Abstract: A method is described which enables automatic determination of the monitor sensitivity of a radiation emitting arrangement (in particular a laser diode and photodiode arrangement), which monitor sensitivity relates a level of a monitor signal (I.sub.M) generated by the arrangement to a corresponding optical output level (O.sub.L) of the arrangement. The method comprises the steps of: (i) supplying a varying drive signal (I.sub.L1,I.sub.L2) to the arrangement and measuring the rate of change (.DELTA.I.sub.M /.DELTA.I.sub.L) of the monitor signal (I.sub.M) with respect to the supplied drive signal (I.sub.L); and (ii) combining the measured rate of change with an assumed differential efficiency (k) of the arrangement to determine the monitor sensitivity (O.sub.L /I.sub.M) of the arrangement. The provision of a control system able to implement such a method eliminates the need for a factory adjustment in the manufacture of apparatus such as optical recording and/or reproducing apparatus.

Abstract: An apparatus for writing and/or reading information in substantially concentric tracks on a disc-shaped record carrier. The tracks are scanned by a beam of radiation focussed into a light spot thereon, and detection means responsive to the light reflected from the tracks generates a radial error signal which varies substantially proportionally to the radial excursion of the light spot relative to a track over a control range of p/4, p being the track pitch. The detection means comprises an error signal correction circuit for deriving from such signal a control signal (S.sub.1) having a substantially proportional control range for excursions of the light spot up to a value exceeding p/2 from a track. The control signal is supplied to radial positioning means, and controls the radial position of the light spot on a track.