Patent Publication Number: US-6339681-B1

Title: Optical apparatus

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an optical apparatus, such as a camera, capable of moving an optical system between a usage position and a stowage position. 
     2. Description of Related Art 
     In conventional cameras performing a magnification-varying action and a focus-adjusting action by moving a plurality of lens groups in the optical axis direction, there is known a camera which is arranged to move the lens groups to a stowage position in which the lens groups are stowed within a camera body when the camera is not being used for photo-taking, so as to improve the portability of the camera. 
     In moving the lens groups, an actuator, such as a DC motor or the like, is used for the magnification-varying action and another actuator, such as a stepping motor or the like, is used for the focus-adjusting action. In moving the lens groups to the stowage position, the actuator provided for the magnification-varying action is further driven to stow the lens groups within the camera body. 
     The camera of such a kind is provided with a lens barrel having a rear-focus type lens system in which a focus-adjusting (focusing) lens is disposed in rear of a magnification-varying (variator) lens. 
     The conventional camera of the above-stated kind, however, has presented a problem in that, since, even if the magnification-varing lens is moved to the stowage position, the presence of the focus-adjusting lens causes a spece corresponding to the driving range of the focus-adjusting lens to be left without being used for stowing the lens groups, it is impossible to sufficiently reduce the size of the camera in which the lens groups has been stowed within the camera body. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with one aspect of the invention, there is provided an apparatus, such as an image pickup apparatus, comprising a first optical unit constituting part of an optical system, a first motor which drives the first optical unit, a second optical unit disposed behind the first optical unit and constituting part of the optical system, a second motor which drives the second optical unit, and a control device which controls the first motor and the second motor in such a way as to draw in the second optical unit in response to an instruction for stowing the optical system and draw the first optical unit into a space made vacant by drawing in the second optical unit, the control device controlling the first motor in such a way as to draw the first optical unit into the space after the space is made vacant by drawing in the second optical unit, so that it is possible to sufficiently reduce the size of the optical system in the state of being stowed. 
     The above and other aspects and features of the invention will become apparent from the following detailed description of a preferred embodiment thereof taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING 
     FIG. 1 is an exploded perspective view showing a lens barrel part of a camera according to an embodiment of the invention. 
     FIG. 2 is a sectional view taken across a central part of the lens barrel shown in FIG. 1 when the lens barrel is in a stowage position. 
     FIG. 3 is a sectional view taken across a central part of the lens barrel shown in FIG. 1 when the lens barrel is in a wide-angle position. 
     FIG. 4 is a sectional view taken across a central part of the lens barrel shown in FIG. 1 when the lens barrel is in a telephoto position. 
     FIG. 5 is an exploded perspective view showing a diaphragm unit shown in FIG.  1 . 
     FIG. 6 is an exploded perspective view showing a stepping motor unit shown in FIG.  1 . 
     FIG. 7 is a front view showing a driving part for a third-lens-group tube shown in FIG.  1 . 
     FIG. 8 is a perspective view showing a driving gear train for driving a driving ring shown in FIG.  1 . 
     FIG. 9 is a development view showing the inner side of a fixed tube shown in FIG.  1 . 
     FIG. 10 is a development view showing the inner side of a moving cam ring shown in FIG.  1 . 
     FIGS.  11 ( a ) and  11 ( b ) are diagrams showing a characteristic of a linear sensor shown in FIG.  1 . 
     FIG. 12 is a front view showing the linear sensor and parts therearound shown in FIG.  1 . 
     FIG. 13 is a development view showing the outer side of the driving ring shown in FIG.  1 . 
     FIGS.  14 ( a ) and  14 ( b ) are diagrams for explaining an opening-and-closing mechanism for a barrier shown in FIG.  1 . 
     FIG. 15 is a block diagram showing the electrical arrangement of the camera shown in FIG.  1 . 
     FIGS.  16 ( a ) to  16 ( e ) are diagrams for explaining the loci of cams and the lens barrel shown in FIG.  1 . 
     FIGS.  17 ( a ) and  17 ( b ) are flow charts showing sequences of driving actions on the lens barrel shown in FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, a preferred embodiment of the invention will be described in detail with reference to the drawings. 
     FIG. 1 is an exploded perspective view showing a lens barrel part of a camera according to the embodiment of the invention. FIGS. 2,  3  and  4  are sectional views taken across a central part of the lens barrel shown in FIG.  1 . Of these sectional views, FIG. 2 shows the lens barrel in a stowage position. FIG. 3 shows the lens barrel in a wide-angle position. FIG. 4 shows the lens barrel in a telephoto position. 
     Referring to FIGS. 1 to  4 , a base  1  serving as a base part of a lens barrel unit constitutes a structural body of the lens barrel unit in conjunction with a fixed tube  2  which is secured to the front end of the base  1  with screws. A first-lens-group tube  3  holds lenses  4 ,  5  and  6 . Three follower pins  7  which have tapered fore end parts are press-fitted into the outer circumferential side surface of the first-lens-group tube  3 . A cap  8  is secured by bonding to the front surface of the first-lens-group tube  3 . 
     A second-lens-group tube  9 , which holds lenses  10 ,  11  and  12 , is secured by bonding to a diaphragm base plate  14  of a diaphragm unit  13  integrally therewith. 
     FIG. 5 is an exploded perspective view showing the diaphragm unit  13 . Referring to FIG. 5, three follower parts are formed on the peripheral part of the diaphragm base plate  14  at equal intervals. The three follower parts include two follower parts  14   a  having tapered fore end parts and formed integrally with the peripheral part and one movable follower  81  arranged to be axially movable. 
     The movable follower  81  is pushed on its rear end by an urging force of a leaf spring  82  to be offset toward one side of a mechanical clearance for maintaining a required rate of precision. The movable follower  81  is disposed in a position to be located uppermost among the three follower parts when the camera is at a normal posture. This positional arrangement makes the offsetting direction and the direction of gravity approximately coincide with each other to give a space saving effect and also to lessen a driving load. 
     A coil  83  is wound around a bobbin. A magnetic flux generated by energizing the coil  83  is arranged to generate through yokes  84  and  85  a magnetic rotating force at a magnet  87  which is formed integrally with an arm  86 . 
     Diaphragm blades  88  and  89  are provided with linear slot parts  88   b  to  88   d  and  89   b  to  89   d  and are thus arranged to be slidable while being guided by shafts  14   b  to  14   e  provided on the diaphragm base plate  14 . Two shaft parts  86   a  and  86   b  provided on the arm part of the arm  86  are inserted respectively in slot parts  88   a  and  89   a  of the diaphragm blades  88  and  89 . 
     A cap  90  is arranged to fix the coil  83  and the yokes  84  and  85  in their positions between the cap  90  and the diaphragm base plate  14  and to swingably hold the arm  86  (and the magnet  87 ). A case  91  is arranged to prevent the diaphragm blades  88  and  89  from coming off. 
     The diaphragm unit  13  which is arranged in the above manner is disposed on the inner side of a rectilinear guide tube  49 . For the purpose of having the diaphragm unit  13  disposed there, the coil  83  and the magnet  86 , which need certain fixed amounts of space within the diaphragm unit  13 , are separately allocated on two sides of an optical axis, and their longitudinal directions are thus arranged to coincide with the sliding direction of the diaphragm blades  88  and  89 , in such a way that is suited for arranging the diaphragm unit  13  within a tubular part such as the rectilinear guide tube  49 . Thus, the above arrangement of the diaphragm unit  13  contributes to a reduction in size of the camera. 
     A third-lens-group tube  15 , which holds a lens  16 , is arranged to be guided by guide bars  17  and  18 , to have its axial position restricted by a nut  19  having a female thread pinched by the arm part of the third-lens-group tube  15 , and to be in a state of being biased by a tension spring  20  in the drawing-in direction of the lens barrel. As shown in FIG. 7, the nut  19  has a slit part  19   a.  A projection  15   a  which is provided on the third-lens-group tube  15  is fitted into the slit part  19   a  in such a way as to restrict the rotating motion of the third-lens-group tube  15 . 
     A screw  21  is formed integrally with a magnet  22  to have a male thread part arranged to engage the female thread part of the nut  19 . A bearing metal piece  23  is press-fitted into the base  1  and has one end of the screw  21  fitted therein in a rotatable manner. 
     A stepping motor  24  is arranged to drive and move the third-lens-group tube  15 . As shown in FIG. 6, the stepping motor  24  has a pair of yokes  25  and  26  and coils  27  wound around bobbins arranged in two sets. The two sets of these parts are linearly allocated across the above-stated magnet  22 . The stepping motor  24  is secured to the base  1  by attaching a yoke plate  28  to the base  1  with screws. 
     In FIG. 7, which shows the driving part of the third-lens-group tube  15 , reference numeral  29  denotes a photo-interrupter. A slit plate  30  which is secured to the third-lens-group tube  15  integrally therewith is disposed in a position to be insertable and retractable into and from the slit part of the photo-interrupter  29 . 
     A cap  31 , which is secured to the base  1 , has the fore ends of the guide bars  17  and  18  secured thereto and is arranged to rotatably hold the screw  21 . 
     An image sensor  32  is secured by bonding to a holding plate  33 , which is secured to the base  1  with screws. A flexible printed circuit board  34  is arranged to supply a photoelectrically-converted image signal to a signal processing circuit which will be described later herein. A dust-proof rubber piece  35  and an optical low-pass filter (LPF)  36  are both secured by bonding to the base  1 . 
     A driving ring  37  is rotatably fitted on the outer (circumferential) side of the fixed tube  2 . The driving ring  37  has a gear part  37   a  formed at a part on the outer side thereof. As shown in FIG. 8, a DC motor  38  is arranged on the outer side of the driving ring  37  to have a pinion gear  39  firmly press-fitted to its output shaft. The driving force of the DC motor  38  is transmitted from the pinion gear  39  to the gear part  37   a  of the driving ring  37  through gears  40 ,  41 ,  42 ,  43 ,  44  and  45  one after another. These gears  40  to  45  are placed in gear boxes  46  and  47  and are secured to the base  1  in that state. The DC motor  38  is also secured to the gear box  46 . 
     A moving cam ring  48  is fitted in on the inner side of the fixed tube  2 . A rectilinear guide tube  49  is fitted in on the inner side of the moving cam ring  48 . 
     On the outer side of the moving cam ring  48 , are mounted three driving pins  50  and three follower pins  51  having tapered parts, at equal intervals. The driving pins  50  pierce through hole parts  2   a  of the fixed tube  2  to fittingly engage groove parts  37   b  which are provided on the inner side of the driving ring  37 . The follower pins  51  has their fore-end tapered parts in sliding contact with tapered cam grooves  2   b  which are formed on the inner side of the fixed tube  2 . FIG. 9 shows in an inner circumferential-surface development view how the driving pins  50  and the follower pins  51  are arranged. 
     FIG. 10 is a development view showing the inner circumferential side of the moving cam ring  48 . As shown in FIG. 10, tapered cam grooves  48   a  and  48   b  are formed on the inner circumferential side of the moving cam ring  48 . Followers  7  which are provided on the first-lens-group tube  3  and followers  14   a  (or  81 ) which are formed on the diaphragm base plate  14  are in sliding contact with the tapered cam grooves  48   a  and  48   b.    
     At the same time, the side surfaces of the followers  7  and  14   a  are fittingly engaging the rectilinear grooves  49   a  and  49   b  of the rectilinear guide tube  49 , so that the positions of the followers  7  and  14   a  in the direction of rotation are restricted. The first-lens-group tube  3  and the diaphragm unit  13  are thus restrained from rotating and are allowed to make only rectilinear motions. 
     Projections  49   c  formed at the front part on the outer circumferential side of the rectilinear guide tube  49  are in abutting contact with the groove parts  48   c  which are provided on the inner side of the moving cam ring  48 . Meanwhile, a flange part  49   d  which is formed at the rear end of the rectilinear guide tube  49  is abutting on the end part of the moving cam ring  48 . By this arrangement, the rectilinear guide tube  49  is restrained from moving in the optical axis direction with respect to the moving cam ring  48 . At the same time, as shown in FIG. 9, rear projections  49   e  which are provided at the rear end of the rectilinear guide tube  49  fittingly engage the linear groove parts  2   c  on the inner side of the fixed tube  2  in a state of being allowed to make a linear motion but being restrained from moving in the direction of rotation. 
     As shown in FIGS. 1 to  6 , in the present embodiment, the stepping motor  24  is arranged at about the same height as the height obtained with the LPF  36  superposed on the image sensor  32  and is arranged to linearly extend along one side of the combination of the LPF  36  and the image sensor  32 . The screw  21  and the magnet  22  are disposed near to the center of the above-stated one side. This arrangement of the stepping motor  24  enables the third-lens-group tube  15  to be formed in a flat-plate shape and also enables tubular parts, such as the moving cam ring  48  and the rectilinear guide tube  49 , to be closely allocated, so that the lens barrel of the camera can be made compact. 
     The longitudinal direction of the diaphragm unit  13  and the longitudinal direction of the stepping motor  24  are arranged to coincide with each other. By virtue of this arrangement, the guide bars  17  and  18  and the screw  21  can be allocated around the diaphragm unit  13  and within a vacant space inside the moving cam ring  48 . The arrangement thus permits the reduction of the total length of the lens barrel to be obtained with the lens barrel set in the stowage position, as shown in FIG.  2 . 
     Referring to FIGS. 1 to  4 , a cap  52  is arranged to hold a dust-proof sheet  53  between the fixed tube  2  and the cap  52 . The cap  52  has rail parts  52   a  and  52   b  arranged on a front surface thereof to guide a barrier  54  which will be described later. Another dust-proof sheet  55  is inserted in the groove part  48   c  of the moving cam ring  48 . 
     A linear sensor  56  is secured to the base  1  with screws or the like. The circuit arrangement of the linear sensor  56  is a variable resistor as shown in FIG.  11 ( a ). As shown in FIG.  11 ( b ), when a predetermined voltage is applied between terminals A and C shown in FIG.  11 ( a ), the output of a terminal B linearly varies accordingly as a sliding piece  56   a  of the linear sensor  56  slides. A lever  57  is arranged to pinch and carry the sliding piece  56   a  by its arm part  57   a  and to be guided by a guide bar  58 . The lever  57  is provided with a follower part  57   b  which has a tapered part at its fore end. The side surface of the lever  57  is fittingly engaging a slot part la of the base  1 . A spring  59  urges the lever  57  to move toward one side. FIG. 12 shows these parts as viewed from the front side of them. 
     FIG. 13 is a development view of the outer side of the driving ring  37 . As shown in FIG. 13, the follower part  57   b  of the lever  57  is in sliding contact with the linear cam groove  37   c  of the driving ring  37 . Tapered cam grooves  37   d  and  37   e  are provided for zoom-driving a viewfinder lens (not shown). A follower part  60  is arranged integrally with a compensator lens (not shown). A follower part  61  is arranged integrally with a variator lens (not shown). The follower parts  60  and  61  are in sliding contact respectively with the cam grooves  37   d  and  37   e.    
     Referring to FIG.  1  and FIGS.  14 ( a ) and  14 ( b ), the barrier  54  is supported to be rotatable around a shaft  63  mounted on a barrier base  62 . The barrier  54  is urged by a closing spring  64  hooked on its hook part  54   a  to move clockwise as viewed from the front of the camera. A barrier driving lever  65  is supported to be rotatable around a shaft  66  mounted on the barrier base  62 . The barrier driving lever  65  is urged to move clockwise by an opening spring  67  which is hooked on a hook part  65   a  of the barrier driving lever  65 . 
     Here, the urging forces of the two springs  64  and  67  are set as “the closing springs  64  &lt;&lt; the opening spring  67 ”. A shaft  68  is mounted at one end of the barrier driving lever  65  in a position corresponding to one side face of the barrier  54 . A leaf switch  69  which is formed by integral molding is secured to the barrier base  62  with screws. The barrier base  62  is secured to the base  1  with screws. 
     FIG.  14 ( a ) shows the state where the barrier  54  is closed. In this state, a stepped part  37   f  of the driving ring  37  pushes a bent part  65   b  of the barrier driving lever  65  to cause the barrier driving lever  65  to be swung counterclockwise against the urging force of the opening spring  67  and to be locked at that position. The barrier  54  is, in the meantime, caused to swing in the direction of closing by the urging force of the closing spring  64  and to be in a closed state with its bent part  54   b  abutting on a stopper part  2   d  of the fixed tube  2 . 
     FIG. 15 is a block diagram showing the electric connection arrangement of the camera according to the embodiment of the invention. In FIG. 15, the lens barrel  71  is the same as the lens barrel that has been described above, and the components of the lens barrel  71  are indicated by the same reference numerals as those used in the foregoing description. 
     Referring to FIG. 15, an image signal obtained through photoelectric conversion by the image sensor  32  is supplied to a signal processing circuit  72  for a color-conversion process, a gamma correction process, etc. After these processes, the image signal is recorded in a memory  73  which is, for example, a card medium or the like. A control part  74 , which controls the whole camera, is arranged to control the stepping motor  24 , the DC motor  38  and the diaphragm unit  13  while watching the outputs of the linear sensor  56 , the photo-interrupter  29 , the leaf switch  69 , etc., which are disposed within the lens barrel  71 , and also to control the signal processing circuit  72  and the memory  73 . 
     A nonvolatile memory  75 , which is, for example, an EEPROM or the like, is arranged to permit electrical erasure and recording. 
     A mode dial switch  76  is arranged to permit selection and setting of various operation modes, such as turning-off of the power supply, a photo-taking mode, a reproduction mode, a PC connection mode, etc. 
     The lens barrel of the camera arranged according to the present embodiment as described above operates as follows. 
     When the DC motor  38  is driven, the driving ring  37  is caused to rotate through the gears  39  to  45  (see FIG.  8 ). The driving pins  50  of the moving cam ring  48  which pierce through the hole parts  2   a  of the fixed tube  2  are fittingly engaging the linear groove parts  37   b  formed on the inner side of the driving ring  37  to extend in the optical axis direction as mentioned above. The rotation of the driving ring  37 , therefore, causes the moving cam ring  48  to rotate through the driving pins  50 . However, since the follower pins  51  of the moving cam ring  48  are engaging the cam grooves  2   b  of the fixed tube  2 , the moving cam ring  48  is allowed to move in the optical axis direction along the cam grooves  2   b  of the fixed tube  2  (see FIG.  9 ). 
     The movement of the moving cam ring  48  in the optical axis direction causes the rectilinear guide tube  49  to move also in the optical axis direction integrally with the moving cam ring  48 . Then, since the projections  49   e  on the outer circumferential side of the rectilinear guide tube  49  is under restriction of the groove parts  2   c  of the fixed tube  2 , the rectilinear guide tube  49  is allowed to move only in the optical axis direction without rotating. 
     When the moving cam ring  48  rotates, the first-lens-group tube  3  and the second-lens-group tube  9  which is secured to the diaphragm unit  13  relatively move in the optical axis direction respectively along the grooves  49   a  and  49   b  of the rectilinear guide tube  49  according to the lifts of the cams  48   a  and  48   b  of the moving cam ring  48  (FIG.  10 ). 
     FIGS.  16 ( a ) to  16 ( e ) are diagrams showing only the loci of the cam parts of the lens barrel. FIG.  16 ( a ) shows the cam locus of the fixed tube  2 . FIG.  16 ( b ) shows the cam locus of the moving cam tube  48  for the first-lens-group tube  3 . FIG.  16 ( c ) shows the cam locus of the moving cam ring  48  for the second-lens-group tube  9 . FIG.  16 ( d ) shows the locus of movement of the first-lens-group tube  3 , which is the sum of the loci shown in FIGS.  16 ( a ) and  16 ( b ). FIG.  16 ( e ) shows the locus of movement of the second-lens-group tube  9 , which is the sum of the loci shown in FIGS.  16 ( a ) and  16 ( c ). 
     In each of FIGS.  16 ( a ) to  16 ( e ), a point W represents a wide-angle end position, a point T represents a telephoto end position, and a point S represents a stowage position. Each cam is provided with a flat area extending from the stowage position S to a position B. According to the loci shown in FIGS.  16 ( a ) to  16 ( e ), a change-over between the stowage position and a photo-taking position (S-W) and a zooming action in the photo-taking range (W-T) are carried out by driving the DC motor  38 . 
     When the driving ring  37  rotates, a viewfinder lens (not shown) is moved in the optical axis direction along the grooves  37   d  and  37   e  through the followers  60  and  61  and, as mentioned above, acts in association with the zooming action of the lens barrel. 
     At the same time, the lever  57  moves along the cam groove  37   c  in the optical axis direction to displace the sliding piece  56   a  of the linear sensor  56  and thus to vary the output of the linear sensor  56  as shown in FIG.  11 ( b ). Thus, every zoom position is successively detectable through the output of the linear sensor  56 . 
     As shown in FIG.  16 ( d ), the reciprocating motion of the first-lens-group tube  3  between the wide-angle end position W and the telephoto end position T draws a locus convex toward the image side. Therefore, each of the three cams as shown in FIGS.  16 ( a ) to  16 ( c ) is arranged to have a non-linear cam part between the wide-angle end position W and the telephoto end position T. By virtue of this arrangement, the inclination of each cam can be minimized for reduction in driving load. 
     Further, by arranging each of the cam of the fixed tube  2  shown in FIG.  16 ( a ) and the cam of the moving cam ring  48  for the first-lens-group tube  3  shown in FIG.  16 ( b ) to have a maximal value between the stowage position S and the wide-angle end position W, the amount of drawing-out of the first-lens-group tube  3  can be dispersed to the two cams shown in FIGS.  16 ( a ) and  16 ( b ). By this arrangement, the total length of the fixed tube  2  and that of the moving cam ring  48  can be reduced for compact arrangement of the camera. 
     As mentioned above with reference to FIG.  14 ( a ), the stepped part  37   f  of the driving ring  37  locks the barrier driving lever  65  when the lens barrel is in the stowage position. However, when the driving ring  37  rotates, the barrier driving lever  65  is unlocked to allow the barrier driving lever  65  to be swung clockwise by the urging force of the opening spring  67 . The barrier driving lever  65  thus comes to push the side surface of the barrier  54  through the shaft  68 . 
     Since the urging force of the closing spring  64  is weaker than the urging force of the opening spring  67  as mentioned above, the barrier  54  is caused to be swung counterclockwise by the barrier driving lever  65  into an open position as shown in FIG.  14 ( b ). At this time, the bent part  54   b  of the barrier  54  pushes a contact  69   a  of the leaf switch  69  to turn on the leaf switch  69 . The opening and closing actions on the barrier  54  are thus arranged to be carried out within the flat areas of the cam loci, i.e., between the positions S and B, shown in FIGS.  16 ( a ) to  16 ( e ). 
     When the stepping motor  24  is driven, the screw  21  is caused to rotate through the magnet  22 . Since the nut  19  is under the restriction of the projection  15   a  of the third-lens-group tube  15  as mentioned above, the nut  19  moves in the optical axis direction. Then, following the movement of the nut  19 , the third-lens-group tube  15  also moves in the optical axis direction to perform a focus adjusting action. Within the stroke of the action of the third-lens-group tube  15 , the slit plate  30  is either inserted into or retracted from the slit part of the photo-interrupter  29  to change the output of the photo-interrupter  29 . At this time, a counter for the stepping motor  24  is reset accordingly. 
     FIGS.  17 ( a ) and  17 ( b ) are flow charts showing the actions of the camera. FIG.  17 ( a ) shows the actions to be performed in causing the camera to start operating. At a step S 101  of FIG.  17 ( a ), the mode dial switch  76  is operated to select a photo-taking mode. At a step S 102 , the control part  74  checks the output of the linear sensor  56  to find whether the zoom position of the lens barrel  71  is the stowage position or the photo-taking position between the wide-angle end position and the telephoto end position. 
     If the zoom position is found to be the photo-taking position between the wide-angle end position and the telephoto end position, the flow of operation proceeds to a step S 107 . If the zoom position is found to be the stowage position, the flow proceeds from the step S 102  to a step S 103 . At the step S 103 , the DC motor  38  is driven by a predetermined amount in the direction of drawing out the lens barrel. This predetermined amount corresponds to the area between the positions S and B shown in each of FIGS.  16 ( a ) to  16 ( e ). At a step S 104 , the zoom (drawing-out) driving action is temporarily brought to a stop to make a check to find if the leaf switch  69  is in an on-state. If so, the flow proceeds to a step S 106 . If not, the off-state of the leaf switch  69  is considered to indicate occurrence of some error, and the flow proceeds to a step S 105 . At the step S 105 , a warning display or the like is made without further performing the zoom driving action and without further driving the stepping motor  24 . At the step S 106 , the zoom driving action is further carried on to draw out the lens barrel to the wide-angle end position. 
     At the step S 107 , when the drawing-out of the lens barrel up to the wide-angle end position by the zoom driving action is completed, the stepping motor  24  is driven in the direction of the change-over position of the photo-interrupter  29 . Upon detection of the change-over of the output of the photo-interrupter  29 , the stepping motor  24  is brought to a stop at that position, and the counter for the stepping motor  24  is reset. At a step S 108 , a check is made for the reset state of the counter. If the change-over is not detected and the counter is not reset due to some reason, the flow proceeds to a step S 109 . At the step S 109 , some error is considered to have occurred and, for example, a warning display or the like is made. At the same time, the further driving of the stepping motor  24  and the further zoom driving are inhibited. If the counter is found at the step S 108  to have been reset, the flow proceeds to a step S 110 . At the step S 110 , the stepping motor  24  is driven further to a standby position where a focusing (AF) action can be allowed to start. The camera is thus set in the standby state in which a photo-taking operation can be performed. 
     FIG.  17 ( b ) shows the actions of the camera to be performed in terminating the photo-taking mode. At a step S 111 , when the mode dial switch  76  is operated to select any operation other than the photo-taking mode, such as the turning-off of the power supply, the reproduction mode or the like, the flow proceeds to a step S 112 . At the step S 112 , the stepping motor  24  is first driven to cause the third-lens-group tube  15  to move to a stowage standby position (stowage completion position). This position is adjusted beforehand in a manufacturing process for each individual camera, and information on this position is stored in the nonvolatile memory  75  as the amount of count from the position where the counter for the stepping motor  24  has been reset. At the next step S 113 , the DC motor  38  is driven to move the lens barrel to the stowage position. At a step S 114 , the photo-taking mode is terminated. 
     After termination of the photo-taking mode, there is obtained a state as shown in FIG.  2 . In the case of the present embodiment, as shown in FIGS. 2 to  4 , the driving stroke of the third-lens-group tube  15  at the photo-taking position overlaps with the stowage position of the second-lens-group tube  9  shown in FIG.  2 . 
     Therefore, in starting a photo-taking operation as described above, the zoom driving action is first performed. In stowing the lens barrel, the third-lens-group tube  15  is always first moved to the stowage standby position. By virtue of such a control arrangement, lens-group tubes can be prevented from colliding with each other, so that spacing distances among the lens-group tubes in the stowage position can be arranged to be extremely short. Besides, the arrangement for inhibiting the driving of the DC motor  38  and the driving of the stepping motor  24  in the event of occurrence of a trouble in the reset action on the third-lens-group tube  15  effectively prevents the camera from being damaged. 
     Further, the change-over position of the photo-interrupter  29  individually varies to a considerable extent in general. However, the above-stated arrangement for storing information on the stowage standby position in the nonvolatile memory  75  permits stowing the lens barrel within an extremely limited space, while preventing the third-lens-group tube  15  from colliding with the base  1 . 
     The individual components shown in schematic or block form in the drawings are all well-known in the camera arts and their specific construction and operation are not critical to the operation or best mode for carrying out the invention. 
     While the present invention has been described with respect to what is presently considered to be the preferred embodiment, it is to be understood that the invention is not limited to the disclosed embodiment. To the contrary, the invention is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions. 
     For example, in the above-described embodiment, the first-lens-group tube  3 , the second-lens-group tube  9  and the third-lens-group  15  are arranged not to simultaneously move in drawing out the lens barrel to the photo-taking position or in drawing in the lens barrel to the stowage position. However, according to the invention, the first-lens-group tube  3 , the second-lens-group tube  9  and the third-lens-group  15  may be made to simultaneously move, if such a sequence of operations as to prevent those tubes from colliding with each other is adopted. 
     Further, in the above-described embodiment, a rear focus zoom lens is employed as an optical arrangement. However, the invention is applicable also to another zoom arrangement or to a focal-length changeover optical arrangement other than the zoom arrangement. 
     Further, in the above-described embodiment, an optical system composed of three lens groups is employed. However, the invention is applicable also to an optical system composed of a plurality of, other than three, lens groups, such as two or four lens groups. 
     Further, in the above-described embodiment, an optical arrangement is composed of a magnification-varying lens group and a focusing lens group. However, the invention is applicable also to an optical arrangement composed of other lens groups or to another optical unit arrangement including a filter or the like. 
     Further,the software arrangement and the hardware arrangement in the above-described embodiment may be adaptively replaced with each other. 
     Further, in the invention, the technical elements of the above-described embodiment may be combined with each other according to necessity. 
     Further, the invention also applies to cases where each claim or the whole or a part of the arrangement of the embodiment constitutes one apparatus or is used in combination with another apparatus or as a component element of an apparatus. 
     Further, the invention is also applicable to various types of cameras, such as an electronic still camera, a video camera and a camera using a silver-halide film, various image pickup apparatuses other than cameras, various optical apparatuses, such as a lens barrel, other types of apparatuses, and, moreover, to apparatuses adapted for the cameras, the image pickup apparatuses, optical apparatuses and the other types of apparatuses, and elements constituting the above-mentioned apparatuses.