Patent Document

FIELD OF THE INVENTION 
   This invention relates to a lens barrel and more particularly to a lens barrel used in a monitoring camera, etc. 
   BACKGROUND OF THE INVENTION 
   One kind of monitoring camera adapted for use in both of the visible region (in the daytime) and the near-infrared region (at night) is of the type in which an infrared cutoff filter for cutting off near-infrared light is positioned on the optical axis in front of an imaging device (CCD) when the camera is used to take images in the visible region, while a dummy filter replaces the infrared cutoff filter when the camera is used to take images in the near-infrared region, so that it may be possible to correct any deviation of image focus location occurring under the influence of axial chromatic aberration. 
   The mechanism for an infrared cutoff filter as stated above (hereinafter referred to as the infrared cutoff filter mechanism) has hitherto been installed in a camera body with an imaging device. In a recently sold monitoring camera having a lens barrel forming an integral part of the camera body, however, the installation of the infrared cutoff filter mechanism in the camera body has been made difficult by a reduction in size of the camera body, etc. 
   Accordingly, there has been proposed a technique for installing an infrared cutoff filter mechanism in a lens barrel (see, for example, JP-A-2002-189238). According to the literature, an infrared cutoff filter mechanism is integrally connected to an aperture mechanism and installed in a lens barrel. 
     FIG. 3  is a schematic illustration of a monitoring camera equipped with a lens barrel having an aperture mechanism connected integrally to an infrared cutoff filter mechanism. As shown in  FIG. 3 , the monitoring camera  200  includes a camera body  202  and a lens barrel  204 . The lens barrel  204  includes a front fixing cylinder  206  for fixing a first lens (group)  212 , a rear fixing cylinder  208  for fixing a second lens (group)  214  and a CCD fixing cylinder  210  for fixing a CCD  216 . An aperture mechanism  218  connected integrally to an infrared cutoff filter mechanism is positioned between the front and rear fixing cylinders  206  and  208 . 
   In the aperture mechanism  218 , an aperture  220  formed by two aperture blades and a filter fixing plate  222  for fixing an optical filter, such as an infrared cutoff filter, are disposed along the front and rear surfaces, respectively, of a base plate  224 . The aperture mechanism  218  also includes on the outer periphery of the lens barrel  204  an aperture driving device  226  for adjusting the size of a clear aperture in the aperture  220  and a filter driving device  228  for installing and uninstalling the optical filter on the optical axis. 
   However, the presence of the aperture mechanism connected integrally to the infrared cutoff filter mechanism between the first and second lenses  212  and  214  as shown in  FIG. 3  makes it necessary to design an especially wide spacing between the lenses as compared with any ordinary lens barrel. Moreover, the provision of the aperture driving device  226  and the filter driving device  228  on the outer periphery of the lens barrel  204  makes it necessary to design new component parts, etc. on the outer periphery of the lens barrel  204 . Accordingly, they fail to be common with many component parts on any ordinary lens barrel, but objectionably add to the cost of manufacturing the lens barrel. 
   The integral connection of the aperture and infrared cutoff filter mechanisms makes it necessary to disassemble them as a whole in the event of failure of any component part of either of them to examine the cause of its failure and repair it. 
   SUMMARY OF THE INVENTION 
   Under these circumstances, an object of an illustrative, non-limiting embodiment of the invention is to provide a lens barrel having an optical filter, such as an infrared cutoff filter, at a low cost. Also, the invention is not required to overcome the disadvantage described above (i.e., high cost of the manufacturing or so), and an illustrative, non-limiting embodiment of the invention may overcome a different disadvantage or may not overcome any disadvantages. 
   (1) A lens barrel of the invention is a lens barrel capable of being mounted to a camera body, which includes an aperture between two lenses held in the lens barrel and at least one optical filter disposed to rearward of one of the two lenses, wherein the one of the two lenses is situated closer to the camera body than the other of the two lenses, and the at least one optical filter blocks or transmits (or passes) light depending on a wavelength of the light. 
   According to the invention, the optical filter is installed independently of the aperture between the lenses, and the optical filter is installed to rearward of the lens situated closer to the cameral body. Therefore, the installation of the optical filter in the lens barrel does not require any change in design between the lenses, but makes it possible to use many parts common to any ordinary lens barrel and thereby manufacture the lens barrel at a low cost. 
   As the optical filter is installed separately from the aperture, they are easy to maintain, since in the event of failure of any component part of one of the mechanisms including them, it is sufficient to disassemble the mechanism in question, examine the cause of the failure and repair the mechanism. 
   (2) A lens barrel of the invention is a lens barrel as set forth in (1) above, further including a filter switching unit for installing the at least one optical filter on an optical axis of the lens barrel and for uninstalling the at least one optical filter from the optical axis. 
   The aspect of (2) above makes it possible to install or uninstall the optical filter easily, depending on the situation of taking images, as well as exhibiting the effects of the aspect of (1) above. 
   (3) A lens barrel of the invention is a lens barrel as set forth in (1) or (2) above, wherein the at least one optical filter blocks light in a near-infrared region. 
   The aspect of above (3) makes it possible to intercept light in the near-infrared region when taking images in the visible region, as well as exhibiting the effects of the aspect of (1) or (2) above. 
   (4) A lens barrel of the invention is a lens barrel as set forth in (1) or (2) above, wherein the optical filter comprises a first optical filter blocking light in a near-infrared region and a second optical filter transmitting light in the near-infrared region. 
   The aspect of (4) above makes it possible to correct any deviation of image focus location occurring under the influence of axial chromatic aberration when taking images in both of the visible and near-infrared regions of wavelengths, as well as exhibiting the effects of the aspect of (1) or (2) above. 
   (5) A lens barrel of the invention is a lens barrel as set forth in any of (1) to (4) above, further including a first fixing cylinder holding the two lenses and a second fixing cylinder situated to rearward of the first fixing cylinder, the second fixing cylinder holding an imaging device, wherein the at least one optical filter is disposed (or installed) in the second fixing cylinder. 
   The aspect of (5) above makes it possible to eliminate  the necessity for any change in design of the first fixing cylinder and thereby use many parts common to any ordinary lens barrel and manufacture the lens barrel at a low cost. 
   An embodiment of the lens barrel according to the invention eliminates the necessity for any change in design between the lenses, since the optical filter is situated separately from the aperture between the lenses and rearwardly of the lens closer to the camera body. 
   Therefore, it shares many parts with any ordinary lens barrel and can be manufactured at a low cost. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a side elevational view, partly in section, of a lens barrel according to an illustrative, non-limiting embodiment of the invention. 
       FIGS. 2A and 2B  each are a front elevational view of the filter mechanism in the lens barrel shown in  FIG. 1 . 
       FIG. 3  shows a schematic diagram of a monitoring camera equipped with a lens barrel having an aperture mechanism united integrally with an infrared cutoff filter mechanism. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   An exemplary embodiment of the lens barrel of the invention will now be described with reference to drawings. 
     FIG. 1  is a side elevational view, partly in section, showing the construction of a lens barrel for a monitoring camera according to an exemplary embodiment of the invention. The lens barrel  10  includes: a first fixing cylinder including a front fixing cylinder  12  and a rear fixing cylinder  14 ; and a second fixing cylinder including a CCD fixing cylinder  16 . 
   An aperture mechanism  40  is disposed between the front and rear fixing cylinders  12  and  14 , and the inner peripheral portion of the rear end (the side toward a camera body) of the front fixing cylinder  12  is adhesively bonded to the outer peripheral portion of the front end of the rear fixing cylinder  14 . 
   The rear fixing cylinder  14  and the CCD fixing cylinder  16  are joined together by bayonet connection. The rear fixing cylinder  14  has a male bayonet mount ring  18  formed at its rear end and having bayonet pawls projecting radially outwardly from its outer periphery and spaced from one another along its circumference and bayonet engaging grooves each having one wall defined by one of the bayonet pawls. The CCD fixing cylinder  14  has a female bayonet mount ring  20  attached to its front end and having bayonet protrusions projecting radially inwardly from its inner peripheral surface. After the bayonet protrusions of the female bayonet mount ring  20  are inserted through insertion spaces formed discontinuously between the bayonet pawls of the male bayonet mount ring  18 , they are turned relative to each other, whereby the bayonet protrusions of the female bayonet mount ring  20  are engaged in the bayonet engaging grooves of the male bayonet mount ring  18  to join the rear fixing cylinder  14  and the CCD fixing cylinder  16  together. 
   The CCD fixing cylinder  16  has a plurality of screw holes  22  formed in its rear end portion and is fastened to the body of a monitoring camera not shown by screws not shown, either. 
   A focus lens (group)  26  held in a lens frame  24  is situated in the front fixing cylinder  12 . The lens frame  24  has engaging portions  27  projecting from its peripheral surface and the front fixing cylinder  12  has straight grooves  28  in which the engaging portions  27  are engageable to move the lens frame  24  and the focus lens  26  straight along the optical axis P, as they are guided along the straight grooves  28 . 
   A focus ring  30  is rotatably situated about the outer periphery of the front fixing cylinder  12  and has cam grooves  32  formed in its inner peripheral surface. Cam pins  34  project from the ends of the engaging portions  27  of the lens frame  24  and engage in the cam grooves  32  to cause the crossings between the cam grooves  32  of the focus ring  30  and the straight grooves  28  of the front fixing cylinder  12  to shift along the optical axis P and thereby cause the lens frame  24  and the focus lens  26  to shift along the optical axis P. The rotation of the focus ring  30  makes it possible to control the set position of the focus lens  26  for focus adjustment. The engaging portions  27  are formed at three locations spaced equally apart from one another about the lens frame  24  and accordingly, the straight grooves  28  of the front fixing cylinder  12  and the cam grooves  32  of the focus ring  30  are each three in number. 
   The focus ring  30  has a handle fixing member  36  attached to its outer periphery. The handle fixing member  36  has a threaded hole  37  extending therethrough from its outer surface to its inner surface and a handle  38  has a threaded portion  39  engaged in the threaded hole  36  and is thereby held by the handle fixing member  36 . The operator can rotate the focus ring  30  by using the handle  38  and turning its threaded portion  39  until it contacts the outer peripheral surface of the focus ring  30 . By turning the threaded portion  39  of the handle  38  to a further extent to press its end against the outer peripheral surface of the focus ring  30  to a further extent, it is possible to hold the focus ring  30  in its position for desired focus adjustment. 
   The aperture mechanism  40  disposed between the front and rear fixing cylinders  12  and  14  includes two aperture blades  42  and  44 , a holding frame  46  situated behind the aperture blades  42  and  44  for holding them and for mounting and holding the aperture mechanism  40  on the lens barrel  10  (front fixing cylinder  12 , rear fixing cylinder  14  and CCD fixing cylinder  16 ) and a holding plate  48  situated in front of the aperture blades  42  and  44  for holding them. The aperture mechanism  40  is fixed to the front and rear fixing cylinders  12  and  14  by screw not shown. 
   A holding unit  50  for mounting and holding a driving mechanism for opening and closing the aperture blades  42  and  44  is integrally formed under the holding frame  46  for the aperture mechanism  40  for containing an electrically operated driving machine. The electrically operated driving machine is a driving mechanism for opening and closing the aperture blades  42  and  44  electrically (by an Iris meter). The driving mechanism may alternatively be of the type in which the aperture blades  42  and  44  are opened and closed manually. 
   A zoom lens (group)  54  held by a lens frame  52  is positioned in the rear fixing cylinder  14 . The lens frame  52  has engaging portions  56  projecting from its peripheral surface, while the rear fixing cylinder  14  has straight grooves  58  extending along the optical axis P, and the engaging portions  56  of the lens frame  52  are engageable in the straight grooves  58  of the rear fixing cylinder  14  to move the lens frame  52  and the zoom lens  54  straight along the optical axis P, as they are guided along the straight grooves  58 . 
   A zoom ring  60  is rotatably situated about the outer periphery of the rear fixing cylinder  14  and has cam grooves  62  formed in its inner peripheral surface. The male bayonet mount ring  18  is attached to the rear end of the zoom ring  60  and is engaged with the female bayonet mount ring  20  attached to the front end of the CCD fixing cylinder  16  to join the rear and CCD fixing cylinders  14  and  16  together, as stated before. 
   Cam pins  63  project from the ends of the engaging portions  56  of the lens frame  52  and engage in the cam grooves  62  of the zoom ring  60 . Accordingly, the crossings between the cam grooves  62  of the zoom ring  60  and the straight grooves  58  of the rear fixing cylinder  14  are caused to shift along the optical axis P and the lens frame  52  and the zoom lens  54  are thereby caused to shift along the optical axis P. The rotation of the zoom ring  60  makes it possible to control the set position of the zoom lens  54  for the adjustment of the focal distance (or zoom angle). The engaging portions  56  are formed at three locations spaced equally apart from one another about the lens frame  52  and accordingly, the straight grooves  58  of the rear fixing cylinder  14  and the cam grooves  62  of the zoom ring  60  are each three in number. 
   The zoom ring  60  has a handle fixing member  64  attached to its outer periphery. The handle fixing member  64  has a threaded hole  65  extending therethrough from its outer surface to its inner surface and a handle  66  has a threaded portion  67  engaged in the threaded hole  65  and is thereby held by the handle fixing member  64 . The operator can rotate the zoom ring  60  by using the handle  66  and turning its threaded portion  67  until it contacts the outer peripheral surface of the zoom ring  60 . By turning the threaded portion  67  of the handle  66  to a further extent to press its end against the outer peripheral surface of the zoom ring  60  to a further extent, it is possible to hold the zoom ring  60  in its position for desired focal distance adjustment. 
   The CCD fixing cylinder  16  includes a filter mechanism  70 , a correcting glass  72 , a cushioning material  74  and a CCD  76  arranged in their order along the optical axis P from the front end of the CCD fixing cylinder  16  to its rear end. 
   The correcting glass  72  is held in position by a holding portion  78  on the inner peripheral surface of the CCD fixing cylinder  16  and the cushioning material  74 . The correcting glass  72  corrects light projected from the zoom lens  54  onto the CCD  76  as by blocking light having a certain wavelength in order to achieve the desired image effect. The material, thickness, etc. of the correcting glass depend on the function and performance of the CCD  76 , the desired image effect, etc. 
   In addition to holding the correcting glass  72  in position, the cushioning material  74  serves as a spacer to make an image forming surface (image focus)  80  coincide with the light receiving surface  82  of the CCD  76  (hereinafter referred to as the imaging surface). 
   The CCD  76  is attached to the center of a CCD base  84  on the front side of the CCD base  84 . The CCD  76  transforms an optical image formed on the imaging surface  82  into an electrical signal. The electrical signal is sent to the monitoring camera body through a cable connected to the CCD base  84 , but not shown. 
   The filter mechanism  70  situated behind the zoom lens  54  is so formed as to extend through the CCD fixing cylinder  16  and is fixed to the CCD fixing cylinder  16  by screws not shown. 
   The filter mechanism  70  has a filter fixing plate  86  to which optical filters including an infrared cutoff filter  95  blocking infrared rays (e.g., light in a near-infrared region) and a clear filter  97  passing infrared rays are attached, a holding frame  88  for holding the filter fixing plate  86  and for mounting and holding the filter mechanism  70  on the lens barrel  10  (front fixing cylinder  12 , rear fixing cylinder  14  and CCD fixing cylinder  16 ) and a holding portion  90  mounting and holding an electrically operated driving machine for moving the filter fixing plate  86  vertically to change the filters on the optical axis P. 
   The invention is, however, not limited to the filter mechanism  70  having the filters changed on the optical axis P by means of an electrically operated driving machine. It is alternatively possible to employ, for example, an operating member for manually moving the filter fixing plate  86  vertically. 
     FIGS. 2A and 2B  each are a front elevational view of the filter mechanism  70  shown in  FIG. 1 .  FIG. 2A  shows the state in which the infrared cutoff filter  95  is positioned on the optical axis P, and  FIG. 2B  shows the state in which the clear filter  97  is positioned on the optical axis P. 
   The filter fixing plate  86  is a substantially rectangular thin metal plate having a longitudinally extending arm  92  formed at one end, as shown in  FIG. 2A . The arm  92  has a link hole  98  formed at its distal end. 
   The filter fixing plate  86  has substantially square openings  94  and  96  formed one after the other along its length. The opening  94  is covered with the infrared cutoff filter  95  and the opening  96  is covered with the clear filter  97 . The infrared cutoff and clear filters  95  and  97  are larger than the openings  94  and  96 , respectively, and have their edges fixed to the filter fixing plate  86  by an adhesive, etc. 
   The clear filter  97  corrects any deviation of the image focus location when the infrared cutoff filter  95  is set aside from the optical axis P. Accordingly, the clear filter  97  is so designed in thickness, material, etc. that the image focus location when the clear filter  97  is positioned on the optical axis P may coincide with the image focus location when the infrared cutoff filter  95  is positioned on the optical axis P. 
   The holding frame  88  has two lugs  100  formed on its opposite longitudinal edges, respectively, for securing the filter mechanism  70  to the CCD fixing cylinder  16 . Each lug  100  has a hole  102  formed at its center for passing a screw therethrough. The holes  102  are aligned with holes formed in the CCD fixing cylinder  16 , but not shown, and screws not shown are threadedly engaged therethrough for securing the filter mechanism  70  to the CCD fixing cylinder  16 . 
   The holding frame  88  has a circular opening  104  formed substantially at its center for passing incident light. The opening  104  has its center aligned with the optical axis P when the filter mechanism  70  is secured to the CCD fixing cylinder  16 . 
   The filter fixing plate  86  is laid on the surface of the holding frame  88 . The filter fixing plate  86  is held against separation from the holding frame  88  by e.g. protrusions extending from the edges of the holding frame  88  to its inside, but not shown, and is slidable along its length. 
   The holding frame  88  has a substantially circular connecting portion  106  formed toward its lower end. The connecting portion  106  includes a rotary shaft  108  of the electrically operated driving machine (but not shown) mounted in the holding portion  90 , a rotary arm  110  attached to the rotary shaft  108  and a link member  112  connecting one end of the rotary arm  110  with the link hole  98  of the arm  92 . 
   The rotary shaft  108 , the rotary arm  110 , the link member  112 , the link hole  98 , the arm  92 , and the filter fixing plate  86  perform a function of a filter switch portion for installing and uninstalling (or changing) optical filters on the optical axis P. When the electrically operated driving machine is driven, the rotary shaft  108  is rotated and the rotary arm  110  is rotated within a specific angular range about the rotary shaft  108 . With the rotation of the rotary arm  110 , the link member  112  at one end thereof moves along the circumference of the connecting portion  106  and thereby causes the filter fixing plate  86  having the arm  93  connected by the link member  112  to slide longitudinally. 
   When the rotary arm  110  stays at one of the limits of rotation as shown in  FIG. 2A , the infrared cutoff filter  95  is aligned with the opening  104 . When the rotary arm  110  stays at the other limit of rotation as shown in  FIG. 2B , the clear filter  97  is aligned with the opening  104 . 
   When the monitoring camera to which the lens barrel  10  as described is mounted is used in the visible region, the electrically operated driving machine is driven to position the infrared cutoff filter  95  on the optical axis P. When it is, on the other hand, used in the infrared region, the electrically operated driving machine is driven to position the clear filter  97  on the optical axis P. There is no deviation in focus between when an image is taken in the visible region and when an image is taken in the infrared region, since the image focus location when the infrared cutoff filter  95  is positioned on the optical axis coincides with the image focus location when the clear filter  97  is positioned, as stated before. Therefore, there is no need for focus adjustment every time image taking is switched between the visible region and the infrared region. 
   The infrared cutoff and clear filters  95  and  97  in the filter mechanism  70  do not have any effect on the distance between the focus lens  26  held in the first fixing cylinder  12  and the zoom lens  54  held in the second fixing cylinder  14 , since those filters are installed in the CCD fixing cylinder  16  situated to rearward of the second fixing cylinder  14 . The holding portion  90  of the filter mechanism  70  is formed around the CCD fixing cylinder  16  and does not affect any component part situated around the first or second fixing cylinder  12  or  14 . Therefore, the lens barrel according to the invention shares many parts with any ordinary lens barrel and can, therefore, be manufactured at a low cost. 
   As the filter mechanism  70  is installed separately from the aperture mechanism  40 , they are easy to maintain, since in the event of failure of any component part of one of those mechanisms, it is sufficient to disassemble the mechanism in question, examine the cause of the failure and repair it. 
   While the lens barrel of the invention has been described in detail, it is needless to say that this invention is not limited to the example as described above, but that improvements or variations may be made without departing from the gist of this invention. 
   The entire disclosure of each and every foreign patent application from which the benefit of foreign priority has been claimed in the present application is incorporated herein by reference, as if fully set forth herein.

Technology Category: 3