IL94155A - Infra-red camera apparatus - Google Patents

Description

INFRA-RED CAMERA APPARATUS ISRAEL AIRCRAFT INDUSTRIES LTD. 7NIK">7 η'τιχπ n'tvynn C:09741 FIELD OF THE INVENTION The present invention relates to detectors generally and more particularly to infra-red detectors.

BACKGROUND OF THE INVENTION Conventional infra-red thermal imaging cameras which employ thermal detectors such as CCD arrays have the disadvantage that they tend to be driven into saturation by spurious radiation from the upstream optics and; lens housing.

Various techniques have been employed to reduce the spurious radiation reaching the detector, including the use of cold shields. Cold shields are used to prevent the detector from receiving radiation from the lens housing. However, even the use of a cold shield of high efficiency, which effectively prevents the lens housing radiation from reaching the detector, cannot prevent the detector from collecting radiation emitted from the lenses in the optical path. ^ _ Furthermore, for lenses with low F numbers, it is extremely difficult to reach high cold shield efficiency due to considerations of optical design.

U.S. Patent No. 4,041,314 describes an IR detection system including a device for cooling the IR detector and modulating system. However, the two imaging mirrors of the detection system are not cooled.

U.S. Patent No. 4,431,917 describes a compact catadioptric optical system for use with an IR detection device. The optical system is cooled by a cold shield device. However, the IR detection device is not cooled.

U.S. Patent No. 4,783,593 describes an IR detection system, including a cryogenic cold shield enclosure comprising a telecentric lens arrangement and an IR detector array. The first objective lens of the IR detection system is not cooled.

The prior art does not teach of an IR apparatus in which all the optical and detection elements of the device are cooled. t la- SUMMARY OF THE INVENTION The present invention seeks to provide an infra-red camera which overcomes the disadvantages of the prior art.

There is thus provided in accordance with a preferred embodiment of the invention infra-red detection apparatus including a CCD detector, lens apparatus transmitting light from a field of view to the CCD detector, and apparatus for cooling the CCD detector and the lens means.

In accordance with a preferred embodiment of the present invention, the apparatus for cooling includes thermoelectric apparatus for cooling the lens means and cryogenic apparatus for cooling the CCD detector.

In accordance with an alternative embodiment of the invention, the apparatus for cooling comprises means for causing cold air to cool the camera.

Further in accordance with a preferred embodiment of the invention a cold shield may be arranged in association with the CCD detector. In accordance with a preferred embodiment of the invention, a cold shield of lower efficiency than was heretofore required may be employed. This removes a significant constraint on the optical design of the lens and may enable a more compact lens to be employed than would otherwise be possible.

Additionally in accordance with an embodiment of the invention, lens apparatus having an F-number less than 1.2 may be used in applications where they were previously unable to be used. 2 BRIEF DESCRIPTION OF THE DRAWING The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawing in which: Fig. 1 is a generalized sectional illustration of infra-red camera apparatus constructed and operative in accordance with a preferred embodiment of the invention. 3 DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Reference is now made to "Fig. 1, which illustrates an infra-red camera comprising a CCD detector array 10, which is mounted on the cold finger 12 of a cryocooler 14. The detector array 10 is surrounded by a cold shield 16 cooperating with a dewar 17 defining an IR window 18.

A plurality of lenses 20 are arranged to direct infrared energy from a field of view to CCD detector array 10. In accordance with a preferred embodiment of the present invention, the lenses as well as the cold shield are enclosed in an open-ended housing 22 and the housing is cooled, preferably by a thermoelectric coil 24 extending in spiral form along its length and cooperating with a power supply 26.

Additionally or alternatively, the lenses may be cooled by an air flow indicated by arrows 28. The air flow passes through an outer, generally cylindrical, housing 30, which surrounds the entire assembly described above. Normally the air flow is produced at relatively high altitudes by relative motion of an flying platform. Alternatively the air flow may be produced by a fan or compressor 32.

It will be appreciated by persons skilled in the art that the present invention is not limited by what has been particularly shown and described hereinabove. Rather the scope of the present invention is defined only by the claims which follow: 4

Claims (8)

C L A I M S

1. Infra-red camera apparatus comprising: a thermal detector; lens means transmitting light from a field of view to said thermal detector; and means for cooling said thermal detector and said lens means.

2. Apparatus according to claim 1 and wherein said means for cooling comprises thermoelectric means for cooling said lens means and cryogenic means for cooling said thermal detector.

3. Apparatus according to either of the preceding claims and also comprising a cold shield^ arranged in association with said thermal detector.

4. Apparatus according to any of the preceding claims and wherein said lens means have an F-number less than 1.2.

5. Apparatus according to claim 1 and wherein said means for cooling comprises means for causing cold air to cool said camera apparatus.

6. Apparatus according to any of the preceding claims and wherein said thermal detector comprises a CCD detector.

7. Apparatus substantially as shown and described hereinabove . 5

8. Apparatus substantially as illustrated in any of the drawings . For the applicant, Attorneys 6