Light point scanner

Light point scanners were used in (color) television studios for scanning slides, epi templates ( epidiascopes ), films and (in the early days of television technology) by people.

At the beginning of the history of television broadcasting, there were announcement studios in which the speaker was together with photocells in a darkened booth and was scanned by a beam of light. A white image created with a lamp and decomposed using a Nipkow disk could serve as the light source, which was then projected onto the speaker using optics.

With the transition to electronic image decomposition, the white image was written by a Braun tube , which is known as a scanning tube . In contrast to the usual picture tubes , in which an appreciable afterglow period is aimed for in order to reduce flicker , scanning tubes have the shortest possible afterglow period. However, an electronic afterglow correction must be made to compensate for flag pulling. The task of collecting the light passing through a slide or a film or reflected and thereby scattered by an epi original could be achieved with an integrating sphere . In the case of color transmission, the integrating sphere also had the task of distributing the light to three SEVs ( secondary electron multipliers ) with color filters in front of them. The term white picture refers to the shape of the television signal driving the tube; the color of the image written by the scanning tube was not necessarily a pure white (reference white).

The use of the principle of light point scanning in color television studios has the advantage that this technique is free from convergence errors that occur in camera scanners with beam splitters . In the 1960s, Fernseh GmbH produced the FC35LP49B (Flying Spot, 35mm) film scanner system. Light point scanning is still used today in Rank-Cintel film scanners.

literature

The Big TV Book (ca.1935)
PV Schmakow: Television (general course) . Moscow 1960