Cryogenically cooled adjustable apertures for infrared cameras

• US 7,157,706 B2
• Filed: 05/28/2003
• Issued: 01/02/2007
• Est. Priority Date: 05/28/2003
• Status: Expired due to Term

• Current Assignee: OPTO-Knowledge Systems, Inc.
• Original Assignee: OPTO-Knowledge Systems, Inc.
• Inventors: Gat, Nahum, Garman, John Dwight
• Primary Examiner(s): Gabor; Otilia
• Assistant Examiner(s): Sung; Christine
• Application Number:
  US10/250,016
• Publication Number:
  US 20040238741A1
• Time in Patent Office: 1,315 Days
• Field of Search: 250/338.1, 250/347
• US Class Current: 250/338.1
• CPC Class Codes: G01J 5/06 Arrangements for eliminating effects of disturbing radiation; Arrangements for compensating changes in sensitivity for adjusting of solid angle of collected radiation G01J5/07; means for wavelength selection G01J5/0801
• CPC Class Codes: G01J 5/061 by controlling the temperature of the apparatus or parts thereof, e.g. using cooling means or thermostats
• CPC Class Codes: G01J 5/08 Optical arrangements
• CPC Class Codes: G01J 5/0831 Masks; Aperture plates; Spatial light modulators
• CPC Class Codes: G01J 5/084 Adjustable or slidable
• CPC Class Codes: G01J 5/0865 having means for replacing an element of the arrangement by another of the same type, e.g. an optical filter
• CPC Class Codes: G03B 9/04 Single movable plate with two or more apertures of graded size, e.g. sliding plate or pivoting plate
• CPC Class Codes: G03B 9/06 Two or more co-operating pivoted blades, e.g. iris type shutters functioning as diaphragms by limiting extent of opening movement G03B9/08
• CPC Class Codes: H04N 23/23 from thermal infrared radiation
• CPC Class Codes: H04N 23/75 by influencing optical camera components
• CPC Class Codes: H04N 5/33 Transforming infrared radiation cameras or camera modules for generating image signals from infrared radiation H04N23/20; circuitry of SSIS for transforming infrared radiation into image signals H04N25/20

Abstract

A continuously variable diaphragm or swappable fixed aperture for use in thermal infrared cameras, which aperture or diaphragm can be cooled to cryogenic temperatures. The invention contemplates mounting aperture control means, if necessary, in a vacuum or extending the control mechanism through a vacuum in a thermally isolated manner to avoid radiation load on the photocell. The inventive method implements such a diaphragm and control system. The invention makes possible the object of using a single thermal infrared camera under a wide variety of target-scene radiation conditions that may be rapidly changing, with interchangeable or zoom camera lenses requiring matching or different size cold stops, and under other such dynamic situations.

Claims

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.

2. The infra-red imaging camera as defined in claim 1, comprising:

cryogenic cooling means for cooling said infra-red photocell, said radiation shield, and said variable aperture device to a cryogenic 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.

3. The infrared camera as in claim 2, wherein said variable aperture device is controlled by a logic control means, said logic control means receiving the f-stop of said optical lens and causing said mechanical adjusting means to adjust said aperture to maintain a desired cold stop.

4. The infrared camera as in claim 2 wherein said lens is comprised of a wide field of view configuration and a narrow field of view configuration and said aperture selection means provides at least two aperture sizes.

5. An improvement to an infrared camera as in claim 2 wherein said variable aperture device is selected from one of an aperture wheel, a partial aperture wheel, and an aperture stick.

6. The infra-red imaging camera as defined in claim 2, wherein said variable aperture device comprises:

a variable iris, said variable iris including a plurality of fingers, each of said fingers being coated with a non-outgassing greaseless solid lubricant material.

7. The infra-red imaging camera as defined in claim 2, wherein said variable aperture device includes:

a plurality of apertures, each of said apertures being of a different area in size for transmission of respectively different intensity levels of said infra-red image to said infra-red photocell with one of said plurality of apertures comprising a default aperture that is positioned coaxial of said central axis for passing received infra-red images to said infra-red photocell,

aperture selection means for selecting another one of said plurality of apertures to replace said default aperture and pass infra-red images, and

wherein said mechanical adjusting means comprises;

motor means for moving said aperture selected by said aperture selection means from a position off of said central axis into coaxial position on said central axis, whereby said selected aperture may pass an infra-red image to said infra-red photocell;

said plurality of apertures in said variable aperture device, other than said default aperture, being initially stowed in said vacuum chamber behind said vacuum window off of said central axis and in front of and spaced relationship to said infra-red photocell.

8. The infra-red imaging camera as defined in claim 7, wherein said variable aperture device further comprises:

a circular disk having a center, a major axis and being mounted for rotation about said major axis;

said circular disk Including a plurality of circular apertures of different size, said circular apertures being angularly spaced about the center of said disk and being located between said center and the periphery of said disk, wherein each of said plurality of apertures may be positioned coaxial of said central axis in sequential order in response to rotation of said circular disk.

9. The infra-red imaging camera as defined in claim 8, wherein said circular disk includes gear teeth along the periphery of said disk to define a gear;

a drive gear coupled to said gear teeth on said disk; and

wherein said motor means drives said drive gear.

10. The infra-red imaging camera as defined in claim 7, wherein said variable aperture device further comprises:

a sector of a circular disk, said sector including a disk center and a major axis of rotation of said disk sector;

said disk sector including a circular aperture therethrough of a size smaller than said default aperture, said aperture being located between said disk center and the periphery of said sector, wherein rotation of said sector moves said circular aperture to a position coaxial of said central axis and in line with said default aperture.

11. The infra-red imaging camera as defined in claim 10, wherein said sector includes gear teeth along the circular periphery of said sector to define a gear;

a drive gear coupled to said gear teeth on said disk; and

wherein said motor means drives said drive gear.

12. The infra-red imaging camera as defined in claim 7, wherein said motor means comprises a piezoelectric motor.

13. The infra-red imaging camera as defined in claim 2, wherein said mechanical adjusting means comprises:

a first portion external of said vacuum chamber;

a second portion internal to said vacuum chamber;

and a third portion mechanically coupling said first and second portions;

said third portion comprising a minimally heat-conductive material to prevent heat from the exterior of said vacuum chamber from entering said vacuum chamber.

14. The infra-red imaging camera as defined in claim 2, wherein said mechanical adjusting means includes a piezoelectric motor.