Abstract: A helically scanned optical tape recording and replay system has a rotating drum with a galvanometer mirror for controlling the tracking of a number of write and read light beams during recording and replay. Dynamic focussing of the beams on the recording medium is controlled by means of a voice-coil actuator operating on a lens situated outside the drum. An optical rotator is provided through which the write and read beams pass following beam combinations, the optical rotator being driven by a motor to rotate at half the rotational velocity of the drum, and thereby present an image to the optical tape which rotates synchronously with the drum.

Abstract: Production of a magnetically and visibly detectable two-layer structure by coating a first layer including a binder with a visibly distinct magnetic material in a dispersion comprising a partial solvent for the binder and selectively applying a magnetic field to cause the magnetic material to migrate into the first layer.