Low cost night vision camera

• US 5,763,882 A
• Filed: 11/18/1996
• Issued: 06/09/1998
• Est. Priority Date: 04/12/1994
• Status: Expired due to Fees

• Current Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Hughes Aircraft Company (Rtx Corporation)
• Inventors: Cook, Lacy G., Klapper, Stuart H.
• Primary Examiner(s): Glick, Edward J.
• Application Number:
  US08/751,393
• Time in Patent Office: 568 Days
• Field of Search: 250/330, 250/332, 250/349, 250/353, 250/338.3, 250/338.2, 250/334, 250/352, 250/33, 250/364, 250/365, 250/366, 250/350, 250/351, 359/859, 359/861
• US Class Current: 250/332
• CPC Class Codes: G02B 17/0652 on-axis systems with at least one of the mirrors having a central aperture
• CPC Class Codes: G02B 17/0657 off-axis or unobscured systems in which all of the mirrors share a common axis of rotational symmetry
• CPC Class Codes: H04N 3/09 for electromagnetic radiation in the invisible region, e.g. infrared
• 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 low cost infrared camera (1) for night vision. The camera (1) is disposed within a housing (2) having an infrared transmissive window (6) disposed at an input aperture (5) thereof. A compact optical arrangement (10) is disposed within the housing (2) to focus energy from the window (5) onto a focal plane array (20). A chopper disk (19) is positioned between the reflective optical arrangement (10) and the focal plane array (20) to establish a reference level for the array (20) and to facilitate a sequential readout thereof. A signal processing circuit (100) is included for processing the output of the array (20) for display on a standard video screen. Thus, the problems with uncooled detectors are overcome by use of a fast optical system in combination with an uncooled detector. The fast optical system provides a high signal level to the uncooled detector, thereby compensating for losses in collection of thermal radiation. Reflective optical systems can be manufactured inexpensively from plastic or aluminum and reduce the need for expensive infrared materials commonly used in military systems. The combination of the fast optics and uncooled detector provides a truly low cost thermal camera for night vision.

Claims

1. A night vision camera comprising:

a housing having an upper portion, a lower portion and a subhousing disposed therebetween, said subhousing having upper and lower parts, said lower art comprising a cap, and said upper portion having an aperture therethrough;

a window disposed on the housing at the aperture, the window being transmissive to infrared energy;

an array of uncooled detectors disposed within the housing, each detector providing an electrical output signal when illuminated with radiant electromagnetic energy;

a reflective optical arrangement disposed within the subhousing for focusing energy from the aperture onto the array, the optical arrangement including;

a primary mirror mounted in the upper part of the subhousing and having an aspheric surface and a negative power for reflecting energy from the aperture,

a secondary mirror mounted on an inner surface of said cap and having an aspheric surface and a positive power for reflecting energy from the primary mirror,

a fold mirror for reflecting energy from the secondary mirror, and

a tertiary mirror mounted on an inner surface of said cap and having an aspheric surface and a positive power for focusing and redirecting energy from the fold mirror to the array;

a chopper disk disposed within said housing in optical alignment and between said tertiary mirror and said array;

means disposed within said housing for actuating said chopper disk; and

signal processing means disposed within said housing for processing an electrical output signal from the array.

2. The invention of claim 1 wherein the power of the secondary and tertiary mirrors is balanced by the negative power of the primary mirror to provide a zero Petzval curvature or flat field condition.

3. The invention of claim 1 wherein the primary and secondary mirrors form a non-reimaging afocal telescope of the Galilean type at an afocal magnification of approximately 2×

.

4. The invention of claim 1 wherein the primary and secondary mirrors relay a virtual entrance pupil located behind the primary mirror to a real aperture stop.

5. The invention of claim 4 wherein the fold mirror is positioned at the aperture stop to receive the energy from the secondary mirror and reflect the energy to the tertiary mirror.

6. The invention of claim 1 wherein the reflective optical arrangement is a non-relayed three-mirror arrangement with a mirror power distribution of negative, positive, positive used on-axis in aperture and off-axis in field.