Abstract: A mother for manufacturing long-playing video records is provided by (1) selectively exposing a photoresist disposed as the outer layer on a substrate comprising a disc-shaped plate, a thin layer of base material, e.g., an oxide of nitride, adhering to the plate and a thin metal layer, e.g., chromium, silver, nickel or titanium, coating the base material layer, (2) removing non-activated sections of the photoresist layer and (3) sputter or chemically etching the thin metal and base material layers in sections corresponding to the removed sections of the photoresist layer.

Abstract: In an opto-electronic focus detection system for determining a deviation between the plane of focussing of an objective and a radiation-reflecting surface the path of a focussing beam which is reflected by said surface includes an assembly of two radiation-sensitive detection elements. The difference in the output signals of said elements is proportional to said deviation. By disposing a lenslike element of which only the outer zone has a lens action before the detection elements, the measuring range can be extended while maintaining the sensitivity for small deviations.