Abstract:
A lens barrel extending and retracting mechanism. A photographic optical axis and a central axis of a lens barrel are eccentric such that a first lens group and a second lens group are housed in a side of a CCD separated from the optical axis. The lens barrel is rotatably extended around the central axis thereof, and a picture is taken when lens optical axes of the first lens group and the second lens group coincide with the optical axis. The lens barrel extending and retracting mechanism prevents displacement and tilt of the lens optical axes of the first lens group and the second lens group, maintaining optical performance and reducing the size of the lens barrel in the housed position.

Description:
BACKGROUND  
       [0001]     The invention relates to lens barrel extending and retracting mechanisms, and in particular to slim-sized lens barrel extending and retracting mechanisms with a zoom lens having a housed position and a photographic position.  
         [0002]     The size of cameras is increasingly required to be more slim and thin. A thin and compact camera particularly in size is demand for those traveling light. Thus, in order to provide a slimmer design, the size of lens barrel units must be reduced. The size of most conventional cameras is reduced by decreasing the gap between the lens group and photographing device when the camera is not in use by housing the lens barrel in the body thereof.  
         [0003]     Japan patent No. 2003-315861 discloses a collapsible lens barrel and method for collapsing a lens barrel. A part of a lens group in the housed position is retracted from a photographing optical axis. A second lens group is retracted from the object side and housed in a camera body.  
         [0004]     Japan patent No. 2004-85934 discloses an extending cam mechanism for a zoom lens barrel, which not only limits the extent of movement of lenses and movement precision but also makes a cam ring small-sized.  
         [0005]     Although the size of the lens barrel is reduced, the optical performance should be maintained as well. In a conventional zoom digital camera, an optical photography system typically comprises three lens groups. Zooming and retracting are performed by moving each lens group in the direction of the photographic optical axis. Deviation of the photographic optical axes of the lens groups, particularly deviation of the photographic optical axes of the first lens group and the second lens group from the object side, and relative tilt of the photographic optical axes of the first lens group and the second lens group may greatly affect optical performance of the camera. In both Japan patent No. 2003-315861 and No. 2004-85934, since only the second lens group is retracted via individual retracting mechanism, the lens groups may be tilted and eccentric in parallel such that optical performance is difficult to maintain.  
       SUMMARY  
       [0006]     An extending and retracting mechanism for retracting and housing the lens groups while maintaining relative positions and optical performance thereof is provided to reduce the size thereof.  
         [0007]     A lens barrel extending and retracting mechanism is provided. The lens barrel extending and retracting mechanism, for extending an optical photography system out of an electronic device and retracting the optical photography system therein, comprises a fixing barrel, a rotary barrel, a guiding barrel, and a driving mechanism. The fixing barrel comprises a first cam groove and a second cam groove formed on an inner circumference thereof. The rotary barrel comprises a first cam-follower formed on an outer circumference thereof and engaged with the first cam grooves of the fixing barrel, rotating about a central axis parallel to an optical axis of an optical photography system. The guiding barrel comprises a second cam-follower formed on an outer circumference thereof and rotatably supported with respect to the rotary barrel to maintain a portion of the optical photography system. The driving mechanism turns the rotary barrel such that the guiding barrel rotates about the central axis and moves along the central axis.  
         [0008]     The second cam groove has a first linear trench engaging the second cam-follower so as to move the guiding barrel along the central axis when the portion of the optical photography system is out of the optical axis.  
         [0009]     The second cam groove has a second linear trench engaging the second cam-follower so as to moving the guiding barrel along the central axis when the portion of the optical photography system is positioned along the optical axis.  
         [0010]     The first and second cam grooves of the fixing barrel are formed without intersecting each other.  
         [0011]     The first and second cam grooves of the fixing barrel share the same cam loci and have different depths.  
         [0012]     The rotary barrel further comprises a protrusion, engaged with the first cam groove of the fixing barrel and disposed in the vicinity of the first cam-follower.  
         [0013]     The portion of the optical photography system is positioned along the optical axis so as to perform zooming by rotating the rotary barrel.  
         [0014]     The guiding barrel supports the portion of the optical photography system, and the optical photography system comprises a first lens groups and a second lens groups from the object side.  
         [0015]     The guiding barrel maintaining the optical photographic system can rotate via the rotary barrel and extend in the rotary shaft direction or both. For example, the lens housed in a lateral side of a photographic device can be rotated and extended and positioned on the front side thereof. Thus, when taking a picture, the lens on the front side can be housed in the lateral side of the photographic device. Thus, the lens barrel can become miniaturized when retracted.  
         [0016]     Since the lens is located in the lateral side thereof, the lens does not interfere with other elements of the photographic device such that the lens can rotate in the optical axial direction after the optical photographic system is extended out, and the gap surrounding the optical photographic system can be minimized, providing a compact-sized lens barrel.  
         [0017]     In the photographing position, the optical photographic system moves linearly in the optical axial direction such that rotational direction of the guiding barrel can be eliminated. The optical photographic system can be designed in the front side of the photographic device to maintain optical performance.  
         [0018]     The cam grooves do not intersect each other such that the cam-followers do not deviate and separate from the cam grooves, thus, irregular motion is avoided.  
         [0019]     The cam grooves of the rotary barrel and those of the guiding barrel share the same cam loci with different depths such that the cam-followers can be guided, preventing separation therefrom. If the cam grooves of the rotary barrel and the guiding barrel have cam loci that are partially overlapped, the range of the cam grooves of the fixing barrel can be expanded. Thus, the degree of freedom is increased.  
         [0020]     Separation of the cam-followers from the cam grooves of the overlapped region of the rotary barrel and the guiding barrel can be prevented to avoid loading variation. Thus, the rotary barrel and the guiding barrel can be operated smoothly.  
         [0021]     After the rotary barrel rotates from a housed position to a photographing position and moves the optical photography system, focus can be performed by continuously rotating the rotary barrel such that retracting and zooming are easy to control.  
         [0022]     The relative position of the first lens group and the second lens group, at the object side where optical performance influence is significant, can be maintained, and the lens groups can be retracted and housed while maintaining optical performance of the lens barrel, and size is reduced.  
     
    
     DESCRIPTION OF THE DRAWINGS  
       [0023]     The invention can be more fully understood by reading the subsequent detailed description in conjunction with the examples and references made to the accompanying drawings, wherein:  
         [0024]      FIG. 1  is a cross section of an embodiment of a lens barrel in a full zoom position;  
         [0025]      FIG. 2  is a cross section of a lens barrel of a focus driving mechanism;  
         [0026]      FIG. 3  is a front perspective view of a lens barrel in a photographing position;  
         [0027]      FIG. 4  is a development viewed from an outer circumference of a fixing barrel;  
         [0028]      FIG. 5  is a cross section of a cam groove of the fixing barrel;  
         [0029]      FIG. 6  is a development viewed from an outer circumference of a rotary barrel;  
         [0030]      FIG. 7  is a development viewed from an outer circumference of a guiding barrel;  
         [0031]      FIG. 8  is a cross section of a cam-follower of a guiding barrel;  
         [0032]      FIG. 9  is a development viewed from an outer circumference of a cam barrel;  
         [0033]      FIG. 10  is a development viewed from an outer circumference of a straight barrel;  
         [0034]      FIG. 11  is a development viewed from an outer circumference of a first lens frame;  
         [0035]      FIG. 12  is a development viewed from an outer circumference of a second lens frame;  
         [0036]      FIG. 13  is a cross section of a lens barrel in a housed position;  
         [0037]      FIG. 14  is a front perspective view of a lens barrel in a housed position;  
         [0038]      FIG. 15  is a front view of a lens barrel in a housed position;  
         [0039]      FIG. 16  is a front view of a lens barrel in a photographing position;  
         [0040]      FIG. 17  is a schematic view indicating positions of cam grooves of a fixing barrel;  
         [0041]      FIG. 18  is a schematic view indicating positions of cam grooves of a guiding barrel;  
         [0042]      FIG. 19  is a schematic view indicating positions of cam grooves of a cam barrel;  
         [0043]      FIG. 20  is a cross section of a lens barrel in a minimum zoom of the photographing position;  
         [0044]      FIG. 21  is a relationship between the rotational angle of the rotary barrel and moving distance of each moving element along an optical axis;  
         [0045]      FIG. 22  is a development viewed from an outer circumference of a fixing barrel of another embodiment;  
         [0046]      FIG. 23  is a cross section of a cam groove of the fixing barrel of  FIG. 22 . 
     
    
     DETAILED DESCRIPTION  
       [0047]     FIGS.  1  to  21  are schematic views of an embodiment of a lens barrel. The embodiment is applicable in a zoom lens barrel of a digital camera.  
         [0048]      FIG. 1  is a cross section of an embodiment of a lens barrel  2  in a full zoom or wide-angled view of a photographing position. An optical photography system comprises a first lens group  31 , a second lens group  32 , a third lens group  33 , a low-pass filer  34 , and a charge-coupled device (CCD)  35 , arranged in order from a photographic subject. An optical axis of the optical photography system is defined as J 1 , parallel to a central axis J 2  of the lens barrel, and the optical axis J 1  is eccentric from the central axis J 2 . Zooming is performed by moving the first lens group  31  and the second lens group  32  in a direction of the optical axis J 1 , respectively. Focusing is performed by moving the third lens group  33  in the direction of the optical axis J 1 . A light from the object side passing through the first lens group  31 , the second lens group  32 , and the third lens group  33  passes through the low-pass filter  34  and is guided to the CCD  35 . Note that the term “optical axial direction” used in the following is particularly defined as directions parallel to the optical axis J 1 .  
         [0049]     The fixing barrel  61  is fixed on a body  1 . A CCD holder  21  located behind the fixing barrel  61  covers an opening of the fixing barrel  61 . The low-pass filter  34  is attached to and supported by the CCD holder  21  at a front opening  21   a . The CCD  35  and a heat sink  22  are integrally connected. The CCD  35  is fixed on the CCD holder  21  via the heat sink  22 . A CCD flexible printed circuit board (FPC)  23  for transmitting electronic signals produced by the CCD is disposed behind the heat sink  22 .  
         [0050]     The third lens group  33  for focus and a focus driving mechanism  3  for driving the third lens group  33  are correspondingly disposed near the CCD holder  21 .  FIG. 2  is a cross section of a lens barrel of a focus driving mechanism  3 . A third lens frame  41  supporting the third lens group  33  is slidably disposed on a pair of guide shafts A 42  and A 43  of the CCD holder  21  in the optical axial direction. The guide shaft A 42  is a main shaft of the third lens frame  41 , and the guide shaft B 43  is used for rotational control of the third lens frame  41 . The guide shafts A 42  and A 43  can be slidably inserted into guiding holes  41   a  and  41   b  formed on the third lens frame  41 .  
         [0051]     Focus motor  44  is fixed in the inner side of the fixing barrel  61  corresponding to the third lens group  33  and the CCD holder  21  at a side of the CCD  35 . The rotational driving force of the focus motor  44  is transferred to feed screws  48  from the focus motor gear  45  via the focus gears  46  and  47 . The feed screws  48  and nuts  49  are engaged to allow back and forth movement of the third lens frame  41  along the optical axis. The rotational driving force of the focus motor  44  can be reduced by focus gears  46  and  47  such that the feed screws  48  have sufficient rotational torque. The third lens frame  41  is biased by the spring  50  thereof. The focus motor  44  is controlled by camera control circuit via the FPC  51  for driving the lens disposed behind the CCD holder  21 .  
         [0052]      FIG. 3  is a front perspective view of a lens barrel  2  in a photographing position. The upper portion of the fixing barrel  61  is disposed with zoom motor  81  and speed-reduction gear set  82 . The driving force of the zoom motor  81  is transferred to the zoom gear  83  via the speed-reduction gear  82 . The zoom gear  83  is rotatably supported with respect to the fixing barrel  61  by the gear shaft  84  parallel to the optical axial direction. The zoom motor  81 , the speed-reduction gear  82 , and the zoom gear  83  constitute an extending and retracting mechanism of the driving mechanism. The zoom motor  81  is controlled by a camera control circuit via the FPC  51  located behind the CCD holder  21 .  
         [0053]      FIG. 4  is a development viewed from an outer circumference of a fixing barrel  61 . Three cam grooves  61   a  for guiding the rotary barrel  62  and three cam grooves  61   b  for guiding the guiding barrel  63  are formed on the inner circumference of the fixing barrel  61 . The cam grooves  61   b  of the guiding barrel  63  are deeper than the cam grooves  61   a  of the rotary barrel  62 . The cam grooves  61   a  and  61   b  have the same grooved trace region  61   c . The region  61   c  is divided into two sections, as shown in  FIG. 5 .  
         [0054]      FIG. 6  is a development viewed from an outer circumference of a rotary barrel  62 . The rotary barrel  62  is disposed on the inner circumference of the fixing barrel  61 . Three rotary barrel cam-followers  64  are inserted into the holes  62   a  of the rotary barrel  62  to engage with the cam groove  61   a  of the fixing barrel  61 . A protrusion  62   b  engaged with the cam groove  61   a  of the fixing barrel  61  is formed in the vicinity of the inserting position of the three rotary barrel cam-followers  64  on the outer circumference of the rotary barrel  62 . The function of the protrusion  62   b  is discussed hereinafter. The outer circumference of the rotary barrel  62  comprises a gear portion  62   c  meshed with the zoom gear  83 . The zoom motor  81 , speed-reduction gear  82 , zoom gear  83  constitute a driving mechanism for generating rotational driving force. The rotary barrel  62  rotates about the central axis J 2  such that the rotary barrel  62  extends or retracts along the cam groove  61   a  of the fixing barrel  61 .  
         [0055]      FIG. 7  is a development viewed from an outer circumference of a guiding barrel  63 . The guiding barrel  63  is disposed on the inner circumference of the rotary barrel  62 . A hook  63   a  formed on the outer circumference of the guiding barrel  63  is engaged with a groove  62   d  on the inner circumference of the rotary barrel  62 . The hook  63   a  corresponding to the rotary barrel  62  is moved and controlled in the optical axial direction and mutually rotatably supported. Three cam-followers  63   b  formed on the outer circumference of the guiding barrel  63  are engaged with the cam grooves  61   b  of the fixing barrel  61 . A cam-follower  63   b  of the guiding barrel  63  has a parallelogram cross section, as shown in  FIG. 8 . The cam groove  61   b  of the fixing barrel  61  has a linear trench  61   d  and  61   e  engaged with a plane  63   c  of the cam-follower  63   b . The cam groove  61   b  of the fixing barrel  61  has a sloped region engaged with the plane  63   d  of the cam-follower  63   b.    
         [0056]      FIG. 9  is a development viewed from an outer circumference of a cam barrel  65 . The cam barrel  65  is located on an inner circumference of the guiding barrel  63 . Three cam-followers  65   a  are formed on the outer circumference. The cam-followers  65   a  are engaged with the guiding barrel  63  and rotate with respect to the guiding barrel  63  to extend and retract from the cam groove  63   e . The cam barrel  65  comprises holes  65   b  defined thereon and three cam barrel guide shafts  66  inserted therein. The cam barrel guide shafts  66  penetrate through the holes  63   f  of the guiding barrel  63  to engage the linear trench  62   e  in the optical axial direction on the inner circumference of the rotary barrel  62 . Thus, the cam barrel  65  does not rotate with respect to the rotary barrel  62 , but is movable in the optical axial direction.  
         [0057]     Namely, when the rotary barrel  62  rotates with the guiding barrel  63 , the cam barrel  65  moves in and out along the cam groove  63  of the guiding barrel  63 .  
         [0058]      FIG. 10  is a development viewed from an outer circumference of a straight barrel  67 . The straight barrel  67  is disposed on an inner side of the cam barrel  65 . The hook  65   c  on the inner circumference of the cam barrel  65  grasps protrusions  67   a  and  67   b  on the outer circumference of the straight barrel  67  such that movement in the optical axial direction is controlled and the cam barrel  65  and the straight barrel  67  are mutually rotatably supported. The guiding hook  67   c  disposed on the outer circumference of the straight barrel  67  is engaged with the linear trench  63   g  in the optical axial direction on the inner circumference of the guiding barrel  63 . Thus, the straight barrel  67  cannot rotate with the guiding barrel  63  but can rotate in the optical axial direction.  
         [0059]      FIG. 11  is a development viewed from an outer circumference of a first lens frame  68 . The first lens frame  68  is disposed on an inner side of the cam barrel  65  and supports the first lens group  31 . Three cam-followers  69  of the first lens frame are inserted into the holes  68   a  of the first lens frame  68 , and the cam-follower portion  69   a  on the outer periphery of the cam-followers  69  is engaged with the cam groove  65   d  on the inner circumference of the cam barrel  65 . Additionally, a guiding portion  69   b  on the inner side of the cam-follower  69  of the first lens frame is engaged with a straight guiding hole  67   d  of the straight barrel  67  in the optical axial direction. Thus, the cam barrel  65  rotates with respect to the straight barrel  67 , and the cam barrel  65  rotates with respect to the guiding barrel  63 , corresponding to relative rotations between the straight barrel  67  and the guiding barrel  63 , such that the first lens frame  68  can extend or retract along the cam groove  65   d  of the cam barrel  65  in the optical axial direction.  
         [0060]      FIG. 12  is a development viewed from an outer circumference of a second lens frame  70 . The second lens frame  70  is disposed on an inner side of the straight barrel  67  and supports the second lens group  32 . Three cam-followers  70   a  formed on the outer circumference of the second lens frame  70  are engaged with the cam groove  65   e  on the inner circumference of the cam barrel  65 . Additionally, a root  70   b  of the cam-followers  70   a  of the second lens frame  70  is engaged with a straight guiding hole  67   e  of the straight barrel  67  in the optical axial direction. Thus, the cam barrel  65  rotates with respect to the straight barrel  67 , and the cam barrel  65  rotates with respect to the guiding barrel  63 , corresponding to relative rotations between the straight barrel  67  and the guiding barrel  63 , such that the second lens frame  70  can extend or retract along the cam groove  65   e  of the cam barrel  65  in the optical axial direction.  
         [0061]     The second lens frame  70  comprises a shutter unit  71  for blocking incident light from the side of the photographic subject. The shutter unit  71  is disposed on an actuator  71   a . A flexible printed circuit board (FPC) for shutter  72  connects the actuator  71   a  and the camera control circuit. The FPC  72  passing from the shutter unit  71  through the internal of the lens barrel  2  is connected to another lens driving FPC  51  disposed behind the CCD holder  21 .  
         [0062]     A bias spring  73  is disposed between the first lens frame  68  and the second lens frame  70  such that the first lens frame  68  and the second lens frame  70  are biased to each other in the optical axial direction and detached from each other. Thus, the cam engaging portion of the cam barrel  65  of the first lens frame  68  and that of the cam barrel  65  of the second lens frame  70  can be eliminated, stabilizing the optical performance.  
         [0063]     The movement of the lens barrel  2  from a housed position to a photographing position is discussed in the following.  
         [0064]      FIG. 13  is a cross section of a lens barrel  2  in a housed position.  FIG. 14  is a front perspective view of a lens barrel  2  in a housed position. The central axis of the first lens group  31  and the second lens group  32  is defined as “J 3 ”, housed at a side of the third lens group  33 , the low-pass filter  34 , and the CCD  35 , at a position biased from the photographic optical axis J 1  at the side of the focus driving mechanism  3 . Namely, the first lens group  31 , the second lens group  32 , the third lens group  33 , the low-pass filter  34 , the CCD  35 , and three blocks of the focus driving mechanism  3  are housed on a plane, substantially perpendicular to the optical axis.  
         [0065]     The first and second lens groups  31  and  32  rotate about the central axis J 2  of the lens barrel  2  as a center, and are extended in the optical axial direction to a photographing position, as shown in  FIG. 1 . If viewed from a front view of the lens barrel  2 , as shown in  FIG. 15 , the first and second lens groups  31  and  32  rotate in a direction Z 1  and extend to the photographing position of  FIG. 16 . In the photographing position, the central axis J 3  of the first and second lens groups  31  and  32  corresponds to the photographic optical axis J 1 . An eccentric distance between the central axis J 2  of the lens barrel  2  and the photographic optical axis J 1  is equal to an eccentric distance between the central axis J 2  of the lens barrel  2  and the central axis J 3  of the first and second lens groups  31  and  32 .  
         [0066]     When the lens barrel  2  is in a housed position, the cam-follower  64  of the rotary barrel  62  is disposed at a position  61 ( 1 ) of the cam groove of the fixing barrel  61 . The cam-follower  65   a  of the cam barrel  65  is disposed at a position  63 ( 1 ) of the cam groove of the guiding barrel  63 . A cam-follower pin  69  inserted into the first lens frame  68  is disposed at a position  65 ( 1 ) of the cam groove of the cam barrel  65 . A cam-follower  67  of the second lens frame  70  is disposed at a position  65 ( 11 ) of the cam groove of the cam barrel  65 , as shown in  FIGS. 17, 18 , and  19 .  
         [0067]     By rotating the zoom gear  83 , the rotary barrel  62  rotating about the central axis J 2 , the rotary barrel cam-follower pin  64  is withdrawn in the optical axial direction from the position  61 ( 1 ) of the cam groove of the fixing barrel  61  to the position  61 ( 2 ). Additionally, the guiding barrel  63  controls the movement of the rotary barrel  62  in the optical axial direction, and is extended in the optical axial direction from the position  61 ( 11 ) to the position  61 ( 12 ) via the guidance of the cam groove  61   b  of the fixing barrel  61 . The guiding barrel  63  moving between the position  61 ( 11 ) and  61 ( 12 ) of the cam groove of the fixing barrel  61  such that relative rotation is generated between the rotary barrel  62  and the guiding barrel  63 . The cam-follower  65   a  of the cam barrel  65  moves from position  63 ( 1 ) to  63 ( 2 ) of the cam groove of the guiding barrel  63 , and meanwhile, in order to generate relative rotation between the cam barrel  65  and the guiding barrel  63 , the first lens frame cam-follower pin  69  moves from the position  65 ( 1 ) to  65 ( 2 ) of the cam groove of the cam barrel  65 , and the second lens frame cam-follower pin  70   a  moves from the position  65 ( 11 ) to  65 ( 12 ) of the cam groove of the cam barrel  65 .  
         [0068]     When the rotary barrel cam-follower pin  64  reaches a position  61 ( 12 ) of the cam groove of the fixing barrel  61 , the cam-follower  63   b  of the guiding barrel  63  is driven at the position  61 ( 12 ) of cam groove of the fixing barrel  61 . The cam-follower  65   a  of the cam barrel  65  is driven at the position  63 ( 2 ) of the cam groove of the guiding barrel  63 . The cam-follower pin  69  of the first lens frame is driven at the position  65 ( 2 ) of the cam groove of the cam barrel  65 . The cam-follower  70   a  of the second lens frame  70  is driven at the position  65 ( 12 ) of the cam groove  65 .  
         [0069]     Due to the described motions, the guiding barrel  63 , the cam barrel  65 , the first lens frame  68 , and the second lens frame  70  are directly extended in the optical axial direction. Thus, the first lens group  31  and the second lens group  32  are extended from the object side in the optical axial direction.  
         [0070]     As a result, before rotational movement of the first lens group  31  and the second lens group  32 , the first lens group  31  and the second lens group  32  are at a position not interfering with the third lens group  33 , the low-pass filter  34 , the CCD  35 , and the focus driving mechanism  3  when extending.  
         [0071]     As the cam-follower pin  64  of the rotary barrel is extended while rotating from a position  61 ( 2 ) of the cam groove of the fixing barrel  61  to the position  61 ( 3 ) to extend the rotary barrel  62 , the cam-follower  63   b  of the guiding barrel  63  reaches the position  61 ( 13 ) of the fixing barrel  61 . During the motion, the extended amount of the angle of the rotary barrel  62  is the same as that of the angle of the guiding barrel  63  such that the cam grooves  61   a  and  61   b  of the fixing barrel  61  are formed without relative rotation between the rotary barrel  62  and the guiding barrel  63 .  
         [0072]     Thus, the rotary barrel  62 , the guiding barrel  63 , the cam barrel  65 , the straight barrel  67 , the first lens frame  68 , the second lens frame  70  are extended together by rotating about the central axis J 2 .  
         [0073]     During rotation, when the cam-follower pin  64  of the rotary barrel passes through the position  61 ( 13 ) of the cam groove of the fixing barrel  61 , since the cam groove  61   b  thereof is deeper than the cam groove  61   a , the cam-follower pin  64  of the rotary barrel is engaged with the cam groove  61   a  of the fixing barrel  61  at position  61 ( 14 ). Since the protrusion  62   b  of the rotary barrel  62  is substantially engaged with the cam groove  61   a  of the fixing barrel  61 , the zooming can be extended without varying loading. Namely, the cam-follower pin  64  of the rotary barrel is corresponding to the main guiding portion of the cam groove  61   a  of the fixing barrel  61 . However, the cam-follower pin  64  passing through the position  61913 ) of the cam groove of the fixing barrel  61  is restricted, and thus, it is guided by a secondary guiding portion, which is a protrusion  62   b  of the rotary barrel  62 . “Substantially engaged”, as mentioned above, is defined in that engagement of the protrusion  62   b  of the rotary barrel  62  of the secondary guiding portion, compared with the engagement of the cam-follower  64  of the main guiding portion, does not over-limit guiding performance thereof.  
         [0074]     When the cam-follower pin  64  of the rotary barrel is at the position  61 ( 3 ) of the cam groove of the fixing barrel  61 , and the cam-follower  63   b  of the guiding barrel  63  reaches the position  61 ( 13 ), the photographic optical axis J 1  and the central axes J 3  of the first and second lens group  31 ,  32  coincide.  
         [0075]     If the cam follower pin  64  of the rotary cam is rotated from the position  61 ( 3 ) of the cam groove of the fixing barrel  61  to the position  61 ( 4 ) while extending therefrom, the cam-follower  63   b  of the guiding barrel  63  moves from the position  61 ( 13 ) to the position  61 ( 14 ), extending in the optical axial direction. The described motion is the same as when the cam-follower pin  64  of the rotary barrel is moved from the position  61 ( 1 ) to  61 ( 2 ). That is, the relative rotation between the cam barrel  65  and the guiding barrel  63  makes the cam-follower pin  69  of the first lens frame move from the position  65 ( 2 ) to the position  65 ( 4 ) of the cam groove of the cam barrel  65 , and the cam-follower  70   a  of the second lens frame  70  move from the position  65 ( 12 ) to the position  65 ( 14 ). This position is the full zoom position of the lens barrel  2 , same as position of the cross section of  FIG. 1 .  
         [0076]     Zooming motion from a full zoom to a minimum zoom of photographic position is discussed in the following.  
         [0077]     When the zoom gear  83  rotates, and the rotary barrel  62  rotates, the cam follower pin  64  of the rotary barrel is moved from a position  61 ( 4 ) of the cam groove of the fixing barrel  61 , a full zoom of the photographic position, to a position  61 ( 5 ). The cam groove of the fixing barrel  61  in this range is perpendicular to the optical axial direction. The rotary barrel is extended in the optical axial direction and rotated about the axis J 2 . The guiding barrel  63  is stopped. Meanwhile, the rotary barrel  62  and the guiding barrel  63  rotate relatively to each other such that the cam-follower  65   a  of the cam barrel  65  is moved from the position  63 ( 4 ) to the position  63 ( 5 ) of the cam groove of the guiding barrel  65 . The cam barrel  65  and the guiding barrel rotate relatively to each other such that the cam-follower pin  69  of the first lens frame is moved from the position  65 ( 4 ) to the position  65 ( 5 ). The cam-follower  70   a  of the second lens frame  70  is guided from the position  65 ( 14 ) to the position  65 ( 15 ) of the cam barrel  65 . Since the guiding barrel  63  is stopped, the first lens frame  68  for supporting the first lens group  31  and the second lens frame  70  for supporting the second lens group  32 , move in and out in the optical axial direction, respectively, while rotating about the central axis J 2 . Each cam groove of the cam barrel  65  and the guiding barrel  63  is formed from the full zoom to the minimum zoom with various zooming distance therebetween.  FIG. 20  is a cross section of a lens barrel  2  at the minimum zoom of photographing position.  
         [0078]     When it is moved from the minimum zoom to the full zoom of the photographing position, the zoom gear  83  can rotate in an opposite direction. The control of the zoom motor  81  for driving the zoom gear  83  can obtain any focal distance. If it is moved from the full zoom to the housed position, the zoom gear can also rotate in an opposite direction to achieve a housed position, as shown in  FIG. 13 .  
         [0079]      FIG. 21  is a relationship between the rotational angle of the rotary barrel and the moving distance of each moving element along an optical axis. The horizontal axis represents the rotational angle of the rotary barrel  62 . The vertical axis represents the absolute moving distance of the rotary barrel  62 , the guiding barrel  63 , the cam barrel  65 , the first lens frame  68 , and the second lens frame  70  in the optical axial direction. The positions of each moving element passing therethrough (as shown in  FIGS. 17, 18 , and  19 ) are shown in  FIG. 21 . Thus, the movement relationship of each element of the lens barrel  2  in the optical axial direction.  
         [0080]     According to the described structure, the lens barrel  2  can be in a housed position (when the camera is idle), and the first lens group  31  and the second lens group  32  can be retracted to a lateral side of the third lens group  33 , the low-pass filter  34 , and the CCD  35  such that the size of the lens barrel  2  can be reduced. In the photographing position, the first lens group  31  and the second lens group  32  can move in the direction of the photographing optical axis J 1  to a desired position and can also perform zooming.  
         [0081]     Moreover, the first lens group  31  and the second lens group  32  are supported in an interior side of the guiding barrel  63  with a cylindrical shape. Thus, the deviation or relative tilt of the first lens group  31  and the second lens group  32  where optical performance influence is high can be reduced. Thus, the optical performance can be maintained in the photographing position.  
         [0082]     Additionally, the zoom motor  81  is a drive source of the extending and retracting mechanism to rotate the rotary barrel  62 . Thus, another retracting mechanism or other drive source for the first lens group  31  and the second lens group  32  can be eliminated. The structure of the lens barrel  2  can be simplified and miniaturized.  
         [0083]     The invention is not limited to the above disclosure. There are other variations.  
         [0084]     For example, the cam groove  61   b , engaged with the cam-follower  63   b  of the guiding barrel  63  disposed in the fixing barrel  61 , is deeper than the cam groove  61   a , engaged with the cam-follower pin  62  of the rotary barrel. Conversely, the cam groove  61   b  can be shallower than the cam groove  61   a.    
         [0085]     Furthermore, the cam groove  61   a , engaged with the cam-follower pin  64  of the rotary barrel in the fixing barrel  61 , and the cam groove  61   b , engaged with the cam-follower  63   b  of the guiding barrel  63 , share the same cam locus region  61   c . As shown in  FIG. 22 , however, the cam groove  161   a , engaged with the rotary barrel&#39;s cam-follower pin  64  of the fixing barrel  161 , and the cam groove  161   b , engaged with the cam-follower  63   b  of the guiding barrel  63 , are formed without intersecting each other. If the cam grooves  161   a  and  161   b  do not intersect each other, as shown in  FIG. 23 , the basic thickness D 2  of the fixing barrel  161  with smaller outer circumference can be thinner than the basic thickness D 1  of the fixing barrel  61  of the described embodiment. Thus, the size of the lens barrel  2  can be reduced.  
         [0086]     Additionally, the position  61 ( 1 ) to the position  61 ( 4 ) of the cam groove  61   a  of the fixing barrel  61  and the position  61 ( 12 ) to the position  61 ( 13 ) of the cam groove  62   b  are at the same angle and linearly formed a certain amount of extending structure. The loci of the cam grooves  61   a  and  61   b , however, can be freely determined, respectively, accordingly to curved lines. The relationship of moving amount of the rotary barrel  62  and the guiding barrel  63  in the optical axial direction and the rotational amount of the central axis J 2  can be arbitrarily decided.  
         [0087]     Moreover, the cam-follower pin  64  of the rotary barrel and the rotary barrel  62  are individually formed. However, they can also be formed integrally into a cam-follower. Similarly, that of the guiding barrel  63  can be integrally formed into a cam-follower, or the cam-follower and the guiding barrel  63  can be separately formed.  
         [0088]     The quantities of the cam-follower pin  64 , engaged with the cam groove of the fixing barrel  61  and the cam-follower  63   b  of the guiding barrel  63  are not limited to three. One or two or more than four are applicable.  
         [0089]     The guiding barrel  63  indirectly maintains the first lens frame  68  and the second lens frame  70  for supporting the first lens group  31  and the second lens group  32  via the cam barrel  65  and the straight barrel  67 . The cam barrel, however, can indirectly maintain the optical photography system by other elements. The guiding barrel  63  can also directly maintain the optical photography system.  
         [0090]     The optical system of the lens barrel not necessarily comprises three lens groups, can also comprise one, two, or more than four lens groups. The lens groups maintained and retracted by the guiding barrel  63  are not limited to the first lens group  31  and the second lens group  32 , and can be any lens group from the optical system.  
         [0091]     The zoom lens barrel is applicable to any lens extending and retracting mechanism. Other lens barrel without zoom operation or single-focus lens barrel are also applicable. The single-focus lens barrel and the zoom lens barrel can be applied in the same place and retracted to provide a simplified structure.  
         [0092]     The lens barrel of the invention provides lowered costs and minimizes the size thereof. Thus, it has potential market value and is applicable in any camera.  
         [0093]     While the invention has been described by way of example and in terms of preferred embodiment, it is to be understood that the invention is not limited thereto. To the contrary, it is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.