Variable pitch grating for diffraction range finding system

The present invention relates to a species of diffractive optical element called chirp gratings as used in diffraction range finders. A means for overcoming perspective foreshortening in the receiver of a diffraction range finder by use of chirp diffraction grating . In a diffraction range finder, a diffraction grating with variations in pitch such that the displacement of higher-order diffraction images in a receiver are separated from their associated zero-order image by an arbitrary displacement with respect to an arbitrary target distance. A system for ranging a target comprising a variable pitch grating and a receiver of the diffraction images formed by said grating.