5.6 How are multiple projectors interlocked to run the same piece of film in multiple auditoria?
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This article is from the rec.arts.movies.tech FAQ, by Scott E. Norwood snorwood@nyx.nyx.net with numerous contributions by others.
5.6 How are multiple projectors interlocked to run the same piece of film in multiple auditoria?
(information courtesy David Richards daverich@netcom.com)
This is occasionally done in multiple-screen theaters; the projectors
which are going to be interlocked need to be adjacent to each other
(or at least reasonably close), and must be fitted with synchronous
motors, whose speed is controlled by the 60hz (in the U.S.; 50hz in
many other countries) AC line frequency. The film is loaded from a
platter through the first projector (as usual), and then passes over
several rollers, mounted on a wall or ceiling, across the booth to the
second projector, into which it is then also loaded normally.
Somewhere between the two machines, there is usually a bit of slack in
the film, where a weighted roller is placed in order to keep the film
running smoothly if there happens to be a small speed variation during
the show.
Both projectors must be started at exactly the same time in order to
maintain the proper amount of slack between them. This is done either
by two projectionists, or by an automation system capable of handling
this function.
It should be noted that the term `interlocked' is also commonly used
in the context of a sound mix facility, where several magnetic
dubbers, and, usually, a projector, must be mechanically or
electronically interlocked together in order to ensure that the
multiple soundtracks being mixed are in perfect sync with each other
and with the workprint being projected.
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