Patent ID: 7157706
Filing Date: 2007-01-02
Classification: G01J,G03B,H04N

Abstract:
1. An infra-red imaging camera comprising: a housing defining a housing chamber; an optical lens for coupling infra-red images of objects incident on said lens from the exterior to the interior of said housing, said optical lens including a central axis and further including an adjustable focal length to permit a user to selectively change the focal length of said optical lens at least between a short focal length to permit a distant view of a given exterior object and defining a first optical f-stop and a long focal length to permit a close-up view of said given exterior object and defining a second optical f-stop; a vacuum chamber located inside said housing, said vacuum chamber being in-vacuum and including a vacuum window located at a front end of said vacuum chamber for admitting to the interior of said vacuum chamber infra-red images that enter said housing through said optical lens, said vacuum window being positioned coaxial of said central axis and in spaced relation to said optical lens; an infra-red photocell for converting incident infra-red images to electrical signals, said infra-red photocell being housed inside said vacuum chamber coaxial of said central axis and in heat insulated relationship with the walls of said vacuum chamber, and said infra-red photocell including a planar photosensitive surface that is suitable for cooling to a cryogenic temperature; a variable aperture device located in said vacuum chamber for permitting passage of infra-red images admitted into said vacuum chamber via said vacuum window to said infra-red photocell and defining a camera f-stop, said variable aperture device including a front side facing said optical lens and a rear side facing said infra-red photocell; said rear side of said variable aperture device including a radiation absorbing coating for preventing reflection of light to said photocell and said front side of said variable aperture device including a radiation reflective coating for reflecting incident light away from said variable aperture device; a radiation shield for supporting said variable aperture device inside said vacuum chamber in front of and surrounding said infra-red photocell, said radiation shield being in thermal conductive relationship with said variable aperture device and comprising a heat transmissive material; said radiation shield including an inside surface facing said central axis that contains a parasitic radiation absorbent coating to prevent parasitic radiation from being reflected to said photocell and an outer heat reflective surface for reflecting incident radiation thereon outwardly to inhibit heating; and mechanical adjusting means coupled to said variable aperture device for adjusting the aperture to match said camera f-stop to the optical f-stop exhibited by said optical lens to minimize entry of extraneous rays of light, and, should the infrared radiation received when said camera f-stop is so matched to said optical f-stop be too intense for said photocell, for increasing said camera f-stop to reduce the infrared radiation received by said photocell.