Patent Publication Number: US-7215489-B2

Title: Optical apparatus

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to an optical apparatus having a driving source for driving a lens in an optical axis direction, and particularly, to an optical apparatus which includes a vibration type linear actuator for use as a driving source. 
   Some optical apparatuses include a vibration type linear actuator for use as a driving source for driving a lens (for example, see Japanese Patent Laid-Open No. 10(1998)-90584). 
   In the optical apparatuses proposed in Japanese Patent Laid-Open No. 10(1998)-90584 having the vibration type linear actuator, the vibration type linear actuator is formed of a vibrator which produces vibration through an electromechanical energy conversion action and a contact member which is in press contact with the vibrator. The vibrator is fixed to a lens holding member, the contact member is fixed to a stationary member of a lens barrel, and the vibrator is caused to produce driving vibration, thereby moving the lens holding member together with the vibrator, or the contact member is fixed to the lens holding member, the vibrator is fixed to the stationary member of the lens barrel, and the vibrator is caused to produce driving vibration, thereby moving the lens holding member together with the contact member. 
   The description will be made of the lens barrel proposed in Japanese Patent Laid-Open No. 10(1998)-90584 using  FIGS. 21 and 22 . 
   In  FIGS. 21A to 21D , reference numeral  901  denotes a lens holding frame,  902  denotes a guide bar which guides the lens holding frame  901  in the optical axis direction. Reference numeral  904  denotes a vibrator,  905  a supporting portion which supports the vibrator  904 ,  906  a contact member which is in press contact with the vibrator  904 , and  907  a biasing member which produces the press contact force acting between the vibrator  904  and the contact member  906 . 
   In  FIG. 22 , reference numeral  911  a denotes a lens holding frame, and  913  a guide bush which is attached to the lens holding frame  911  and engages with a guide bar  930  in a movable condition in the optical axis direction. Reference numeral  920  denotes a vibrator holding frame which is provided on the guide bush  913 , and  925   a  and  925   b  supporting portions which support a vibrator  923 . Reference numeral  922  denotes a contact member which is fixed to a lens barrel main body, and  926  a spring which produces the press contact force acting between the vibrator  923  and the contact member  922 . 
   As shown in  FIGS. 21C and 21D , in a case where the vibrator  904  or the contact member  906  is supported only by the biasing member  907 , though the press contact between the vibrator  904  and the contact member  906  is ensured, there is no structure that supports the vibrator  904  or the contact member  906  in the optical axis direction. This causes a deformation of the biasing member  907  in the lens driving direction, thereby deteriorating the accuracy of the driving position of the lens holding frame  901 . 
   On the other hand, as shown in  FIGS. 21A ,  21 B, and  22 , in a case where the vibrator  904  or  923  is supported by the supporting member  905  or  925   a ,  925   b  in a movable condition only in a direction perpendicular to the press contact surface, a so-called point contact state or line contact state is generated between the vibrator and the contact member by relative inclinations of the guide bar  902  or  930 , the supporting portion  905  or  925   a,    925   b,  and the contact member  906  or  922 . This reduces the driving force in comparison with the driving force generated by the surface contact of the vibrator and the contact member. 
   Further, the biasing force (or spring force) generated by the biasing member which brings the vibrator and the contact member into press contact with each other is extremely large, so that the reaction force of the press contact force acting on the engagement part of the lens holding member and the guide bar increases the friction force (or driving load) generated in the engagement part in the driving direction. This causes problems that an increase of the size and output power of the vibration type linear actuator is required, a fine lens drive cannot be performed, and the engagement part is worn. 
   BRIEF SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide an optical apparatus which can well maintain a surface contact state between a vibrator and a contact member of a vibration type linear actuator to perform a stable lens drive. In addition, it is another object of the present invention to provide an optical apparatus which can reduce wear (abrasion) caused by the lens drive. 
   According to an aspect, the present invention provides an optical apparatus comprising a lens, a vibration type linear actuator which drives the lens in an optical axis direction. The vibration type linear actuator includes a vibrator on which vibration is produced through an electromechanical energy conversion action and a contact member which is in press contact with the vibrator. Further, the optical apparatus comprises a holding mechanism which holds one member of the vibrator and the contact member so as to change at least one of the position and inclination of the one member in response to a force smaller than a press contact force between the vibrator and the contact member. 
   Other objects and features of the present invention will become readily apparent from the following description of the preferred embodiments with reference to accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIGS. 1A to 1D  show the structure of a lens barrel of an image-taking apparatus which is Embodiment 1 of the present invention when viewed from four directions. 
       FIG. 2  is a section view showing the lens barrel in Embodiment 1 taken along a plane in parallel with an optical axis. 
       FIG. 3  is an exploded perspective view of the lens barrel in Embodiment 1. 
       FIG. 4A  is a perspective view showing a second lens holding member in the lens barrel in Embodiment 1. 
       FIG. 4B  is a perspective view showing a first vibration type linear actuator in the lens barrel in Embodiment 1. 
       FIG. 5A  is a perspective view showing a fourth lens holding member in the lens barrel in Embodiment 1. 
       FIG. 5B  is a perspective view showing a second vibration type linear actuator in the lens barrel in Embodiment 1. 
       FIG. 5C  schematically shows the structure of a light amount adjusting unit in the lens barrel in Embodiment 1. 
       FIG. 6  is a block diagram showing the electrical structure of the image-taking apparatus of Embodiment 1. 
       FIG. 7  is a section view showing a lens barrel in Embodiment 2 of the present invention taken along a plane in parallel with an optical axis. 
       FIG. 8  is a section view showing the lens barrel in Embodiment 2 taken along a plane perpendicular to the optical axis. 
       FIG. 9  is a section view showing the lens barrel in Embodiment 2 taken along a plane perpendicular to the optical axis. 
       FIG. 10  is an exploded perspective view showing the lens barrel in Embodiment 2. 
       FIG. 11  is a section view showing a lens barrel in Embodiment 3 of the present invention taken along a plane in parallel with an optical axis. 
       FIG. 12  is a section view showing the lens barrel in Embodiment 3 taken along a plane perpendicular to the optical axis. 
       FIG. 13  is a section view showing the lens barrel in Embodiment 3 taken along a plane perpendicular to the optical axis. 
       FIG. 14  is an exploded perspective view showing the lens barrel in Embodiment 3. 
       FIGS. 15A to 15D  show the structure of a lens barrel of an image-taking apparatus which is Embodiment 4 of the present invention when viewed from four directions. 
       FIG. 16  is a section view showing the lens barrel in Embodiment 4 taken along a plane in parallel with an optical axis. 
       FIG. 17  is a section view showing the lens barrel in Embodiment 4 taken along a plane perpendicular to the optical axis. 
       FIG. 18  is a section view showing the lens barrel in Embodiment 4 taken along a plane perpendicular to the optical axis. 
       FIG. 19  is an exploded perspective view showing the lens barrel in Embodiment 4. 
       FIG. 20  is a block diagram showing the electrical structure of the image-taking apparatus of Embodiment 4. 
       FIGS. 21A to 21D  show an optical apparatus using a conventional vibration type linear actuator. 
       FIG. 22  shows an optical apparatus using a conventional vibration type linear actuator. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will hereinafter be described with reference to the drawings. 
   Embodiment 1 
     FIGS. 1A to 1D  show a lens barrel, with its exterior removed, in an image-taking apparatus (optical apparatus) which is Embodiment 1 of the present invention when viewed from four directions, the front, right, back, and left, respectively.  FIG. 2  is a section view of the lens barrel taken along the plane including the optical axis of the lens barrel.  FIG. 3  is an exploded perspective view of the lens barrel.  FIGS. 4A and 4B  are partial enlarged views showing a vibration type linear actuator for driving a second lens unit which forms part of the lens barrel.  FIGS. 5A and 5B  are partial enlarged views showing a vibration type linear actuator for driving a fourth lens unit which forms part of the lens barrel.  FIG. 5C  schematically shows the structure of a light amount adjusting unit which forms part of the lens barrel.  FIG. 6  shows the electrical structure of the image-taking apparatus of Embodiment 1. 
   In  FIGS. 1A to 6 , in order from an object side, reference numerals  1  shows a fixed first lens unit,  2  the second lens unit which is movable in the optical axis direction for varying magnification,  15  the light amount adjusting unit,  3  a fixed third lens unit, and  4  the fourth lens unit which is movable in the optical axis direction for correcting image plane changes associated with varied magnification and for focal adjustment. 
   Reference numeral  5  shows a rear barrel which holds an image-pickup device, later described, and a low pass filter (LPF), and is fixed to a camera body, not shown. Reference numeral  6  shows a first lens holding member which holds the first lens unit  1  and is fixed to the rear barrel  5  by screws  7 ,  8 , and  9 . 
   Reference numerals  10  and  11  show guide bars (guide members) which are held substantially in parallel with the optical axis direction by the rear barrel  5  and the first lens holding member  6 . 
   Reference numeral  12  shows a second lens holding member which holds the second lens unit  2  and to which a mask  32  for cutting unnecessary light is fixed. The second lens holding member  12  engages with the guide bar  10  at an engaging portion  12   a  to be guided in the optical axis direction and engages with the guide bar  11  at an engaging portion  12   b  to be prevented from rotation around the guide bar  10 . Reference numeral  13  shows a third lens holding member which holds the third lens unit  3  and is fixed to the rear barrel  5  by a screw  16 . Reference numeral  14  shows a fourth lens holding member which holds the fourth lens unit  4 , and engages with the guide bar  11  at an engaging portion  14   a  to be guided in the optical axis direction and engages with the guide bar  10  at an engaging portion  14   b  to be prevented from rotation around the guide bar  11 . 
   The light amount adjusting unit  15  has an outer shape which is longer in a vertical direction (first direction) than in a horizontal direction (second direction) when viewed from the optical axis direction. The light amount adjusting unit  15  is fixed to the rear barrel  5  by a screw  17 . As shown in  FIG. 5C , the light amount adjusting unit  15  is a so-called guillotine type aperture stop in which a pair of aperture blades  15   a  and  15   b  are substantially translated vertically by a lever  15   c  rotated by a motor  15   d  to increase or reduce the diameter of the aperture. Reference numeral  15   f  shows an opening formed by the plates of the light amount adjusting unit  15 . The aperture blades  15   a  and  15   b  are guided vertically by guide pins  15   e  provided on the left and right. Unlike a so-called iris type or scissors type, the guillotine type aperture stop has the horizontal dimension substantially smaller than the vertical dimension since the aperture blades  15   a  and  15   b  are substantially translated vertically. 
   Reference numeral  18  shows a slider (contact member) which is formed of a magnet and a friction material bonded to each other and is fixed into a groove  12   c  formed in the second lens holding member  12  through adhesion or the like. Reference numeral  19  shows a vibrator which is formed of an electromechanical energy conversion element and a plate-shaped elastic member on which vibration is produced by the electromechanical energy conversion element. The elastic member of the vibrator  19  is made of ferromagnet which is attracted by the magnet of the slider  18  to bring a press contact surface  18   a  of the friction material of the slider  18  into press contact with press contact surfaces  19   a  and  19   b  formed at two positions in the optical axis direction in the elastic member of the vibrator  19 . 
   In a first vibration type linear actuator formed of the slider  18  and the vibrator  19 , two frequency signals (pulse signals or alternate signals) in difference phases are input to the electromechanical energy conversion element through a flexible wiring board  20  to create a substantially elliptic motion in the press contact surfaces  19   a  and  19   b  of the vibrator  19  to produce driving force in the optical axis direction in the press contact surface  18   a  of the slider  18 . 
   Reference numeral  21  shows a spacer to which the vibrator  19  is fixed, and  22  a plate spring to which the spacer  21  is fixed. The plate spring  22  has a shape which is not easily deformed in the in-plane direction of the plate and is easily deformed in the direction perpendicular to the plate plane. The plate spring  22  is easily deformed in the rotation direction around an arbitrary axis included in the plane, and when deformed, it holds the press contact surfaces  19   a  and  19   b  of the vibrator  19  in parallel with the press contact surface  18   a  of the slider  18 . The plate spring  22  not easily deformed in the in-plane direction limits displacement of the vibrator  19  in the optical axis direction (that is, the driving direction). 
   Reference numeral  23  shows a vibrator holding member which is fixed to the first lens holding member  6  by screws  26  and  27  and to which the plate spring  22  is fixed by screws  24  and  25 . Reference numeral  28  shows a scale which detects the moving amount (position) of the second lens holding member  12  and is fixed into a groove  12   d  formed in the second lens holding member  12  through adhesion or the like. Reference numeral  29  shows a light transmitter/receiver element which applies light to the scale  28  and receives the light reflected by the scale  28  to detect the moving amount of the second lens holding member  12 . The light transmitter/receiver element  29  and the scale  28  constitute a first linear encoder serving as a detector. Reference numeral  30  shows a flexible wiring board which sends and receives a signal to and from the light transmitter/receiver element  29  and is fixed to the first lens holding member  6  by a screw  31 . 
   As shown in  FIG. 1A , the guide bar  10 , the first vibration type linear actuator formed of the vibrator  19  and the slider  18 , and the first linear encoder formed of the light transmitter/receiver element  29  and the scale  28  are arranged along or close to a planar right side of the light amount adjusting unit  15  (linear long side on the right when viewed from the optical axis direction) that is one of the outer surfaces closest to the optical axis position of the light amount adjusting unit  15  of all of the outer surfaces thereof when viewed from the front of the optical axis direction. The first vibration type linear actuator and the first linear encoder are disposed vertically next to the guide bar  10  to sandwich the guide bar  10 . 
   Reference numeral  33  shows a plate spring which is fixed to the fourth lens holding member  14 . Reference numeral  34  shows a slider (contact member) which is formed of a magnet and a friction material bonded to each other and is fixed to the plate spring  33  through adhesion or the like. The plate spring  33  has a shape which is not easily deformed in the in-plane direction of the plate and is easily deformed in the direction perpendicular to the plate plane. The plate spring  33  is easily deformed in the rotation direction around an arbitrary axis included in the plane, and it holds a press contact surface  34   a  of the slider  34  in parallel with press contact surfaces  35   a  and  35   b  of a vibrator  35 . The plate spring  33  not easily deformed in the in-plane direction limits displacement of the slider  34  in the optical axis direction (that is, the driving direction). 
   The vibrator  35  is formed of an electromechanical energy conversion element and a plate-shaped elastic member on which vibration is produced by the electromechanical energy conversion element. The elastic member of the vibrator  35  is made of ferromagnet which is attracted by the magnet of the slider  34  to bring the press contact surface  34   a  of the friction material of the slider  34  into press contact with the press contact surfaces  35   a  and  35   b  formed at two positions in the optical axis direction in the elastic member of the vibrator  35 . 
   In a second vibration type linear actuator formed of the slider  34  and the vibrator  35 , two frequency signals (pulse signals or alternate signals) in difference phases are input to the electromechanical energy conversion element through a flexible wiring board  36  to create a substantially elliptic motion in the press contact surfaces  35   a  and  35   b  of the vibrator  35   b  to produce driving force in the optical axis direction in the press contact surface  34   a  of the slider  34 . 
   As shown in  FIG. 2 , the second lens holding member  12  (engaging portion  12   a  engaging with the guide bar  10 ) has a movable range L 2  in the optical axis direction which extends from the object side (the left in  FIG. 2 ) of the light amount adjusting unit  15  toward the image plane side when viewed from the direction perpendicular to the optical axis. The fourth lens holding member  14  (engaging portion  14   a  engaging with the guide bar  11 ) has a movable range L 4  in the optical axis direction which extends from the image plane side of the light amount adjusting unit  15  into the light amount adjusting unit  15 . In other words, the movable ranges of the second lens holding member  12  and the fourth lens holding member  14  overlap each other in the optical axis direction. Accordingly, the range in which the first vibration type linear actuator is placed (the range in which the slider  18  is provided) and the range in which the second vibration type linear actuator is placed (the range in which the slider  34  is provided) overlap each other in the optical axis direction. 
   Reference numeral  37  shows a spacer to which the vibrator  35  is fixed, and  38  a plate spring to which the spacer  37  is fixed. The plate spring  38  has a shape which is not easily deformed in the in-plane direction of the plate and is easily deformed in the direction perpendicular to the plate plane. The plate spring  38  is easily deformed in the rotation direction around an arbitrary axis included in the plane, and it holds the press contact surfaces  35   a  and  35   b  of the vibrator  35  in parallel with the press contact surface  34   a  of the slider  34 . The plate spring  38  not easily deformed in the in-plane direction limits displacement of the vibrator  35  in the optical axis direction (that is, the driving direction). 
   Reference numeral  39  shows a vibrator holding member which is fixed to the rear barrel  5  by screws  42  and  43  and to which the plate spring  38  is fixed by screws  46  and  47 . 
   Reference numeral  48  shows a scale which detects the moving amount (position) of the fourth lens holding member  14  and is fixed into a groove  14   d  formed in the fourth lens holding member  14  through adhesion or the like. Reference numeral  49  shows a light transmitter/receiver element which applies light to the scale  48  and receives the light reflected by the scale  48  to detect the moving amount of the fourth lens holding member  14 . The light transmitter/receiver element  49  and the scale  48  constitute a second linear encoder serving as a detector. Reference numeral  50  shows a flexible wiring board which sends and receives a signal to and from the light transmitter/receiver element  49  and is fixed to the rear barrel  5  by a screw  51 . 
   As shown in  FIG. 1A , the guide bar  11 , the second vibration type linear actuator formed of the vibrator  35  and the slider  34 , and the second linear encoder formed of the light transmitter/receiver element  49  and the scale  48  are arranged along or close to a planar left side of the light amount adjusting unit  15  (linear long side on the left when viewed from the optical axis direction) that is the other outer surface closest to the optical axis position of the light amount adjusting unit  15  of all of the outer surfaces thereof when viewed from the front of the optical axis direction. The second vibration type linear actuator and the second linear encoder are disposed vertically next to the guide bar  11  to sandwich the guide bar  11 . 
   The set of the first vibration type linear actuator, the guide bar  10 , and the first linear encoder, and the set of the second vibration type linear actuator, the guide bar  11 , and the second linear encoder are arranged substantially symmetrically with respect to an axis extending vertically through the center of the optical axis. 
   In  FIG. 6 , reference numeral  101  shows the image-pickup device formed of a CCD sensor, a CMOS sensor or the like. Reference numeral  102  shows the first vibration type linear actuator which includes the slider  18  and the vibrator  19 , and serves as a driving source of the second lens unit  2  (second lens holding member  12 ). Reference numeral  103  shows the second vibration type linear actuator which includes the slier  34  and the vibrator  35 , and serves as a driving source of the fourth lens unit  4  (fourth lens holding member  14 ). 
   Reference numeral  104  shows the motor which serves as a driving source of the light amount adjusting unit  15 . Reference numeral  105  shows a second lens encoder realized by the first linear encoder which includes the scale  28  and the light transmitter/receiver element  29 ,  106  a fourth lens encoder realized by the second linear encoder which includes the scale  48  and the light transmitter/receiver element  49 . These encoders detect the relative positions (moving amounts from a reference position) of the second lens unit  2  and the fourth lens unit  4  in the optical axis direction, respectively. While Embodiment 1 employs optical encoders as the encoders, it is possible to use a magnetic encoder or an encoder which detects an absolute position by using electrical resistance. 
   Reference numeral  107  shows an aperture encoder which is, for example, of the type in which a hall element is provided within the motor  104  as the driving source of the light amount adjusting unit  15  and is used to detect a rotational position relationship between a rotor and a stator of the motor  104 . 
   Reference numeral  117  shows a CPU serving as a controller responsible for control of operation of the image-taking apparatus. Reference numeral  108  shows a camera signal processing circuit which performs amplification, gamma correction or the like on the output from the image-pickup device  101 . After the predetermined processing, a contrast signal of a video signal is transmitted through an AE gate  109  and an AF gate  110 . The gates  109  and  110  set an optimal range in the entire screen for extracting the signal for exposure setting and focusing. These gates  109  and  110  may have variable sizes, or a plurality of gates  109  and  110  may be provided. 
   Reference numeral  114  shows an AF (auto-focus) signal processing circuit for auto-focus which extracts a high-frequency component of the video signal to produce an AF evaluation value signal. Reference numeral  115  shows a zoom switch for zooming operation. Reference numeral  116  shows a zoom tracking memory which stores information about target positions to which the fourth lens unit  4  is to be driven in accordance with the camera-to-object distance and the position of the second lens unit  2  in order to maintain an in-focus state in varying magnification. Memory in the CPU  117  may be used as the zoom tracking memory. 
   In the abovementioned structure, when a user operates the zoom switch  115 , the CPU  117  controls the first vibration type linear actuator  102  for driving the second lens unit  2  and calculates the target driving position of the fourth lens unit  4  based on the information in the first zoom tracking memory  116  and the current position of the second lens unit  2  determined from the detection result of the second lens unit encoder  105  to control the second vibration type linear actuator  103  for driving of the fourth lens unit  4  to that target driving position. Whether or not the fourth lens unit  4  has reached the target driving position is determined by the matching of the current position of the fourth lens unit  4  determined from the detection result of the fourth lens unit encoder  106  with the target driving position. 
   In the auto-focus, the CPU  117  controls the second vibration type linear actuator  103  to drive the fourth lens unit  4  to search for the position where the AF evaluation value determined by the AF signal processing circuit  114  is at the peak. 
   To provide appropriate exposure, the CPU  117  controls the motor  104  of the light amount adjusting unit  15  to increase or reduce the aperture diameter such that the average value of the luminance signal through the AE gate  109  is equal to a predetermined value, that is, such that the output from the aperture encoder  107  has a value corresponding to the predetermined value. 
   In the abovementioned structure, the slider  18  is formed by using the magnet which attracts the vibrator  19  to provide the press contact force necessary for producing the driving force as the vibration type linear actuator. Thus, any reaction force of the press contact force does not act on the second lens holding member  12 . As a result, the frictional force produced at the engaging portions  12   a  and  12   b  of the second lens holding member  12  engaging with the guide bars  10  and  11  is not increased, and the driving load due to the friction is not increased. In addition, the plate spring  22  produces small force, so that the force acting from the plate spring  22  on the engaging portions  12   a  and  12   b  engaging with the guide bars  10  and  11  is small and hardly increases the frictional force produced at the engaging portions  12   a  and  12   b.  This enables the use of the low-power and small vibration type linear actuator, resulting in a reduction in size of the lens barrel. 
   Since large press contact force does not act on the second lens holding member  12 , the frictional force produced at the engaging portions  12   a  and  12   b  of the second lens holding member  12  engaging with the guide bars  10  and  11  is not increased. The power or size of the first vibration type linear actuator  102  does not need to be increased, and the wear (abrasion) due to the friction between the guide bars  10 ,  11  and the engaging portions  12   a,    12   b  can be reduced. Also, the fine driving of the second lens holding member  12  (second lens unit  2 ) can be accurately achieved. 
   Even when a manufacturing error or the like changes the position of any press contact surface with respect to an axis in parallel with the optical axis or the inclination around that axis in the optical axis direction, the plate spring  22  is deformed to change the position or inclination (orientation) of the vibrator  19  to maintain both of the press contact surfaces in parallel with each other, thereby holding an appropriate contact state between the surfaces. The plate spring  22  has a spring constant set such that it is deformed in response to a smaller force than the abovementioned press contact force. The press contact force is not changed greatly even when the position or inclination of any press contact surface is changed. Consequently, it is possible to provide stably an output consistent with the performance inherent in the first vibration type linear actuator  102 . 
   On the other hand, the slider  34  is formed by using the magnet which attracts the vibrator  35  to provide the press contact force necessary for producing the driving force as the vibration type linear actuator. Thus, any reaction force of the press contact force does not act on the fourth lens holding member  14 . As a result, the frictional force produced at the engaging portions  14   a  and  14   b  of the fourth lens holding member  14  engaging with the guide bars  11  and  10  is not increased, and the driving load due to the friction is not increased. In addition, the plate springs  33  and  38  produce small force, so that the force acting from the plate springs  33  and  38  on the engaging portions  14   a  and  14   b  engaging with the guide bars  11  and  10  is small and hardly increases the frictional force produced at the engaging portions  14   a  and  14   b.  This enables the use of the low-power and small vibration type linear actuator, resulting in a reduction in size of the lens barrel. 
   Since large press contact force does not act on the fourth lens holding member  14 , the frictional force produced at the engaging portions  14   a  and  14   b  of the fourth lens holding member  14  engaging with the guide bars  11  and  10  is not increased. The power or size of the second vibration type linear actuator  103  does not need to be increased, and the wear due to the friction between the guide bars  10 ,  11  and the engaging portions  14   a,    14   b  can be reduced. Also, the fine driving of the fourth lens holding member  14  (fourth lens unit  4 ) can be accurately achieved. 
   Even when a manufacturing error or the like changes the position of any press contact surface with respect to an axis in parallel with the optical axis or the inclination around that axis in the optical axis direction, the plate springs  33  and  38  are deformed to change the position or inclination (orientation) of the vibrator  34  to maintain both of the press contact surfaces in parallel with each other, thereby holding an appropriate contact state between the surfaces. Each of the plate springs  33  and  38  has a spring constant set such that it is deformed in response to a smaller force than the abovementioned press contact force. The press contact force is not changed greatly even when the position or inclination of any press contact surface is changed. Consequently, it is possible to provide stably an output consistent with the performance inherent in the second vibration type linear actuator  103 . 
   As described above, in Embodiment 1, the guide bar  10 , the first vibration type linear actuator, and the first linear encoder are arranged along (close to) the right side which is one of the flat surfaces of the light amount adjusting unit  15  closest to the optical axis when viewed from the optical axis direction. The first vibration type linear actuator and the first linear encoder are disposed next to the guide bar  10  below and above, respectively. In addition, the guide bar  11 , the second vibration type linear actuator, and the second linear encoder are arranged along (close to) the left side which is one of the flat surfaces of the light amount adjusting unit  15  closest to the optical axis when viewed from the optical axis direction. The second vibration type linear actuator and the second linear encoder are disposed next to the guide bar  11  below and above, respectively. 
   Thus, although the optical apparatus has the light amount adjusting unit  15 , the two vibration type linear actuators for driving the second and fourth lens holding members  12  and  14  (second and fourth lens units  2  and  4 ) disposed on the object side and the image plane side of the light amount adjusting unit  15 , the two guide bars  10  and  11  for guiding the lens holding members  12  and  14  in the optical axis direction, and the two linear encoders for detecting the positions of the lens holding members  12  and  14 , it can be formed in a compact size. 
   Since the sliders  18  and  34  are disposed next to the guide bars  10  and  11 , respectively, the second and fourth lens holding members  12  and  14  can be driven smoothly. In addition, the scales  28  and  48  disposed next to the guide bars  10  and  11  reduce displacement of the scales  28  and  48  due to backlash of the engaging portions  12   a,    12   b  and  14   a,    14   b  of the second and forth lens holding members  12  and  14  engaging with the guide bars  10  and  11  to enable accurate detection of positions. 
   When the linear actuator and the linear encoder are disposed across the optical axis from the guide bar for guiding the lens holding member which is driven and whose position is detected by them, the linear encoder may be moved in the direction opposite to the driving direction with the guide bar as the supporting point at the start of the driving due to backlash at the engaging portion of the lens holding member engaging with the guide bar. This may reduce the accuracy of the position detection. In Embodiment 1, however, the linear actuator and the linear encoder are disposed on the same side as the guide bar for guiding the lens holding member which is driven and whose position is detected by them, so that such a problem does not arise and the position can be detected accurately. 
   Embodiment 2 
     FIG. 7  shows a section view of a lens barrel of an image-taking apparatus which is Embodiment 2 of the present invention taken along a plane in parallel with an optical axis and perpendicular to a press contact surface between a slider and a vibrator of a vibration type linear actuator.  FIG. 8  shows a section view of the lens barrel in Embodiment 2 taken along a plane perpendicular to the optical axis and perpendicular to a press contact surface of a vibration type linear actuator for driving a second lens unit when viewed from an object side.  FIG. 9  shows a section view of the lens barrel in Embodiment 2 taken along a plane perpendicular to the optical axis and perpendicular to a press contact surface of a vibration type linear actuator for driving a fourth lens unit when viewed from the object side.  FIG. 10  is an exploded view showing the lens barrel in Embodiment 2. The image-taking apparatus of Embodiment 2 has the same electrical structure as that in Embodiment 1. 
   In  FIGS. 7 to 10 , in order from the object side, reference numeral  201  shows a fixed first lens unit,  202  the second lens unit which is movable in the optical axis direction for varying magnification,  215  a light amount adjusting unit,  203  a fixed third lens unit, and  204  the fourth lens unit which is movable in the optical axis direction for correcting image plane changes associated with varied magnification and for focal adjustment. 
   Reference numeral  205  shows a rear barrel which holds an image-pickup device and a low pass filter (LPF), and is fixed to a camera body, not shown. Reference numeral  206  shows a first lens holding member which holds the first lens unit  201  and is fixed to the rear barrel  205  by screws  207 ,  208 , and  209 . 
   Reference numerals  210  and  211  show guide bars (guide members) which are held substantially in parallel with the optical axis direction by the rear barrel  205  and the first lens holding member  206 . 
   Reference numeral  212  shows a second lens holding member which holds the second lens unit  202  and to which a mask  232  for cutting unnecessary light is fixed. The second lens holding member  212  engages with the guide bar  210  at an engaging portion  212   a  to be guided in the optical axis direction and engages with the guide bar  211  at an engaging portion  212   b  to be prevented from rotation around the guide bar  210 . Reference numeral  213  shows a third lens holding member which holds the third lens unit  203  and is fixed to the rear barrel  205  by a screw  216 . Reference numeral  214  shows a fourth lens holding member which holds the fourth lens unit  204 , and engages with the guide bar  211  at an engaging portion  214   a  to be guided in the optical axis direction and engages with the guide bar  210  at an engaging portion  214   b  to be prevented from rotation around the guide bar  211 . 
   The light amount adjusting unit  215  has an outer shape which is longer in a vertical direction (first direction) than in a horizontal direction (second direction) when viewed from the optical axis direction. The light amount adjusting unit  215  is fixed to the rear barrel  205  by a screw  217 . The light amount adjusting unit  215  has the same structure as that in Embodiment 1 shown in  FIG. 5C . 
   Reference numeral  218  shows a slider which is formed of a friction material. Reference numeral  219  shows a vibrator which is formed of an electromechanical energy conversion element and a plate-shaped elastic member on which vibration is produced by the electromechanical energy conversion element. Reference numeral  220  shows a flexible wiring board which is connected to the vibrator  219  and transmits a signal to the electromechanical energy conversion element. The flexible wiring board  220  has a bend portion (deformation portion)  220   a  which is deformed as the second lens holding member  212  is moved in the optical axis direction. 
   In a first vibration type linear actuator formed of the slider  218  and the vibrator  219 , while the slider  218  is in press contact with the vibrator  219 , two frequency signals (pulse signals or alternate signals) in difference phases are input to the electromechanical energy conversion element through the flexible wiring board  220  to create a substantially elliptic motion in press contact surfaces  219   a  (formed at two positions in the optical axis direction as in Embodiment 1) of the vibrator  219  to produce driving force in the optical axis direction in a press contact surface  218   a  of the slider  218 . 
   Reference numeral  221  shows a spacer which fixes the vibrator  219  and has a hole  221   a  formed in its center. A spherical projection  212   e  formed on the second lens holding member  212  is fitted into the hole  221   a  to hold the spacer  221  such that its movement is prevented (limited) in the optical axis direction (that is, the driving direction) and its rotation and movement in a direction other than the optical axis direction are permitted. The outer periphery of the spacer  221  is held with some backlash by projections  212   c,    212   d,  and a projection, not shown, formed on the second lens holding member  212 . This enables the spacer  221  to be moved such that the press contact surfaces  219   a  of the vibrator  219  is in parallel with the press contact surface  218   a  of the slider  218 . 
   Reference numeral  222  shows a press contact bar which retains the surface of the slider  218  opposite to the press contact surface  218   a,    224  a coil spring which is hung from a projection  221   b  of the spacer  221  to the press contact bar  222 , and  225  a coil spring which is hung from a projection  221   c  of the spacer  221  to the press contact bar  222 . The press contact bar  222  and the spacer  221  pull each other through the pull force of the coil springs  224  and  225 . The slider  218  retained by the press contact bar  222  and the vibrator  219  fixed to the spacer  221  are held such that their press contact surfaces  218   a  and  219   a  are in press contact with each other. 
   Reference numeral  223  shows a slider holding member having a holding portion  223   a  to which the slider  218  is fixed through adhesion or the like. The slider  223  is fixed to the first lens holding member  206  by screws  226  and  227 . 
   Reference numeral  228  shows a scale which detects the position of the second lens holding member  212  and is fixed into a groove  212   f  formed in the second lens holding member  212  through adhesion or the like. Reference numeral  229  shows a light transmitter/receiver element which applies light to the scale  228  and receives the light reflected by the scale  228  to detect the moving amount of the second lens holding member  212 . The scale  228  and the light transmitter/receiver element  229  constitute a first linear encoder serving as a detector. 
   Reference numeral  230  shows a flexible wiring board which sends and receives a signal to and from the light transmitter/receiver element  229  and is fixed to the first lens holding member  206  by a screw  231 . 
   As shown in  FIG. 8 , the guide bar  210 , the first vibration type linear actuator formed of the vibrator  219  and the slider  218 , and the first linear encoder formed of the light transmitter/receiver element  229  and the scale  228  are arranged along or close to a planar left side of the light amount adjusting unit  215  (linear long side on the left when viewed from the optical axis direction) that is one of the outer surfaces closest to the optical axis position of the light amount adjusting unit  215  of all of the outer surfaces thereof when viewed from the front of the optical axis direction. The first vibration type linear actuator and the first linear encoder are disposed vertically next to the guide bar  210  to sandwich the guide bar  210 . 
   Reference numeral  233  shows a press contact bar,  240  and  241  coil springs whose ends are hung on the press contact bar  233 . Reference numeral  234  shows a slider which is made of a friction material retained by the press contact bar  233  and is fixed to a groove  214   e  of the fourth lens holding member  214 . 
   Reference numeral  235  shows a vibrator which is formed of an electromechanical energy conversion element and a plate-shaped elastic member on which vibration is produced by the electromechanical energy conversion element. Reference numeral  236  shows a flexible wiring board which is connected to the electromechanical energy conversion element of the vibrator  235 . In a second vibration type linear actuator formed of the slider  234  and the vibrator  235 , while the slider  234  is in press contact with the vibrator  235 , two frequency signals (pulse signals or alternate signals) in difference phases are input to the electromechanical energy conversion element through the flexible wiring board  236  to create a substantially elliptic motion in press contact surfaces  235   a  (formed at two positions in the optical axis direction as in Embodiment 1) of the vibrator  235  to produce driving force in the optical axis direction in a press contact surface  234   a  of the slider  234 . 
   As shown in  FIG. 7 , the range in which the first vibration type linear actuator is placed in the optical axis direction (the range in which the slider  218  is placed) and a movable range L 2  of the second lens holding member  212  in the optical axis direction extend from the object side (the left in  FIG. 7 ) of the light amount adjusting unit  215  toward the image plane side. On the other hand, the range in which the second vibration type linear actuator is placed in the optical axis direction (the range in which the slider  234  is placed) and a movable range L 4  of the fourth lens holding member  214  in the optical axis direction extend from the image plane side of the light amount adjusting unit  215  toward the object side. In other words, the ranges in which the first and second vibration type linear actuators are placed (the movable ranges of the second and fourth lens holding members  212  and  214 ) overlap each other in the optical axis direction. 
   Reference numeral  237  shows a spacer which holds the vibrator  235  and has projections  237   b  and  237   c  on which the other ends of the coil springs  240  and  241  are hung. The coil springs  240  and  241  pull the press contact bar  233  and the spacer  237 , the press contact bar  233  pushes the slider  234 , and the spacer  237  pushes the vibrator  235 , so that the press contact surface  234   a  of the slider  234  is in press contact with the press contact surfaces  235   a  of the vibrator  235 . 
   Reference numeral  239  shows a vibrator holding member which holds the vibrator  235 . The vibrator holding member  239  has shafts  239   a  and  239   b  which extend toward the object side and the image plane side and rotatably engage with bearings  205   a  and  205   b  of the rear barrel  205 , respectively. A spherical projection  239   c  formed on the inner side of the vibrator holding member  239  is fitted into a conical hole  237   a  formed in the spacer  237 . The vibrator holding member  239  is biased toward the object by a torsion coil spring  238  disposed on the shaft  239   b  and thus is held without backlash in the optical axis direction. The vibrator holding member  239  is urged toward the inward rotation direction around the shafts  239   a  and  239   b  by the torsion coil spring  238 , which presses the spherical projection  239   c  into the hole  237   a.  The spacer  237  and the vibrator  235  held thereby are kept such that their movement is prevented (limited) in the optical axis direction (that is, the driving direction) and their rotation around the spherical projection  239   c  and their movement in the direction substantially perpendicular to the press contact surface  235   a  are permitted. 
   Reference numeral  248  shows a scale which detects the position of the fourth lens holding member  214  and is fixed into a groove  214   d  formed in the fourth lens holding member  214  through adhesion or the like. Reference numeral  249  shows a light transmitter/receiver element which applies light to the scale  248  and receives the light reflected by the scale  248  to detect the moving amount of the fourth lens holding member  214 . The scale  248  and the light transmitter/receiver element  249  constitute a second linear encoder serving as a detector. 
   Reference numeral  250  shows a flexible wiring board which sends and receives a signal to and from the light transmitter/receiver element  249  and is fixed to the rear barrel  205  by a screw  251 . 
   As shown in  FIG. 9 , the guide bar  211 , the second vibration type linear actuator formed of the vibrator  235  and the slider  234 , and the second linear encoder formed of the light transmitter/receiver element  249  and the scale  248  are arranged along or close to a planar right side of the light amount adjusting unit  215  (linear long side on the right when viewed from the optical axis direction) that is one of the outer surfaces closest to the optical axis position of the light amount adjusting unit  215  of all of the outer surfaces thereof when viewed from the front of the optical axis direction. The second vibration type linear actuator and the second linear encoder are disposed vertically next to the guide bar  211  to sandwich the guide bar  211 . 
   The set of the first vibration type linear actuator, the guide bar  210 , and the first linear encoder, and the set of the second vibration type linear actuator, the guide bar  211 , and the second linear encoder are arranged substantially symmetrically with respect to an axis extending vertically through the center of the optical axis. 
   In the abovementioned structure, the coil springs  224  and  225  pull the press contact bar  222  and the spacer  221  to press the slider  218  against the vibrator  219  to provide the press contact force necessary for producing the driving force as the vibration type linear actuator. Thus, any reaction force of the press contact force does not act on the second lens holding member  212 . As a result, the frictional force produced at the engaging portions  212   a  and  212   b  of the second lens holding member  212  engaging with the guide bars  210  and  211  is not increased and the driving load due to the friction is not increased. 
   The slider  218  is fixed to the slider holding member  223 . On other hand, the spacer  221  engages with the spherical projection  212   e  of the second lens holding member  212  and transmits the force necessary for driving the second lens holding member  212  without backlash in the optical axis direction, but transmits only small force in the moving direction other than the driving direction and in the rotation direction. Thus, any press contact force does not act on the second lens holding member  212 . 
   This enables the use of the low-power and small vibration type linear actuator, resulting in a reduction in size of the lens barrel. 
   In addition, the hole  221   a  of the spacer  221  for holding the vibrator  219  receives the spherical projection  212   e  of the second lens holding member  212  to hold the second lens holding member  212  to allow the rotation around the spherical projection  212   e  and the movement in the direction other than the optical axis direction. Even when a manufacturing error or the like changes the position or inclination of any press contact surface in the optical axis direction, the position or inclination (orientation) of the vibrator  219  is changed to maintain both of the press contact surfaces in parallel with each other, thereby holding an appropriate contact state between the surfaces. The press contact force is not changed greatly even when the position or inclination of the spacer  221  is changed. Consequently, it is possible to provide stably an output consistent with the performance inherent in the first vibration type linear actuator  102 . 
   Since large press contact force does not act on the second lens holding member  212 , the frictional force produced at the engaging portions  212   a  and  212   b  of the second lens holding member  212  engaging with the guide bars  210  and  211  is not increased. The power or size of the first vibration type linear actuator does not need to be increased, and the wear due to the friction between the guide bars  210 ,  211  and the engaging portions  212   a,    212   b  can be reduced. Also, the fine driving of the second lens holding member  212  (second lens unit  202 ) can be accurately achieved. 
   On the other hand, the coil springs  240  and  241  pull the press contact bar  233  and the spacer  237  to press the slider  234  against the vibrator  235  to provide the press contact force necessary for producing the driving force as the vibration type linear actuator. Thus, any reaction force of the press contact force does not act on the fourth lens holding member  214 . As a result, the frictional force produced at the engaging portions  214   a  and  214   b  of the fourth lens holding member  214  engaging with the guide bars  211  and  210  is not increased and the driving load due to the friction is not increased. 
   The slider  234  is fixed into the groove  214   e  of the fourth lens holding member  214 . The conical hole  237   a  of the spacer  237  receives the spherical projection  239   c  of the vibrator holding member  239 , so that only retaining force for supporting the spacer  237  without backlash acts on the spacer  237 . Since the retaining force for supporting the spacer  237  without backlash is smaller than the abovementioned press contact force, the frictional force produced at the engaging portions  214   a  and  214   b  of the fourth lens holding member  214  engaging with the guide bars  211  and  210  is hardly increased, and the driving load due to the friction is hardly increased. 
   This enables the use of the low-power and small vibration type linear actuator, resulting in a reduction in size of the lens barrel. 
   As described above, the press contact surface  234   a  of the slider  234  is in press contact with the press contact surfaces  235   a  of the vibrator  235  by the pull force of the coil springs  240  and  241 , and the spherical projection  239   c  of the vibrator holding member  239  is pressed into the conical hole  237   a  to engage without backlash by the biasing force of the coil spring  238 . This enables the vibrator  235  to rotate around the spherical projection  239   c.  The vibrator holding member  239  is rotated around the shafts  239   a  and  239   b  to allow the vibrator  235  to be moved in the direction substantially perpendicular to the press contact surfaces  235   a  or inclined to rotate around the spherical projection  239   c.    
   Even when a manufacturing error or the like changes the position of any press contact surface with respect to an axis in parallel with the optical axis or the inclination around that axis in the optical axis direction, the position or inclination (orientation) of the vibrator  235  is changed to maintain both of the press contact surfaces in parallel with each other, thereby holding an appropriate contact state between the surfaces. 
   The coil spring  238  may produce only enough force to cause the spherical projection  239   c  of the vibrator holding member  239  to engage with the conical hole  237   a  of the spacer  237  without backlash, and the force may be smaller than the force for bringing the slider  234  into press contact with the vibrator  235  to produce the driving force. Thus, the press contact force is not substantially changed even when the position of the press contact surface is changed. 
   Consequently, it is possible to provide stably an output consistent with the performance inherent in the second vibration type linear actuator. 
   Since large press contact force does not act on the fourth lens holding member  214 , the frictional force produced at the engaging portions  214   a  and  214   b  of the fourth lens holding member  214  engaging with the guide bars  211  and  210  is not increased. The power or size of the second vibration type linear actuator does not need to be increased, and the wear due to the friction between the guide bars  211 ,  210  and the engaging portions  214   a,    214   b  can be reduced. Also, the fine driving of the fourth lens holding member  214  (second lens unit  204 ) can be accurately achieved. 
   When the lens holding member is moved by a large amount, the slider needs to have a great length. To allow the movement of that long slider in the optical axis direction, long space for the slider movement needs to be ensured in the optical axis direction. 
   In Embodiment 2, however, in the first vibration type linear actuator for driving the second lens holding member  212  which is moved by a larger amount as compared with the fourth lens holding member  214 , the slider  218  having a greater length in the optical axis direction than that of the slider  234  of the second vibration type linear actuator is fixed, while the vibrator  219  is moved together with the second lens holding member  212  in the optical axis direction. Since the long slider  218  is not moved in the optical axis direction in this manner, only the short space maybe required for placing the first vibration type linear actuator in the optical axis direction, which enables a reduction in size of the lens barrel. 
   In Embodiment 2, in the second vibration type linear actuator for driving the fourth lens holding member  214  which is moved by a smaller amount as compared with the second lens holding member  212 , the slider  234  is fixed to the fourth lens holding member  214  and is moved in the optical axis direction, while the vibrator  235  is fixed and is not moved in the optical axis direction. Thus, the flexible wiring board  250  does not need to have any deformation portion, so that the flexible wiring board  250  can be easily handled to enhance the flexibility in design. This also allows a reduction in size of the lens barrel. 
   As described above, in Embodiment 2, the guide bar  210 , the first vibration type linear actuator, and the first linear encoder are arranged along (close to) the left side which is one of the flat surfaces of the light amount adjusting unit  215  closest to the optical axis when viewed from the optical axis direction. The first vibration type linear actuator and the first linear encoder are disposed next to the guide bar  210  above and below, respectively. 
   In addition, the guide bar  211 , the second vibration type linear actuator, and the second linear encoder are arranged along (close to) the right side which is one of the flat surfaces of the light amount adjusting unit  215  closest to the optical axis when viewed from the optical axis direction. The second vibration type linear actuator and the second linear encoder are disposed next to the guide bar  211  above and below, respectively. 
   Thus, although the optical apparatus has the light amount adjusting unit  215 , the two vibration type linear actuators for driving the second and fourth lens holding members  212  and  214  (second and fourth lens units  202  and  204 ) disposed on the object side and the image plane side of the light amount adjusting unit  215 , the two guide bars  210  and  211  for guiding the lens holding members  212  and  214  in the optical axis direction, and the two linear encoders for detecting the positions of the lens holding members  212  and  214 , it can be formed in a compact size. 
   Since the sliders  218  and  234  are disposed next to the guide bars  210  and  211 , the second and fourth lens holding members  212  and  214  can be driven smoothly. In addition, the scales  228  and  248  disposed next to the guide bars  210  and  211  reduce displacement of the scales  228  and  248  due to backlash of the engaging portions  212   a,    212   b  and  214   a,    214   b  of the second and forth lens holding members  212  and  214  engaging with the guide bars  210  and  211  to enable accurate detection of positions. 
   When the linear actuator and the linear encoder are disposed across the optical axis from the guide bar for guiding the lens holding member which is driven and whose position is detected by them, the linear encoder may be moved in the direction opposite to the driving direction with the guide bar as the supporting point at the start of the driving due to backlash at the engaging portion of the lens holding member engaging with the guide bar. This may reduce the accuracy of the position detection. In Embodiment 2, however, the linear actuator and the linear encoder are disposed on the same side as the guide bar for guiding the lens holding member which is driven and whose position is detected by them, so that such a problem does not arise and the position can be detected accurately. 
   Embodiment 3 
     FIGS. 11 to 14  show the structure of a lens barrel of an image-taking apparatus which is Embodiment 3 of the present invention.  FIG. 11  shows a section view of the lens barrel in Embodiment 3 taken along a plane in parallel with an optical axis and perpendicular to a press contact surface between a slider and vibrator of a vibration type linear actuator.  FIG. 12  shows a section view of the lens barrel in Embodiment 3 taken along a plane perpendicular to the optical axis and perpendicular to a press contact surface of a vibration type linear actuator for driving a second lens unit when viewed from an object side.  FIG. 13  shows a section view of the lens barrel in Embodiment 3 taken along a plane perpendicular to the optical axis and perpendicular to a press contact surface of a vibration type linear actuator for driving a fourth lens unit when viewed from the object side.  FIG. 14  is an exploded view showing the lens barrel in Embodiment 3. The image-taking apparatus of Embodiment 3 has the same electrical structure as that in Embodiment 1. 
   In  FIGS. 11 to 14 , in order from the object side, reference numeral  301  shows a fixed first lens unit,  302  the second lens unit which is movable in the optical axis direction for varying magnification,  315  a light amount adjusting unit,  303  a fixed third lens unit, and  304  the fourth lens unit which is movable in the optical axis direction for correcting image plane changes associated with varied magnification and for focal adjustment. 
   Reference numeral  305  shows a rear barrel which holds an image-pickup device, later described, and a low pass filter (LPF), and is fixed to a camera body, not shown. Reference numeral  306  shows a first lens holding member which holds the first lens unit  301  and is fixed to the rear barrel  305  by screws  307 ,  308 , and  309 . 
   Reference numerals  310  and  311  show guide bars (guide members) which are held substantially in parallel with the optical axis direction by the rear barrel  305  and the first lens holding member  306 . 
   Reference numeral  312  shows a second lens holding member which holds the second lens unit  302  and to which a mask  332  for cutting unnecessary light is fixed. The second lens holding member  312  engages with the guide bar  310  at an engaging portion  312   a  to be guided in the optical axis direction and engages with the guide bar  311  at an engaging portion  312   b  to be prevented from rotation around the guide bar  310 . Reference numeral  313  shows a third lens holding member which holds the third lens unit  303  and is fixed to the rear barrel  305  by a screw  316 . Reference numeral  314  shows a fourth lens holding member which holds the fourth lens unit  304 , and engages with the guide bar  311  at an engaging portion  314   a  to be guided in the optical axis direction and engages with the guide bar  310  at an engaging portion  314   b  to be prevented from rotation around the guide bar  311 . 
   The light amount adjusting unit  315  has an outer shape which is longer in a vertical direction (first direction) than in a horizontal direction (second direction) when viewed from the optical axis direction. The light amount adjusting unit  315  is fixed to the rear barrel  305  by a screw  317 . The light amount adjusting unit  215  has the same structure as that in Embodiment 1 shown in  FIG. 5C . 
   Reference numeral  318  shows a slider which is formed of a magnet and a friction material bonded to each other. Reference numeral  319  shows a vibrator which is formed of an electromechanical energy conversion element and a plate-shaped elastic member on which vibration is produced by the electromechanical energy conversion element. The elastic member of the vibrator  319  is made of ferromagnet which is attracted by the magnet of the slider  318  to bring an press contact surface  318   a  of the friction material of the slider  318  into press contact with press contact surfaces  319   a  (formed at two positions in the optical axis direction as in Embodiment 1) of the elastic member of the vibrator  319 . 
   Reference numeral  320  shows a flexible wiring board which is connected to the vibrator  319  and transmits a signal to the electromechanical energy conversion element. The flexible wiring board  320  has a bend portion (deformation portion)  320   a  which is deformed as the second lens holding member  312  is moved in the optical axis direction. 
   In a first vibration type linear actuator formed of the slider  318  and the vibrator  319 , while the slier  318  is in press contact with the vibrator  319 , two frequency signals (pulse signals or alternate signals) in difference phases are input to the electromechanical energy conversion element through the flexible wiring board  320  to create a substantially elliptic motion in the press contact surfaces  319   a  of the vibrator  319  to produce driving force in the optical axis direction in the press contact surface  318   a  of the slider  318 . 
   Reference numeral  321  shows a spacer which fixes the vibrator  319 ,  322  a plate spring which fixes the spacer  321 . The plate spring  322  has a shape which is not easily deformed in the in-plane direction, is easily deformed in the direction perpendicular to the plane, and is easily deformed in the rotation direction around an arbitrary axis included in the plane. The plate spring  322  not easily deformed in the in-plane direction limits displacement of the vibrator  319  in the optical axis direction (that is, the driving direction). 
   Reference numerals  324  and  325  show screws which secure the plate spring  322  to the second lens holding member  312 . Reference numeral  323  shows a vibrator frame to which the slider  318  is fixed through adhesion or the like. The vibrator frame  323  is fixed to the first lens holding member  306  by screws  326  and  327 . 
   Reference numeral  328  shows a scale which detects the position of the second lens holding member  312  and is fixed into a square hole  312   d  of the second lens holding member  312  through adhesion or the like. 
   Reference numeral  329  shows a light transmitter/receiver element which applies light to the scale  328  and receives the light reflected by the scale  28  to detect the moving amount of the second lens holding member  312 . The scale  328  and the light transmitter/receiver element  329  constitute a first linear encoder serving as a detector. 
   Reference numeral  330  shows a flexible wiring board which sends and receives a signal to and from the light transmitter/receiver element  329  and is fixed to the first lens holding member  306  by a screw  331 . 
   As shown in  FIG. 12 , the guide bar  310 , the first vibration type linear actuator formed of the vibrator  319  and the slider  318 , and the first linear encoder formed of the light transmitter/receiver element  329  and the scale  328  are arranged along or close to a planar left side of the light amount adjusting unit  315  (linear long side on the left when viewed from the optical axis direction) that is one of the outer surfaces closest to the optical axis position of the light amount adjusting unit  315  of all of the outer surfaces thereof when viewed from the front of the optical axis direction. The first vibration type linear actuator and the first linear encoder are disposed vertically next to the guide bar  310  to sandwich the guide bar  310 . 
   Reference numeral  334  shows a slider which is formed of a magnet and a friction material bonded to each other and is fixed to a square frame  314 c of the fourth lens holding member  314  through adhesion or the like. Reference numeral  335  shows a vibrator which is formed of an electromechanical energy conversion element and a plate-shaped elastic member on which vibration is produced by the electromechanical energy conversion element. The elastic member of the vibrator  335  is made of ferromagnet which is attracted by the magnet of the slider  334  to bring an press contact surface  334   a  of the friction material of the slider  334  into press contact with press contact surfaces  335   a  (formed at two positions in the optical axis direction as in Embodiment 1) of the elastic member of the vibrator  335 . 
   Reference numeral  336  shows a flexible wiring board which is connected to the electromechanical conversion element of the vibrator  335 . In a second vibration type linear actuator formed of the slider  334  and the vibrator  335 , while the slider  334  is in press contact with the vibrator  335 , two frequency signals (pulse signals or alternate signals) in difference phases are input to the electromechanical energy conversion element through the flexible wiring board  336  to create a substantially elliptic motion in the press contact surfaces  335   a  of the vibrator  335  to produce driving force in the optical axis direction in the press contact surface  334   a  of the slider  334 . 
   As shown in  FIG. 11 , the range in which the first vibration type linear actuator is placed in the optical axis direction (the range in which the slider  318  is placed) and a movable range L 2  of the second lens holding member  312  in the optical axis direction extend from the object side (the left in  FIG. 11 ) of the light amount adjusting unit  315  toward the image plane side when viewed from the direction orthogonal to the optical axis direction. The range in which the second vibration type linear actuator is placed in the optical axis direction (the range in which the slider  334  is placed) and a movable range L 4  of the fourth lens holding member  314  in the optical axis direction extend from the image plane side of the light amount adjusting unit  315  toward the object side. In other words, the ranges in which the first and second linear actuators are placed (the movable ranges of the second and fourth lens holding members  312  and  314 ) overlap each other in the optical axis direction. 
   Reference numeral  337  shows a spacer for holding the vibrator  335 ,  338  a plate spring for holding the spacer  337 . The plate spring  338  has a shape which is not easily deformed in the in-plane direction, is easily deformed in the direction perpendicular to the plane, and is easily deformed in the rotation direction around an arbitrary axis included in the plane. The plate spring  338  not easily deformed in the in-plane direction limits displacement of the vibrator  335  in the optical axis direction (that is, the driving direction). 
   Reference numeral  339  shows a vibrator holding member which holds the plate spring  338  and to which the plate spring  338  is attached  6  by screws  346  and  347 . The vibrator holding member  339  is fixed to the rear barrel  305  by screws  342  and  343 . 
   Reference numeral  348  shows a scale which detects the position of the fourth lens holding member  314  and is fixed into a square hole  314   d  in the fourth lens holding member  314  through adhesion or the like. Reference numeral  349  shows a light transmitter/receiver element which applies light to the scale  348  and receives the light reflected by the scale  348  to detect the moving amount of the fourth lens holding member  314 . Reference numeral  350  shows a flexible wiring board which sends and receives a signal to and from the light transmitter/receiver element  349  and is fixed to the rear barrel  305  by a screw  351 . 
   As shown in  FIG. 13 , the guide bar  311 , the second vibration type linear actuator formed of the vibrator  335  and the slider  334 , and the second linear encoder formed of the light transmitter/receiver element  349  and the scale  348  are arranged along or close to a planar right side of the light amount adjusting unit  315  (linear long side on the right when viewed from the optical axis direction) that is one of the outer surfaces closest to the optical axis position of the light amount adjusting unit  315  of all of the outer surfaces thereof when viewed from the front of the optical axis direction. The second vibration type linear actuator and the second linear encoder are disposed vertically next to the guide bar  311  to sandwich the guide bar  311 . 
   In addition, the set of the first vibration type linear actuator, the guide bar  310 , and the first linear encoder, and the set of the second vibration type linear actuator, the guide bar  311 , and the second linear encoder are arranged substantially symmetrically with respect to an axis extending vertically through the center of the optical axis. 
   In the abovementioned structure, the slider  318  is formed by using the magnet which attracts the vibrator  319  to provide the press contact force necessary for producing the driving force as the vibration type linear actuator. Thus, any reaction force of the press contact force does not act on the second lens holding member  312 . As a result, the frictional force produced at the engaging portions  312   a  and  312   b  of the second lens holding member  312  engaging with the guide bars  310  and  311  is not increased and the driving load due to the friction is not increased. In addition, the plate spring  322  produces small force, so that the force acting from the plate spring  322  on the engaging portions  312   a  and  312   b  engaging with the guide bars  310  and  311  is small and hardly increases the frictional force produced at the engaging portions  312   a  and  312   b.  This enables the use of the low-power and small vibration type linear actuator, resulting in a reduction in size of the lens barrel. 
   Since large press contact force does not act on the second lens holding member  312 , the frictional force produced at the engaging portions  312   a  and  312   b  of the second lens holding member  312  engaging with the guide bars  310  and  311  is not increased. The power or size of the first vibration type linear actuator does not need to be increased, and the wear due to the friction between the guide bars  310 ,  311  and the engaging portions  312   a,    312   b  can be reduced. Also, the fine driving of the second lens holding member  312  (second lens unit  302 ) can be accurately achieved. 
   Even when a manufacturing error or the like changes the position of any press contact surface with respect to an axis in parallel with the optical axis or the inclination around that axis in the optical axis direction, the plate spring  322  is deformed to change the position or inclination (orientation) of the vibrator  319  to maintain both of the press contact surfaces in parallel with each other, thereby holding an appropriate contact state between the surfaces. The plate spring  322  has a spring constant set such that it is deformed in response to a smaller force than the abovementioned press contact force. The press contact force is not changed greatly even when the position or inclination of any press contact surface is changed. Consequently, it is possible to provide stably an output consistent with the performance inherent in the first vibration type linear actuator. 
   On the other hand, the slider  334  is formed by using the magnet which attracts the vibrator  335  to provide the press contact force necessary for producing the driving force as the vibration type linear actuator. Thus, any reaction force of the press contact force does not act on the fourth lens holding member  314 . As a result, the frictional force produced at the engaging portions  314   a  and  314   b  of the fourth lens holding member  314  engaging with the guide bars  311  and  310  is not increased and the driving load due to the friction is not increased. In addition, the plate springs  338  produce small force, so that the force acting from the plate springs  338  on the engaging portions  314   a  and  314   b  engaging with the guide bars  311  and  310  is small and hardly increases the frictional force produced at the engaging portions  314   a  and  314   b.  This enables the use of the low-power and small vibration type linear actuator, resulting in a reduction in size of the lens barrel. 
   Since large press contact force does not act on the fourth lens holding member  314 , the frictional force produced at the engaging portions  314   a  and  314   b  of the fourth lens holding member  314  engaging with the guide bars  311  and  310  is not increased. The power or size of the second vibration type linear actuator does not need to be increased, and the wear due to the friction between the guide bars  311 ,  310  and the engaging portions  314   a,    314   b  can be reduced. Also, the fine driving of the fourth lens holding member  314  (fourth lens unit  304 ) can be accurately achieved. 
   Even when a manufacturing error or the like changes the position of any press contact surface with respect to an axis in parallel with the optical axis or the inclination around that axis in the optical axis direction, the plate spring  338  is deformed to change the position or inclination (orientation) of the vibrator  335  to maintain both of the press contact surfaces in parallel with each other, thereby holding an appropriate contact state between the surfaces. The plate spring  338  has a spring constant set such that it is deformed in response to a smaller force than the abovementioned press contact force. The press contact force is not changed greatly even when the position or inclination of any press contact surface is changed. Consequently, it is possible to provide stably an output consistent with the performance inherent in the second vibration type linear actuator. 
   When the lens holding member is moved by a large amount, the slider needs to have a great length. To allow the movement of that long slider in the optical axis direction, long space for the slider movement needs to be ensured in the optical axis direction. In Embodiment 3, however, in the first vibration type linear actuator for driving the second lens holding member  312  which is moved by a larger amount as compared with the fourth lens holding member  314 , the slider  318  having a greater length in the optical axis direction than that of the slider  334  of the second vibration type linear actuator is fixed, while the vibrator  319  is moved together with the second lens holding member  312  in the optical axis direction. Since the long slider  318  is not moved in the optical axis direction in this manner, only the short space may be required for placing the first vibration type linear actuator in the optical axis direction, which enables a reduction in size of the lens barrel. 
   In Embodiment 3, in the second vibration type actuator for driving the fourth lens holding member  314  which is moved by a smaller amount as compared with the second lens holding member  312 , the slider  334  is fixed to the fourth lens holding member  314  and is moved in the optical axis direction, while the vibrator  335  is fixed and is not moved in the optical axis direction. Thus, the flexible wiring board  350  does not need to have any deformation portion, so that the flexible wiring board  350  can be easily handled to enhance the flexibility in design. This allows a reduction in size of the lens barrel. 
   As described above, in Embodiment 3, the guide bar  310 , the first vibration type linear actuator, and the first linear encoder are arranged along (close to) the left side which is one of the flat surfaces of the light amount adjusting unit  315  closest to the optical axis when viewed from the optical axis direction. The first vibration type linear actuator and the first linear encoder are disposed next to the guide bar  310  above and below, respectively. 
   In addition, the guide bar  311 , the second vibration type linear actuator, and the second linear encoder are arranged along (close to) the right side which is one of the flat surfaces of the light amount adjusting unit  315  closest to the optical axis when viewed from the optical axis direction. The second vibration type linear actuator and the second linear encoder are disposed next to the guide bar  311  above and below, respectively. 
   Thus, although the optical apparatus has the light amount adjusting unit  315 , the two vibration type linear actuators for driving the second and fourth lens holding members  312  and  314  (second and fourth lens units  302  and  304 ) disposed on the object side and the image plane side of the light amount adjusting unit  315 , the two guide bars  310  and  311  for guiding the lens holding members  312  and  314  in the optical axis direction, and the two linear encoders for detecting the positions of the lens holding members  312  and  314 , it can be formed in a compact size. 
   Since the sliders  318  and  334  are disposed next to the guide bars  310  and  311 , the second and fourth lens holding members  312  and  314  can be driven smoothly. In addition, the scales  328  and  348  disposed next to the guide bars  310  and  311  reduce displacement of the scales  328  and  348  due to backlash of the engaging portions  312   a,    312   b  and  314   a,  and  314   b  of the second and forth lens holding members  312  and  314  engaging with the guide bars  310  and  311  to enable accurate detection of positions. 
   When the linear actuator and the linear encoder are disposed across the optical axis from the guide bar for guiding the lens holding member which is driven and whose position is detected by them, the linear encoder may be moved in the direction opposite to the driving direction with the guide bar as the supporting point at the start of the driving due to backlash at the engaging portion of the lens holding member engaging with the guide bar. This may reduce the accuracy of the position detection. In Embodiment 3, however, the linear actuator and the linear encoder are disposed on the same side as the guide bar for guiding the lens holding member which is driven and whose position is detected by them, so that such a problem does not arise and the position can be detected accurately. 
   Embodiment 4 
     FIGS. 15A to 19  show the structure of a lens barrel of an image-taking apparatus which is Embodiment 4 of the present invention.  FIGS. 15A to 15D  show the lens barrel in Embodiment 4, with its exterior removed, when viewed from four directions, the right, back, left, and front, respectively.  FIG. 16  shows a section view of the lens barrel in Embodiment 4 taken along a plane in parallel with an optical axis and perpendicular to a press contact surface between a slider and a vibrator of a vibration type linear actuator.  FIG. 17  shows a section view of the lens barrel in Embodiment 4 taken along a plane perpendicular to the optical axis and perpendicular to a press contact surface of a vibration type linear actuator for driving a second lens unit when viewed from an object side.  FIG. 18  shows a section view of the lens barrel in Embodiment 4 taken along a plane perpendicular to the optical axis and perpendicular to a press contact surface of a vibration type linear actuator for driving a fourth lens unit when viewed from the object side.  FIG. 19  is an exploded view showing the lens barrel in Embodiment  4 .  FIG. 20  shows an electrical structure of the image-taking apparatus of Embodiment 4. 
   In  FIGS. 15A to 20 , in order from the object side, reference numerals  401  shows a fixed first lens unit,  402  the second lens unit which is movable in the optical axis direction for varying magnification,  415  a light amount adjusting unit,  403  a fixed third lens unit, and  404  the fourth lens unit which is movable in the optical axis direction for correcting image plane changes associated with varied magnification and for focal adjustment. 
   Reference numeral  405  shows a rear barrel which holds an image-pickup device, later described, and a low pass filter (LPF), and is fixed to a camera body, not shown. Reference numeral  406  shows a first lens holding member which holds the first lens unit  401  and is fixed to the rear barrel  405  by screws  407 ,  408 , and  409 . 
   Reference numerals  410  and  411  show guide bars (guide members) which are held substantially in parallel with the optical axis direction by the rear barrel  405  and the first lens holding member  406 . 
   Reference numeral  412  shows a second lens holding member which holds the second lens unit  402  and to which a mask  432  for cutting unnecessary light is fixed. The second lens holding member  412  engages with the guide bar  410  at an engaging portion  412   a  to be guided in the optical axis direction and engages with the guide bar  411  at an engaging portion  412   b  to be prevented from rotation around the guide bar  410 . Reference numeral  413  shows a third lens holding member which holds the third lens unit  403  and is fixed to the rear barrel  405  by a screw  416 . Reference numeral  414  shows a fourth lens holding member which holds the fourth lens unit  404 , and engages with the guide bar  411  at an engaging portion  414   a  to be guided in the optical axis direction and engages with the guide bar  410  at an engaging portion  414   b  to be prevented from rotation around the guide bar  411 . 
   The light amount adjusting unit  415  has an outer shape which is longer in a vertical direction (first direction) than in a horizontal direction (second direction) when viewed from the optical axis direction. The light amount adjusting unit  415  is fixed to the rear barrel  405  by a screw  417 . The light amount adjusting unit  415  has the same structure as that shown in  FIG. 5C . 
   Reference numeral  418  shows a slider which is formed of a magnet and a friction material bonded to each other and is fixed into a square hole  412   c  in the second lens holding member  412  through adhesion or the like. 
   Reference numeral  419  shows a vibrator which is formed of an electromechanical energy conversion element and a plate-shaped elastic member on which vibration is produced by the electromechanical energy conversion element. The elastic member of the vibrator  419  is made of ferromagnet which is attracted by the magnet of the slider  418  to bring an press contact surface  418   a  of the friction material of the slider  418  into press contact with press contact surfaces  419   a  and  419   b  formed at two positions in the optical axis direction in the elastic member of the vibrator  419 . 
   Reference numeral  420  shows a flexible wiring board which is connected to the vibrator  419  and transmits a signal to the electromechanical energy conversion element. 
   In a first linear actuator (vibration type linear actuator) formed of the slider  418  and the vibrator  419 , while the slider  418  is in press contact with the vibrator  419 , two frequency signals (pulse signals or alternate signals) in difference phases are input to the electromechanical energy conversion element through the flexible wiring board  420  to create a substantially elliptic motion in the press contact surfaces  419   a  and  419   b  of the vibrator  419  to produce driving force in the optical axis direction in the press contact surface  418   a  of the slider  418 . 
   Reference numeral  421  shows a spacer to which the vibrator  419  is fixed, and  422  a plate spring to which the spacer  421  is fixed. The plate spring  422  has a shape which is not easily deformed in the in-plane direction, is easily deformed in the direction perpendicular to the plane, and is easily deformed in the rotation direction around an arbitrary axis included in the plane. The plate spring  422  not easily deformed in the in-plane direction limits displacement of the vibrator  419  in the optical axis direction (that is, the driving direction). 
   Reference numeral  423  shows a vibrator frame to which the plate spring  422  is fixed by screws  424  and  425 . The vibrator frame  423  is fixed to the first lens holding member  406  by screws  426  and  427 . 
   Reference numeral  428  shows a scale which detects the position of the second lens holding member  412  and is fixed into a square hole  412   d  in the second lens holding member  412  through adhesion or the like. 
   Reference numeral  429  shows a light transmitter/receiver element which applies light to the scale  428  and receives the light reflected by the scale  428  to detect the moving amount of the second lens holding member  412 . The scale  428  and the light transmitter/receiver element  429  constitute a first linear encoder serving as a detector. 
   Reference numeral  430  shows a flexible wiring board which sends and receives a signal to and from the light transmitter/receiver element  429  and is fixed to the first lens holding member  406  by a screw  431 . 
   As shown in  FIG. 17 , the guide bar  410 , the first linear actuator formed of the vibrator  419  and the slider  418 , and the first linear encoder formed of the light transmitter/receiver element  429  and the scale  428  are arranged along or close to a planar left side of the light amount adjusting unit  415  (linear long side on the left when viewed from the optical axis direction) that is one of the outer surfaces closest to the optical axis position of the light amount adjusting unit  415  of all of the outer surfaces thereof when viewed from the front of the optical axis direction. In Embodiment 4, the guide bar  410 , the first linear encoder, and the first linear actuator are disposed in order from the bottom and next to each other. 
   Reference numeral  433  shows a coil which is fixed to the fourth lens holding member  414 . Reference numeral  434  shows a flexible wiring board for transmitting a signal to the coil  433 . The flexible wiring board  434  is deformed as the fourth lens holding member  414  is moved in the optical axis direction. 
   Reference numerals  435  and  436  show a magnet and a yoke, respectively. The coil  433 , the magnet  435 , and the yoke  436  constitute a magnetic circuit, in which the coil  433  is energized to form a second linear actuator (voice coil motor) which is an electromagnetic type linear actuator which produces driving force in the optical axis direction. Reference numeral  439  shows a yoke holding member which holds the yoke  436  and is fixed to the rear barrel  405  by screws  442  and  443 . 
   As shown in  FIG. 16 , the range in which the first linear actuator is placed in the optical axis direction (the range in which the slider  418  is placed) and a movable range L 2  of the second lens holding member  412  in the optical axis direction extend from the object side (the left in  FIG. 16 ) of the light amount adjusting unit  415  toward the image plane side. The range in which the second linear actuator is placed in the optical axis direction (the range in which the magnet  435  is placed) and a movable range L 4  of the fourth lens holding member  414  in the optical axis direction extend from the image plane side of the light amount adjusting unit  415  toward the object side. In other words, the ranges in which the first and second linear actuators are placed (the movable ranges of the second and fourth lens holding members  412  and  414 ) overlap each other in the optical axis direction. 
   Reference numeral  448  shows a scale which detects the position of the fourth lens holding member  414  and is fixed into a square hole  414   d  in the fourth lens holding member  414  through adhesion or the like. Reference numeral  449  shows a light transmitter/receiver element which applies light to the scale  448  and receives the light reflected by the scale  448  to detect the moving amount of the fourth lens holding member  414 . Reference numeral  450  shows a flexible wiring board which is used to send and receive a signal to and from the light transmitter/receiver element  449  and is fixed to the rear barrel  405  by a screw  451 . 
   As shown in  FIG. 18 , the guide bar  411 , the second linear actuator formed of the coil  433 , the magnet  435 , and the yoke  436 , and the second linear encoder formed of the light transmitter/receiver element  449  and the scale  448  are arranged along or close to a planar right side of the light amount adjusting unit  415  (linear long side on the right when viewed from the optical axis direction) that is one of the outer surfaces closest to the optical axis position of the light amount adjusting unit  415  of all of the outer surfaces thereof when viewed from the front of the optical axis direction. In Embodiment 4, the guide bar  411 , the second linear actuator, and the second linear encoder are disposed in order from the top and next to each other. 
   The set of the guide bar  410 , the first linear actuator, and the first linear encoder, and the set of the guide bar  411 , the second linear actuator, and the second encoder are arranged substantially point-symmetrically with respect to the optical axis. To be point-symmetric in a strict sense, for example, the guide bar  411 , the second linear encoder, and the second linear actuator should be disposed in this order from the top on the side of the guide bar  411 , but the arrangement of Embodiment 4 may be considered to be substantially point-symmetric if the guide bars, the linear actuators, and the linear encoders are seen individually. The guide bar  411  and the second linear actuator disposed next to each other as in Embodiment 4 can drive the fourth lens holding member  414  more smoothly as compared with the case where the guide bar  411  and the second linear actuator are disposed apart, as later described. However, a strictly point-symmetric arrangement may be used. 
   In  FIG. 20 , reference numeral  471  shows the image-pickup device formed of a CCD sensor, a CMOS sensor or the like. Reference numeral  472  shows the vibration type linear actuator which includes the slider  418  and the vibrator  419 , and serves as a driving source of the second lens unit  402  (second lens holding member  412 ). Reference numeral  473  shows the electromagnetic type linear actuator which is formed of the coil  433 , the magnet  435 , and the yoke  436 , and serves as a driving source of the fourth lens unit  404  (fourth lens holding member  414 ). 
   Reference numeral  474  shows a motor which serves as a driving source of the light amount adjusting unit  415 . Reference numeral  475  shows a second lens encoder realized by the first linear encoder which includes the scale  428  and the light transmitter/receiver element  429 ,  476  a fourth lens encoder realized by the second linear encoder which includes the scale  448  and the light transmitter/receiver element  449 . These encoders detect the relative positions (moving amounts from a reference position) of the second lens unit  402  and the fourth lens unit  404  in the optical axis direction, respectively. While Embodiment 4 employs optical encoders as the encoders, it is possible to use a magnetic encoder or an encoder which detects an absolute position by using electrical resistance. 
   Reference numeral  477  shows an aperture encoder which is, for example, of the type in which a hall element is provided within the motor  474  as the driving source of the light amount adjusting unit  415  and is used to detect a rotational position relationship between a rotor and a stator of the meter  474 . 
   Reference numeral  487  shows a CPU serving as a controller responsible for control of operation of the image-taking apparatus. Reference numeral  478  shows a camera signal processing circuit which performs amplification, gamma correction or the like on the output from the image-pickup device  471 . After the predetermined processing, a contrast signal of a video signal is transmitted through an AE gate  479  and an AF gate  480 . The gates  479  and  480  set an optimal range in the entire screen for extracting the signal for exposure setting and focusing. These gates  479  and  480  may have variable sizes, or a plurality of gates  479  and  480  may be provided. 
   Reference numeral  484  shows an AF (auto-focus) signal processing circuit for auto-focus which extracts a high-frequency component of the video signal to produce an AF evaluation value signal. Reference numeral  485  shows a zoom switch for zooming operation. Reference numeral  486  shows a zoom tracking memory which stores information about target positions to which the fourth lens unit  404  is to be driven in accordance with the camera-to-object distance and the position of the second lens unit  402  in order to maintain an in-focus state in varying magnification. Memory in the CPU  487  maybe used as the zoom tracking memory. 
   In the abovementioned structure, when a user operates the zoom switch  485 , the CPU  487  controls the vibration type linear actuator  472  for driving the second lens unit  402  and calculates the target driving position of the fourth lens unit  404  based on the information in the zoom tracking memory  486  and the current position of the second lens unit  402  determined from the detection result of the second lens unit encoder  475  to control the electromagnetic type linear actuator  473  for driving of the fourth lens unit  404  to that target driving position. Whether or not the fourth lens unit  404  has reached the target driving position is determined by the matching of the current position of the fourth lens unit  404  provided from the detection result of the fourth lens unit encoder  476  with the target driving position. 
   In the auto-focus, the CPU  487  controls the electromagnetic type linear actuator  473  to drive the fourth lens unit  404  to search for the position where the AF evaluation value determined by the AF signal processing circuit  484  is at the peak. 
   To provide appropriate exposure, the CPU  487  controls the motor  474  of the light amount adjusting unit  415  to increase or reduce the aperture diameter such that the average value of the luminance signal through the AE gate  479  is equal to a predetermined value, that is, such that the output from the aperture encoder  477  has a value corresponding to the predetermined value. 
   In the abovementioned structure, the slider  418  is formed by using the magnet which attracts the vibrator  419  to provide the press contact force necessary for producing the driving force as the vibration type linear actuator. Thus, any reaction force of the press contact force does not act on the second lens holding member  412 . As a result, the frictional force produced at the engaging portions  412   a  and  412   b  of the second lens holding member  412  engaging with the guide bars  410  and  411  is not increased and the driving load due to the friction is not increased. In addition, the plate spring  422  produces small force, so that the force acting from the plate spring  422  on the engaging portions  412   a  and  412   b  engaging with the guide bars  410  and  411  is small and hardly increases the frictional force produced at the engaging portions  412   a  and  412   b.  This enables the use of the low-power and small vibration type linear actuator, resulting in a reduction in size of the lens barrel. 
   Since large press contact force does not act on the second lens holding member  412 , the frictional force produced at the engaging portions  412   a  and  412   b  of the second lens holding member  412  engaging with the guide bars  410  and  411  is not increased. The power or size of the first linear actuator does not need to be increased, and the wear due to the friction between the guide bars  410 ,  411  and the engaging portions  412   a,    412   b  can be reduced. Also, the fine driving of the second lens holding member  412  (second lens unit  402 ) can be accurately achieved. 
   Even when a manufacturing error or the like changes the position of any press contact surface with respect to an axis in parallel with the optical axis or the inclination around that axis in the optical axis direction, the plate spring  422  is deformed to change the position or inclination (orientation) of the vibrator  419  to maintain both of the press contact surfaces in parallel with each other, thereby holding an appropriate contact state between the surfaces. The plate spring  422  has a spring constant set such that it is deformed in response to a smaller force than the abovementioned press contact force. The press contact force is not changed greatly even when the position or inclination of any press contact surface is changed. Consequently, it is possible to provide stably an output consistent with the performance inherent in the first linear actuator. 
   The vibration type linear actuator is not displaced even when it is not powered since the vibrator is always in press contact with the slider. Particularly, the second lens unit  402  is moved only in varying magnification and often stationary, so that the use of the vibration type linear actuator for driving the second lens unit can save power as compared with the linear actuator using electromagnetic force. 
   On the other hand, in the linear actuator using electromagnetic force, no contact portion is provided and thus no portion is worn. Since force is produced only in the driving direction and any lateral pressure does not act on the driven member (fourth lens holding member  414 ), any lateral pressure does not act on the engaging portions  414   a  and  414   b  of the driven member engaging with the guide bars  411  and  410 , and the engaging portions  414   a  and  414   b  are hardly worn. Particularly, the fourth lens unit is moved in varying magnification and focusing, and its moving amount is larger than that of the second lens unit due to the AF operation. Therefore, the electromagnetic type linear actuator is more effective for use in driving the fourth lens unit than the vibration type linear actuator in order to enhance the durability. 
   As described above, in Embodiment 4, the guide bar  410 , the first linear actuator, and the first linear encoder are disposed next to each other along (close to) the left side which is one of the outer surfaces of the light amount adjusting unit  415  closest to the optical axis position when viewed from the optical axis direction. The guide bar  411 , the second linear actuator, and the second linear encoder are disposed next to each other along (close to) the right side which is one of the outer surfaces of the light amount adjusting unit  415  closest to the optical axis position when viewed from the optical axis direction. Thus, although the optical apparatus has the light amount adjusting unit  415 , the two linear actuators for driving the second and fourth lens holding members  412  and  414  (second and fourth lens units  402  and  404 ) disposed on the object side and the image plane side of the light amount adjusting unit  415 , the two guide bars  410  and  411  for guiding the lens holding members  412  and  414  in the optical axis direction, and the two linear encoders for detecting the positions of the lens holding members  412  and  414 , it can be formed in a compact size. 
   The scale  428  of the first linear encoder disposed next to the guide bar  410  reduces displacement of the scale  428  due to backlash of the engaging portions  412   a  and  412   b  of the second lens holding member  412  engaging with the guide bars  410  and  411  to enable accurate detection of positions. 
   When the linear actuator and the linear encoder are disposed across the optical axis from the guide bar for guiding the lens holding member which is driven and whose position is detected by them, the linear encoder may be moved in the direction opposite to the driving direction with the guide bar as the supporting point at the start of the driving due to backlash at the engaging portion of the lens holding member engaging with the guide bar. This may reduce the accuracy of the position detection. In Embodiment 4, however, the linear actuator and the linear encoder are disposed on the same side as the guide bar for guiding the lens holding member which is driven and whose position is detected by them, so that such a problem does not arise and the position can be detected accurately. 
   In addition, since the second linear actuator is disposed next to the guide bar  411 , the fourth lens holding member  414  can be driven smoothly. 
   According to each of Embodiments 1 to 4, the optical apparatus has a holding mechanism which holds one member of the vibrator and the contact member in a condition in which at least one of the position and inclination of the one member can be changed. This makes it possible to constantly parallelize the press contact surfaces of the vibrator and the contact member to maintain their surface contact state even when the other member is not parallel to the optical axis or inclines around an axis parallel to the optical axis. Thereby, it is possible to provide stably an output consistent with the performance inherent in the vibration type linear actuator. 
   In particular, when an elastic member which is deformable in response to a smaller force than the press contact force is provided in the holding member, since the force generated by the deformation of the elastic member is small, the force acting from the elastic member on the engagement part of the lens holding member and the guide member is also reduced. Therefore, the friction generated in the engagement part of the lens holding member and the guide member is reduced, thereby making it possible to drive the lens using a low-power vibration type actuator, reduce the wear in the engagement part, and perform a fine, smooth and accurate drive of the lens. 
   The preferred embodiments of the present invention have been described. However, the present invention is not limited to the structures described in Embodiments 1 to 4, and various modifications may be made in each of Embodiments 1 to 4. 
   While each of Embodiments 1 to 4 has been descried in conjunction with the image-taking apparatus integral with the lens, the present invention is applicable to an interchangeable lens (optical apparatus) which is removably mounted on an image-taking apparatus body. The present invention is applicable not only to the image-taking apparatus, but also to various optical apparatuses for driving a lens by a vibration type linear actuator. 
   While each of Embodiments 1 to 4 has been described in conjunction with the holding mechanism which holds the vibrator and the slider at variable positions and inclinations, it is possible to provide a holding mechanism which allows one of the position and inclination to be variable. 
   This application claims a foreign priority benefit based on Japanese Patent Application No. 2005-125754, filed on Apr. 22, 2005, which is hereby incorporated by reference herein in its entirety as if fully set forth herein.