Optical apparatus

An apparatus, such as an image pickup apparatus, includes an optical unit a moving direction of which changes from one of a drawing-out direction and a drawing-in direction to the other of the drawing-out direction and the drawing-in direction in process of varying a focal length from one of a shortest focal length end and a longest focal length end to the other of the shortest focal length end and the longest focal length end, the optical unit having possibility of receiving an external force in the drawing-in direction, a driving device which drives the optical unit, and a control device which controls the driving device. When the optical unit is determined to move in the drawing-in direction to reach a stop position on the basis of a position of the optical unit and a direction of varying the focal length, the control device controls and causes the driving device to move the optical unit in the drawing-out direction after moving the optical unit in the drawing-in direction beyond the stop position and, then, to stop the optical unit at the stop position.

BACKGROUND OF THE INVENTION
 1. Field of the Invention
 The present invention relates to an optical apparatus, such as a camera,
 which performs the drawing-out and drawing-in of an optical unit.
 2. Description of Related Art
 Heretofore, in zoom lens cameras capable of performing a zooming action, a
 cam ring is used as a means for driving a lens to perform the zooming
 action. A cam groove provided in the cam ring is formed, for example, in
 the shape as shown in FIG. 10(a). In FIG. 10(a), the cam groove 101 in the
 cam ring 100 is provided for driving a variator lens. A cam pin provided
 on a lens barrel holding the variator lens is fitted in the cam groove 101
 and the lens barrel is arranged to move between a stowage position where
 the lens barrel is stowed within a camera body and a telephoto end
 position, according to the rotation of the cam ring 100. Incidentally,
 when the lens barrel is in the stowage position, a barrier (not shown)
 provided on the front end portion of the lens barrel is closed to protect
 the lens.
 In the conventional zoom mechanism as described above, there is provided
 such a cam groove as to cause the variator lens to be drawn out
 monotonously (without being drawn in on its way) during the zooming action
 from the wide-angle side to the telephoto side and to be drawn in
 monotonously (without being drawn out on its way) during the zooming
 action from the telephoto side to the wide-angle side, and the lens barrel
 holding the variator lens is driven by a DC motor, serving as a zoom
 motor, and a train of gears so as to be moved in the optical axis
 direction.
 In the meantime, there exists backlash in a train of gears. Specifically,
 when the lens barrel holding the variator lens is driven from the
 wide-angle side to the telephoto side, the backlash exists on the
 telephoto side. On the other hand, when the lens barrel holding the
 variator lens is driven from the telephoto side to the wide-angle side,
 the backlash exists on the wide-angle side.
 In order to cause the lens barrel holding the variator lens to stop always
 at the same zoom position regardless of whether the zooming operation is
 performed by an operator from the telephoto side to the wide-angle side or
 from the wide-angle side to the telephoto side, it becomes necessary to
 perform a biasing operation for eliminating backlash.
 A problem might arise in a case where the lens barrel is driven from the
 telephoto side, i.e., the position where the lens barrel protrudes from
 the camera body at the full length, to the wide-angle side, i.e., the
 position where the lens barrel is drawn within the camera body. In such a
 case, if the lens barrel happens to come into contact with an obstacle, or
 if the operator erroneously pushes in the lens barrel, exerting an
 external force on the lens barrel, the lens barrel would be pushed in as
 much as the backlash, so that the photo-taking magnification is caused to
 change.
 In view of the above points of view, there has been proposed a camera in
 which, when zooming is effected from the telephoto side to the wide-angle
 side, a biasing operation, i.e., the operation of drawing in the lens
 barrel further by an extra amount from the position desired by the
 operator and, after that, drawing out the lens barrel, is performed to
 eliminate the backlash of a train of gears, so that the lens barrel can be
 stopped at the stop position desired by the operator, thereby solving the
 above conveniences.
 On the other hand, there is another zoom mechanism in which, as shown in
 FIG. 10(b), an extreme value is set between the wide-angle end and the
 telephoto end in a cam groove 201 provided in a cam ring 200. In that zoom
 mechanism, when advancing from the wide-angle end to the telephoto end,
 the lens is moved toward the image side before reaching the extreme value,
 and is moved toward the object side after passing the extreme value.
 In the above zoom mechanism, assuming that the zooming action is stopped
 between the wide-angle end and the extreme value during the process of
 zooming toward the telephoto end (herein, the rotating direction of a gear
 at this time is referred to as the normal rotating direction), the
 backlash occurring in a train of gears for driving the cam ring 200 is
 considered to exist on the side in the normal rotating direction. Then,
 since, in such a stop position, the direction in which the lens barrel
 advances toward the extreme value is the abovementioned normal rotating
 direction, if any external force is exerted on the lens barrel, the lens
 barrel would be drawn in, so that the photo-taking magnification is caused
 to change.
 In order to remove such inconveniences, it is necessary to perform the
 biasing operation. However, since, in the conventional method, the biasing
 operation is performed only when the lens barrel is moved from the
 telephoto side to the wide-angle side, the biasing operation is not
 performed in a case where the lens barrel is moved from the wide-angle
 side to the telephoto side. Therefore, there is the possibility that, if
 the lens barrel happens to come into contact with an obstacle, or if the
 operator erroneously pushes in the lens barrel, exerting an external force
 on the lens barrel, the lens barrel would be pushed in slightly, so that
 the photo-taking magnification is caused to change.
 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 an optical unit a
 moving direction of which changes from one of a drawing-out direction and
 a drawing-in direction to the other of the drawing-out direction and the
 drawing-in direction in process of varying a focal length from one of a
 shortest focal length end and a longest focal length end to the other of
 the shortest focal length end and the longest focal length end, the
 optical unit having possibility of receiving an external force in the
 drawing-in direction, a driving device which drives the optical unit, and
 a control device which controls the driving device, the control device,
 when the optical unit is determined to move in the drawing-in direction to
 reach a stop position on the basis of a position of the optical unit and a
 direction of varying the focal length, controlling and causing the driving
 device to move the optical unit in the drawing-out direction after moving
 the optical unit in the drawing-in direction beyond the stop position and,
 then, to stop the optical unit at the stop position, so that the optical
 unit can be prevented from being moved by an external force due to
 backlash, regardless of a stop position of the optical unit.
 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.

DETAILED DESCRIPTION OF THE INVENTION
 Hereinafter, a preferred embodiment of the invention will be described in
 detail with reference to the drawings.
 Among FIGS. 1 to 9, which show the embodiment of the invention, FIG. 1 is
 an exploded perspective view showing a lens barrel part of a camera
 according to the embodiment of the invention.
 Referring to FIG. 1, 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 a plurality of lenses (not shown).
 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 (not shown) is secured by bonding to the front surface of the
 first-lens-group tube 3.
 A second-lens-group tube 9, which holds a plurality of lenses (not shown),
 is secured by bonding to a diaphragm base plate of a diaphragm unit 13
 integrally therewith.
 A third-lens-group tube 15, which holds a lens, is arranged to be guided by
 guide bars 17 and 18 which extend in the optical axis direction, to have
 its axial position restricted by a nut (not shown) having a female thread
 pinched by the arm part of the third-lens-group tube 15 and arranged to
 engage a screw 21, and to be in a state of being biased by a tension
 spring 20 in the drawing-in direction of the lens barrel. Further, a
 projection which is provided on the third-lens-group tube 15 is fitted
 into a slit part provided on the nut in such a way as to restrict the
 rotating motion of the third-lens-group tube 15. The 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. A bearing metal piece 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. The stepping motor 24 constitutes a magnetic
 circuit including the magnet 22, and is secured to the base 1. 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 a slit part of a photo-interrupter (not shown), so that the
 position of the third-lens-group tube 15 can be detected.
 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. As shown in FIG. 4, the driving ring 37 has a gear
 part 37a formed at a part on the outer side thereof. A zoom 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 zoom
 motor 38 is transmitted from the pinion gear 39 to the gear part 37a of
 the driving ring 37 through gears 42, 41, 40, 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 zoom 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. As shown in FIGS. 2 and 6, the driving pins 50 pierce through
 hole parts 2a of the fixed tube 2 to fittingly engage groove parts 37b
 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 2b which are formed on the inner side of the
 fixed tube 2, as shown FIG. 6. FIGS. 2 and 6 are inner
 circumferential-surface development views for explaining the
 above-described arrangement.
 Two kinds of tapered cam grooves (not shown) 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 which are provided
 on the diaphragm unit 13 are in sliding contact with the two kinds of
 tapered cam grooves. At the same time, the side surfaces of the respective
 followers are fittingly engaging the rectilinear grooves 49a and 49b of
 the rectilinear guide tube 49, so that the positions of the respective
 followers in the direction of rotation are restricted.
 Further, front-side projections 49c provided on the outer circumferential
 side of the rectilinear guide tube 49 are in contact with a groove part
 48c provided on the inner circumferential side of the moving cam ring 48,
 and a flange part 49d of the rectilinear guide tube 49 is in contact with
 an end part of the moving cam ring 48. By this arrangement, the
 rectilinear guide tube 49 is restrained from relatively moving in the
 optical axis direction with respect to the moving cam ring 48. At the same
 time, rear-side projections 49e provided on the outer circumferential side
 of the rectilinear guide tube 49 are fitted in linear groove parts 2c
 provided on the inner circumferential side of the fixed tube 2, in such a
 way that the rectilinear guide tube 49 is rectilinearly movable while
 being restrained from moving in the rotating direction.
 A cap 52 is arranged to hold a dust-proof sheet (not shown) between the
 fixed tube 2 and the cap 52. The cap 52 has rail parts 52a and 52b formed
 on a front surface thereof to guide a barrier 54 which will be described
 later.
 A linear sensor 56, which is composed of a variable resistor, is secured to
 the base 1 with screws or the like. A lever 57 is arranged to pinch and
 carry a sliding piece of the variable resistor and to be guided by a guide
 bar 58. A spring 59 urges the lever 57 to move toward one side. The
 rotational angle of the driving ring 37 is detected by A/D-converting the
 terminal voltage of the linear sensor 56, so that the position of the
 first-lens-group tube 3 also can be detected accordingly.
 Referring to FIG. 1 and FIGS. 3(a) and 3(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 54a 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 65a
 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. 3(a) shows the state where the barrier 54 is closed. In this state, a
 stepped part 37f of the driving ring 37 pushes a bent part 65b 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 54b abutting on a
 stopper part 2d of the fixed tube 2.
 The lens barrel of the camera arranged according to the present embodiment
 as described above operates as follows.
 When the zoom motor 38 is driven, the driving ring 37 is caused to rotate
 through the gears 39 to 45. Then, the rotation of the driving ring 37
 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 2b of the fixed tube 2, the moving cam ring 48 is allowed
 to also move in the optical axis direction along the cam grooves 2b of the
 fixed tube 2. 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 49e on the outer circumferential side of the rectilinear guide
 tube 49 is under restriction of the groove parts 2c 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 49a and 49b of the rectilinear guide tube 49 according to the
 lifts of the respective cams of the moving cam ring 48.
 FIGS. 5(a) to 5(c) are diagrams showing only the loci of the cam parts of
 the lens barrel. FIG. 5(a) shows the cam locus of the fixed tube 2. FIG.
 5(b) shows the cam locus of the moving cam tube 48 for the
 first-lens-group tube 3. FIG. 5(c) shows the locus of movement of the
 first-lens-group tube 3, which is the sum of the cam loci shown in FIGS.
 5(a) and 5(b). Referring to the locus of movement shown in FIG. 5(c), the
 first-lens-group tube 3 is driven in the drawing-in direction and in the
 drawing-out direction with the boundary set to the position of an extreme
 value between the wide-angle end and the telephoto end.
 In each of FIGS. 5(a) to 5(c), 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. 5(a) to 5(c), 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 zoom
 motor 38.
 When the driving ring 37 rotates, the lever 57 moves along a cam groove
 (not shown) in the optical axis direction to displace the sliding piece of
 the linear sensor 56 and thus to vary the output of the linear sensor 56.
 Thus, by detecting the output of the liner sensor 56, every zoom position
 is successively detectable and the position of the extreme value is also
 detectable.
 As mentioned in the foregoing, the stepped part 37f 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 opened position as shown in FIG. 3(b). At this time, if no external
 force is exerted on the barrier driving lever 65, the L-shaped bent part
 54b of the barrier 54 pushes a contact 69a of the leaf switch 69 to turn
 on the leaf switch 69. Therefore, it is possible to electrically detect
 the state in which the barrier 54 is opened.
 However, when the lens barrel is in the stowage position, i.e., when the
 camera is not in the photo-taking state, the stepped part 37f of the
 driving ring 37 acts on the bent part 65b of the barrier lever 65 to move
 the bent part 65b downward. At this time, the barrier 54 is closed by the
 action of the closing spring 64.
 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. 5(a) to 5(c).
 FIG. 8 is a block diagram showing the electrical arrangement for driving
 the lens barrel according to the embodiment of the invention.
 In FIG. 8, 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. 8, 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 zoom 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 (personal computer) connection mode, etc. A zoom switch 77 is
 arranged to output signals indicative of the direction of varying
 magnification, i.e., a direction toward the telephoto end or a direction
 toward the wide-angle end. According to the output signals of the zoom
 switch 77, the zoom motor 38 is driven to make a normal rotation or a
 reverse rotation.
 The operation of the camera as described above is shown in the flow chart
 of FIG. 7.
 Referring to the flow chart of FIG. 7, when a power supply is turned on in
 step S001, the zoom motor 38 makes a normal rotation in step S002. The
 rotation of the zoom motor 38 is transmitted to the gear 37a of the
 driving gear 37 through the gears 39 to 45, so that the driving gear 37 is
 made to rotate counterclockwise as viewed in FIG. 4.
 In step S003, a check is made to find if the barrier 54 is in the opened
 position. The opened position of the barrier 54 is decided according to
 the rotational angle of the driving ring 37, and the rotational angle of
 the driving ring 37 is detectable by the linear sensor 56. When the
 driving ring 37 has rotated up to the opened position of the barrier 54,
 the barrier driving lever 65 rotates clockwise, as viewed in FIG. 1, by
 the action of the opening spring 67, so that the shaft 68 of the barrier
 driving lever 65 pushes down the barrier 54 to bring the barrier 54 into
 the opened state as shown in FIG. 3(b).
 At this point of time, the zoom motor 38 is stopped in step S004. In step
 S005, a timer in which a predetermined time is set is started.
 In step S006, a check is made to find if the leaf switch 69 is in an
 on-state, i.e., if the barrier 54 has been completely opened.
 When the barrier 54 comes into the completely-opened state, the bent part
 54b of the barrier 54 pushes the contact 69a of the leaf switch 69,
 thereby turning on the leaf switch 69. If the leaf switch 69 is not in the
 on-state, the flow proceeds to step S007. In step S007, a check is made to
 find if the time set in the timer in step S005 has elapsed. If not, the
 flow returns to step S006, repeating the above operation until the leaf
 switch 69 is turned on within the predetermined time set in the timer,
 i.e., waiting until the barrier 54 is completely opened.
 If it is not detected in step S007 that the barrier 54 has been completely
 opened within the predetermined time set in the timer, assuming that an
 error has occurred in the opening operation of the barrier 54, an error
 code (for example, code "15" indicative of the error of the opening
 operation of the barrier 54) is set to perform an error processing
 operation.
 Incidentally, from the start of rotation of the driving ring 37 in response
 to the turning-on of the power supply until the barrier 54 is opened, the
 follower 7 of the first-lens-group tube 3 is moving on a section A-A' of
 the cam groove 201 shown in FIG. 10(b). Therefore, during that period, the
 first-lens-group tube 3 is made not to be drawn out.
 Accordingly, since the rotation of the zoom motor 38 is stopped in the
 section A-A', even if an error occurs in the barrier opening operation,
 the first-lens-group tube 3 is prevented from being drawn out to collide
 with the barrier 54.
 On the other hand, if it is detected that the leaf switch 69 has been
 turned on within the predetermined time set in the timer and the barrier
 54 has been completely opened, the flow proceeds to step S010.
 In step S010, with the on-state of the leaf switch 69 detected, the driving
 ring 37 is again rotated by the zoom motor 38. Accordingly, the moving cam
 ring 48 is rotated and is also moved in the optical axis direction along
 the cam groove 2b provided on the inner side of the fixed tube 2.
 Further, according to the rotation of the moving cam ring 48, the
 first-lens-group tube 3 is moved along the cam groove 48a provided on the
 inner side of the moving cam groove 48. When the first-lens-group tube 3
 is drawn out up to the wide-angle end position W shown in FIG. 5(c), a
 photo-taking operation becomes possible. The moved position of the
 first-lens-group tube 3 is recognized on the basis of the detection
 information of the linear sensor 56. When the first-lens-group tube 3
 reaches the wide-angle end position W, the driving of the zoom motor 38 is
 stopped.
 According to the present embodiment, the first-lens-group tube 3 is once
 driven from the stowage position to the barrier opening position in
 response to the turning-on of the power supply. Then, after it is
 confirmed that the barrier 54 has been completely opened, the
 first-lens-group tube 3 is driven up to the wide-angle end position.
 Therefore, the first-lens-group tube 3 is prevented from colliding with
 the barrier 54.
 After that, when the operator performs a zooming operation, the zoom motor
 38 rotates and the driving cam 37 rotates, so that the variator lens is
 moved to vary the photo-taking magnification. Accordingly, the operator
 can select a desired zoom position.
 In addition, A/D-converted values of the terminal voltages of the linear
 sensor 56 corresponding to the respective positions, the respective zoom
 positions and the extreme value of the first-lens-group tube 3 are
 beforehand stored in the nonvolatile memory 75. The position of the
 first-lens-group tube 3 can be electrically detected by reading such
 A/D-converted values of the linear sensor 56 from the nonvolatile memory
 75.
 Next, the zooming action of the camera according to the embodiment of the
 invention will be described with reference to the flow chart of FIG. 9.
 The characteristic feature of the zooming action resides in that, in a case
 where the first-lens-group tube 3 stops before reaching the extreme value
 P in process of moving from the wide-angle side to the telephoto side, and
 in a case where the first-lens-group tube 3 stops before reaching the
 extreme value P in process of moving from the telephoto side to the
 wide-angle side, because the backlash of the zoom gear train (39-45)
 exists on the side in the direction of drawing in the first-lens-group
 tube 3, a biasing operation is made to be performed. The biasing operation
 is performed by driving the driving ring 37 toward the telephoto side from
 a target stop position extra as much as a predetermined amount to draw in
 the first-lens-group tube 3 and, after that, reversing the driving
 direction of the driving ring 37 and then stopping the first-lens-group
 tube 3 at the target stop position. As a result, the backlash of the gear
 train (39-45) is eliminated, so that, even if an external force is exerted
 on the first-lens-group tube 3 in the drawing-in direction, the
 first-lens-group tube 3 is prevented from moving.
 Further, in a case where, during the zooming action from the telephoto side
 to the wide-angle side, the zooming action is stopped on the telephoto
 side of the extreme value provided between the wide-angle end and the
 telephoto end, because the backlash of the gear train (39-45) exists on
 the side in the direction of drawing in the first-lens-group tube 3, a
 biasing operation is also performed. In this case, the biasing operation
 is performed by driving the driving ring 37 toward the wide-angle side
 from a target stop position extra as much as a predetermined amount to
 draw in the first-lens-group tube 3 and, after that, reversing the driving
 direction of the driving ring 37 and then stopping the first-lens-group
 tube 3 at the target stop position.
 On the other hand, in a case where, during the zooming action from the
 wide-angle side to the telephoto side, the zooming action is stopped on
 the telephoto side of the extreme value provided between the wide-angle
 end and the telephoto end, because the backlash of the gear train (39-45)
 exists on the side in the direction of drawing out the first-lens-group
 tube 3, a biasing operation is unnecessary.
 Further, in a case where, during the zooming action from the telephoto side
 to the wide-angle side, the zooming action is stopped on the wide-angle
 side of the extreme value provided between the wide-angle end and the
 telephoto end, because the backlash of the gear train (39-45) exists on
 the side in the direction of drawing out the first-lens-group tube 3, a
 biasing operation is also unnecessary.
 In the flow chart shown in FIG. 9, with the zooming action started, a check
 is made in step S011 to find if a telephoto switch T (not shown) of the
 zoom switch 77 for indicating the zooming action from the wide-angle side
 to the telephoto side is turned on or a wide-angle switch W (not shown) of
 the zoom switch 77 for indicating the zooming action from the telephoto
 side to the wide-angle side is turned on. If the telephoto switch T is
 turned on, the flow proceeds to step S012. If the wide-angle switch W is
 turned on, the flow proceeds to step S017.
 In step S012, the zoom motor 38 is driven to make a normal rotation so as
 to move the zoom lens toward the telephoto side. When the zoom motor 38
 makes the normal rotation, the first-lens-group tube 3 moves in the
 drawing-in direction toward the extreme value P, as shown in FIG. 5(c).
 Then, in step S013, a check is made to find if the zoom switch 77 is
 turned off. If not, the zoom motor 38 remains driven in the same
 direction. If so, the flow proceeds to step S014. In step S014, the
 driving of the zoom motor 38 is stopped to stop the first-lens-group tube
 3 and the second-lens-group tube 9 at the respective positions.
 The position of the first-lens-group tube 3 is detected, as described in
 the foregoing, by the linear sensor 56 according to the rotational angle
 of the driving ring 37. Accordingly, in step S015, a check is made to find
 if the stop position in the step S014 is between the wide-angle end and
 the extreme value P.
 If the stop position of the first-lens-group tube 3 is found in step S015
 to be between the extreme value P and the telephoto end during the driving
 from the wide-angle end to the telephoto end, the biasing operation for
 eliminating backlash is unnecessary, as described above. However, if the
 stop position of the first-lens-group tube 3 is found in step S015 to be
 between the wide-angle end and the extreme value P during the driving from
 the wide-angle end to the telephoto end, the biasing operation for
 eliminating backlash (the operation for eliminating hysteresis) is
 necessary, as described above, so that the flow proceeds to step S016.
 In step S016, the biasing operation for eliminating hysteresis in the zoom
 driving from the wide-angle end to the telephoto end. Since the backlash
 of the gear train (39-45) exists on the side in the direction of drawing
 in the first-lens-group tube 3, the biasing operation is performed by
 driving the driving ring 37 toward the telephoto side (in the drawing-in
 direction) from a target stop position extra as much as a predetermined
 amount to draw in the first-lens-group tube 3 and, after that, causing the
 zoom motor 38 to rotate in the reverse direction and then stopping the
 first-lens-group tube 3 at the target stop position. Thus, as the stop
 position of the first-lens-group tube 3 obtained when the zoom switch 77
 is turned off is stored, the first-lens-group tube 3 is made to be
 returned to the stop position as stored.
 As a result, the backlash of the gear train (39-45) is eliminated, so that,
 even if an external force is exerted on the first-lens-group tube 3 in the
 drawing-in direction, the first-lens-group tube 3 is prevented from
 moving.
 On the other hand, in step S017, the zoom motor 38 is driven to make a
 reverse rotation so as to move the zoom lens toward the wide-angle side.
 When the zoom motor 38 makes the reverse rotation, the first-lens-group
 tube 3 moves in the drawing-in direction toward the extreme value P, as
 shown in FIG. 5(c). Then, in step S018, a check is made to find if the
 zoom switch 77 is turned off. If not, the zoom motor 38 remains driven in
 the same direction. If so, the flow proceeds to step S014. In step S019,
 the driving of the zoom motor 38 is stopped to stop the first-lens-group
 tube 3 and the second-lens-group tube 9 at the respective positions.
 The position of the first-lens-group tube 3 is detected, as described in
 the foregoing, by the linear sensor 56 according to the rotational angle
 of the driving ring 37. Accordingly, in step S020, a check is made to find
 if the stop position in the step S019 is between the telephoto end and the
 extreme value P.
 If the stop position of the first-lens-group tube 3 is found in step S020
 to be between the extreme value P and the wide-angle end during the
 driving from the telephoto end to the wide-angle end, the biasing
 operation for eliminating backlash is unnecessary, as described above.
 However, if the stop position of the first-lens-group tube 3 is found in
 step S020 to be between the extreme value P and the telephoto end during
 the driving from the telephoto end to the wide-angle end, the biasing
 operation for eliminating backlash (the operation for eliminating
 hysteresis) is necessary, as described above, so that the flow proceeds to
 step S016.
 In step S016, the biasing operation for eliminating hysteresis in the zoom
 driving from the telephoto end to the wide-angle end. Since the backlash
 of the gear train (39-45) exists on the side in the direction of drawing
 in the first-lens-group tube 3, the biasing operation is performed by
 driving the driving ring 37 toward the wide-angle side (in the drawing-in
 direction) from a target stop position extra as much as a predetermined
 amount to draw in the first-lens-group tube 3 and, after that, causing the
 zoom motor 38 to rotate in the normal direction and then stopping the
 first-lens-group tube 3 at the target stop position. Thus, as the stop
 position of the first-lens-group tube 3 obtained when the zoom switch 77
 is turned off is stored, the first-lens-group tube 3 is made to be
 returned to the stop position as stored.
 As a result, the backlash of the gear train (39-45) is eliminated, so that,
 even if an external force is exerted on the first-lens-group tube 3 in the
 drawing-in direction, the first-lens-group tube 3 is prevented from
 moving.
 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, although, in the above-described embodiment, the extreme value
 in the zoom area (zoom locus) of the first-lens-group tube 3 is on the top
 of a locus which is protrusive toward the image side, the invention is
 applicable also to an arrangement in which the extreme value is on the top
 of a locus which is protrusive toward the object side, or to an
 arrangement in which the zoom locus is composed of a plurality of
 protrusive loci.
 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.