Abstract:
An imaging apparatus includes a first member including a holding member, the retaining member holding a lens; a second member surrounding the first member; an imaging device arranged opposite to the first member and the lens; and a driving member arranged in a region adjacent to the first member driving the first member in the vertical direction relative to the imaging device. The first member includes at least a first portion and a second portion, the first portion having a first outer diameter and the second portion having a second outer diameter smaller than the first outer diameter, the first and second portions respectively having a first corner and a second corner, the first and second corners respectively having a first cutout portion and a second cutout portion. At least a portion of the driving member is disposed at a region corresponding to the second portion.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a Continuation of application Ser. No. 14/157,036, filed Jan. 16, 2014, which is a Continuation of application Ser. No. 12/814,973, filed on Jun. 14, 2010, now Abandoned, and claims priority to Japanese Patent Application JP 2009-163284 filed in the Japanese Patent Office on Jul. 10, 2009, the entire contents of which are hereby incorporated by reference. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to an imaging apparatus, and particularly to an imaging apparatus that allows reduction in size of a lens driving portion. 
         [0004]    2. Description of the Related Art 
         [0005]      FIG. 1  shows the configuration of an exemplary imaging apparatus of related art. An imaging apparatus  10  shown in  FIG. 1  includes a housing  11 , a lens barrel  12 , and an imaging device  13 . The imaging apparatus  10  is manufactured by assembling the lens barrel  12  and the imaging device  13  into the housing  11 . 
         [0006]    Lenses  21 ,  22 , and  23  are assembled into the lens barrel  12  and held therein. A thread  24  is provided on the outer side surface of the lens barrel  12 . The thread  24  engages a thread (not shown) provided on a lens carrier  31  disposed in the housing  11 . The thread engagement between the lens barrel  12  and the lens carrier  31  allows the distance to the imaging device  13  to be adjusted at the time of manufacture (the focus of the lenses to be adjusted). After the focus adjustment, the lens barrel  12  is glued to the lens carrier  31  so that the lens barrel  12  is fixed to the lens carrier  31 . 
         [0007]    Coils  32 - 1  and  32 - 2  are provided on the side surface of the lens carrier  31 . The coils  32 - 1  and  32 - 2  are shown as separate members for illustration purposes only, but a single coil  32  is in practice provided on the side surface of the lens carrier  31 . A magnet  33 - 1  is provided in the housing  11  and faces the coil  32 - 1 . Similarly, a magnet  33 - 2  is provided in the housing  11  and faces the coil  32 - 2 . Each of the magnets  33 - 1  and  33 - 2  is provided with a yoke, which is omitted in  FIG. 1 . The coil  32 , the magnets  33 , and the yokes form a voice coil motor. 
         [0008]    When a current is conducted through the coil  32 , a force is produced in the upward or downward direction in  FIG. 1 . The produced force moves the lens carrier  31  in the upward or downward direction. When the lens carrier  31  is moved, the lens barrel  12  fixed to the lens carrier  31  is also moved. The distance between the lenses  21  to  23  held in the lens barrel  12  and the imaging device  13  therefore changes. The mechanism described above enables autofocusing (AF) (see JP-A-2007-17791, for example). 
       SUMMARY OF THE INVENTION 
       [0009]    It is desirable in recent years to reduce the size of an AF driver as the size of digital cameras has been reduced and mobile phones having a digital camera capability have become popular. The size of an AF driver can be reduced by reducing the size of an optical system, such as lenses, but in return the amount of light likely decreases, disadvantageously resulting in degradation in image quality. It is therefore not preferable to reduce the size of lenses or similar optical components in order to reduce the size of an AF driver. Nevertheless, further reduction in size of the driver (an imaging apparatus including the driver) is desired, as described above. 
         [0010]    It is difficult to achieve further size reduction unless a change is made to the configuration shown in  FIG. 1 . The size of the imaging apparatus can be reduced by reducing the sizes of the lenses  21  to  23  to reduce the size of the lens barrel  12  with no change made to the configuration shown in  FIG. 1 . In this case, however, it is difficult to avoid the degradation in image quality described above. 
         [0011]    JP-A-2007-17791 describes an imaging apparatus that has a sector disposed between a subject and a lens and blocking light incident to the lens and how to reduce the size of the imaging apparatus. The imaging apparatus described in JP-A-2007-17791 includes a lens group containing a plurality of lenses having different diameters, and the sector is disposed between a subject and the lens group and blocks light incident to the lens group. The lens group is accommodated in a lens barrel. The outer circumferential sidewall of the lens barrel has a plurality of stepped sections having different diameters corresponding to the diameters of the lenses accommodated in the lens barrel, and a sidewall recess is formed along one of the stepped sections. Sector drive means for driving the sector is disposed in the sidewall recess. 
         [0012]    The imaging apparatus described in JP-A-2007-17791 is desired to be further reduced in size. The imaging apparatus described in JP-A-2007-17791 has a disadvantageous structure in which, for example, the lens barrel has no thread mechanism, which does not allow focus adjustment between the lens group and the imaging device at the time of manufacture. 
         [0013]    Lens driving methods have also been proposed without using the driving method described with reference to  FIG. 1 . For example, a driving method using a piezoelectric device and a driving method using a shape memory alloy have been proposed. It is desirable that the other driving methods described above can also be used and the size of a drive-related portion can be reduced. 
         [0014]    Thus, it is desirable to reduce a lens driving portion. 
         [0015]    An imaging apparatus according to an embodiment of the invention includes a first member that holds a lens, a second member to which the first member is fixed, and drive means for driving the second member in the vertical direction relative to an imaging plane of an imaging device. The first member has diameters different from each other, and a portion having a small diameter has a portion that engages the second member. The drive means is disposed in a space created by the difference between the different diameters. 
         [0016]    The first member may hold a plurality of lenses having diameters different from one another and may be shaped to have diameters corresponding to the diameters of the lenses. 
         [0017]    The drive means may be a voice coil motor formed of a coil, a magnet, and a yoke. The voice coil motor may be disposed in the space described above. The coil of the voice coil motor may be disposed on the side surface of the second member. 
         [0018]    The drive means may include a piezoelectric device, a shaft connected to the piezoelectric device, and a hook which is connected to the second member and through which the shaft passes. The piezoelectric device, the shaft, and the hook may be disposed in the space described above. 
         [0019]    The drive means may include a wire made of a shape memory alloy, a hook to which the wire is hooked, and electrodes connected to the wire. The wire, the hook, and the electrodes may be disposed in the space described above. 
         [0020]    In an imaging apparatus according to another embodiment of the invention, a thread is provided on a portion of a member that holds lenses, specifically, on the portion whose diameter corresponds to the lens having the smallest diameter, and the thread allows the portion to engage a member that drives the lenses. Drive means is provided in the space created by the different diameters. 
         [0021]    According to the embodiments of the invention, the size of a lens driving portion can be reduced. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  shows the configuration of an exemplary imaging apparatus of related art; 
           [0023]      FIG. 2  shows the configuration of an imaging apparatus of an embodiment to which the invention is applied; 
           [0024]      FIG. 3  describes the configuration of the imaging apparatus; 
           [0025]      FIG. 4  describes the size of the imaging apparatus; 
           [0026]      FIGS. 5A and 5B  show the configuration of an exemplary imaging apparatus of related art for comparison; 
           [0027]      FIGS. 6A and 6B  show the configuration of the imaging apparatus of another embodiment to which the invention is applied; 
           [0028]      FIGS. 7A and 7B  show the configuration of an exemplary imaging apparatus of related art for comparison; and 
           [0029]      FIGS. 8A and 8B  show the configuration of the imaging apparatus of another embodiment to which the invention is applied. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0030]    Embodiments of the invention will be described below with reference to the drawings. 
         [0031]    The invention can be applied to an imaging apparatus. The imaging apparatus described herein is specifically an apparatus accommodated in, for example, a digital still camera and a mobile phone having a digital still camera capability. In such an imaging apparatus, autofocusing (AF) is performed by driving a lens (for example, moving a lens relative to an imaging device in such a way that the lens approaches the imaging device or travels away therefrom). 
         [0032]    An imaging apparatus including a driver for performing autofocusing has a configuration, for example, shown in  FIG. 1 . Referring to  FIG. 1  again, the imaging apparatus  10  is formed of the housing  11 , which accommodates the lens carrier  31 . The lens carrier  31  is configured to be movable relative to the housing  11  in the upward and downward directions in  FIG. 1  (approaching the imaging device  13  or traveling away therefrom). The lens barrel  12 , which accommodates the plurality of lenses  21  to  23 , is disposed in the lens carrier  31  and fixed thereto. 
         [0033]    The embodiments described below primarily relate to the lens barrel and the lens carrier of the imaging apparatus described above. An imaging apparatus using a lens barrel and a lens carrier to which any of the embodiments described below is applied can be smaller than an imaging apparatus of related art. When such a smaller imaging apparatus is accommodated in an apparatus, such as a digital still camera and a mobile phone, the size of the apparatus can be reduced. Further, the space for the portion other than the imaging apparatus can be increased, whereby other functions can be enhanced. 
         [0034]    A description will next be made of an imaging apparatus expected to show the advantageous effects described above. Methods for performing autofocusing having been proposed include a method using a voice coil motor (the method described with reference to  FIG. 1 ), a method using a piezoelectric device, and a method using a wire made of a shape memory alloy. In the following description, the embodiments will be described with reference to the methods described above. That is, the following description includes a first embodiment in which a voice coil motor is used to perform autofocusing, a second embodiment in which a piezoelectric device is used to perform autofocusing, and a third embodiment in which a wire made of a shape memory alloy is used to perform autofocusing. 
         [0035]    In the following description, a member that holds a lens is referred to as a lens barrel, a member to which the lens barrel is fixed is referred to as a lens carrier, and a portion that drives the lens carrier is referred to as a driver, as appropriate. The lens barrel is a cylinder shaped in such a way that an upper diameter (outer diameter) and a lower diameter (outer diameter) are designed to match the respective lens diameters and hence different from each other. A portion (thread) that engages the lens carrier is provided on one of the upper and lower portions of the lens barrel, the portion having a smaller diameter. The difference in diameter creates a space, and drive means is provided in the created space. The drive means in the first to third embodiment differ from one another as described above and will be described below. 
       First Embodiment 
       [0036]    A first embodiment will be described below.  FIG. 2  shows an exemplary configuration of an imaging apparatus  100  in the first embodiment and is a cross-sectional view of the imaging apparatus  100 . The imaging apparatus  100  shown in  FIG. 2  includes a housing  101 , a lens barrel  102 , and an imaging device  103 .  FIG. 3  is an exploded view of respective parts of the imaging apparatus  100  shown in  FIG. 2 . 
         [0037]    Referring to  FIG. 3 , lenses  21 ,  22 , and  23  are assembled into the lens barrel  102  and held therein. A thread  111  is provided on the outer side surface of the lens barrel  102 . 
         [0038]    A lens carrier  121  is provided in the housing  101 . A thread  122  is provided on the inner side (inner diameter) of the lens carrier  121 . A coil  123  is provided on the outer (outer shape) side surface of the lens carrier  121 . The coil  123  surrounds the side surface of the lens carrier  121 . Magnets  124 - 1  and  124 - 2  are provided in predetermined positions on the inner side (inner diameter) of the housing  101  and face the coil  123 . The magnets  124 - 1  and  124 - 2  are disposed on opposite sides of the coil  123 . 
         [0039]    Each of the magnets  124 - 1  and  124 - 2  is provided with a yoke, but shown as a combined magnet and yoke in  FIGS. 2 and 3  as magnet  124 - 1  or magnet  124 - 2 . When it is not necessary to distinguish the magnets  124 - 1  and  124 - 2  from each other, the magnets  124 - 1  and  124 - 2  are hereinafter simply referred to as magnets  124 . 
         [0040]    The thread  111  on the lens barrel  102  engages the thread  122  provided on the lens carrier  121 . The engagement between the lens barrel  102  and the lens carrier  121  allows the distance to the imaging device  103  to be adjusted at the time of manufacture (the focus of the lenses to be adjusted). After the focus adjustment, the lens barrel  102  is glued to the lens carrier  121  so that the lens barrel  102  is fixed to the lens carrier  121 . 
         [0041]    After the lens barrel  102  is inserted into the housing  101  and fixed to the lens carrier  121 , the imaging device  103  is inserted into the housing  101  and fixed thereto. The imaging apparatus  100  having the configuration shown in  FIG. 2  is manufactured by sequentially assembling the lens barrel  102  and the imaging device  103  into the housing  101  as described above. 
         [0042]    In the imaging apparatus  100  having the configuration described above, when a current is conducted through the coil  123  provided on the lens carrier  121 , the interaction between the current and the magnets  124  produces a force oriented in the upward or downward direction in  FIGS. 2 and 3  depending on the direction in which the current flows. The produced force moves the lens carrier  121  in the upward or downward direction. When the lens carrier  121  is moved, the lens barrel  102  fixed to the lens carrier  121  is also moved. The distance between the lenses  21  to  23  held in the lens barrel  102  and the imaging device  103  therefore changes. Autofocusing (AF) is performed by the mechanism described above. 
         [0043]    The structure of the lens barrel  102  will further be described. Referring to  FIG. 3 , the lens barrel  102  has a stepped shape, a shape having two stepped sections in the configuration shown in  FIG. 3 . A stepped section  151  contains the lens  23 , and a stepped section  152  contains the lenses  21  and  22 . As shown in  FIG. 3 , the sizes of the lenses  21  to  23  satisfy the following relationship. 
         [0000]      lens 21&lt;lens 22&lt;lens 23 
         [0044]    The diameter of the stepped section  151  containing the lens  23  is therefore larger than that of the stepped section  152  containing the lenses  21  and  22 . The diameter of the stepped section  151  is slightly larger than that of the lens  23 . The diameter of the stepped section  152  is slightly larger than that of the lens  22  but smaller than that of the lens  23 . 
         [0045]    The thread  111  is provided on the stepped section  152 . The thread  111  provided on the stepped section  152  engages the thread  122  provided on the lens carrier  121 . The diameter of the lens carrier  121  is sized in such a way that the thread ill engages the thread  122 . The diameter of the lens carrier  121  is therefore sized to be slightly larger than that of the stepped section  152 . 
         [0046]    Further, the height of the stepped section  152  is shorter than that of the lens carrier  121 . The height used herein means the length in the up-down direction in  FIG. 3  (the direction toward or away from the imaging device). The height of the lens carrier  121  is determined in such a way that the stepped section  151  of the lens barrel  102  does not come into contact with an end of the lens carrier  121  when the lens barrel  102  is fixed to the lens carrier  121 . 
         [0047]    The imaging apparatus  10  of related art is now compared with the imaging apparatus  100  in the first embodiment. The upper portion of  FIG. 4  shows the configuration of the imaging apparatus  10  of related art shown in  FIG. 1 , and the lower portion of  FIG. 4  shows the configuration of the imaging apparatus  100  in the first embodiment of the invention shown in  FIG. 2 . 
         [0048]    Each of the imaging apparatus  10  and the imaging apparatus  100  includes the lenses  21  to  23 . The imaging apparatus  10  and the imaging apparatus  100  therefore do not differ from each other in terms of optical system and can hence capture images having the same image quality. Further, the imaging device  13  in the imaging apparatus  10  and the imaging device  103  in the imaging apparatus  100  have the same number of pixels and can capture images having the same image quality in this regard as well. 
         [0049]    It is, however, obvious that the imaging apparatus  100  is smaller than the imaging apparatus  10 . The reason for this is that the lens barrel  102  in the imaging apparatus  100  has a stepped shape and the diameter of the stepped section  152  accommodating the smaller lenses is smaller than the diameter of the stepped section  151  accommodating the larger lens. The size of the imaging apparatus  100  can be reduced accordingly. The size of the imaging apparatus  100  is reduced because the space created by the difference between the stepped sections  151  and  152 , specifically, the difference in diameter between the stepped sections  151  and  152 , accommodates the lens carrier  121 , the thread  122 , the coil  123 , and the magnets  124 . 
         [0050]    That is, the size of the imaging apparatus  100  can be reduced by shaping the lens barrel  102  in such a way that the diameter thereof gradually decreases in correspondence with the sizes of the lenses to be accommodated, providing the thread  111  on the stepped section having the smaller diameter so that the threaded portion engages the lens carrier  121 , and assembling a driver including the coil  123  and the magnets  124  on the side where the diameter is smaller. 
         [0051]    In the above description of “shaping the lens barrel  102  in such a way that the diameter thereof gradually decreases in correspondence with the sizes of the lenses to be accommodated,” “the diameter thereof gradually decreases” means that the following shapes can be employed. That is, for example, a stepped shape, like the stepped sections  151  and  152  shown in  FIG. 3 , can be employed. Although not shown, when three lenses, such as the lenses  21  to  23  shown in  FIG. 3 , are incorporated, a stepped shape not formed of two stepped sections but formed of three stepped sections corresponding to the number of lenses can be employed. 
         [0052]    Alternatively, although not shown, instead of a stepped shape, for example, a cone shape (part of a cone shape) whose diameter gradually and continuously decreases in the direction away from the imaging device  103  can be employed. Still alternatively, for example, a combined shape in which the threaded portion (corresponding to the stepped section  152  in  FIG. 3 ) has a cylindrical shape and the non-threaded portion (corresponding to the stepped section  151  in  FIG. 3 ) has part of a cone shape can be employed. Still alternatively, any shape one can think of from the shapes described above can be employed. 
         [0053]    In the imaging apparatus  10  of related art shown in the upper portion of  FIG. 4 , the lens carrier  31  is positioned outside the lens barrel  12 , and the coil  32  and the magnets  33  are further positioned outside the lens carrier  31 . That is, when the configuration described above is employed, the diameter of the lens carrier  31  is greater than that of the lens barrel  12 , and the coil  32  and the magnets  33  are further positioned outside the large-diameter lens carrier  31 , disadvantageously resulting in an increased size of the imaging apparatus  10  itself. 
         [0054]    On the other hand, since the imaging apparatus  100  shown in the lower portion of  FIG. 4 , to which the first embodiment of the invention is applied, has the configuration described above, the lens carrier  121  is positioned outside the lens barrel  102  but inside the largest-diameter portion (outer diameter) of the lens barrel  102 . Further, the coil  123  and the magnets  124  positioned outside the lens carrier  121  are positioned inside the outer diameter of the lens barrel  102 . Since none or only part of the lens carrier  121 , the coil  123 , and the magnets  124  is thus positioned outside the outer diameter of the lens barrel  102 , the size of the imaging apparatus  100  itself is reduced. 
         [0055]    In other words, the diameter of the lens barrel  102  on the side where the imaging device  103  is present is large, whereas the diameter of the lens barrel  102  on the opposite side is small. Since the diameters of the two portions of the lens barrel  102  differ from each other, a space is created where the difference is present. Accommodating drive means (the coil  123 , the magnets  124 , and the yokes in this case) for vertically moving the lens carrier  121  relative to the imaging plane of the imaging device  103  in the space allows the size of the imaging apparatus  100  to be reduced. 
         [0056]    As described above, the size of the imaging apparatus can be reduced by applying the invention. Further, the size reduction will not degrade the quality of a captured image. 
         [0057]    The focus adjustment carried out at the time of manufacture by using the engagement between the lens barrel  102  and the lens carrier  121  can be carried out in the same manner as the imaging apparatus  10  of related art. 
       Second Embodiment 
       [0058]    A second embodiment will be described below. The second embodiment relates to a case where a piezoelectric device is used to perform autofocusing. A piezoelectric device is a passive device using a piezoelectric effect in which a force applied to a piezoelectric member is converted into a voltage and vice versa. To describe an imaging apparatus using a piezoelectric device to perform autofocusing, the configuration of an imaging apparatus of related art is first shown in  FIGS. 5A and 5B  for comparison.  FIG. 5A  is a top view of an imaging apparatus  200 , and  FIG. 5B  is a side view (cross-sectional view) of the imaging apparatus  200 . 
         [0059]    The imaging apparatus  200  includes a housing  201 , a lens barrel  202 , and an imaging device  203 . Lenses  21 ,  22 , and  23  are assembled into the lens barrel  202  and held therein. A thread  211  is provided on the outer side surface of the lens barrel  202 . 
         [0060]    A lens carrier  221  is provided in the housing  201 . A thread  222  is provided on the inner side (inner diameter) of the lens carrier  221 . A slide hook  223  is provided in a predetermined position on the outer (outer shape) side surface of the lens carrier  221 . One of the ends of the slide hook  223  is connected to the lens carrier  221 , and the other end has a circular shape having a circular hole at the center thereof. A shaft  224  passes through the hole. 
         [0061]    A piezoelectric device  225  fixed to the housing  201  is attached to the shaft  224 . When a current is conducted through the piezoelectric device  225 , a force is produced and then the slide hook  223  slides. When the slide hook  223  slides, the lens carrier  221  moves relative to the housing  201  in the upward or downward direction (the direction toward or away from the imaging device  203 ). Autofocusing is thus performed. 
         [0062]    In the imaging apparatus  200  of related art shown in  FIGS. 5A and 5B , the lens carrier  221  is positioned outside the lens barrel  202  and the slide hook  223 , the shaft  224 , and the piezoelectric device  225  are further positioned outside the lens carrier  221 . That is, when the configuration described above is employed, the diameter of the lens carrier  221  is greater than that of the lens barrel  202 , and the slide hook  223 , the shaft  224 , and the piezoelectric device  225  are further positioned outside the large-diameter lens carrier  221 , resulting in an increased size of the imaging apparatus  200  itself. 
         [0063]    To address the problem, the imaging apparatus in the second embodiment to which the invention is applied has the configuration shown in  FIGS. 6A and 6B  to reduce the size of the imaging apparatus.  FIG. 6A  is a top view of an imaging apparatus  250 , and  FIG. 6B  is a side view (cross-sectional view) of the imaging apparatus  250 . 
         [0064]    The imaging apparatus  250  shown in  FIGS. 6A and 6B  has a configuration that is basically the same as that of the imaging apparatus  200  of related art shown in  FIGS. 5A and 5B . The imaging apparatus  250  includes a housing  251 , a lens barrel  252 , and an imaging device  253 . Lenses  21 ,  22 , and  23  are assembled into the lens barrel  252  and held therein. A thread  261  is provided on the outer side surface of the lens barrel  252 . 
         [0065]    A lens carrier  271  is provided in the housing  251 . A thread  272  is provided on the inner side (inner diameter) of the lens carrier  271 . A slide hook  273  is provided in a predetermined position on the outer (outer shape) side surface of the lens carrier  271 . One of the ends of the slide hook  273  is connected to (integrated with) the lens carrier  271 , and the other end has a circular shape having a circular hole at the center thereof. A shaft  274  passes through the hole. 
         [0066]    A piezoelectric device  275  fixed to the housing  251  is attached to the shaft  274 . When a current is conducted through the piezoelectric device  275 , a force is produced and then the slide hook  273  slides. When the slide hook  273  slides, the lens carrier  271  moves relative to the housing  251  in the upward or downward direction (the direction toward or away from the imaging device  253 ). Autofocusing is thus performed. 
         [0067]    The structure of the lens barrel  252  will further be described. Referring to  FIG. 6B , the lens barrel  252  has a stepped shape, a shape having two stepped sections in the configuration shown in  FIG. 6B . A stepped section  281  contains the lens  23 , and a stepped section  282  contains the lenses  21  and  22 . As shown in  FIG. 6B , the sizes of the lenses  21  to  23  satisfy the following relationship. 
         [0000]      lens 21&lt;lens 22&lt;lens 23 
         [0068]    The diameter of the stepped section  281  containing the lens  23  is therefore larger than that of the stepped section  282  containing the lenses  21  and  22 . The diameter of the stepped section  281  is slightly larger than that of the lens  23 . The diameter of the stepped section  282  is slightly larger than that of the lens  22  but smaller than that of the lens  23 . 
         [0069]    The thread  261  is provided on the stepped section  282 . The thread  261  provided on the stepped section  282  engages the thread  272  provided on the lens carrier  271 . The diameter of the lens carrier  271  is sized in such a way that the thread  261  engages the thread  272 . The diameter of the lens carrier  271  is therefore sized to be slightly larger than that of the stepped section  282 . 
         [0070]    Further, the height of the stepped section  282  is shorter than the height of the lens carrier  271 . The height used herein means the length in the up-down direction in  FIG. 6B  (the direction toward or away from the imaging device  253 ). The height of the lens carrier  271  is determined in such a way that the stepped section  281  of the lens barrel  252  does not come into contact with an end of the lens carrier  271  when the lens barrel  252  is fixed to the lens carrier  271 . 
         [0071]    The imaging apparatus  200  of related art is now compared with the imaging apparatus  250  in the second embodiment. Each of the imaging apparatus  200  and the imaging apparatus  250  includes the lenses  21  to  23 . The imaging apparatus  200  and the imaging apparatus  250  therefore do not differ from each other in terms of optical system and can hence capture images having the same image quality. Further, the imaging device  203  in the imaging apparatus  200  and the imaging device  253  in the imaging apparatus  250  have the same number of pixels and can capture images having the same image quality in this regard as well. 
         [0072]    It is, however, obvious that the imaging apparatus  250  is smaller than the imaging apparatus  200 . The reason for this is that the lens barrel  252  in the imaging apparatus  250  has a stepped shape and the diameter of the stepped section  282  accommodating the smaller lenses is smaller the diameter of the stepped section  281  accommodating the larger lens. The size of the imaging apparatus  250  can be reduced accordingly. The size of the imaging apparatus  250  is reduced because the space created by the difference between the stepped sections  281  and  282 , specifically, the difference in diameter between the stepped sections  281  and  282 , accommodates all or part of the lens carrier  271 , the slide hook  273 , and the shaft  274 . 
         [0073]    That is, the size of the imaging apparatus  250  can be reduced by shaping the lens barrel  252  in such a way that the diameter thereof gradually decreases in correspondence with the sizes of the lenses to be accommodated, providing the thread  261  on the stepped section having the smaller diameter so that the threaded portion engages the lens carrier  271 , and assembling a driver including the slide hook  273 , the shaft  274 , and the piezoelectric device  275  on the side where the diameter is smaller. 
         [0074]    In the above description of “shaping the lens barrel  252  in such a way that the diameter thereof gradually decreases in correspondence with the sizes of the lenses to be accommodated,” “the diameter thereof gradually decreases” means that the following shapes can be employed. That is, for example, a stepped shape, like the stepped sections  281  and  282  shown in  FIG. 6B , can be employed. Although not shown, when three lenses, such as the lenses  21  to  23  shown in  FIG. 6B , are incorporated, a stepped shape not formed of two stepped sections but formed of three stepped sections corresponding to the number of lenses can be employed. 
         [0075]    Alternatively, although not shown, instead of a stepped shape, for example, a cone shape (part of a cone shape) whose diameter gradually and continuously decreases in the direction away from the imaging device  253  can be employed. Still alternatively, for example, a combined shape in which the threaded portion (corresponding to the stepped section  282  in  FIG. 6B ) has a cylindrical shape and the non-threaded portion (corresponding to the stepped section  281  in  FIG. 6B ) has part of a cone shape can be employed. Still alternatively, any shape one can think of from the shapes described above can be employed. 
         [0076]    The imaging apparatus  200  of related art shown in  FIGS. 5A and 5B  disadvantageously has a structure that causes an increase in size of the imaging apparatus  200  itself, as described above. However, since the imaging apparatus  250  shown in  FIGS. 6A and 6B , to which the second embodiment of the invention is applied, has the configuration described above, the lens carrier  271  is positioned outside the lens barrel  252  but inside the largest-diameter portion of the lens barrel  252 . 
         [0077]    Further, all or part of the driver including the slide hook  273 , the shaft  274 , and the piezoelectric device  275  positioned outside the lens carrier  271  is positioned inside the largest-diameter portion (largest outer diameter) of the lens barrel  252 . Since none or only part of the lens carrier  271 , the slide hook  273 , the shaft  274 , and the piezoelectric device  275  is thus positioned outside the largest outer diameter of the lens barrel  252 , the size of the imaging apparatus  250  itself is reduced. 
         [0078]    In other words, the diameter of the lens barrel  252  on the side where the imaging device  253  is present is large, whereas the diameter of the lens barrel  252  on the opposite side is small. Since the diameters of the two portions of the lens barrel  252  differ from each other, a space is created where the difference is present. Accommodating drive means (the slide hook  273 , the shaft  274 , and the piezoelectric device  275  in this case) for vertically moving the lens carrier  271  relative to the imaging plane of the imaging device  253  in the space allows the size of the imaging apparatus  250  to be reduced. 
         [0079]    As described above, the size of the imaging apparatus can be reduced by applying the invention. 
         [0080]    The focus adjustment carried out at the time of manufacture by using the engagement between the lens barrel  252  and the lens carrier  271  can be carried out in the same manner as the imaging apparatus  200  of related art. 
         [0081]    The imaging apparatus  250  shown in  FIGS. 6A and 6B  includes one set of the slide hook  273  and the shaft  274 , two to four sets of a slide hook and a shaft can be provided. The sets of a slide hook and a shaft other than the set of the slide hook  273  and the shaft  274  are provided to support the lens carrier  271  but provided with no piezoelectric device. Providing a plurality of sets of a slide hook and a shaft in the imaging apparatus  250  does not increase the size of the configuration of the imaging apparatus  250 , but the imaging apparatus  250  can still be reduced in size. 
       Third Embodiment 
       [0082]    A third embodiment will be described below. The third embodiment relates to a case where a wire made of a shape memory alloy is used to perform autofocusing. A shape memory alloy is characterized in that the length thereof increases or decreases when a current is conducted therethrough. To describe an imaging apparatus using a wire made of a shape memory alloy to perform autofocusing, the configuration of an imaging apparatus of related art is first shown in  FIGS. 7A and 7B  for comparison.  FIG. 7A  is a top view of an imaging apparatus  300 , and  FIG. 7B  is a side view (cross-sectional view) of the imaging apparatus  300 . 
         [0083]    The imaging apparatus  300  includes a housing  301 , a lens barrel  302 , and an imaging device  303 . Lenses  21 ,  22 , and  23  are assembled into the lens barrel  302  and held therein. A thread  311  is provided on the outer side surface of the lens barrel  302 . 
         [0084]    A lens carrier  321  is provided in the housing  301 . A thread  322  is provided on the inner side (inner diameter) of the lens carrier  321 . Hooks  323 - 1  and  323 - 2  are provided in predetermined positions on the outer (outer shape) side surface of the lens carrier  321 . The hooks  323 - 1  and  323 - 2  are disposed on opposite sides of the lens carrier  321 . A wire  332  made of a shape memory alloy is hooked to the hooks  323 - 1  and  323 - 2  (hereinafter simply referred to as the hooks  323  when they are not necessary to be distinguished and the same applies to other portions in the following description). 
         [0085]    The wire  332  is also connected to electrodes  331 - 1  and  331 - 2 . When a current is conducted from the electrodes  331 - 1  and  331 - 2  through the wire  332  and the temperature thereof increases, the wire  332  made of a shape memory alloy decreases in length. When the length of the wire  332  decreases, the hooks  323  to which the wire  332  is hooked are lifted relative to the housing  301 . 
         [0086]    Since the hooks  323  are integrated with the lens carrier  321 , the hooks  323  lifted relative to the housing  301  lift the lens carrier  321  relative to the housing  301 . In this way, the lens carrier  321  is driven. Conversely, when the current flowing through the wire  332  is terminated, the temperature thereof decreases and the length thereof increases. When the length of the wire  332  increases (returns back to its original length), the hooks  323  and hence the lens carrier  321  are lowered. 
         [0087]    The lens barrel  302 , which holds the lenses, fits into the lens carrier  321 . Driving the lens carrier  321  in the way described above therefore changes the position of the lenses held in the lens barrel  302  and hence the focal distance is adjusted. That is, autofocusing is performed. 
         [0088]    In the imaging apparatus  300  of related art shown in  FIGS. 7A and 7B , the lens carrier  321  is positioned outside the lens barrel  302 , and the hooks  323 , the wire  332 , and the electrodes  331  are further positioned outside the lens carrier  321 . That is, when the configuration described above is employed, the diameter of the lens carrier  321  is greater than that of the lens barrel  302 , and the hooks  323 , the wire  332 , and the electrodes  331  are further positioned outside the large-diameter lens carrier  321 , resulting in an increased size of the imaging apparatus  300  itself. 
         [0089]    To address the problem, the imaging apparatus in the third embodiment to which the invention is applied has the configuration shown in  FIGS. 8A and 8B  to achieve size reduction.  FIG. 8A  is a top view of an imaging apparatus  350 , and  FIG. 8B  is a side view (cross-sectional view) of the imaging apparatus  350 . 
         [0090]    The imaging apparatus  350  shown in  FIGS. 8A and 8B  has a configuration that is basically the same as that of the imaging apparatus  300  of related art shown in  FIGS. 7A and 7B . The imaging apparatus  350  includes a housing  351 , a lens barrel  352 , and an imaging device  353 . Lenses  21 ,  22 , and  23  are assembled into the lens barrel  352  and held therein. A thread  361  is provided on the outer side surface of the lens barrel  352 . 
         [0091]    A lens carrier  371  is provided in the housing  351 . A thread  372  is provided on the inner side (inner diameter) of the lens carrier  371 . Hooks  373 - 1  and  373 - 2  are provided in predetermined positions on the outer (outer shape) side surface of the lens carrier  371 . The hooks  373 - 1  and  373 - 2  are disposed on opposite sides of the lens carrier  371 . A wire  382  made of a shape memory alloy is hooked to the hooks  373 - 1  and  373 - 2 . 
         [0092]    The wire  382  is also connected to electrodes  381 - 1  and  381 - 2 . When a current is conducted from the electrodes  381 - 1  and  381 - 2  through the wire  382  and the temperature thereof increases, the wire  382  made of a shape memory alloy decreases in length. When the length of the wire  382  decreases, the hooks  373  to which the wire  382  is hooked are lifted relative to the housing  351 . 
         [0093]    Since the hooks  373  are integrated with the lens carrier  371 , the hooks  373  lifted relative to the housing  351  lift the lens carrier  371  relative to the housing  351 . In this way, the lens carrier  371  is driven. Conversely, when the current flowing through the wire  382  is terminated, the temperature thereof decreases and the length thereof increases. When the length of the wire  382  increases (returns back to its original length), the hooks  373  and hence the lens carrier  371  are lowered. 
         [0094]    The lens barrel  352 , which holds the lenses, fits into the lens carrier  371 . Driving the lens carrier  371  in the way described above therefore changes the position of the lenses held in the lens barrel  352  and hence the focal distance is adjusted. That is, autofocusing is performed. 
         [0095]    The structure of the lens barrel  352  will further be described. Referring to  FIG. 8B , the lens barrel  352  has a stepped shape, a shape having two stepped sections in the configuration shown in  FIG. 8B . A stepped section  391  contains the lens  23 , and a stepped section  392  contains the lenses  21  and  22 . As shown in  FIG. 8B , the sizes of the lenses  21  to  23  satisfy the following relationship. 
         [0000]      lens 21&lt;lens 22&lt;lens 23 
         [0096]    The diameter of the stepped section  391  containing the lens  23  is therefore larger than that of the stepped section  392  containing the lenses  21  and  22 . The diameter of the stepped section  391  is slightly larger than that of the lens  23 . The diameter of the stepped section  392  is slightly larger than that of the lens  22  but smaller than that of the lens  23 . 
         [0097]    The thread  361  is provided on the stepped section  392 . The thread  361  provided on the stepped section  392  engages the thread  372  provided on the lens carrier  371 . The diameter of the lens carrier  371  is sized in such a way that the thread  361  engages the thread  372 . The diameter of the lens carrier  371  is therefore sized to be slightly larger than that of the stepped section  392 . 
         [0098]    Further, the height of the stepped section  392  is shorter than the height of the lens carrier  371 . The height used herein means the length in the up-down direction in  FIG. 8B  (the direction toward or away from the imaging device  353 ). The height of the lens carrier  371  is determined in such a way that the stepped section  391  of the lens barrel  352  does not come into contact with an end of the lens carrier  371  when the lens barrel  352  is fixed to the lens carrier  371 . 
         [0099]    The length of the hooks  373  attached to the lens carrier  371  is sized in such a way that part of the tips of the hooks  373  extends off the largest diameter (largest outer diameter) of the lens barrel  352  or the tips are preferably within the diameter of the lens barrel  352 . 
         [0100]    The imaging apparatus  300  ( FIGS. 7A and 7B ) of related art is now compared with the imaging apparatus  350  ( FIGS. 8A and 8B ) in the third embodiment. Each of the imaging apparatus  300  and the imaging apparatus  350  includes the lenses  21  to  23 . The imaging apparatus  300  and the imaging apparatus  350  therefore do not differ from each other in terms of optical system and can hence capture images having the same image quality. Further, the imaging device  303  in the imaging apparatus  300  and the imaging device  353  in the imaging apparatus  350  have the same size or the same number of pixels and can capture images having the same image quality in this regard as well. 
         [0101]    It is, however, obvious that the imaging apparatus  350  is smaller than the imaging apparatus  300 . The reason for this is that the lens barrel  352  in the imaging apparatus  350  has a stepped shape and the diameter of the stepped section  392  accommodating the smaller lenses is smaller than the diameter of the stepped section  391  accommodating the larger lens. The size of the imaging apparatus  350  can be reduced accordingly. The size of the imaging apparatus  350  is reduced because the space created by the difference between the stepped sections  391  and  392 , specifically, the difference in diameter between the stepped sections  391  and  392 , accommodates all or part of the lens carrier  371 , the hooks  373 , and the electrodes  381 . 
         [0102]    That is, the size of the imaging apparatus  350  can be reduced by shaping the lens barrel  352  in such a way that the diameter thereof gradually decreases in correspondence with the sizes of the lenses to be accommodated, providing the thread  361  on the stepped section having the smaller diameter so that the threaded portion engages the lens carrier  371 , and assembling a driver including the hooks  373 , the electrodes  381 , and the wire  382  on the side where the diameter is smaller. 
         [0103]    In the above description of “shaping the lens barrel  352  in such a way that the diameter thereof gradually decreases in correspondence with the sizes of the lenses to be accommodated,” “the diameter thereof gradually decreases” means that the following shapes can be employed. That is, for example, a stepped shape, like the stepped sections  391  and  392  shown in  FIG. 8B , can be employed. Although not shown, when three lenses, such as the lenses  21  to  23  shown in  FIG. 8B , are incorporated, a stepped shape not formed of two stepped sections but formed of three stepped sections corresponding to the number of lenses can be employed. 
         [0104]    Alternatively, although not shown, instead of a stepped shape, for example, a cone shape (part of a cone shape) whose diameter gradually and continuously decreases in the direction away from the imaging device  353  can be employed. Still alternatively, for example, a combined shape in which the threaded portion (corresponding to the stepped section  392  in  FIG. 8B ) has a cylindrical shape and the non-threaded portion (corresponding to the stepped section  391  in  FIG. 8B ) has part of a cone shape can be employed. Still alternatively, any shape one can think of from the shapes described above can be employed. 
         [0105]    The imaging apparatus  300  of related art shown in  FIGS. 7A and 7B  disadvantageously has a structure that causes an increase in size of the imaging apparatus  300  itself, as described above. However, since the imaging apparatus  350  shown in  FIGS. 8A and 8B , to which the third embodiment of the invention is applied, has the configuration described above, the lens carrier  371  is positioned outside the lens barrel  352  but inside the largest-diameter (outer diameter) portion of the lens barrel  352 . 
         [0106]    Further, all or part of the driver including the hooks  373 , the electrodes  381 , and the wire  382  positioned outside the lens carrier  371  is positioned inside the largest-diameter portion of the lens barrel  352 . Since none or only part of the lens carrier  371 , the hooks  373 , the electrodes  381 , and the wire  382  is thus positioned outside the largest diameter of the lens barrel  352 , the size of the imaging apparatus  350  itself is reduced. 
         [0107]    In other words, the diameter of the lens barrel  352  on the side where the imaging device  353  is present is large, whereas the diameter of the lens barrel  352  on the opposite side is small. Since the diameters of the two portions of the lens barrel  352  differ from each other, a space is created where the difference is present. Accommodating drive means (the hooks  373 , the electrodes  381 , and the wire  382  in this case) for vertically moving the lens carrier  371  relative to the imaging plane of the imaging device  353  in the space allows the size of the imaging apparatus  350  to be reduced. 
         [0108]    As described above, the size of the imaging apparatus can be reduced by applying the invention. Further, the size reduction will not degrade the quality of a captured image. 
         [0109]    The focus adjustment carried out at the time of manufacture by using the engagement between the lens barrel  352  and the lens carrier  371  can be carried out in the same manner as the imaging apparatus  300  of related art. 
         [0110]    The imaging apparatus  350  shown in  FIGS. 8A and 8B  includes the two hooks  373 , the two electrodes  381 , and the wire  382  connected to the hooks  373  and the electrodes  381  and surrounding the lens carrier  371 . The imaging apparatus  350  may alternatively include one of the hooks  373 , the two electrodes  381 , and the wire  382  connected to the hook  373  and the electrodes  381  and surrounding the lens carrier  371 . That is, the imaging apparatus  350  can, for example, be configured in such a way that the ends of the wire  382  are connected to the electrodes  381 - 1  and  381 - 2  and the hook  373 - 1  (or hook  373 - 2 ) is positioned in a central portion of the wire  382 . 
         [0111]    The configuration described above does not increase the size of the configuration of the imaging apparatus  350 , but the imaging apparatus  350  can still be reduced in size. 
         [0112]    The above first to third embodiments have been described with reference to a case where the lens closer to the imaging device is larger and the size of the lenses decreases in the direction away from the imaging device. The invention is, however, not limited to the lens layout described above. That is, for example, the invention can be applied to a case where the lens farther away from the imaging device is larger and the size of the lenses decreases in the direction toward the imaging device. 
         [0113]    When the lens layout described above is employed, the threads and the driver are provided on the side where the stepped portion accommodating smaller lenses is present. The size of the imaging apparatus can, of course, be reduced even when the lens layout described above is employed, as in the above embodiments. 
         [0114]    The above embodiments have been described with reference to the imaging apparatus including the three lenses  21  to  23 , but the invention is not necessarily applied to an imaging apparatus including three lenses. That is, the invention can be applied to an imaging apparatus including a plurality of lenses. 
         [0115]    When a plurality of lenses are provided and the diameter of the lenses increases (or decreases) toward the imaging device, the lens barrel holding the plurality of lenses is configured not to simply have a cylindrical shape but have a stepped shape according to the diameters of the lenses or a shape at least part of which gradually decreases in diameter. Shaping the lens carrier that holds the lens barrel in accordance with the shape of the lens barrel provides a sufficient space between the lens carrier and the inner wall of the lens module on the side where a subject is present, whereby the actuator can be disposed in the space. The lens module can therefore be reduced in size. 
         [0116]    In an imaging apparatus of related art having a structure in which no thread is provided on the lens barrel and the lens carrier, the focus adjustment with respect to the imaging device may not be carried out. In the present invention, threads are provided on the lens barrel and the lens carrier. Providing threads on the lens barrel and the lens carrier allows the focus adjustment with respect to the imaging device to be carried out, for example, at the time of manufacture. 
         [0117]    The stroke typically required to perform autofocusing can be minimized and the requirements on actuator characteristics can be lowered by applying the invention. Further, the resultant smaller stroke or movable range advantageously reduces power consumption. 
         [0118]    Embodiments of the invention are not limited to those described above, but a variety of changes can be made to the extent that they do not depart from the spirit of the invention. 
         [0119]    The present application contains subject matter related to that disclosed in Japanese Priority Patent Application JP 2009-163284 filed in the Japan Patent Office on Jul. 10, 2009, the entire contents of which is hereby incorporated by reference.