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 automa
