Abstract:
A lens drive mechanism, enabled to move lens holding member in a stable state, is disclosed. The lens drive mechanism comprises: first and second guide members, each extending in a predetermined direction; a first lens holding member holding a first lens and including a first cam follower portion and a first sleeve portion which engages with the first guide member and is guided in the predetermined direction; a second lens holding member holding a second lens and including a second cam follower portion and a second sleeve portion, which engages with the second guide member and is guided in the predetermined direction; and a cam member engaging with the first and second cam follower portions and driving the first and second lens holding members.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   This invention relates to a lens drive mechanism used in an image-taking optical system or a viewfinder optical system of an image-taking apparatus. 
   2. Description of the Related Art 
   A viewfinder optical system of an image-taking apparatus is disposed so that an optical axis of the viewfinder optical system will be substantially parallel to an optical axis of an image-taking optical system. In the driving of lens elements in the viewfinder optical system in the optical axis direction, cam follower portions, which are provided on lens holding members that hold the lens elements in the viewfinder optical system, are made to contact cam groove portions of a cam ring provided in the image-taking optical system, and by converting the rotation of the cam ring to movement in the optical axis direction of the lens holding members in the viewfinder optical system, the field angle of the viewfinder optical system is changed according to a variation of the focal length of the image-taking optical system. 
     FIG. 4  shows diagrams of a viewfinder drive mechanism disclosed in Patent Document 1. 
     FIG. 4A  is a front view of the viewfinder drive mechanism,  FIG. 4B  is a side view of the viewfinder drive mechanism, and  FIG. 4C  is a rear view of the viewfinder drive mechanism. 
   In  FIG. 4 , Reference Numeral  101  denotes a first lens, Reference Numeral  102  denotes a first holding frame (lens holding member) that holds the first lens  101 , and Reference Numeral  103  denotes a cam follower portion that is provided on the first holding frame  102 . 
   Reference Numeral  107  denotes a second lens, Reference Numeral  108  denotes a second holding frame that holds the second lens  107 , and Reference Numeral  109  denotes a cam follower portion that is provided on the second holding frame  108 . 
   Reference Numeral  104  denotes a cam ring that rotates in the direction of the arrow C about an optical axis (image-taking optical axis) L 1  of the image-taking optical system. Reference Numeral  104   a  denotes a first cam groove portion and Reference Numeral  104   b  denotes a second cam groove portion that are formed on the cam ring  104 . 
   The cam follower portions  103  and  109  are engaged with the first cam groove portion  104   a  and the second cam groove portion  104   b , respectively. 
   Reference Numeral  105  denotes a guide bar, which guides the holding frames  102  and  108  in the direction of an optical axis (viewfinder optical axis) L 2 , and Reference Numeral  106  denotes a rotation stopping bar, which prevents the rotation of the holding frames  102  and  108  about the guide bar  105 . 
   On the first holding frame  102 , a sleeve portion  102   a , which engages with the guide bar  105  in a manner enabling movement in the optical axis L 2  direction, and a U-shaped groove portion  102   b , which engages with the guide bar  106  and blocks the rotation of the first holding frame  102 , are formed. 
   Likewise, on the second holding frame  108 , a sleeve portion  108   a , which engages with the guide bar  105  in a manner enabling movement in the optical axis L 2  direction, and a U-shaped groove portion  108   b , which engages with the guide bar  106  and blocks the rotation of the second holding frame  108 , are formed. 
   Reference Numeral  110  denotes an extension coil spring. The extension coil spring  110  is spanned across the first holding frame  102  and the second holding frame  108  in a state in which it forms a predetermined angle with respect to the guide bar  105 . 
   The first holding frame  102  is thereby energized in the direction of the arrow A in  FIG. 4B , the second holding frame  108  is energized in the direction of the arrow B in  FIG. 4B , the cam follower  103  is pressed against a side wall of the cam groove portion  104   a , and the cam follower  109  is pressed against a side wall of the cam groove portion  104   b.    
   Also, since the extension coil spring  110  is positioned in a state in which it forms a predetermined angle with respect to the guide bar  105 , component forces F 1  and F 2  (see  FIG. 4A  and  FIG. 4C ) are generated in directions substantially orthogonal to the optical axis L 2  direction, and by these component forces, the sleeve portions  102   a  and  108   a  of the lens holding frames  102  and  108  are pressed against the guide bar  105  and eliminated of play. Vibrations of the lenses  101  and  107  during movement are thereby lessened to restrain vibrations of an image. 
   When in this state, the cam ring  104  rotates in the direction of the arrow C in the  FIG. 4 , the cam follower portions  103  and  109  are made, by the energizing force of the extension coil spring  110 , to move without play along the cam groove portions  104   a  and  104   b  and the holding frames  102  and  108  moves in the optical axis L 2  direction. 
     FIG. 5  shows diagrams of a viewfinder drive mechanism disclosed in Patent Document 2. 
     FIG. 5A  is a sectional view resulting from sectioning the viewfinder drive mechanism along a plane containing an optical axis L 2  of a viewfinder optical system, and  FIG. 5B  is a sectional view resulting from sectioning the viewfinder drive mechanism along a plane orthogonal to the optical axis L 2 . 
   A first movable lens unit  210  and a second movable lens unit  211  are lens units (each including lens and a lens holding member), which move when the zoom setting is changed in a variable zoom viewfinder optical system. Lenses  209  and  212  are fixed to a viewfinder block  208 . Lens units  210  and  211  are engaged, in a manner enabling movement in the direction of the optical axis L 2 , to a rectilinear guide shaft  213 , which is fixed to the viewfinder block  208 . 
   The first movable lens unit  210  and the second movable lens unit  211  have rotation stopping bosses  210   a  and  211   a , respectively. The rotation stopping bosses  210   a  and  211   a  engage with groove portions, which are formed on the viewfinder block  208  and extend in the optical axis L 2  direction, to prevent the rotation of the lens units  210  and  211  about the axis of the rectilinear guide shaft  213 . 
   The first movable lens unit  210  and the second movable lens unit  211  have cam follower bosses  210   b  and  211   b  as follower pins and respectively have spring latch bosses  211   c  (the spring latch boss of the first movable lens unit  210  is unillustrated). The cam follower bosses  210   b  and  211   b  are put in contact with cam groove portions  214   a  and  214   b  of a cylindrical cam  214  by the energizing force of a movable lens energizing spring  219  that is latched onto the spring latch bosses  211 C formed on the lens units  210  and  211 . 
   The cylindrical cam  214  is a part of a viewfinder zooming mechanism that rotates via a rotation shaft  215  and is held by the viewfinder block  208 . The cylindrical cam  214  is set in the position in the optical axis L 2  direction by receiving the energizing force of a cylindrical cam energizing spring  216 . 
   The cylindrical cam  214  also has a second gear  214   c  as a follower gear, which engages with a first gear  217   b , provided on an arcuate cam  217 , and rotates by receiving the driving force from the arcuate cam  217 . 
   Furthermore, the cylindrical cam  214  has, as viewfinder lens drive cams, cam groove portions  214   a  and  214   b , which are provided in spiral form. By the rotation of cylindrical cam  214 , the first movable lens unit  210  and second movable lens unit  211  are driven in the optical axis L 2  direction via the cam follower bosses  210   b  and  211   b  that are in contact with the cam groove portions  214   a  and  214   b.    
   The arcuate cam  217  is a principal portion of a coupling mechanism that couples the cylindrical cam  214 , which is the part the viewfinder zooming mechanism of the variable zoom viewfinder optical system, according to the changing of the image-taking magnification of the image-taking lens barrel. The arcuate cam  217  is disposed to be movable within a predetermined range along an outer circumference of a fixed barrel  201  and is set in position in the optical axis L 1  direction by flange portions  201   b  and  201   c  that are provided on the fixed barrel  201 . 
   Also, the arcuate cam  217  has a cam groove portion  217   a , a drive pin  218  serving as a drive portion is engaged with the cam groove portion  217   a , and the cam groove portion  217   a  serving as a follower portion receives a driving force from the drive pin  218 . The arcuate cam  217  is furthermore equipped with the first gear  217   b  serving as a drive gear portion that engages with the second gear  214   c  provided on the cylindrical cam  214 . And when the image-taking lens barrel performs a zooming operation and the drive pin  218  moves in the optical axis L 1  direction, the cam groove portion  217   a  is pushed and the arcuate cam  217  is thereby moved along the outer circumference of the fixed barrel  201 . By this operation of the arcuate cam  217 , driving force is transmitted to the cylindrical cam  214 .
     [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-75187   [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-242507   

   However, with each of the above-described conventional viewfinder drive mechanisms, since two lens units are engaged to a single guard bar, the length of a sleeve portion that is formed integral to each lens unit cannot be made adequately long. There is thus play, etc., between the lens units and the guide bar and the lens units cannot be moved in a stable manner in the optical axis direction. 
   SUMMARY OF THE INVENTION 
   One aspect of a lens drive mechanism according to this invention comprises: first and second guide members, each extending in a predetermined direction; a first lens holding member holding a first lens and including a first cam follower portion and a first sleeve portion, the first sleeve portion engaging with the first guide member and being guided in the predetermined direction; a second lens holding member holding a second lens and including a second cam follower portion and a second sleeve portion, the second sleeve portion engaging with the second guide member and being guided in the predetermined direction; and a cam member engaging with the first and second cam follower portions and driving the first and second lens holding members. 
   One aspect of an image-taking apparatus according to this invention comprises: the abovementioned lens drive mechanism; an image-taking lens unit; an image pickup element performing photoelectric conversion of an optical image formed by the image taking lens unit; and a drive member driving the image-taking lens unit and the cam member in the lens drive mechanism. 
   The characteristics of the lens drive mechanism and image-taking apparatus according to this invention shall be made clear by the following description of specific embodiments with reference to the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a sectional view of an image-taking apparatus that includes a viewfinder drive mechanism of Embodiment 1 of the present invention. 
       FIG. 2A  is an upper view of the viewfinder drive mechanism in Embodiment 1,  FIG. 2B  is a front view of the viewfinder drive mechanism,  FIG. 2C  is a side view of the viewfinder drive mechanism, and  FIG. 2D  is a rear view of the viewfinder drive mechanism. 
       FIG. 3A  is an upper view of a viewfinder drive mechanism in Embodiment 2 of the present invention,  FIG. 3B  is a front view of the viewfinder drive mechanism,  FIG. 3C  is a side view of the viewfinder drive mechanism, and  FIG. 3D  is a rear view of the viewfinder drive mechanism. 
       FIG. 4A  is a front view of a conventional viewfinder drive mechanism,  FIG. 4B  is a side view of the viewfinder drive mechanism, and  FIG. 4C  is a rear view of the viewfinder drive mechanism. 
       FIG. 5A  is a sectional view showing a part of an image-taking apparatus having a conventional viewfinder drive mechanism and  FIG. 5B  is a rear view showing a part of the image-taking apparatus. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiment 1 
     FIG. 1  is a sectional view of an image-taking apparatus that includes a viewfinder drive mechanism (lens drive mechanism) of Embodiment 1 of the present invention. 
     FIG. 2  shows the structure of the viewfinder drive mechanism in the image-taking apparatus of this embodiment.  FIG. 2A  is an upper view of the viewfinder drive mechanism,  FIG. 2B  is a front view of the viewfinder drive mechanism,  FIG. 2C  is a side view of the viewfinder drive mechanism, and  FIG. 2D  is a rear view of the viewfinder drive mechanism. 
   An image-taking optical system of this embodiment shall first be described with reference to the drawings. 
   In  FIG. 1 , Reference Numeral  10  denotes a drive ring, which drives the respective lens units that make up the image-taking optical system, and Reference Numeral  20  denotes a fixing member, which fixes the image-taking optical system to a main body  40  of the image-taking apparatus. Reference Numeral  21  denotes a first lens unit, which makes up a part of the image-taking optical system, Reference Numeral  22  denotes a first lens holding frame, which holds the first lens unit  21 , and Reference Numeral  23  denotes a cam follower portion, provided on the first lens holding frame  22 . 
   Reference Numeral  25  denotes a guide bar, which engages with a sleeve portion  22   a  of the first lens holding frame  22  and guides the first lens holding frame  22  in the direction of an optical axis (image-taking optical axis) L 1 . 
   Reference Numeral  27  denotes a second lens unit, which makes up a part of the image-taking optical system, Reference Numeral  28  denotes a second lens holding frame, which holds the second lens unit  27 , and Reference Numeral  29  denotes a cam follower portion, provided on the second lens holding frame  28 . 
   Reference Numeral  26  denotes a guide bar, which engages with a sleeve portion  28   a  of the second lens holding frame  28  and guides the second lens holding frame  28  in the optical axis L 1  direction. 
   Furthermore, Reference Numerals  30  and  31  denote compression coil springs, which are respectively disposed on the outer peripheries of the guide bars  25  and  26  and between the respective lens holding frames  22  and  28  and the wall surface of the fixing member  20 . The compression coil springs  30  and  31  energize the respective lens holding frames  22  and  28  towards the object side (left side in  FIG. 1 ), and by this energizing force, the cam follower portions  23  and  29  that are disposed on the respective lens holding frames  22  and  28  are pressed without play against cam groove portions  10   c  and  10   d , which are formed on the inner surface of the drive ring  10 . 
   When the drive ring  10  rotates about the optical axis L 1  of the image-taking optical system by receiving a driving force from an unillustrated actuator, since the cam follower portions  23  and  29  are in contact with the cam groove portions  10   c  and  10   d , the cam follower portions  23  and  29  move along the cam track of the cam groove portions  10   c  and  10   d . As a result, the lens holding frames  22  and  28 , on which the cam follower portions  23  and  29  are formed, move in the optical axis L 1  direction. 
   Also, by the contacting of a protruding portion  10   d , formed on the outer circumferential surface of the drive ring  10 , and a protruding portion  1   c  formed on a cam plate  1 , the rotation force of the drive ring  10  is transmitted to the cam plate  1 , and the cam plate  1  is thus also made to rotate about the optical axis L 1  of the image-taking optical system. 
   Reference Numeral  32  denotes a third lens unit, which makes up a part of the image-taking optical system, and Reference Numeral  33  denotes a third lens holding frame which holds the third lens unit  32 . The third lens holding frame  33  is driven in the optical axis L 1  direction by receiving a driving force from an unillustrated actuator. 
   Reference Numeral  34  denotes a diaphragm unit, which is mounted to the second lens holding frame  28 . The diaphragm unit  34  adjusts the amount of light that is made incident on an image surface and also functions as a shutter. 
   The first lens unit  21  functions as a compensator lens for correcting the variation of the focal point position due to movement of the second lens unit  27 . The second lens unit  27  functions as a variator lens for varying the focal length of the image-taking optical system. The third lens unit  32  functions as a focusing lens for performing a focusing operation in the image-taking optical system. 
   Reference Numeral  42  denotes an image pickup element such as a CCD, CMOS sensor, that is fixed onto fixing member  20  and photoelectrically converts an object image (optical image), formed by the image taking optical system, to electrical signals. The image data that are read out from the image pickup element  42  are subject to a predetermined image processing and then recorded onto a recording medium (not shown) or are displayed on a display unit (not shown), provided in the main body  40 . Reference Numeral  41  denotes an optical filter, positioned at the object side of the image pickup element  42 , and functions as an optical low-pass filter and an infrared cut filter. 
   The structure of the viewfinder drive mechanism of this embodiment shall now be described in detail with reference to  FIG. 1  and  FIG. 2 . As shown in  FIG. 1 , the viewfinder mechanism of this embodiment is used upon being mounted onto or built into the image-taking apparatus. 
   Reference Numeral  1  denotes the cam plate (cam member) that drives the respective lens units in the viewfinder optical system. The cam plate  1  has formed thereon the protruding portion  1   c , which contacts the protruding portion of the drive ring  10 , and rotates about the optical axis L 1  of the image-taking optical system in conjunction with the driving ring  10 . 
   Reference Numeral  2  denotes a first lens holding member, which holds a first viewfinder lens  2   a  that makes up a part of the viewfinder optical system, and Reference Numeral  3  denotes a second lens holding member, which holds a second viewfinder lens  3   a  that makes up a part of the viewfinder optical system. 
   Reference Numerals  4  and  5  denote guide bars (guide members), which guide the lens holding members  2  and  3 , respectively, in the direction of an optical axis L 2 , and Reference Numerals  6  and  7  denote compression springs, which respectively energize lens holding members  2  and  3  in mutually separating directions (towards the object side and towards the image surface side) along the optical axis L 2  and are disposed on the guide bars  4  and  5 , respectively. 
   By the compression springs  6  and  7 , a cam follower  2   d  of the first lens holding member  2  is put in contact with a side wall at the object side of a cam groove portion  1   a  and a cam follower  3   d  of the second lens holding member  3  is put in contact with a side wall at the image surface side of a cam groove portion  1   b.    
   Reference Numeral  8  denotes a viewfinder lens barrel member, which houses the viewfinder mechanism, and Reference Numeral  9  denotes a viewfinder ocular optical system including a prism and lenses. 
   On the cam plate  1 , the first cam groove portion  1   a , which contacts the cam follower  2   d  of the first lens holding member  2 , and the first cam groove portion  1   b , which contacts the cam follower  3   d  of the second lens holding member  3  are formed. 
   A lens element  2   a  for image forming is mounted to the first lens holding member  2 . A sleeve portion  2   b  is a portion that engages with the guide bar  4  and is for guiding the first lens holding member  2  in the optical axis L 2  direction. A slot portion (rotation block portion)  2   c  is a portion that engages with the guide bar  5  to prevent the rotation of the first lens holding member  2  about the axis of the guide bar  4 . The cam follower  2   d  is a portion that contacts the cam groove portion  1   a  formed on the cam plate  1 . The cam follower  2   d  is disposed between the guide bars  4  and  5 . In this embodiment, the cam follower  2   d  is disposed between the sleeve portions  2   b  and  3   b  in the optical axis direction. The sleeve portion  2   b , slot portion  2   c  and cam follower  2   d  are disposed integrally on a portion of the first lens holding member  2  that opposes the cam plate  1 . 
   A sleeve portion  3   b  is a portion that engages with the guide bar  5  and is for guiding the second lens holding member  3  in the optical axis L 2  direction. A slot portion  3   c  is a portion that engages with the guide bar  4  to prevent the rotation of the second lens holding member  3  about the axis of the guide bar  5 . The cam follower  3   d  is a portion that contacts the cam groove portion  1   b  formed on the cam plate  1 . The cam follower  3   d  is disposed between the guide bars  4  and  5 . In this embodiment, the cam follower  3   d  is disposed between the sleeve portions  2   b  and  3   b  in the optical axis direction. The sleeve portion  3   b , slot portion  3   c  and cam follower  3   d  are disposed integrally on a portion of the second lens holding member  3  that opposes the cam plate  1 . 
   The guide bar  4  is engaged with the sleeve portion  2   b  of the first lens holding member  2  and the slot portion  3   c  of the second lens holding member  3 . The guide bar  5  is engaged with the sleeve portion  3   b  of the second lens holding member  3  and the slot portion  2   c  of the first lens holding member  2 . 
   Furthermore, by the energizing forces of the compression springs  6  and  7 , the cam followers  2   d  and  3   d  of the lens holding member  2  and  3  are put in contact with the cam groove portions  1   a  and  1   b  without play. 
   When the drive ring  10  rotates about the optical axis L 1  of the image-taking optical system by receiving the driving force from the unillustrated actuator, the cam plate  1  rotates about the optical axis L 1  of the image-taking optical system in conjunction with the drive ring  10 . The cam followers  2   d  and  3   d  are in contact with the cam groove portions  1   a  and  1   b  of the cam plate  1  and are thus moved along the cam track of the cam groove portions  1   a  and  1   b  by the rotation of the cam plate  1 . The lens holding members  2  and  3  are thereby moved in the optical axis L 2  direction. 
   As described above, since the sleeve portion of one of the lens holding members  2  and  3  and the slot portion of the other lens holding member are engaged with each of the guide bars  4  and  5 , the sleeve portions of the respective lens holding members can be disposed in a space-efficient manner, thereby enabling the making of the viewfinder mechanism compact. Here, if the sleeve portions  2   b  and  3   b  of the lens holding members  2  and  3  are engaged with a single guide bar, the operation spaces (spaces in the optical axis L 2  direction) of the lens holding members  2  and  3  must be made large to avoid interference of the sleeve portions  2   b  and  3   b . On the other hand, by providing the arrangement of this embodiment, the operation spaces of the lens holding members  2  and  3  can be made compact while avoiding the interference of the sleeve portions  2   b  and  3   b.    
   Also, since the length (length in the optical axis direction) of the sleeve portions  2   b  and  3   b  can be secured, a play between the guide bars  4  and  5  and the sleeve portions  2   b  and  3   b  are reduced and the lens holding members  2  and  3  can thus be driven in the optical axis L 2  direction with stability. 
   Furthermore, even if the cam followers  2   d  and  3   d  are positioned away from the sleeve portions  2   b  and  3   b , since the play between the sleeve portions  2   b  and  3   b  and the guide bars  4  and  5  is reduced in comparison to the conventional lens drive mechanism as described above, a lens drive mechanism, which, though being compact, can guide the lens holding members  2  and  3  in the optical axis L 2  direction with stability, can be realized. 
   The cam followers  2   d  and  3   d  are positioned, as shown in  FIG. 2A , between the two guide bars  4  and  5 , in particular with this embodiment, at substantially middle positions between the two guide bars  4  and  5 . That is, the cam followers  2   d  and  3   d  are disposed at portions of the respective lens holding members  2  and  3  that oppose the cam plate  1  and are positioned at substantially the center of the interval between the guide bars  4  and  5 . Priorly, the cam follower is positioned near the sleeve portion in order to guide the lens unit in the viewfinder optical system in the optical axis L 2  direction with stability. Such an arrangement is used in the abovementioned Patent Document 1 and Patent Document 2. However, with this embodiment, the two cam followers  2   d  and  3   d  are disposed at positions that are substantially in the middle of the two guide bars  4  and  5  and are on a single axis (the axis B in  FIG. 2 ), which extends parallel to the optical axis L 2  of the viewfinder optical system. 
   The rotational phase positions of the cam groove portions  1   a  and  1   b  of the cam plate  1  with respect to the optical axis L 1  of the image-taking optical system can thereby be matched substantially. Consequently, the length in the arc direction (outer circumferential direction of the drive ring  10 ) of the cam plate  1  can be restrained and it becomes possible to make the cam plate  1  compact. It thus becomes possible to make the image-taking apparatus compact. 
   Also, since the cam followers  2   d  and  3   d  are disposed at substantially middle positions between the two guide bars  4  and  5 , the loads on the cam followers  2   d  and  3   d  by the energizing forces of the compression springs  6  and  7  are balanced uniformly, thereby enabling stable guiding of the lens holding members  2  and  3  in the optical axis direction. 
   Though in this embodiment, compression springs  6  and  7  are used, extension springs may be used instead. In the case where extension springs are used, energizing forces in mutually approaching directions along the optical axis L 2  direction act on the lens holding members  2  and  3 . Also, a compression spring may be disposed on the outer circumference of one of the guide bars  4  and  5  and an extension spring may be disposed on the outer circumference of the other guide bar. 
   Also, with this embodiment, the cam followers  2   d  and  3   d  are disposed at substantially middle positions between the two guide bars  4  and  5  and are disposed so as to fit within the thickness (length in the optical axis L 2  direction) of the lens holding members  2  and  3 , including the viewfinder lenses  2   a  and  3   a . Here, the positions of the cam followers  2   d  and  3   d  may be shifted in accordance with the sensitivities of the viewfinder lenses (movable lenses)  2   a  and  3   a.    
   For example, if the sensitivity, as optical performance, of the viewfinder lens  2   a  is higher than that of the viewfinder lens  3   a , the cam follower  3   d  may be disposed at a position close to the first lens holding member  2 . 
   Oppositely, if the sensitivity, as optical performance, of the viewfinder lens  3   a  is higher than that of the viewfinder lens  2   a , the cam follower  2   d  may be disposed at a position close to the second lens holding member  3 . 
   As has been described above, with this embodiment, since each of the two guide bars  4  and  5  is engaged with the sleeve portion ( 2   b  or  3   b ) of one of the lens holding members  2  and  3  and the slot portion ( 2   c  or  3   c ) of the other lens holding member, the sleeve portions  2   b  and  3   b  can be provided in a space-efficient manner on the lens holding members  2  and  3 , thereby enabling the viewfinder drive mechanism to be made compact. 
   Also, since the lengths of sleeve portions  2   b  and  3   b  can be secured, the play between the guide bars  4  and  5  and the sleeve portions  2   b  and  3   b  is reduced and the lens holding members  2  and  3  can be driven with stability in the optical axis L 2  direction. 
   And by disposing the two cam followers  2   d  and  3   d  along substantially the same axis B in the direction parallel to the optical axis L 2  of the viewfinder optical system, the rotational phase positions of the cam groove portions  1   a  and  1   b  of the cam plate  1  with respect to the optical axis L 1  of the image-taking optical system can be matched substantially. Consequently, the length in the arc direction of the cam plate  1  can be held down and it becomes possible to make the cam plate  1  compact. The image-taking apparatus can thus be made compact. 
   Embodiment 2 
   Embodiment 2 of the present invention shall now be described using  FIG. 3 . In  FIG. 3 , the same symbols are used for members that are the same as the members described in Embodiment 1. 
   Embodiment 2 differs from Embodiment 1 in that a guide bar  13 , which guides lens holding members  50  and  60  (corresponding to the lens holding members  2  and  3  in Embodiment 1), holding viewfinder lenses  50   a  and  60   a  (corresponding to viewfinder lenses  2   a  and  3   a  in Embodiment 1), in the optical axis L 2  direction, is provided in the viewfinder drive mechanism and prevents the rotations of the lens holding members  50  and  60 . 
   The lens holding members  50  and  60  are engaged with the guide bars  4  and  5  as in Embodiment 1, and the lens holding members  50  and  60  are movable in the optical axis L 2  direction along the guide bars  4  and  5 . Also, cam followers  50   d  and  60   d  (corresponding to the cam followers  2   d  and  3   d  in Embodiment 1) are formed on the lens holding members  50  and  60  and put in contact with the cam groove portions  1   a  and  1   b  of the cam plate  1 , respectively. 
   As shown in  FIG. 3B  and  FIG. 3D , slot portions  50   e  and  60   e  are provided at respective upper portions of the first lens holding member  50  and the second lens holding member  60 , that is, at respective side portions opposite the side portions of the lens holding members  50  and  60 , on which the cam followers  50   d  and  60   d  are formed. 
   And by the engagement of guide bar  13  with slot portions  50   e  and  60   e , the lens holding members  50  and  60  are prevented from rotating. 
   By this arrangement, the rotations of the respective lens holding members  50  and  60  can be prevented at positions away from sleeve portions  50   b  and  60   b  (corresponding to the sleeve portions  2   b  and  3   b  in Embodiment 1), which engage with the guide bar  4 , and even if the play becomes large due to manufacturing errors of the sleeve portions  50   b  and  60   b , etc., deviations of the viewfinder lenses  50   a  and  60   a  with respect to the optical axis L 2  can be restrained. 
   As described above, with Embodiment 2 of the present invention, by engaging the guide bar  13  with the slot portions  50   e  and  60   e  and thereby preventing the rotations of the lens holding members  50  and  60 , the rotations of the respective lens holding members  50  and  60  can be prevented at positions away from the sleeve portions  50   b  and  60   b , and even if the play becomes large due to manufacturing errors of the sleeve portions  50   b  and  60   b , etc., optical axis deviations of the viewfinder lenses  50   a  and  60   a  can be restrained. 
   Though with Embodiments 1 and 2 described above, cam groove portions  1   a  and  1   b  are formed on the cam plate  1 , these do not have to be groove portions and may instead be cams having protruding shapes. 
   While preferred embodiments have been described, it is to be understood that modification and variation of the present invention may be made without departing from the scope of the following claims. “This application claims priority from Japanese Patent Application No. 2003-307381 filed Aug. 29, 2003, which is hereby incorporated by reference herein.”