Abstract:
A light-amount adjusting apparatus includes two aperture diaphragms that move in such a direction that the two aperture diaphragms come close or get away with respect to an optical axis of an incident light to adjust a size of an aperture opening. At least one of the two aperture diaphragms includes an optical filter having a predetermined light transmittance characteristic. The optical filter freely advances and retreats in a direction of the aperture opening in conjunction with a movement of the aperture diaphragm.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1) Field of the Invention  
         [0002]     The present invention relates to a light-amount adjusting apparatus used in an optical system of an imaging apparatus such as a video camera.  
         [0003]     2) Description of the Related Art  
         [0004]     As a light-amount adjusting apparatus according to a conventional technology, to be used in an optical system in an imaging apparatus such as a video camera, there is a device where in adjusting light amount, in consideration of reduction of resolution deterioration owing to light diffraction, an ND filter and an aperture diaphragm are operated (see, for example, Japan Patent Application Publication No. 2002-14384). In this device, as the illuminance of an object changes to low illuminance, middle illuminance, and high illuminance, the ND filter and the aperture diaphragm are driven independently, and light-amount adjustment is carried out. Further, there is a device where an ND filter is attached to two aperture diaphragms, and the ND filter is structured so that light transmittance should become lower from the center of light axis toward the outside in radial direction (see, for example, Japan Patent Application Publication No. 8-43878). Furthermore, there is a device where an aperture opening is formed by aperture diaphragms moving on a plane perpendicular to light axis in the direction in which the aperture diaphragms become away from each other, and an ND filter having at least 2 stages of light transmittance is attached to an aperture diaphragm (see, for example, Japan Patent Application Publication No. 2001-272709).  
         [0005]     However, in the devices disclosed in the above literatures, part of the ND filter is left in the light path even at the maximum aperture (maximum opening) of the aperture diaphragms, accordingly even at the maximum aperture, light going through the opening is subject to influence of the ND filter, and sufficient light amount cannot be obtained.  
         [0006]     Further, in the device disclosed in Japan Patent Application Publication No. 2001-272709, the opening and closing mechanism of aperture diaphragms is structured so as to move in the same direction (vertical direction) as the moving frame mechanism of the ND filter. Further, the aperture and the ND filter are driven in two stages in vertical direction, accordingly the device is long in vertical direction and the size thereof is large. Furthermore, the opening and closing mechanism of aperture diaphragms and the moving frame mechanism of ND filter are driven by different driving motors, and the respective driving motors are arranged in the front and rear of the device, accordingly the device is large in the anteroposterior direction.  
       SUMMARY OF THE INVENTION  
       [0007]     It is an object of the present invention to solve at least the above problems in the conventional technology.  
         [0008]     A light-amount adjusting apparatus according to one aspect of the present invention includes two aperture diaphragms that move in such a direction that the two aperture diaphragms come close or get away with respect to an optical axis of an incident light to adjust a size of an aperture opening. At least one of the two aperture diaphragms includes an optical filter having a predetermined light transmittance characteristic. The optical filter freely advances and retreats in a direction of the aperture opening in conjunction with a movement of the aperture diaphragm.  
         [0009]     A light-amount adjusting apparatus according to another aspect of the present invention includes two aperture diaphragms that move in such a direction that the two aperture diaphragms come close or get away with respect to an optical axis of an incident light to adjust a size of an aperture opening; a moving unit that moves the aperture diaphragms; and an optical filter that freely advances and retreats in a direction of the aperture opening in conjunction with a movement of the aperture diaphragm by the moving unit, and has a predetermined light transmittance in the direction of the aperture opening.  
         [0010]     The other objects, features, and advantages of the present invention are specifically set forth in or will become apparent from the following detailed description of the invention when read in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a disassembled perspective view showing the structure of a light-amount adjusting apparatus according to a first embodiment of the present invention;  
         [0012]      FIG. 2  is a front view of the light-amount adjusting apparatus according to the first embodiment;  
         [0013]      FIGS. 3A and 3B  are series of action figures for explaining the aperture actions of the light-amount adjusting apparatus according to the first embodiment;  
         [0014]      FIG. 4  is a front view of the light-amount adjusting apparatus according to a second embodiment of the present invention;  
         [0015]      FIGS. 5A  to  5 D are series of action figures for explaining the aperture actions of the light-amount adjusting apparatus according to the second embodiment;  
         [0016]      FIG. 6  is a disassembled perspective view showing the structure of a light-amount adjusting apparatus according to a third embodiment of the present invention;  
         [0017]      FIG. 7  is a front view of the light-amount adjusting apparatus according to a third embodiment of the present invention;  
         [0018]      FIGS. 8A  to  8 D are series of action figures for explaining the aperture actions of the light-amount adjusting apparatus according to the third embodiment;  
         [0019]      FIG. 9  is a disassembled perspective view showing the structure of a light-amount adjusting apparatus according to a fourth embodiment of the present invention;  
         [0020]      FIG. 10  is a front view of the light-amount adjusting apparatus according to the fourth embodiment; and  
         [0021]      FIGS. 11A  to  11 D are series of action figures for explaining the aperture actions of the light-amount adjusting apparatus according to the fourth embodiment. 
     
    
     DETAILED DESCRIPTION  
       [0022]     Exemplary embodiments of a light-amount adjusting apparatus according to the present invention will be explained in detail with reference to the accompanying drawings. A light-amount adjusting apparatus according to the present invention is one where aperture diaphragms and optical filters move on a plane perpendicular to the light axis, thereby its opening area (aperture opening) is changed. The explanations hereinafter are described on assumption that directions of respective components are viewed from an object in front of a light-amount adjusting apparatus.  
         [0023]      FIG. 1  is a disassembled perspective view showing the structure of a light-amount adjusting apparatus according to a first embodiment of the present invention. The light-amount adjusting apparatus according to the first embodiment includes an aperture holder  1 , a lower optical filter  2 , a lower aperture diaphragm  3 , an upper aperture diaphragm  4 , an upper optical filter  5 , a driving motor  28 , and a driving unit  29 .  
         [0024]     At the position above the roughly center of the aperture holder  1 , a roughly circular light pass hole  24  is formed. At the lower portion of the aperture holder  1 , a driving attaching portion  23  for attaching the driving motor  28  is arranged. In the driving attaching portion  23 , a roughly circular driving motor attaching portion  27  is formed. Further, on both the sides of the light pass hole  24 , two rotating shafts (diaphragm guide pins)  25   a  and  25   b  are formed to protrude toward the front in the figure (object side). On the upper left and right sides of the driving attaching portion  23 , two diaphragm guide pins  26   a  and  26   b  are formed to protrude toward the object side.  
         [0025]     The lower optical filter  2  is formed of an ND filter having a specified light transmittance characteristic, and is of a bow shape, and has an internal circumference  2   a  that roughly meets the shape of the light pass hole  24 . Further, in the roughly center of the lower optical filter  2 , a cam hole  6   a  that is cut into an arc shape is formed, and in the upper end portion, a rotation center hole  7  is formed.  
         [0026]     The lower aperture diaphragm  3  is of a shape whose lower roughly right half is cut out, and in the upper portion thereof, a roughly semi circular opening forming portion  8  that roughly meets the shape of the light pass hole  24  is formed. In the opening forming portion  8 , both the sides thereof are smoothly circular first toward the lower side, and the width thereof becomes sharply narrow at the center and the most lower end portion  8   a  is downwardly convex.  
         [0027]     Further, in the left end of the lower aperture diaphragm  3 , vertically long straight guide holes  9   a  and  9   b  are formed. The straight guide holes  9   a  and  9   b  are same in size and shape, and the straight guide hole  9   b  is formed just under the straight guide hole  9   a . Under the straight guide hole  9   b , in the lower end portion of the lower aperture diaphragm  3 , a horizontally long rotation connection hole  10  is formed. On the other hand, in the right end of the lower aperture diaphragm  3 , a vertically long straight guide hole  11  is formed. The size and shape of the straight guide hole  11  are same as those of the straight guide hole  9   a , and is axisymmetric with the straight guide hole  9   a  to the center line of the lower aperture diaphragm  3 . In the left side of the straight guide hole  11 , a driving shaft  12   a  is formed to protrude forward (to the object side).  
         [0028]     The upper aperture diaphragm  4  is of a shape whose lower roughly left half is cut out, and in the center portion thereof, a roughly semi circular opening forming portion  13  that roughly meets the shape of the light pass hole  24  is formed. In the opening forming portion  13 , both the sides thereof are smoothly circular first toward the upper side, and the width thereof becomes sharply narrow at the center and the most upper end portion  13   a  is upwardly convex.  
         [0029]     Further, in the right end of the upper aperture diaphragm  4 , vertically long straight guide holes  15   a  and  15   b  are formed. The straight guide holes  15   a  and  15   b  are same in size and shape, and the straight guide hole  15   b  is formed just under the straight guide hole  15   a . In the lower end portion of the upper aperture diaphragm  4 , under the straight guide hole  15   b , a horizontally long rotation connection hole  17  is formed. On the other hand, in the left end of the upper aperture diaphragm  4 , a vertically long straight guide hole  14  is formed. The size and shape of the straight guide hole  14  are same as those of the straight guide hole  15   a , and is axisymmetric with the straight guide hole  15   a  to the center line of the upper aperture diaphragm  4 . In the right side of the straight guide hole  14 , a driving shaft  16   a  is formed to protrude backward (to the image side).  
         [0030]     The upper optical filter  5  is formed of a ND filter having a specified light transmittance characteristic, and is of a bow shape, and has an internal circumference  5   a  that roughly meets the shape of the light pass hole  24 . Further, in the roughly center of the upper optical filter  5 , a cam hole  18   a  that is cut into an arc shape is formed, and in the lower end portion, a rotation center hole  19  is formed. The shape of the upper optical filter  5  is same as that of the lower optical filter  2 , and the light transmittance thereof is also same. Further, the sizes, shapes and formation positions of the cam hole  18   a  and the rotation center hole  19  are same as those of the cam hole  6   a  and the rotation center hole  7 .  
         [0031]     As the raw material of the lower aperture diaphragm  3  and the upper aperture diaphragm  4 , a thin film that blocks out light is employed.  
         [0032]     The driving unit  29  comprises a rotation lever  20  at the center, an arm  21  that expands horizontally from the rotation level  20 , a left connection pin  22   a  and a right connection pin  22   b  that are arranged respectively at the left and right ends of the arm  21 . By the way, the left connection pin  22   a  and the right connection pin  22   b  are formed to protrude forward (to the object side).  
         [0033]     In this light-amount adjusting apparatus, from not illustrated object side (left side of the figure), the lower optical filter  2 , the lower aperture diaphragm  3 , the upper aperture diaphragm  4 , and the upper optical filter  5  are arranged sequentially.  
         [0034]     To the driving shaft  12   a  arranged on the lower aperture diaphragm  3 , the cam hole  6   a  of the lower optical filter  2  is engaged. Further, to the driving shaft  16   a  arranged on the upper aperture diaphragm  4 , the cam hole  18   a  of the upper optical filter  5  is engaged. Then, to the rotating shaft  25   a  on the aperture holder  1 , the rotation center hole  19  in the upper optical filter  5  is engaged, further, the straight guide hole  14  in the upper aperture diaphragm  4 , and the straight guide hole  9   a  of the lower aperture diaphragm  3  are engaged.  
         [0035]     Meanwhile, to the rotating shaft  25   b  on the aperture holder  1 , the straight guide hole  15   a  of the upper aperture diaphragm  4 , and the straight guide hole  11  of the lower aperture diaphragm  3  are engaged, and further, the rotation center hole  7  of the lower optical filter  2  is engaged. To the diaphragm guide pin  26   a  of the aperture holder  1 , the straight guide hole  9   b  of the lower aperture diaphragm  3  is engaged. To the diaphragm guide pin  26   b  of the aperture holder  1 , the straight guide hole  15   b  of the upper aperture diaphragm  4  is engaged. Thereby, the lower optical filter  2  and the upper optical filter  5  are arranged point symmetrically to the center (light axis) of the light pass hole  24  of the aperture holder  1 .  
         [0036]     Further, from the rear side (image side) of the driving attaching portion  23 , the driving motor  28  is attached to the driving motor attaching portion  27  arranged in the driving attaching portion  23 . Then, the rotating shaft  28   a  of the driving motor  28  is attached to the rotation lever  20  of the driving unit  29 . The left connection pin  22   a  and the right connection pin  22   b  arranged at both the ends of the arm  21  of the driving unit  29  are engaged to the rotation connection hole  10  of the lower aperture diaphragm  3  and the rotation connection hole  17  of the upper aperture diaphragm  4  respectively. The left connection pin  22   a  and the right connection pin  22   b  freely slide to the rotation connection hole  10  and the rotation connection hole  17  respectively.  
         [0037]     When the driving motor  28  is driven (rotated), the arm  21  of the driving unit  29  swings. At this moment, the left connection pin  22   a  and the right connection pin  22   b  of the arm  21  move in mutually reverse vertical directions, thereby, the lower aperture diaphragm  3  and the upper aperture diaphragm  4  move in mutually reverse vertical directions. Accordingly, the lower optical filter  2  and the upper optical filter  5  respectively arranged on the lower aperture diaphragm  3  and the upper aperture diaphragm  4  move in mutually reverse vertical directions, too.  
         [0038]     The driving shaft  16   a  of the upper aperture diaphragm  4  slides in the cam hole  18   a  formed in the upper optical filter  5 , and the upper optical filter  5  rotates around the rotation center hole  19 . At the same time, the driving shaft  12   a  of the lower aperture diaphragm  3  slides in the can hole  6   a  formed in the lower optical filter  2 , and the lower optical filter  2  rotates around the rotation center hole  7 . The lower optical filter  2  and the upper optical filter  5  rotate, while holding their point symmetrical conditions to the center of the light pass hole  24 . Through these actions, the size of an aperture opening (opening area  40  to be explained hereinafter) to be formed in the light pass hole  24  portion of the light-amount adjusting apparatus changes.  
         [0039]      FIG. 2  is a front view of the light-amount adjusting apparatus according to the first embodiment. The maximum aperture condition (aperture release) is shown in the figure. At the moment of this maximum aperture, the left connection pin  22   a  of the arm  21  of the driving unit  29  shown in  FIG. 1  is positioned diagonally downward, and the right connection pin  22   b  is positioned diagonally upward. Accordingly, the lower aperture diaphragm  3  is positioned at the lower end of the move range thereof, and the upper aperture diaphragm  4  is positioned at the upper end of the move range thereof.  
         [0040]     The opening forming portion  8  of the lower aperture diaphragm  3  and the opening forming portion  13  of the upper aperture diaphragm  4  nearly overlap the light pass hole  24  of the aperture holder  1 , and do not get into the light pass hole  24 . Further, the most lower end portion  8   a  of the opening forming portion  8  of the lower aperture diaphragm  3  and the most upper end portion  13   a  of the opening forming portion  13  of the upper aperture diaphragm  4 , that are convex, are outside of the light pass hole  24  of the aperture holder  1 . Further, at this maximum aperture, the lower optical filter  2  and the upper optical filter  5  are outside of the light pass hole  24 , therefore, light that is guided to an imaging element (not illustrated) to be arranged at the rear of the device is free of influence by the lower optical filter  2  and the upper optical filter  5 . The size of an opening area  40  to be formed by the lower aperture diaphragm  3 , and the opening forming portions  8  and  13  of the upper aperture diaphragm  4  changes continuously as the lower aperture diaphragm  3  and the upper aperture diaphragm  4  move. Further, as the lower aperture diaphragm  3  and the upper aperture diaphragm  4  move, the lower optical filter  2  and the upper optical filter  5  go in and out of the opening area  40 .  
         [0041]      FIGS. 3A and 3B  show action figures for explaining the aperture actions of the light-amount adjusting apparatus according to the first embodiment.  FIG. 3A  is a condition where the aperture is a bit stopped down from the maximum aperture condition shown in  FIG. 2 . In this condition, the lower aperture diaphragm  3  and the upper aperture diaphragm  4  are moved, and the most lower end portion  8   a  of the opening forming portion  8  of the lower aperture diaphragm  3  and the most upper end portion  13   a  of the opening forming portion  13  of the upper aperture diaphragm  4  are positioned a bit inside from the edge of the light pass hole  24 . At this moment, as the lower aperture diaphragm  3  and the upper aperture diaphragm  4  move, the driving shafts  12   a  and  16   a  move vertically. The opening area  40  formed by the opening forming portion  8  of the lower aperture diaphragm  3  and the opening forming portion  13  of the upper aperture diaphragm  4  is positioned inside from the edge of the light pass hole  24  (Refer to  FIG. 2 .), and becomes a horizontally long oval shape.  
         [0042]     Further, as for the lower optical filter  2  and the upper optical filter  5 , to the rotation center holes  7  and  19  engaged with the rotating shafts  25   a  and  15   b  at their respectively fixed positions on the aperture holder  1  (Refer to  FIG. 1 .), the driving shafts  12   a  and  16   a  arranged on the lower aperture diaphragm  3  and the upper aperture diaphragm  4  move vertically. Accordingly, the driving shafts  12   a  and  16   a  move vertically in the engaging cam holes  6   a  and  18   a , and the lower optical filter  2  and the upper optical filter  5  rotate around the rotation center holes  7  and  19  toward the light pass hole  24 . Then, part of the lower optical filter  2  covers the most lower end portion  8   a  of the opening forming portion  8 , and part of the upper optical filter  5  covers the most upper end portion  13   a  of the opening forming portion  13 .  
         [0043]      FIG. 3B  is a middle aperture condition where the lower aperture diaphragm  3  and the upper aperture diaphragm  4  are moved further from the condition in  FIG. 3A . The opening area  40  formed by the opening forming portion  8  of the lower aperture diaphragm  3  and the opening forming portion  13  of the upper aperture diaphragm  4  becomes a roughly rhombic shape. In this condition, the opening area  40  is positioned completely inside of the light pass hole  24 . At this moment, parts of the lower optical filter  2  and the upper optical filter  5  cover about ½ of the inside of the roughly rhombic shape formed by the opening forming portions  8  and  13 , and the remaining about ½ thereof lets light go through.  
         [0044]      FIG. 3C  is a condition where the lower aperture diaphragm  3  and the upper aperture diaphragm  4  are moved furthermore from the condition in  FIG. 3D . The opening area  40  of a roughly rhombic shape formed by the opening forming portion  8  of the lower aperture diaphragm  3  and the opening forming portion  13  of the upper aperture diaphragm  4  in the area of the light pass hole  24  becomes further smaller. In this condition, in the opening area  40 , the lower optical filter  2  and the upper optical filter  5  overlap, and there is no portion where light goes through. However, the lower optical filter  2  and the upper optical filter  5  overlap not in the entire area in the opening area  40 , accordingly, a portion with different light transmittance is formed in the opening area  40 . As shown in the figure, the light transmittance becomes low at the center of the opening area  40 , and becomes high at the peripheral portion thereof.  
         [0045]      FIG. 3D  is a figure showing the minimum aperture condition. At this moment, the left connection pin  22   a  of the arm  21  of the driving unit  29  shown in  FIG. 1  is positioned diagonally upward, and the right connection pin  22   b  is positioned diagonally downward. Accordingly, the lower aperture diaphragm  3  is positioned at the upper end of the move range thereof, and the upper aperture diaphragm  4  is positioned at the lower end of the move range thereof. In this condition, the opening area  40  is positioned at the center of the light pass hole  24 , and becomes the smallest rhombic shape. In this condition, the lower optical filter  2  and the upper optical filter  5  overlap in all the area of the opening area  40 . Accordingly, the light transmittance becomes rather low. This condition is made on assumption of the case where illuminance of an object is extremely high, and enables to restrict what is called “vignetting” on an image forming plane of an imaging element.  
         [0046]     According to the first embodiment, in the maximum aperture condition, the lower optical filter  2  and the upper optical filter  5  do not get into the light pass hole  24  as a light path, as a result, it is possible to secure sufficient light amount. Further, in this device, the lower optical filter  2  and the upper optical filter  5  rotate while holding their point symmetrical relation to the light axis, as a result, it is possible to continue (quantify) the move of the lower optical filter  2  and the upper optical filter  5 , and to continuously control light amount passing the light pass hole  24  according aperture degrees.  
         [0047]     Furthermore, according to the first embodiment, toward the minimum aperture condition, it is possible to increase the portion of the area where the lower optical filter  2  and the upper optical filter  5  overlap. Accordingly, it is possible to restrict shading that occurs especially from the middle aperture condition to the minimum aperture condition.  
         [0048]     Moreover, according to the first embodiment, two optical filters (the lower optical filter  2  and the upper optical filter  5 ) are driven in connection with aperture diaphragms (the lower aperture diaphragm  3  and the upper aperture diaphragm  4 ), as a result, only one unit of driving motor will do well as the power source for driving them. Accordingly, it is possible to make smallest the space for arranging the power source. Further, move areas of the respective optical filters are within the move areas of the respective aperture diaphragms. Accordingly, the vertical size of the device may be limited to the space where the respective aperture diaphragms move, as a consequence, it is possible to achieve a compact size of the device.  
         [0049]      FIG. 4  is a front view of the light-amount adjusting apparatus according to a second embodiment of the present invention. An example of a structure of a light-amount adjusting apparatus where upper and lower optical filters are driven asymmetrically is shown in the figure. The shapes of a lower aperture diaphragm  3  and an upper aperture diaphragm  4  are same as those in the structure according to the first embodiment. A lower optical filter  2  and an upper optical filter of a same shape are arranged in vertically symmetrical manners. However, the shapes of a cam hole  6   a  formed in the lower optical filter  2  is different from that of a cam hole  18   a  formed in the upper optical filter  5 . The cam hole  6   a  formed in the lower optical filter  2  is formed into a roughly J shape, meanwhile, the cam hole  18   a  formed in the upper optical filter  5  is formed into a roughly S shape.  
         [0050]     A maximum aperture condition (aperture release) is shown in the figure. In this condition, the lower optical filter  2  and the upper optical filter  5  are outside of a light pass hole  24 , and light that is guided to an imaging element (not illustrated) to be arranged at the rear of the device is free of influence by the lower optical filter  2  and the upper optical filter  5 .  
         [0051]      FIGS. 5A  to  5 D show action figures for explaining the aperture actions of the light-amount adjusting apparatus according to the second embodiment.  FIG. 5A  is a condition where the aperture is a bit stopped down from the maximum aperture condition shown in  FIG. 4 . In this condition, the lower aperture diaphragm  3  and the upper aperture diaphragm  4  are moved, and the most lower end portion  8   a  of the opening forming portion  8  of the lower aperture diaphragm  3  and the most upper end portion  13   a  of the opening forming portion  13  of the upper aperture diaphragm  4  are positioned a bit inside from the edge of the light pass hole  24 . At this moment, the driving shaft  12   a  is positioned in the diagonal portion of the cam hole  6   a , therefore, the lower optical filter  2  goes partially into the light pass hole  24 . On the other hand, the driving shaft  16   a  is positioned in the vertical portion of the cam hole  18   a , therefore, the upper optical filter  5  does not get into the light pass hole  24  yet and is positioned outside thereof.  
         [0052]      FIG. 5B  is a middle aperture condition where the lower aperture diaphragm  3  and the upper aperture diaphragm  4  are moved further from the condition in  FIG. 5A . In this condition, the lower optical filter  2  increases its advance amount into the light pass hole  24  according to move amount of the lower aperture diaphragm  3 . Then, when the driving shaft  16   a  is positioned at the arc portion of the cam hole  18   a , the upper optical filter  5  starts getting into the light pass hole  24 . At this moment, parts of the lower optical filter  2  and the upper optical filter  5  cover about ½ of the inside of the roughly rhombic shape formed by the opening forming portions  8  and  13 , and the remaining about ½ thereof lets light go through. In the condition shown in the figure, in comparison with the middle aperture condition shown in  FIG. 3B , it is known that the advance portion to the light pass hole  24  is high at the lower optical filter  2 , and low at the upper optical filter  5 .  
         [0053]      FIG. 5C  is a condition where the lower aperture diaphragm  3  and the upper aperture diaphragm  4  are moved furthermore from the condition in  FIG. 5D . In this condition, the roughly rhombic opening area  40  becomes further smaller, and the lower optical filter  2  and the upper optical filter  5  overlap in the opening area  40 , and there is no portion where light goes through. However, the lower optical filter  2  and the upper optical filter  5  overlap not in the entire area in the opening area  40 , but in the opening area  40 , a portion of only the upper optical filter  5  is formed, and a portion with different light transmittance is formed in the opening area  40 . As shown in the figure, the light transmittance becomes low at the diagonally right rhombic portion of the opening area  40 , and becomes high at the diagonally left rhombic portion.  
         [0054]      FIG. 5D  is a figure showing the minimum aperture condition. In this condition, the opening area  40  is positioned at the center of the light pass hole  24 , and becomes the smallest rhombic shape. In this condition, the lower optical filter  2  and the upper optical filter  5  overlap in all the area of the opening area  40 , accordingly, the light transmittance in the size of the opening area  40  becomes lowest. This condition is made on assumption of the case where illuminance of an object is extremely high, and enables to restrict what is called “vignetting” on an image forming plane of an imaging element.  
         [0055]     According to the second embodiment, only by making different the shapes of the cam holes to be formed in the upper optical filter  5  and the lower optical filter  2 , it is possible to easily move the upper optical filter  5  and the lower optical filter  2  that move into the light pass hole  24  with mutually different move amounts, and in asymmetrical manners. By making asymmetrical the driving of the lower optical filter  2  and the upper optical filter  5 , it is possible to further reduce harmful influences by flare that occurs owing to light reflection at optical filter end surface.  
         [0056]      FIG. 6  is a disassembled perspective view showing the structure of a light-amount adjusting apparatus according to a third embodiment of the present invention. The light-amount adjusting apparatus according to the third embodiment includes an aperture holder  1 , a lower driving diaphragm  30 , a lower aperture diaphragm  3 , an upper aperture diaphragm  4 , an upper driving diaphragm  31 , a driving motor  28 , and a driving unit  29 .  
         [0057]     The aperture holder  1 , the driving motor  28 , and the driving unit  29  are same as those used in the device according to the first embodiment. Further, the lower aperture diaphragm  3  and the upper aperture diaphragm  4  are of the same structures as those used in the first embodiment, with exception that the portions where the driving shafts  12   b  and  16   b  are formed are different. The driving shaft  12   b  is formed at the left side by the most lower portion of the straight guide hole  11  of the lower aperture diaphragm  3 . Meanwhile, the driving shaft  16   b  is formed at the right side by the most upper portion of the straight guide hole  14  of the upper aperture diaphragm  4 .  
         [0058]     The lower driving diaphragm  30  is made of a relatively thin film that blocks light, and to a dogleg shaped internal edge portion  30   a  by the end thereof, a roughly fan shaped optical filter (ND filter)  32  is attached. Further, in this lower driving diaphragm  30 , a cam hole  6   b  that is cut out into a roughly S shape, and a rotation center hole  7  are formed.  
         [0059]     The upper driving diaphragm  31  is made of a relatively thin film, and to a dogleg shaped internal edge portion  31   a  by the end thereof, a roughly fan shaped optical filter (ND filter)  33  is attached. Further, in this upper driving diaphragm  31 , a cam hole  18   b  that is cut out into a roughly S shape, and a rotation center hole  19  are formed. By the way, this upper driving diaphragm  31  is of the same shape as that of the lower driving diaphragm  30 . Further, the sizes, shapes, and formation positions of the cam hole  18   b  and the rotation center hole  19  are same as those of the cam hole  6   b  and the rotation center hole  7 . The light transmittance of the optical filters  32  and  33  is same. As explained above, the structure of the third embodiment is a structure where optical filters (filter plates) of the shapes that correspond only to the portions of driving diaphragms that go into and out of the light pass hole  24  are arranged.  
         [0060]     According to the third embodiment, from not illustrated object side (left side of the figure), the lower driving diaphragm  30  having the optical filter  32 , the lower aperture diaphragm  3 , the upper aperture diaphragm  4 , and the upper driving diaphragm  31  having the optical filter  33  are arranged sequentially.  
         [0061]     To the driving shaft  12   b  arranged on the lower aperture diaphragm  3 , the cam hole  6   b  of the lower driving diaphragm  30  is engaged. To the driving shaft  16   a  arranged on the upper aperture diaphragm  4 , the cam hole  18   b  of the upper driving diaphragm  31  is engaged. Then, to the rotating shaft  25   a  of the aperture holder  1 , the rotation center hole  19  of the upper driving diaphragm  31  is engaged, further the straight guide hole  14  of the upper aperture diaphragm  4 , and the straight guide hole  9   a  of the lower aperture diaphragm  3  are engaged thereto.  
         [0062]     Further, to the rotating shaft  25   b  of the aperture holder  1 , the straight guide hole  15   a  of the upper aperture diaphragm  4 , and the straight guide hole  11  of the lower aperture diaphragm  3  are engaged, and further the rotation center hole  7  of the lower driving diaphragm  30  is engaged thereto. To the diaphragm guide pin  26   a  of the aperture holder  1 , the straight guide hole  9   b  of the lower aperture diaphragm  3  is engaged. To the diaphragm guide pin  26   b  of the aperture holder  1 , the straight guide hole  15   b  of the upper aperture diaphragm  4  is engaged. The lower driving diaphragm  30  and the upper driving diaphragm  31  are arranged point symmetrically to the center (light axis) of the light pass hole  24  of the aperture holder  1 .  
         [0063]     Further, from the rear side (image side) of the driving attaching portion  23 , the driving motor  28  is attached to the driving motor attaching portion  27  arranged in the driving attaching portion  23 . Then, the rotating shaft  28   a  of the driving motor  28  is attached to the rotation lever  20  of the driving unit  29 . The left connection pin  22   a  and the right connection pin  22   b  arranged at both the ends of the arm  21  of the driving unit  29  are engaged to the rotation connection hole  10  of the lower aperture diaphragm  3  and the rotation connection hole  17  of the upper aperture diaphragm  4  respectively. The left connection pin  22   a  and the right connection pin  22   b  freely slide to the rotation connection hole  10  and the rotation connection hole  17  respectively.  
         [0064]     When the driving motor  28  is driven (rotated), the arm  21  of the driving unit  29  swings. At this moment, the left connection pin  22   a  and the right connection pin  22   b  of the arm  21  move in mutually reverse vertical directions, thereby, the lower aperture diaphragm  3  and the upper aperture diaphragm  4  move in mutually reverse vertical directions. Accordingly, the lower driving diaphragm  30  and the upper driving diaphragm  31  respectively arranged to the shafts on the lower aperture diaphragm  3  and the upper aperture diaphragm  4  move in mutually reverse vertical directions, too.  
         [0065]     The driving shaft  16   b  of the upper aperture diaphragm  4  slides in the cam hole  18   b  formed in the upper driving diaphragm  31 , and the upper driving diaphragm  31  rotates around the rotation center hole  19 . At the same time, the driving shaft  12   b  of the lower driving diaphragm  30  slides in the can hole  6   b  formed in the lower driving diaphragm  30 , and the lower driving diaphragm  30  rotates around the rotation center hole  7 . The lower driving diaphragm  30  and the upper driving diaphragm  31  rotate, while holding their point symmetrical conditions to the center of the light pass hole  24 . Through these actions, the size of an opening area  40  to be formed of the light-amount adjusting apparatus changes as shown in  FIGS. 8A  to  8 D to be explained later herein.  
         [0066]      FIG. 7  is a front view of the light-amount adjusting apparatus according to the third embodiment. A maximum aperture condition is shown in the figure. At the moment of this maximum aperture, the left connection pin  22   a  of the arm  21  of the driving unit  29  shown in  FIG. 6  is positioned diagonally downward, and the right connection pin  22   b  is positioned diagonally upward. Accordingly, the lower aperture diaphragm  3  is positioned at the lower end of the move range thereof, and the upper aperture diaphragm  4  is positioned at the upper end of the move range thereof.  
         [0067]     The most lower end portion  8   a  of the opening forming portion  8  of the lower aperture diaphragm  3  and the most upper end portion  13   a  of the opening forming portion  13  of the upper aperture diaphragm  4 , that are convex, are outside of the light pass hole  24  of the aperture holder  1 . Further, at this maximum aperture, the lower driving diaphragm  30  and the upper driving diaphragm  31  are outside of the light pass hole  24 . At the same time, the optical filter  32  arranged on the lower driving diaphragm  30  and the optical filter  33  arranged on the upper driving diaphragm  31  are also outside of the light pass hole  24 .  
         [0068]      FIGS. 8A  to  8 D shows action figures for explaining the aperture actions of the light-amount adjusting apparatus according to the third embodiment.  FIG. 8A  is a condition where the aperture is a bit stopped down from the maximum aperture condition shown in  FIG. 7 . In this condition, the lower aperture diaphragm  3  and the upper aperture diaphragm  4  are moved, and the most lower end portion  8   a  of the opening forming portion  8  of the lower aperture diaphragm  3  and the most upper end portion  13   a  of the opening forming portion  13  of the upper aperture diaphragm  4  are positioned a bit inside from the edge of the light pass hole  24 . And in this condition, the lower driving diaphragm  30  and the upper driving diaphragm  31 , and the optical filters  32  and  33  arranged on these are positioned outside of the opening area  40  formed by the opening forming portion  8  of the lower aperture diaphragm  3  and the opening forming portion  13  of the upper aperture diaphragm  4 . The cam hole  6   b  and  18   b  arranged in the lower driving diaphragm  30  and the upper driving diaphragm  31  are of a roughly S shape, and at this stage, the gum hole  6   b  and  18   b  are in the direction along the direction where the lower aperture diaphragm  3  and the upper aperture diaphragm  4  move vertically, accordingly, the lower driving diaphragm  30  and the upper driving diaphragm  31  remain at the position shown in  FIG. 7  and do not move.  
         [0069]      FIG. 8B  is a middle aperture condition where the lower aperture diaphragm  3  and the upper aperture diaphragm  4  are moved further from the condition in  FIG. 8A . The opening area  40  formed by the opening forming portion  8  of the lower aperture diaphragm  3  and the opening forming portion  13  of the upper aperture diaphragm  4  becomes a roughly rhombic shape. In this condition, the opening area  40  is positioned inside of the light pass hole  24 . And in this condition, parts of the optical filters  32  and  33  get into the opening area  40  by specified amount. By the way, in the opening area  40 , between the two optical filters  32  and  33 , roughly hexagonal space where light goes through is formed.  
         [0070]      FIG. 8C  is a condition where the lower aperture diaphragm  3  and the upper aperture diaphragm  4  are moved furthermore from the condition in  FIG. 8D . The opening area  40  of a roughly rhombic shape formed by the opening forming portion  8  of the lower aperture diaphragm  3  and the opening forming portion  13  of the upper aperture diaphragm  4  in the area of the light pass hole  24  becomes further smaller. In this condition, in the opening area  40 , the optical filter  32  of the lower driving diaphragm  30  and the optical filter  33  of the upper driving diaphragm  31  overlap, and there is no portion where light goes through. However, the two optical filters overlap not in the entire area in the opening area  40 , accordingly, a portion with different light transmittance is formed in the opening area  40 . In the example shown in the figure, the two optical filters overlap near the center of the opening area  40  and the light transmittance becomes lowest therein, meanwhile only one of the optical filter exists at the peripheral portion thereof (right top and left bottom portions), and the light transmittance becomes higher therein than at the center.  
         [0071]      FIG. 8D  is a figure showing the minimum aperture condition. In this condition, the left connection pin  22   a  of the arm  21  of the driving unit  29  shown in  FIG. 6  is positioned diagonally upward, and the right connection pin  22   b  is positioned diagonally downward. Accordingly, the lower aperture diaphragm  3  is positioned at the upper end of the move range thereof, and the upper aperture diaphragm  4  is positioned at the lower end of the move range thereof. In this condition, the opening area  40  becomes a small rhombic shape positioned near the center of the light pass hole  24 . In this condition, the optical filter  32  and the optical filter  33  overlap in all the area of the opening area  40 , accordingly, the light transmittance to the size of the opening area  40  becomes lowest. This condition is made on assumption of the case where illuminance of an object is extremely high, and enables to restrict what is called “vignetting” on an image forming plane of an imaging element.  
         [0072]     According to the third embodiment, in the maximum aperture condition, parts of the optical filters do not get into the light pass hole  24 , as a result, it is possible to secure sufficient light amount. Further, in this device, the lower driving diaphragm  30  and the upper driving diaphragm  31  having the optical filters  32  and  33  respectively rotate while holding their point symmetrical relation to the light axis, and the move amounts of the optical filters  32  and  33  in the opening area  40  become quantitative, as a result, it is possible to easily control light amount passing the light pass hole  24 .  
         [0073]     Furthermore according to the third embodiment, toward the minimum aperture condition, the portion of the area where the two optical filters overlap increases. Accordingly, it is possible to restrict shading that occurs especially from the middle aperture condition to the minimum aperture condition.  
         [0074]     Moreover, according to the third embodiment, driving diaphragms having optical filters are driven in connection with aperture diaphragms, as a result, only one unit of driving motor will do well as the power source for driving them. Accordingly, it is possible to make smallest the space for arranging the power source. Further, move areas of the driving diaphragms having the respective optical filters are within the move areas of the respective aperture diaphragms. Accordingly, the vertical size of the device may be limited to the space where the respective aperture diaphragms move, as a consequence, it is possible to achieve a compact size of the device. By the way, it is needless to say that in the third embodiment, too, in the same manner as explained in the second embodiment, by making different the shapes of the cam holes formed in the lower driving diaphragm  30  and the upper driving diaphragm  31 , it is possible to drive the optical filters  32  and  33  in asymmetrical manners.  
         [0075]     A fourth embodiment of the present invention shows an example of a light-amount adjusting apparatus having an optical filter (infrared cut filter).  FIG. 9  is a disassembled perspective view showing the structure of a light-amount adjusting apparatus according to the fourth embodiment. The light-amount adjusting apparatus according to the fourth embodiment includes an aperture holder  1 , an optical filter  34 , a lower aperture diaphragm  3 , an upper aperture diaphragm  4 , a driving motor  28 , and a driving unit  29 .  
         [0076]     The aperture holder  1 , the driving motor  28 , and the driving unit  29  are same as those used in the previously described respective embodiments. The lower aperture diaphragm  3  is same as one used in the device according to the third embodiment. Further, the upper aperture diaphragm  4  is of the same structure as those used in the previous respective embodiments, with exception that any driving shaft is not formed therein.  
         [0077]     The optical filter  34  is made of a relatively thin film, and has a function as a NIR (near infrared) cut filter. This optical filter  34  is of a roughly bow shape, and has an inner edge portion  34   a  that roughly meets the shape of the light pass hole  24 . Further, in this optical filter  34 , a cam hole  6   c  that is cut out into a roughly arc shape, and a rotation center hole  7  are formed. The cam hole  6   c  is formed so as to have a relative small vertical interval of both the ends (horizontal direction in the figure).  
         [0078]     In the light-amount adjusting apparatus according to the fourth embodiment, from not illustrated object side (left side of the figure), the optical filter  34 , the lower aperture diaphragm  3 , and the upper aperture diaphragm  4  are arranged sequentially. First, to the driving shaft  12   b  arranged on the lower aperture diaphragm  3 , the cam hole  6   c  of the optical filter  34  is engaged.  
         [0079]     Then, to the rotating shaft  25   a  of the aperture holder  1 , the straight guide hole  14  of the upper aperture diaphragm  4  and the straight guide hole  9   a  of the lower aperture diaphragm  3  are engaged. Further, to the rotating shaft  25   b  of the aperture holder  1 , the straight guide hole  15   a  of the upper aperture diaphragm  4 , and the straight guide hole  11  of the lower aperture diaphragm  3  are engaged, and further, the rotation center hole  7  of the optical filter  34  is engaged thereto. To the diaphragm guide pin  26   a  of the aperture holder  1 , the straight guide hole  9   b  of the lower aperture diaphragm  3  is engaged. To the diaphragm guide pin  26   b  of the aperture holder  1 , the straight guide hole  15   b  of the upper aperture diaphragm  4  is engaged.  
         [0080]     Further, from the rear side (image side) of the driving attaching portion  23 , the driving motor  28  is attached to the driving motor attaching portion  27  arranged in the driving attaching portion  23 . Then, the rotating shaft  28   a  of the driving motor  28  is attached to the rotation lever  20  of the driving unit  29 . The left connection pin  22   a  and the right connection pin  22   b  arranged at both the ends of the arm  21  of the driving unit  29  are engaged to the rotation connection hole  10  of the lower aperture diaphragm  3  and the rotation connection hole  17  of the upper aperture diaphragm  4  respectively. The left connection pin  22   a  and the right connection pin  22   b  freely slide to the rotation connection hole  10  and the rotation connection hole  17  respectively.  
         [0081]     When the driving motor  28  is driven (rotated), the arm  21  of the driving unit  29  swings. At this moment, the left connection pin  22   a  and the right connection pin  22   b  of the arm  21  move in mutually reverse vertical directions, thereby, the lower aperture diaphragm  3  and the upper aperture diaphragm  4  move in mutually reverse vertical directions. Accordingly, the optical filter  34  moves in vertical direction, too. As a result, the driving shaft  12   b  of the lower aperture diaphragm  3  slides in the cam hole  6   c  formed in the optical filter  34 , and the optical filter  34  rotates around the rotation center hole  7 . Through these actions, the size of an opening area  40  of the light-amount adjusting apparatus according to the fourth embodiment changes as shown in  FIG. 11  to be explained later herein.  
         [0082]      FIG. 10  is a front view of the light-amount adjusting apparatus according to the fourth embodiment. A maximum aperture condition (aperture release) is shown in the figure. At the moment of this maximum aperture, the left connection pin  22   a  of the arm  21  of the driving unit  29  shown in  FIG. 9  is positioned diagonally downward, and the right connection pin  22   b  is positioned diagonally upward. Accordingly, the lower aperture diaphragm  3  is positioned at the lower end of the move range thereof, and the upper aperture diaphragm  4  is positioned at the upper end of the move range thereof.  
         [0083]     The most lower end portion  8   a  of the opening forming portion  8  of the lower aperture diaphragm  3  and the most upper end portion  13   a  of the opening forming portion  13  of the upper aperture diaphragm  4 , that are convex, are positioned outside of the light pass hole  24  of the aperture holder  1 . And at this maximum aperture, the optical filter  34  is positioned outside of the light pass hole  24 .  
         [0084]      FIGS. 11A  to  11 D show action figures for explaining the aperture actions of the light-amount adjusting apparatus according to the fourth embodiment.  FIG. 11A  is a condition where the aperture is a bit stopped down from the maximum aperture condition shown in  FIG. 10 . In this condition, the lower aperture diaphragm  3  and the upper aperture diaphragm  4  are moved, and the most lower end portion  8   a  of the opening forming portion  8  of the lower aperture diaphragm  3  and the most upper end portion  13   a  of the opening forming portion  13  of the upper aperture diaphragm  4  are positioned a bit inside from the edge of the light pass hole  24 . Further, the optical filter  34  is positioned outside of the opening area  40  formed by the opening forming portion  8  of the lower aperture diaphragm  3  and the opening forming portion  13  of the upper aperture diaphragm  4 . Namely, because the engaging cam hole  6   c  is faced in nearly vertical direction, the driving shaft  12   b  moves in nearly vertical direction in this cam hole  6   c , accordingly the optical filter  34  is in a status where its move amount toward the light pass hole  24  is small.  
         [0085]      FIG. 11D  is a middle aperture condition where the lower aperture diaphragm  3  and the upper aperture diaphragm  4  are moved further from the condition in  FIG. 11A . The opening area  40  formed by the opening forming portion  8  of the lower aperture diaphragm  3  and the opening forming portion  13  of the upper aperture diaphragm  4  becomes a roughly rhombic shape. In this condition, the opening area  40  is positioned inside of the light pass hole  24 . And in this condition, too, the optical filter  34  is still positioned outside of the opening area  40 .  
         [0086]      FIG. 11C  is a condition where the lower aperture diaphragm  3  and the upper aperture diaphragm  4  are moved furthermore from the condition in  FIG. 11D . The roughly rhombic shape (opening area  40 ) formed by the opening forming portion  8  of the lower aperture diaphragm  3  and the opening forming portion  13  of the upper aperture diaphragm  4  in the area of the light pass hole  24  becomes further smaller. In this condition, by the move of the driving shaft  12   b  in the cam hole  6   c , part (inner edge portion  34   a ) of the optical filter  34  gets into the opening area  40 . In other portion of the opening area  40 , light goes through.  
         [0087]      FIG. 11D  is a figure showing the minimum aperture condition. At this moment, the left connection pin  22   a  of the arm  21  of the driving unit  29  shown in  FIG. 9  is positioned diagonally upward, and the right connection pin  22   b  is positioned diagonally downward. Accordingly, the lower aperture diaphragm  3  is positioned at the upper end of the move range thereof, and the upper aperture diaphragm  4  is positioned at the lower end of the move range thereof. In this condition, the opening area  40  becomes a small rhombic shape positioned near the center of the light pass hole  24 . In this condition, the optical filter  34  covers the entire area of the opening area  40 .  
         [0088]     According to the fourth embodiment, in the maximum aperture condition, part of the optical filter  34  do not get into the light pass hole  24 , as a result, it is possible to secure sufficient light amount. Further, the optical filter  34  is driven in connection with the lower aperture diaphragm  3 , as a result, only one unit of driving motor will do well as the power source for driving them. Accordingly, it is possible to make smallest the space for arranging the power source. Further, move areas of the optical filter  34  is within the move areas of the lower aperture diaphragm  3 . Accordingly, the vertical size of the device may be limited to the space where the lower aperture diaphragm  3  moves, as a consequence, it is possible to achieve a compact size of the device.  
         [0089]     Furthermore, when an infrared cut filter is used as an optical filter, by making this infrared cut filter going into the light pass hole  24  near the minimum aperture, it becomes possible to effectively cut infrared light. According to the above structure, it becomes possible to get in and out this infrared cut filter with a simple structure.  
         [0090]     According to the respective embodiments, actions from the maximum aperture to the minimum aperture have been explained, and structures where optical filters go into the light pass hole have been explained, on the contrary, actions from the minimum aperture to the maximum aperture are just reverse actions, therefore, explanations thereof are omitted herein. In this instance, optical filters shift from the condition where they get into the light pass hole into the condition where they get out from the light pass hole. Further, the present invention is not limited to the respective embodiment herein, but the present invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. For example, each optical filter or driving diaphragm are structured so as to rotate by forming a cam hole therein, however, other means than a cam hole may be selected so long as each optical filter or driving diaphragm may rotate.  
         [0091]     According to the present invention, it is possible to continuously change the portion that an optical filter occupies to the size of a changing aperture opening. Especially, it is possible to appropriately set the advance and retreat amount of an optical filter from the middle aperture to the minimum aperture, and to restrict shading.  
         [0092]     Furthermore, according to the present invention, it is possible to obtain the above effects with a compact size of the device. Furthermore, in the maximum aperture condition, part of an optical filter does not go into the light pass hole, as a consequence, it is possible to secure sufficient light amount.  
         [0093]     Although the invention has been described with respect to a specific embodiment for a complete and clear disclosure, the appended claims are not to be thus limited but are to be construed as embodying all modifications and alternative constructions that may occur to one skilled in the art which fairly fall within the basic teaching herein set forth.