Pattern recognition system

A star pattern recognition system comprises an optical filter arrangement in the form of an array of independently tiltable mirrors (M), (M). Light from a distant starfield is incident upon the mirror array. Each mirror (M), (M) reflects a respective image of the starfield, and these images are brought to a common overlapping focus at a detector by a parabolic mirror. The mirrors M, M are tilted relative to each other such that when a given star pattern to be recognised is present in the field of view of the filter, each mirror reflects the image of a different star in the pattern onto a common point on a detector, thereby providing a detectable output intensity peak that indicates the presence of the star pattern in the field of view of the filter arrangement.