Abstract: Apparatus for use in a projectile-borne passive infra-red proximity fuse for detecting infra-red radiation emitted from a target. The apparatus includes at least one pair of optical means which are respectively located at spaced locations around the periphery of the projectile. The pair of optical means is so located that the beams of infra-red radiation associated therewith, which are both imaged upon a common detector, form an angle therebetween both in a plane through the longitudinal axis of the projectile and in a plane normal to such axis. Logic circuitry is provided and controlled by the detector to provide a distinctive output in response to the signals which are generated by the beams of radiation received from a target which is spinning about its longitudinal axis and is within a predetermined distance of the projectile.

Abstract: The invention relates to optical target tracking. A target image, particularly based on reflected laser light, is projected by an optical system onto a light-sensitive detector, control signals for directing purposes being generated depending on the position of the target image on the detector surface. At least when a clear target image on the detector surface would be small in comparison with the detector surface, the area of the target image is increased by blurring the target image, for instance by displacing the detector plane from the image plane of the optical system.