Cryogenically cooled adjustable apertures for infra-red cameras

An infrared imaging camera comprising:

• a housing;
• 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 having an f-number;
• a vacuum chamber located inside said housing, said vacuum chamber being maintained in-vacuum and including a vacuum window located at a front end of said vacuum chamber for admitting infra-red images that enter said housing through said optical lens to the interior of said vacuum chamber, said vacuum window being positioned coaxial of said central axis and in spaced relation to said optical lens;
• an imaging type infra-red photocell having a plurality of radiation sensitive pixels for converting incident infra-red images to electrical signals, said infra-red photocell being located inside said vacuum chamber, spaced from said vacuum window, positioned coaxial of said central axis and in heat insulated relationship with the walls of said vacuum chamber;
• an integrated variable aperture and radiation shield assembly located in said vacuum chamber via said vacuum window to said imaging type infra-red photocell and defining an aperture of said f-number of said optical lens, said variable aperture device including a front side facing said optical lens and a rear side facing said infrared photocell and further comprising:
• a radiation shield;
• a rigid structural framework, said rigid structural framework having an upper end and a lower end, a central axis and large open areas in the sides and comprising a bridge between a warm region and a cold region in the infrared imaging camera;
• said radiation shield being positioned inside said rigid structural framework coaxial to the central axis framework thereof and including a central infrared radiation admitting passage, an input end and an output end for propagating infrared light energy admitted through said input end out through said output end thereof;
• said input end facing said upper end of said rigid structural framework and including a first aperture ring;
• said first aperture ring including a central circular opening positioned coaxial with said central axis for passing infrared radiation and a circumferential portion surrounding said central circular opening;
• said upper end of said rigid structural framework including a second aperture ring;
• said second aperture ring including a central circular opening positioned coaxial with said central axis for passing infrared radiation and a circumferential portion surrounding said central circular opening;
• said lower end of said rigid structural framework including a driving ring, said driving ring including a central circular opening positioned coaxial with said central axis, said driving ring having a peripherally extending rim for supporting said rigid structural framework;
• one of said circumferential portion of said first aperture ring and said circumferential portion of said second aperture ring including a plurality of pivot holes and the other one of said circumferential portion of said first aperture ring and said circumferential portion of said first aperture ring and said circumferential portion of said second aperture ring including a plurality of slots, said slots having an open end that opens into said central circular opening;
• each of said pivot holes and said slots being evenly distributed about said central axis;
• a plurality of aperture blades arranged to define an aperture for passage of infrared radiation, said defined aperture being coaxial with said central circular openings in said first and second aperture rings;
• each of said aperture blades including a front blade surface, a rear blade surface, a first pivot pin attached to, located proximate one end of said blade and projecting from and normal to one of said front and rear blade surfaces, and a second pivot pin attached to, located proximate an opposite end of said blade and projecting from and normal to the other one of said front and rear surface blades, and comprising a flat curved geometry;
• said first pivot pin of respective ones of said plurality of aperture blades being received within respective ones of said pivot holes;
• and
• said second pivot pin of respective ones of said plurality of aperture blades being received with respective ones of said slots, whereby rotation of said second aperture ring in one direction relative to said first aperture ring increases size of said defined aperture in said blades and rotation in an opposite direction decreases the size of said defined aperture;
• wherein rotation of said driving ring while maintaining said second end of said rigid structure framework fixed in position rotates said rigid structural framework and thereby rotates said second aperture ring relative to said first aperture ring to change the size of said defined aperture;
• said sides of said variable aperture device including a radiation absorbing coating for preventing reflection of light to said infrared photocell;
• said radiation shield surrounding said infra-red photocell being in thermal conductive relationship with said first aperture ring 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 being reflected to said photocell;
• and
• mechanical adjusting means coupled to said variable aperture device for adjusting said aperture to match said f-number of said aperture to said f-number exhibited by said optical lens to minimize entry of extraneous rays of light, and, should the infrared radiation received when said camera f-number is so matched to said optical f-stop be too intense for said photocell, for increasing said camera f-number to reduce radiation received by said photocell;
• and
• cryogenic cooling means for cooling said infra-red photocell, said radiation shield, and said variable aperture device to a cryogenic temperature to maintain said infrared photocell, said variable aperture device and said radiation shield, at a significantly lower temperature than said housing and said walls of said vacuum chamber.

An infra-red imaging camera comprising:

• a housing;
• an optical lens for coupling infra-red images of objects incident on said lens from the exterior to the interior of said housing;
• a vacuum chamber located inside said housing, said vacuum chamber including a vacuum window located at a front end of said vacuum chamber for admitting infra-red images that enter said housing through said optical lens to the interior of said vacuum chamber, said vacuum window being positioned 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 located inside said vacuum chamber, spaced from said vacuum window, and in heat insulated relationship with the walls of said vacuum chamber;
• a variable aperture assembly 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, said variable aperture assembly including a front side facing said optical lens and a rear side facing said infra-red photocell comprising:
• a radiation shield;
• a rigid structural framework, said rigid structural framework having an upper end and a lower end, a central axis and being essentially open and comprising a bridge between a warm region and a cold region in the infrared imaging camera;
• said radiation shield being positioned inside said rigid structural framework coaxial to the central axis thereof having a central infra-red radiation admitting passage, an input end and an output end for propagating light energy admitted through said input end through said output end thereof;
• said input end including a first aperture ring;
• said first aperture ring including a central circular opening for passing infra-red radiation;
• said upper end of said rigid structural framework including a second aperture ring, said second aperture ring including a central circular opening for passing infra-red radiation;
• and
• said lower end of said rigid structural framework including a driving ring;
• one of said circumferential portion of said first aperture ring and said circumferential portion of said second aperture ring including a plurality of pivot holes and the other one of said circumferential portion of said first aperture ring and said circumferential portion of said second aperture ring including a plurality of radially directed slots, said radially directed slots having an open end that opens into said central circular opening;
• each of said pivot holes and said slots being evenly distributed about said central axis;
• a plurality of aperture blades arranged to define an aperture for passage of infra-red radiation, said defined aperture being coaxial with said central circular openings in said first and second aperture rings;
• each of said aperture blades comprising a flat curved geometry and having a front blade surface, a rear blade surface, a first pivot pin attached to, located proximate one end of said blade and projecting from and normal to one of said front and rear blade surfaces, and a second pin attached to, located proximate an opposite end of said blade and projecting from and normal to the other one of said front and rear blade surfaces;
• said first pivot pin of respective ones of said plurality of aperture blades being received within respective ones of said pivot holes;
• and
• said second pivot pin of respective ones of said plurality of aperture blades being received within respective ones of said slots, whereby rotation of said second aperture ring in one direction relative to said first aperture ring increases the size of said defined aperture in said blades and rotation in an opposite direction decreases the size of said defined aperture;
• wherein rotation of said driving ring axially while maintaining said second end of said rigid structure framework fixed in position rotates said rigid structural framework and thereby rotates said second aperture ring relative to said first aperture ring to change the size of said defined aperture and thereby vary the f-number of said defined aperture;
• a radiation shield surrounding said in infra-red photocell, said radiation shield being in thermal conductive relationship with said first aperture ring and comprising a heat transmissive material;
• cooling means for cooling said infra-red photocell said radiation shield, and said variable aperture device to a low temperature to maintain said infra-red photocell, said variable aperture device and said radiation shield, at a significantly lower temperature than said housing and said walls of said vacuum chamber

An infrared imaging camera, said camera including a lens possessing an f-number and an adjustable aperture device defining an f-number for said camera that is dependent on the size of the aperture defined by said aperture device, and means for detecting the f-number of said aperture produced by said adjustable aperture device, comprising:

• an indicator ring, said indicator ring for rotating in angular position in response to a change in adjustment of said adjustable aperture device to change the size of said aperture, said degree of rotation being related to the size of said aperture;
• position detecting means for determining the angular position of said indicator ring;
• and
• converter means coupled to said position detecting means for correlating the angular position of said indicator ring determined by said position detecting means to a corresponding f-number.