Abstract:
A lens apparatus includes four lens groups and a plurality of barrels with grooves that guide and drive the lens frames of the four lens groups in order to achieve a high zoom ratio and retraction of the lens apparatus into a camera body when the lens apparatus is not in use. Two sets of three guide grooves in a fixed barrel and three cam grooves in a cam barrel are unequally spaced around the circumference of the barrels so as to provide more room for an additional groove in the cam barrel. Some of the lens frames are fully supported by pins in the grooves and some of the lens frames are partially supported by guide rods in the lens apparatus. A single guide rod helps support two lens frames in order to save space in the lens apparatus.

Description:
BACKGROUND OF THE INVENTION 
     Recent electronic still cameras include a lens barrel that can be housed in a camera body when not in use in order to satisfy the requirement for compactness when the camera is not in use. The lens barrel and lens groups forming the lens system of the camera are supported in the camera to be movable along the optical axis. The lens barrel and the lens groups are extended to various positions toward an object being imaged when the camera is being used for imaging, and the lens barrel and lens groups are retracted to or toward positions inside the camera body when the camera is not in use. 
     For example, Japanese Laid-Open Patent Application No. 2001-242368 discloses a lens apparatus with a lens barrel and lens groups that are movable along the optical axis. First and second lens groups, in order from the object side, are movably supported in three-way suspensions by pins. Third and fourth lens groups, in order from the object side, are movably supported by guide bars. The lens apparatus may be retracted to a position where its retracted length is only 60 percent of its maximum extended length. 
     The lens apparatuses of recent electronic still cameras are also required to provide a bright image along with high zoom ratios. This, in turn, requires an increased number of lenses and lens groups. Additionally, an increasing number of lens apparatuses have been designed to house drive mechanisms such as motors in the lens barrel for further compactness. Especially recently, much higher zoom ratios have been demanded. However, the prior art structures hamper achieving a high zoom ratio with compactness. 
     For example, the lens apparatus described in Japanese Laid-Open Patent Application No. 2001-242368, discussed above, includes three lens frames that are movable by cam pins on their outer periphery that are engaged with forwarding grooves on a fixed barrel and with cam grooves on a cam barrel provided on the outer periphery of the fixed barrel. More specifically, three forwarding grooves for each of the fixed lens group and the zoom lens group are provided on the fixed barrel at regular intervals circumferentially around the periphery of the fixed barrel, and three cam grooves for each of the fixed lens group and the zoom lens group are provided on the cam barrel at regular intervals circumferentially around the cam barrel. Additionally, a forwarding groove for a relay lens group is provided on the fixed barrel, and a cam groove for the relay lens group is provided on the cam barrel. 
     With the above described structure, in order to obtain a zoom ratio of eight, the cam grooves are highly inclined so as to increase the movements of the lens groups. Thus, the cam grooves must be made more nearly parallel to the optical axis or the cam barrel must have a larger circumference in order to increase the movements of the lens groups. However, if the cam grooves are made more nearly parallel to the optical axis, the cam grooves receive an increased force in the normal direction and, therefore, the frictional drag between the cam groove and the cam pins increases, which can lead to malfunctioning of the lens apparatus. On the other hand, making the circumference of the cam barrel larger is counter to the requirement for compactness. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention relates to a compact lens apparatus that provides a high zoom ratio that can be used in an electronic still camera. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will become more fully understood from the detailed description given below and the accompanying drawings, which are given by way of illustration only and thus are not limitative of the present invention, wherein: 
     FIG. 1 shows a perspective view of the exterior of an electronic still camera that includes a lens apparatus according to a preferred embodiment of the present invention; 
     FIG. 2 shows the lens apparatus of FIG. 1 in the retracted state; 
     FIG. 3 shows the lens apparatus of FIG. 1 in the extended state at a wide-angle setting; 
     FIG. 4 shows the lens apparatus of FIG. 1 in the extended state at a telephoto setting; 
     FIG. 5 shows an exploded perspective view of the lens apparatus of FIG. 1; 
     FIG. 6 shows a cross-sectional view of the lens apparatus of FIG. 1 taken along the  5 — 5  line of FIG. 2; 
     FIG. 7 shows a cross-sectional view of the lens apparatus of FIG. 1 taken along the  6 — 6  line of FIG. 2; and 
     FIG. 8 is a diagram of an interior view of the cam barrel, including cams, of the lens apparatus of FIG.  1 . 
    
    
     DETAILED DESCRIPTION 
     A preferred embodiment of a lens apparatus of the present invention will now be described with reference to the attached drawings. In the following description, elements that are essentially identical, except for their location, are denoted by the same reference symbol that will be recited only once when the essentially identical elements are being referenced. 
     FIG. 1 shows a perspective view of the exterior of an electronic still camera  1  that includes a lens apparatus  2  according to the present invention. As shown in FIG. 1, the electronic still camera  1  has generally a rectangular box-shaped body that is provided with a lens apparatus  2 , a strobe light adjusting sensor  3 , and a self-timer  4  on a front surface of the camera. The top of the camera includes a shutter button  5  and a pop-up strobe  6 . The back of the camera, which is not shown in the drawings, may include a finder ocular, a liquid crystal display panel, and controls for operation of the camera. 
     The electronic still camera  1  is of the retractable type. The lens apparatus  2  is extended for use, and the lens apparatus is retracted when not in use so that the front of the lens apparatus  2  is nearly flat when the camera is not in use. 
     FIGS. 2 to  4  show cross-sectional views of the lens apparatus  2  of FIG.  1 . FIG. 2 shows the lens apparatus  2  in the retracted state, and FIGS. 3 and 4 show the lens apparatus  2  in the extended state at different lens settings. FIG. 5 shows an exploded perspective view of the lens apparatus of FIG.  1 . As shown in FIGS. 2 to  5 , the lens apparatus  2  includes a lens barrel  12 , a camera lens  14 , a diaphragm shutter unit  16 , and a CCD unit  18 . 
     First, the structure of the lens barrel  12  will be described. The lens barrel  12  includes a fixed barrel  20 , a movable barrel  22  that is movable in the fixed barrel  20 , and a cam barrel  24  that is rotatable on the outer periphery of the fixed barrel  20 . The fixed barrel  20  has a cylindrical body with a flat base  26  at the image end. The lens apparatus  2  is mounted on the camera body with the base  26  fixed to the camera body, a connection that is not shown in the drawings. 
     The movable barrel  22  has a cylindrical shape and is movable back and forth in the fixed barrel  20 . The movable barrel  22  includes three first cam pins  28  unequally spaced in the circumferential direction on the outer periphery of the movable barrel  22  near its base end. Each first cam pin  28  is engaged with a different one of three first forwarding grooves  30  formed on the fixed barrel  20 . The first forwarding grooves  30  are parallel to the longitudinal axis of the fixed barrel  20  that defines an optical axis so that the movable barrel  22  can move back and forth along the optical axis with respect to the fixed barrel  20 . 
     The cam barrel  24  has a cylindrical body and is rotatable on the outer periphery of the fixed barrel  20 . The cam barrel  24  has three first cam grooves  32 , three second cam grooves  34 , and a third cam groove  36  (FIG. 7) on its inner periphery. The cam grooves are arranged so that they do not overlap each other. 
     The first cam grooves  32  and the second cam grooves  34  are unequally spaced in the circumferential direction on the inner periphery of the cam barrel  24  so as to use the surface of the cam barrel  24  most efficiently. The third cam groove  36  is provided on the cam barrel  24  between the first cam groove  32  and the second cam groove  34  that are separated the greatest distance in the circumferential direction on the cam barrel  24 . 
     The three first cam pins  28  on the outer periphery of the movable barrel  22  fit through the three forwarding grooves  30  on the fixed barrel  20  into three first cam grooves  32  on the cam barrel  24 . The first cam grooves  32  and the first forwarding grooves  30  serve to move the movable barrel  22  back and forth along the optical axis when the cam barrel  24  rotates. The first cam groove  32  includes a section A and a section B as shown in FIG.  8 . Section A guides the movable barrel  22  from the retracted position to the extended position, and Section B retains the movable barrel  22  at the extended position. 
     The cam barrel  24  is driven by a cam barrel driving motor  38  housed in the fixed barrel  20  with a drive mechanism configured as follows. As shown in FIGS. 3,  5 , and  7 , where FIG. 7 shows a cross-sectional view of the lens apparatus of FIG. 1 taken along line  6 — 6  of FIG. 2, the cam barrel driving motor  38  is fixed to the inner surface of the base  26  via a gear box  40 . The gear box  40  serves to reduce the rotation rate of the cam barrel driving motor  38  at a certain gear ratio, and its output shaft is fixed to a driving gear  42 . Additionally, an internal gear  44  is provided on the inner periphery of the cam barrel  24  at its base end. The driving gear  42  is engaged with the internal gear  44 . With the driving mechanism described above, the cam barrel driving motor  38  is driven to rotate the driving gear  42  that transmits the rotation to the internal gear  44  so as to rotate the cam barrel  24 . 
     A photo-interrupter  45  (see FIG. 5) for detecting the amount of rotation of the cam barrel  24  is provided on the cam barrel driving motor  38 . The photo-interrupter  45  outputs pulse signals to a control unit in the camera body according to the amount of rotation of the output shaft of the cam barrel driving motor  38  when the cam barrel driving motor  38  is driven. The control unit in the camera body counts the output pulses from the photo-interrupter  45  to calculate the amount of rotation of the cam barrel  24 . 
     Next, the structure of the camera lens  14  will be described. The camera lens  14  is a four-group zoom lens that includes a fixed lens group  46 , a zoom lens group  48 , a relay lens group  50 , and a focusing lens group  52 . The fixed lens group  46  is held by a first lens frame  54 . A male screw member  54   a  is provided on the outer periphery of the lens frame  54  at its base end. A female thread (i.e., screw member)  22   a  is provided on the inner periphery of the movable barrel  22  at its front or object end, opposite the base end. The male screw member  54   a  is screwed into the female thread  22   a  in order to fix the first lens frame  54  to the movable barrel  22  at its front or object end. With the first lens frame  54  fixed to the movable barrel  22  in this way, the fixed lens group  46  moves together with the movable barrel  22  as one piece. A decorative ring  55  is provided at the object end of the movable barrel  22  where the fixed lens group is mounted. 
     The fixed lens group  46  is followed, on its image side, by the zoom lens group  48 , which is held by a second lens frame  56 . FIG. 6 shows a cross-sectional view of the lens apparatus of FIG. 1 taken along the  5 — 5  line of FIG.  2 . The second lens frame  56  has three second cam pins  58  unequally spaced on the outer periphery at its base end as shown in FIG.  6 . That is, the second cam pins  58  are spaced at irregular intervals in the circumferential direction of the lens barrels. As shown in FIG. 6, the circumferential distances of the right second cam pin  58  from the other two second cam pins  58  is about equal, but the circumferential distance of the left second cam pin  58  from the top second cam pin  58  is substantially less than those distances. The second cam pins  58  fit in three second forwarding grooves  60  formed on the fixed barrel  20 . The second forwarding grooves  60  are formed in the longitudinal direction (i.e., parallel to the optical axis) of the fixed barrel  20  so that the second cam pins  58  support the second lens frame  56  to be movable along the optical axis within the fixed barrel  20 . The second cam pins  58  also fit in three second cam grooves  34  on the cam barrel  24 . The three second cam grooves  34  and the three second forwarding grooves  60  serve to move the second lens frame  56  back and forth along the optical axis when the cam barrel  24  rotates. 
     FIG. 8 is a diagram of an interior view of the cam barrel  24 , including cams, of the lens apparatus of FIG.  1 . As shown in FIG. 8, the three second cam grooves  34  guide the second lens frame  56  from the retracted position to the wide-angle end in the section C of the three second cam grooves  34  and from the wide-angle end to the telephoto end in the section D. 
     The zoom lens group  48  is followed by the relay lens  50 , which is held by a third lens frame  62 . The third lens frame  62  is integrally provided with two guide members or guide blocks  64 ,  66  and a third cam pin  68  as shown in FIG.  7 . The two guide blocks  64 ,  66  have cylindrical and U-letter shapes, respectively. The cylindrical guide block  64  is fitted on a first guide bar  70  provided in the fixed barrel  20 . The U-letter shaped guide block  66  is fitted on a second guide bar  72  provided in the fixed barrel  20 . 
     The first and second guide bars  70  and  72  are arranged to be parallel to the longitudinal axis of the fixed barrel  20 , as shown in FIGS. 2 to  4 . The base ends of the first and second guide bars are fixed to the inner surface of the base  26  and the front ends of the first and second guide bars are supported by a front supporting mechanism  104  that is provided in the movable barrel  22  (the detailed structure of the front supporting mechanism  104  will be described later). The guide blocks  64 ,  66  are slidably fixed to the first and second guide bars  70  and  72 , respectively. Thus, the third lens frame  62  is supported so that it is movable along the optical axis within the fixed barrel  20 . 
     A single cam pin  68  is fitted in a third forwarding groove  74  on the fixed barrel  20  and in the third cam groove  36  on the cam barrel  24 . The third forwarding groove  74  is parallel to the longitudinal axis of the fixed barrel  20 . The third cam groove  36  and the third forwarding groove  74  serve to move the third lens frame  62  back and forth along the optical axis when the cam barrel  24  rotates. As shown in FIG. 8, the third cam groove  36  guides the third lens frame  62  from the retracted position to the imaging position in the section E of the third cam groove  36  and retains the third lens frame  62  at the extended position in the section F. 
     The relay lens  50  is followed by the focusing lens group  52 , which is held by the fourth lens frame  76 . As shown in FIG. 7, the fourth lens frame  76  is integrally provided with two guide blocks  78 ,  80  on its outer periphery. The two guide blocks  78 ,  80  have cylindrical and U-letter shapes, respectively. The cylindrical guide block  78  is fitted on a third guide bar  82  provided in the fixed barrel  20 . The U-letter shaped guide block  80  is fitted on the second guide bar  72  provided in the fixed barrel  20 . 
     The second guide bar  72  on which the U-letter shaped guide block  80  is fitted also guides the third lens frame  62 . Thus, the third and fourth lens frames  62  and  76  share a guide bar. Sharing a guide bar leaves more usable space in the fixed barrel  20  where motors and other devices can be placed. 
     The third guide bar  82  on which the cylindrical guide block  78  is fitted is used only by the guide block  78 . The third guide bar  82  is arranged so as to be parallel to the longitudinal axis of the fixed barrel  20  with the base end being fixed to the inner surface of the base  26  and the front end being supported by the front supporting mechanism  104  that supports the first and second guide bars  70  and  72 . 
     As described above, the guide blocks  78  and  80  are slidably fitted on the third and second guide bars  82  and  72 , respectively. In this way, the fourth lens frame  76  is supported so that it is movable along the optical axis within the fixed barrel  20 . The lens apparatus  2  moves the fourth lens frame  76  along the optical axis for focusing. 
     The fourth lens frame  76  is driven by a focusing lens driving unit  84  as follows. A lead screw  86  is provided along the optical axis in the fixed barrel  20  as shown in FIGS. 4 to  7 . The lead screw  86  is rotatably supported at both ends by a bracket  88  that is fixed to the inner surface of the base  26 . A guide rod  90  is provided near and parallel to the lead screw  86 . Both ends of the lead screw  86  are fixed to the bracket  88 . A slide piece  92  is slidably supported by the guide rod  90 . The slide piece  92  has a nut  94  that is screwed on the lead screw  86 . Thus, the slide piece  92  moves back and forth according to the rotation of the lead screw  86  when the lead screw  86  rotates. 
     A follower gear  96  is fixed to the lead screw  86  at the front end of the lead screw  86 . The follower gear  96  is engaged with a driving gear  98  that is fixed to the output shaft of a focusing lens driving motor  100 . The focusing lens driving motor  100  is fixed to the bracket  88 . The focusing lens driving motor  100  operates to rotate the driving gear  98 . The rotation of the driving gear  98  is transmitted to rotate the lead screw  86 . Rotation of the lead screw  86  causes the slide piece  92  to move along the guide rod  90 . 
     The fourth lens frame  76  is connected to the slide piece  92  via a spring  102 . Moving the slide piece  92  causes the fourth lens frame  76  to move. Moving the slide piece  92  backward triggers the spring  102  to pull and move the fourth lens frame  76  backward. In contrast, moving the slide piece  92  forward triggers the slide piece  92  to push and move the fourth lens frame  76  forward. The fourth lens frame  76  is pushed by the slide piece  92  through a projection  76   a  that protrudes from the rear end of the fourth lens frame  76  and abuts the slide piece  92 . In this way, the fourth lens frame  76  moves back and forth along the optical axis when the focusing lens driving motor  100  is driven to move the slide piece  92  back and forth. The spring  102  connects the fourth lens frame  76  to the slide piece  92  so that the fourth lens frame  76  moves without backlash between the nut  94  and the lead screw  86 . This ensures accurate movements of the fourth lens frame  76 . A focusing lens driving unit  84  receives power and control signals via a focusing lens driving unit flexible board  103 . 
     The camera lens  14 , as described above, includes four lens groups: a fixed lens group  46 , a zoom lens group  48 , a relay lens group  50 , and a focusing lens group  52 . Among them, the fixed and zoom lens groups  46  and  48  are supported in three-way suspensions by pins, as well as the relay lens group  50  and the focusing lens group  52 , are supported by guide bars. As described above, the relay and focusing lens groups  50  and  52  are supported by the first, second, and third guide bars  70 ,  72 , and  82 . The guide bars are supported by the front supporting mechanism  104  at their front ends. The front supporting mechanism  104  will now be described. 
     As shown in FIGS. 2 to  5 , the front supporting mechanism  104  includes primarily a middle frame  106  and a stopper ring  108 . The middle frame  106  has a cylindrical body that is slidably fitted in the inner periphery of the movable barrel  22 . The middle frame  106  has three supporting parts  110  on the inner periphery of the middle frame  106  at the positions of the guide bars for supporting the front ends of the guide bars. Each supporting part  110  includes a bore  110   a  that extends parallel to the optical axis and has nearly the same diameter as the corresponding guide bar. Each guide bar is fitted into a bore  110   a  to obtain support at its front end. 
     The stopper ring  108  has a ring shape and is fixed to the inner periphery of the base end of the movable barrel  22 . The middle frame  106  is supported so that it is slidable in the movable barrel  22  except for backward movement being restricted by the stopper ring  108 . A pair of spring hooks  108   a  protrude on the inner periphery of the stopper ring  108 . A pair of spring hooks  106   a  protrude on the inner periphery of the middle frame  106 . Each spring  112  is hooked between a spring hook  106   a  and a spring hook  108   a . This gives backward bias to the middle frame  106  as it slides in the movable barrel  22 . 
     The front supporting mechanism  104 , as described above, operates as described below. 
     The middle frame  106  is situated at the base end of the movable barrel  22  in an extended state of the lens apparatus  2 , as shown FIGS. 3 and 4. This is because the spring  112  biases the middle frame  106  backward. In this state, the guide bars are supported by the front supporting part  110  with their front ends fitted in the bores  110   a.    
     When the movable barrel  22  is retracted, the middle frame  106  is pulled and moves backward. However, as shown in FIG. 2, with the front supporting part  110  contacting the guide block  64 , the middle frame  106  withdraws against the bias force of the spring  112  because it is slidable in the movable barrel  22 . This avoids the problem that the movable barrel  22  cannot be further retracted because the middle frame  106  contacts guide block  64 . With the base ends of the guide bars fixed and the front ends supported by the front supporting mechanism  104 , the guide bars are able to guide the lens frame without vibrations and other problems of moving the lens frames. 
     An additional pair of spring hooks (not shown in the drawings), other than spring hooks  106   a , are provided on the inner periphery of the middle frame  106 . These two spring hooks are used with the two hook springs  113  shown in FIG.  5 . The other ends of the two hook springs  113  are hooked by spring hooks formed on the second lens frame  56  that are the spring hooks not shown in the drawings. In this way, the hook springs  113  continuously bias the middle frame  106  and the second lens frame  56  toward each other. This eliminates looseness that may occur while the movable barrel  22  and the second lens frame  56  move. 
     Both the movable barrel  22  and the second lens frame  56  are supported by the cam pins in the three-way suspensions. There is a gap between the cam pins and the cam grooves in which the cam pins fit. This causes looseness during movements of the lens frames, particularly when the rotational directions of the lens frames driving structures are reversed. Biasing the middle frame  106  and the second lens frame  56  toward each other causes the cam pin to constantly press the inner wall of the cam groove. This eliminates looseness during these movements and securely guides the lens frames. 
     The structure of the diaphragm shutter unit  16  is described below. The diaphragm shutter unit  16  is positioned between the zoom lens group  48  and the relay lens group  50  and is fixed to the third lens frame  62  as shown in FIGS. 2 to  4 . The diaphragm shutter unit  16  is provided with a diaphragm and a shutter, which are not shown in the drawings. The diaphragm is driven by a diaphragm motor  114  (see FIG. 6) to adjust the aperture. The shutter is driven by a shutter motor  116  (see FIG. 6) that opens and closes the shutter. 
     Both the diaphragm motor  114  and shutter motor  116  are provided in the diaphragm shutter unit  16  and operate based on driving signals from the control unit in the camera body. They are driven based on driving signals from the control unit in the camera body to set the diaphragm and shutter for certain diaphragm stop settings and shutter speeds. The diaphragm shutter unit  16  receives power and driving signals via a diaphragm shutter unit flexible printed circuit board  122  as shown in FIG.  5 . 
     As shown in FIG. 7, a through-channel  118  is formed on the outer periphery of the third lens frame into which the diaphragm shutter unit flexible printed circuit board  122  is inserted. Being inserted in the through-channel  118 , the diaphragm shutter unit flexible printed circuit board  122  cannot become dislocated in the fixed barrel  20 . 
     The structure of the CCD unit  18  will now be described. The CCD unit  18  is behind, that is, on the image side, of the focusing lens group  52  and fits in an opening  120  formed in the center of the base  26  that is centered on the optical axis of the lens apparatus  2 , as shown in FIGS. 2 to  4 . Light that has entered the camera lens  14  is converted to image signals by the CCD unit  18  and is output to the camera body via a main printed circuit board  124  (see FIG.  5 ). 
     The lens apparatus  2  having the structure described above is mounted in the camera body with the base  26  fixed to the camera body. The lens apparatus  2  is mounted with most or all of the lens apparatus  2  being inside the camera body when the lens apparatus  2  is in the retracted position. The driving mechanisms, including motors, are driven based on driving signals from the control part in the camera body to move the lens apparatus to an extended state. 
     The lens apparatus  2  of this embodiment, which has the structure described above, operates as described below. As shown in FIG. 2, the movable barrel  22  is housed in the fixed barrel  20  when the lens apparatus  2  is not in use. This is the retracted state. When the camera body is set for the stand-by state from the retracted state, the cam barrel driving motor  38  (see FIG. 7) is driven to rotate the cam barrel  24  at a certain rate. This results in extending the movable barrel  22  from the fixed barrel  20  to the extended position shown in FIG.  3 . With the movable barrel  22  being extended, the second and third lens frames  56  and  62  move forward by a certain distance and stop. Consequently, the zoom lens group  48  reaches the wide-angle end and the relay lens group  50  reaches the imaging position. 
     The focusing lens driving motor  100  drives the fourth lens frame  76  forward by a certain distance while the cam barrel driving motor  38  is driven. This positions the focusing lens group  52  at a stand-by focus position. The lens apparatus  2  is now in the stand-by state in which the camera lens  14  is at the wide-angle end. Here, the following detection mechanism is used to detect that the zoom lens group  48  is at the wide-angle end. 
     As shown in FIG. 5, a photodetector  128  is provided inside the base  26  via a mounting plate  126 . A reflecting plate  130  is provided on the inner periphery of the cam barrel  24  at a certain position. An opening  132  is formed on the outer periphery of the fixed barrel  20  at the position corresponding to the photodetector  128 . The photodetector  128  is turned on when the reflecting plate  130  is aligned with the opening  132 . The reflecting plate  130  is positioned so that it is aligned with the opening  132  when the zoom lens group  48  reaches the wide-angle end. Thus the photodetector  128  detects when the zoom lens group  48  is at the wide-angle end. 
     A detection mechanism detects when the focusing lens group  52  is at the stand-by focus position as described below. A photo-interrupter  136  is provided inside the base  26  via a mounting plate  134  as shown in FIG. 5. A target member (not shown in the drawings) is provided on the fourth lens frame  76 . The photo-interrupter  136  is turned on when the target member is aligned with it. The photo-interrupter  136  and the target member are arranged so that the target member is aligned with the photo-interrupter  136  when the focusing lens group  52  has reached the focus position. Thus, the status that the focusing lens group  52  is at the stand-by focus position is detected. The photo-interrupters  45  and  136  and the photodetector  128  operate with power and pulse signals that are transmitted or received via a flexible printed circuit board  138 . 
     In this way, the lens apparatus obtains the stand-by state. With the lens apparatus  2  in the stand-by state, a zoom switch (not shown in the drawings) provided on the camera body can be switched to the telephoto setting so that the zoom lens group  48  moves in a zooming mode toward the telephoto end. When the zoom switch is switched to the telephoto setting, the cam barrel driving motor  38  (see FIG. 7) drives the cam barrel  24  in the direction that causes the zoom lens group  48  to move forward in the extended direction toward the object side. As a result, the zoom lens group  48  moves toward the telephoto end in the zoom mode. FIG. 4 shows the camera lens  14  at the telephoto end of the zoom range. During zooming, the zoom lens group  48  moves between the wide-angle end shown in FIG.  3  and the telephoto end shown in FIG. 4 while the fixed lens group  46  and the relay lens group  50  remain at fixed positions. 
     A new position of the zoom lens group  48  can be detected using the amount of rotation of the cam barrel  24 . The zoom lens group  48  moves in proportion to the amount of rotation of the cam barrel  24 . The amount of rotation of the cam barrel  24  after the zoom lens group  48  reaches the wide-angle end can be used to determine the position along the optical axis of the zoom lens group  48 . The zoom ratio can be obtained based on the position of the zoom lens group  48 . 
     The zoom ratio corresponding to the rotated position of the cam barrel  24  is calculated based on the number of pulses from the photo-interrupter  45  in accordance with the amount of rotation of the cam barrel  24  caused by the cam barrel driving motor  38 , as described above. In this way, the camera lens  14  is set for a desired zoom ratio and is ready for recording an image. 
     In this state, the user pushes the shutter button on the camera body so that focusing is conducted based on the information of the distance of the object being imaged. The focusing lens driving motor  100  is driven to move the focusing lens group  52  to an in-focus position from the stand-by focus position. Then, the diaphragm motor  114  (see FIG. 6) and shutter motor  116  are driven based on the exposure information of the object so that a picture is taken with a certain diaphragm stop and a certain shutter speed. After recording an image, the focusing lens driving motor  100  is driven again to return the focusing lens group  52  to the stand-by focus position. 
     After recording of an image is completed, the camera is turned off, and the movable barrel  22  group is retracted. In this process of retraction, the movable barrel  22  and the lens groups are retracted as follows. First, the focusing lens driving motor  100  is driven to move the fourth lens frame  76  backward toward the image position (to the right as shown in FIGS.  2 - 4 ). When the focusing lens group  52  reaches a predetermined position, the cam barrel driving motor  38  is driven to move the movable barrel  22 , the second lens frame  56 , and the third lens frame  62  backward (to the right as shown in FIGS.  2 - 4 ). In this way, the movable barrel  22  is retracted and both the moveable barrel  22  and the fixed barrel  20  are housed, as shown in FIG.  2 . 
     As described above, the focusing lens group  52  is first retracted to a predetermined position and, then, the other lens groups are retracted. This is to prevent the relay lens group  50  from contacting the focusing lens group  52 , which may occur if all the lens groups were retracted simultaneously. The cam barrel driving motor  38  is designed to operate after the focusing lens group  52  is retracted to a position out of contact with the relay lens group  50 . 
     With the lens apparatus  2  of the embodiment described above, the movable barrel  22  is extended from the fixed barrel  20  only for recording an image. The lens apparatus  2  of this embodiment moves the lens groups to respective predetermined positions to take pictures. When the lens groups move, two lens groups, the fixed and zoom lens groups  46  and  48 , move with support from the three-way suspensions and the other lens groups, the relay and focusing lens groups  50  and  52 , move with support from the guide bars in the lens apparatus  2 , which require less space for movement compared to the three-way suspensions. Reducing the space required for lens frame movements in the lens barrel  12  allows other devices, such as the driving motors, to be housed in the lens barrel while reducing the overall size of the lens apparatus. 
     Having lens frames share a guide bar, as in this embodiment, also leaves more usable space in the lens barrel  12 . Still, all the guide bars are securely supported at the both ends while they guide the lens groups. 
     The invention being thus described, it will be obvious that the same may be varied in many ways. For example, in the lens apparatus in which multiple lens groups move, only one lens group can be supported in a three-way suspension and the others can be supported by the guide bars that require less space for movement compared to the three-way suspension. This may further assist in obtaining high zoom ratios and reducing the space required for lens frame movement in the lens barrel  12 . Additionally, although in the preferred embodiment described above, the first and second lens groups of the four-group zoom lens are supported in three-way suspensions, the lens groups that are supported in the three-way suspension are not confined to the first and second lens groups. For example, the first and third lens groups can be supported in three-way suspensions. Selection between the three-way suspension and the guide bars may be made depending on the diameter of the lens groups. For example, two lens groups with larger diameters may be supported in three-way suspensions and the other lens groups may be supported by the guide bars. This ensures secure operations of the lens groups. Furthermore, although in the preferred embodiment described above, a four-group zoom lens is used, the present invention is applicable to lens apparatuses that includes fewer or more lens groups. Also, although the preferred embodiment relates to an electronic still camera, the present invention can relate to various cameras, including cameras using photographic film, and to similar imaging systems in general. Such variations are not to be regarded as a departure from the spirit and scope of the invention. Rather, the scope of the invention shall be defined as set forth in the following claims and their legal equivalents. All such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims.