Optical reader for information on disc - has correction for spot diameter as function of disc radial position

摘要

A disc on which information is recorded as variable length microelements in concentric or spiral tracks is read by optical system. Correction is provided for read spot diameter as function of position on disc radius. A disc (2) on prestabiliser platform (1) is supported by carriage (3) on base (4). An optical bench (5) comprises laser source (6) with mirrors (7, 8) to transmit beam to mirror (9). The beam is focussed by objective lens (10) onto the disc track. A wheel (12) rolling on prestabiliser platform drives pulley system (13, 14) to rotate axis (15) to move supports (16, 17) forming a diaphragm to correct beam spot size for radial position on disc.