Abstract:
Disclosed herein is a light amount adjustment apparatus, including: a shutter blade and a filter blade each configured to operate in a predetermined direction to adjust the amount of light transmitted through a lens group; a first magnet configured to drive the shutter blade; a first core and a first coil; a second magnet configured to drive the filter blade; and a second core and a second coil. The filter blade has a control portion for controlling and adjusts the amount of light transmitted through the lens group. The filter blade has at least one hole or one cutaway portion formed at a portion of the filter blade other than the control portion.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority from Japanese Patent Application No. JP 2007-009443 filed in the Japanese Patent Office on Jan. 18, 2007, the entire content of which is incorporated herein by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a light amount adjustment apparatus and an image pickup apparatus. 
     2. Description of the Related Art 
     An image pickup apparatus of a video camera, a still camera or a light apparatus includes a light amount adjustment apparatus for adjusting the amount of light fetched through a lens group. 
     In one of such light amount adjustment apparatus, shutter blades, a filter blade or the like serving as light amount adjustment members are supported for pivotal motion on a base member. The light amount adjustment members are pivoted by an electromagnet or actuator including a magnet, a coil and a core having a pair of confronting portions to adjust the light amount. One of light amount adjustment apparatus of the type described is disclosed, for example, in Japanese Patent Laid-Open No. 2004-95703 (hereinafter referred to as Patent Document 1). 
     SUMMARY OF THE INVENTION 
     Incidentally, in some light amount adjustment apparatus, when the coil is not energized, the magnet is attracted to one side or the opposite side in the direction of rotation by the core to hold the shutter blades and the filter blade at an open position at which incoming light is not intercepted or a closed position at which incoming light is intercepted. 
     In such a holding method as just described, an outer circumferential face of the magnet in the form of a disk and part of the core are opposed to each other so that the magnet is attracted by the core. In this instance, as the confronting angle between the magnet and the core, that is, the central angle between the outer circumferential face of the magnet and a portion of the core which opposes to the magnet, decreases, the holding force of the core for the magnet increases. Accordingly, the force for retaining the shutter blades and the filter blade, which are pivoted in response to rotation of the magnet, at the open position when the coil is not energized increases as the confronting angle described above decreases. 
     However, as regards driving of the shutter blades, if the holding force for the shutter blade when the coil is not energized increases, then such a disadvantage occurs that power gets higher upon starting of the shutter blades or the shutter speed is decreased. Therefore, it is desirable to reduce the holding force. 
     On the other hand, as regards driving of the shutter blades, since they have a comparatively great thickness and have a comparatively high weight, it is necessary to assure high holding force in order to stabilize the holding position of the filter blade when the coil is not energized. 
     In this manner, if it is designed to reduce the holding force for the shutter blades when the coil is not energized and increase the holding force for the filter blade when the coil is not energized, then it is difficult to achieve use of common parts in regard to the core and the magnet between an actuator for driving the shutter blades and another actuator for driving the filter blade. This gives rise to disadvantages that a high fabrication cost may be required and that the assemblability is deteriorated. 
     Therefore, it is demanded to provide a light amount adjustment apparatus and an image pickup apparatus by which common use of parts can be anticipated. 
     According to an embodiment of the present invention, the shape of shutter blades and the positional relationship of the shutter blades with some other members are contrived to achieve such common use of parts. 
     In particular, according to an embodiment of the present invention, there is provided a light amount adjustment apparatus including a shutter blade and a filter blade each configured to operate in a predetermined direction to adjust the amount of light transmitted through a lens group, a first magnet configured to drive the shutter blade, a first core and a first coil, a second magnet configured to drive the filter blade, and a second core and a second coil, the filter blade having a control portion for controlling and adjusting the amount of light transmitted through the lens group, the filter blade having at least one hole or one cutaway portion formed at a portion of the filter blade other than the control portion. 
     With the light amount adjustment apparatus, the weight of the filter blade is reduced. Therefore, the holding force for the filter blade when the coil is not energized can be reduced, and common use of parts for a driving section for operating the shutter blade and another driving section for operating the filter blade can be achieved. As a result, reduction of the fabrication cost and improvement of the assemblability can be anticipated as much. 
     The light amount adjustment apparatus may be configured such that the second magnet is formed as a disk and supported for rotation in a circumferential direction, the filter blade being supported for pivotal motion to adjust the amount of light, the light amount adjustment apparatus further including a driving arm connected for pivotal motion by rotation of the second magnet and having a driving pin connected to the filter blade for pivoting the filter blade, the center of pivotal motion of the filter blade being positioned on the opposite side to the center of rotation of the second magnet with respect to the driving pin over an overall range of the pivotal motion of the filter blade from a line segment perpendicular to a line segment interconnecting the center of rotation of the second magnet and the driving pin on a plane within which the filter blade is pivoted. With the light amount adjustment apparatus, the holding force for the filter blade when the coil is not energized can be reduced. 
     According to another embodiment of the present invention, there is provided an image pickup apparatus including a lens barrel having a predetermined lens group disposed inside, an apparatus body configured to support the lens barrel, and a light amount adjustment apparatus incorporated in the lens barrel and configured to adjust the amount of light fetched through the lens group, the light amount adjustment apparatus having a shutter blade configured to be operated in a predetermined direction by a first actuator, which includes a first magnet, a first core and a first coil, to adjust the amount of light transmitted through the lens group, and a filter blade configured to be operated in a predetermined direction by a second actuator, which includes a second magnet, a second core and a second coil, to adjust the amount of the light transmitted through the lens group, the filter blade having a control portion for controlling and adjusting the amount of the light transmitted through the lens group, the filter blade having at least one hole or one cutaway portion formed at a portion of the filter blade other than the control portion. 
     With the image pickup apparatus, the weight of the filter blade is reduced. Therefore, the holding force for the filter blade when the coil is not energized can be reduced, and common use of parts for a driving section for operating the shutter blade and another driving section for operating the filter blade can be achieved. As a result, reduction of the fabrication cost and improvement of the assemblability can be anticipated as much. 
     According to a further embodiment of the present invention, there is provided a light amount adjustment apparatus including a shutter blade and a filter blade each configured to operate in a predetermined direction to adjust the amount of light transmitted through a lens group, a first magnet configured to drive the shutter blade, a first core and a first coil, a second magnet configured to drive the filter blade, and a second core and a second coil, the second magnet being formed as a disk and supported for rotation in a circumferential direction, and the filter blade being supported for pivotal motion to adjust the amount of light. The light amount adjustment apparatus further includes a driving arm connected for pivotal motion by rotation of the second magnet and has a driving pin connected to the filter blade for pivoting the filter blade, the center of pivotal motion of the filter blade being positioned on the opposite side to the center of rotation of the second magnet with respect to the driving pin over an overall range of the pivotal motion of the filter blade from a line segment perpendicular to a line segment interconnecting the center of rotation of the second magnet and the driving pin on a plane within which the filter blade is pivoted. 
     With the light amount adjustment apparatus, the force of rotation acting upon the magnet when pivoting force is applied to the filter blade is low. Therefore, the holding force for the filter blade when the coil is not energized can be reduced, and common use of parts for a driving section for operating the shutter blade and another driving section for operating the filter blade can be achieved. As a result, reduction of the fabrication cost and improvement of the assemblability can be anticipated as much. 
     The light amount adjustment apparatus may be configured such that the filter blade has a control portion for controlling and adjusting the amount of light transmitted through the lens group, and the filter blade has at least one hole or one cutaway portion formed at a portion of the filter blade other than the control portion. With the light amount adjustment apparatus, the weight of the filter blade is reduced, and therefore, the holding force for the filter blade when the coil is not energized can be reduced. 
     According to a still further embodiment of the present invention, there is provided an image pickup apparatus including a lens barrel having a predetermined lens group disposed inside, an apparatus body configured to support the lens barrel, and a light amount adjustment apparatus incorporated in the lens barrel and configured to adjust the amount of light fetched through the lens group. The light amount adjustment apparatus includes a shutter blade configured to be operated in a predetermined direction by a first actuator, which includes a first magnet, a first core and a first coil, to adjust the amount of light transmitted through the lens group, and a filter blade configured to be operated in a predetermined direction by a second actuator, which includes a second magnet, a second core and a second coil, to adjust the amount of the light transmitted through the lens group, the second magnet being formed as a disk and supported for rotation in a circumferential direction, the filter blade being supported for pivotal motion to adjust the amount of light The light amount adjustment apparatus further includes a driving arm connected for pivotal motion by rotation of the second magnet and having a driving pin connected to the filter blade for pivoting the filter blade, the center of pivotal motion of the filter blade being positioned on the opposite side to the center of rotation of the second magnet with respect to the driving pin over an overall range of the pivotal motion of the filter blade from a line segment perpendicular to a line segment interconnecting the center of rotation of the second magnet and the driving pin on a plane within which the filter blade is pivoted. 
     With the image pickup apparatus, the force of rotation acting upon the magnet when pivoting force is applied to the filter blade is low. Therefore, the holding force for the filter blade when the coil is not energized can be reduced, and common use of parts for a driving section for operating the shutter blade and another driving section for operating the filter blade can be achieved. As a result, reduction of the fabrication cost and improvement of the assemblability can be anticipated as much. 
     The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view showing an image pickup apparatus to which the present invention is applied in a state wherein a lens barrel is accommodated in an apparatus body; 
         FIG. 2  is a similar view but showing the image pickup apparatus in another state wherein the lens barrel is projected from the apparatus body; 
         FIG. 3  is a perspective view of the image pickup apparatus in a state wherein it is viewed from the opposite side to that in  FIGS. 1 and 2 ; 
         FIG. 4  is an explode perspective view of the lens barrel; 
         FIG. 5  is an enlarged perspective view of the lens barrel; 
         FIG. 6  is an enlarged cross sectional view of the lens barrel in a collapsed position; 
         FIG. 7  is an enlarged perspective view showing an intermediate movable unit and a light amount adjustment apparatus of the lens barrel in a disassembled state; 
         FIG. 8  is an enlarged perspective view of a second movable unit of the lens barrel; 
         FIG. 9  is an exploded perspective view of the light amount adjustment apparatus; 
         FIG. 10  is an enlarged perspective view of the light amount adjustment apparatus; 
         FIG. 11  is an enlarged perspective view of a base member of the light amount adjustment apparatus; 
         FIG. 12  is an enlarged exploded perspective view of a filter blade of the light amount adjustment apparatus; 
         FIG. 13  is an enlarged perspective view of the filter blade; 
         FIG. 14  is an enlarged front elevational view showing an actuator of the light amount adjustment apparatus; 
         FIG. 15  is an enlarged front elevational view showing an actuator of the light amount adjustment apparatus; 
         FIG. 16  is an enlarged front elevational view showing the shutter blades at an open position and the filter blade at an open position and illustrating an operation of the shutter blades and the filter blade; 
         FIG. 17  is a similar view but showing the shutter blades at a closed position and the filter blade at a closed position and illustrating another operation of the shutter blades and the filter blade; 
         FIG. 18  is a schematic view illustrating force acting upon driving of the shutter blades; 
         FIG. 19  is a schematic view illustrating force acting upon driving of the filter blade where a filter pivotal motion center shaft is positioned between the center of rotation of a magnet and a driving pin of the actuator; 
         FIG. 20  is a schematic view illustrating force acting upon driving of the filter blade where the filter pivotal motion center shaft is positioned on the opposite side to the center of rotation of the magnet with respect to the driving pin; and 
         FIG. 21  is a schematic view showing positions at which the filter pivotal motion center shaft is positioned. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the following, a preferred embodiment of the present invention is described in detail with reference to the accompanying drawings. 
     In the embodiment described below, the present invention is applied to a still camera. It is to be noted that the application of the present invention is not limited to a still camera, but the present invention can be applied widely, for example, to video cameras and various image pickup apparatus incorporated in various other apparatus. 
     In the following description, the directions such as forward, backward, upward, downward, leftward and rightward directions are represented as directions as viewed from an image pickup person upon image pickup of the still camera. 
     Accordingly, the image pickup object side is represented as the front side while the image pickup person side is represented as the rear side. 
     It is to be noted that the forward, backward, upward, downward, leftward and rightward directions used in the following description are determined for the convenience of description, but such directions can be applied suitably when the present invention is carried out. 
     Referring first to  FIGS. 1 and 2 , the image pickup apparatus  1  shown includes an apparatus body  2  and a lens barrel  3  supported for movement in forward and backward directions, that is, in the opposite directions of an optical axis, on the apparatus body  2 . When the image pickup apparatus  1  is not used for image pickup or in a like case, the lens barrel  3  is accommodated in the apparatus body  2  as seen in  FIG. 1 , but when the image pickup apparatus  1  is used for image pickup or in some other case, the lens barrel  3  is projected forwardly from the apparatus body  2  as seen in  FIG. 2 . Thus, in the present image pickup apparatus  1 , the lens barrel  3  is formed as a lens barrel of the collapsible type. 
     Since the image pickup apparatus  1  includes the collapsible lens barrel  3 , both of miniaturization or reduced thickness in a non-image pickup state of the image pickup apparatus  1  and assurance of a good optical performance in an image pickup state. 
     Referring to  FIGS. 1 to 3 , the apparatus body  2  has various elements disposed on the inner side and the outer side of a housing  4  of a horizontally elongated and flattened outer profile. 
     A flash  5  and a finder window  6  are provided on the front face of the apparatus body  2 . A shutter button  7 , a mode changeover dial  8  and a power supply button  9  are provided on the top face of the apparatus body  2 . A battery cover  10  is provided on the right face of the apparatus body  2  such that it can be opened or closed to allow insertion and removal of a battery not shown into and from the apparatus body  2 . A finder  11 , a zoom switch  12 , a display screen  13 , operation buttons  14  and a terminal cover  15  are provided on the rear face of apparatus body  2 . A power supply terminal, input and output terminals and so forth not shown are provided on the inner side of the terminal cover  15 . 
     Referring now to  FIGS. 4 to 6 , the lens barrel  3  includes a fixation member  16 , a fixation ring  17  secured to the fixation member  16 , and a cam cylinder  18  supported for rotation on the fixation ring  17 . The lens barrel  3  further includes a first movable unit  19  supported for movement in the forward and backward directions, that is, in the directions of the optical axis, on the cam cylinder  18 . 
     The fixation member  16  includes a base plate portion  20  formed in a substantially plate form and directed in the forward and backward directions, and an attaching projection  21  projecting forwardly from a lower end portion of the base plate portion  20 . 
     A guide rod  22  is attached to the base plate portion  20 . 
     A focusing motor unit  23  is attached to the attaching projection  21 . A focusing movement unit  24  is moved in the forward and backward direction, that is, in the opposite directions of the optical axis, by the focusing motor unit  23 . The focusing movement unit  24  includes a holding arm  25 , and a focusing lens group  26  attached to the holding arm  25 . 
     When the focusing motor unit  23  is driven, the focusing movement unit  24  is moved in a direction of the optical axis under the guidance of the guide rod  22 . 
     An image pickup unit  27  is attached to a rear portion of the fixation member  16  as seen in  FIG. 4 . The image pickup unit  27  includes a holding frame member  28 , and an image pickup element  29  such as, for example, a CCD (Charge Coupled Device) unit, held by the holding frame member  28 . The image pickup unit  27  is attached at the holding frame member  28  thereof to the fixation member  16 . 
     The fixation ring  17  is attached to the front of the fixation member  16  as seen in  FIGS. 4 and 5 . The fixation ring  17  has a cylindrical base portion  30  formed in a substantially cylindrical shape, a unit holding down portion  31  projecting from an lower end portion of the right end side of the cylindrical base portion  30 , and a case attaching portion  32  projecting from a lower end portion of the left end side of the cylindrical base portion  30 . 
     A gear arrangement hole not shown is formed at a position of the cylindrical base portion  30  corresponding to the case attaching portion  32 . 
     In a state wherein the fixation ring  17  is attached to the fixation member  16 , the guide rod  22  and the focusing motor unit  23  are held from forwardly by the unit holding down portion  31 . 
     In the state wherein the fixation ring  17  is attached to the fixation member  16 , a transmission gear  33  elongated in the axial direction is supported for rotation between the case attaching portion  32  and the fixation member  16 . The transmission gear  33  is disposed in the gear arrangement hole formed in the cylindrical base portion  30 . 
     A case body  34  is attached to the case attaching portion  32  of the fixation ring  17 . 
     A motor  35  is attached in the case body  34  as seen in  FIG. 4 . A transmission gear group not shown is disposed in the case body  34  and held in meshing engagement with the transmission gear  33 . When the motor  35  rotates, the driving force thereof is transmitted to the transmission gear  33  through the transmission gear group. 
     The case body  34  is attached to the fixation ring  17  and the fixation member  16  through an attaching leaf spring  36 . 
     The cam cylinder  18  is supported for movement in the backward and forward directions and for rotation in a circumferential direction on the fixation ring  17  (referred to as  FIGS. 4 and 6 ). 
     The cam cylinder  18  is substantially in a ring shape and has a rack gear  18   a  provided at part of an outer circumferential face at a rear end thereof. 
     The cam cylinder  18  is supported for movement in the backward and forward directions and for rotation in a circumferential direction on the fixation ring  17 . 
     In the state wherein the cam cylinder  18  is supported on the fixation ring  17 , the rack gear  18   a  meshes with the transmission gear  33  supported for rotation between the fixation member  16  and the fixation ring  17 . Accordingly, when the motor  35  held on the case body  34  rotates, the driving force thereof is transmitted to the rack gear  18   a  through the transmission gear set and the transmission gear  33  so that the cam cylinder  18  is rotated in a direction corresponding to the direction of rotation of the motor  35 . Consequently, the cam cylinder  18  is moved in the forward or backward direction while it rotates relative to the fixation ring  17 . 
     A straightforward guide  37  is supported for movement in the backward and forward directions on the fixation ring  17 . The straightforward guide  37  is formed as a unitary member from an annular portion  38  and three guide projections  39  projecting forwardly from the annular portion  38 . 
     The straightforward guide  37  is supported for movement in the forward and backward directions and for rotation relative to the cam cylinder  18  on the fixation ring  17 . 
     An ornamental ring  40  is attached to a front half of the fixation ring  17  as seen in  FIGS. 4 and 6 . 
     A second movable unit  41  is supported on the cam cylinder  18  as seen in  FIG. 6 . The second movable unit  41  includes an intermediate movable unit  42  and a light amount adjustment apparatus  43  attached to the intermediate movable unit  42  as seen in  FIG. 7 . 
     The intermediate movable unit  42  includes several members supported on or attached to a base frame  44 . 
     The base frame  44  includes a disk portion  45 , and a supported face portion  46  provided on an outer circumferential portion of the disk portion  45 . 
     A transmission opening  45   a  is formed at a central portion of the disk portion  45  such that it extends forwardly and backwardly through the disk portion  45 . 
     A first correcting movable frame  47  is supported for movement in the leftward and rightward directions on the front face side of the base frame  44 . A second correcting movable frame  48  is supported for movement in the upward and downward directions on the first correcting movable frame  47 . A lens group  48   a  is attached to the second correcting movable frame  48 . 
     A circuit board  49  is attached to the front face of the second correcting movable frame  48 . 
     As described hereinabove, the first correcting movable frame  47  is supported on the base frame  44  while the second correcting movable frame  48  is supported on the first correcting movable frame  47 , and in a state wherein the circuit board  49  is attached to the second correcting movable frame  48 , an outer core  50  is attached to the front face of the base frame  44  to construct the intermediate movable unit  42 . 
     The light amount adjustment apparatus  43  is attached to the rear face side of the intermediate movable unit  42 , and the second movable unit  41  is formed from the intermediate movable unit  42  and the light amount adjustment apparatus  43  (as reference to  FIGS. 7 and 8 ). 
     The second movable unit  41  is supported for movement in the forward and backward directions on the guide projections  39  of the straightforward guide  37  and supported for sliding movement on the cam cylinder  18 . Accordingly, the second movable unit  41  is moved in the forward direction or the backward direction, that is, in a direction of the optical axis, under the guidance of the straightforward guide  37  by rotation of the cam cylinder  18 . 
     The light amount adjustment apparatus  43  is attached to the rear face side of the base frame  44  as seen in  FIGS. 7 and 8 . 
     The light amount adjustment apparatus  43  includes a base member  51  and several members supported on or attached to the base member  51  as seen in  FIGS. 7 to 10 . 
     The base member  51  is formed in a substantially ring shape and has a mounting recessed portion  53  opened forwardly at a portion thereof except an outer circumferential portion  52  on the front face side as seen in  FIG. 11 . The base member  51  is formed at a portion thereof, at which the mounting recessed portion  53  is formed, with a thickness smaller than that of the outer circumferential portion  52 . 
     A large perforation  53   a  is formed in the mounting recessed portion  53 . A filter pivotal motion center shaft  53   b  and shutter pivotal motion center shafts  53   c  and  53   d  are provided at positions of the mounting recessed portion  53  around the perforation  53   a  such that they project forwardly. Arcuate fitting holes  53   e  and  53   f  are formed at the mounting recessed portion  53  such that they project forwardly and backwardly through the mounting recessed portion  53 . 
     The filter pivotal motion center shaft  53   b  and the shutter pivotal motion center shafts  53   c  and  53   d  are positioned substantially on the opposite sides to each other across the perforation  53   a . The shutter pivotal motion center shafts  53   c  and  53   d  are positioned in a spaced relationship from each other in a circumferential direction, and the fitting hole  53   e  is positioned in the proximity of the filter pivotal motion center shaft  53   b  while the fitting hole  53   f  is positioned between the shutter pivotal motion center shafts  53   c  and  53   d.    
     A cover plate  54 , a first separator  55  and a second separator  56  are attached to the front face side of the base member  51  as seen in  FIGS. 9 and 10 . 
     The cover plate  54  is formed, for example, from a metal material and has a covering portion  57  directed in the forward and backward directions, and attached projections  58  projecting rearwardly from outer circumferential portions of the straightforward guide  37 . 
     A light passing hole  57   a  smaller than the perforation  53   a  of the base member  51  is formed at a central portion of the covering portion  57 . A pair of first sliding projections  57   b  and a pair of second sliding projections  57   c  are formed on the covering portion  57  so as to be swollen rearwardly by stamping as seen in  FIGS. 9 and 12 . 
     Three shaft insertion holes  57   d ,  57   e  and  57   f  and two arcuate fitting holes  57   g  and  57   h  are formed at outer circumferential portions of the covering portion  57 . The shaft insertion hole  57   d  and the shaft insertion holes  57   e  and  57   f  are formed on the substantially opposite sides to each other across the light passing hole  57   a , and the shaft insertion holes  57   e  and  57   f  are positioned in a spaced relationship from each other in the circumferential direction. Further, the fitting hole  57   g  is positioned in the proximity of the shaft insertion hole  57   d , and the fitting hole  57   h  is positioned between the shaft insertion holes  57   e  and  57   f.    
     Referring to  FIG. 9 , the first separator  55  has a transmission hole  55   a  formed at a central portion thereof with a size substantially equal to that of the light passing hole  57   a  of the cover plate  54 . Three shaft insertion holes  55   b ,  55   c  and  55   d  and arcuate fitting holes  55   e  and  55   f  are formed at outer circumferential portions of the first separator  55 . The shaft insertion hole  55   b  and the shaft insertion holes  55   c  and  55   d  are positioned on the substantially opposite sides to each other across the transmission hole  55   a , and the shaft insertion holes  55   c  and  55   d  are positioned in a spaced relationship from each other in the circumferential direction. Further, the fitting hole  55   e  is positioned in the proximity of the shaft insertion hole  55   b , and the fitting hole  55   f  is positioned between the shaft insertion holes  55   c  and  55   d.    
     The second separator  56  has a transmission hole  56   a  formed at a central portion thereof with a size substantially equal to that of the light passing hole  57   a  of the cover plate  54 . Two shaft insertion holes  56   b  and  56   c  and two arcuate fitting holes  56   d  and  56   e  are formed at outer circumferential portions of the second separator  56 . The shaft insertion hole  56   b  and the shaft insertion hole  56   c  are positioned on the substantially opposite sides to each other across the transmission hole  56   a , and the fitting holes  56   d  and  56   e  are positioned in the proximity of the shaft insertion holes  56   b  and  56   c , respectively. 
     A pair of shutter blades  59  and  60  and a filter blade  61  are supported for pivotal motion on the base member  51  as seen in  FIGS. 9 and 12 . 
     The shutter blades  59  and  60  are each formed from a material in the form of a sheet and have shaft insertion holes  59   a  and  60   a  and action holes  59   b  and  60   b  formed at one end portion thereof. The action holes  59   b  and  60   b  are elongated in one direction. 
     Referring to  FIGS. 13 and 14 , the filter blade  61  is from two sheet members  63  formed on the opposite faces of a dimming filter  62  and coupled in a laminated state to each other. Each of the sheet members  63  has a circular hole  63   a  formed therein. The circular hole  63   a  has a diameter greater than that of the transmission hole  55   a  of the first separator  55 . Accordingly, the filter blade  61  is exposed at the dimming filter  62  thereof at a position corresponding to the circular holes  63   a . The exposed portion of the filter blade  61  is provided as a control portion  62   a  which controls and adjusts the amount of light. The dimming filter  62  is formed from an ND (Neutral Density) filter. 
     The filter blade  61  has formed at one end portion thereof a shaft insertion hole  61   a  and an action hole  61   b  which is elongated in one direction. 
     The filter blade  61  has a hole  61   c  formed therein as seen in  FIG. 14 . The hole  61   c  is provided to reduce the weight of the filter blade  61 . Accordingly, in order to reduce the weight of the filter blade  61 , the hole  61   c  may be replaced, for example, by a plurality of small holes or by at least one cutaway portion formed in the filter blade  61 . 
     The second separator  56  is disposed at the mounting recessed portion  53  of the base member  51 , and the filter pivotal motion center shaft  53   b  and the shutter pivotal motion center shaft  53   c  of the base member  51  are inserted in the shaft insertion holes  56   b  and  56   c  of the second separator  56 , respectively. The shutter pivotal motion center shaft  53   d  is positioned on the immediately outer side of the second separator  56 . 
     The filter blade  61  is supported on the front face side of the second separator  56  as seen in  FIG. 9 . The filter pivotal motion center shaft  53   b  of the base member  51  is inserted in the shaft insertion hole  61   a  of the filter blade  61  such that the filter blade  61  is supported for pivotal motion around the filter pivotal motion center shaft  53   b  on the base member  51 . 
     The filter blade  61  has such a three-member configuration that the sheet members  63  are coupled in a layered fashion to the opposite faces of the dimming filter  62  as described hereinabove such that otherwise possible damage to the dimming filter  62  upon pivotal motion of the dimming filter  62  between the first separator  55  and the second separator  56  can be prevented. 
     In a state wherein the first separator  55  is attached to the base member  51 , the shutter blades  59  and  60  are supported for pivotal motion on the base member  51  as seen in  FIG. 12 . In particular, the shutter pivotal motion center shafts  53   c  and  53   d  of the base member  51  are inserted in the shaft insertion holes  59   a  and  60   a  of the shutter blades  59  and  60 , respectively. Consequently, the shutter blades  59  and  60  are supported in a partially overlapping relationship with each other for pivotal motion around the shutter pivotal motion center shafts  53   c  and  53   d  of the base member  51  on the base member  51 , respectively. 
     In a state wherein the shutter blades  59  and  60  are supported on the base member  51 , the cover plate  54  is attached to the base member  51  as seen in  FIGS. 9 and 10 . The cover plate  54  is attached to the base member  51  with the attached projections  58  thereof engaged with the outer circumferential portion  52  of the base member  51 . Accordingly, the shutter blades  59  and  60  are disposed for pivotal motion between the cover plate  54  and the first separator  55 . 
     A first actuator  64  and a second actuator  65  are attached to the rear face of the base member  51  as seen in  FIG. 9 . 
     As shown in  FIG. 15 , the first actuator  64  has a core  66 , and a coil  67 , a magnet  68  and a driving arm  69  held on the core  66 . The driving arm  69  has a base portion  69   a , and an arm portion  69   b  projecting forwardly from the base portion  69   a . A driving pin  69   c  is provided at a free end portion of the arm portion  69   b.    
     The core  66  has a pair of confronting portions  66   a  and  66   b  positioned so as to sandwich the magnet  68  therebetween from an outer circumference side, and a connecting portion  66   c  for connecting end portions of the confronting portions  66   a  and  66   b  to each other. The other end portions of the confronting portions  66   a  and  66   b  are formed arcuately along the outer circumferential face of the magnet  68 . 
     The second actuator  65  has a core  70 , and a coil  71 , a magnet  72  and a driving arm  73  held on the core  70 . The driving arm  73  has a base portion  73   a , and an arm portion  73   b  projecting forwardly from the base portion  73   a . A driving pin  73   c  is provided at a free end portion of the arm portion  73   b.    
     The core  70  has a pair of confronting portions  70   a  and  70   b  positioned so as to sandwich the magnet  72  from an outer circumference side, and a connecting portion  70   c  for interconnecting end portions of the confronting portions  70   a  and  70   b . End portions of the confronting portions  70   a  and  70   b  are shaped arcuately along the outer circumferential face of the magnet  68 . 
     Inner faces of the arcuately shaped end portions of the confronting portions  66   a ,  66   b  and  70   a ,  70   b  are positioned in an opposing relationship to an outer circumferential face of the magnets  68  and  72 , respectively. In the light amount adjustment apparatus  43 , when the coil  67  or  71  is energized, the magnet  68  or  72  is attracted to one side or the outer side in the direction of rotation by the magnet  68  or  72  to hold the shutter blades  59  and  60  or the filter blade  61  at one end or the other end in the direction of pivotal motion of the same. 
     As the value of the confronting angle of the magnet  68  or  72  and the core  66  or  70 , that is, the value of the central angle α of a portion of the outer circumferential face of the magnet  68  or  72  which confronts the core  66  or  70 , decreases, the holding force of the core  66  or  70  for the magnet  68  or  72  increases. Accordingly, the force for holding the shutter blades  59  and  60  or the filter blade  61  which are or is pivoted in response to rotation of the magnet  68  or  72  increases as the confronting angle α decreases. 
     The first actuator  64  and the second actuator  65  exert rotating force between the cores  66  and  70  and the magnets  68  and  72  in response to current flowing through the coils  67  and  71 , respectively. By the rotating force, the driving arms  69  and  73  are pivoted in a direction corresponding to the direction of the current flowing through the coils  67  and  71 , respectively. 
     The first actuator  64  and the second actuator  65  are attached to positions of the base member  51  spaced away from each other in a circumferential direction while they are held from rearwardly by a holding plate  74  as seen in  FIGS. 7 to 9 . 
     In the state wherein the first actuator  64  and the second actuator  65  are attached to the base member  51 , the driving pin  69   c  of the driving arm  69  is fitted in order into the fitting hole  53   f  of the base member  51 , the shaft insertion hole  56   e  of the second separator  56 , the action holes  59   b  and  60   b  of the shutter blades  59  and  60 , the fitting hole  55   f  of the first separator  55  and the fitting hole  57   h  of the cover plate  54 . Meanwhile, the driving pin  73   c  of the driving arm  73  is fitted in order into the fitting hole  53   e  of the base member  51 , the fitting hole  56   d  of the second separator  56 , the action hole  61   b  of the filter blade  61 , the fitting hole  55   e  of the first separator  55  and the fitting hole  57   g  of the cover plate  54 . 
     If the driving arm  69  is driven to pivot by the first actuator arm  64 , then opening edges of the action holes  59   b  and  60   b  are pressed by the arm portion  69   b  as seen in  FIGS. 16 and 17 . Consequently, the shutter blades  59  and  60  are pivoted between their open position wherein they open the perforation  53   a  and their closing position wherein they close the perforation  53   a  in response to the direction of current flowing through the coil  67 . On the other hand, if the driving arm  73  is driven to pivot by the second actuator  65 , then an opening edge of the action hole  61   b  is pressed by the driving pin  73   c . Consequently, the filter blade  61  is pivoted between its open position wherein it opens the perforation  53   a  and its closing position wherein it closes the perforation  53   a  in response to the direction of current flowing through the coil  71 . 
     As regards driving of the shutter blades  59  and  60 , the shutter blades  59  and  60  are pivoted in the opposite directions to each other by pivotal motion of the driving arm  69  to open or close the perforation  53   a  as shown in  FIG. 18 . 
     If impact force G is generated when the shutter blades  59  and  60  are positioned, for example, at the open position, then a moment M 1  is generated in the shutter blade  59  while another moment M 2  is generated in the shutter blade  60 . If the weight of the shutter blades  59  and  60  is represented by W 1  and W 2 , respectively, then the force acting upon the center of gravity of the shutter blades  59  and  60  is given by W 1 ·G and W 2 ·G, respectively. At this time, where the distance between the center of pivotal motion and the center of gravity of the shutter blade  59  is represented by L 1 , the distance between the center of pivotal motion and the center of gravity of the shutter blade  60  is represented by L 2  and the force components W 1 ·G and W 2 ·G in directions perpendicular to the directions of the distances L 1  and L 2  are represented by F 1  and F 2 , respectively, the moments M 1  and M 2  are given by M 1 =L 1 ·F 1  and M 2 =L 2 ·F 2 , respectively. Since the directions of the force components F 1  and F 2  are much different from each other, the force acting upon the driving pin  69   c  when the impact force G is generated is low when compared with the overall weight of the shutter blades  59  and  60 . Accordingly, as regards the shutter blades  59  and  60 , the holding force of the core  66  for the magnet  68  when the coil  67  is not energized may be low. 
     In driving of the filter blade  61 , the filter blade  61  is pivoted by pivotal motion of the driving arm  73  to open or close the perforation  53   a.    
     For example, where the filter pivotal motion center shaft  53   b  which serves as the center of pivotal motion of the filter blade  61  is positioned between the center of rotation of the magnet  72  and the driving pin  73   c  as seen in  FIG. 19 , if impact force G is generated when the filter blade  61  is in its open position, then a moment Ma′ is generated in the filter blade  61 . Where the weight of the filter blade  61  is represented by W, the force acting upon the center of gravity of the filter blade  61  is given by W·G. At this time, where the distance between the center of pivotal motion and the center of gravity of the filter blade  61  is represented by L 3  and the force component of the force W·G in a direction perpendicular to the distance L 3  is represented by F 3 ′, the moment Ma is given by Ma=L 3 ·F 3 ′. 
     In this instance, where the distance between the filter pivotal motion center shaft  53   b  and the driving pin  73   c  is represented by L 4  and the force acting in a direction perpendicular to the distance L 4  is represented by F 4 ′, the moment Ma′ is given by Ma′=L 4 ·F 4 ′. 
     A moment Mb′ is generated in the driving pin  73   c . The moment Mb′ is given by Mb′=L 5 ·F 5 ′ where L 5  is the distance between the center of rotation of the magnet  72  and the driving pin  73   c , and F 5 ′ is the force component of the force F 4 , in a direction perpendicular to the distance L 5 . 
     In this manner, where the filter pivotal motion center shaft  53   b  is positioned between the center of rotation of the magnet  72  and the driving pin  73   c , since the angle β′ defined by the force F 4 ′ and the force component F 5 ′ is small, a moment substantially equal to the moment Ma′ which is generated in the filter blade  61  is generated as the moment Mb′ in the driving pin  73   c . Accordingly, it is necessary to set the holding force of the core  70  for the magnet  72  when the coil  71  is not energized to a high level. 
     Meanwhile, the image pickup apparatus  1  is configured such that the filter pivotal motion center shaft  53   b  which serves as the center of pivotal motion of the filter blade  61  is positioned on the opposite side to the center of rotation of the magnet  72  with respect to the driving pin  73   c.    
     In this instance, for example, if impact force G is generated when the filter blade  61  is in its open position as seen in  FIG. 20 , then a moment Ma is generated in the filter blade  61 . If the weight of the filter blade  61  is represented by W, then the force acting upon the center of gravity of the filter blade  61  is given by W·G. At this time, where the distance between the center of pivotal motion and the center of gravity of the filter blade  61  is represented by L 3  and the force component of the force W·G in a direction perpendicular to the distance L 3  is represented by F 3 , the moment Ma is given by Ma=L 3 ·F 3 . 
     In this instance, where the distance between the filter pivotal motion center shaft  53   b  and the driving pin  73   c  is represented by L 4  and the force acting in a direction perpendicular to the distance L 4  is represented by F 4 , the moment Ma is given by Ma=L 4 ·F 4 . 
     A moment Mb is generated in the driving pin  73   c . The moment Mb is given by Mb=L 5 ·F 5  where L 5  is the distance between the center of rotation of the magnet  72  and the driving pin  73   c , and F 5  is the force component of the force F 4  in a direction perpendicular to the distance L 5 . 
     Where the filter pivotal motion center shaft  53   b  is positioned on the opposite side to the center of rotation of the magnet  72  with respect to the driving pin  73   c  as in the image pickup apparatus  1 , the angle β defined by the force F 4  and the force component F 5  is great. Therefore, the moment Mb generated in the driving pin  73   c  is low when compared with the moment Ma generated in the filter blade  61 . Accordingly, the holding force of the core  70  for the magnet  72  when the coil  71  is not energized can be set low. 
     In particular, the image pickup apparatus  1  is configured such that the filter pivotal motion center shaft  53   b  remains positioned on the opposite side to the center of rotation of the magnet  72  with respect to the driving pin  73   c  over the overall range of the pivotal motion of the filter blade  61  as seen in  FIG. 21 . More particularly, the image pickup apparatus  1  is configured such that, where, in the open position, the region on the opposite side to the center of rotation of the magnet  72  with respect to the driving pin  73   c  is represented by a range A and, in the closing position, the range on the opposite side to the center of rotation of the magnet  72  with respect to the driving pin  73   c  is represented by a range B, the filter pivotal motion center shaft  53   b  is positioned within a range C within which the range A and the range B overlap with each other. 
     A wiring line plate  75  is attached to the rear face of the holding plate  74  as seen in  FIG. 4 . The wiring line plate  75  is connected to the coils  67  and  71  and has a function of supplying power to the coils  67  and  71 . 
     The light amount adjustment apparatus  43  configured in such a manner as described above is attached to the intermediate movable unit  42  with the base member  51  thereof engaged with the base frame  44 , and the second movable unit  41  is formed from the intermediate movable unit  42  and the light amount adjustment apparatus  43 . 
     The first movable unit  19  includes a movable frame  76  and a lens group  77  held on the movable frame  76  as seen in  FIGS. 4 and 6 . The lens group  77  is attached to a central portion of the movable frame  76  through a lens holder  78 . 
     The first movable unit  19  is supported at the movable frame  76  thereof for sliding motion on the guide projections  39  of the straightforward guide  37  and supported for sliding motion on the cam cylinder  18 . Accordingly, the first movable unit  19  is moved in the forward or backward direction, that is, in a direction of the optical axis, under the guidance of the straightforward guide  37  by rotation of the cam cylinder  18 . 
     A lens barrier  79  is attached to the front face side of the first movable unit  19  as seen in  FIGS. 4 and 6 . 
     In a state wherein the lens barrier  79  is attached to the first movable unit  19 , an ornamental ring  80  is attached to the outer face side of the movable frame  76  and the lens barrier  79 . 
     As described above, in the image pickup apparatus  1 , the hole  61   c  or a cutaway portion is formed on the filter blade  61  to reduce the weight of the filter blade  61 . Accordingly, with regard to the shutter blades  59  and  60  which may require reduction of the holding force when the coil  67  is not energized in order to achieve reduction of the power consumption upon starting and increase of the shutter speed and the filter blade  61  which has a comparatively high weight and may require increase of the holding force in order to achieve stability of the holding state when the coil  67  is not energized, the holding force for the filter blade  61  when the coil  67  is not energized can be reduced by the reduction of the weight of the filter blade  61  and common use of parts of the first actuator  64  and the second actuator  65  can be anticipated. As a result, reduction of the fabrication cost and improvement of the assemblability can be anticipated. 
     Further, since the image pickup apparatus  1  is configured such that the filter pivotal motion center shaft  53   b  remains positioned on the opposite side to the center of rotation of the magnet  72  with respect to the driving pin  73   c  over the overall range of the pivotal motion of the filter blade  61  as seen in  FIG. 21 , the holding force for the filter blade  61  when the coil  71  is not energized can be reduced. Consequently, common use of parts of the first actuator  64  and the second actuator  65  can be anticipated, and reduction of the fabrication cost and improvement of the assemblability as much can be anticipated. 
     While a preferred embodiment of the present invention has been described using specific terms, such description is for illustrative purpose only, and it is to be understood that changes and variations may be made without departing from the spirit or scope of the following claims.