PATTERN RECOGNITION SYSTEM

A star pattern recognition system (1) comprises an optical filter arrangement (10) in the form of an array (12) of independently tiltable mirrors (M1), (M2). Light from a distant starfield (2) is incident upon the mirror array (12). Each mirror (M1), (M2) reflects a respective image of the starfield, and these images are brought to a common overlapping focus at a detector (18) by a parabolic mirror (14). The mirrors M1, M2 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 (18), thereby providing a detectable output intensity peak that indicates the presence of the star pattern in the field of view of the filter arrangement.