Abstract:
This disclosure aims to miniaturize a lens barrel. The lens barrel includes: a movable frame which has two cam followers provided in a circumferential direction about an optical axis and two guide protrusions arranged along an optical axis direction; a cam frame having two cam grooves with which the two cam followers of the movable frame are engaged respectively; and a guide frame having one guide groove with which the two guide protrusions are engaged. The two cam followers and the two guide protrusions restrict tilting of the movable frame with respect to the cam frame and the guide frame.

Description:
BACKGROUND 
       [0001]    1. Technical Field 
         [0002]    This disclosure relates to a lens barrel. 
         [0003]    2. Description of the Related Art 
         [0004]    Unexamined Japanese Patent Publication No. 2001-215390 (Patent Literature 1) discloses a lens barrel. Patent Literature 1 discloses a technique for reducing eccentric errors between a plurality of lens groups in the lens barrel. 
       SUMMARY 
       [0005]    This disclosure aims to miniaturize a lens barrel. 
         [0006]    A lens barrel according to this disclosure includes: a movable frame which has two cam followers provided in a circumferential direction about an optical axis and two guide protrusions provided along an optical axis direction; a cam frame having two cam grooves with which the two cam followers of the movable frame are engaged respectively; and a guide frame having one guide groove with which the two guide protrusions are engaged. 
         [0007]    The lens barrel of this disclosure restricts tilting of the movable frame with respect to the cam frame and the guide frame by the two cam followers and the two guide protrusions, whereby the lens barrel can be miniaturized. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0008]      FIG. 1  is a perspective view of a lens barrel according to a first embodiment; 
           [0009]      FIG. 2  is an exploded perspective view of the lens barrel according to the first embodiment; 
           [0010]      FIG. 3  is an exploded perspective view of second group lens unit  200  according to the first embodiment; 
           [0011]      FIG. 4  is an explanatory view showing a shape of second group lens frame  220  according to the first embodiment; 
           [0012]      FIG. 5  is an explanatory view showing a shape of rectilinear guide frame  300  according to the first embodiment; 
           [0013]      FIG. 6  is an inner-diameter developed view of cam frame  500  according to the first embodiment; 
           [0014]      FIG. 7  is an explanatory view showing a shape of sixth group lens unit  900  according to the first embodiment; 
           [0015]      FIG. 8  is an explanatory view showing the relationship among second group lens unit  200 , rectilinear guide frame  300 , and cam frame  500  according to the first embodiment; 
           [0016]      FIGS. 9A to 9D  are an explanatory view showing the relationship between cam followers of the respective lens units and the respective cam grooves of cam frame  500  according to the first embodiment; and 
           [0017]      FIGS. 10A and 10B  are an explanatory view showing the relationship between second group lens frame  220  and a position of a center of gravity thereof in the first embodiment. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0018]    Hereinafter, an embodiment will be described in detail with reference to the drawings as appropriate. However, detailed description more than necessary may be omitted. For example, the detailed description of well-known matters or the repeated description of substantially the same configuration may be omitted. This is for preventing the following description from being unnecessarily redundant, thus facilitating the understanding by those skilled in the art. 
         [0019]    Inventors of this disclosure provide the attached drawings and the following description for enabling those skilled in the art to sufficiently understand this disclosure, and the subject matters defined in the claims are not intended to be restricted by the attached drawings and the following description. 
       First Embodiment 
       [0020]    Hereinafter, a first embodiment will be described with reference to  FIGS. 1 to 10 . 
       1. Configuration of Lens Barrel 
       [0021]      FIG. 1  is a perspective view of a lens barrel. The lens barrel shown in  FIG. 1  is fixed to a digital still camera (not shown). 
         [0022]      FIG. 2  is an exploded perspective view of the lens barrel. The lens barrel holds an optical system which focuses light as an image on an imaging element in a zooming manner. In the first embodiment, for the sake of convenience, as shown in  FIG. 2 , assuming an optical axis as a Z axis, a predetermined direction in a plane perpendicular to the optical axis is defined as an X axis, and a direction perpendicular to the X axis is defined as a Y axis. Note that a direction parallel to the optical axis is referred to as “optical axis direction”, a direction perpendicular to the optical axis direction is referred to as “radial direction”, and the direction along a circle having the optical axis as a center is referred to as “circumferential direction”. Further, with respect to “radial direction”, the direction toward the optical axis side is referred to as “radially inward direction” and the direction away from the optical axis is referred to as “radially outward direction”. The optical axis substantially agrees with axes of the respective frames which configure the lens barrel. 
         [0023]    As shown in  FIG. 2 , the lens barrel includes first group lens unit  100 , second group lens unit  200 , rectilinear guide frame  300 , focus motor unit  400 , cam frame  500 , third group lens unit  600 , fourth group lens unit  700 , fifth group lens unit  800 , sixth group lens unit  900 , master flange  1000 , zoom motor unit  1100 , imaging element unit  1200 , and flexible printed circuit board  1300 . 
         [0024]    First group lens unit  100  has a substantially cylindrical shape, and lenses for zooming are fixed to first group lens unit  100 . Guide grooves and first group cam followers are provided to an inner peripheral surface of first group lens unit  100 . The guide grooves of first group lens unit  100  engage with rectilinear protrusions formed on flange portion  310  of rectilinear guide frame  300  so that the rotation of first group lens unit  100  in the circumferential direction is restricted and the movement of first group lens unit  100  in the optical axis direction is guided. The first group cam follower also engages with first group cam groove  511  of cam frame  500 . The first group cam follower is guided along first group cam groove  511  due to the rotation of cam frame  500  so that first group lens unit  100  moves in the optical axis direction. 
         [0025]      FIG. 3  is an exploded perspective view of second group lens unit  200 . Second group lens unit  200  includes second group lens frame  220 , light blocking sheet  210 , and lenses L4, L5, L6 for zooming in. Second group lens frame  220  has a substantially cylindrical shape, and lenses L4, L5, L6 are fixed to second group lens frame  220 . Light blocking sheet  210  to which reflection prevention treatment is applied is fixed to a subject side of second group lens frame  220  for suppressing undesired reflection in the lens barrel. 
         [0026]      FIG. 4  is an explanatory view showing a shape of second group lens frame  220 . Second group lens frame  220  has second group cam followers  221 ,  222  on an outer peripheral surface thereof. Second cam followers  221 ,  222  are respectively inserted into second group guide grooves  301 ,  302  of rectilinear guide frame  300 , and engage with second group cam grooves  501 ,  502  formed on an inner peripheral surface of cam frame  500 . The configuration of cam frame  500  will be described later. In second group lens unit  200 , due to the rotation of cam frame  500 , second group cam followers  221 ,  222  are guided by second group cam grooves  501 ,  502  so that second group lens unit  200  moves in the optical axis direction. Second group lens frame  220  is one example of a movable frame. 
         [0027]    As shown in  FIG. 2 , rectilinear guide frame  300  has a substantially cylindrical shape, and holds focus motor unit  400  on an outer peripheral surface thereof on an image formation side. Rectilinear guide frame  300  has flange portion  310  which is raised in the radially outward direction at an end portion thereof on the subject side. Rectilinear protrusions which are raised in the radially outward direction are formed on flange portion  310 . The rectilinear protrusions engage with guide grooves formed on an inner peripheral surface of first group lens unit  100 , and guide a rectilinear movement of first group lens unit  100 . That is, first group lens unit  100  is held by rectilinear guide frame  300  movably in the optical axis direction in a state where the rotation of first group lens unit  100  is restricted by rectilinear guide frame  300 . 
         [0028]      FIG. 5  is an explanatory view showing a shape of rectilinear guide frame  300 . As shown in  FIG. 5 , rectilinear guide frame  300  has second group guide grooves  301 ,  302  which penetrate rectilinear guide frame  300  from an inner peripheral surface to an outer peripheral surface. Second group guide grooves  301 ,  302  are formed to extend in the optical axis direction toward the image formation side from an end portion of rectilinear guide frame  300  on the subject side. As shown in  FIG. 5 , rectilinear guide frame  300  also has two third-fifth group guide grooves  305 , sixth group guide groove  306 , and third-fifth-sixth group guide groove  307 . All of third-fifth group guide grooves  305 , sixth group guide groove  306 , and third-fifth-sixth group guide groove  307  penetrate rectilinear guide frame  300  from the inner peripheral surface to the outer peripheral surface, and are formed to extend in the optical axis direction toward the subject side from the edge portion of rectilinear guide frame  300  on the image formation side. That is, a total of four guide grooves are formed from the end portion of rectilinear guide frame  300  on the image formation side. The respective cam followers of third group lens unit  600 , fifth group lens unit  800  and sixth group lens unit  900  are inserted into one third-fifth-sixth group guide groove  307 . That is, the lens barrel is configured such that the respective cam followers of three lens units can be inserted into one guide groove formed in rectilinear guide frame  300 . Accordingly, the number of guide grooves formed in rectilinear guide frame  300  can be reduced, thus realizing the miniaturization of the lens barrel. 
         [0029]    Cam frame  500  is fitted on an outer peripheral side of rectilinear guide frame  300 . Cam frame  500  is held with its movement in the optical axis direction being restricted with respect to rectilinear guide frame  300 , and is rotatable about the optical axis with respect to rectilinear guide frame  300 . 
         [0030]    As shown in  FIG. 2 , cam frame  500  is provided with first group cam groove  511  and driven gear  512  on an outer peripheral surface thereof. Driven gear  512  is formed on the image formation side. 
         [0031]      FIG. 6  is an inner diameter developed view of cam frame  500 . Cam frame  500  has, on an inner peripheral surface thereof, second group cam grooves  501 ,  502 , three third group cam grooves  503 , three fifth group cam grooves  505 , and sixth group cam grooves  506 ,  507  in this order from the subject side. 
         [0032]    Third group lens unit  600  shown in  FIG. 2  holds a correction lens for correcting image blur and an image blur correction device which drives the correction lens. Third group lens unit  600  holds the correction lens movably in a plane perpendicular to the optical axis. Third group lens unit  600  has an aperture function and a shutter function. 
         [0033]    Third group lens unit  600  includes three third group cam followers  621  projecting in the radially outward direction, and moves in the optical axis direction with respect to cam frame  500  due to the rotation of cam frame  500 . Two of third group cam followers  621  are inserted into third-fifth group guide grooves  305  of rectilinear guide frame  300  (see  FIG. 5 ), and one remaining third group cam follower  621  is inserted into third-fifth-sixth group guide groove  307  of rectilinear guide frame  300  (see  FIG. 5 ). Three third group cam followers  621  engage with third group cam grooves  503  of cam frame  500  (see  FIG. 6 ). Third group cam followers  621  are guided by third group cam grooves  503  due to the rotation of cam frame  500  so that third group lens unit  600  moves in the optical axis direction. 
         [0034]    Fourth group lens unit  700  holds a lens for performing focus adjustment. For performing the focus adjustment, fourth group lens unit  700  is moved in the optical axis direction by focus motor unit  400 . Focus motor unit  400  includes a lead screw and a focus motor for rotatably driving the lead screw. Lead screw is directly connected to a motor shaft of the focus motor. Fourth group lens unit  700  includes a rack which engages with the lead screw. Fourth group lens unit  700  is moved in the optical axis direction due to rotational driving of the lead screw. 
         [0035]    Fifth group lens unit  800  holds a lens for zooming in. Fifth group lens unit  800  includes three fifth group cam followers  821  projecting in the radially outward direction. Two fifth group cam followers  821  are respectively inserted into two third-fifth group guide grooves  305  of rectilinear guide frame  300  (see  FIG. 5 ), and one remaining fifth group cam follower  821  is inserted into third-fifth-sixth group guide groove  307  (see  FIG. 5 ). Three fifth group cam followers  821  respectively engage with three fifth group cam grooves  505  of cam frame  500  (see  FIG. 6 ). Fifth group cam followers  821  are guided by fifth group cam grooves  505  due to rotation of cam frame  500  so that fifth group lens unit  800  moves in the optical axis direction. 
         [0036]      FIG. 7  is an explanatory view showing a shape of sixth group lens unit  900 . Sixth group lens unit  900  includes a lens for zooming in and sixth group lens frame  920  which holds the lens. Sixth group lens unit  900  includes sixth group cam followers  921 ,  922  which project in the radially outward direction. Sixth group cam follower  921  is inserted into third-fifth-sixth group guide groove  307  of rectilinear guide frame  300  (see  FIG. 5 ), and sixth group cam follower  922  is inserted into sixth group guide groove  306  of rectilinear guide frame  300  (see  FIG. 5 ). Further, sixth group cam followers  921 ,  922  respectively engage with two sixth group cam grooves  506 ,  507  of cam frame  500  (see  FIG. 6 ). Sixth group cam followers  921 ,  922  are guided by sixth group cam grooves  506 ,  507  due to the rotation of cam frame  500  so that sixth group lens unit  900  moves in the optical axis direction. Sixth group lens frame  920  is one example of a movable frame. 
         [0037]    Master flange  1000  is a member which is mounted on the camera body. Master flange  1000  has a substantially cylindrical shape, and imaging element unit  1200  is mounted on an end surface of master flange  1000  on an image formation side. Master flange  1000  also holds rectilinear guide frame  300  and zoom motor unit  1100  thereon. Zoom motor unit  1100  is mounted on a side surface of master flange  1000 . 
         [0038]    Zoom motor unit  1100  includes a drive gear and a motor. The drive gear is rotated by rotatably driving the motor. The drive gear is meshed with driven gear  512  of cam frame  500 . Cam frame  500  is rotatably driven by rotating the drive gear by the motor. 
         [0039]    Imaging element unit  1200  includes an imaging element. The imaging element converts light formed into an image by an optical system configured by a plurality of optical elements into an electric signal. 
         [0040]    Flexible printed circuit board  1300  electrically connects actuators such as focus motor unit  400 , third group lens unit  600 , and zoom motor unit  1100 , position detection sensors, and the like with a main body circuit. 
         [0041]    As described above, in the lens barrel, when cam frame  500  is rotated by a predetermined angle, first group lens unit  100 , second group lens unit  200 , third group lens unit  600 , fifth group lens unit  800 , and sixth group lens unit  900  move to predetermined positions, thus performing zooming. Further, in the lens barrel, fourth group lens unit  700  is moved to a predetermined position by driving of focus motor unit  400 , thus performing focus adjustment. 
       2. Configuration of Cam 
       [0042]    Next, a mechanism for moving second group lens unit  200  and sixth group lens unit  900  in the optical axis direction will be described with reference to  FIGS. 4 to 9 . 
         [0043]    Firstly, second group lens frame  220  will be described. As shown in  FIG. 4 , on the outer periphery of second group lens frame  220 , second group cam followers  221 ,  222  which project in the radially outward direction are formed at positions opposite to each other in the circumferential direction by 180°. Second group cam followers  221 ,  222  opposite to each other by 180° in the circumferential direction engage with second group cam grooves  501 ,  502  shown in  FIG. 6 , whereby the inclination of second group lens frame  220  about the Y axis shown in  FIG. 4  is restricted. 
         [0044]    Second group lens frame  220  has a substantially cylindrical shape, and extension portion  229  is formed on the second group cam follower  222  side such that a portion of an outer peripheral portion of second group lens frame  220  extends toward the image formation side from the outer peripheral portion. Further, as shown in  FIGS. 3 and 4 , projections  231 ,  232  which project in the radially outward direction from the outer peripheral surface are respectively formed at positions where second group cam followers  221 ,  222  are provided. Projection  231  on the second group cam follower  221  side is formed so as to extend from the subject-side end portion to the image-formation-side end portion of the outer peripheral portion of second group lens frame  220  in the optical axis direction. Projection  232  on the second group cam follower  222  side is formed so as to extend from the subject-side end portion of the outer peripheral portion of second group lens frame  220  to the image-formation-side end portion of extension portion  229  in the optical axis direction. 
         [0045]    As shown in  FIGS. 3 and 4 , on portions of projections  231 ,  232  in the vicinity of second group cam followers  221 ,  222 , restricting protrusions  233 ,  234  are formed. Restricting protrusion  235  is formed on the image formation side of projection  232  formed on extension portion  229 . Restricting protrusions  233 ,  234 ,  235  have a shape in which a portion of an outer-peripheral-side end portion of each of projections  231 ,  232  extends on both sides in the circumferential direction with a fixed width. 
         [0046]    Guide protrusions  236 ,  237  are respectively formed on projections  231 ,  232  in the vicinity of second group cam followers  221 ,  222 , and guide protrusion  238  is formed on the image formation side of projection  232  formed on extension portion  229 . Guide protrusions  236 ,  237 ,  238  are formed into a shape in which a portion of each of projections  231 ,  232  slightly projects toward both sides in the circumferential direction with a fixed width in the optical axis direction as well as in the radial direction. 
         [0047]    In this first embodiment, widths of guide protrusions  236 ,  237 ,  238  in the optical axis direction are set smaller than widths of restricting protrusions  233 ,  234 ,  235  in the optical axis direction. Heights of guide protrusions  236 ,  237 ,  238  which project in the circumferential direction are set smaller than heights of restricting protrusions  233 ,  234 ,  235  extending in the circumferential direction. 
         [0048]    Guide protrusions  236 ,  237  are formed on the radially inner peripheral side of restricting protrusions  233 ,  234  and on the subject side. Guide protrusion  238  is formed on an end portion of projection  232  formed on extension portion  229  on the image formation side. 
         [0049]    Guide protrusion  236  of second group lens frame  220  is fitted into second group guide groove  301  of rectilinear guide frame  300  shown in  FIG. 5 , and guide protrusions  237 ,  238  are fitted into second group guide grooves  302  of rectilinear guide frame  300 . In conformity with the configuration where the guide formed on extension portion  229  of second group lens frame  220  is elongated to the image formation side in the optical axis direction, second group guide groove  302  is formed longer than second group guide groove  301  toward the image formation side in the optical axis direction. 
         [0050]    Next, sixth group lens frame  920  will be described. As shown in  FIG. 7 , on the outer periphery of sixth group lens frame  920 , sixth group cam followers  921 ,  922  which project from the outer peripheral surface in the radial direction are formed at positions opposite to each other in the circumferential direction by 180°. Sixth group cam followers  921 ,  922  opposite to each other by 180° in the circumferential direction engage with sixth group cam grooves  506 ,  507  shown in  FIG. 6 , whereby the inclination of sixth group lens frame  920  about the Y axis shown in  FIG. 4  is restricted. 
         [0051]    Sixth group lens frame  920  has extension portion  929  formed on the sixth group cam follower  922  side such that a portion of an outer peripheral portion of sixth group lens frame  920  extends toward the subject side from the outer peripheral portion. Further, as shown in  FIG. 7 , projections  931 ,  932  which project in the radially outward direction from the outer peripheral surface are respectively formed at positions where sixth group cam followers  921 ,  922  are provided. Projection  931  on the sixth group cam follower  921  side is formed so as to extend from the subject-side end portion to the image-formation-side end portion of the outer peripheral portion of sixth group lens frame  920  in the optical axis direction. Projection  932  on the sixth group cam follower  922  side is formed so as to extend from the image-formation-side end portion of the outer peripheral portion of sixth group lens frame  920  to the subject-side end portion of extension portion  929  in the optical axis direction. 
         [0052]    As shown in  FIG. 7 , on portions of projections  931 ,  932  in the vicinity of sixth group cam followers  921 ,  922 , restricting protrusions  933 ,  934  are formed respectively. Restricting protrusion  935  is formed on the subject side of projection  932  formed on extension portion  929 . Restricting protrusions  933 ,  934 ,  935  have a shape in which a portion of an outer-peripheral-side end portion of each of projections  931 ,  932  extends on both sides in the circumferential direction with a fixed width. 
         [0053]    Guide protrusions  936 ,  937  are respectively formed on image-formation-side end portions of projections  931 ,  932  in the vicinity of sixth group cam followers  921 ,  922 , and guide protrusion  938  is formed on the subject-side end portion of projection  932  formed on extension portion  929 . Guide protrusions  936 ,  937 ,  938  have a shape in which a portion of each of projections  931 ,  932  slightly projects toward both sides in the circumferential direction with a fixed width in the optical axis direction as well as in the radial direction. 
         [0054]    In the first embodiment, widths of guide protrusions  936 ,  937 ,  938  in the optical axis direction are set smaller than widths of restricting protrusions  933 ,  934 ,  935  in the optical axis direction. Heights of guide protrusions  936 ,  937 ,  938  projecting in the circumferential direction are set smaller than heights of restricting protrusions  933 ,  934 ,  935  extending in the circumferential direction. 
         [0055]    Guide protrusions  936 ,  937  are formed closer to the image formation side in the optical axis direction than sixth group cam followers  921 ,  922  and restricting protrusions  933 ,  934 . Guide protrusion  938  is formed closer to the subject side in the optical axis direction than restricting protrusion  935 . 
         [0056]    Guide protrusion  936  of sixth group lens frame  920  is fitted into third-fifth-sixth group guide groove  307  of rectilinear guide frame  300  shown in  FIG. 5 , and guide protrusions  937 ,  938  are fitted into sixth group guide grooves  306  of rectilinear guide frame  300 . 
         [0057]      FIG. 8  is an explanatory view showing the relationship among second group lens unit  200 , rectilinear guide frame  300 , and cam frame  500 .  FIG. 8  shows the vicinity of second group cam follower  222  of second group lens unit  200  in an enlarged manner. As shown in  FIG. 8 , a groove width in the circumferential direction of second group guide groove  302  of rectilinear guide frame  300  is set in two stages in the radial direction, wherein the groove width on the inner peripheral side is smaller than the groove width on the outer peripheral side. Guide protrusions  237 ,  238  of second group lens frame  220  are fitted into portions of second group guide grooves  302  on the inner peripheral side having a small groove width. Restricting protrusions  234 ,  235  pass through portions of second group guide grooves  302  on the outer peripheral side having a large groove width with a slight gap therebetween in the radial direction as well as in the circumferential direction. 
         [0058]    Although  FIG. 8  shows the vicinity of second group guide groove  302  into which guide protrusion  237  is fitted, second group guide groove  301 , sixth group guide groove  306 , and third-fifth-sixth group guide groove  307  have substantially the same structure. That is, guide protrusions  236  are fitted into portions of second group guide groove  301  on the inner peripheral side having a small groove width, and restricting protrusions  233  pass through portions of second group guide groove  301  on the outer peripheral side having a large groove width. Guide protrusions  937 ,  938  of sixth group lens frame  920  are fitted into portions of sixth group guide grooves  306  on the inner peripheral side having a small groove width, and restricting protrusions  934 ,  935  of sixth group lens frame  920  pass through portions of sixth group guide groove  306  on the outer peripheral side having a large groove width. Further, guide protrusions  936  of sixth group lens frame  920  are fitted into portions of third-fifth-sixth group guide grooves  307  on the inner peripheral side having a small groove width, and restricting protrusion  933  pass through portions of third-fifth-sixth group guide grooves  307  on the outer peripheral side having a large groove width. 
         [0059]    By partially fitting these parts with each other within a narrow range in this manner there is provided an effect that the size adjustment of the respective parts is facilitated and rattling can be reduced. Further, by setting a distance in the optical axis direction between guide protrusions  237  and guide protrusions  238  large, the inclination of second group lens frame  220  about the X axis can be reduced even when the gap between guide protrusions  237  and guide protrusions  238  is held equal. Further, by forming guide protrusions  236  with respect to guide protrusions  237  and guide protrusions  238 , the inclination of second group lens frame  220  about the Z axis can be reduced. Guide protrusions  936 ,  937 ,  937  of sixth group lens frame  920  third-fifth-sixth group guide groove  307  have substantially the same structure. 
         [0060]    As described above, the inclination about the Y axis is restricted by two second group cam followers  221 ,  222 , and the inclination about the X axis is restricted by guide protrusions  237 ,  238 . In this manner, by separately providing the restrictions on inclination in the respective directions, the sizes of the respective parts can be relatively easily adjusted, and at the same time, second group lens frame  220  can be moved with high accuracy with a simple configuration. Further, the inclination of second group lens frame  220  about the Z axis can be restricted by guide protrusions  236 . The same applies for sixth group cam followers  921 ,  922  and guide protrusions  936 ,  937 ,  938  of sixth group lens frame  920 . 
         [0061]    In addition, restricting protrusions  233 ,  234 ,  235  prevent second group lens frame  220  from being detached from rectilinear guide frame  300  and cam frame  500  when a large force is applied to the lens barrel such as the case where the lens barrel is dropped. In the same manner, restricting protrusions  933 ,  934 ,  935  prevent sixth group lens frame  920  from being detached from rectilinear guide frame  300  and cam frame  500  when a large force is applied to the lens barrel such as the case where the lens barrel is dropped. 
         [0062]    Next, the relationship between cam frame  500  and the respective lens units will be described. As shown in  FIG. 6 , three third group cam grooves  503  are formed on the whole circumference of cam frame  500 . In the same manner as third group cam groove  503 , three fifth group cam grooves  505  are also formed on the whole circumference of cam frame  500 . On the other hand, with respect to second group cam grooves provided for moving second group lens unit  200 , two second group cam grooves (second group cam grooves  501 ,  502 ) are formed on the whole circumference of cam frame  500 . In the same manner, two sixth group cam grooves (sixth group cam grooves  506 ,  507 ) for moving sixth group lens unit  900  are formed on the whole circumference of cam frame  500 . 
         [0063]    The number of second group cam grooves and the number of sixth group cam grooves are set to two as described above because the following drawbacks occur when the number of second group cam grooves and the number of three sixth group cam grooves are set to three. 
         [0064]    For example, when three second group cam grooves and three sixth group cam grooves are formed while changing neither the diameter of the cam frame nor the inclination angle of the second group cam grooves, the second group cam grooves intersect with each other. When the second group cam groove intersect with each other, since these cam grooves have the same groove width and the same groove depth, there is a possibility that rattling occurs and the lens frame is detached at the portion where the cam grooves intersect with each other. 
         [0065]    On the other hand, for example, when the inclination angle of the second group cam grooves is set steep without changing the diameter of the cam frame to prevent three second group cam grooves from intersecting with each other, a load necessary for rotating the cam frame is increased. 
         [0066]    Further, for example, when the diameter of the cam frame is increased without changing the inclination angle of the second group cam grooves to prevent three second group cam grooves from intersecting with each other, the diameter of the lens barrel is increased. 
         [0067]    In view of the above drawbacks, in the first embodiment, the number of second group cam grooves of cam frame  500  is set to two (second group cam grooves  501 ,  502 ), and the number of cam followers provided to second group lens frame  220  is set to two (second group cam followers  221 ,  222 ). With such a configuration, a load imposed on the lens barrel is reduced, thus realizing the configuration advantageous for miniaturizing the lens barrel. Although the description has been made above with respect to second group cam grooves  501 ,  502 , the same applies to sixth group cam grooves  506 ,  507 . 
         [0068]    In the case where two second group cam grooves (second group cam grooves  501 ,  502 ) for moving the second group lens unit and three third group cam grooves  503  for moving the third group lens unit are formed on cam frame  500 , the number of grooves differs between the second group cam grooves and third group cam grooves  503 . Hence, insertion portions  503   a  of third group cam grooves  503  inevitably intersect with second group cam grooves  501 ,  502 . 
         [0069]    In view of the above, in the first embodiment, as shown in  FIGS. 9A and 9B , depths of second group cam grooves  501 ,  502  are set larger than a depth of third group cam groove  503 . Further, distal ends of second group cam followers  221 ,  222  are formed into a stepped shape so that second group cam followers  221 ,  222  slide only at portions of second group cam grooves  501 ,  502  where the groove depth is large. With such a configuration, the occurrence of rattling or catching can be suppressed at portions where second group cam grooves  501 ,  502  intersect with insertion portion  503   a.    
         [0070]    In the same manner, as shown in  FIGS. 9C and 9D , depths of sixth group cam grooves  506 ,  507  are set larger than a depth of fifth group cam groove  505  so that sixth group cam followers  921 ,  922  slide only at portions of sixth group cam grooves  506 ,  507  where the groove depth is large. Accordingly, the occurrence of rattling or catching can be suppressed at portions where sixth group cam grooves  506 ,  507  intersect with the insertion portion of fifth group cam groove  505 . 
         [0071]    As described above, according to this configuration, it is possible to move the lens unit with a simple configuration and with high accuracy, and further, this configuration is advantageous in reducing a load imposed on the lens barrel as well as in miniaturizing the lens barrel. 
       3. Conditions for Acquiring Maximum Advantageous Effects 
       [0072]    Next, conditions under which the maximum advantageous effects can by acquired by the above configuration of the lens barrel will be described with reference to  FIG. 10 .  FIGS. 10A and 10B  are explanatory views showing the relationship between second group lens frame  220  and the position of the center of gravity thereof.  FIG. 10A  corresponds to the side view shown in  FIG. 4 , and  FIG. 10B  corresponds to the bottom view shown in  FIG. 4 . Arrows shown in  FIG. 10A  indicate the direction of inclination about the X axis. 
       Condition 1: 
       [0073]    It is preferable that the position in the optical axis direction of a straight line connecting second group cam follower  221  and second group cam follower  222  and a position in the optical axis direction of the center of gravity of second group lens frame  220  substantially agree with each other. That is, the position in the optical axis direction of second group cam follower  221  and the position in the optical axis direction of second group cam follower  222  substantially agree with the position in the optical axis direction of the center of gravity of second group lens frame  220 . 
       Advantageous Effect Obtained Under Condition 1: 
       [0074]    The moment force which is applied to second group lens frame  220  due to a change in posture of the lens barrel, an impact which occurs when the lens barrel falls or the like can be suppressed to a low level, so that the deformation or the breakage of extension portion  229  can be suppressed. These advantageous effects particularly contribute to the miniaturization and the narrowing of extension portion  229 . 
       Condition 2: 
       [0075]    The position in the optical axis direction of guide protrusions  237  and the position in the optical axis direction of guide protrusions  238  are on both sides of second group lens frame  220  with the center of gravity therebetween. That is, in the optical axis direction, the center of gravity of second group lens frame  220  is positioned between the position of guide protrusion  237  and the position of guide protrusion  238 . 
       Advantageous Effect Obtained Under Condition 2: 
       [0076]    When both second group cam followers  221 ,  222  take the horizontal posture, second group lens frame  220  is supported on rectilinear guide frame  300  by three respective surfaces on one side of guide protrusion  237 , guide protrusion  238 , and guide protrusion  236 . The movement of second group lens frame  220  is retained only within a range of play so that the inclination of second group lens frame  220  can be suppressed. 
       Condition 3: 
       [0077]    The position in the optical axis direction of guide protrusions  237  and the position in the optical axis direction of guide protrusions  238  are arranged on both sides of second group lens frame  220  with second group cam followers  221 ,  222  therebetween. That is, in the optical axis direction, second group cam followers  221 ,  222  are positioned between the position of guide protrusions  237  and the position of guide protrusions  238  in the optical axis direction. 
       Advantageous Effect Obtained Under Condition 3: 
       [0078]    At the time of zooming, a pushing force is applied to surfaces on one side of guide protrusions  237 ,  238  due to a frictional force generated by the cam followers. Hence, the movement of second group lens frame  220  is retained only within a range of play so that the inclination of second group lens frame  220  can be suppressed. Accordingly, it is possible to suppress the difference in inclination of second group lens frame  220  between at the time of zooming in the telephoto direction from a wide angle state and at the time of zooming in the wide angle direction from a telephoto state. 
       Condition 4: 
       [0079]    Guide protrusion  236  in the optical axis direction is positioned close to second group cam follower  221 . That is, in the optical axis direction, second group cam follower  221  is positioned in the vicinity of guide protrusions  236 . 
       Advantageous Effect Obtained Under Condition 4: 
       [0080]    At the time of zooming, it is possible to reduce a moment force generated due to the difference in position in the optical axis direction between second group cam follower  221  and guide protrusions  236  by a frictional force generated by the cam followers. It is possible to suppress the difference in inclination of second group lens frame  220  between at the time of zooming in the telephoto direction from a wide angle state and at the time of zooming in the wide angle direction from a telephoto state. 
         [0081]    Although conditions 1 to 4 are described as conditions with respect to second group lens frame  220 , the same conditions are applied to sixth group lens frame  920 . 
         [0082]    The embodiment has been described above as an example of the technique according to this disclosure. For this purpose, the attached drawings and the detailed description are provided. 
         [0083]    Accordingly, the constituent elements described in the accompanying drawings and the detailed description may include not only the constituent elements necessary for overcoming the problems but also constituent elements which are unnecessary for overcoming the problems in order to exemplify the above techniques. Therefore, such unnecessary constituent elements should not be immediately determined to be necessary, for the reason that these unnecessary constituent elements are described in the accompanying drawings and the detailed description. 
         [0084]    Further, the above embodiment is merely for exemplifying the techniques according to the present disclosure, and therefore, various changes, replacements, additions, omissions, and the like can be made thereto within the scope of the claims and scopes equivalent thereto. 
         [0085]    The lens barrel of this disclosure is applicable to a lens barrel of a digital still camera, an interchangeable lens, or the like.