Compact optical tracking system

Claim 1

AN INFRARED TRACKING HEAD COMPRISING IN COMBINATION AN OPTICAL SYSTEM AND AN INFRARED DETECTOR, SAID OPTICAL SYSTEM COMPRISING A SPHERICAL POSITIVE MIRROR, A THICK SPHERICAL NEGATIVE MIRROR POSITIONED IN FRONT OF THE POSITIVE MIRROR, A COLLIMATING LENS POSITIONED BETWEEN THE POSITIVE AND NEGATIVE MIRRORS TO COLLIMATE THE PRINCIPAL RAYS PASSING THROUGH THE CENTER OF SAID OPTICAL SYSTEM SO THAT THE PRINCIPAL RAYS ARE MADE PARALLEL TO THE AXIS OF SAID OPTICAL SYSTEM, A TRANSPARENT PLATE MOUNTED ON THE AXIS OF SAID OPTICAL SYSTEM, SAID PLATE HAVING FRONT AND REAR PLANAR MAJOR SURFACES EACH OF WHICH IS INCLINED AT AN ANGLE RELATIVE TO SAID OPTICAL AXIS, A SPHERICAL CORRECTING LENS CEMENTED ON THE FRONT PLANAR MAJOR SURFACE OF THE TRANSPARENT PLATE FOR CORRECTING ABERRATIONS INTRODUCED BY SAID PLATE, A RETICLE POSITIONED ON SAID OPTICAL AXIS ADJACENT THE REAR PLANAR MAJOR SURFACE OF SAID PLATE AND POSITIONED SO THE IMAGE OF AN OBJECT IN THE FIELD OF VIEW OF THE OPTICAL SYSTEM IS SHARPLY FOCUSED THEREON, MEANS FOR ROTATING SAID TRANSPARENT PLATE AND SAID SPHERICAL CORRECTING LENS TO CAUSE THE IMAGE ON SAID RETICLE TO MOVE IN A GENERALLY CIRCULAR PATH, SAID RETICLE HAVING AT LEAST ONE OPENING IN PART OF THE GENERALLY CIRCULAR PATH OF THE IMAGE MOVING THEREON, AND A FIELD LENS MOUNTED ON THE OPTICAL AXIS TO THE REAR OF SAID RETICLE TO FOCUS THE IMAGE OF THE ENTRANCE APERTURE ON THE INFRARED DETECTOR SO THAT ANY INFRARED LIGHT PULSE PASSING THROUGH THE RETICLE ILLUMINATES THE IMAGE OF THE ENTRANCE APERTURE ON THE INFRARED DETECTOR AND PRODUCES A CORRESPONDING OUTPUT SIGNAL IN THE DETECTOR.