in a short distance by forming a refractive index distribution so that a refractive index of a liquid crystal lens may be significantly changed and by making the flash light and the distance measurement fill light from the liquid crystal lens reach in a short distance.  
      Furthermore, it is also preferable that voltage application control to the selected liquid crystal pixels in the liquid crystal lens of the present invention is performed in sequential selection.  
      Hereby, it is possible to simplify configuration of a circuit which performs voltage application control to the selected liquid crystal pixels.  
      In addition, in an image taking apparatus which has an image taking optical system with a variable focal length, captures an object image which is incident through the image taking optical system, and generates image data, the image taking apparatus of the present invention includes:  
      a light source which radiates fill light toward an object in image taking;  
      an optically transparent liquid crystal plate which is arranged in front of the light source, and is composed of two or more liquid crystal pixels divided two-dimensionally; and  
      a liquid crystal drive section which selects only a part of the liquid crystal pixels simultaneously and controls voltage application to the selected liquid crystal pixels, so as to form in the liquid crystal plate a refractive index distribution, according to a focal length of the image taking optical system, of the fill light emitted from the light source.  
      The image taking apparatus of the present invention is made with paying attention to that a response speed of a liquid crystal used for the liquid crystal lens is comparatively slow, and hence, it is also possible to keep a refractive index distribution since a state of the liquid crystal is kept even if a voltage is applied to only a part at the same time. In addition, it is possible to make also a center and a distribution itself of a refractive index distribution variable by using two or more liquid crystal pixels divided two-dimensionally. For example, it is possible to form in the liquid crystal plate a first refractive index distribution according to a first focus length by selecting only a first part of two or more liquid crystal pixels at the same time to apply a predetermined voltage, and to emit fill light from a center section of the liquid crystal plate, or to form in the liquid crystal plate a second refractive index distribution according to a second focus length by selecting only a second part of the two or more liquid crystal pixels at the same time to apply a predetermined voltage, and to emit fill light from a left section of the liquid crystal plate. Hence, it is possible to provide the image taking apparatus which is given miniaturization and weight saving, and can make an irradiation position or an irradiation angle of fill light variable.  
      Here, it is preferable that the voltage application control to the selected liquid crystal pixels in the image taking apparatus of the present invention is performed to liquid crystal pixels outside an approximate distribution range of the refractive index distribution.  
      Hereby, it is possible to radiate light, which is radiated from a flash light emitting unit or an AF light emitting unit, which constructs the image taking apparatus of the present invention, toward the front, left side, lower left side, or the like of an object, and hence, it is possible to raise condensing efficiency in the front, left side, lower left side, or the like.  
      In addition, it is a preferable that the voltage application control to the selected liquid crystal pixels in the image taking apparatus of the present invention is performed to liquid crystal pixels inside an approximate distribution range of the refractive index distribution.  
      Hereby, in a flash light emitting unit, or an AF light emitting unit which construct the image taking apparatus of the present invention, it is possible to form a refractive index distribution according to a focal length of an image taking optical system. Hence, it is possible to radiate flash light or distance measurement fill light on an object located in a long distance by making the flash light and the distance measurement fill light reach up to a long distance, or to radiate the flash light or distance measurement fill light on an object located in a short distance by making the flash light and the distance measurement fill light reach in a short distance.  
      Furthermore, it is also preferable that voltage application control to the selected liquid crystal pixels in the image taking apparatus of the present invention is performed in sequential selection.  
      Hereby, it is possible to simplify configuration of a circuit which performs voltage application control to the selected liquid crystal pixels.  
      Additionally, a flash light emitting unit of the present invention has:  
      a light source;  
      an optically transparent liquid crystal plate which is arranged in front of the light source, and includes a plurality of liquid crystal pixels divided two-dimensionally; and  
      a liquid crystal drive section which selects only a part of the liquid crystal pixels simultaneously and controls voltage application to the selected liquid crystal pixels, so as to form in the liquid crystal plate a refractive index distribution of the fill light emitted from the light source.  
      The flash light emitting unit of the present invention is made with paying attention to that a response speed of a liquid crystal used for the liquid crystal lens is comparatively slow, and hence, it is also possible to keep a refractive index distribution since a state of the liquid crystal is kept even if a voltage is applied to only a part at the same time. In addition, it is possible to make also a center and a distribution itself of a refractive index distribution variable by using two or more liquid crystal pixels divided two-dimensionally. For example, it is possible to form in the liquid crystal plate a first refractive index distribution according to a first focus length by selecting only a first part of two or more liquid crystal pixels at the same time to apply a predetermined voltage, and to emit fill light from a center section of the liquid crystal plate, or to form in the liquid crystal plate a second refractive index distribution according to a second focus length by selecting only a second part of the two or more liquid crystal pixels at the same time to apply a predetermined voltage, and to emit fill light from a left section of the liquid crystal plate. Hence, it is possible to provide the flash light emitting unit which is given miniaturization and weight saving, and can make an irradiation position or an irradiation angle of fill light variable.  
      Here, it is preferable that the voltage application control to the selected liquid crystal pixels in the flash light emitting unit of the present invention is performed to liquid crystal pixels outside an approximate distribution range of the refractive index distribution.  
      Hereby, it is possible to radiate light, which is radiated from a flash light emitting unit or an AF light emitting unit, which constructs the image taking apparatus of the present invention, toward the front, left side, lower left side, or the like of an object, and hence, it is possible to raise condensing efficiency in the front, left side, lower left side, or the like.  
      In addition, it is a preferable that the voltage application control to the selected liquid crystal pixels in the flash light emitting unit of the present invention is performed to liquid crystal pixels inside an approximate distribution range of the refractive index distribution.  
      Hereby, in the flash light emitting unit, or the AF light emitting unit, it is possible to form a refractive index distribution of the light emitted from the light source. Hence, it is possible to radiate flash light or distance measurement fill light on an object located in a long distance by making the flash light and the distance measurement fill light reach up to a long distance, or to radiate the flash light or distance measurement fill light on an object located in a short distance by making the flash light and the distance measurement fill light reach in a short distance.  
      Furthermore, it is also preferable that voltage application control to the selected liquid crystal pixels in the flash light emitting unit of the present invention is performed in sequential selection.  
      Hereby, it is possible to simplify configuration of the circuit which performs voltage application control to the selected liquid crystal pixels.  
      As described above, the present invention can provide the liquid crystal lens which can achieve miniaturization and weight saving of an apparatus, and can transmit light, which is incident, in an optical axis direction and also a direction other than the optical axis direction, and the image taking apparatus and the flash light emitting unit which are given miniaturization and weight saving, and can make an irradiation position and an irradiation angle of fill light variable. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a sectional view of a first embodiment of a liquid crystal lens of the present invention;  
       FIG. 2  is a diagram schematically showing transparent electrodes and transparent XY address selection sections which construct the liquid crystal lens shown in  FIG. 1 ;  
       FIGS. 3A through 3C  are drawings showing examples that the transparent XY address selection sections shown in  FIG. 2  select a part of the two or more liquid crystal pixels of the transparent electrodes;  
       FIGS. 4A through 4C  are drawings showing other examples that the transparent XY address selection sections shown in  FIG. 2  select a part of the two or more liquid crystal pixels of the transparent electrodes;  
       FIGS. 5A and 5B  are external perspective views of a digital camera which is a first embodiment of an image taking apparatus of the present invention;  
       FIG. 6  is a block diagram showing circuit configuration of the digital camera shown in  FIGS. 5A and 5B ;  
       FIG. 7  is a diagram showing positional relation among a light source, a reflector, and a liquid crystal lens which construct the flash light emitting unit shown in  FIG. 6 ;  
       FIG. 8  is a diagram showing a state that an irradiation position and irradiation angle of flash light which is emitted from the light source shown in  FIG. 7  are made variable with the liquid crystal lens;  
       FIGS. 9A and 9B  are external perspective views of a digital camera which is a second embodiment of the image taking apparatus of the present invention;  
       FIG. 10  is a block diagram showing circuit configuration of the digital camera shown in  FIGS. 9A and 9B ;  
       FIG. 11  is a diagram showing configuration of the light source shown in  FIG. 10 ;  
       FIG. 12  is a diagram showing positional relation between the light source and the liquid crystal lens which are shown in  FIG. 11 ; and  
       FIG. 13  is a drawing showing a state that an irradiation position and an irradiation angle of distance measurement fill light which is emitted from the light source shown in  FIG. 12  are made variable with the liquid crystal lens.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED INVENTION  
      Hereafter, embodiments of the present invention will be explained with reference to the attached drawings.  
       FIG. 1  is a sectional view of a first embodiment of a liquid crystal lens of the present invention.  
      A liquid crystal lens  3  shown in  FIG. 1  has a spacer  31 , tabular transparent substrates  32  and  33  arranged oppositely through the spacer  31 , transparent XY address selection sections  38  and  39  arranged inside the transparent substrates  32  and  33 , transparent electrodes  34  and  35  arranged inside the transparent XY address selection sections  38  and  39 , light distribution films  36  and  37  arranged inside the transparent electrodes  34  and  35 , and liquid crystal  40  filled in a space defined by the spacer  31  and light distribution films  36  and  37 . The liquid crystal  40  has liquid crystal molecules  40   a.    
      The transparent substrates  32  and  33  are formed of a material which has a high transmission factor in a wavelength band of incident light, and glass, a high polymer film, or the like can be used for them.  
      The transparent electrodes  34  and  35  are equivalent to the examples of the optically transparent liquid crystal plates called in the present invention, and, although their details will be mentioned later, they are optically transparent liquid crystal plates which are composed of two or more liquid crystal pixels divided two-dimensionally.  
      The transparent XY address selection sections  38  and  39  are equivalent to examples of the liquid crystal drive sections called in the present invention, and, although details will be described later, they select only a part of the two or more liquid crystal pixels at the same time, and control voltage application to the selected liquid crystal pixels with a control signal from an Liquid crystal controller  1 _ 3 .  
      The light distribution films  36  and  37  are for orienting the liquid crystal molecules  40   a  in a predetermined array direction, when a voltage is not applied to the transparent electrodes  34  and  35 .  
       FIG. 2  is a diagram schematically showing transparent electrodes and transparent XY address selection sections which construct the liquid crystal lens shown in  FIG. 1 .  
       FIG. 2  shows the transparent electrodes  34  and  35  which construct the liquid crystal lens  3 , the transparent XY address selection section  38  which is composed of an X-direction selection circuit  38 _ 1  and a Y-direction selection circuit  38 _ 2 , and the transparent XY address selection section  39  which is composed of an X-direction selection circuit  39 _ 1  and a Y-direction selection circuit  39 - 2 .  
      The transparent electrode  34  is the electrode which is composed of two or more liquid crystal pixels  34   a  divided two-dimensionally. In addition, the transparent electrode  35  is an electrode which is composed of two or more liquid crystal pixels  35   a  divided two-dimensionally.  
      While voltages are supplied from a power source  1 _ 5  into the X-direction selection circuit  38 _ 1  and the Y-direction selection circuit  38 _ 2 , control signals from the liquid crystal controller  1 _ 3  shown in  FIG. 1  are inputted into them. In addition, while voltages are supplied from the power source  1 _ 5 , control signals from the liquid crystal controller  1 _ 3  shown in  FIG. 1  are inputted into the X-direction selection circuit  39 _ 1  and the Y-direction selection circuit  39 _ 2 .  
       FIGS. 3A through 3C  are drawings showing examples that the transparent XY address selection sections shown in  FIG. 2  select a part of the two or more liquid crystal pixels of the transparent electrodes.  
      In addition, here, although an example of selecting a part of two or more liquid crystal pixels  34   a  of the transparent electrode  34  by the transparent XY address selection section  38  is explained, the transparent XY address selection section  39  selects also a part of the two or more liquid crystal pixels  35   a  of the transparent electrode  35  together which are equivalent to the part of the two or more liquid crystal pixels  34   a  of the transparent electrode  34 .  
       FIG. 3A  shows a state that the transparent XY address selection section  38  selects the liquid crystal pixels  34   a  in a peripheral section shown by hatching except a center section A in the two or more liquid crystal pixels  34   a  of the transparent electrode  34 . Specifically, addresses corresponding to the peripheral section except the center section A are specified (turned on) one by one by the transparent XY address selection section  38 , the liquid crystal pixels  34   a  in the peripheral section are selected one by one, and a voltage with a predetermined value is applied to those liquid crystal pixels  34   a  one by one. Here, since a reaction rate of the liquid crystal  40  is comparatively slow, the liquid crystal pixels  34   a  in the peripheral section, as shown in  FIG. 3A , are to be selected almost simultaneously. In such a state, the array direction of the liquid crystal molecules  38   a  in the peripheral section is in a state perpendicular to an optical axis. On the other hand, the array direction of the liquid crystal molecules  38   a  in the center section A is in a state horizontal to the optical axis. Hence, light which is incident into this liquid crystal lens  3  is to be transmitted from the center section A. Therefore, although details will be described later, when this liquid crystal lens  3  is used for a flash light emitting unit, or an AF light emitting unit, light which is radiated from one of those light emitting units is radiated toward the front of an object in the state shown in  FIG. 3A . In addition, a depth of focus is controllable with ON/OFF time of addresses, and also is controllable with a voltage when an applied voltage is controllable.  
      Here, when it is desired to radiate light, which is radiated from the light emitting unit, toward the left side of an object, as shown in  FIG. 3B , addresses corresponding to the peripheral section except the left center section B are sequentially designated (turned on). Hereby, a voltage with a predetermined value is applied to the liquid crystal pixels  34   a , which are arranged with corresponding to those addresses, one by one. Hence, light which is incident into this liquid crystal lens  3  is to be transmitted from the left center section B. In this manner, it is possible to radiate light, which is radiated from the light emitting unit, toward the left side of the object.  
      In addition, when it is desired to radiate light, which is radiated from the light emitting unit, toward the lower left side of an object, as shown in  FIG. 3C , addresses corresponding to the peripheral section except the lower left section C are sequentially designated (turned on). Hereby, a predetermined voltage is applied to the liquid crystal pixels  34   a , which are arranged with corresponding to those addresses, one by one. Hence, light which is incident into this liquid crystal lens  3  is to be transmitted from the lower left section C. In this manner, it is possible to radiate light, which is radiated from this light emitting unit, toward the lower left side of the object.  
      Furthermore, here, the example of applying a voltage with such a value that an array direction of the liquid crystal pixels  34   a  in the peripheral section is in a state perpendicular to the optical axis to those liquid crystals pixels  34   a  is explained. But, it is possible to achieve a concave (or convex) lens function by applying a voltage with magnitude, in which array directions of the liquid crystal pixels  34   a  in the peripheral section have a predetermined angle to the optical axis, to these liquid crystals pixels  34   a.    
       FIGS. 4A through 4C  are drawings showing other examples that the transparent XY address selection sections shown in  FIG. 2  select a part of the two or more liquid crystal pixels of the transparent electrodes.  
       FIG. 4A  shows a state that the transparent XY address selection section  38  sequentially selects the liquid crystal pixels  34   a  in the peripheral section shown by hatching except the center section A in the two or more liquid crystal pixels  34   a  of the transparent electrode  34 . Here, since an area of the center section A is larger than an area of the peripheral section, most of the light which is incident into the liquid crystal lens  3  is to be transmitted from the center section A.  
      In addition, although it does not limit to explanation of this figure, the part to be selected may become reverse (exclusive) depending on a liquid crystal and initial orientation.  
      Moreover, when it is desired to radiate a large part of light, which is radiated from the light emitting unit, toward the left side of an object, as shown in  FIG. 4B , the liquid crystal pixels  34   a  in the peripheral section except the left section B are sequentially selected. Hereby, the large part of light which is incident into this liquid crystal lens  3  is to be transmitted from the left section B.  
      Further, when it is desired to radiate a large part of light, which is radiated from the light emitting units, toward the lower left side of an object, as shown in  FIG. 4C , the liquid crystal pixels  34   a  in the peripheral section except the lower left section C are sequentially selected. Hereby, the large part of light which is incident into this liquid crystal lens  3  is to be transmitted from the lower left section C. Hereby, it is possible to raise condensing efficiency.  
      The liquid crystal lens  3  of this embodiment can form in the transparent electrodes  34  and  35  a first refractive index distribution that light is emitted from center sections of the transparent electrodes  34  and  35  by sequentially selecting only the peripheral section, which is shown in  FIG. 3A , of the two or more liquid crystal pixels  34   a  and  35   a , which are divided two-dimensionally, at the same time to apply a predetermined voltage, or can form in the transparent electrodes  34  and  35  a second refractive index distribution that light is emitted from left sections of the transparent electrodes  34  and  35  by sequentially selecting only the peripheral section, which is shown in  FIG. 3B , of the two or more liquid crystal pixels  34   a  and  35   a , which are divided two-dimensionally, at the same time to apply a predetermined voltage. Hence, it is possible to achieve miniaturization and weight saving of an apparatus, and to transmit light, which is incident, in an optical axis direction and also a direction other than the optical axis direction.  
       FIGS. 5A and 5B  are external perspective views of a digital camera which is a first embodiment of the image taking apparatus of the present invention.  
       FIG. 5A  shows a drawing in view of the upper front part of the digital camera which is the first embodiment of the image taking apparatus of the present invention. In addition,  FIG. 5B  shows a drawing in view of the upper back part of the digital camera which is the first embodiment of the image taking apparatus of the present invention.  
      The digital camera  100  shown in  FIGS. 5A and 5B  is a digital camera which has an image taking optical system with a variable focal length, and captures an object image, which is incident through the image taking optical system, to generate image data.  
      As shown in  FIG. 5A , a lens barrel  10  is arranged in the center of a camera body of the digital camera  100  of this embodiment. In the lens barrel  10 , the image taking optical system including a shooting lens  101  in which a zoom lens is embedded, and an image of an object is guided through the image taking optical system up to a CCD solid state image pickup device (hereafter, this is called a CCD) which is an image pickup device arranged inside the digital camera  100 .  
      In addition, a finder  105 , a metering section  16 , a distance measurement section  17 , and a flash light emitting unit  1  are arranged in the upper part of the lens barrel  10  of the digital camera  100  shown in  FIG. 5A . In order to obtain a suitable exposure value in image taking, the metering section  16  measures a metering range with a metering sensor, and obtains a metering value. The distance measurement section  17  has AF receiving windows  17   a  and  17   b  arranged in the positions mutually separated by a predetermined distance, and receives reflected light which is the spontaneously scattered light (the flash light emitting unit  1 , sunlight, or the like) from an object with a light-receiving device through these AF receiving windows  17   a  and  17   b  to measure an object distance by using a so-called principle of triangular distance measuring. The flash light emitting unit  1  has the liquid crystal lens  3  mentioned above.  
      In addition, as shown in  FIG. 5B , an operating switch group  111  for performing various operations when a user uses this digital camera  100  is provided in the backface and the upper face of the digital camera  100  of this embodiment.  
      This operating switch group  111  includes a shutter button  111   b , a cross key  111   c , a menu/OK key  111   d , a cancel key  111   e , a mode lever  111   f , and the like as well as a power switch  111   a  for operating the digital camera  100 . The mode lever  111   f  in this operating switch group  111  switches a playback mode and a shooting mode, and further switches a moving image mode and a still image mode in the shooting mode. When this mode lever  111   f  is switched to the shooting mode, a through image is displayed. When the shutter button  111   b  is pressed with looking at the through image, image taking of an object is performed. On the other hand, when being switched to the playback mode, a playback display of a shot image is performed on a LCD panel  150 .  
      In addition, a focal length is changed by the shooting lens  101 , provided in the lens barrel  10 , being moved along the optical axis between a wide (wide angle) end and a tele (telescopic) end by the operation of the cross key  111   c.    
       FIG. 6  is a block diagram showing circuit configuration of the digital camera shown in  FIGS. 5A and 5B .  
      This digital camera  100  has the shooting lens  101 , metering section  16 , distance measurement section  17 , and flash light emitting unit  1 . In addition, the configuration of the flash light emitting section  1  will be mentioned later.  
      Furthermore, this digital camera  100  has a shutter unit  121 , an imaging device (CCD)  122 , an analog signal processing section  123 , a CPU  124  which controls operations of this digital camera  100  as a whole, a drive circuit  125 , and an A/D (analog to digital) section  126 . The drive circuit  125  drives the shooting lens  101 , shutter unit  121 , imaging device  122 , metering section  16 , distance measurement section  17 , and flash light emitting section  1  according to the image taking conditions.  
      Object light passing through the shooting lens  101  and shutter unit  121  is incident into the imaging device  122 . The imaging device  122  converts the incident object light into an analog image signal which is an electric signal, and outputs it to an analog signal processing section  123 .  
      The analog signal processing section  123  gives noise reduction processing and the like to the analog image signal outputted from the imaging device  122 , and outputs the analog image signal, which is given the processing and the like, to the A/D section  126 . The A/D section  126  gives A/D (analog to digital) conversion processing to the analog image signal and outputs a digital image signal.  
      In addition, the digital camera  100  has a digital signal processing section  127 , temporary memory  128 , a compression/decompression section  129 , internal memory (or a memory card)  130 , and an image monitor  150 . A digital image signal which is converted into digital by being given A/D conversion processing by the A/D section  126  is inputted into the digital signal processing section  127 . The digital signal processing section  127  gives predetermined digital signal processing to the inputted digital image signal to complete image data which represents the object image taken by the shooting operation, and stores it temporarily in the temporary memory  128 . The data stored in the temporary memory  128  is compressed by the compression/decompression section  129 , and is recorded in the internal memory (or memory card)  130 . In addition, a compression process may be skipped depending on a shooting mode, and may be directly recorded in the internal memory  130 . The data stored in the temporary memory  128  is read by the image monitor  150 , and, hereby, the image of the object is displayed on the image monitor  150 .  
      Furthermore, the digital camera  100  has the operating switch group  111  mentioned above. In image taking, the operating switch group  111  is operated for a desired image taking state to be set, and the shutter button  111   b  is depressed. Here, when object brightness is insufficient, flash light as image taking fill light is radiated toward an object from the flash light emitting unit  1 , explained below, in synch with a shutter operation.  
      The flash light emitting unit  1  has the liquid crystal lens  3  mentioned above, liquid crystal controller  1 _ 3 , and a power source  1 _ 5 . In addition, this flash light emitting unit  1  has a light source  1 _ 1 , a reflector  1 _ 2 , and a communication unit  1 _ 4 .  
      The light source  1 _ 1  radiates flash light as image taking fill light toward an object in image taking.  
      The reflector  1 _ 2  is arranged in the backface of the light source  1 _ 1  to reflect flash light, which is emitted from the light source  1 _ 1  and goes to the backface, to the liquid crystal lens  3 .  
      The communication unit  1 _ 4  receives data from the CPU  124  for controlling the liquid crystal lens  3 , and transmits it to the liquid crystal controller  1 _ 3 .  
       FIG. 7  is a diagram showing positional relation between the light source, reflector, and liquid crystal lens which construct the flash light emitting unit shown in  FIG. 6 , and  FIG. 8  is a diagram showing a state that an irradiation position and irradiation angle of flash light which is emitted from the light source shown in  FIG. 7  are made variable with the liquid crystal lens.  
      As shown in  FIG. 7 , the liquid crystal lens  3  is arranged in the front face of the light source  1 _ 1 , and both of flash light emitted by the light source  1 _ 1  and flash light reflected by the reflector  1 _ 2  are incident into the liquid crystal lens  3 . As mentioned above, the liquid crystal lens  3  has the transparent electrodes  34  and  35  which are composed of two or more liquid crystal pixels  34   a  and  35   a  divided two-dimensionally, and forms in the transparent electrodes  34  and  35  a refractive index distribution according to a focal length of an image taking optical system for flash light emitted from the light source  1 _ 1  by sequentially selecting only a part of the two or more liquid crystal pixels  34   a  and  35   a  in the transparent XY address selection sections  38  and  39  at the same time, and controlling only the part of the liquid crystal pixels  34   a  and  35   a , which are selected sequentially, at the same time. For this reason, as shown in  FIG. 8 , it is possible to radiate the flash light A 1  in the optical axis direction according to an object distance, or to radiate the flash light A 2  in the lower direction other than the optical axis direction. In addition, a mechanical mechanism does not need to be used for this flash light emitting unit  1 , and, hence, the miniaturization and the weight saving are achieved.  
       FIGS. 9A and 9B  are external perspective views of a digital camera which is a second embodiment of the image taking apparatus of the present invention, and  FIG. 10  is a block diagram showing the circuit configuration of the digital camera shown in  FIGS. 9A and 9B .  
      In addition, the same reference numerals are applied to the same components as the components of the digital camera  100  shown in  FIGS. 5A and 5B , and  FIG. 6 , and only different points will be explained.  
      A digital camera  200  shown in  9 B has a conventional flash light emitting unit  201 , and the AF light emitting unit  2  and an AF light receiving section  202  which construct an auto-focusing (AF) apparatus generally called an active type. The AF light emitting unit  2  is a unit which assists an auto-focusing (AF) function by emitting distance measurement fill light at the time of image taking under low illuminance. As shown in  FIG. 10 , this AF light emitting unit  2  has the liquid crystal lens  3  mentioned above, liquid crystal controller  1 _ 3 , communication section  1 _ 4 , and power source  1 _ 5 . Furthermore, this AF light emitting unit  2  has a light source  20  mentioned later. Distance measurement fill light A emitted from the AF light emitting unit  2  toward the front side of the digital camera  200  is reflected by an object, and distance measurement fill light B which is reflected and returned is received by the AF light receiving section  202 , and, thereby, a distance to the object is obtained by the CPU  124 .  
       FIG. 11  is a diagram showing the configuration of the light source shown in  FIG. 10 .  
      The light source  20  shown in  FIG. 11  has a metal base composite layered substrate  25  that is composed of composite layers  25 _ 1  and  25 _ 2 , and a base metal  25 _ 3 , LED  21  in which a flip-chip is mounted on the layered substrate  25  and a phosphor  22 , a lens section  23  which are formed so as to cover these LED  21  and the phosphor  22 , and a reflecting plate  24 . A light emitting layer of the LEDs  21  are located downward in  FIG. 11 , and is defined at a predetermined irradiation angle by the surrounding reflecting plate  24  and lens section  23 .  
       FIG. 12  is a diagram showing positional relation between the light source and liquid crystal lens which are shown in  FIG. 11 , and  FIG. 13  is a diagram showing a state that an irradiation position and irradiation angle of distance measurement fill light which is emitted from the light source shown in  FIG. 12  are made variable with the liquid crystal lens.  
      As shown in  FIG. 12 , the liquid crystal lens  3  is arranged in the. front of the light source  20 , and, as shown in  FIG. 13 , the shooting lens  101  is provided in the lower section of the light source  20  and liquid crystal lens  3 . The distance measurement fill light emitted by the light source  20  is incident into the liquid crystal lens  3 . As mentioned above, when a refractive index distribution is formed in this liquid crystal lens  3  so that the refractive index may be changed so small as to form the refractive index distribution according to a focal length of the image taking optical system, as shown in  FIG. 13 , the distance measurement fill light A 1  emitted from this liquid crystal lens  3  reaches in a long distance. Hence, it is possible to radiate the distance measurement fill light on the object located in a long distance. On the other hand, when a refractive index distribution is formed so that the refractive index may be changed largely, the distance measurement fill light A 2  transmitted from this liquid crystal lens  3  reaches in a short distance. Hence, it is possible to radiate the distance measurement fill light on the object located in a short distance, as shown in  FIG. 13 .  
      The distance measurement fill light which is radiated on an object and is reflected by the object is incident into an imaging device (CCD) through the shooting lens  101  and a focus lens (not shown), and thereby, image data is generated. A focusing operation is performed on the basis of this image data. In this focusing operation, for example, so-called “hill-climbing type” continuous AF processing is performed. Thus, a focused position is decided by gradually moving a focus lens till a maximal point of an evaluation value while checking directions of increase and decrease of a focal evaluation value with performing minute movement of a focus lens along an optical axis back and forth.  
      Here, although the AF light emitting unit  2  is arranged above the optical axis of the shooting lens  101 , it is possible to form refractive index distributions of the transparent electrodes  34  and  35  of the liquid crystal lens  3  so that the distance measurement fill light may be radiated in a lower direction other than the optical axis direction. Hence, even if the distance measurement fill light is radiated on an object located in a short distance, it is possible to prevent interference with an AF operation under the influence of parallax. In addition, it is not necessary to enlarge a light source which emits distance measurement fill light, and hence, it is possible not only to achieve miniaturization of the AF light emitting unit  2 , but also to suppress power consumption.  
      In addition, in the embodiments mentioned above, although the examples of a digital camera are explained, the present invention is not limited to these, but can be applied to a camera, which is mounted in a cellular phone, a video camera, or the like.