Wraparound screen
The rotating screen is a rotating device with cutout (s) in the analog filmstrip projectors that were used in the past and covers the picture window while the film is being transported. It fulfills the same function as the rotary shutter of a film camera and also that of eliminating the flicker by one or more further interruptions of the luminous flux, although the image does not change. This ideally increases the flicker frequency to such an extent that the eye can no longer (disruptively) perceive it. With the duplex method , on the other hand, 2 projections are released alternately in order to have more time for the image change and to be able to work without any dark breaks.
There are disc, cone and drum screens. The rotating screen of film projectors has one, two, three or more blades. It can be coupled to the film drive in a ratio of 1: 1 or it can be translated. The Paillard-Bolex G 3 (1933) narrow film projector has a four-winged rotating screen and can be operated between 24 and 12 images per second. Well-known projectors with a translated single-wing rotating screen are the Philips-F.-P. 20 and its successors, the Filmo models from Bell & Howell or the Eumig P-8 series.
In the cinema, each phase image is revealed twice - the frame rate of 24 frames per second "flickers" at 48 Hz. Narrow film projectors, which are intended for frame rates of 16 or 18 frames per second, have rotating shutters with three light sectors, individual models enable flicker-free projection down to 5 frames per second.
Today's digital projectors no longer have a rotating screen.
literature
- Hans-H. Heunert, Kurt Philipp: Basics of Narrow Film Technology: Guide for Scientific Cinematography. Springer-Verlag 2013, ISBN 3-642-9270-17 , p. 47.