CROSS-REFERENCE TO RELATED APPLICATION 
   N/A 
   STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
   N/A 
   BACKGROUND OF THE INVENTION 
   The present invention relates to video surveillance cameras and, more particularly, to an assembly for adjusting the back focus of a video surveillance camera. 
   Video surveillance cameras must be able to provide clear and distinct images since such images may be used for security, evidentiary, identification, or other similar purposes. Present camera systems generally provide for adjustment of the back focus by moving the image sensor forward or backward while the lens stays stationary. Alternatively, for camera systems where the image sensor remains stationary, back focus is accomplished by physically adjusting the linear location of the lens assembly by screwing the lens assembly in and out of the camera body&#39;s threaded bushing. The first method is not efficient or practical for thermal management of the image sensor. The second method requires the use of tools to secure the position of the lens, which generally is not a user-friendly solution. 
   It is therefore desirable to provide a video surveillance camera in which the back focus can be easily adjusted and securely set. Moreover, the back focus assembly of the surveillance camera should have a minimum number of movable parts and be easy and inexpensive to manufacture, use, and maintain. 
   SUMMARY OF THE INVENTION 
   In accordance with the present invention there is provided a video surveillance camera comprising a lens, lens holder, image sensor, base, and ring. The base has a plurality of slots, and the image sensor is mounted on the base. The lens is positioned in the lens holder, which has a plurality of arms with a pin. Each of the arms is positioned so that its respective pin is located in one of the plurality of slots in the base. The ring has a plurality of grooves for engagement with the pins and is rotatably engaged with the base such that rotation of the ring imparts axial movement to the lens relative to the image sensor. 
   The present invention also provides an apparatus for adjusting the back focus of a camera comprising a base, lens holder, and a ring. The base has a plurality of slots and a location for mounting an image sensor. The lens holder has a plurality of arms with a pin. Each of the arms is positioned so that its respective pin is located in one of the plurality of slots in the base. The ring has a plurality of grooves for engagement with the pins and is rotatably engaged with the base such that rotation of the ring imparts axial movement to the lens holder relative to the location for mounting an image sensor. When a lens is mounted in the lens holder, the rotary input adjustment is translated into axial movement of the lens. 
   Among the many advantages of the present invention is the ability to adjust the back focus of a camera system without twisting or turning the camera lens while still minimizing the number of movable parts. In addition, the present invention allows the position of the lens to be easily adjusted and then securely fastened relative to the camera body. In one embodiment this function can be accomplished by using a thumbscrew that acts as a securing mechanism and as an adjustment lever. Alternatively, the adjusting ring can be motor driven. Still further, the base provides a conduit for heat removal from the image sensor. Moreover, the present invention is inexpensive to make, operate and maintain. 
   Other advantages and applications of the present invention will be made apparent by the following detailed description of the preferred embodiment of the invention. 


   
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       FIG. 1  is schematic block diagram of a video surveillance system utilizing the present invention. 
       FIG. 2  is an exploded front perspective view of the back focus assembly of the present invention. 
       FIG. 3  is an exploded back perspective view of the back focus assembly of the present invention. 
       FIG. 4  is a front perspective view of the back focus assembly of the present invention. 
       FIG. 5  is a back perspective view of the back focus assembly of the present invention. 
       FIG. 6  is a front perspective of a video surveillance camera utilizing the present invention. 
   


   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIG. 1 , a video surveillance system  10  utilizing the present invention is shown in block diagram form. Video surveillance system  10  comprises a camera  12  having a lens  14 . Camera  12  is connected to network  16 , which can be a closed network, local area network, or wide area network, such as the Internet. A controller  18  is connected to network  16  to control video surveillance system  10  as is known in the art. The video images captured by camera  12  can be viewed by the user on display  20 . Video surveillance system  10  can comprise a plurality of video cameras, video recorders, and other surveillance devices as is known in the art. 
   Referring to  FIGS. 2 and 3 , a back focus assembly  22  has a housing  24 , lens holder  26 , adjustment ring  28 , filter holder  30 , imager board  32 , and base  34 . Lens holder  26  has a front end  36  with an aperture  38  for receiving commercially available camera lenses and/or lens adaptors (not shown). Lens holder  26  is preferably a single plastic injection molded component, but may also be made of other suitable material, such as metal and/or plastic parts that are attached together. Aperture  38  may be threaded, slotted or otherwise configured to securely receive and mount a lens or lens adaptor. Lens holder  26  has an annular flange  40  with three arms  42 . While three arms  42  are illustrated in the drawings, any suitable number of arms  42  may be used. Arms  42  are made of semi-flexible material so that they may bend radially inwardly relative to flange  40  during assembly of back focus assembly  22  but return to and retain their original position following assembly. One end of each arm  42  is attached to flange  40 , and the opposite end is provided with a pin  44  that extends radially outwardly. Pins  44  must be of sufficient length to protrude through longitudinal slots  46  in annular flange  48  of base  34  and into angled grooves  50  of adjustment ring  28 . Slots  46  are sized so that pins  44  can slide therein. During assembly, arms  42  are depressed so pins  44  can be positioned through slots  46  and into grooves  50 . Once arms  42  are no longer depressed, they return to their original position and thereby maintain their position in slots  46  and grooves  50 . 
   Imager board  32  has an image sensor  52 , which can be for example, a commercially available charge-coupled device (CCD) or complementary metal oxide semiconductor (CMOS) sensor to capture the video image viewed by camera  12 . Imager board  32  has a diameter slightly smaller than the inner diameter of flange  48  of base  34 . Filter holder  30  and imager board  32  are fastened to base  34  by screws  56  which pass through apertures  58  in filter holder  30  and apertures  60  in imager board  32  and mate with threaded apertures  62  in the flat portion  64  of base  34  to fixedly attach imager board  32  to flat portion  64  of base  34 . Flat portion  64  has an aperture  66  that permits an electrical connection to connector  68  on imager board  32 . The inside diameter of flange  48  of base  34  is greater than the outside diameter of flange  40  of lens holder  26 . 
   Adjustment ring  28  is a cylindrical tube having an inner diameter slightly larger than the outer diameter of flange  48  of base  34 , allowing adjustment ring  28  to be inserted over flange  48  and slidably rotated around it. Adjustment ring  28  includes three equidistantly positioned, grooves  50  of equal length angularly traversing a portion of the circumference of adjustment ring  28  from the rear end to the front end. Grooves  50  are positioned to receive pins  44  of arms  42  of lens holder  26 . Pins  44  extend through slots  46  of base  34  so that rotation of adjustment ring  28  causes grooves  50  to impart frictional pressure on pins  44 . This pressure causes pins  44  to move axially within slots  46 , thereby imparting axial movement to lens holder  26  relative to base  34 . The direction of axial movement (retracting or extending) depends upon the direction of rotation of adjustment ring  28  (clockwise or counterclockwise). The sliding movement of pins  44  within slots  46  causes lens holder  26  to move longitudinally back and forth within flange  48  of base  34 . Because slots  46  are longitudinal, they also prevent lens holder  26  from being turned, twisted or rotated as it moves in and out of base  34 . Adjustment ring  28  can be a plastic injection molded part or can be made of other suitable material. 
   According to the present invention, the rotational movement of adjustment ring  28  translates into axial motion by lens holder  26 . Since imager board  32  is in a fixed position relative to base  34 , movement of lens holder  26  relative to base  34  changes the distance between the lens supported by lens holder  26  and image sensor  52 , thereby allowing for changes and adjustments in the back focus. The length of grooves  50  should be sufficient to permit a full range of desired axial motion as defined by arms  42  with pins  44  in slots  46 . The length of grooves  50  may be varied according to the amount of rotation of adjustment ring  28  that is desired to cause pins  44  to travel the desired length. A steeper angle will allow this axial distance to be covered with a smaller rotation of adjustment ring  28 , providing a coarser adjustment of back focus. A more gradual angle will require a larger rotation of adjustment ring  28  to accomplish axial movement through the same distance, allowing for finer adjustment of the back focus. Lever  70 , which can be a thumbscrew with a flattened or roughened head to allow a user to tighten and loosen lever  70  with his thumb and forefinger, is positioned through slot  72  in housing  24 . Threads on one end of lever  70  mate with threaded aperture  74  in adjustment ring  28 . When lever  70  is tightened, it makes contact with the surface of housing  24  to act as a securing mechanism to prevent adjustment ring  28  from rotating, thus fixing the position of lens holder  26  relative to imager board  32 . When lever  70  is loosened it can be used to impart rotational movement to adjustment ring  28  to adjust the back focus as desired. Slot  72  is of sufficient length to allow lever  70  to be moved by a user to rotate adjustment ring  28  so that the full linear motion of lens holder  26  is provided to adjust the back focus. Alternatively, the mechanism for rotating adjustment ring  28  and mechanism for fixing adjustment ring  28  to prevent rotation thereof may be provided in the form of separate mechanisms. 
   Screws  76  are inserted through apertures  78  in flat portion  64  of base  34  and mate with threaded apertures  80  in housing  24  to securely assemble back focus assembly  22 . Threaded apertures  82  in housing  24  are provided to allow attachment of back focus assembly  22  to a camera housing. Housing  24  can be a plastic injection molded part or can be made of other suitable material.  FIGS. 4 and 5  show front and rear perspectives of back focus assembly  22  fully assembled.  FIG. 6  illustrates back focus assembly  22  incorporated into a camera housing  84 . 
   It is to be understood that variations and modifications of the present invention may be made without departing from the scope thereof. It is also to be understood that the present invention is not to be limited by the specific embodiments disclosed herein, but only in accordance with the appended claims when read in light of the foregoing specification.
A video surveillance camera comprising a lens, lens holder, image sensor, base, and ring. The base has a plurality of slots, and the image sensor is mounted on the base. The lens is positioned in the lens holder, which has a plurality of arms with a pin. Each of the arms is positioned so that its respective pin is located in one of the plurality of slots in the base. The ring has a plurality of grooves for engagement with the pins and is rotatably engaged with the base such that rotation of the ring imparts axial movement to the lens relative to the image sensor.