startrekfan237

The videodisc you are now watching began with the production of a glass photoresist master. Chosen because of its uniformity and freedom from blemishes, the plate glass is ground and reground with extremely fine abrasive, to remove all pits, then optically polished and carefully cleaned. Finally, a thin, uniform layer of positive photoresist is applied to the glass in preparation for mastering. Either videotape or film can be used as program source material, and all master recording is done in real time. Here we see the actual recording of an optical videodisc master. The program material is being supplied by a helical scan videotape machine

This is a microscopic photograph of the surface of a videodisc. The craters you see are really minute pits, the information source of the system. On a typical half-hour disc, there may be as many as fourteen billion of these tiny indentations, arranged in up to fifty-four thousand circular tracks. A beam of light focused down to one thirty thousandths of an inch, passes through the plastic layer, striking the pits, which interrupt the reflected beam. This on-off reflected beam is then translated into electronic impulses. Each of the fifty four thousand circular tracks is equivalent to one television frame, making it possible to have as many