Abstract:
There is provided a collapsible lens barrel including plural barrels of different outside diameter from one another and enabled to move coaxially and perform relative movement in an axial direction, and an image-capturing optical system disposed within the plural barrels; wherein the image-capturing optical system includes at least two lens holding frames arranged in a direction of an optical axis of the image-capturing optical system; and, considering an object side is set as a front side and an opposite side is set as a rear side, each of a rearmost lens holding frame, placed at a rearmost position, and one of the lens holding frames placed immediately in front of the rearmost lens holding frame, are respectively movably supported by a corresponding guide mechanism to move in the direction of the optical axis and to move in the direction of the optical axis by a corresponding drive mechanism.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     The present invention contains subject matter related to Japanese Patent Application JP2004-123173, filed to the Japanese Patent Office on Apr. 19, 2004, the contents of which being incorporated herein by reference.  
       BACKGROUND OF THE INVENTION  
       [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a collapsible lens barrel and to an imaging apparatus.  
         [0004]     2. Description of Related Art  
         [0005]     A collapsible lens barrel is available, which incorporates an image-capturing optical system and which is adapted to collapse and/or expand in an axial direction along its optical axis thereof and used as a lens barrel for an imaging apparatus, such as a digital still camera and a digital video camera, for example.  
         [0006]     Such a collapsible lens barrel has plural lens holding frames, which are disposed at places in front of an imaging device for electronically imaging an object, which optical image is formed by the image-capturing optical system, in such a way as to move along the direction of he optical axis thereof, and also has plural drive mechanisms for moving each of the lens holding frames in the direction of the optical axis thereof.  
         [0007]     For the drive mechanisms, there have been proposed mechanisms, each having a male screw member extending in the direction of the optical axis, a motor for rotation-driving the male screw member, and a female screw member screwed in to the male screw member and moved in the extending direction of the male screw member and which is adapted so that this female member is connected to the lens holding frame and that the lens holding frame is moved, together with the female screw member, in the direction of the optical axis by rotation of the motor (see, for example, Japanese Patent Application Laid-Open No. 2002-286988 Official Gazette).  
         [0008]     In such a collapsible lens barrel, each of the lens holding frames is moved to a rear end position, which is located at the rearmost place in the direction of the optical axis, in a collapsed condition. At that time, to prevent each of the lens holding frames and the drive mechanisms therefor from being damaged, clearances should be ensured between the lens holding frames and between the lens holding frame, which is positioned at the rearmost place, and a component provided at the rear end of the barrel.  
         [0009]     On the other hand, there has been proposed a collapsible lens barrel in which an abutting member is provided at the frontmost position of the plural lens holding frames arranged in the direction of the optical axis in such a way as to be able to move in the direction of the optical axis, and in which a compression coil spring is disposed between the rear end of the abutting member and the adjacent lens holding frame (see, for example, Japanese Patent Application Laid-Open No. 2002-383449 Official Gazette).  
         [0010]     Such collapsible lens barrel is adapted so that in the collapsed condition, each of the lens holding frames is retreated through the compression coil spring by backwardly moving the abutting member, that the plural lens holding frames are made to abut against each other, and that the lens holding frame provided to the rearmost position is made to abut against the rear end of the lens barrel.  
       SUMMARY OF THE INVENTION  
       [0011]     In the former collapsible lens barrel, a clearance should be ensured between adjacent plural lens holding frames. Thus, the former collapsible lens barrel presents some issues when considering miniaturization of the barrel in the collapsed condition.  
         [0012]     The latter collapsible lens barrel needs specific components, such as the abutting member and the compression coil spring that, therefore, increases the cost of the components. In addition, space is required in which the abutting member and the compression coil spring are disposed. Consequently, the latter collapsible lens barrel also presents issues when pursuing miniaturization of the barrel in the collapsed condition.  
         [0013]     The present invention has been conceived in view of such circumstances. A preferred embodiment of the present invention provides a lens barrel and an imaging apparatus, which are advantageous for miniaturization of the barrel in the collapsed condition without requiring exclusive components therein.  
         [0014]     It is preferable, according to a preferred embodiment of the present invention, to provide a collapsible lens barrel including plural barrels of different outside diameter from one another and enabled to move coaxially and perform relative movement in an axial direction, and an image-capturing optical system disposed within the plural barrels; wherein the image-capturing optical system includes at least two lens holding frames arranged in a direction of an optical axis of the image-capturing optical system; and, considering an object side is set as a front side and an opposite side is set as a rear side, each of a rearmost lens holding frame, placed at a rearmost position, and one of the lens holding frames placed immediately in front of the rearmost lens holding frame, are respectively movably supported by a corresponding guide mechanism to move in the direction of the optical axis and to move in the direction of the optical axis by a corresponding drive mechanism, the collapsible lens barrel having a drive mechanism for moving the rearmost lens holding frame in the direction of the optical axis and including a moving piece driven by a motor to move rectilinearly along the direction of the optical axis; wherein: the rearmost lens holding frame is pushed forwardly by a coil spring; an engaging piece provided in the rearmost lens holding frame is abutted against the moving piece from behind the moving piece and follows a rectilinear movement of the moving piece so as to move the rearmost lens holding frame in the direction of the optical axis; the rearmost lens holding frame is moved by the corresponding drive mechanism to a rear end position, which is located most backwardly, in a collapsed status in which a total length of the plural barrels is minimum; and the lens holding frame placed immediately in front of the rearmost lens holding frame is backwardly moved by the corresponding drive mechanism and abuts against the rearmost lens holding frame placed at the rear end position, to then move backwardly together with the rearmost lens holding frame to a rear end place at which the moving piece is separated from the engaging piece.  
         [0015]     Also, according to another preferred embodiment of the present invention, there is provided an imaging apparatus including plural barrels of different outside diameter from one another and enabled to move coaxially and perform relative movement in an axial direction, and an image-capturing optical system disposed within the plural barrels; wherein the image-capturing optical system includes at least two lens holding frames arranged in a direction of an optical axis of the image-capturing optical system; and, considering an object side is set as a front side and an opposite side is set as a rear side, each of a rearmost lens holding frame, placed at a rearmost position, and one of the lens holding frames placed immediately in front of the rearmost lens holding frame, are respectively movably supported by a corresponding guide mechanism to move in the direction of the optical axis and to move in the direction of the optical axis by a corresponding drive mechanism, the imaging apparatus comprising:  
         [0016]     a drive mechanism for moving the rearmost lens holding frame in the direction of the optical axis and including a moving piece driven by a motor to move rectilinearly along the direction of the optical axis; wherein:  
         [0017]     the rearmost lens holding frame is pushed forwardly by a coil spring;  
         [0018]     an engaging piece provided in the rearmost lens holding frame is abutted against the moving piece from behind the moving piece and follows a rectilinear movement of the moving piece so as to move the rearmost lens holding frame in the direction of the optical axis;  
         [0019]     the rearmost lens holding frame is moved by the corresponding drive mechanism to a rear end position, which is located most backwardly, in a collapsed status in which a total length of the plural barrels is minimum; and  
         [0020]     the lens holding frame placed immediately in front of the rearmost lens holding frame is backwardly moved by the corresponding drive mechanism and abuts against the rearmost lens holding frame placed at the rear end position, to then move backwardly together with the rearmost lens holding frame to a rear end place at which the moving piece is separated from the engaging piece.  
         [0021]     According to the preferred embodiments of the present invention, in the collapsed condition of the barrel, the rearmost lens holding frame may be made to abut against the lens holding frame placed immediately in front of the rearmost one. Thus, there is no need for ensuring the clearance between these two lens holding frames. Consequently, the dimension in the direction of the optical axis of the barrel in the collapsed condition may be reduced. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]     The above and other objects, features and advantages of the present invention will become more apparent from the following description of the presently preferred exemplary embodiments of the invention taken in conjunction with the accompanying drawings, in which:  
         [0023]      FIG. 1  is a perspective view of an imaging apparatus as a First example of preferred embodiment of the present invention;  
         [0024]      FIG. 2  is a block view illustrating the configuration of the imaging apparatus as a First example of preferred embodiment of the present invention;  
         [0025]     FIGS.  3 (A) and  3 (B) are perspective views illustrating the conditions of a lens barrel  10 ;  
         [0026]     FIGS.  4 (A) to  4 (C) are cross-sectional views illustrating the conditions of the lens barrel  10 ;  
         [0027]      FIG. 5  is an exploded perspective view illustrating a collapsible lens;  
         [0028]      FIG. 6  is a development view of a fixed ring  20 ;  
         [0029]      FIG. 7  is a development view of a cam ring  24 ;  
         [0030]      FIG. 8  is a perspective view illustrating the configuration of each of a third group lens holding frame  1802  and a base  12 ;  
         [0031]      FIG. 9  is a perspective view illustrating the configuration of each of a second lens holding frame  1602 , the third group lens holding frame  1802 , and the base  12 ;  
         [0032]      FIG. 10  is a perspective view illustrating the configuration of a drive mechanism  29 ;  
         [0033]      FIG. 11  is an explanatory view illustrating the configuration of each of the third group lens holding frame  1802  and the base  12 ;  
         [0034]     FIGS.  12 (A) and  12 (B) are perspective views illustrating a condition in which the third group lens holding frame  1802  is moved to a rear position;  
         [0035]      FIG. 13  is a longitudinally cross-sectional view of a lens barrel  10  in a used condition; and  
         [0036]      FIG. 14  is a longitudinally cross-sectional view of the lens barrel  10  in a collapsed condition. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0037]     An attempt at miniaturizing the barrel in the collapsed condition without requiring exclusive components is achieved by causing the rearmost lens holding frame to abut against the lens holding frame placed immediately in front of the rearmost one.  
         [0038]     Next, an example of preferred embodiment of the present invention is described hereinbelow by referring to the accompanying drawings.  
         [0039]      FIG. 1  is a perspective view of an imaging apparatus according to the example of preferred embodiment of the present invention.  FIG. 2  is a block view illustrating the configuration of the imaging apparatus according to the example of preferred embodiment of the present invention.  
         [0040]     As shown in  FIG. 1 , the imaging apparatus  100 , which constitutes this example of preferred embodiment, is a digital still camera having a case  102 , which constitutes an outer cover or body thereof.  
         [0041]     A collapsible lens barrel  10  for accommodating and holding an image-capturing optical system  104  is provided at a location to the right side of the front face of the case  102 . A flash section  106  and an objective lens  108  of an optical finder  40  are provided at a location to the top of the front face of the case  102  (see FIGS.  3 (A) and  3 (B)).  
         [0042]     The lens barrel  10  is configured in such a way as to be moved by a drive section  124  (see  FIG. 2 ), which is incorporated in the case  102 , between a use position (corresponding to a wide-angle condition, a telescopic condition, and an intermediate condition between the wide-angle condition and the telescopic condition) projecting frontwardly from the front face of the case  102  and an accommodation position (corresponding to a collapsed condition), at which the lens barrel  10  is accommodated in the front face of the case  102 .  
         [0043]     A shutter button  110  is provided on the top face of the case  102 . An eyepiece window (not shown) of the optical finder, plural operation switches  112  for performing various operations, such as the on/off of a power supply, and the changeover among a photographing mode and a reproducing mode, and a display  114  (see  FIG. 2 ) for displaying a photographed image are provided on the rear face of the case  102 .  
         [0044]     As shown in  FIG. 2 , an imaging device  116 , which is constituted by a CCD and a CMOS sensor, for electronically imaging an object, whose optical image is formed by the image-capturing optical system  104 , is disposed in the rear portion of the lens barrel  10 . The imaging apparatus  100  has an image processor  120  for generating image data according to imaging signals outputted from the imaging device  116  and for recording the image data in a storage medium  118 , and also has a display processor  122  for displaying the image data in a display  114 , a driver  124 , and a controller  126  that includes a CPU for controlling the image processor  120 , the display processor  122  and a driver  124  in response to operations performed on the operating switch  112  and the shutter button  110 .  
         [0045]     Next, the outline of the configuration of the lens barrel  10  is described hereinbelow.  
         [0046]     FIGS.  3 (A) and  3 (B) are perspective views each illustrating the condition of the lens barrel.  FIG. 3 (A) shows a lens accommodated condition, in other words, a collapsed condition in which the lens is not in use.  FIG. 3 (B) shows a lens projected condition (in other words, the wide-angle condition or the telescopic condition) in which the lens is used. FIGS.  4 (A) to  4 (C) are cross-sectional views of the lens barrel  10 .  FIG. 4 (A) shows the collapsed condition thereof.  FIG. 4 (B) shows the wide-angle condition thereof.  FIG. 4 (C) shows the telescopic condition thereof.  FIG. 5  is an exploded perspective view illustrating the lens barrel  10 .  
         [0047]     As shown in FIGS.  3 (A) and  3 (B), the lens barrel  10  is attached to a base  12  in other words fixed to the case  102 .  
         [0048]     As shown in FIGS.  4 (A) to  4 (C), the lens barrel  10  optically has a three-group configuration. In other words, assuming that an object side in the direction of an optical axis of the lens barrel  10  is a front side, and that the side of the imaging device  116  in the direction of an optical axis thereof is a rear side, three groups constituting the lens barrel  10  include a first group lens  14 , a second group lens  16 , and a third group lens  18  disposed in this order from the front side to the rear side.  
         [0049]     The first group lens  14  and the second group lens  16  of the lens barrel  10  are driven in the direction of the optical axis thereof along a predetermined camcurve to thereby perform zooming (in other words, focal length adjustment). The third group lens  18  of the lens barrel  10  is minutely displaced in the direction of the optical axis thereof to thereby perform focusing (in other words, focus adjustment). In other words, the lens barrel is configured so that the displacement of each of the first group lens  14  and the second group lens  16  enables the change of a focal length, and that a deviation of a focusing position, which is caused by this change of the focal length, is corrected by the displacement of the third group lens  18  to thereby suitably achieve focusing.  
         [0050]     As shown in  FIG. 5 , in the lens barrel  10 , a fixed ring  20 , a rotating ring  22 , a cam ring  24 , and a rectilinear guide ring  26  are used as constituents for moving the first group lens  14  and the second group lens  16  in the direction of the optical axis thereof. A guide mechanism  28  and a drive mechanism  29  are used as constituents for moving the third group lens  18  in the direction of the optical axis thereof.  
         [0051]     As shown in  FIG. 3 (B), the lens barrel  10  is of the collapsible type that comprises a first barrel  10 A, a second barrel  10 B, and a third barrel  10 C, which differ in outside diameter from one another and performs relative movement in an axial direction. The first barrel  10 A is constituted by a fixed ring  20  in other words disposed in the case  102 . The second barrel  10 B is constituted by a cam ring  24  in other words disposed inside the fixed ring  20 . The third barrel  10 C is constituted by the first group lens holding frame  1402  in other words disposed inside the cam ring  24 . Incidentally, the lens barrel is constituted by the first group lens  14 , the second group lens  16 , the third group lens  18 , and the drive systems therefor disposed in this barrel  10 .  
         [0052]     More specifically, the fixed ring  20  is fixed to the base  12 . As shown in  FIG. 6 , cam grooves  2002  and  2004 , which circumferentially extend, and a rectilinear guide groove  2006  extending in parallel with the direction of the optical axis of the image-capturing optical system are provided in an inner peripheral surface of the fixed ring  20 .  
         [0053]     The rotating ring  22  is rotatably provided on an outer periphery of the fixed ring  20  in such a way as to be unable to move in the direction of the optical axis.  
         [0054]     Plural cam grooves  2202  penetrating the inner peripheral surface and the outer peripheral surface of the rotating ring  22  and extending in the direction of the circumference thereof are provided therein. A rectilinear groove  2205  rectilinearly extending along the direction of the optical axis is provided in the inner peripheral surface of the rotating ring  22 . A gear section  2204  is formed in a rear portion of the outer peripheral surface of the rotating ring  22  in such a way as to have a predetermined length in the circumferential direction thereof. Plural fins  2206  for detecting a rotational position are provided on the rear end of the rotating ring  22  in such a manner as to project therefrom.  
         [0055]     A gear section  2204  is meshed with a gear  2302  of a rotating ring drive mechanism  23  attached to the base  12 . A rotation driving force fed from the rotating ring drive mechanism  232  is supplied to the rotating ring  22  through a gear  2302  and a gear section  2204 , so that the rotating ring  22  is driven in such a way as to rotate around the optical axis thereof.  
         [0056]     The rotating ring drive mechanism  23  has a DC motor for rotation-driving the gear  2302 , a rotary encoder for counting the number of revolutions of this DC motor or the gear  2302 , and a photo sensor for detecting the movement of the fins  2206 . The rotational speed and the rotational position of the rotating ring  22  are controlled according to detection signals of the rotary encoder and the photo sensor.  
         [0057]     The third group lens  18  is held by a third group lens holding frame  1802  that is disposed on the base  12  in such a way as to move in the direction of the optical axis thereof and as to be unable to rotate around the optical axis thereof. The third group lens moving mechanism  28  has a male screw member (or lead screw) to be screwed to a female screw member connected to the third group lens holding frame  1802 , and also has a motor for rotation-driving the third group lens  18  in the direction of the optical axis. This motor is rotation-driven to thereby move the third group lens  18  in the direction of the optical axis, so that focusing operation is performed.  
         [0058]     As shown in  FIG. 5 , a cam ring  24  is provided in a radially inner portion of the fixed ring  20  in such a way as to rotate and move in the direction of the optical axis thereof. Cam grooves  2402  and  2404  are provided in the inner peripheral surface of the cam ring  24 , as shown in  FIG. 7 . Three protruding sections  2406  projecting radially and outwardly are provided on the rear end of the cam ring  24  in such a way as to be spaced in the circumferential direction thereof, as shown in  FIG. 5 . Further, during a state in which these three protruding sections  2406  engage with the cam grooves  2002  and  2004  of the fixed ring  20 , the cam ring  24  performs rotational motions with respect to the fixed ring  20 , so that these three protruding sections  2406  are moved along the cam grooves  2002  and  2004 . Consequently, the cam ring  24  is moved in the direction of the optical axis thereof.  
         [0059]     Furthermore, at least one of the cam grooves  2002  of the fixed ring  20  penetrates therethrough. An end of an arm (not shown) provided on the protruding portion  2406  of the cam ring  24 , which corresponds to the cam groove  2002  penetrating therethrough, engages with the rectilinear groove  2205  of the rotating ring  22  through the cam grooves  2002 . Consequently, the cam ring  24  and the rotating ring  22  are connected to each other and rotate with respect to the fixed ring  20 . In other words, when the rotating ring  22  is rotated, the cam ring  24  moves in the direction of the optical axis while rotating.  
         [0060]     The rectilinear guide ring  26  is provided in the radially inner portion of the cam ring  24  in such a manner as to be unable to rotate and as to move in the direction of the optical axis by being connected to the cam ring  24 . Particularly, three protruding sections  2602  projecting radially and outwardly are provided on the rear end of the rectilinear guide ring  26  are provided by being spaced in the circumferential direction. Further, in a state in which these three protruding sections  2602  extend through the rear of the cam ring  24  and engage with the rectilinear guide grooves  2008  of the fixed ring  20 , the cam ring  24  performs rotational motions with respect to the fixed ring  20 . Thus, these three protruding sections  2602  are moved along the rectilinear guide groove  2006  of the fixed ring  20 . Consequently, the guide ring  26  are linked with the cam ring  24  and moved only in the direction of the optical axis without rotating.  
         [0061]     Further, guide pieces  2604  are provided on the rectilinear guide ring  26  in such a way as to be respectively projected frontward from two places located across a radial direction of the front edge thereof in parallel to the direction of the optical axis.  
         [0062]     The second group lens  16  is held by the second group lens holding frame  1602 . The second group lens  16  is disposed on the inner periphery of the cam ring  24 . Guide sections  16  positioned at two places, which are located across a radial direction, in such a way as to extend in parallel to the direction of the optical axis and as to be guided by two guide pieces  2604  of the rectilinear guide ring  26 , guide rails  1605  positioned at two places, which are located across a radial direction, in such a manner as to extend in parallel to the direction of the optical axis and as to frontward project, and three cam pins  1606  engaged with the cam grooves  2404  of the cam ring  24  are provided on the outer peripheral surface of the second group lens holding frame  1602 .  
         [0063]     Further, in a state in which the guide sections  1604  are guided by the guide pieces  2604  and in which the three cam pins  1606  are engaged with the cam grooves  2404  of the cam ring  24 , the cam ring  24  rotates, so that the second group lens  16  (or the second group lens holding frame  1602 ) is moved along the camcurves set in the cam grooves  2404  only in the direction of the optical axis without rotating.  
         [0064]     Therefore, in this example of preferred embodiment, the guide mechanism for holding the second group lens holding frame  1602  is constituted by the guide pieces  2604  and the guide section  1604 . The guide mechanism for moving the second group lens holding frame  1602  is constituted by the rotating ring drive mechanism  23 , the rotating ring  22 , the cam ring  24 , the cam groove  2404 , and the cam pin  1606 .  
         [0065]     The second group lens holding frame  1602  is provided with a second group light shielding plate  1608  for shielding stray light in the lens barrel  10  and for preventing stray light from entering the imaging device  116 .  
         [0066]     The second group light shielding plate  1608  is attached to the second group lens holding frame  1602  in such a way as to swing around an axis line extending in a direction parallel to a plane perpendicular to the optical axis.  
         [0067]     In a condition in which the lens barrel  10  is projected, the second group light shielding plate  1608  is placed at a shielding position for shielding light, by being pushed by a pushing member (not shown) in such a way as to abut against a stopper (not shown) provided on the second group lens holding frame  1602 . In a process in which the condition of the lens barrel  10  is changed from the projected condition to the accommodated condition, the second group light shielding plate  1608  is made to abut against the front portion of the third group lens moving mechanism  28 . Thus, the second group light shielding plate  1608  is swung from the shielding position and retreated from the front portion of the third group lens moving mechanism  28 . Consequently, the second group light shielding plate  1608  and the second group lens holding frame  1602  can be placed nearer to the vicinity of the base  12 . This is advantageous in reducing the space in the direction of the optical axis, which is occupied by the second group lens holding frame  1602 , in the accommodated condition of the lens barrel  10 .  
         [0068]     Further, an automatic exposure device  1610  having the function of a shutter and the function of an adjustable diaphragm is provided at the front portion of the second group lens holding frame  1602 . An end of a flexible wiring board  1612  made of a flexible material is connected to the automatic exposure device  1610 . An intermediate section of this flexible wiring board  1612  is led from the rear end of the cam ring  24  to the outside of the fixed ring  20  through an opening (not shown) provided in the fixed ring  20 . The other end of the flexible wiring board  1612  is fixed to the fixed ring  20  and the base  12 . The flexible wiring board  1612  is formed in such a manner as not to strain the wiring groups while a bent portion thereof continuously changes during a rotational operation of the rotating ring  22  and the movement in the direction of the optical axis of each of the second group lens holding frame  1602  and the rectilinear guide ring  26 .  
         [0069]     This flexible wiring board  1612  has a wiring group for supplying electrical signals that are used for causing an actuator group provided in the automatic exposure device  1610 . Further, the flexible wiring board  1612  has another wiring group functioning as a flow path of instantaneous large current flowing when static electricity is applied to a portion of the barrel  10 , which is exposed to the outside from the case  102 . A connecting terminal of the latter wiring group of the flexible wiring board  1612 , which is placed at the side of the base  12 , is electrically connected to a grounded portion having electric potential being equal to that of the case  102 .  
         [0070]     The first group lens  14  is held by the first group lens holding frame  1402 . The first group lens holding frame  1402  is disposed in the inner periphery of the cam ring  24  and in front of the second group lens holding frame  1602 . The inner peripheral surface of the first group lens holding frame  1602  is provided with guide grooves (not shown) formed in two places, which are located across a radial direction, in such a way as to extend in parallel to the direction of the optical axis and as to be guided by two guide rails  1605  of the second group lens holding frame  1602 , and with three cam pins  1406  engaged with the cam grooves  2404  of the cam rig  24 .  
         [0071]     Further, in a state in which the guide grooves are guided by the guide rails  1605  and in which the three cam pins  1406  are engaged with the cam grooves  2402  of the cam ring  24 , the cam ring  24  rotates, so that the first group lens  14  (thus, the first group lens holding frame  1402 ) is moved only in the direction of the optical axis along the cam curve set in the cam groove  2402  without rotating.  
         [0072]     Therefore, in this example of preferred embodiment, the guide mechanism for supporting the first group lens holding frame  1402  in such a way as to move in the direction of the optical axis is constituted by the guide rails  1605  and the guide grooves. The drive mechanism for moving the first group lens holding frame  1402  in the direction of the optical axis is constituted by the rotating ring drive mechanism  23 , the rotating ring  22 , the cam ring  24 , the cam groove  2402 , and the cam pin  1405 .  
         [0073]     Also, two metallic coil springs  15  are provided in a stretched condition between the first group lens holding frame  1402  and the second group lens holding frame  1602 . The first group lens frame  1402  and the second group lens frame  1602  are pushed by the pushing forces of these coil springs  15  in a direction in which the first group lens frame  1402  and the second group lens frame  1602  come close to each other. Consequently, the backlash between the cam pin  1406  and the cam groove  2402  and that between the cam pin  1606  and the cam groove  2404  are absorbed.  
         [0074]     Further, a conducting plate  31  is incorporated into the second lens holding frame  1602 . An end portion of one of the two coil springs  15  is locked in this conducting plate  31 . Moreover, among the connecting terminals of the latter wiring group of the flexible wiring board  1612 , the connecting terminal placed at the side of the first group lens holding frame  1402  is electrically connected to this conducting plate  31 . Consequently, the one of the coil springs  15  is connected to the grounded portion through the conducting plate  31  and the latter wiring group of the flexible wiring board  1612 .  
         [0075]     Further, a barrier mechanism  30  for opening and closing an optical path of the image-capturing optical system is provided at the front portion of the first group lens  14 . A metallic decorative ring  32  for arranging the appearance of the lens barrel  10  is attached to the front portion of the first group lens holding frame  14 . A metallic decorative ring  34  for arranging the appearance of the lens barrel is attached to the front portion of the cam ring  24 .  
         [0076]     A light shielding ring  36  for preventing dust and stray light from entering the gap between the outer periphery of the first group lens holding frame  14  and the inner periphery of the cam ring  24  is disposed in the gap therebetween. This light shielding ring  36  is attached onto the first group lens holding frame  14  and disposed in a state in which a clearance is provided between the decorative ring  34  and the cam ring  24 .  
         [0077]     A light shielding ring  38  for preventing dust and stray light from entering the gap between the outer periphery of cam ring  24  and the inner periphery of the fixed ring  20  is disposed in the gap therebetween. This light shielding ring  38  is attached to the outer periphery of the cam  24  and brought into elastic contact with the inner periphery of the fixed ring  20 .  
         [0078]     Further, the optical finder  40  incorporates a movable lens and is attached to the base  12 . The movable lens is connected to the cam groove  2202  of the rotating ring  22  through a cam pin (not shown). The movable lens moves in conjunction with the rotating ring  22  in the direction of the optical axis, so that an operation of zooming the visual field is performed.  
         [0079]     Next, the configuration of each of the third lens holding frame, the guide mechanism  28 , and the drive mechanism  29  is described hereinbelow in detail.  
         [0080]      FIG. 8  is a perspective view illustrating the configuration of each of the third group lens holding frame  1802  and the base  12 .  FIG. 9  is a perspective view illustrating the configuration of each of the second lens holding frame  1602 , the third group lens holding frame  1802 , and the base  12 .  FIG. 10  is a perspective view illustrating the configuration of the drive mechanism  29 .  FIG. 11  is an explanatory view illustrating the configuration of each of the third group lens holding frame  1802  and the base  12 .  FIG. 12 (A) is a perspective views illustrating a condition in which the third group lens holding frame  1802  is moved to a rear position.  FIG. 12 (B) is a perspective views illustrating a condition in which the third group lens holding frame  1802  is moved to a more rear position.  
         [0081]     As shown in  FIGS. 8 and 9 , the third group lens holding frame  1802  is formed like an annular plate, and holds the third group lens in the central opening thereof.  
         [0082]     As shown in  FIG. 11 , an engaging piece  1802 C is provided in such a way as to protrude radially outwardly from the outer periphery of the third group lens holding frame  1802 .  
         [0083]     Further, a first bearing portion  50  and a second bearing portion  60  are disposed at places spaced in the circumferential direction in the radially outer portions of the third group lens holding frame  1802 .  
         [0084]     Guide shafts  28 A and  12 A extending along the direction of the optical axis are passed through the first bearing portion  50  and the second bearing portion  60 , respectively. The guide shafts  28 A and  12 A are formed like, for example, a column having a uniform outside diameter, and attached to the base  12 .  
         [0085]     The guide mechanism  28  for guiding the third group lens holding frame  1802 , in other words, the movable lens in such a way as to reciprocally and rectilinearly move the lens is constituted by the guide shafts  28 A and  12 A and the first bearing portion  50  and the second bearing portion  60 .  
         [0086]     Concretely, as shown in  FIG. 11 , the attachment of the guide shaft  28 A to the base  12  is performed by supporting both the front end and the rear end of the guide shaft  28 A through the use of a guide shaft supporting wall  91  and a guide shaft pressing member  9 . In other words, both ends of the guide shaft  28 A are supported by the lens barrel  10 .  
         [0087]     The guide shaft supporting wall  91  is provided integrally with the base  12  by, for instance, die-forming.  
         [0088]     The guide shaft supporting wall  91  is constituted by two extension sections  91 A frontward extending along the optical axis from a portion of the base  12 , which faces the front face of the imaging device  116 , and an end section  91 B for connecting the ends of the extension sections  91 A. The end section  91 B faces the base  12 . Further, the two extension sections  91 A are provided at two places in such a way as to put the guide shaft  28 A therebetween along the circumferential direction.  
         [0089]     A concave portion  91 C for holding the front end of the guide shaft  28 A is provided at the end section  91 B, in other words, the front end of the guide shaft supporting wall  91 . The concave portion  91 C is formed like a bottom cylindrical hole, into which the end of the guide shaft  28 A is inserted. This bottomed hole has a D-shaped cross-section, for example.  
         [0090]     A hole portion is provided in the front portion of the base  12 , which faces the guide shaft supporting wall  91 . The guide shaft pressing member  9  is mounted in the hole portion. The guide shaft pressing member  9  is provided with a fitting hole  9 A for holding the rear end of the guide shaft  28 A. This fitting hole  9 A has, for instance, a D-shaped cross-section.  
         [0091]     When the guide shaft  28 A is in a state in which the front end thereof is inserted into the concave portion  91 C, and which the rear end thereof is fitted into and fixed to the fitting hole  9 A, the guide shaft pressing member  9   s  is moved in a direction perpendicular to a direction, in which the guide shaft  28 A extends. Thus, the position thereof is adjusted so that the optical axis of the third group lens  18  is parallel to those of the first group lens and the second group lens. During such a state, the guide shaft pressing member  9  and the base  12  are bonded and fixed to each other by an adhesive agent.  
         [0092]     The drive mechanism  29  is operative to move the third group lens holding frame  1802  in the direction of the optical axis, as shown in  FIGS. 10 and 11 . The drive mechanism  29  has a male screw member  2902  extending along the direction of the optical axis, a motor  2904  constituted by a stepping motor for turning the male screw member  2902 , a female screw member  2906  (which may be referred to from time to time as the moving piece)) to be screwed to the male screw member  2902 , the engaging piece  1802 C of the third group lens holding frame  1802 , and a coil spring  2908 . A metallic material is used as the material of the male screw member  2902  and the female screw member  2906 .  
         [0093]     As shown in  FIG. 10 , the motor  2904  is attached to a motor disposing member  2910 . The male screw member  2902  is connected to the motor  2904  and extends in a direction parallel to the direction of the optical axis of the third group lens  18 .  
         [0094]     The motor disposing member  2910  has a first supporting piece  2910 A to be attached to the end face of the case of the motor  2904 , a second supporting piece  2910 B facing the first supporting piece  2910 A, and a third supporting piece  2910 C connecting the first supporting piece  2910 A and the second supporting piece  2910 B to each other.  
         [0095]     The first supporting piece  2910 A is provided with a projecting portion  2910 D formed in such a way as to project along a face perpendicular to the direction in which the male screw member  2902  extends. A screw insertion hole  2910 E and a positioning hole  2910 F are formed in this projecting portion  2910 D. In a state in which the positioning hole  2910 F is engaged with the boss of the base  12 , as shown in  FIG. 8 , a screw  202  is screwed into a screw hole provided in the base  12  from the hole  2910 E, so that the motor disposing member  2910  is attached to the base  12 . Incidentally, an engaging groove  2910 E- 1  is formed in a radially outward portion of the screw insertion hole  2910 E. The engaging groove  2910 E- 1  is engaged with a protruding portion provided at the side of the base  12 . This prevents the motor disposing member  2910  from swinging around the hole  2910 E.  
         [0096]     As shown in  FIG. 10 , the third supporting piece  2910 C extends from the base end of the first supporting piece  2910 A. The second supporting piece  2910 B is provided at an end of the third supporting piece  2910 C.  
         [0097]     The end of the male screw member  2902  (in other words, the front end in the direction of the optical axis of the third group lens  18 ) is rotatably supported through a bearing hole of the second supporting piece  2910 B.  
         [0098]     A rod  2912  for whirl-stop is mounted between the first supporting piece  2910 A and the second supporting piece  2910 B of the motor disposing member  2910  in such a manner as to be spaced from the male screw member  2902  and as to extend nearly in parallel thereto.  
         [0099]     The female screw member  2906  is screwed into the male screw member  2902 . An engaging concave portion  2906 B of the female screw member  2906  engages with the rod  2912  to thereby block the rotation of the female screw member  2906 . The female screw member  2906  is reciprocally moved along the longitudinal direction of the male screw member  2902  by the normal rotation and the reverse rotation of the male screw member  2902 .  
         [0100]     An end portion  2906 A of the female screw member  2906 , which faces the rear in the direction of the optical axis of the third group lens  18 , is provided in such a way as to abut against an engaging portion  1802 B, which is a portion of the outer periphery of the third group lens holding frame  1802 .  
         [0101]     The male screw member  2902  has a male screw portion  2902 A to be screwed into the female screw member  2906 , as shown in  FIGS. 10 and 11 . The female screw member  2906  is disposed in such a manner as to move along the male screw member  2902  over the entire length in the direction in which the male screw portion  2902 A thereof extends.  
         [0102]     The coil spring  2908  is provided by being wound around the guide shaft  28 A so that an end of the coil spring  2908  is locked in the third group lens holding frame  1802 , while the other end thereof is locked in the base side  12  (in other words, the guide shaft pressing member  9 ). The third group lens holding frame  1802  is pushed in a direction in which the engaging portion  1802 C is caused to abut against the end portion  2906 A of the female screw member  2906 . In other words, the coil spring  2908  pushes the third group lens holding frame  1802  frontward in the direction of the optical axis to thereby cause the engaging portion  1802 C of the third group lens holding frame  1802  to always abut against the female screw member  2906 . Thus, the third group lens holding frame  1802 , in other words, the third group lens  18  reciprocally and rectilinearly moves by following the motion of the female screw member  2906 .  
         [0103]     Therefore, in a case where it is assumed that the normal rotation of the motor  2904  causes the third group lens  18  (thus, the third group lens holding frame  1802 ) to frontward move in the direction of the optical axis, and that the reverse rotation thereof causes the third group lens  18  to backwardly move in the direction of the optical axis, the female screw member  2906  is moved frontward in response to the normal rotation of the male screw member  2902 . Consequently, the third group lens  18  (in other words, the third group lens holding frame  1802 ) is moved frontward in the direction of the optical axis. The normal rotation and the reverse rotation of the motor  2904  causes the female screw member  2906  to reciprocally and rectilinearly move in the direction of the optical axis on the male screw portion  2902 A. Consequently, the third group lens  18  is moved in the direction of the optical axis.  
         [0104]     In this example of preferred embodiment, as shown in  FIG. 13 , among the first group lens holding frame  1402 , the second group lens holding frame  1602 , and the third group lens holding frame  1802 , the third group lens frame  1802  is placed at the rearmost position. The second group lens holding frame  1602  is placed immediately in front of the third group lens holding frame  1802 .  
         [0105]     As shown in  FIGS. 9, 12 , and  13 , in the vicinity of the first bearing portion  50  at the front portion of the third group lens holding frame  1802 , in this example of preferred embodiment, at an intermediate between the first bearing portion  50  and the engaging piece  1802 C, an abutting portion  1802 D is provided in such a way as to frontward project. An end of the abutting portion  1602 D constitutes a flat face perpendicular to the optical axis.  
         [0106]     Further, as shown in  FIG. 13 , in the rear portion of the second group lens holding frame  1602 , the abutting portion  1602 D, which can abut against the abutting portion  1802 D of the third group lens holding frame  1802 , is provided at a place corresponding to the abutting portion  1802 D thereof in such away as to frontward project therefrom. An end of the abutting portion  1602 D constitutes a flat face perpendicular to the optical axis.  
         [0107]     Furthermore, this example of preferred embodiment is configured so that a clearance is assured between the rear surface of the lens, which is disposed at the rearmost position among those of the second group lens  16 , and the front face of the lens, which is disposed at the frontmost position among those of the third group lens  1802 , in a state in which the abutting portion  1602 D of the second group lens holding frame  1602  abuts against the abutting portion  1802 D of the third group lens holding frame  1802 , as shown in  FIG. 14 .  
         [0108]     Next, an operation of the barrel  10  is described hereinbelow.  
         [0109]      FIG. 13  is a longitudinally cross-sectional view of the barrel  10  in a used condition.  FIG. 14  is a longitudinally cross-sectional view of the barrel  10  in a collapsed condition.  
         [0110]     First, the used condition is described hereunder. As shown in  FIG. 13 , the rotating ring  22  is rotation-driven by the rotating ring drive mechanism  23 . Thus, the cam ring  24  and the first group lens holding frame  1402  are frontward projected from the case  102 . In other words, the first barrel  10 A and the second barrel  10 B are brought into the used condition in which the first barrel  10 A and the second barrel  10 B are most frontward projected therefrom.  
         [0111]     A zooming operation is performed by moving the second group lens holding frame  1602  frontward and rearward along the direction of the optical axis through the use of the drive mechanism for the second group lens holding frame  1602 . A focusing operation is performed by moving the third group lens holding frame  1802  frontward and rearward along the direction of the optical axis through the use of the drive mechanism  29  for the third group lens holding frame  1802 .  
         [0112]     Next, the collapsed condition is described hereinbelow.  
         [0113]     First, regarding the barrel  10 , as shown in  FIG. 14 , the rotating ring  22  is rotation-driven by the rotating ring drive mechanism  23 . Thus, the cam ring  24  and the first group lens holding frame  1402  retreat and are accommodated in the case  102 . Consequently, the barrel  10  is put into a collapsed condition in which a total length of the first barrel  10 A, the second barrel  10 B, and the third barrel  10 C is minimum.  
         [0114]     Next, regarding the lens holding frame, when the state thereof is changed from the used condition to the collapsed condition, the third group lens holding frame  1802  is retreated by the drive mechanism  29  to a predetermined rear position, in other words, to the rear end position that is the rearmost position. Then, the second group lens holding frame  1602  is rearward moved by the drive mechanism therefor and made to abut against the third group lens holding frame  1802  that is placed at the rear end position. Subsequently, the second group lens holding frame  1602  is more rearward moved to the rear end position of the second group lens holding frame  1602  that is moved to the rearmost position. Therefore, the third group lens holding frame  1802  is more backwardly moved, together with the second group lens holding frame  1602 , by the drive mechanism  29  from the rear end position to which the third group lens holding frame  1802  has been moved by the drive mechanism  29 . At the rear end position of the second group lens holding frame  1602 , to which the second group lens holding frame  1602  is most backwardly moved by the drive mechanism therefor, the coil spring  2808  is compressed, so that the female screw member  2906  is separated from the engaging piece  1802 C. Further, the first group lens holding frame  1402  is retreated to the rear end position at which the predetermined clearance between the first group lens holding frame  1402  and the second group lens holding frame  1602  placed at the rear end position is maintained.  
         [0115]     Thus, in the collapsed condition, a clearance is ensured among the third group lens holding frame  1802 , the base  12  and a member attached to the base  12 , in other words, the member attached to the inner rear end of the barrel  10 .  
         [0116]     According to this example of preferred embodiment, in the collapsed condition of the barrel  10 , it is sufficient to ensure clearances provided at two places, in other words, a clearance between the first group lens holding frame  1402  and the second group lens holding frame  1602 , and a clearance between the third group lens holding frame  1802  and the member attached to the inner rear end of the barrel  10 . Thus, as compared with the conventional case where clearances provided at three places, in other words, the clearance between the first group lens holding frame  1402  and the second group lens holding frame  1602 , the clearance between the second group lens holding frame  1602  and the third group lens holding frame  1802 , and the clearance between the third group lens holding frame  1802  and the member attached to the inner rear end of the barrel  10  should be ensured, the assurance of the clearance at one of the places can be omitted. Consequently, the size in the direction of the optical axis of the barrel  10  can be reduced.  
         [0117]     Further, when the second group lens holding frame  1602  is made to abut against the third group lens holding frame  1802 , the coil spring  2808  for pushing the third group lens holding frame  1802  in a direction, in which the third group lens holding frame  1802  abuts against the female screw member  2906 , is utilized and compressed. Thus, the second group lens holding frame  1602  can be made to abut against the third group lens holding frame  1802 , without increasing the number of components, and without damaging the drive mechanism for the second group lens holding frame  1602  and the drive mechanism  29  for the third group lens holding frame  1802 .  
         [0118]     Further, in the collapsed condition, the female screw member  2906  of the drive mechanism  29  is separated from the engaging piece  1802 C of the third group lens holding frame  1802 . Thus, it is unnecessary to precisely control the rear end position of the third group lens holding frame  1802 . Therefore, it is also unnecessary for the drive mechanism  29  to exactly control an amount of movement of the third group lens holding frame  1802  placed at the rear end position thereof. Consequently, this example of preferred embodiment is advantageous in that it may simplify a controlling operation.  
         [0119]     Additionally, in this example of preferred embodiment, the place, at which the second group lens holding frame  1602  abuts against the third group lens holding frame  1802 , is positioned in the vicinity of the portion through which the guide shaft  2808  penetrates. Thus, a prizing force can be prevented from being generated between the first bearing portion  50  of the third group lens holding frame  1802  and the guide shaft  2808  when the third group lens holding frame  1802  is retreated after the second group lens holding frame  1602  abuts against the third group lens holding frame  1802 . Thus, this example of preferred embodiment is advantageous in smoothly retreating the third group lens holding frame  1802 .  
         [0120]     By the way, although the description of this example of preferred embodiment has described the digital still camera employed as the imaging apparatus, the present invention can be applied to various kinds of the imaging apparatus, such as a video camera. Therefore, while the preferred embodiments of the present invention have been described with reference to the attached drawings, it is to be understood that the present invention is not limited to the embodiments described above. It will be obvious to those of ordinary skill in the art that various changes, modifications, combinations, sub combinations, alterations and the like may be made depending on design requirements and other factors insofar as they are within the scope of the appended claims and equivalents thereof.