a cold finger;

an infrared detector means secured to a terminus of said cold finger;

an outer casing surrounding said cold finger;

a stiffener means for stiffening said cold finger, said stiffener means interposed between said outer casing and said cold finger in the vicinity of said terminus,

wherein said stiffener means comprises:

first eyelets distributed around the periphery of a first ring, wherein said first ring is attachable by a first securing means to the inside of said outer casing;

second eyelets distributed around the periphery of a second ring, wherein said second ring is attachable by a second securing means to the outside of said cold finger;

said first eyelets and said second eyelets being mutually angularly offset; and

a cable, passing freely through said first and second eyelets, said cable, once said cold finger has been placed in a balanced situation, being secured under tension, to provide radial support, as a closed loop to said first ring and said second ring.