Abstract:
A lens apparatus is disclosed, which allows an optical adjustment of each lens unit, and facilitates the assembly and maintenance. The lens apparatus comprises a plurality of lens units constituting an image-forming optical system that forms an object image, and a plurality of lens-holding members holding the plurality of lens units, respectively. Each of the lens units and the lens-holding member holding the lens unit are unitized. The lens apparatus is formed by joining each of the plurality of lens-holding members to at least one of the other lens-holding members.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to lens apparatuses such as zoom lenses, and to image-taking apparatus with the same, such as digital cameras and video cameras. 
   Conventional image-taking apparatuses, such as digital cameras and video cameras, are known on which an interchangeable rear focus zoom lens can be mounted or a rear focus zoom lens is provided integrally. The rear focus zoom lens (or inner focus zoom lens) includes a magnification-varying lens, and a focus lens disposed at a position closer to an image plane than the magnification-varying lens. The focus lens corrects (or compensates) image plane displacements caused by the movement of the magnification-varying lens, and performs focusing. 
   The above-described rear focus zoom lens is generally constituted by a front lens unit (or first lens unit), a variator lens unit (or second lens unit) for varying the magnification, an afocal lens unit (or third lens unit), and a focus lens unit (or fourth lens unit) having a compensating function, the lens units being arranged in order from the object side to the image side. 
   In a lens apparatus with such a rear focus zoom lens, the focus lens unit, the afocal lens unit, a stop unit, and the variator lens unit are assembled in this order on a rear barrel that is a base member on which an image-pickup element, such as a CCD sensor, is mounted. And finally, the front lens unit is assembled on the rear barrel. 
     FIG. 5  shows an example of such a conventional rear focus zoom lens. In  FIG. 5 ,  61  denotes a first lens unit,  62  a second lens unit,  63  a third lens unit, and  64  a fourth lens unit. 
   The first lens unit  61 , second lens unit  62 , third lens unit  63 , and fourth lens unit  64  are held by first lens-holding member  65 - 1 , second lens-holding member  65 - 2 , third lens-holding member  623 , and fourth lens-holding member  627 , respectively. 
   The second lens unit  62  is moved with the movement of the second lens-holding member  65 - 2  that is guided by a straight-proceeding key  611  provided on a fixed lens barrel  610 . The fourth lens unit  64  is moved with the movement of the fourth lens-holding member  627  that is guided by a straight-proceeding key  625  provided on the fixed lens barrel  610 . 
   The first lens-holding member  65 - 1  and third lens-holding member  623  are held by the fixed lens barrel  610 . 
   In a zoom lens apparatus disclosed in Japanese Patent Laid-Open Application No. H7-120663, a first lens barrel unit in which the first lens unit and the second lens unit are unitized and a second lens barrel unit in which the third lens unit and the fourth lens unit are unitized are assembled to each other for facilitating the assembly and optical adjustment of the lens apparatus. 
   However, in the conventional zoom lens apparatus shown in  FIG. 5 , the straight-proceeding keys guiding straight the lens-holding members that hold the second and fourth lens units are provided on the fixed lens barrel that holds the first and third lens units. Therefore, it is difficult to make an optical adjustment of each lens unit (for example, adjustment of tilting and decentering with respect to the optical axis) separately from the other lens units. 
   In addition, since the fixed lens barrel holding the first to fourth lens units has a long length in the optical axis direction, mounting the third and fourth lens unit into the fixed lens barrel needs extra efforts, and the maintenance is difficult. 
   Moreover, in the zoom lens apparatus disclosed in Japanese Patent Laid-Open Application No. H7-120663, since a lens barrel unit is constituted by two lens units, it is difficult to make the optical adjustment of each lens unit separately from the other lens unit. 
   BRIEF SUMMARY OF THE INVENTION 
   An object of the present invention is to provide a lens apparatus allowing an optical adjustment of each lens unit, adjustment which is separated from that of other lens units, and facilitating the assembly and maintenance, and to provide an image-taking apparatus with the same. 
   A lens apparatus that is one aspect of the present invention comprises a plurality of lens units constituting an image-forming optical system that forms an object image, and a plurality of lens-holding members holding the plurality of lens units, respectively. Each of the lens units and the lens-holding member holding the lens unit are unitized. The lens apparatus is formed by joining each of the plurality of lens-holding members to at least one of the other lens-holding members. 
   Other objects and further 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 
       FIG. 1  is a perspective view showing the zoom lens apparatus that is an embodiment of the present invention. 
       FIG. 2  is a sectional view showing a video camera including the zoom lens apparatus of the embodiment. 
       FIG. 3  is an exploded perspective view showing the shift lens barrel unit constituting the zoom lens apparatus of the embodiment. 
       FIG. 4  is an exploded perspective view showing the focus lens barrel unit constituting the zoom lens apparatus of the embodiment. 
       FIG. 5  is a sectional view showing a conventional zoom lens apparatus. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Preferred embodiments of the present invention will hereinafter be described with reference to the drawings. 
     FIGS. 1 and 2  show the structure of the zoom lens barrel (lens apparatus) that is an embodiment of the present invention. 
   As shown in  FIGS. 1 and 2 , the zoom lens barrel of this embodiment holds a rear focus zoom optical system, as an image-forming optical system, which is constituted by four lens units L 1  to L 4  that are convex (positive), concave (negative), convex (positive), and convex (positive), respectively, in order from an object side (right side in the figure). 
   L 1  denotes a fixed front lens unit as a first lens unit, L 2  a variator lens unit as a second lens unit that moves in the optical axis direction to vary the magnification. 
   L 3  denotes an image-stabilizing lens unit that shifts in a direction orthogonal to the optical axis to optically correct image shakes caused by camera shakes. The image-stabilizing lens unit L 3  is constituted by a fixed lens element L 3   a  and a shift lens element L 3   b.    
   L 4  denotes a focus lens unit as a fourth lens unit that moves in the optical axis direction to perform focusing. 
   In this embodiment, four lens barrel units U 1  to U 4  holding these lens units L 1  to L 4 , respectively, are formed; each lens barrel unit is independent of the other lens barrel units. 
   Although each of the lens units L 1  to L 4  seems to be constituted by one lens element in the figure, each lens unit is actually constituted by one or more lens elements. 
   U 1  denotes a front lens barrel unit holding the front lens unit L 1 , and U 2  a variator lens barrel unit holding the variator lens unit L 2  movably in the optical axis direction. 
   U 3  denotes an image-stabilizing lens barrel unit holding the image-stabilizing lens unit L 3 , and U 4  a focus lens barrel unit holding the focus lens unit L 4  movably in the optical axis direction. 
   U 5  denotes a stop unit changing the amount of light passing through the zoom lens barrel, and U 6  a variator motor unit driving the variator lens unit L 2  in the variator lens barrel unit U 2 . 
   In this embodiment, since each of the lens barrel units U 1  to U 4  is independent of the other barrel units, the optical adjustment of each lens unit can be made independently without affecting the other lens units. Therefore, combining and joining these lens barrel units U 1  to U 6  make it possible to assemble the zoom lens barrel including four lens units L 1  to L 4  that constitute the image-forming optical system. 
     FIG. 2  shows the general structure of a video camera including the zoom lens barrel. 
     105  denotes an image-pickup element such as a CCD sensor or a CMOS sensor. The output signals from the image-pickup element  105  are input into an image processor  101 . The image processor  101  executes image processing of the input signals to generate image signals. The image signals are recorded on a recording medium such as a semiconductor memory, optical disk, or magnetic tape, in a recording circuit  102 . In addition, the image signals are displayed on a display  103  provided on the back or side of the camera. 
     104  denotes a lens controller. The lens controller  104  generates AF evaluation signals from the image signals and brightness signals taken from the image processor  101 , and controls drive of a stop actuator  51  provided on the stop unit U 5  and a focus motor, not shown in the figure, provided on the focus lens barrel unit U 4  to perform automatic light amount adjustment and automatic focusing. 
     110  denotes an acceleration sensor. The lens controller  104  controls drive of an optical image-stabilizing mechanism including the image-stabilizing lens unit L 3  based on vibration signals from the acceleration sensor  110 . 
   The lens controller  104  drives the variator motor unit U 6  in accordance with an operation direction of a zoom switch, not shown in the figure, to vary the magnification, the zoom switch operation being made by a photographer. At this time, the lens controller  104  controls drive of the focus motor so as to correct the displacement of the image plane associated with the magnification varying to maintain an in-focus state. 
   Next, the description will be made of the detailed structure of each of the lens barrel units U 1  to U 4  and the stop unit U 5  with reference to  FIGS. 2 to 4 . 
   First, the description will be made of the front lens barrel unit U 1  with reference to  FIG. 2. 1  denotes a first lens barrel that is a first lens-holding member holding the front lens unit L 1 . The front lens barrel unit U 1  is unitized as an independent lens-holding unit. 
   Next, the description will be made of the variator lens barrel unit U 2 .  3  denotes a variator-holding member holding the variator lens unit L 2 .  2  denotes a fixed lens barrel. A cam ring  4  is arranged inside of the fixed lens barrel  2 . The variator-holding member  3  and fixed lens barrel  2  constitute the second lens-holding member. 
   The cam ring has a cam groove portion  4   a  with which a cam follower  3   a  provided on the variator-holding member  3  engages. 
   The inner circumferential surface of the fixed lens barrel  2  has a straight-proceeding groove portion  2   a  extending in the optical axis direction. The cam follower  3   a  engages with the straight-proceeding groove portion  2   a.    
   The output gear of the variator motor unit U 6  attached on the fixed lens barrel  2  engages with a gear member  6  fixed on the outer circumferential surface of the cam ring  4 . The rotation of the cam ring  4  caused by the rotational power of the variator motor unit U 6  drives the variator-holding member  3  (that is, the variator lens unit L 2 ) in the optical axis direction, the rotation of the variator-holding member  3  being prevented by the straight-proceeding groove portion  2   a.    
   At this time, the variator-holding member  3  is guided by a guide bar, not shown in the figure, in the optical axis direction. Both ends of this guide bar are held by the fixed lens barrel  2  and a holding member  5  fixed on the rear end (end on the image plane side) of the fixed lens barrel  2 . 
   The position of the variator lens unit L 2  is detected by a linear potentiometer, not shown in the figure, that is a variable resistor. 
   The variator lens barrel unit U 2  as an independent lens-holding unit is constituted by unitizing the above-mentioned members. 
   Next, the description will be made of the image-stabilizing lens barrel unit U 3  constituting an optical image-stabilizing mechanism with reference to  FIG. 3. 10  denotes a fixed-lens-holding member. The fixed-lens-holding member  10  holds the fixed lens element L 3   a  of the image-stabilizing lens unit L 3 . In addition, the fixed-lens-holding member  10  holds a shift lens holding member  11  movably in the direction orthogonal to the optical axis. Magnets  18   a  and yokes  18   b  and  19  that constitute part of an actuator for driving the shift-lens-holding member  11  in the direction orthogonal to the optical axis are attached to the fixed-lens-holding member  10 .  23  denotes a cover member for preventing the magnets  18   a  and yokes  18   b  and  19  from dropping off the fixed-lens-holding member  10  in the optical axis direction. 
   The shift-lens-holding member  11  holds the shift lens element L 3   b . The shift-lens-holding member  11  also holds magnet coils  17  that constitute part of the actuator for driving the shift-lens-holding member  11 . The third lens-holding member is constituted by the fixed and shift-lens-holding members  10  and  11 . 
   Furthermore, slide members  12  and  14  for smoothing the movement of the shift-lens-holding member  11  in the direction orthogonal to the optical axis are attached to three portions of the fixed and shift-lens-holding members  10  and  11 , respectively. 
   The shift-lens-holding member  11  is biased forward (on the side closer to the fixed-lens-holding members  10 ) by a spring  15  whose one end is fixed to a shift-lens-pressing member  16  that is arranged rearward of the shift-lens-holding member  11 , thereby causing the slide members  12  and  14  to contact one another under pressure. 
   The shift-lens-pressing member  16  is fixed to the fixed-lens-holding member  10  by screws. In addition, a light-emitting element  20  for detecting the position of the shift-lens-holding member  11  (that is, the shift lens element L 3   b ) is bonded to the shift-lens-holding member  11  with an adhesive. 
   On the other hand, a light-receiving-element-holding member  21  is fixed to the fixed-lens-holding member  10  by screws. A light-receiving element  22  for detecting the position of the shift-lens-holding member  11  is bonded to the light-receiving-element-holding member  21  with an adhesive. 
   Each of the lens elements L 3   a  and L 3   b  is constituted by one or more lens elements. 
   The image-stabilizing lens barrel unit U 3  as an independent lens-holding unit is constituted by unitizing the above-mentioned members. 
   Next, the description will be made of the focus lens barrel unit U 4  with reference to  FIG. 4. 8  denotes a rear lens barrel that is a base member of the focus lens barrel unit U 4 .  9  denotes an image-pickup element holder that holds the image-pickup element  105 . The image-pickup element holder  9  also holds an optical filter such as an infrared cutting filter or a low-pass filter. The image-pickup element holder  9  also has a role of a cover closing the rear end of the rear lens barrel  8 . 
   The rear lens barrel  8  and image-pickup element holder  9  support both ends of two guide bars  25  and  26 . 
     24  denotes a focus-moving member holding the focus lens unit L 4 . The focus-moving member  24  is supported movably in the optical axis direction by the guide bars  25  and  26 . A magnet coil  27  constituting part of a voice coil motor is attached to the focus-moving member  24 . The voice coil motor is the actuator driving the focus-moving member  24  in the optical axis direction. A magnet  28  constituting part of the voice coil motor is attached to the inside surface of the rear lens barrel  8 . The fourth lens-holding member is constituted by the rear lens barrel  8  and the focus-moving member  24 . 
     31  denotes a magnetoresistive element for detecting the movement amount of the focus-moving member  31 .  30  denotes a magnet member used with the magnetoresistive element  31 , the magnet member  31  being bonded to the focus-moving member  31  with an adhesive. On the magnetoresistive element  31 , two magnetic poles are provided alternately in the optical axis direction at predetermined intervals. 
   The focus-moving member  24  has a protrusion, not shown in the figure. When the focus-moving member  24  is moved to a position where the protrusion shields a photo interrupter, not shown, fixed on the inside surface of the rear lens barrel  8 , the photo interrupter detects that the focus-moving member  24  (that is, the focus lens unit L 4 ) is located at the reference position for controlling drive thereof. 
   The focus lens barrel unit U 4  as an independent lens-holding unit is constituted by unitizing the above-mentioned members. 
   Next, the description will be made of the stop unit U 5 . The stop unit U 5  is an iris diaphragm having six light-shielding blades (not shown) that change the diameter of the aperture through which an image-taking luminous flux passes to adjust the amount of light reaching the image-pickup element  105 . The light-shielding blades are driven by the stop actuator  51 . 
   Next, the description will be made of the assembling sequence of the zoom lens barrel constituted by the above-mentioned barrel units U 1  to U 4  and the stop unit U 5 . 
   First, the front lens barrel unit U 1  is fixed to the fixed lens barrel  2  that constitutes the variator lens barrel unit U 2  by screws. 
   Then, the image-stabilizing lens barrel unit U 3  and stop unit U 5  are fixed to the rear barrel  8  that constitutes the focus lens barrel unit U 4  by screws. 
   As the final step, the fixed lens barrel  2  of the variator lens barrel unit U 2  is fixed to the rear barrel  8  of the focus lens barrel unit U 4  by screws. The zoom lens barrel having the first to fourth lens units L 1  to L 4  and the stop unit U 5  is thus assembled. 
   The decentering and tilting of the lens unit in each lens barrel unit are adjusted before assembling the zoom lens barrel as mentioned above. Since one lens barrel unit is constituted for one lens unit in this embodiment, it is possible to easily make this optical adjustment for each lens barrel unit separately from the other lens barrel units (or lens units). 
   After the optical adjustment for each lens barrel unit is made, the zoom lens barrel is assembled according to the above-mentioned sequence. Then, optical adjustments for the entire optical system such as a decentering adjustment and a tilting adjustment between the four lens units U 1  to U 4  are made. 
   As an example of the optical adjustments for the entire optical system, an adjustment of the position of a lens unit decentered from the other lens units in the direction orthogonal to the optical axis is made by inserting a tool into the lens barrel unit that holds the lens unit from outside, or by rotating an adjusting screw that exposes on the outer surface of the lens barrel unit. In this case, since the adjustment work can be made within the lens barrel unit holding the lens unit that should be adjusted, the adjustment does not affect the other lens units or lens barrel units. In other words, the adjustment does not change the positions of the lens units held by the other lens barrel units, and does not need disassembly of the other lens barrel units. 
   As described above, according to this embodiment, since each of the lens barrel units U 1  to U 4  that hold the first to fourth lens units L 1  to L 4  is unitized completely and independently, it is possible to easily make the optical adjustment of the lens unit for each lens barrel unit. Moreover, it is possible to make the optical adjustment in the assembled zoom lens barrel without affecting lens units other than the lens unit that should be adjusted. 
   In addition, it is possible to facilitate the assembly of the zoom lens barrel and the maintenance thereof. 
   Although a video camera with a lens was described in this embodiment, the present invention is not limited thereto. The present invention can be applied to other image-taking apparatuses such as digital cameras, and lens apparatuses such as interchangeable lenses. 
   This application claims a foreign priority benefit based on Japanese Patent Applications No. 2005-152263, filed on May 25, 2005, which is hereby incorporated by reference herein in its entirety as if fully set forth herein.