Patent Publication Number: US-6657793-B2

Title: Lens barrel

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application relates to the following U.S. patent applications, all filed concurrently herewith on Sep. 24, 2001, and all of which are expressly incorporated herein by reference in their entireties: “ZOOM LENS MECHANISM” having U.S. application Ser. No. 09/960,308, “ZOOM LENS MECHANISM” having U.S. application Ser. No. 09/961,231, “ECCENTRICITY-PREVENTION MECHANISM FOR A PAIR OF LENS-SUPPORTING RINGS” having U.S. application Ser. No. 09/960,515, “REDUCTION GEAR MECHANISM” U.S. application Ser. No. 09/960,521, “RING MEMBER SHIFT MECHANISM AND LENS GROUP SHIFT MECHANISM” having U.S. application Ser. No. 09/960,518, “LENS BARREL” having U.S. application Ser. No. 09/960,520, “LENS BARREL” having U.S. application Ser. No. 09/960,382, “LENS BARREL” having U.S. application Ser. No. 09/960,516, “LENS BARREL” having U.S. application Ser. No. 09/961,233, and “ZOOM LENS BARREL” having U.S. application Ser. No. 09/961,185, each naming as inventors Hiroshi NOMURA et al.; and “LENS DRIVE CONTROL APPARATUS FOR ZOOM LENS SYSTEM HAVING A SWITCHING LENS GROUP” having U.S. application Ser. No. 09/961,186 and naming as inventor Norio NUMAKO. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a lens barrel suitable for use with a zoom lens system such as that proposed by the assignee of the present application in U.S. patent application No. 09/534,307 (Japanese Patent Application No. Hei 11-79572). 
     2. Description of the Related Art 
     In a zoom lens system of the prior art, there are contradictory demands for a high zoom ratio and miniaturization. For example, in a two-lens-group zoom lens system which can be miniaturized, if the paths of the lens groups thereof (hereinafter, zoom paths) are determined (i.e., solutions for zoom paths) so that the zoom ratio becomes high, interference of the lens groups occurs on the telephoto side, or interference of a lens group and the image plane occurs on the wide-angle side. On the other hand, in a three-lens-group zoom lens system, the zoom ratio thereof can be made higher than that of a two-lens-group zoom lens system; however, miniaturization is difficult. Furthermore, if an attempt is made to obtain a higher zoom ratio, and if the power of these three lens groups is determined accordingly, precision on the operations of the zoom lens system cannot be obtained due to the mechanical structure thereof. 
     The assignee of the present application has proposed an unprecedented zoom lens system that meets the contradictory demands of high zoom ratio and miniaturization (U.S. patent application No. 09/534,307). This zoom lens system has the following characteristics: it includes a plurality of movable lens groups for varying the focal length; at least one of the lens groups is a switching lens group which includes two sub-lens groups, one of the sub-lens groups being a movable sub-lens group that can be selectively positioned at either one movement extremities in the optical axis direction with respect to the other sub-lens group; the movable sub-lens group of the switching lens group is positioned at an extremity of a short-focal-length zooming range, from the short focal length extremity to an intermediate focal length, and at the opposite extremity of a long-focal-length zooming range, from the intermediate focal length to a long focal length extremity; and zoom paths of the switching lens group and the other lens groups are discontinuous at the intermediate focal length and are defined to focus on a predetermined image plane corresponding to the position of the movable sub-lens group. There may be one or more intermediate focal lengths. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is an object of the present invention to provide a lens barrel suitable for use with a zoom lens system that includes the switching lens group as described above. 
     In order to achieve the above-mentioned object, a lens barrel having a zoom lens system is provided, the zoom lens system including a plurality of variable power lens groups which are movable in an optical axis direction for varying the focal length of the zoom lens system; wherein at least one of the variable power lens groups includes a switching lens group having two sub-lens groups, one of the sub-lens groups constituting a movable sub-lens group that is selectively positioned at one of two movement extremities, in the optical axis direction, with respect to the other of the sub-lens groups; the movable sub-lens group of the switching lens group is positioned at one of the movement extremities in a short-focal-length side zooming range from a short focal length extremity to an intermediate focal length, and at the other of the movement extremities in a long-focal-length side zooming range from the intermediate focal length to a long-focal-length extremity; zoom paths of the two sub-lens groups of the switching lens group and the other of the variable power lens groups are discontinuous at the intermediate focal length and are defined so that the zoom lens system forms an image on a predetermined image plane in accordance with a position of the movable sub-lens group; and the switching lens group is a focusing lens group which integrally advances and retreats in the optical axis direction regardless of the zooming range. The lens barrel includes a first sub-lens group frame for supporting one of the sub-lens groups; a second sub-lens group frame for supporting the other of the sub-lens groups; a switching lens group frame for supporting the first sub-lens group frame and the second sub-lens group frame in this order from object side in such a manner that allows the first and second sub-lens group frames to move in the optical axis direction; a lens shutter mechanism secured to the switching lens group frame on the image side of the second sub-lens group frame; and a focusing mechanism for making the second sub-lens group frame advance or retreat, depending on the object distance, with respect to a reference position provided by the lens shutter mechanism secured to the switching lens group frame. The first sub-lens group frame is moved along with the second sub-lens group frame in the optical axis direction in the long-focal-length zooming range and in the short-focal-length zooming range via the focusing mechanism. 
     In an embodiment, the first sub-lens group frame is maintained in a mutually close position with respect to the second sub-lens group frame in the long-focal-length zooming range and maintained in a mutually distant position with respect to the second sub-lens group frame in the short-focal-length zooming range; and the first sub-lens group frame is moved along integrally with the second sub-lens group frame by the focusing mechanism in the optical axis direction, in the mutually close position and in the mutually distant position. 
     In an embodiment, the switching lens group frame is moved so that the path of the lens shutter mechanism is not discontinuous between the short-focal-length zooming range and the long-focal-length zooming range, which extend on both sides of the intermediate focal length. 
     In an embodiment, a diaphragm mechanism is further secured to the switching lens group frame on the object side of the lens shutter mechanism. 
     According to another aspect of the present invention, a lens barrel having a zoom lens system, the zoom lens system including a plurality of variable power lens groups which are movable in an optical axis direction for varying the focal length of the zoom lens system, at least one of the variable power lens groups including a switching lens group having two sub-lens groups functioning optically in a mutually close position and in a mutually distant position, in the optical axis direction, the lens barrel includes a first sub-lens group frame for supporting one of the sub-lens groups; a second sub-lens group frame for supporting the other of the sub-lens groups; a switching lens group frame for supporting the first sub-lens group frame and the second sub-lens group frame in this order from object side in such a manner that allows the first and second sub-lens group frames to move in the optical axis direction; a lens shutter mechanism secured to the switching lens group frame on the image side of the second sub-lens group frame; and a focusing mechanism for making the second sub-lens group frame advance or retreat, depending on object distance, with respect to a reference position provided by the lens shutter mechanism secured to the switching lens group frame. The first sub-lens group frame is moved along with the second sub-lens group frame in the optical axis direction in the long-focal-length zooming range and in the short-focal-length zooming range via the focusing mechanism. 
     The present disclosure relates to subject matter contained in Japanese Patent Application No. 2000-293761 (filed on Sep. 27, 2000) which is expressly incorporated herein in its entirety. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic drawing of a first embodiment of a zoom lens system having switching lens groups and the fundamental zoom path thereof, to which the present invention is applied. 
     FIG. 2 is a schematic drawing of a second embodiment of a zoom lens system having switching lens groups and the fundamental zoom path thereof, to which the present invention is applied. 
     FIG. 3 is a schematic drawing of a third embodiment of a zoom lens system having switching lens groups and the fundamental zoom path thereof, to which the present invention is applied. 
     FIG. 4 is a schematic drawing of a fourth embodiment of a zoom lens system having switching lens groups and the fundamental zoom path thereof, to which the present invention is applied. 
     FIG. 5 is a schematic drawing of a fifth embodiment of a zoom lens system having switching lens groups and the fundamental zoom path thereof, to which the present invention is applied. 
     FIG. 6 is a schematic drawing of a sixth embodiment of a zoom lens system having switching lens groups and the fundamental zoom path thereof, to which the present invention is applied. 
     FIG. 7 is a schematic drawing of a seventh embodiment of a zoom lens system having switching lens groups and the fundamental zoom path thereof, to which the present invention is applied. 
     FIG. 8 shows one example of stopping positions of the lens groups when a photographic operation is carried out, to which the present invention is applied. 
     FIG. 9A shows an example of the stopping positions of FIG.  8  and an example of an actual zoom path of the lens groups, to which the present invention is applied. 
     FIGS. 9B and 9C depict an additional schematic view of the concepts shown in FIGS. 8 and 9A. 
     FIG. 10 is a cross-sectional view showing an embodiment of a zoom lens barrel which includes the zoom lens systems having switching lens groups shown in FIGS. 1,  8  and  9 . 
     FIG. 11 is a developed view of an inner surface of a cam ring of the zoom lens barrel of FIG. 10 showing an exemplary arrangement of cam grooves. 
     FIG. 12 is an exploded perspective view showing components of a switching lens group frame of the zoom lens barrel. 
     FIG. 13 is an exploded perspective view showing some of the components of the switching lens group frame of the zoom lens barrel. 
     FIG. 14 is a perspective view showing a different assembly of some of the components of the switching lens group frame of the zoom lens barrel. 
     FIG. 15 is a cross-sectional view of an upper half of the switching lens group in which a first sub-lens group and a second sub-lens group are in a mutually distant position at the wide-angle extremity. 
     FIG. 16 is a cross-sectional view of an upper half of the switching lens group in which the first sub-lens group and the second sub-lens group are in a mutually close position at the telephoto extremity. 
     FIG. 17A is an exploded view in which components are exploded in the optical axis direction, wherein the first sub-lens group and the second sub-lens group are in the mutually distant position at the wide-angle side and are focused on an object at infinity. 
     FIG. 17B is a developed view showing the components of FIG. 17A in actual engagement. 
     FIG. 18A is an exploded view in which components are exploded in the optical axis direction, wherein the first sub-lens group and the second sub-lens group are in the mutually distant position at the wide-angle side and are focused on an object at a minimum distance. 
     FIG. 18B is a developed view showing the components of FIG. 18A in actual engagement. 
     FIG. 19A is an exploded view in which components are exploded in the optical axis direction, wherein the first sub-lens group and the second sub-lens group are in the mutually close position at the telephoto side and are focused on an object at infinity. 
     FIG. 19B is a developed view showing the components of FIG. 19A in actual engagement. 
     FIG. 20A is an exploded view in which components are exploded in the optical axis direction, wherein the first sub-lens group and the second sub-lens group are in the mutually close position at the telephoto side and are focused on an object at a minimum distance. 
     FIG. 20B is a developed view showing the components of FIG. 20A in actual engagement. 
     FIG. 21 is an exploded view illustrating how the mutually close position of the first sub-lens group and the second sub-lens group on the telephoto side switches to/from the mutually distant position on the wide-angle side via the rotation of an actuator ring. 
     FIG. 22 illustrates how focusing is carried out by the actuator ring. 
     FIG. 23 is an enlarged expanded view showing a face cam of a first sub-lens group frame. 
     FIG. 24 is an enlarged developed view showing the relationship of the first sub-lens group frame, the second sub-lens group frame, and the actuator ring with respect to a front shutter retaining ring. 
     FIG. 25 is a front view showing the relationship between the first sub-lens group frame and the front shutter retaining ring when viewed in a direction of the arrows indicated by a line XXV—XXV in FIG.  14 . 
     FIG. 26 is a partially enlarged view showing an encircled portion indicated by XXVI in FIG.  25 . 
     FIG. 27 is a front view showing the relationship between the second sub-lens group frame and the front shutter retaining ring when viewed in a direction of the arrows indicated by the line XXVII—XXVII in FIG.  14 . 
     FIG. 28 is a partially enlarged view showing an encircled part XXVIII in FIG.  27 . 
     FIG. 29 is a front view showing an arrangement of reduction gears of a driving system of the actuator ring, the reduction gears being retained between the front shutter retaining ring and the gear holding ring. 
     FIG. 30 is a developed plan view of FIG.  29 . 
     FIG. 31 is a block diagram showing a control system of the zoom lens barrel shown in FIG.  10 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     First, embodiments of a zoom lens system with a switching lens group proposed in the U.S. patent application No. 09/534,307 will be herein described. U.S. patent application No. 09/534,307 is expressly incorporated herein by reference in its entirety. 
     FIG. 1 shows the first embodiment of the zoom lens system. The zoom lens system includes a positive first variable lens group  10 , and a negative second variable lens group  20 , in that order from the object side. The first variable lens group  10  includes a negative first lens group L 1  (first sub-lens group S 1 ) and a positive second lens group L 2  (second sub-lens group S 2 ), in that order from the object side. The second variable lens group  20  includes a negative third lens group L 3 . The second sub-lens group S 2  of the first variable lens group  10  is fixed to a first lens group frame  11 . The first sub-lens group S 1  is mounted on a movable sub-lens group frame  12 . The movable sub-lens group frame  12  is arranged to move in the optical axis direction, by a predetermined distance, along a guide groove  13  which is formed on the first lens group frame  11 . The first sub-lens group S 1  is selectively moved to either the object-side movement extremity at which the movable sub-lens group frame  12  comes into contact with the front end of the guide groove  13 , or the image-side movement extremity at which the movable sub-lens group frame  12  comes into contact with the rear end of the guide groove  13 . The third lens group L 3  is fixed to a second lens group frame  21 . A diaphragm D is arranged to move together with the first variable lens group  10  (first lens group frame  11 ). Throughout FIGS. 1 through 9, IM indicates an image plane (film surface, and so forth) which is at a predetermined position. 
     In the zoom paths according to the first embodiment, the first variable lens group  10  (first lens group frame  11 ), the second variable lens group  20  (second lens group frame  21 ), and the first sub-lens group S 1  (movable sub-lens group frame  12 ) move in the following manner: 
     [A] In a short-focal-length zooming range Zw from the short focal length extremity fw to an intermediate focal length fm, the first sub-lens group S 1  and the second sub-lens group S 2  maintain a distance d 1  therebetween (first separation space/wide space); and the first variable lens group  10  (first lens group frame  11 ) and the second variable lens group  20  (second lens group frame  21 ) move towards the object side while mutually changing the distance therebetween. 
     [B] At the intermediate focal length fm, the first variable lens group  10  and the second variable lens group  20  move towards the image side at the long focal-length extremity of the short-focal-length zooming range Zw; and the first sub-lens group S 1  moves to the image-side movement extremity of the guide groove  13 , wherein the first sub-lens group S 1  moves toward the second sub-lens group S 2  so that the distance therebetween is determined by a shorter distance (second separation space/narrow space) d 2 . 
     [C] In a long-focal-length zooming range Zt from the intermediate focal length fm to the long focal length extremity ft, the first sub-lens group S 1  maintains the shorter distance (second separation space/narrow space) d 2  with respect to the second sub-lens group S 2 ; and the first variable lens group  10  and the second variable lens group  20  move towards the object, based on the positions thereof which are determined at the intermediate focal length fm, after the first through third lens groups L 1  through L 3  have been moved towards the image side, while changing the distance therebetween. 
     The zoom paths for the first variable lens group  10  and the second variable lens group  20  are simply depicted as straight lines in FIG.  1 . It should be noted, however, that the actual zoom paths are not necessarily straight lines. 
     Focusing is performed by integrally moving, in the optical axis direction, the first sub-lens group S 1  and the second sub-lens group S 2 , i.e., the first variable lens group  10  (first lens group frame  11 ) regardless of the zooming range. 
     FIG. 2 shows the second embodiment of the zoom lens system. The zoom lens system includes a positive first variable lens group  10 , a positive second variable lens group  20 , and a negative third variable lens group  30 , in that order from the object side. The first variable lens group  10  includes a positive first lens group L 1 . The second variable lens group  20  includes a negative second lens group L 2  (first sub-lens group S 1 ) and a positive third lens group L 3  (second sub-lens group S 2 ), in that order from the object side. The third variable lens group  30  includes a negative fourth lens group L 4 . The first lens group L 1  is fixed to a first lens group frame  11 . The second sub-lens group S 2  of the second variable lens group  20  is fixed to a second lens group frame  21 . The first sub-lens group S 1  is mounted on a movable sub-lens group frame  22 . The movable sub-lens group frame  22  is arranged to move, in the optical axis direction, by a predetermined distance, along a guide groove  23  which is formed on the second lens group frame  21 . The first sub-lens group S 1  is selectively moved to either the object-side movement extremity at which the movable sub-lens group frame  22  comes into contact with the front end of the guide groove  23 , or the image-side movement extremity at which the movable sub-lens group frame  22  comes into contact with the rear end of the guide groove  23 . The fourth lens group L 4  is fixed to a third lens group frame  31 . A diaphragm D is arranged to move together with the second variable lens group  20  (second lens group frame  21 ). 
     In the zoom paths according to the second embodiment, the first variable lens group  10  (first lens group frame  11 ) the second variable lens group  20  (second lens group frame  21 ), the third variable lens group  30  (third lens group frame  31 ), and the first sub-lens group S 1  (movable sub-lens group frame  22 ) move in the following manner: 
     [A] In a short-focal-length zooming range Zw from the short focal length extremity fw to an intermediate focal length fm, the first sub-lens group S 1  and the second sub-lens group S 2  maintain a distance d 1  (first separation space/wide space); and the first variable lens group  10  (first lens group frame  11 ), the second variable lens group  20  (second lens group frame  21 ) and the third variable lens group  30  (third lens group frame  31 ) move towards the object side while mutually changing the distances therebetween. 
     [B] At the intermediate focal length fm, the first variable lens group  10 , the second variable lens group  20  and the third variable lens group  30  are moved towards the image side at the long focal-length extremity of the short-focal-length zooming range Zw; and the first sub-lens group S 1  moves to the image-side movement extremity of the guide groove  23 , wherein the first sub-lens group S 1  moves toward the second sub-lens group S 2  so that the distance therebetween is determined by a shorter distance (second separation space/narrow space) d 2 . 
     [C] In a long-focal-length zooming range Zt from the intermediate focal length fm to the long focal length extremity ft, the first sub-lens group S 1  and the second sub-lens group S 2  maintain the shorter distance d 2 ; and the first variable lens group  10 , the second variable lens group  20  and third variable lens group  30  move towards the object side based on the positions thereof which are determined at the intermediate focal length fm, after the first through fourth lens groups  1  through  4  have been moved towards the image side, while changing the distances therebetween. 
     The zoom paths for the first variable lens group  10 , the second variable lens group  20  and the third variable lens group  30  are simply depicted as straight lines in FIG.  2 . It should be noted, however, that actual zoom paths are not necessarily straight lines. 
     Focusing is performed by integrally moving, in the optical axis direction, the first sub-lens group S 1  and the second sub-lens group S 2 , i.e., the second variable lens group  20  (second lens group frame  21 ) regardless of the zooming range. 
     Likewise with the first embodiment, the zoom paths are discontinuous at the intermediate focal length fm; however, a solution for continuously forming a correct image plane exists by appropriately determining the positions of the first lens group L 1 , the first sub-lens group S 1  (second lens group L 2 ) and the second sub-lens group S 2  (third lens group L 3 ) and the fourth lens group L 4  respectively at the short focal length extremity fw, the intermediate focal length fm (discontinuous line) and the long focal length extremity ft. According to such a zoom path, a miniaturized zoom lens system having a high zoom ratio can be obtained. 
     FIG. 3 shows the third embodiment of the zoom lens system with a switching lens system. In this embodiment, the first lens group L 1  is constructed so as to have negative refractive power, which is the only difference compared with the second embodiment. Apart from this characteristic, the third embodiment is substantially the same as the second embodiment. 
     FIG. 4 shows the fourth embodiment of the zoom lens system with a switching lens group. The zoom lens system includes a positive first variable lens group  10 , and a negative second variable lens group  20 , in that order from the object side. The first variable lens group  10  includes a negative first lens group L 1  (first sub-lens group S 1 ) and a positive second lens group L 2  (second sub-lens group S 2 ), in that order from the object side. The second variable lens group  20  includes a positive third lens group L 3  (third sub-lens group S 3 ) and a negative fourth lens group L 4  (fourth sub-lens group S 4 ), in that order from the object side. 
     The second sub-lens group S 2  of the first variable lens group  10  is fixed to a first lens group frame  11 . The first sub-lens group S 1  is mounted on a movable sub-lens group frame  12 . The movable sub-lens group frame  12  is arranged to move in the optical axis direction, by a predetermined distance, along a guide groove  13  which is formed on the first lens group frame  11 . The first sub-lens group S 1  is selectively moved to either the object-side movement extremity at which the movable sub-lens group frame  12  comes into contact with the front end of the guide groove  13 , or the image-side movement extremity at which the movable sub-lens group frame  12  comes into contact with the rear end of the guide groove  13 . Similarly, the fourth sub-lens group S 4  of the second variable lens group  20  is fixed to a second lens group frame  21 . The third sub-lens group S 3  is mounted on a movable sub-lens group frame  22 . The movable sub-lens group frame  22  is arranged to move in the optical axis direction, by a predetermined distance, along a guide groove  23  which is formed on the second lens group frame  21 . The third sub-lens group S 3  is selectively moved to either the object-side movement extremity at which the movable sub-lens group frame  22  comes into contact with the front end of the guide groove  23 , or the image-side movement extremity at which the movable sub-lens group frame  22  comes into contact with the rear end of the guide groove  23 . A diaphragm D is arranged to move together with the first variable lens group  10  (first lens group frame  11 ). 
     In the zoom paths according to the fourth embodiment, the first variable lens group  10  (first lens group frame  11 ), the second variable lens group  20  (second lens group frame  21 ), the first sub-lens group S 1 , and the third sub lens group S 3  move in the following manner: 
     [A] In a short-focal-length zooming range Zw from the short focal length extremity fw to an intermediate focal length fm, the first sub-lens group S 1  and the second sub-lens group S 2  maintain a distance d 1  therebetween (first separation space/wide space), and the third sub-lens group S 3  and the fourth sub-lens group S 4  maintain a distance d 3  therebetween (first separation space/wide space); and the first variable lens group  10  (first lens group frame  11 ) and the second variable lens group  20  (second lens group frame  21 ) move towards the object side while mutually changing the distance therebetween. 
     [B] At the intermediate focal length fm, the first variable lens group  10  and the second variable lens group  20  are moved towards the image side at the long focal-length extremity of the short-focal-length zooming range Zw; and the first sub-lens group S 1  moves to the image-side movement extremity of the guide groove  13 , wherein the first sub-lens group S 1  moves toward the second sub-lens group S 2  so that the distance therebetween is determined by a shorter distance (second separation space/narrow space) d 2 , and also the third sub-lens group S 3  moves toward the fourth sub-lens group S 4  so that the distance therebetween is determined by a shorter distance (second separation space/narrow space) d 4 . 
     [C] In a long-focal-length zooming range Zt from the intermediate focal length fm to the long focal length extremity ft, the first sub-lens group S 1  and the second sub-lens group S 2  maintain the shorter distance d 2  therebetween, and the third sub-lens group S 3  and the fourth sub-lens group S 4  maintain the shorter distance d 4  therebetween; and the first variable lens group  10  and the second variable lens group  20  move towards the object side based on the positions thereof which are determined at the intermediate focal length fm, after the first through fourth lens groups L 1  through L 4  have been moved towards the image side, while changing the distance therebetween. 
     The zoom paths for the first variable lens group  10  and the second variable lens group  20  are simply depicted as straight lines in FIG.  4 . It should be noted, however, that the actual zoom paths are not necessarily straight lines. 
     Focusing is performed by integrally moving, in the optical axis direction, the first sub-lens group S 1  and the second sub-lens group S 2 , i.e., the first variable lens group  10  (first lens group frame  11 ) regardless of the zooming range. 
     Similar to the first through third embodiments, in the fourth embodiment, the zoom paths are discontinuous at the intermediate focal length fm; however, a solution for continuously forming a correct image plane exists by appropriately determining the positions of the first sub-lens group S 1  (first lens group L 1 ), the second sub-lens group S 2  (second lens group L 2 ), the third sub-lens group S 3  (third lens group L 3 ), and the fourth sub-lens group S 4  (fourth lens group L 4 ), respectively, at the short focal length extremity fw, the intermediate focal length fm (discontinuous line), and the long focal length extremity ft. According to such a zoom path, a miniaturized zoom lens system having a high zoom ratio can be obtained. 
     FIG. 5 shows the fifth embodiment of the zoom lens system with a switching lens group. The zoom lens system includes a positive first variable lens group  10 , and a negative second variable lens group  20 , in that order from the object side. The first variable lens group  10  includes a negative first lens group L 1  (first sub-lens group S 1 ) and a positive second lens group L 2  (second sub-lens group S 2 ), in that order from the object side. The second variable lens group  20  includes a positive third lens group L 3  (third sub-lens group S 3 ) and a negative fourth lens group L 4  (fourth sub-lens group S 4 ), in that order from the object side. 
     The second sub-lens group S 2  of the first variable lens group  10  is fixed to a first lens group frame  11 . The first sub-lens group S 1  is mounted on a movable sub-lens group frame  12 . The movable sub-lens group frame  12  is arranged to move in the optical axis direction, by a predetermined distance, along a guide groove  13  which is formed on the first lens group frame  11 . The first sub-lens group S 1  is selectively moved to either the object-side movement extremity at which the movable sub-lens group frame  12  comes into contact with the front end of the guide groove  13 , or the image-side movement extremity at which the movable sub-lens group frame  12  comes into contact with the rear end of the guide groove  13 . Similarly, the fourth sub-lens group S 4  of the second variable lens group  20  is fixed to a second lens group frame  21 . The third sub-lens group S 3  is mounted on a movable sub-lens group frame  22 . The movable sub-lens group frame  22  is arranged to move in the optical axis direction, by a predetermined distance, along a guide groove  23  which is formed on the second lens group frame  21 . The third sub-lens group S 3  is selectively moved to either the object-side movement extremity at which the movable sub-lens group frame  22  comes into contact with the front end of the guide groove  23 , or the image-side movement extremity at which the movable sub-lens group frame  22  comes into contact with the rear end of the guide groove  23 . A diaphragm D is arranged to move together with the first variable lens group  10  (first lens group frame  11 ). 
     In the zoom paths according to the fifth embodiment, the first variable lens group  10  (first lens group frame  11 ), the second variable lens group  20  (second lens group frame  21 ), the first sub-lens group S 1 , and the third sub lens group S 3  move in the following manner: 
     [A] In a short-focal-length zooming range Zw from the short focal length extremity fw to a first intermediate focal length fm 1  the first sub-lens group S 1  and the second sub-lens group S 2  maintain a distance d 1  therebetween (first separation space/wide space), and the third sub-lens group S 3  and the fourth sub-lens group S 4  maintain a distance d 3  therebetween (first separation space/wide space); and the first variable lens group  10  (first lens group frame  11 ) and the second variable lens group  20  (second lens group frame  21 ) move towards the object side while mutually changing the distance therebetween. 
     [B] At the first intermediate focal length fm 1  the first variable lens group  10  and the second variable lens group  20  are moved towards the image side at the long focal-length extremity of the short-focal-length zooming range Zw; and the first sub-lens group S 1  moves to the image-side movement extremity of the guide groove  13 , wherein the first sub-lens group S 1  moved toward the second sub-lens group S 2  so that the distance therebetween is determined by a shorter distance (second separation space/narrow space) d 2 . 
     [C] In an intermediate zooming range Zm from the first intermediate focal length fm 1  to a second intermediate focal length fm 2 , the first sub-lens group S 1  and the second sub-lens group S 2  maintain the shorter distance d 2 , and the third sub-lens group S 3  and the fourth sub-lens group S 4  maintain the longer distance d 3 ; and the first variable lens group  10  and the second variable lens group  20  move towards the object side based on the positions thereof which are determined at the first intermediate focal length fm 1  after the first through fourth lens groups L 1  through L 4  have been moved towards the image side, while changing the distance therebetween. 
     [D] At the second intermediate focal length fm 2 , the first variable lens group  10  and the second variable lens group  20  are moved towards the image side at the long focal length extremity of the intermediate zooming range Zm; and the third sub-lens group S 3  moves to the image-side movement extremity of the guide groove  23 , wherein the third sub-lens group S 3  moves toward the fourth sub-lens group S 4  so that the distance therebetween is determined by a shorter distance (second separation space/narrow space) d 4 . 
     [E] In a long-focal-length zooming range Zt from the second intermediate focal length fm 2  to the long focal length extremity ft, the first sub-lens group S 1  and the second sub-lens group S 2  maintain the shorter distance d 2  therebetween, and the third sub-lens group S 3  and the fourth sub-lens group S 4  maintain the shorter distance d 4  therebetween; and the first variable lens group  10  and the second variable lens group  20  move towards the object side based on the positions thereof which are determined at the second intermediate focal length fm 2 , after the first through fourth lens groups L 1  through L 4  have been moved towards the image side, while changing the distance therebetween. 
     The zoom paths for the first variable lens group  10  and the second variable lens group  20  are simply depicted as straight lines in FIG.  5 . It should be noted, however, that the actual zoom paths are not necessarily straight lines. 
     Focusing is performed by integrally moving, in the optical axis direction, the first sub-lens group S 1  and the second sub-lens group S 2 , i.e., the first variable lens group  10  (first lens group frame  11 ) regardless of the zooming range. 
     Similar to the first through fourth embodiments, in the fifth embodiment, the zoom paths are discontinuous at the first intermediate focal length fm 1  and the second intermediate focal length fm 2 ; however, a solution for continuously forming a correct image plane exists by appropriately determining the positions of the first sub-lens group S 1  (first lens group L 1 ), the second sub-lens group S 2  (second lens group L 2 ), the third sub-lens group S 3  (third lens group L 3 ) and the fourth sub-lens group S 4  (fourth lens group L 4 ), respectively, at the short focal length extremity fw, the first and second intermediate focal lengths fm 1  fm 2  (discontinuous line), and the long focal length extremity ft. According to such a zoom path, a miniaturized zoom lens system having a high zoom ratio can be obtained. 
     FIG. 6 shows the sixth embodiment of the zoom lens system with a switching lens group. The zoom lens system includes a positive first variable lens group  10 , and a negative second variable lens group  20 , in that order from the object side. The first variable lens group  10  includes a negative first lens group L 1  (first sub-lens group S 1 ) and a positive second lens group L 2  (second sub-lens group S 2 ), in that order from the object side. The second variable lens group  20  includes a positive third lens group L 3  (third sub-lens group S 3 ) and a negative fourth lens group L 4  (fourth sub-lens group S 4 ), in that order from the object side. 
     The second sub-lens group S 2  of the first variable lens group  10  is fixed to a first lens group frame  11 . The first sub-lens group S 1  is mounted on a movable sub-lens group frame  12 . The movable sub-lens group frame  12  is arranged to move in the optical axis direction, by a predetermined distance, along a guide groove  13  which is formed on the first lens group frame  11 . The first sub-lens group S 1  is selectively moved to either the object-side movement extremity at which the movable sub-lens group frame  12  comes into contact with the front end of the guide groove  13 , or the image-side movement extremity at which the movable sub-lens group frame  12  comes into contact with the rear end of the guide groove  13 . Similarly, the fourth sub-lens group S 4  of the second variable lens group  20  is fixed to a second lens group frame  21 . The third sub-lens group S 3  is mounted on a movable sub-lens group frame  22 . The movable sub-lens group frame  22  is arranged to move in the optical axis direction, by a predetermined distance, along a guide groove  23  which is formed on the second lens group frame  21 . The third sub-lens group S 3  is selectively moved to either the object-side movement extremity at which the movable sub-lens group frame  22  comes into contact with the front end of the guide groove  23 , or the image-side movement extremity at which the movable sub-lens group frame  22  comes into contact with the rear end of the guide groove  23 . A diaphragm D is arranged to move together with the first variable lens group  10  (first lens group frame  11 ). 
     In the zoom paths according to the sixth embodiment, the first variable lens group  10  (first lens group frame  11 ), the second variable lens group  20  (second lens group frame  21 ), the first sub-lens group S 1 , and the third sub lens group S 3  move in following manner: 
     [A] In a short-focal-length zooming range Zw from the short focal length extremity fw to a first intermediate focal length fm 1  the first sub-lens group S 1  and the second sub-lens group S 2  maintain a distance d 1  therebetween (first separation space/wide space), and the third sub-lens group S 3  and the fourth sub-lens group S 4  maintain a distance d 3  therebetween (first separation space/wide space); and the first variable lens group  10  (first lens group frame  11 ) and the second variable lens group  20  (second lens group frame  21 ) move towards the object side while mutually changing the distance therebetween. 
     [B] At the first intermediate focal length fm 1 , the first variable lens group  10  and the second variable lens group  20  are moved towards the image side at the long focal length extremity of the short-focal-length zooming range Zw; and the third sub-lens group S 3  moves to the image-side movement extremity of the guide groove  23 , and wherein the third sub-lens group S 3  moves toward the fourth sub-lens group S 4  so that the distance therebetween is determined by a shorter distance (second separation space/narrow space) d 4 . 
     [C] In an intermediate zooming range Zm from the first intermediate focal length fm 1  to a second intermediate focal length fm 2 , the first sub-lens group S 1  and the second sub-lens group S 2  maintain the longer distance d 1  therebetween, and the third sub-lens group S 3  and the fourth sub-lens group S 4  maintain the shorter distance d 4  therebetween; and the first variable lens group  10  and the second variable lens group  20  move towards the object side based on the positions thereof which are determined at the first intermediate focal length fm 1 , after the first through fourth lens groups L 1  through L 4  have been moved towards the image side, while changing the distance therebetween. 
     [D] At the second intermediate focal length fm 2 , the first variable lens group  10  and the second variable lens group  20  are moved towards the image side at the long focal length extremity of the intermediate zooming range Zm; and the first sub-lens group S 1  moves to the image-side movement extremity of the guide groove  13 , and wherein the first sub-lens group S 1  moves toward the second sub-lens group S 2  so that the distance therebetween is determined by a shorter distance (second separation space/narrow space) d 2 . 
     [E] In a long-focal-length zooming range Zt from the second intermediate focal length fm 2  to the long focal length extremity ft, the first sub-lens group S 1  and the second sub-lens group S 2  maintain the shorter distance d 2  therebetween, and the third sub-lens group S 3  and the fourth sub-lens group S 4  maintain the shorter distance d 4  therebetween; and the first variable lens group  10  and the second variable lens group  20  move towards the object side based on the positions thereof which are determined at the second intermediate focal length fm 2 , after the first through fourth lens groups L 1  through L 4  have been moved towards the image side, while changing the distance therebetween. 
     The zoom paths for the first variable lens group  10  and the second variable lens group  20  are simply depicted as straight lines in FIG.  6 . It should be noted, however, that the actual zoom paths are not necessarily straight lines. 
     Focusing is performed by integrally moving, in the optical axis direction, the first sub-lens group S 1  and the second sub-lens group S 2 , i.e., the first variable lens group  10  (first lens group frame  11 ) regardless of the zooming range. 
     Similar to the first through fifth embodiments, in the sixth embodiment, the -zoom paths are discontinuous at the first intermediate focal length fm 1  and the second intermediate focal length fm 2 ; however, a solution for continuously forming a correct image plane exists by appropriately determining the positions of the first sub-lens group S 1  (first lens group L 1 ), the second sub-lens group S 2  (second lens group L 2 ), the third sub-lens group S 3  (third lens group L 3 ), and the fourth sub-lens group S 4  (fourth lens group L 4 ), respectively, at the short focal length extremity fw, the first and second intermediate focal lengths fm 1 , fm 2  (discontinuous line), and the long focal length extremity ft. According to such a zoom path, a miniaturized zoom lens system having a high zoom ratio can be obtained. 
     FIG. 7 shows the seventh embodiment of the zoom lens system with a switching lens group. The zoom lens system includes a positive first variable lens group  10 , and a negative second variable lens group  20 , in that order from the object side. The first variable lens group  10  includes a positive first lens group L 1  (first sub-lens group S 1 ), a negative second lens group L 2  (second sub-lens group S 2 ) and a positive third lens group L 3  (third sub-lens group S 3 ), in that order from the object side. The second variable lens group  20  includes a negative fourth lens group L 4 . The first sub-lens group S 1  and the third sub-lens group S 3  are fixed to a first lens group frame  11 . The second sub-lens group S 2  is mounted on a movable sub-lens group frame  12 . The movable sub-lens group frame  12  is arranged to move in the optical axis direction, by a predetermined distance, along a guide groove  13  which is formed on the first lens group frame  11 . The second sub-lens group S 2  is selectively moved to either the object-side movement extremity at which the movable sub lens group frame  12  comes into contact with the front end of the guide groove  13 , or the image-side movement extremity at which the movable sub-lens group frame  12  comes into contact with the rear end of the guide groove  13 . The fourth lens group L 4  of the second variable lens group  20  is fixed to a second lens group frame  21 . A diaphragm D is arranged to move together with the first variable lens group  10  (first lens group frame  11 ). 
     In the zoom paths according to the seventh embodiment, the first variable lens group  10  (first lens group frame  11 ), the second variable lens group  20  (second lens group frame  21 ), and the second sub-lens group S 2  move in the following manner: 
     [A] In a short-focal-length zooming range Zw from the short focal length extremity fw to an intermediate focal length fm, the first sub-lens group S 1  and the second sub-lens group S 2  maintain a shorter distance therebetween; however, the second sub-lens group S 2  and the third sub-lens group S 3  maintain a longer distance therebetween; and the first variable lens group  10  (first lens group frame  11 ) and the second variable lens group  20  (second lens group frame  21 ) move towards the object side while changing the distance therebetween. 
     [B] At the intermediate focal length fm, the first variable lens group  10  and the second variable lens group  20  are moved towards the image side at the long focal-length extremity of the short-focal-length zooming range Zw; and the second sub-lens group S 2  moves to the image-side movement extremity of the guide groove  13 , and wherein the second sub-lens group S 2  moves away from the first sub-lens group S 1  and moves toward the third sub-lens group S 3 . 
     [C] In a long-focal-length zooming range Zt from the intermediate focal length fm to the long focal length extremity ft, the first sub-lens group S 1  and the second sub-lens group S 2  maintain the longer distance therebetween, and the second sub-lens group S 2  and the third sub-lens group S 3  maintain the shorter distance therebetween; and the first variable lens group  10  and the second variable lens group  20  move towards the object side based on the positions thereof which are determined at the intermediate focal length fm, after the first through fourth lens groups L 1  through L 4  have been moving towards the image side, while changing the distance therebetween. 
     The zoom paths for the first variable lens group  10  and the second variable lens group  20  are simply depicted as straight lines in FIG.  7 . It should be noted, however, that the actual zoom paths are not necessarily straight lines. 
     Focusing is performed by integrally moving, in the optical axis direction, the first sub-lens group S 1  through the third sub-lens group S 3 , i.e., the first variable lens group  10  (first lens group frame  11 ) regardless of the zooming range. 
     Similar to the first through sixth embodiments, in the seventh embodiment, the zoom paths are discontinuous at the intermediate focal length fm; however, a solution for continuously forming a correct image plane exists by appropriately determining the positions of the first sub-lens group S 1  (first lens group L 1 ), the second sub-lens group S 2  (second lens group L 2 ), the third sub-lens group S 3  (third lens group L 3 ), and the fourth lens group L 4 , respectively, at the short focal length extremity fw, the intermediate focal length fm, (discontinuous line), and the long focal length extremity ft. According to such a zoom path, a miniaturized zoom lens system having a high zoom ratio can be obtained. 
     As can be understood from the above description, it is practical to apply the above-described zoom lens system having switching lens groups to a photographing lens system of a camera in which the photographing lens system and a finder optical system are independently provided. Moreover, with respect to each of the first through fourth lens groups L 1  through L 4 , stopping positions at which the lens group stops upon zooming are preferably determined in a stepwise manner along a fundamental zoom path, i.e., it is preferable to provide a plurality of focal-length steps. FIGS. 8 and 9 show zoom lens systems in which positions for stopping each lens group are determined in a stepwise manner along the fundamental zoom paths. Since these zoom lens systems are the same as that of the first embodiment, identical components are provided with the same designators. The zoom paths are depicted with fundamental dotted lines; and positions at which the first lens group frame  11  and the second lens group frame  21  stop are indicated with black dots along the dotted lines. Further, in FIG. 9A, the dots are connected by smooth (continuous) curved lines to form an actual zoom path. The actual mechanical structure thereof allows the first lens group frame  11  and the second lens group frame  21  to be moved along the smooth curved lines (actual zoom path). 
     In the first through seventh embodiments, each lens group is illustrated as a single lens element; however, a lens group can of course include a plurality of lens elements. 
     FIGS. 9B and 9C depict an additional schematic view of the concepts shown in FIGS. 8 and 9A. It should be noted in the following explanation that FIGS. 9B and 9C are schematic in nature (e.g., not to scale and/or not depicting actual shape) and that one skilled in the art will recognize that the zoom paths are not necessarily straight, and the manner in which the schematics of FIGS. 9B and 9C relate to a designed (zooming) cam groove shape (which will differ depending at least on the optical configuration). As shown in FIGS. 9B and 9C, if, in order to arrange movement in accordance with FIG. 9A, it is determined that one zoom path will be connected in an uninflected line (i.e., essentially without discontinuity or inflection and without switching), then the cam ring, shape, and orientation of cam groove(s) can be adapted for this purpose. As shown in FIG. 9B, each of the three fundamental zoom paths can include a discontinuity. By smoothly connecting one zoom path, in this case the second zoom path (e.g., depicted in the FIGS. 9B and 9C by shifting all of the zoom paths in the intermediate-to-telephoto range “up” so that the path of the second lens group is connected), it becomes possible to carry out the movements of the combined groups more simply. In this case, it is decided to use “switching” for the first group and a smooth inflection in the second group. As noted, the stepwise movement/positioning and prohibition of photography in the switching/inflection range also form part of this system. 
     Although FIG. 9C depicts a shift in which the second zoom path is made essentially connected, the amount of shifting “up” does not need to fully align the curve to be made smoother, but need only take up a portion of the discontinuity (e.g., reducing any inflection to a selected amount, such as an imperceptible amount). In the following description, it is noted that cam groove  44   f  is essentially without discontinuity or inflection, relating to the second group zoom path in FIGS. 9A-9C, and that cam groove  44   r  has a small inflection, relating to the third group zoom path in FIGS. 9A-9C. However, the adaptation depicted in FIGS. 9B and 9C can be used for any of the systems depicted in FIGS. 1-7 or variations thereof. 
     It can be decided to use at least one smooth or uninflected line for various reasons, including simplicity of movement, simplicity of manufacturing, or to improve exterior appearance of movement of lens barrels (e.g., to avoid visible discontinuity in the operation of the lens barrels, so that an unsophisticated operator does not become concerned about the proper operation of the camera). In the example given, the movement of the lens barrel supporting the second lens group is essentially continuous, while the switching movement of the first lens group and the inflected movement of the third lens group cannot be seen from the exterior of the camera. 
     In each of the above-described embodiments, the first variable lens group  10  in FIGS. 1,  8 , and  9 A- 9 C, the second variable lens group  20  in FIG. 2, the second variable lens group  20  in FIG. 3, the first variable lens group  10  in FIG. 4, the first variable lens group  10  in FIG. 5, the first variable lens group  10  in FIG. 6, and the first variable lens group  10  in FIG. 7 (including the first lens L 1  and the third lens L 3  as a unit) are each switching lens groups which serve as focusing lens groups in any focal length range. 
     A preferred embodiment will now be described in which the present invention has been applied to the zoom lens barrel in the examples shown in FIGS. 1,  8 , and  9 A- 9 C, which have a first variable lens group  10  (switching lens group) and a second variable lens group  20 . 
     FIGS. 10 through 31 show an embodiment of a zoom lens barrel (system). Unlike the zoom lens systems shown in FIGS. 1,  8  and  9 , in which one of the first and second sub-lens groups S 1  and S 2 , which together form a switching lens group  10 , is fixed to the first lens group frame  11 , the first and second sub-lens groups S 1  and S 2  in this embodiment are both movable with respect to the switching lens group frame in the optical axis direction. In this embodiment, a moving path of the switching lens group frame upon zooming and a path of the first sub-lens group S 1  and the second sub-lens group S 2  within the switching lens group frame can be added to each other to give a composite zoom path, which corresponds to the zoom path shown in FIGS. 1,  8 , and  9 A- 9 C. Upon focusing, the first sub-lens group S 1  and the second sub-lens group S 2  are integrally moved within the switching lens frame in the optical axis direction. In a photographic operation, the first sub-lens group S 1  and the second sub-lens group S 2  are placed at a predetermined position, before the release of the shutter is started, as a result of the movement of the switching lens group frame and the movement of the first sub-lens group S 1  and the second sub-lens group S 2  within the switching lens group frame in accordance with focal length information set by an operator (the photographer) and object distance information detected. 
     As shown in FIG. 10, a stationary barrel  42 , which is fixed to a camera body  41 , has a female helicoid  43  formed on an inner surface of the stationary barrel  42 . A male helicoid  45 , which is formed on the rearmost circumference of a cam ring  44 , engages with the female helicoid  43 . Arranged outside of the stationary barrel  42  is a pinion  47  which is rotated by a zooming motor  46 . Gear teeth (not shown) are formed on the circumference of the cam ring  44  wherein a part of the male helicoid  45  is cut out therefor. The gear teeth, which are formed to have the same oblique direction as the lead of the male helicoid  45 , engages with the pinion  47 . Accordingly, the cam ring  44  advances or retreats along the optical axis direction when the cam ring  44  is rotated in either direction by the zooming motor  46  due to the engagement of the female helicoid  43  and male helicoid  45 . The position of the cam ring  44  resulting from the rotation made by the zooming motor  46  is detected by focal length detecting device  46 C, which can include, for example, of a code plate and a brush. 
     A linear guide ring  48  is supported by the cam ring  44 . The guide ring  48  rotates relative to the cam ring  44  and moves together with the cam ring  44  along the optical axis direction (i.e., no relative displacement is allowed in the optical axis direction). The guide ring  48  is supported by a camera body  41  in a manner that enables the guide ring  48  to move only in the optical axis direction. Arranged inside of the cam ring  44  in order from the front side of the cam ring  44  are a switching lens group frame  50  (first lens group frame) which supports the first variable lens group  10  (i.e., the first sub-lens group S 1  and second sub-lens group S 2 ) and a second lens group frame  49  which supports the second variable lens group  20 . The switching lens group frame  50  and the second lens group frame  49  are linearly guided along the optical axis direction by the guide ring  48 . 
     Cam grooves  44   f  and  44   r  are formed on an inner surface of the cam ring  44 . The cam grooves  44   f  and  44   r  receive the switching lens group frame  50  and second lens group frame  49 , respectively. FIG. 11 shows an arrangement of the cam grooves  44   f  and  44   r  in a developed view. Three sets of the cam grooves  44   f  and  44   r  are formed circumferentially with each groove spaced at equi-angular distances from one another. Radial follower pins  50   p  and  49   p  are provided on the switching lens group frame  50  and the second lens group frame  49  to be received in the cam grooves  44   f  and  44   r , respectively. 
     The cam grooves  44   f  and  44   r  include introducing portions  44   f - a  and  44   r - a  for the follower pins  50   p  and  49   p , retracted portions  44   f - r  and  44   r - r  for the zoom lens system, wide-angle extremity portions  44   f - w  and  44   r - w , and telephoto extremity portions  44   f - t  and  44   r - t , respectively. A rotational angle θ 1  is defined as the rotational angle from the introducing portions  44   f - a  and  44   r - a  to the retracted portions  44   f - r  and  44   r - r , respectively. A rotational angle θ 2  is defined as the rotational angle from the retracted portions  44   f - r  and  44   r - r  to the wide-angle extremity portions  44   f - w  and  44   r - w , respectively. A rotational angle θ 3  is defined as the rotational angle from the wide-angle extremity portions  44   f - w  and  44   r - w  to the telephoto extremity portions  44   f - t  and  44   r - t , respectively. A rotational angle θ 4 , defined as the rotational angle beyond the telephoto extremity portions  44   f - t  and  44   r - t , which serves as a rotational angle for assembly use. Each of the cam grooves  44   r  for the second lens group frame  49  has an intermediate discontinuous position fm that corresponds to the zoom path of the second variable lens group  20  as described in the embodiments in FIGS. 1,  8  and  9 . 
     In contrast, no discontinuous position appears to exist in the cam grooves  44   f  for the first variable lens group  10  between the wide-angle extremity portion  44   f - w  and the telephoto extremity portion  44   f - t  since the change in shape (profile) of each cam groove  44   f  is smooth in this area. This is because, in this embodiment, the switching lens group frame  50  and the sub-lens group S 2  are moved in such a manner that the positions of the sub-lens group S 2  are not discontinuous in the short-focal-length zooming range Zw and in the long-focal-length zooming range Zt, the two ranges extending on both sides of intermediate focal length fm in FIG. 1. A connection line CC is schematically shown in FIG.  1 . The connection line CC connects the zoom path of the short-focal-length zooming range Zw to zoom path of the long-focal-length zooming range Zt, the two ranges extending on both sides of the intermediate focal length fm. The cam groove  44   f  is shaped to correspond to the zoom path connected by the connection line CC. As the follower pin  50   p  moves along a section corresponding to the connection line CC, the sub-lens group S 1  moves from the object-side movement extremity to the image-side movement extremity. It is necessary to control the zoom lens barrel so that the section of the cam groove  44   f  corresponding to the line CC is not used as an actual zooming range in a photographic operation (i.e., the cam ring  44  is not stopped) Alternatively, the cam grove  44   f  can include the discontinuous position similar to that of the cam groove  44   r.    
     In the above-described zoom lens barrel, the cam ring  44  advances or retreats along the optical axis while rotating as the pinion  47  is rotated via the zooming motor  46  in either direction, which causes the switching lens group frame  50  (i.e., the first variable lens group  10 ) and the second lens group frame  49  (i.e., the second variable lens group  20 ), which are guided in the optical axis direction within the cam ring  44 , to move in the optical axis direction along a predetermined path defined by the cam grooves  44   f  and  44   r.    
     Novel features of the present embodiment reside in a support structure by which the first sub-lens group S 1  and the second sub-lens group S 2  are supported in the switching lens group frame  50  and the driving structure thereof. A particular example of an arrangement within the switching lens group frame  50  will now be described by reference to FIGS. 12 through 31. 
     As shown in FIGS. 15 and 16, a front shutter retaining ring  51 , a rear shutter retaining ring  52 , a first sub-lens group frame  53 , a second sub-lens group frame  54 , an actuator ring  55 , and a gear holding ring  56  are arranged within the switching lens group frame  50 . The front shutter retaining ring  51 , the rear shutter retaining ring  52 , and the gear holding ring  56  form a portion of the switching lens group frame  50 . The first sub-lens group S 1  is fixed to the first sub-lens group frame  53 , and the second sub-lens group S 2  is fixed to the second sub-lens group frame  54 . The first sub-lens group frame  53 , the second sub-lens group frame  54 , and the actuator ring  55  are movably fitted in a central opening  51   p  (see FIG. 12) of the front shutter retaining ring  51 . These movable members, i.e., the first sub-lens group frame  53 , the second sub-lens group frame  54 , and the actuator ring  55 , enable the first sub-lens group S 1  and the second sub-lens group S 2  to be at a mutually close position, or be at a mutually distant position, with respect to the optical axis direction, and also enable the first sub-lens group S 1  and the second sub-lens group S 2  to perform focusing. 
     The actuator ring  55  is rotatably supported between the front and rear shutter retaining rings  51  and  52  with the rearmost portion of the actuator ring  55  being restricted by a receiving surface  52   a  (FIGS. 13,  15 , and  16 ) of the rear shutter retaining ring  52 . The actuator ring  55  is a driving member that enables the first sub-lens group S 1  and the second sub-lens group S 2  to become mutually close or mutually distant from each other, and enables the first and the second sub-lens groups S 1  and S 2  to perform focusing via the rotation thereof. The gear holding ring  56  is fixed to the front end of the front shutter retaining ring  51 , and a lens shutter mechanism  57  and a diaphragm mechanism  58  are supported by the rear shutter retaining ring  52  (FIGS. 12,  15 , and  16 ). 
     The first sub-lens group frame  53  has a cylindrical shape and has two linear guide ribs  53   a  on its periphery at the opposite sides thereof at an equi-angular interval of 180 degrees. A guide bore  53   b  is formed in the guide rib  53   a . A guide rod  59  is loosely inserted (or moveably fitted) in the guide bore  53   b . The rear end of the guide rod  59  is fixed in a fixing bore  56   q  formed at the rearmost portion of the gear holding ring  56  while the front end of the guide rod  59  is fixed to the front surface of the gear holding ring  56  by a bracket  60  and a screw  61 . A coil spring  62  is placed over each of the guide rod  59  between the bracket  60  and the guide rib  53   a  so that the coil spring  62  biases the first sub-lens group frame  53  toward the second sub-lens group frame  54 . A U-shaped recess  56   r  is provided on the gear holding ring  56  so as to receive the guide rod  59  and the spring  62  (FIGS.  25  through  27 ). The recess  56   r  communicatively connects with the central opening  51   p  of the front shutter retaining ring  51 . The first sub-lens group frame  53  can be connected to the front shutter retaining ring  51  by engaging the guide ribs  53   a  with the guide rods  59  of the front shutter retaining ring  51  at two positions, wherein the guide ribs  53   a  are provided on the first sub-lens group frame  53  at 180° intervals about the optical axis. 
     As shown in FIGS. 17A,  18 A,  19 A and  20 A, the first sub-lens group frame  53  is provided with four shift leading surfaces (shift cam surfaces)  53   c  that are formed circumferentially at equi-angular intervals on the end-face of the first sub-lens group frame  53 . Annular light-blocking support ribs  53   d  (see FIG. 14) are provided radially outside of the shift leading surfaces  53   c  over the open ends of the shift leading surfaces  53   c . FIG. 23 shows an enlarged expanded view of one of the shift leading surfaces  53   c  which is formed essentially as a straight slope having an inclination angle α with respect to a circumferential edge of the first sub-lens group  53  (i.e., with respect to a plane normal to the optical axis), and is provided with a pair of follower engaging recesses  53   e  and  53   f  on either end of the shift leading surface  53   c . Each of the engaging recesses  53   e  and  53   f  is formed as a shallow V-shaped recess. The follower engaging recess  53   e  defines a mutually distant position on the wide-angle side and the follower engaging recess  53   f  defines a mutually close position on the telephoto side, of the first sub-lens group frame  53  and the second sub-lens group frame  54  (i.e., the first sub-lens group S 1  and second sub-lens group S 2 ). 
     As shown in FIGS. 17A,  18 A,  19 A and  20 A, the second sub-lens group frame  54  is provided on its periphery with four follower projections  54   a , each corresponding to each of the four shift leading surfaces  53   c  of the first sub-lens group frame  53 . An inclined surface  54   b  is provided so as to correspond to the shift leading surface  53   c  of the first sub-lens group frame  53 , and the follower projection  54   a  is provided on the end of the inclined surface  54   b  which is the closest to the shift leading surface  53   c . The tip of the follower projection  54   a  has a substantially semi-circular shape which is symmetrical with respect to the longitudinal axis thereof, so that the shapes of the engaging recesses  53   e  and  53   f  correspond to the tip shape of the projection  54   a . Annular light-blocking support ribs  54   c  are radially provided on the second sub-lens group frame  54  inside the projections  54   a  and the inclined surfaces  54   b . The shift leading surfaces  53   c  formed on the first sub-lens group frame  53  and the follower projections  54   a  formed on the second sub-lens group frame  54  together form a shift cam mechanism (of a lens group shift mechanism) that enables the lens-group frames  53  and  54  either be at a mutually close position, or be at a mutually distant position. As described above, the four shift leading surfaces  53   c  of the first sub-lens group frame  53  and the four projections  54   a  of the second sub-lens group frame  54  are spaced at equi-angular intervals. Accordingly, each of the surfaces can engage with its respective projection at 180° intervals of a relative rotation. Given that N is the number of the shift leading surfaces  53   c  or the follower projections  54   a  (four, in this embodiment) and that M is the number of the guide ribs  53   a  of the first sub-lens group frame  53  or the number of the guide rods  59  of the front shutter retaining ring  51  (two, in this embodiment), the relationship between M and N is that M is a multiple of N, or in other words, N is a divisor of M. This relationship makes it possible to select an assembly position from among different assembly positions, so that for example, an assembly position that provides optimum optical performance can be achieved. 
     Furthermore, a pair of linear guide projections  54   d  are formed on the second sub-lens group frame  54  on the outer surface thereof. The guide projections  54   d  are formed at the same circumferential positions as two of the four follower projections  54   a  that are positioned on the periphery of the second sub-lens group frame  54  at the opposite sides thereof at an equi-angular interval of 180 degrees. Each of the guide projections  54   d  is formed at a position which is rearward with respect to the follower projection  54   a  in the optical axis direction. Also formed on the second sub-lens group frame  54  on the outer surface thereof are three lugs  54   e , which are spaced at equi-angular intervals, and are positioned rearward with respect to the guide projection  54   d  in the optical axis direction. As best shown in FIG. 24, each lug  54   e  has a pair of contact surfaces N 1  and N 2  that are spaced apart from each other in a circumferential direction. Each lug  54   e  also has a smooth circular shaped end surface N 3  that is symmetrical with respect to the central axis of the lug  54   e  extending in the middle of the contact surfaces N 1  and N 2 . 
     As shown in FIG. 24, a pair of rotation preventing surfaces  51   a  and  51   b  are formed on the front shutter retaining ring  51  on the inner surface thereof, in order to define the range of rotation of the second sub-lens group frame  54  relative to the non-rotating front shutter retaining ring  51 , with respect to the guide projection  54   d  of the second sub-lens group frame  54 . The rotation preventing surfaces  51   a  and  51   b  come into contact with contact surfaces M 1  and M 2  of the guide projection  54   d , respectively, when the second sub-lens group frame  54  is rotated in either direction, thereby defining the rotational movement extremities of the second sub-lens group frame  54 . A wide-angle linear guide slot  51   d  is defined between the rotation preventing surface  51   a  and a guide surface  51   c  which comes into contact with the contact surface M 2  of the guide projection  54   d . A telephoto linear guide slot  51   f  is defined between the rotation preventing surface  51   b  and a guide surface  51   e  which comes into contact with the contact surface M 1  of the guide projection  54   d . Thus, the width of both of the wide-angle linear guide slot  51   d  and the telephoto linear guide slot  51   f  in the circumferential direction corresponds to that of the linear guide projection  54   d  in the same direction. Accordingly, the guide projection  54   d  snugly fit in the guide slots  51   d  and  51   f  so as to movable therein. 
     The clearance between the wide-angle linear guide slot  51   d  or the telephoto linear guide slot  51   f  and the guide projection  54   d  is determined smaller (stricter) than the clearance between the guide bore  53   b  of the first sub-lens group frame  53  and the guide rod  59 . The linear guide projections  54   d  are provided on the periphery of the second sub-lens group frame  54  on opposite sides thereof at an equi-angular interval of 180 degrees. A pair of the wide-angle and telephoto linear guide slots  51   d  and  51   f  are provided on the front shutter retaining ring  51  so that two linear guide projections  54   d  can be selectively received in the wide-angle and telephoto linear guide slots  51   d  and  51   f  with respect to the rotational positions thereof (i.e., at an angular interval of 180 degrees). 
     The actuator ring  55  has, on the front end surface thereof, three control recesses  55   a  that each correspond to each of the lugs  54   e  of the second sub-lens group frame  54  (see FIG.  22 ). Each of the control recesses  55   a  has a shape that is symmetrical with respect to the central axis extending parallel to the optical axis and includes a pair of effective surfaces  55   b  and  55   c  that respectively come into contact with contact surfaces N 1  and N 2 . The lugs  54   e  of the second sub-lens group frame  54  and the control recesses  55   a  constitute a focusing cam mechanism of a focusing mechanism. The control recess  55   a  also includes a pair of focus leading surfaces  55   d  and  55   e  (focus cam surfaces) on the telephoto side and on the wide-angle side, respectively. The focus leading surfaces  55   d  and  55   e  each come into contact with the circular end surface N 3  of the lug  54   e . The telephoto-side focus leading surface  55   d  and the wide-angle-side focus leading surface  55   e  are provided between the effective surfaces  55   b  and  55   c  in the form of an end-faced cam having an open front end. The slopes of the leading surfaces  55   d  and  55   e  have opposite directions with respect to the circumferential direction thereof, but have the same absolute value, i.e., the slopes both incline forwards in the optical axis direction. Annular light-blocking support ribs  55   f  (see FIG. 13) are provided radially outside, and over the front portion, of the control recess  55   a  of the actuator ring  55 . The focus leading surfaces  55   d  and  55   e , together with the lug  54   e  provided on the second sub-lens group frame  54 , form a focus cam mechanism. As described above, the three lugs  54   e  of the second sub-lens group frame  54  and the three control recesses  55   a  of the actuator ring  55  are spaced at equi-angular intervals. In the illustrated embodiment, each of the lugs can engage with a respective recess at 120° angular intervals. 
     The aforementioned coil springs  62 , which bias the first sub-lens group frame  53  rearward, so that the shift leading surfaces  53   c  contact the follower projections  54   a , and the lugs  54   e  of the second sub-lens group frame  54  contact the telephoto side or wide-angle side focus leading surfaces  55   d  or  55   e  of the actuator ring  55 . As described above, the rear end surface of the actuator ring  55  abuts the receiving surface  52   a  of the rear shutter retaining ring  52 . Accordingly, the first sub-lens group frame  53 , the second sub-lens group frame  54 , the actuator ring  55 , and the rear shutter retaining ring  52  (receiving surface  52   a  ) can be held in contact by the sole force exerted by the coil springs  62 . As can be clearly seen from FIGS. 15 and 16, when the first sub-lens group frame  53 , the second sub-lens group frame  54 , the actuator ring  55 , and the rear shutter retaining ring  52  are in engagement with each other, the front end of the second sub-lens group frame  54  is positioned inside the first sub-lens group frame  53 , and the actuator ring  55  is situated on the periphery of the second sub-lens group frame  54 . 
     FIG.  21 (A through H) shows the manner in which the first sub-lens group frame  53  and the second sub-lens group frame  54  (i.e., the first sub-lens group S 1  and the second sub-lens group S 2 ) are moved via the effective surfaces  55   b  and  55   c  between a mutually close position on the telephoto side and a mutually distant position on the wide-angle side. Note that, solid line arrows represent the rotational direction of the actuator ring  55 , in FIG.  21 . 
     The arrangement shown in FIG.  21 (A) is the mutually distant position on the wide-angle side, in which the effective surface  55   b  of the actuator ring  55  abuts the lug  54   e , and the linear guide projection  54   d  of the second sub-lens group frame  54  is disengaged from the wide-angle linear guide slot  51   d . As the actuator ring  55  rotates in a clockwise direction (i.e., moves to the right in FIG.  21 ), the effective surface  55   b  biases the contact surface N 1  of the lug  54   e  to rotate the second sub-lens group frame  54  clockwise (to the right in FIG. 21) until the linear guide projection  54   d  abuts the rotation preventing surface  51   b  (FIGS.  21 (A) through  21 (C)). During the rotation of the actuator ring  55  and the second sub-lens group frame  54 , the first sub-lens group frame  53  (i.e., the first sub-lens group S 1 ) follows the shift leading surface  53   c , and the follower projection  54   a  of the second sub-lens group frame  54  so that the first sub-lens group frame  53  linearly moves closer to the second sub-lens group frame  54  (i.e., the second sub-lens group S 1 ) (FIG.  21 (B)). Ultimately, the follower projection  54   a  engages with the follower engaging recess  53   f  and rearward movement of the first sub-lens group frame  53  with respect to the second sub-lens group frame  54  in the optical axis direction is stopped (FIG.  21 (C)). Since the follower projections  54   a  and the follower engaging recesses  53   f  are spaced at equi-angular intervals therebetween, eccentricity between the first sub-lens group frame  53  and the second sub-lens group frame  54  is prevented, with all of the projections and the recesses in engagement. This completes the switching from the mutually distant position on the wide-angle side to the mutually close position on the telephoto side, resulting in the first sub-lens group S 1  being in a mutually close position with respect to the second sub-lens group S 2  (i.e., mutually close extremity). Note that the actuator ring  55  cannot rotate further in this direction. 
     Upon completion of switching to the mutually close position on the telephoto side, the rotation of the actuator ring  55  is reversed. The lug  54   e  (i.e., the second sub-lens group frame  54 ) moves rearward following the telephoto side focus leading surface  55   d  until the linear guide projection  54   d  engages with the telephoto linear guide slot  51   f . This allows the linear projection  54   d  to move only in the optical axis direction (FIG.  21 (D)). Focusing is carried out on the telephoto side from the intermediate focal length to the long focal length extremity, with the second sub-lens group frame  54  and the first sub-lens group  53  being moved integrally at the mutually close position via the telephoto side-focus leading surface  55   d.    
     Once the actuator ring  55  is rotated until the effective surface  55   c  abuts the contact surface N 2  of the lug  54   e , the linear guide projection  54   d  of the second sub-lens group frame  54  disengages from the telephoto linear guide slot  51   f  (FIG.  21 (E)). 
     At this point, the rotation of the actuator ring  55  has been reversed (upon or after completion of the switching to the mutually close position on the telephoto side). As the actuator ring  55  rotates counterclockwise (i.e., moves to the left in FIG.  21 ), the effective surface  55   c  biases the contact surface N 2  of the lug  54   e  to rotate the second sub-lens group frame  54  leftward until the contact surface M 1  of the linear guide projection  54   d  abuts the rotation preventing surface  51   a  (FIGS.  21 (F) and  21 (G)). During the rotation of the actuator ring  55  and the second sub-lens group frame  54 , the first sub-lens group frame  53  follows the shift leading surface  53   c  and the follower projection  54   a  of the second sub-lens group frame  54  so that the first sub-lens group frame  53  linearly moves away from the second sub-lens group frame  54 . Ultimately, the follower projection  54   a  engages with the follower engaging recess  53   e  and forward movement of the first sub-lens group frame  53  with respect to the second sub-lens group frame  54  in the optical axis direction is stopped (FIG.  21 (G)). Since the follower projections  54   a  and the follower engaging recesses  53   f  are spaced at equi-angular intervals therebetween, eccentricity between the first sub-lens group frame  53  and the second sub-lens group frame  54  is prevented, with all of the projections and the recesses in engagement. This completes the switching from the mutually close position on the telephoto side to the mutually distant position on the wide-angle side, resulting in the first sub-lens group S 1  being in a mutually distant position with respect to the second sub-lens group S 2  (i.e., mutually distant extremity). Note that the actuator ring  55  cannot rotate further in this direction. 
     Upon completion of switching to the mutually distant position on the wide-angle side, the rotation of the actuator ring  55  is reversed. The lug  54   e  (i.e., the second sub-lens group frame  54 ) moves rearward following the wide-angle side focus leading surface  55   e  until the linear guide projection  54   d  engages with the wide-angle linear guide slot  51   d . This allows the linear projection  54   d  to move only along the direction of the optical axis (FIGS.  21 (G) and  21 (H)). Focusing is carried out on the wide-angle side from the intermediate focal length to the short focal length extremity, with the second sub-lens group frame  54  and the first sub-lens group frame  53  being moved integrally at the mutually distant extremity via the wide-angle side focus leading surface  55   e.    
     Once the actuator ring  55  is rotated until the effective surface  55   c  abuts the contact surface N 1  of the lug  54   e , the linear guide projection  54   d  of the second sub-lens group frame  54  disengages from the wide-angle linear guide slot  51   d , and the positions of the first sub-lens group frame  53  and the second sub-lens group frame  54  return back to the position shown at FIG.  21 (A). 
     FIG. 22 shows the principle of how the focusing is carried out via the telephoto side-focus leading surface  55   d  and the wide-angle side-focus leading surface  55   e . As the actuator ring  55  is rotated in a telephoto side focusing range pt (from an infinite photographic distance ∞ to a minimum photographic distance (object at a minimum distance) n), with the circular end surface N 3  of the lug  54   e  in contact with the telephoto side focus leading surface  55   d , the second sub-lens group frame  54  (whose rotation is confined by the linear guide projection  54   d  which is in engagement with the telephoto linear guide slot  51   f  ) and the first sub-lens group frame  53  (i.e., the first sub-lens group S 1  and the second sub-lens group S 2 ) integrally moves forwardly or rearwardly along the optical axis to thereby carry out focusing. Similarly, as the actuator ring  55  is rotated in a wide-angle side focusing range pw (from an infinite photographic distance ∞ to a minimum photographic distance (object at a minimum distance) n), with the circular end surface N 3  of the lug  54   e  in contact with the wide-angle side focus leading surface  55   e , the second sub-lens group frame  54  (whose rotation is confined by the linear guide projection  54   d  which is in engagement with the wide-angle linear guide slot  51   d  ) and the first sub-lens group frame  53  (i.e., the first sub-lens group S 1  and the second sub-lens group S 2 ) integrally moves forwardly or rearwardly along the optical axis to provide focusing. 
     In particular, focusing on the telephoto side and focusing on the wide-angle side are achieved by controlling the number of pulses counted by a encoder  64   p  (see FIG. 30) provided in a driving system which drives the actuator ring with respect to a reference position at which the linear guide projection  54   d  of the second sub-lens group frame  54  comes into contact with the rotation preventing surface  51   a  or  51   b  (i.e., the position where the rotation of the actuator ring  55  is reversed). For example, the number of pulses of the driving system required to move the focusing lens groups (i.e., the sub-lens groups S 1  and S 2 ) from a reference position to a position corresponding to a minimum photographic distance n, to a position corresponding to an infinite photographic distance ∞, and to a position corresponding to an intermediate photographic distance can be predetermined by taking the leading angles for the focus leading surfaces  55   d  and  55   e  into consideration. Accordingly, focusing can be properly carried out in accordance with the object distance information by managing the number of the pulses of the encoder. 
     Also, in the illustrated embodiment, the slopes of the telephoto side focus leading surface  55   d  and the wide-angle side focus leading surface  55   e  of the actuator ring  55  have opposite directions with respect to the circumferential direction thereof, but have the same absolute value, i.e., the slopes both incline forwards in the optical axis direction, and the lug  54   e  is shaped to be symmetrical with respect to the central axis extending in the middle of the contact surfaces N 1  and N 2  which are circumferentially spaced apart from each other. Accordingly, focusing can be carried out on the telephoto side in the same manner as on the wide-angle side. This facilitates focusing control. 
     FIGS. 17A and 17B show an arrangement of the first sub-lens group frame  53 , the second sub-lens group frame  54 , the actuator ring  55 , and the front shutter retaining ring  51  when the first sub-lens group frame  53  (i.e., the first sub-lens group S 1 ) and the second sub-lens group frame  54  (i.e., the second sub-lens group S 2 ) are in the mutually distant position at the wide-angle side, and are in a position so as to focus on an object at infinity. FIGS. 18A and 18B show an arrangement of the first sub-lens group frame  53 , the second sub-lens group frame  54 , the actuator ring  55 , and the front shutter retaining ring  51  when the first sub-lens group frame  53  and the second sub-lens group frame  54  are in the mutually distant position on the wide-angle side, and are in a position so as to focus on an object at a minimum distance. FIGS. 19A and 19B show an arrangement of the first sub-lens group frame  53 , the second sub-lens group frame  54 , the actuator ring  55 , and the front shutter retaining ring  51  when the first sub-lens group frame  53  and the second sub-lens group frame  54  are in the mutually close position on the telephoto side, and are in a position so as to focus on an object at infinity. FIGS. 20A and 20B show an arrangement of the first sub-lens group frame  53 , the second sub-lens group frame  54 , the actuator ring  55 , and the front shutter retaining ring  51  when the first sub-lens group frame  53  and the second sub-lens group frame  54  are in the mutually close position on the telephoto side, and are in a position so as to focus on an object at a minimum distance. The first sub-lens group frame  53 , the second sub-lens group frame  54 , the actuator ring  55 , and the front shutter retaining ring  51  are shown separated in the optical axis direction in FIGS. 17A,  18 A,  19 A and  20 A, and are shown in operation in FIGS. 17B,  18 B,  19 B and  20 B. 
     Gear teeth  55   g  are formed over a circumference on the rear-end periphery of the actuator ring  55 . As shown in FIGS. 12,  29  and  30 , the gear teeth  55   g  engage with a series of reduction gears  63   a . The series of reduction gears  63   a  are rotated in either direction by a bi-directional motor  64  which also includes the encoder  64   p . The series of reduction gears  63   a  are held between the front shutter retaining ring  51  and the gear holding ring  56 , and the bi-directional motor  64  is held by the rear shutter retaining ring  52 . The gear teeth  55   g  of the actuator ring  55 , which are formed over the entire periphery thereof, makes it easy for the three control recesses  55   a  to engage with the three lugs  54   e  of the second sub-lens group frame  54  at different relative rotational positions that are separated by 120°. 
     The lens shutter mechanism  57  and the diaphragm mechanism  58  are mounted on the rear shutter retaining ring  52 . In particular, as shown in FIGS. 12,  15  and  16 , the lens shutter mechanism  57  includes a shutter sector support plate  57   a , three shutter sectors  57   b , and a shutter drive ring  57   c  for opening and closing the shutter sectors  57   b . The diaphragm mechanism  58  includes a diaphragm sector support plate  58   a , three diaphragm sectors  58   b , and a diaphragm drive ring  58   c  for opening and closing the diaphragm sectors  58   b . These components are retained in the rear shutter retaining ring  52  by a sector holding ring  57   d . The shutter sector  57   b  and the diaphragm sector  58   b  include a pair of dowels. One of the dowels is rotatably supported by the support plates  57   a  and  58   a  and the other is rotatably fitted to the drive rings  57   c  and  58   c . The lens shutter mechanism  57  opens and closes an aperture formed by the shutter sectors  57   b  as the shutter drive ring  57   c  is rotated. The diaphragm mechanism  58  varies the size of an aperture formed by the diaphragm sectors  58   b  as the diaphragm drive ring  58   c  is rotated. 
     Sector gear teeth  57   g  are formed on a part of the periphery of the shutter drive ring  57   c  and engage with a series of reduction gears  63   b  that are sequentially arranged from a shutter drive motor  57   m  (see FIG.  12 ). When the shutter drive motor  57   m  is rotated in either direction, the aperture, which has been closed by the shutter sectors  57   b , is momentarily opened and is then closed again. In the zoom lens barrel of the illustrated embodiment, the shutter sectors  57   b  serve both as a variable diaphragm to provide an aperture of an arbitrary size, and as a shutter. The shutter sectors  57   b  are electrically controlled so that the size of the aperture of the shutter sectors  57   b  (aperture value) and the length of time during which the aperture is left opened (i.e., shutter speed) can be varied depending on the exposure, upon the release of the shutter. Furthermore, the diaphragm drive ring  58   c  includes a lug  58   g  on the periphery thereof. The lug  58   g  engages with a diaphragm-controlling cam slot  48   s  formed on an inner surface of the linear guide ring  48  (see FIG.  10 ). Upon zooming, the linear guide ring  48  and the rear shutter retaining ring  52  (i.e., the diaphragm drive ring  58   c ) moves relative to each another in the optical axis direction. This causes the lug  58   g  to follow the diaphragm-controlling cam slot  48   s  so as to move in the circumferential direction. This in turn causes the diaphragm drive ring  58   c  to rotate and, as a result, the size of the aperture formed by the diaphragm sectors  58   b  is varied. The diaphragm sector  58   b  is provided to restrict the maximum value of the aperture diameter especially in the wide-angle side photographing range, and the degree of opening of the aperture is mechanically varied in accordance with the amount of extension of the zoom lens barrel. 
     As shown in FIG. 31, the zooming motor  46  for the cam ring  44 , the bi-directional motor  64  for the actuator ring  55 , and the shutter drive motor  57   m  for the lens shutter mechanism  57  are controlled by a control circuit (control device)  66 . Focal length information  67 , which is set by the user (photographer) via a zoom switch or the like, detected object distance information  68 , object brightness information  69 , information on rotational positions of the cam ring  44 , which is provided by a focal length detecting device  46 C, and information on rotational positions of the motor  64 , which is provided by the encoder  64   p , are inputted to the control circuit  66 . The zooming motor  46 , the bi-directional motor  64  and the shutter drive motor  57   m  are controlled according to the inputted information so that exposure is carried out under proper exposure conditions in accordance with the predetermined focal lengths. While the shutter sectors  57   b  serve both as a shutter and as a variable diaphragm, and the diaphragm sectors  58   b  restrict the aperture diameter upon photographing on the wide-angle side in this embodiment, the diaphragm sectors  58   b  can be provided as a motor-driven variable diaphragm mechanism. 
     In the illustrated embodiment, the focal length detecting device  46 C (i.e., a rotational position detecting device for the cam ring  44 ) detects rotational positions of the cam groove  44   f  which correspond to the connection line CC (see FIG.  1 ), such that the control circuit  66  does not allow the cam ring  44  to stop in this section. If the zoom lens system is provided as a step zoom lens, positions at which the cam ring  44  stops are controlled in a stepwise manner. As described above, while the operations, corresponding to the preset focal length, distance to the object, and the brightness of the object, of the zoom lens barrel (i.e., photographing optical system) having the above-described switching lens group can be completed immediately before the shutter is released, the focal length set by an operator can be confirmed via a separate finder optical system (not shown) that is provided separate from the photographing optical system. 
     In the above-described zoom lens barrel, the first sub-lens group S 1  is supported in the first sub-lens group frame  53  while the second sub-lens group S 2  is supported in the second sub-lens group frame  54 . The first sub-lens group frame  53  and the second sub-lens group frame  54  are supported in the switching lens group frame  50  in such a manner that the sub-lens group frames  53  and  54  are each allowed to move in the optical axis direction. The lens shutter mechanism  57  is secured to the switching lens group frame  50  in the rear (i.e., image side) of the second sub-lens group frame  54 . The lens shutter mechanism  57  does not move in the optical axis direction with respect to the switching lens group frame  50 . 
     Upon a focusing operation, the first sub-lens group frame  53  and the second sub-lens group frame  54  are moved along integrally, with respect to the lens shutter mechanism  57  by the focusing mechanism (i.e., actuator ring  55 ) and the cam mechanism (i.e.,  55   d ,  55   e  and  54   a  ) in the short-focal-length side zooming range and in the long-focal-length side zooming range. In this manner, adjustment of components/members as well as optical adjustments near the switching lens group  10  are facilitated. For example, with in the switching lens group frame  50 , if the lens shutter mechanism  57  is fixed at a position behind the switching lens group  10 , if optical problems occur within the switching lens group  10 , the cause thereof is easier to establish due to have the lens shutter mechanism  57  as a reference. 
     Furthermore, the diaphragm mechanism  58  is mounted on the switching lens group frame  50  on the image side of the lens shutter  57 . This construction enables more precise control of exposure. 
     While the first sub-lens group frame  53  and the second sub-lens group frame  54  are maintained in the mutually close position in the long-focal-length side zooming range and in the mutually distant position in the short-focal-length side zooming range in the embodiments shown, this relationship may be reversed depending on the construction of the zoom lens system. 
     As in the above-described embodiments, a smooth zooming action is achieved and unnecessary movements are reduced by moving the lens switching group frame  50  so that the path of the lens shutter mechanism  57  is not discontinuous in the short-focal-length side zooming range and in the long-focal-length side zooming range, which extend on both sides of the intermediate focal length. 
     In the zoom lens barrel using the lens barrel for the switching lens groups, positions at which the switching lens group frame  50 , the first sub-lens group frame  53 , and the second sub-lens group frame  54  stop during photographing can be practically determined in a stepwise manner along the zoom path. 
     As can be understood from the above discussion, the present invention provides a lens barrel for switching lens groups which is essential in achieving a compact zoom lens system with a high zooming ratio. 
     However, the zoom lens barrel according to the present invention is not limited to the illustrated embodiments. For example, while the mechanism for selectively moving the sub-lens group frames  53  and  54  includes the actuator ring  55 , which is rotated in either direction, and the lens group shift mechanism (i.e., the shift cam mechanism) arranged between the first sub-lens group frame  53  and the second sub-lens group frame  54  in the embodiments shown, the first sub-lens group frame  53  and the second sub-lens group frame  54  can be advanced or retreated via known alternative mechanisms such as a feed screw mechanism and a solenoid mechanism. 
     Also, while the actuator ring  55  also serves as the focusing mechanism in the embodiments shown, a mechanism separate from the actuator ring  55  or other linear moving mechanisms may be employed to enable the first sub-lens group frame  53  and the second sub-lens group frame  54  to move integrally in the mutually close position (extremity) and in the mutually distant position (extremity) for focusing. 
     Note that, while the present invention has been described with regard to the first variable lens group  10  shown in FIGS. 1,  8  and  9 , the mechanical construction of the above-described lens barrel is also applicable to the second variable lens group  20  in FIG. 2, the second variable lens group  20  in FIG. 3, the first variable lens group  10  in FIG. 4, the first variable lens group  10  in FIG. 5, the first variable lens group  10  in FIG. 6, and the first variable lens group  10  in FIG. 7 (the first lens L 1  is integrally formed with the third lens L 3 ). 
     Furthermore, obvious changes may be made in the specific embodiments of the present invention described herein, such modifications being within the spirit and scope of the invention claimed. It is indicated that all matter contained herein is illustrative and does not limit the scope of the present invention.