Patent Publication Number: US-9906696-B2

Title: Imaging device and interchangeable lens arranged to have a reduced amount of magnetic field reaching an image pickup element

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation of U.S. patent application Ser. No. 14/720,583, filed on May 22, 2015, entitled “IMAGING DEVICE AND INTERCHANGEABLE LENS ARRANGED TO HAVE A REDUCED AMOUNT OF MAGNETIC FIELD REACHING AN IMAGE PICKUP ELEMENT”, the content of which is expressly incorporated by reference herein in its entirety. This application also claims priority from Japanese Patent Application No. 2014-109036 filed May 27, 2014, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present disclosure relates to a technology of suppressing entering of leakage magnetic field noise, generated from a magnetic field generation source, into an image pickup element. 
     Description of the Related Art 
     Recently, an image pickup element mounted on an imaging device such as a digital camcorder or a digital still camera has higher ISO sensitivity. As such, a clearer image can be taken even in a scene of few light quantities such as night view. Along with improvements in sensitivity, however, an image pickup element is affected by weak noise which has not been a problem, whereby a problem of disturbance caused in an image is becoming apparent. 
     For example, in a digital single lens reflex camera, an interchangeable lens includes a coil provided inside a motor circuit for driving the lens. A slight amount of leakage magnetic flex generated from such a coil may affect the image pickup element to thereby cause disturbance of an image to be generated. 
     Conventionally, Japanese Patent Application Laid-open No. 2011-123432 proposes that in order to shield a magnetic field from a magnetic field generation source located around an image pickup element, part of the image pickup element is surrounded by a ferromagnetic substance having high relative permeability such as permalloy. 
     A plate member of a ferromagnetic substance having high relative permeability (such as permalloy, for example) exhibits a high magnetic field shielding effect if the surface area is large. However, it is expensive compared with stainless or steel sheet generally used for casings of electronic devices. As such, for inexpensive products, it is not allowable to use an effective, large ferromagnetic substance having high relative permeability. As such, it is desirable to have a configuration capable of effectively reducing the amount of a magnetic field reaching an image pickup element, even if the area of a ferromagnetic material having high relative permeability is small. 
     In view of the above, an object of the present technology is to reduce the amount of a magnetic field reaching an image pickup element even if the area (cubic content) of a magnetic body, made of a ferromagnetic material having high relative permeability, is small. 
     SUMMARY OF THE INVENTION 
     An imaging device of the present technology includes an imaging optical system; an image pickup element arranged opposite to the imaging optical system, and configured to perform photoelectric conversion on an optical image formed by the imaging optical system; a magnetic field generation source that generates a magnetic field when receiving an electric current supplied; an annular first magnetic body; and a second magnetic body. The first magnetic body is arranged between the magnetic field generation source and the image pickup element, and has an opening through which light directed from the imaging optical system toward the image pickup element passes. The second magnetic body is arranged at a position which is on the side of the magnetic field generation source with respect to the first magnetic body in an optical axis direction of the imaging optical system, and on the side of the magnetic field generation source with respect to the opening, while at least a portion thereof overlapping the first magnetic body when seen in the optical axis direction. The second magnetic body is made of a ferromagnetic material having higher relative permeability than that of the first magnetic body, and has a smaller area than that of the first magnetic body when seen in the optical axis direction. 
     Further features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings). 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram illustrating a schematic configuration of an imaging device according to a first embodiment of the present technology. 
         FIGS. 2A and 2B  are diagrams illustrating details of main part of the imaging device according to the first embodiment of the present technology. 
         FIG. 3  is a diagram illustrating a measurement system for measuring relative permeability. 
         FIG. 4  is a graph illustrating relative permeability with respect to the frequency of SUS430. 
         FIG. 5  is a graph illustrating results of obtaining a magnetic field reaching an image pickup element through electromagnetic field simulation. 
         FIG. 6  is a graph illustrating results of obtaining a magnetic field reaching an image pickup element through electromagnetic field simulation. 
         FIG. 7  is a graph illustrating results of obtaining a magnetic field reaching an image pickup element through electromagnetic field simulation. 
         FIGS. 8A and 8B  are diagrams illustrating a schematic configuration of an imaging device according to a second embodiment of the present technology. 
         FIG. 9  is a diagram illustrating a schematic configuration of an interchangeable lens according to a third embodiment of the present technology. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     First Embodiment 
     Hereinafter, an embodiment of the present technology will be described in detail with reference to the drawings.  FIG. 1  is a diagram illustrating a schematic configuration of a camera as an imaging device according to a first embodiment of the present technology. A digital camera (camera)  100  as an imaging device is a digital single lens reflex camera, which includes a camera main body  200  that is a main body of the imaging device, and an interchangeable lens (lens barrel)  300  attachable to and detachable from the camera main body  200 . In  FIG. 1 , the interchangeable lens  300  is attached to the camera main body  200 . Hereinafter, description will be given on the assumption that the interchangeable lens  300  is attached to the camera main body  200 . 
     The camera main body  200  includes a casing  201 , and also includes a mirror  222 , a shutter  223 , an imaging unit  202 , and an image processing circuit  224  which are disposed inside the casing  201 . The camera main body  200  also includes a liquid crystal display  225  fixed to the casing  201  so as to be exposed outside from the casing  201 . The imaging unit  202  includes an image pickup element  203  having a semiconductor unit (semiconductor chip)  231 . The semiconductor unit  231  has a light receiving surface  231   a.    
     The interchangeable lens  300  includes a casing  301  that is an interchangeable lens casing, and an imaging optical system  311  disposed inside the casing  301  and configured to form an optical image on the light receiving surface  231   a  of the image pickup element  203  when the casing  301  (interchangeable lens  300 ) is attached to the casing  201 . The imaging optical system  311  is configured of a plurality of lenses. 
     The interchangeable lens  300  also includes an annular lens driving motor  312  arranged around the imaging optical system  311 , and a drive circuit  313  for driving (operating) the lens driving motor  312 . The drive circuit  313  includes a printed wiring board formed in an annular shape, and a boosting coil  321  mounted on the printed wiring board. 
     The casing  301  has a lens-side mount  301   a  having an opening formed therein, and the casing  201  has a camera-side mount  201   a  having an opening formed therein. By fitting the lens-side mount  301   a  and the camera-side mount  201   a , the interchangeable lens  300  (casing  301 ) is attached to the camera main body  200  (casing  201 ). 
     An arrow X direction illustrated in  FIG. 1  is an optical axis direction of the imaging optical system  311 , which is vertical to the light receiving surface  231   a  of the image pickup element  203 . 
     Light traveling in the arrow X direction from the imaging optical system  311  is guided into the casing  201  through an opening in the lens driving motor  312 , an opening in the drive circuit  313 , the opening in the lens-side mount  301   a  of the casing  301 , and the opening in the camera-side mount  201   a  of the casing  201 . 
     Inside the casing  201 , the mirror  222 , the shutter  223 , and the like are provided along the arrow X direction in front side in the arrow X direction (the light receiving surface  231   a  side) of the imaging unit  202 . 
     The image pickup element  203  is an image sensor (solid-state image sensor) such as a CMOS image sensor or a CCD image sensor which performs photoelectric conversion on an optical image formed by the imaging optical system  311 . The image pickup element  203  is formed to have a quadrangle outer shape in a front view (seen from the arrow X direction vertical to the light receiving surface  231   a  of the image pickup element  203 ). 
     The image pickup element  203  is arranged inside the casing  201  such that when the interchangeable lens  300  is attached to the casing  201 , the light receiving surface  231   a  faces the imaging optical system  311  via the mirror  222 , the shutter  223 , and the like. 
     The image pickup element  203  performs photoelectric conversion on an optical image formed on the light receiving surface  231   a  by the imaging optical system  311  when the interchangeable lens  300  is attached to the casing  201 , and outputs an image signal to the image processing circuit  224 . The image processing circuit  224  performs image processing on the obtained image data, and outputs it to the liquid crystal display  225 , a memory (not illustrated), and the like. 
     The coil  321  is a magnetic field generation source which generates a magnetic field when an electric current is supplied, and is a source of magnetic field noise with respect to the image pickup element  203 . 
       FIGS. 2A and 2B  are diagrams illustrating the coil  321  and the imaging unit  202  which are main part of the camera  100 .  FIG. 2A  is a front view of the coil  321  and the imaging unit  202  seen in the arrow X direction.  FIG. 2B  is a side view of the coil  321  and the imaging unit  202  seen in a direction orthogonal to the arrow X direction. The image pickup element  203  includes the semiconductor unit  231  and a package substrate  232  on which the semiconductor unit  231  is mounted, in which a plurality of terminals  233  is fixed on the package substrate  232  and are mounted on (joined by soldering to) the printed wiring board  204 . The package substrate  232  is formed of a ceramic substrate, a resin substrate, a printed wiring board, or the like. 
     The imaging unit  202  includes a frame-like (annular) magnetic member  210  having an opening H disposed between the coil  321  that is a magnetic field generation source, and the image pickup element  203 . The magnetic member  210  is arranged adjacent to the image pickup element  203 . Specifically, as illustrated in  FIG. 2B , a first magnetic body  211  is arranged adjacent to the image pickup element  203  on the side where the coil  321  is arranged with respect to the image pickup element  203 , in the arrow X direction. 
     The magnetic member  210  includes the first magnetic body  211 , and a second magnetic body  212  made of a ferromagnetic material of higher relative permeability than that of the first magnetic body  211  and having a smaller area than that of the first magnetic body  211  when seen in the optical axis direction of the imaging optical system. Further, a region where the second magnetic body is arranged includes a region nearest to the coil  321  that is a magnetic field generation source of the annular magnetic member  210 . 
     The opening H is formed to have a size in which light travelling from the imaging optical system  311  to the light receiving surface  231   a  of the image pickup element  203  passes through. Specifically, the opening H is formed to have a larger area than that of the light receiving surface  231   a  when seen in the arrow X direction. Further, when seen in the arrow X direction, the opening H is formed to have a smaller area than that of the outer shape of the image pickup element  203  (the surface of the package substrate  232  on which the semiconductor unit  231  is mounted). The light receiving surface  231   a  is formed to be in a quadrangle shape when seen in the arrow X direction, and the opening H is also formed to be in a quadrangle shape when seen in the arrow X direction. 
     Further, the imaging unit  202  includes the second magnetic body  212  arranged at a position of the coil  321  side in the arrow X direction with respect to the first magnetic body  211 . The first magnetic body  211  has a surface  211   a  of the side where the coil  321  is arranged in the arrow X direction, and the second magnetic body  212  is arranged adjacent to the surface  211   a . In that case, it is preferable that the second magnetic body  212  is arranged with a slight gap with respect to the first magnetic body  211 , or arranged to be in contact with the first magnetic body  211 . While it is only necessary that the gap between the first magnetic body  211  and the second magnetic body  212  has magnetic coupling, it is preferable to bring the first magnetic body  211  and the second magnetic body  212  into contact with each other because the magnetic resistance is reduced. 
     Further, the first magnetic body  211  may be annular or have a structure in which a portion of the annular shape is cut off. In the case of a structure in which a portion of the annular shape is cut off, it is preferable that the first magnetic body  211  and the second magnetic body  212  are integrated, and that the shape of the integrated first magnetic body  211  and second magnetic body  212  is annular. Further, “annular” in this context may be toric, quadrangle annular, or other annular shapes. 
     As illustrated in  FIG. 2A , the second magnetic body  212  is arranged at a position of the coil  321  side with respect to the opening H when seen in the arrow X direction, while at least a portion thereof (the whole in the present embodiment) overlapping the first magnetic body  211 . Specifically, the second magnetic body  212  is arranged adjacent to one side, nearest to the coil  321 , of the four sides of the opening H. This means that the second magnetic body  212  is arranged on the frame portion of an opening side nearest to the coil  321 , on the surface  211   a  of the coil side of the first magnetic body  211 . 
     The first magnetic body  211  and the second magnetic body  212  are made of a ferromagnetic material and formed in a plate shape or a film shape. The second magnetic body  212  is made of a ferromagnetic material having higher relative permeability than that of the first magnetic body  211 . The second magnetic body  212  is formed to have a smaller area than that of the first magnetic body  211  when seen in the arrow X direction. Further, the second magnetic body  212  is formed to be thinner in the arrow X direction than the first magnetic body  211 . 
     It is preferable that the first magnetic body  211  is formed of stainless SUS430 which is made of a material having lower relative permeability. As the first magnetic body  211  is not an expensive material having high relative permeability such as permalloy which is typically used as a magnetic body, it is possible to suppress an increase in the cost even if the first magnetic body  211  is used in a large area. 
     It should be noted that besides SUS430, as the first magnetic body  211 , it is also possible to use SUS630, SPCC steel (cold rolled steel), or some galvanized steel such as Silver Top (registered trademark), which is a magnetic body having low relative permeability. Here, a magnetic body having low relative permeability means one having relative permeability of not less than 50 but not more than 1000, specifically. This can be preferably used as a material of the first magnetic body  211 . This means that the first magnetic body  211  may be formed including at least one of SUS430, SUS630, SPCC steel, and some galvanized steel. In other words, the first magnetic body  211  may be configured of any one of SUS430, SUS630, SPCC steel, and some galvanized steel, or a combination of two or more of them. For example, the first magnetic body  211  may be configured of a combination of SUS430 and SUS630. However, as the first magnetic body  211 , one having relative permeability of almost 1 which is not a so-called magnetic body, such as aluminum, copper, SUS304, or conductive plastic, is unable to be used. 
     On the other hand, the second magnetic body  212  is formed of a nanocrystal soft magnetic material such as Finemet (registered trademark) which is a ferromagnetic material having higher relative permeability than that of the first magnetic body  211 . Besides, as the second magnetic body  212 , it is also possible to use permalloy having high permeability, amorphous magnetic material, ferrite, electromagnetic steel, a noise suppression sheet having high permeability such as Busteraid (registered trademark)(containing magnetic powder, magnetic filler, or magnetic film), and the like. This means that it is only necessary that the second magnetic body  212  is formed by containing at least one of nanocrystal soft magnetic material, permalloy, amorphous magnetic material, ferrite, electromagnetic steel, and a noise suppression sheet having high permeability (containing magnetic powder, magnetic filler, or magnetic film). In other words, the second magnetic body  212  may be any one of nanocrystal soft magnetic material, permalloy, amorphous magnetic material, ferrite, electromagnetic steel, and a noise suppression sheet having high permeability, or a combination of two or more of them. The noise suppression sheet is one containing magnetic powder, magnetic filler, or magnetic film. 
     As the area of the second magnetic body  212 , seen in the arrow X direction, is significantly smaller than that of the first magnetic body  211 , it is possible to suppress an increase in the cost as a component. 
     Here, description will be added regarding relative permeability of SUS430 in a plate shape which constitutes the first magnetic body  211 . The relative permeability of SUS430 was measured under a condition that initial permeability was calculated by applying a magnetic flux density of not more than 1 μT specified by JIS 2561C. However, JIS 2561C specifies to perform measurement using a ring-shaped measurement sample. As such, permeability of a plate-like magnetic body to be actually used is unable to be calculated accurately with such a measurement method. Accordingly, it is necessary to use a tool capable of measuring a plate-like sample. 
       FIG. 3  is a diagram illustrating a measurement system for measuring relative permeability. A double yoke frame  41  (yokes  412  and a coil  411  surrounded by the yokes  412 ) illustrated in  FIG. 3  is one used in “electromagnetic steel plate veneer magnetism testing method” of JIS C2556, and a measurement sample  413  formed in a plate shape is inserted in the frame. To the coil  411  of the double yoke frame  41 , an LCR meter  42  (impedance analyzer is also acceptable) is connected to thereby obtain an inductance value. With reference to the inductance value of a state where the sample is not inserted, the real part p′ of permeability was calculated from the inductance value and the resistance value when the measurement sample  413  was inserted, using the following Expression (1). 
     
       
         
           
             
               Expression 
               ⁢ 
               
                   
               
               ⁢ 
               1 
             
             ⁢ 
             
                 
             
           
         
       
       
         
           
             
               
                 
                   
                     μ 
                     ′ 
                   
                   = 
                   
                     
                       
                         L 
                         ⁡ 
                         
                           ( 
                           
                             
                               L 
                               eff 
                             
                             - 
                             
                               L 
                               w 
                             
                           
                           ) 
                         
                       
                       
                         
                           μ 
                           0 
                         
                         ⁢ 
                         
                           N 
                           2 
                         
                         ⁢ 
                         A 
                       
                     
                     . 
                   
                 
               
               
                 
                   Expression 
                   ⁢ 
                   
                       
                   
                   ⁢ 
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
       
     
     Here, N=the number of windings of the coil, vacuum permeability μ 0 =4π×10 7  (H/m), A=sectional area of measurement sample, L=length of measurement sample, L eff =inductance measurement value obtained by LCR meter, and L w =inductance measurement value when sample is not inserted. 
       FIG. 4  illustrates relative permeability of stainless SUS430 obtained by this method.  FIG. 4  is a graph illustrating the relative permeability with respect to the frequency of SUS430. The horizontal axis shows the frequency and the vertical axis shows the relative permeability. In the case of low frequencies, relative permeability is almost 150 (no unit). In the case of high frequencies, as a magnetic field is less likely to enter due to an effect of an eddy current, it is found that effective relative permeability drops. 
     It is found that as the thickness is increased to 0.3 mm, 0.5 mm, and 0.9 mm, the relative permeability begins to drop in lower frequencies. Accordingly, a smaller thickness is advantageous for obtaining higher relative permeability in higher frequencies. 
     Accordingly, in the present embodiment, if the thickness of the first magnetic body  211  is 0.9 mm and the current flowing in the coil  321  is about 30 kHz, the relative permeability of the first magnetic body  211  is about 50 (no unit), according to  FIG. 4 . By performing relative permeability measurement depending on this thickness, it is possible to select a magnetic material of a plate member corresponding to the thickness to be used actually, as the first magnetic body  211  of low permeability. 
     Further, the relative permeability at 30 kHz of a nanocrystal soft magnetic material, which is the second magnetic body  212 , is about 20000 (no unit). Other materials such as permalloy, electromagnetic steel, ferrite, and pure iron, having high relative permeability, generally take values shown in Table 1, although depending on the frequency. 
     
       
         
           
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                   
                 Relative 
               
               
                   
                   
                 permeability 
               
               
                   
                   
               
             
            
               
                   
                 Nanocrystal soft magnetic 
                 20000-200000 
               
               
                   
                 material 
                   
               
               
                   
                 Permalloy 
                 2500-70000 
               
               
                   
                 Electromagnetic steel 
                 400-3200 
               
               
                   
                 Ferrite 
                 400-3000 
               
               
                   
                 Pure iron 
                 300-1000 
               
               
                   
                 Magnetic stainless, Steel sheet  
                 150-500   
               
               
                   
                   
               
            
           
         
       
     
     Among these materials, ferromagnetic materials having higher relative permeability than that of the first magnetic body  211  can be used as the second magnetic body  212 . Especially, one having relative permeability not less than 1000 (no unit) but less than 200000 which is the limit of industrial production can be preferably used as a material of the second magnetic body  212 . 
     According to the present embodiment, the following action is made. That is, in order to rotate the lens driving motor  312 , when an AC current of a driving frequency 30 kHz flows in the boosting coil  321 , for example, a slight leakage magnetic field is generated in the space around the coil  321 . The generated leakage magnetic field propagates the space while being attenuated. 
     As the magnetic field reaching near the image pickup element  203  is an alternate current, the direction is switched as constant vibration while being switched by the time period. From the viewpoint of a magnetic circuit, in  FIGS. 2A and 2B , the magnetic field reaching near the image pickup element  203  is shunted to two types of paths, namely, a magnetic transmission path R 1  reaching the image pickup element  203  shown by dotted-line arrows, and a magnetic transmission path R 2  passing through the magnetic bodies  211  and  212  shown by solid-line arrows. 
     As a shunt ratio of the magnetic field varies according to the magnetic resistance of each of the paths R 1  and R 2 , it is important to make the magnetic resistance of the magnetic transmission path R 2 , passing through the magnetic bodies  211  and  212 , lower than the magnetic resistance of the magnetic transmission path R 1  reaching the image pickup element  203 . In the magnetic resistance of the entire magnetic transmission path R 2  passing through the magnetic bodies  211  and  212 , magnetic resistance of a region where the second magnetic body  212  is provided, in which the magnetic field should be transmitted by being bent in a horizontal direction, is dominant. By reducing the magnetic resistance of such a region by providing the second magnetic body  212  having high relative permeability in a long length in a horizontal direction, it is possible to reduce the magnetic resistance of the entire path R 2  passing through the magnetic bodies  211  and  212 . 
     In other words, even if magnetic resistance of another portion (for example, the frame portions on both right and left sides of the first magnetic body  211 , the lower-side frame portion, or the inner peripheral surface on the image pickup element side of the upper-side frame portion) is reduced, while the magnetic resistance of the entire magnetic bodies  211  and  212  can be reduced a little, it cannot be reduced effectively. 
     In the present embodiment, by combining the first magnetic body  211  and the second magnetic body  212 , it is possible to reduce the magnetic resistance of the entire path R 2  passing through the magnetic bodies  211  and  212 . Accordingly, the magnetic field shunted to the magnetic transmission path R 2  is increased, whereby it is possible to reduce the magnetic field shunted to the magnetic transmission path R 1  reaching the image pickup element  203 . Consequently, it is possible to reduce the amount of a leakage magnetic field, generated from the boosting coil  321 , reaching the image pickup element  203 . As such, even if the semiconductor unit  231  of the image pickup element  203  performs operation to read an image signal, the influence by the magnetic field is less, image disturbance is less likely to be caused, and an original image signal is read. 
     The effect of suppressing image disturbance was tested in the digital single lens reflex camera  100  by capturing a dark image in a state of feeding an AC current to the coil  321  with no incident light. In the case of a dark image, as the entire image must show a certain level of luminance, deviation from the luminance value (deviation amount) is used here as an image disturbance amount. Assuming that an image disturbance amount without the first magnetic body  211  and the second magnetic body  212  is 100%, in the camera  100  of the present embodiment having the first magnetic body  211  and the second magnetic body  212 , the image disturbance amount was reduced to about 72%. 
     Next, effects provided by the shape of the second magnetic body  212  will be described in detail based on examples. 
     Example 1 
     In  FIG. 2A  illustrating a front view of the image pickup element  203 , the image pickup element  203  having the semiconductor unit  231  of 25 mm laterally wide and 18 mm vertically wide was used. Around the image pickup element  203 , the first magnetic body  211  (conductivity σ=1.0×10 7  (S/m), relative permeability 50 (no unit)) was provided. The first magnetic body  211  had an opening H of 36 mm laterally wide and 25 mm vertically wide, and the frame shape thereof was 7 mm laterally wide and 0.9 mm thick. Away from the first magnetic body  211  by 0.1 mm, the second magnetic body  212  (conductivity o=1.0×10 7  (S/m), relative permeability 10000 (no unit)) in a rectangle shape of 20 mm laterally wide, 7 mm vertically wide, and 18 μm thick was provided. The coil  321  generating a magnetic field was arranged from a position of 19.5 mm vertically upward of the center of the image pickup element  203  and 10 mm right horizontally, to a position of 50 mm in a front direction orthogonal to the sheet, such that the coil winding axis matched a direction orthogonal to the sheet. 
     It should be noted that at a position of 1.7 mm behind the image pickup element  203 , a conductor, which was not a magnetic body, of 42 mm laterally wide, 38 mm vertically wide, and 0.07 mm thick was provided as a ground pattern in the printed wiring board  204 . This conductor had conductivity σ=5.7×10 7  (S/m), and relative permeability 1.0 (no unit). 
     Example 2 
     The second magnetic body  212  of 30 mm laterally wide, longer than the horizontal width 25 mm of the semiconductor unit  231  of the image pickup element  203 , was provided. As the other aspects were the same as those of Example 1, the description is omitted. 
     Example 3 
     The second magnetic body  212  of 50 mm laterally wide, longer than the horizontal width 36 mm of the opening H of the magnetic member  210 , was provided. As such, the second magnetic body  212  was disposed along one side of the opening H of the magnetic member  210 , and the length in a direction along one side was set to be longer than one side of the opening H. As the other aspects were the same as those of Example 1, the description is omitted. 
     Example 4 
     The second magnetic body  212  of 1 mm vertically wide and 50 mm laterally wide was provided. As the other aspects were the same as those of Example 1, the description is omitted. 
     Example 5 
     The second magnetic body  212  of 2 mm vertically wide and 50 mm laterally wide was provided. As the other aspects were the same as those of Example 1, the description is omitted. 
     Example 6 
     The second magnetic body  212  of 3 mm vertically wide and 50 mm laterally wide was provided. As the other aspects were the same as those of Example 1, the description is omitted. 
     Comparative Example 1 
     Only the first magnetic body  211  was provided, without the second magnetic body  212 . As the other aspects were the same as those of Example 1, the description is omitted. 
     Regarding respective Examples 1 to 6 and Comparative Example 1, a magnetic field reaching the semiconductor unit  231  of the image pickup element  203  was obtained using commercial electromagnetic field simulation (ANSYS “Maxwell 3D”). The current applied to the coil  321  was a sine wave having a frequency of 30 kHz. 
       FIG. 5  is a graph illustrating the results obtained from the electromagnetic field simulation of the magnetic field that reached the semiconductor unit  231  of the image pickup element  203  in Examples 1 to 3 and Comparative Example 1. As illustrated in  FIG. 5 , in Examples 1 to 3, the magnetic field reaching the semiconductor unit  231  of the image pickup element  203  was reduced, compared with Comparative Example 1. Especially, it was reduced largely in Example 3. This means that by providing the second magnetic body  212  of high relative permeability having a horizontal width longer than the length of the opening H of the magnetic member  210 , the magnetic resistance in transmitting the magnetic field in a lateral width direction of the entire magnetic bodies  211  and  212  was reduced. 
       FIG. 6  is a graph illustrating the results obtained from the electromagnetic field simulation of the reached magnetic field in Examples 3 to 6 and Comparative Example 1. As illustrated in  FIG. 6 , in Examples 3 to 6, the magnetic field that reached the semiconductor unit  231  of the image pickup element  203  was reduced, compared with the reached magnetic field of Comparative Example 1. 
     Especially, in Example 4, the reached magnetic field was reduced although the vertical width of the second magnetic body  212  having high relative permeability was 1 mm and the area was only 50 mm 2 , compared with Example 1 having the area of 140 mm 2 . 
     This means that by providing the second magnetic body  212  of high relative permeability having a lateral width longer than the length of the opening H of the magnetic member  210  even though the vertical width is narrow, the magnetic resistance in transmitting the magnetic field in a lateral width direction is effectively reduced. As such, in the case of further reducing the area of the second magnetic body  212  of high relative permeability, it is important to have a lateral width longer than the side length of the opening H of the magnetic member  210 , even though the vertical width is narrow. 
     Further, while it is desirable that a separated distance between the first magnetic body  211  and the second magnetic body  212  is short, the results show that the magnetic field amount reaching the image pickup element  203  is almost the same if the distance is within a range from 0.1 mm to 3 mm. 
     Next, influence of the relative permeability of the first magnetic body  211  will be described.  FIG. 7  is a graph illustrating the result obtained by the electromagnetic field simulation of the magnetic field that reached the image pickup element  203 , while changing the relative permeability of the first magnetic body from 50 in Example 3. The second magnetic body  212  and the other conditions were the same as those of Example 3. However, only magnetic field in a vertical direction horizontal to a notably large sensor surface (light receiving surface  231   a ), in the magnetic field of the magnetic transmission path R 1 , was extracted. It should be noted that the relative permeability of the second magnetic body  212  was assumed to be 40000. 
     When the relative permeability of the first magnetic body  211  was 1 (the case of so-called non-magnetic body) and there was no second magnetic body, the reached magnetic field was 0.138 μT. Meanwhile, when the relative permeability of the first magnetic body  211  was 1 and there was the second magnetic body  212 , the reached magnetic field was 0.135 μT, as illustrated in  FIG. 7 . As such, even with the second magnetic body  212 , magnetic field bypassing effect was hardly obtained. 
     In the case were the relative permeability of the first magnetic body  211  became  50 , magnetic field bypassing effect began to appear rapidly. With the relative permeability higher than that, the magnetic field that reached the image pickup element  203  was reduced as the relative permeability was increased. 
     Accordingly, as the first magnetic body  211 , higher relative permeability is better. It is preferable that the relative permeability is 50 or higher. However, if the relative permeability is higher than 1000, a magnetic material is expensive. As such, it is preferable to use a material having relative permeability of lower than 1000 in practice. 
     Accordingly, the relative permeability of the first magnetic body  211  is preferably not less than 50 but less than 1000 in the driving frequency of the coil  321 . Further, as described above, the relative permeability of the second magnetic body  212  is preferably not less than 1000 but less than 200000 in the driving frequency of the coil  321 . 
     As described above, by using the first magnetic body  211  and the second magnetic body  212  having a smaller area and higher relative permeability than those of the first magnetic body  211 , it is possible to reduce the magnetic field that reaches the image pickup element  203 . As such, image disturbance caused by the image pickup element  203  can be suppressed. Further, as the area of the second magnetic body  212  having high relative permeability, which is expensive, can be reduced, it is possible to suppress image disturbance with an inexpensive configuration. 
     It should be noted that the present technology is not limited to the embodiment described above, and various changes can be made within the technical concept of the present technology. For example, even if the driving frequency of an electric current flowing in the coil, the arrangement, and the number are different, the present technology can be carried out by arranging the magnetic bodies corresponding to the case. Further, as for the first and second magnetic bodies, it is also possible to use materials other than those described in the embodiment by performing permeability measurement described herein. 
     Further, in the embodiment described above, description has been given on the case where the interchangeable lens  300  is configured to be detachable from the camera main body  200 , the coil  321  is provided to the casing  301  of the interchangeable lens  300 , and the first and second magnetic bodies  211  and  212  are provided to the casing  201  of the camera main body  200 . However, the present technology is not limited to this configuration. The present technology is also applicable to an imaging device in which a lens is integrally installed in the imaging device main body. For example, the present technology is applicable not only to a digital single lens reflex camera but also a compact digital camera. In that case, a coil and first and second magnetic bodies are provided to the casing of the camera. 
     As such, according to the present embodiment, by using a first magnetic body and a second magnetic body having a smaller area and higher relative permeability than those of the first magnetic body, it is possible to reduce the magnetic field that reaches the image pickup element. 
     Second Embodiment 
     Next, a second embodiment of the present technology will be described with reference to  FIGS. 8A and 8B .  FIGS. 8A and 8B  are diagrams illustrating a schematic configuration of a camera as an imaging device according to the second embodiment of the present technology. A coil  502 , which is a magnetic field generation source of a power source conversion circuit  501  serving as a power source circuit, is disposed inside the casing  201  of the camera main body  200 . 
     The imaging unit  202  includes a frame-like (annular) first magnetic body  505  having an opening H arranged between the coil  502  that is a magnetic field generation source and the image pickup element  203 . The first magnetic body  505  is arranged adjacent to the image pickup element  203 . More specifically, the first magnetic body  505  is arranged adjacent to the image pickup element  203  on the side where the coil  502  is disposed with respect to the image pickup element  203  in the arrow X direction, as illustrated in  FIG. 8B . 
     The imaging unit  202  also includes a second magnetic body  504  arranged at a position of the coil  502  side with respect to the first magnetic body  505 . The first magnetic body  505  has a surface on the side where the coil  502  is arranged in the arrow X direction, and the second magnetic body  504  is arranged adjacent to the surface. In that case, it is preferable that the second magnetic body  504  is arranged to have a slight gap with the first magnetic body  505  or is brought into contact with the first magnetic body  505 . It is more preferable to bring the first magnetic body  505  and the second magnetic body  504  into contact with each other, because the magnetic resistance is reduced. 
     As illustrated in  FIG. 8A , the second magnetic body  504  is arranged at a position of the coil  502  side with respect to the opening H when seen in the arrow X direction, while at least a portion thereof (the whole in the present embodiment) overlapping the first magnetic body  505 . Specifically, the second magnetic body  504  is arranged adjacent to one side, nearest to the coil  502 , of the four sides of the opening H. This means that the second magnetic body  504  is arranged on the frame portion of an opening side nearest to the coil  502 , on the surface of the coil side of the first magnetic body  505 . 
     The first magnetic body  505  and the second magnetic body  504  are made of a ferromagnetic material and formed in a plate shape or a film shape. The second magnetic body  504  is made of a ferromagnetic material having higher relative permeability than that of the first magnetic body  505 . The second magnetic body  504  is formed to have a smaller area than that of the first magnetic body  505  when seen in the arrow X direction. Further, the second magnetic body  504  is formed to be thinner in the arrow X direction than the first magnetic body  505 . 
     According to this configuration, most of the magnetic field  503 , generated from the coil  502  that is a magnetic field generation source, passes through the second magnetic body  504  having low magnetic resistance, and subsequently passes through the first magnetic body  505 . As such, the magnetic field reaching the image pickup element  203  can be reduced. The materials of the first magnetic body and the second magnetic body are selectable, which is the same as the case of the first embodiment. 
     In this way, by using the first magnetic body  505  and the second magnetic body  504  having a smaller area and higher relative permeability than those of the first magnetic body  505 , it is possible to reduce the magnetic field reaching the image pickup element  203 . As such, image disturbance caused by the image pickup element  203  can be suppressed. Further, as the area of the second magnetic body  504  having high relative permeability, which is expensive, can be reduced, it is possible to suppress image disturbance with an inexpensive configuration. 
     As in the present embodiment, the present technology is applicable even in the case where a magnetic field generation source is provided to the casing of the camera main body, and the camera main body corresponds to the imaging device. 
     Third Embodiment 
     Next, a third embodiment of the present technology will be described with reference to  FIG. 9 .  FIG. 9  is a diagram illustrating a schematic configuration of an interchangeable lens according to the third embodiment of the present technology. In the third embodiment, the coil  321  that is a magnetic field generation source of the drive circuit  313  is disposed inside the casing  301  of the interchangeable lens  300 . The interchangeable lens  300  (casing  301 ) is configured to be detachable from the imaging device main body (camera main body). 
     In  FIG. 9 , an annular first magnetic body  602  having an opening is arranged between the coil  321  that is a magnetic field generation source, and an image pickup element (not illustrated). Further, a second magnetic body  601  is arranged at a position on the coil  321  side with respect to the first magnetic body  602 . The first magnetic body  602  has a surface on the side where the coil  321  is arranged in the arrow X direction, and the second magnetic body  601  is disposed adjacent to the surface. In that case, it is preferable that the second magnetic body  601  is arranged to have a slight gap with the first magnetic body  602  or is brought into contact with the first magnetic body  602 . It is more preferable to bring the first magnetic body  602  and the second magnetic body  601  into contact with each other, because the magnetic resistance is reduced. 
     As illustrated in  FIG. 9 , the second magnetic body  601  is arranged at a position of the coil  321  side with respect to the opening when seen in the arrow X direction, while at least a portion thereof (the whole in the present embodiment) overlapping the first magnetic body  602 . Specifically, the second magnetic body  601  is arranged on a frame portion adjacent nearest to the coil  321 , of the sides of the opening. 
     The first magnetic body  602  and the second magnetic body  601  are made of a ferromagnetic material and formed in a plate shape or a film shape. The second magnetic body  601  is made of a ferromagnetic material having higher relative permeability than that of the first magnetic body  602 . The second magnetic body  601  is formed to have a smaller area than that of the first magnetic body  602  when seen in the arrow X direction. Further, the second magnetic body  601  is formed to be thinner in the arrow X direction than the first magnetic body  602 . 
     According to this configuration, most of the magnetic field  600 , generated from the coil  321  that is the magnetic field generation source, passes through the second magnetic body  601  having low magnetic resistance, and subsequently passes through the first magnetic body  602 . As such, the magnetic field reaching the image pickup element (not illustrated) can be reduced. The materials of the first magnetic body  602  and the second magnetic body  601  are selectable, which is the same as the case of the first embodiment. 
     In this way, by using the first magnetic body  602  and the second magnetic body  601  having a smaller area and higher relative permeability than those of the first magnetic body  602 , it is possible to reduce the magnetic field reaching the image pickup element. As such, image disturbance caused by the image pickup element can be suppressed. Further, as the area of the second magnetic body  601  having high relative permeability, which is expensive, can be reduced, it is possible to suppress image disturbance with an inexpensive configuration. 
     As in the present embodiment, present technology is applicable even in the case where an interchangeable lens has first and second magnetic bodies. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.