Abstract: An optical correlator having an imaging system for the non-contact measuring of the velocity and/or direction of motion and/or the distance of an object, and comprising at least one grating structure having lines thereon mounted at least in the vicinity of the image plane of the imaging system and at least one photoelectric receiver arranged after the grating structure in the direction of the light, the receiver converting the modulated light fluxes resulting from the grating structure into electrical signals, the improvement comprising a supplemental structural device inserted between the imaging system and the grating structure of the correlator for transforming spatial frequencies contained in the image of an object.