Patent Publication Number: US-2021181458-A1

Title: Lens barrel

Description:
TECHNICAL FIELD 
     The present invention relates to a lens barrel. 
     BACKGROUND ART 
     A conventional lens barrel includes, for example, lens units that move synchronously in the optical axis direction; and other lens units between the lens units (see, for example, Patent Document 1). 
     In such a conventional lens barrel, the lens units between the synchronously moving lens units have a limited range of movement. 
     Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2011-33686 
     DISCLOSURE OF THE INVENTION 
     The present invention is directed to a lens barrel including: a lens holding frame that holds a lens; a drive unit that drives the lens holding frame in an optical axis direction; a first tube that holds the drive unit and has a cam follower; a second tube having a cam groove that engages the cam follower; and an energizing part that energizes the first tube in the optical axis direction. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view of a lens barrel according to an embodiment of the present invention; 
         FIG. 2  is an exploded perspective view of a cam tube, a third-fifth lens unit tube, a motor moving tube, and a fourth lens unit frame; 
         FIG. 3  is a developed view of the cam tube; and 
         FIGS. 4A to 4E  are diagrams illustrating the movement of the cam tube, the third-fifth lens unit tube, the motor moving tube, and the fourth lens unit frame. 
     
    
    
     PREFERRED MODE FOR CARRYING OUT THE INVENTION 
     Description of Whole System 
       FIG. 1  is a cross-sectional view of a lens barrel  1  according to an embodiment of the present invention. In the drawing, the left side in the optical axis OA direction is the object side (front side or plus side), and the right side in the optical axis OA direction is the body side (rear side or minus side). The lens barrel  1  has a range of imaging from telephoto to wide angle, and has a contracted state (also called a housed state or a collapsed state). The lens barrel  1  is an interchangeable lens system that is attachable to and detachable from a camera body (not shown). The upper part of  FIG. 1  shows a state in which the lens barrel  1  is contracted to the minimum length, and the lower part shows a telephoto state in which the lens barrel  1  is extended to the maximum length. 
     The lens barrel  1  includes a first lens unit L 1 , a second lens unit L 2 , a third lens unit L 3 , a fourth lens unit L 4 , and a fifth lens unit L 5 . The fourth lens unit L 4  is a focusing lens unit disposed between the third lens unit L 3  and the fifth lens unit L 5 . 
     The lens barrel  1  includes, from the outer circumferential side (outer diameter side), a zoom ring  2 , a rectilinear tube  3 , a first lens unit tube  4 , a cam tube  5 , a fixed tube  6 , a second lens unit tube  7 , a third-fifth lens unit tube  8 , a motor moving tube  9 , and a fourth lens unit frame  10 . 
     The zoom ring  2  rotates about the optical axis in accordance with the zooming operation by the user. 
     The fixed tube  6  is fixed with respect to the mount. 
     The cam tube  5  is provided with a zoom interlocking pin MZ and a rectilinear tube connecting pin MC (see  FIG. 3 ). The zoom interlocking pin MZ engages a rectilinear groove provided at the inner circumference (inner diameter side) of the zoom ring  2 . The rectilinear tube connecting pin MC engages a circumferential groove on the inner circumference of the rectilinear tube  3 . The cam tube  5  has a cam groove MK that engages a cam follower  6   a  of the fixed tube  6 . Thus, while being rotated together with the zoom ring  2 , the cam tube  5  is fed out together with the rectilinear tube  3  with respect to the fixed tube  6 . 
     The rectilinear tube  3  has a circumferential groove on the inner circumference as mentioned above, and is bayonet-coupled to the rectilinear tube connecting pin MC of the cam tube  5 . The rectilinear tube  3  also has a rectilinear key (protrusion) on the inner circumference, which engages the rectilinear groove provided in the fixed tube  6 . Thus, when the cam tube  5  is rotated and fed out due to the rotation of the zoom ring  2 , the rectilinear tube  3  moves straight with respect to the fixed tube  6 . 
     The first lens unit tube  4  holds a first lens unit frame  4   a.  The first lens unit frame  4   a  holds the first lens unit L 1 . The first lens unit tube  4  is provided with a cam follower which engages a first unit cam groove M 1  of the cam tube  5 . The outer circumference of the first lens unit tube  4  is also provided with a connecting pin, which engages a rectilinear groove on the inner circumference of the rectilinear tube  3  so that the first lens unit tube  4  moves straight without rotating. The second lens unit tube  7  holds a second lens unit frame  11 . The second lens unit frame  11  holds the second lens unit L 2 . 
     The second lens unit tube  7  is provided with a cam follower which engages a second unit cam groove M 2  of the cam tube  5 . The outer circumference of the second lens unit tube  7  is further provided with a rectilinear key (protrusion), which engages a rectilinear groove of the fixed tube  6 . Thus, the second lens unit tube  7  moves straight without rotating. 
     The third-fifth lens unit tube  8  is a moving tube that is disposed on the outer circumference of the motor moving tube  9  and is movable in the optical axis direction. The third-fifth lens unit tube  8  will be described in detail later. The motor moving tube  9  is disposed at the inner circumference of the third-fifth lens unit tube  8  and is movable in the optical axis direction. The motor moving tube  9  will be described in detail later. 
     The fourth lens unit frame  10  is a lens frame that holds the fourth lens unit L 4 . 
     An aperture mechanism  20  is attached to the front end of the third-fifth lens unit tube  8 . 
     As the zoom ring  2  is rotated, the cam tube  5  is fed out while being rotated by the same angle as the angle of rotation of the zoom ring  2 . As the cam tube  5  is rotated, the first lens unit L 1 , the second lens unit L 2 , the third lens unit L 3 , the fourth lens unit L 4 , and the fifth lens unit L 5  each move straight along each cam groove in the optical axis direction. The fourth lens unit L 4  is also movable in the optical axis direction by the driving force of a stepping motor  12 , which will be described later. 
     Next, the cam tube  5 , the third-fifth lens unit tube  8 , the motor moving tube  9 , the fourth lens unit frame  10  will be described in detail.  FIG. 2  is an exploded perspective view of the cam tube  5 , the third-fifth lens unit tube  8 , the motor moving tube  9 , and the fourth lens unit frame  10 . 
     Cam Tube  5   
       FIG. 3  is a developed view of the cam tube  5 . The cam tube  5  has a plurality of cam grooves. In  FIG. 3 , the solid lines indicate cam grooves provided on the outer surface or penetrating cam grooves, and the dotted lines indicate cam grooves provided on the inner surface. 
     Each cam groove engages the corresponding cam follower. In  FIG. 3 , the dotted circles drawn in each cam groove indicate the positions of the cam follower, in which the circled S indicates the position of the cam follower located when the barrel is in the contracted state, the circled W indicates the position of the cam follower located when the barrel is in the wide angle state, the circled T indicates the position of the cam follower located when the barrel is in the telephoto state, and the circled M indicates the position of the cam follower located when the barrel is in the middle state between the wide angle state and the telephoto state. 
     The first unit cam groove M 1  is for the drive of the first lens unit tube  4  which holds the first lens unit L 1 . 
     An impact cam groove M 1   a  is provided to address impact. The impact cam groove M 1   a  engages an impact countermeasure pin (not shown) provided in the first lens unit tube  4  when the lens barrel is in a state ranging from the contracted state to the wide angle state. 
     The second unit cam groove M 2  is a through groove for the drive of the second lens unit tube  7  which holds the second lens unit frame  11 . The cam groove MK engages the cam follower  6   a  extending from the fixed tube  6 . 
     The cam groove MK is for rotating the cam tube  5  with respect to the fixed tube  6  and for feeding the cam tube  5 . 
     A third-fifth unit groove M 35  and a motor cam groove MM will be described later. 
     The cam tube  5  is also provided with a zoom interlocking pin MZ, which engages the rectilinear groove provided on the inner surface of the zoom ring  2 , and provided with a rectilinear tube connecting pin MC, which engages the circle groove provided on the inner surface of the rectilinear tube  3 . 
     Third-Fifth Unit Cam Groove M 35   
     The third-fifth unit cam groove M 35  is for the drive of the third-fifth lens unit tube  8 . The third-fifth lens unit tube  8  holds the third lens unit L 3  at the front end and holds the fifth lens unit L 5  at the rear end. The third-fifth unit cam groove M 35  has a width substantially equal to the width (diameter) of the cam follower  8   a  (described later) which moves in the third-fifth unit cam groove M 35 . In other words, when a certain focal length is reached and the cam follower  8   a  is at a predetermined position in the third-fifth unit cam groove M 35 , the cam follower  8   a  can move within the tolerance range in the optical axis direction, but cannot move beyond the tolerance range in the optical axis direction. 
     Motor Cam Groove MM 
     The motor cam groove MM is for the drive of the motor moving tube  9 . 
     The motor cam groove MM engages the cam follower  9   a , which is described later. The cam follower  9   a  moves in the motor cam groove MM when the state of the lens barrel  1  is changed to the telephoto, wide angle, or contracted state. The motor cam groove MM is opened at one side in the optical axis direction. In other words, the motor cam groove MM has no wall at one side in the optical axis direction. The motor cam groove MM has a wall at the other side in the optical axis direction. In the example shown in  FIG. 3 , the rear side of the motor cam groove MM is opened. Alternatively, the front side of the motor cam groove MM may be opened when the motor cam groove MM is provided on a front portion of the cam tube  5 . 
     One side of the motor cam groove MM may be opened over the whole area or opened in a partial area. In the example shown in  FIG. 3 , the motor cam groove MM has walls at both sides when the barrel is in the contracted state, whereas one side (rear side) of the motor cam groove MM is opened when the barrel is in other states. 
     In the area where walls are provided at both sides, the motor cam groove MM has a width that is wider than the width (diameter) of the cam follower  9   a  and about 2 times or more the width of the cam follower  9   a  in the optical axis OA direction. Thus, the cam follower  9   a  can move in the optical axis OA direction. In other words, when a certain focal length is reached and the cam follower  9   a  is at a predetermined position in the motor cam groove MM, the cam follower  9   a  can move within the tolerance range in the optical axis direction. This will be described in detail later. 
     In  FIG. 3, 8S  (circled S) represents the position of the cam follower  8   a  in the third-fifth unit cam groove M 35  of the lens barrel in the contracted state,  8 W (circled W) represents the position of the cam follower  8   a  in the cam groove M 35  of the lens barrel in the wide angle state,  8 T (circled T) represents the position of the cam follower  8   a  in the third-fifth unit cam groove M 35  of the lens barrel in the telephoto state, and  8 M (circled M) represents the position of the cam follower  8   a  in the third-fifth unit cam groove M 35  of the lens barrel in the middle state between the wide angle state and the telephoto state. 
     In  FIG. 3 ,  9 S 1  and  9 S 2  (circled S) respectively represent the front and rear side positions of the cam follower  9   a  in the motor cam groove MM of the lens barrel in the contracted state, and  9 W 1  and  9 W 2  (circled W) respectively represent the front and rear side positions of the cam follower  9   a  in the motor cam groove MM of the lens barrel in the wide angle state. 
     In  FIG. 3, 9T  (circled T) represents the position of the cam follower  9   a  of the lens barrel in the telephoto state. In  FIG. 3, 9M  (circled M) represents the position of the cam follower  9   a  of the lens barrel in the middle state between the wide angle state and the telephoto state. 
     Third-Fifth Lens Unit Tube  8   
     Referring back to  FIG. 2 , the third-fifth lens unit tube  8  includes a third-fifth lens unit tube body  8 A and a third-fifth lens unit tube rear end part  8 B attached to the rear end of the third-fifth lens unit tube body  8 A. 
     A third lens unit holding frame  81  shown in  FIG. 1  (not shown in  FIG. 2 ) is held at a front portion of the lens third-fifth lens unit tube body  8 A. A fifth lens unit holding frame  82  shown in  FIG. 1  (not shown in  FIG. 2 ) is held at a rear portion of the third-fifth lens unit tube rear end part  8 B. Three cam followers  8   a  are provided at positions spaced about 120 degrees apart from each other along the same circumference. 
     The three cam followers  8   a  are provided from the outer surface of the third-fifth lens unit tube  8  toward the outer circumferential side. The cam followers  8   a  each penetrate a rectilinear groove (not shown) of the fixed tube  6  and engage the third-fifth unit cam groove M 35 . The outer circumferential surface of the third-fifth lens unit tube  8  is provided with three rectilinear keys (protrusions), which are located at positions spaced about  120  degrees apart from each other along the same circumference. The rectilinear keys each engage a rectilinear groove  7   c  provided on the inner surface of the second lens unit tube  7 . Thus, the third-fifth lens unit tube  8  moves straight without rotating. 
     Inside the inner circumference of the third-fifth lens unit tube  8 , a main guide bar  8   c  and a sub guide bar  8   d  extend along the optical axis OA to guide the fourth lens unit frame  10 . The main guide bar  8   c  and the sub guide bar  8   d  are supported at the front and rear ends of the third-fifth lens unit tube  8 . 
     Penetrating elongated holes  8   b  are provided at positions spaced about 120 degrees apart from each other along the same circumference of the third-fifth lens unit tube  8 . Cam followers  9   a  (described later) are provided in the elongated holes  8   b.    
     Motor Moving Tube  9   
     The outer surface of the motor moving tube  9  is provided with three cam followers  9   a  at positions spaced about 120 degrees apart from each other along the same circumference. 
     The three cam followers  9   a  are provided toward the outer circumferential side. The cam followers  9   a  each engage the motor cam groove MM through the elongated hole  8   b  of the third-fifth lens unit tube  8  and through a rectilinear groove (not shown) of the fixed tube  6 . The motor moving tube  9  is also provided with a rectilinear key (protrusion) which engages a rectilinear groove provided in the third-fifth lens unit tube  8 . Thus, the motor moving tube  9  moves straight without rotating. 
     A stepping motor  12  is attached to the motor moving tube  9 . 
     A rotary shaft  12   a  with a thread groove on its outer circumference extends from the stepping motor  12  in the optical axis OA direction. 
     Fourth Lens Unit Frame  10   
     As shown in  FIG. 2 , the fourth lens unit frame  10  includes a frame portion  10   a  for covering the outer circumference of the fourth lens unit L 4 ; a main guide bar holding portion  10   b  extending from the frame portion  10   a  toward the front side; and a sub guide holding portion  10   c  provided opposite to the main guide bar holding portion  10   b  on the frame portion l 0   a  about the optical axis OA (or provided at a position spaced about 180 degrees apart from the portion  10   b  about the optical axis OA). In this regard, the sub guide bar holding portion  10   c  does not always have to be provided at a position spaced about 180 degrees apart from the main guide bar holding portion  10   b  about the optical axis OA. 
     The main guide bar holding portion  10   b  holds the main guide bar  8   c.  The fourth lens unit L 4  (fourth lens unit frame  10 ) is movable in the optical axis OA direction, being guided by the main guide bar. The sub guide bar holding portion  10   c  is U-shaped, through which the sub guide bar  8   d  passes. The main guide bar holding portion  10   b  prevents the rotation of the fourth lens unit L 4  (fourth lens unit frame  10 ). In this regard, the sub guide bar holding portion  10   c  may not be U-shaped as long as it can prevent the rotation of the fourth lens unit L 4 . 
     The main guide bar holding portion  10   b  has a predetermined length in the optical axis OA direction to prevent the falling (tilting) of the fourth lens unit L 4 . For example, the main guide bar holding portion  10   b  is longer than the rotary shaft  12   a  of the stepping motor  12 . The main guide bar holding portion  10   b  may be longer than the moving distance from the collapsed state (or wide angle state) of the fourth lens unit L 4  to the telephoto state. This increases the length over which the main guide bar holding portion  10   b  engages the main guide bar and can prevent the falling (tilting) of the fourth lens unit L 4 . In  FIGS. 1 and 2 , the main guide bar holding portion  10   b  extends forward beyond the frame portion  10   a.    
     A rack mount  10   f  is provided in the vicinity of the main guide bar holding portion  10   b  on the frame portion  10   a.  A rack  10   d  is attached to the rack mount  10   f.  The rack  10   d  includes a motor engagement portion  10   e  that is U-shaped in cross-section and has a thread groove on its inner surface. The thread groove on the inner surface of the motor engagement portion  10   e  engages the thread groove on the outer surface of the rotary shaft  12   a  of the stepping motor  12 . This allows the fourth lens unit L 4  to move in the optical axis direction as the stepping motor  12  is driven to rotate the rotary shaft  12   a.    
     Spring Members  13   
     Spring members  13   a,    13   b,  and  13   c  are disposed at three positions spaced about 120 degrees apart from each other between the front side of the third-fifth lens unit tube rear end part  8 B and the rear side of the motor moving tube  9 . Hereinafter, the spring members  13   a,    13   b,  and  13   c  are collectively called the spring member or members  13  when they are not distinguished from each other in the description. The spring members  13  energize the motor moving tube  9  toward the front side with respect to the third-fifth lens unit tube rear end part  8 B. In other words, the spring members  13  energize the motor moving tube  9  in a direction away from the third-fifth lens unit tube rear end part  8 B. Thus, the spring member  13  energizes the cam follower  9   a  forward so that the cam follower  9   a  comes into contact with the front side wall of the motor cam groove MM. In other words, the spring member  13  energizes the motor moving tube  9  toward the front side wall of the motor cam groove MM. Therefore, when the focal length of the lens barrel  1  is changed, the cam follower  9   a  can move along the front side wall of the motor cam groove MM. In this regard, the direction of the energizing by the spring member  13  is not limited to the direction mentioned above as long as the energizing can be toward the wall of the motor cam groove MM. 
     In this case, the motor cam groove MM of the cam tube  5  is opened at the rear side as mentioned above. Otherwise, the width of the motor cam groove MM is wider than the width (diameter) of the cam follower  9   a.  Therefore, when a force toward the minus side (body side) in the optical axis OA direction is applied to the motor moving tube  9 , the cam follower  9   a  can move in the optical axis OA direction within the motor cam groove MM. 
     The third-fifth lens unit tube  8  is provided with the main guide bar  8   c  and the sub guide bar  8   d.  Thus, the main guide bar  8   c  for guiding the fourth lens unit L 4  and the spring member  13  for energizing the motor moving tube  9  equipped with the stepping motor  12  for driving the fourth lens unit L 4  are disposed in the same part (the third-fifth lens unit tube rear end part  8 B). This allows the fourth lens unit L 4  to move in a high performance manner. 
     The spring members  13  are conical springs (conical coil springs). When conical coil springs are used, the springs will not be out of position even in the compressed state, so that they can energize the motor moving tube  9  and the third-fifth lens unit tube  8  in a high performance manner. Therefore, the springs can be prevented from buckling when compressed and can maintain stable position. 
     Moreover, screws  14   a,    14   b,  and  14   c  for fixing the third-fifth lens unit tube body  8 A to the third-fifth lens unit tube rear end part  8 B are each aligned on substantially the same linear line with each of the spring members  13   a,    13   b,  and  13   c  (see  FIG. 2 ). Thus, the spring member  13   a  is disposed closer to the screw  14   a  than to the screws  14   b  and  14   c.  This allows accurate energizing of the third-fifth lens unit tube  8  and the motor moving tube  9 . 
     Furthermore, when the spring members  13  are disposed at the same rotation angle positions as the cam followers  9   a,  the motor moving tube  9  can move stably with respect to the third-fifth lens unit tube  8  even though a force is applied in the OA direction. 
     In the lens barrel  1 , when the zoom ring  2  is rotated, the cam tube  5  also rotates. During this time, the third-fifth unit cam groove M 35  and the motor cam MM respectively allow the third-fifth lens unit tube  8  and the motor moving tube  9  to move in the optical axis OA direction. 
     As the stepping motor  12  is driven, the rotary shaft  12   a  is rotated to allow the rack  10   d,  the fourth lens unit frame  10 , and the fourth lens unit L 4  to move in the optical axis OA direction with respect to the motor moving tube  9 . During this time, the main guide bar holding portion  10   b  of the fourth lens unit frame  10  and the sub guide bar holding portion  10   c  are respectively guided to move straight by the main guide bar  8   c  and the sub guide bar  8   d.    
     Thus, the fourth lens unit L 4  is movable in the optical axis direction along the motor cam groove MM, and is also movable in the optical axis direction by the stepping motor  12 . 
       FIGS. 4A to 4E  are diagrams illustrating how the cam tube  5 , the third-fifth lens unit tube  8 , the motor moving tube  9 , the fourth lens unit frame  10 , and the stepping motor  12  are driven. That is described with reference to  FIGS. 3 and 4A to 4E . 
       FIG. 4A  shows a telephoto state with infinity focus. 
     The relative positional relationship between the third-fifth lens unit tube  8  and the motor moving tube  9  in the optical axis OA direction is determined by the distance S 1  between the cam follower  8   a  in the third-fifth unit cam groove M 35  and the cam follower  9   a  in the motor cam groove MM. 
     In this case, the spring member  13  energizes the cam follower  9   a  forward so that the can follower  9   a  comes into contact with the front side wall of the motor cam groove MM. 
     Therefore, the distance between the front end of the cam follower  8   a  and the front end of the cam follower  9   a  is S 1  shown in  FIGS. 3 and 4A . 
       FIG. 4B  shows a telephoto state with close range focus. Regarding the shooting distance (object distance, focus position), to change, in the telephoto state, from the infinity focus of  FIG. 4A  to the close range focus, the stepping motor  12  is driven to move the fourth lens unit L 4  and the fourth lens unit frame  10  forward along the arrow shown in  FIG. 4A , so that the state of  FIG. 4B  is reached. 
     As mentioned above, the main guide bar holding portion  10   b  engages the main guide bar  8   c  over a long distance and extends forward beyond the frame portion  10   a  in order to prevent the tilting of the fourth lens unit L 4 . 
     Therefore, when the fourth lens unit L 4  and the fourth lens unit frame  10  are moved forward, the front end of the main guide bar holding portion  10   b  projects forward beyond the front end of the motor moving tube  9  as shown in  FIG. 4B . This means that the stepping motor  12  allows the main guide bar holding portion  10   b  (fourth lens unit frame  10 ) to move out of the motor moving tube  9  in the optical axis direction. 
     As shown in  FIG. 4B , when the stepping motor  12  is powered off with the front end of the main guide bar holding portion  10   b  projecting forward beyond the front end of the motor moving tube  9 , the fourth lens unit L 4  (fourth lens unit frame  10 ) is not allowed to move in the optical axis OA direction with respect to the motor moving tube  9 . In other words, the relative positional relationship between the fourth lens unit L 4  and the motor moving tube  9  is fixed. 
     The lens barrel  1  according to an embodiment of the present invention can be changed to the contracted state (housed state) or changed in focal length by the rotation of the zoom ring  2 . Therefore, it is conceivable that the photographer will rotate the zoom ring  2  while the front end of the main guide bar holding portion  10   b  projects forward beyond the front end of the motor moving tube  9  (in the state of  FIG. 4B ). When the photographer rotates the zoom ring  2 , the relative positional relationship between the third-fifth lens unit tube  8  and the motor moving tube  9  changes in accordance with the shapes of the third-fifth unit cam groove M 35  and the motor cam groove MM. 
     In the telephoto state, the distance S 1  shown in  FIG. 3  is the distance in the optical axis OA direction between the front end of the cam follower  8   a  in the third-fifth unit cam groove M 35  and the front end of the cam follower  9   a  in the motor cam groove MM. In the contracted state, the distance S 2  shown in  FIG. 3  is the distance in the optical axis OA direction between the front end of the cam follower  8   a  in the third-fifth unit cam groove M 35  and the front end of the cam follower  9   a  in the motor cam groove MM. The distance S 2  is smaller than the distance S 1  (S 1 &gt;S 2 ). That is, when the telephoto state is changed to the wide angle or contracted state, the distance between the third-fifth lens unit tube  8  and the motor moving tube  9  is reduced. 
     When the zoom ring  2  is rotated with the main guide bar holding portion  10   b  not projecting beyond the motor moving tube  9  (e.g., in the telephoto state with infinity focus), the wide angle or contracted state is reached so that the third-fifth lens unit tube  8  and the motor moving tube  9  come closer to each other. In this case, the main guide bar holding portion  10   b  does not project beyond the motor moving tube  9 , and therefore the third-fifth lens unit tube  8  and the main guide bar holding portion  10   b  (fourth lens unit frame  10 ) do not come into contact with each other. Therefore, even when the stepping motor  12  is powered off in the state of  FIG. 4A  and the relative positional relationship between the motor moving tube  9  and the fourth lens unit frame  10  is fixed, the zoom ring  2  can be rotated from the telephoto state to the contracted state. For example,  FIG. 4E  shows the contracted state reached after the power is turned off in the telephoto state with infinity focus. 
     When the power is turned off with the main guide bar holding portion  10   b  projecting beyond the motor moving tube  9  as shown in  FIG. 4B  (e.g., in the telephoto state with close range focus), the relative positional relationship between the motor moving tube  9  and the fourth lens unit frame  10  is fixed. 
     When the zoom ring  2  is rotated in this state, the third-fifth lens unit tube  8  and the motor moving tube  9  (the fourth lens unit frame  10  and the main guide bar holding portion  10   b ) come closer to each other according to the shapes of the third-fifth group cam groove M 35  and the motor cam groove MM. 
     In this case, the main guide bar holding portion  10   b  projects beyond the motor moving tube  9 , and thus the third-fifth lens unit tube  8  and the main guide bar holding portion  10   b  (fourth lens unit frame  10 ) come into contact with each other. Therefore, the third-fifth lens unit tube  8  and the motor moving tube  9  cannot approach S 2  even when the power is turned off in the telephoto state with close range focus ( FIG. 4B ) and followed by attempts to contract the barrel into a contracted state. This means that the state as shown in  FIG. 4C  cannot be reached. 
     If the motor cam groove MM is not opened at the rear side, the cam follower  8   a  and the cam follower  9   a  can only approach up to S 3  since the rear side wall of the motor cam groove MM obstructs the cam follower  9   a.  For example, the cam follower  8   a  and the cam follower  9   a  cannot move to the wide-angle side (contracted side) beyond the positions  8 M and  9 M shown in  FIG. 3 . 
     Therefore, the user feels a sense of wrongness since the user cannot rotate the zoom ring  2  halfway through when trying to contract the barrel by turning off the power in the telephoto state with close range focus. 
     In the embodiment of the present invention, however, the motor cam groove MM is opened at the rear side. Therefore, the motor moving tube  9  and the fourth lens unit frame  10  can move toward the rear side since they are pushed by the third-fifth lens unit tube  8 . 
     As a result, the cam follower  8   a  and the cam follower  9   a  can move to the wide angle side (contracted side) from the positions  8 M and  9 M shown in  FIG. 3  with the distance S 3  maintained between the third-fifth lens unit tube  8  and the motor moving tube  9  (between the front end of the cam follower  8   a  and the front end of the cam follower  9   a ).  FIG. 4D  shows the contracted state reached after the power is turned off in the telephoto state with close range focus ( FIG. 4B ). 
     When the user turns the power off in the telephoto state with close range focus ( FIG. 4B ) and turns the zoom ring  2 , the cam follower  9   a  of the motor moving tube  9  can move from the position  9 T shown in  FIG. 3  to the position  9 S 2  through the position  9 W 2  so that the collapsed state can be reached. 
     Thereafter, when the power is turned on, the stepping motor  12  first moves the fourth lens unit frame  10  to the infinity focus position. 
     For example, suppose that the user turns the zoom ring  2  to the wide angle position after turning the power off in the telephoto state with close range focus. As a result, the cam follower  8   a  and the cam follower  9   a  reach the positions  8 W and  9 W 2 . 
     If the user turns on the power in this state, a through image with aberration or blurring will be displayed on the display unit. This is because, in the wide angle state, the cam follower  8   a  and the cam follower  9   a  are in the positions  8 W and  9 W 2  despite the positions  8 W and  9 W 1  being the best. 
     Upon this, the stepping motor  12  moves the fourth lens unit frame  10  to the infinity focus position when the power is turned on, so that the fourth lens unit frame  10  will not project beyond the motor moving tube  9 . 
     As a result, the cam follower  8   a  and the cam follower  9   a  can be in the positions  8 W and  9 W 1  appropriate for the wide angle state, so that a through image can be displayed without aberration or blurring. This allows the cam follower  9   a  to come into contact with the front side face of the motor cam grove MM by means of the spring member  13  so that the infinity focus state, which is the initial state, can be recovered. 
     In the embodiment, the stepping motor  12  is fixed on the motor moving tube  9 , which is disposed inside the third-fifth lens unit tube  8  and is allowed to move forward and rearward in the optical axis direction by the cam tube  5 . The third-fifth lens unit tube  8  and the motor moving tube  9  are configured to be driven by means of different third-fifth unit cam grooves M 35  and motor cam grooves MM during zooming. This makes it possible to drive the fourth lens unit L 4  (focusing lens) such that a constant shooting distance can always be maintained in coordination with zooming. 
     The motor cam groove MM of the cam tube  5  is opened at the rear side or the motor cam groove MM has a wider width, and the cam follower  9   a  is allowed to come into contact with the front side face of the motor cam grove MM and used during zooming. This means that there is no need to make the rear side portion with high precision, which makes it easy to manufacture the mold. Since one wall is not necessary, molded components, if used, can be easily manufactured. Moreover, there is no need to form the rear side wall of the motor cam groove MM, which makes it possible to increase the space efficiency in the optical axis OA direction and to downsize the lens barrel  1 . 
     The motor moving tube  9  does not directly hold (fix) the lens. Therefore, the optical performance is less affected even when the motor cam groove MM is opened at one side or the motor cam groove MM has a wider width. Furthermore, energizing by springs affects the optical performance less since the motor moving tube  9  does not directly hold (fix) the lens. 
     The main guide bar  8   c  and the sub guide bar  8   d  are held by the third-fifth lens unit tube  8 . That is, the motor moving tube  9  does not hold any guide bar, so that the optical performance is less affected even when the motor cam groove MM for the motor moving tube  9  is opened at one side or the motor cam groove MM has a wider width. Furthermore, energizing by springs affects the optical performance less since the motor moving tube  9  does not directly hold (fix) the lens. 
     The motor cam groove MM is opened at one side or the motor cam groove MM has a wider width. In addition, the motor moving tube  9  and the third-fifth lens unit tube  8  are energized by springs. Therefore, the fourth lens unit frame  10  can move forward until it goes beyond the motor moving tube  9 . This makes it possible to increase the range of movement of the fourth lens unit L 4  (focusing lens) and to reduce the minimum shooting distance. Furthermore, not needing to reduce the length of engagement of the main guide bar holding portion  10   b  makes it possible to reduce the minimum shooting distance while the tilting of the fourth lens unit L 4  is suppressed. 
     The third-fifth lens unit tube  8  is made with higher precision than the motor moving tube  9  so as to hold the third lens unit L 3  and the fifth lens unit L 5 . Therefore, the fourth lens unit frame  10  can be driven at higher accuracy by using the main and sub guide bars  8   c  and  8   d  on the third-fifth lens unit tube  8  to guide the fourth lens frame  10  than by, for example, providing a guide bar on the motor moving tube  9  and using it to guide the fourth lens unit frame  10 . 
     It should be noted that the main guide bar holding portion  10   b  extending forward beyond the frame portion  10   a  is descried as a non-limiting example. The main guide bar holding portion  10   b  may extend rearward beyond the frame portion  10   a . In that case, the front side wall of the motor cam groove MM may be eliminated and the spring members may be provided to do energizing such that the cam follower  9   a  comes into contact with the rear side wall of the motor cam groove MM. Alternatively, the width of the motor cam groove MM may be made wider than the width of the cam follower  9   a,  and the spring members may be provided to do energizing such that the cam follower  9   a  comes into contact with the rear side wall of the motor cam groove MM. 
     It should be noted that the fourth lens unit frame  10  (main guide bar holding portion  10   b ) projecting beyond the motor moving tube  9  in the telephoto state with close range focus is described as a non-limiting example. Depending on the lens configuration, the fourth lens unit frame  10  (main guide bar holding portion  10   b ) may be allowed to project beyond the motor moving tube  9  in one of the telephoto-infinity focus state, the wide angle-close range focus state, or other states. 
     It should be noted that the third-fifth lens unit tube  8  movable in the optical axis direction is described as a non-limiting example. The third-fifth lens unit tube  8  may be configured not to move in the optical axis direction. It should also be noted that the stepping motor is described as a non-limiting example of the motor for driving the fourth lens unit L 4 . Any other motor may be used, such as a voice coil motor or an ultrasonic motor. 
     It should be noted that the fourth lens unit L 4  is described as a non-limiting example of the focusing lens system. Alternatively, a zoom lens driven by a stepping motor (STM) during zooming may be used. It should be also be noted that the fourth lens unit L 4  provided between the third and fifth lens units L 3  and L 5  movable together is described as a non-limiting example. For example, the second lens unit L 2  may be provided between the first and third lens units L 1  and L 3  movable together, or any other configuration may be used. It will be understood that all the components described above are not always necessary and any combination of the components may be used. 
     EXPLANATION OF REFERENCE NUMERALS 
     L 1 : first lens unit, L 2 : second lens unit, L 3 : third lens unit, L 4 : fourth lens unit, L 5 : fifth lens unit, M 1   a : impact cam groove, M 1 : first unit cam groove, M 2 : second unit cam groove, M 35 : third-fifth unit cam groove, MC: rectilinear tube connecting pin, MK: cam groove, MM: motor cam groove, MZ: zoom interlocking pin, OA: optical axis,  1 : lens barrel,  2 : zoom ring,  3 : rectilinear tube,  4 : first lens unit tube,  5 : cam tube,  6 : fixed tube,  6   a : cam follower,  7  second lens third-fifth lens unit tube  8 : third-fifth lens unit tube,  8 A: third-fifth lens unit tube body,  8 B: third-fifth lens unit tube rear end part,  8   a : cam follower,  8   b : elongated hole,  8   c : main guide bar,  8   d : sub guide bar,  9 : motor moving tube,  9   a : cam follower,  10 : fourth lens unit frame,  10   a : frame portion,  10   b : main guide bar holding portion;  10   c : sub guide bar holding portion,  10   d : motor mount rack,  10   e : motor engagement portion,  10   f : rack mount,  11 : second lens unit frame,  12 : stepping motor,  12   a : rotary shaft,  13 : spring member,  20 : aperture mechanism,  81 : third lens unit holding frame,  82 : fifth lens unit holding frame