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Topic: Drive-in Intermittents
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Frankie Angel
Film Handler
Posts: 6
From: Brooklkyn NY USA
Registered: Dec 1999
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posted 12-04-1999 08:04 AM
Years ago I was told that Drive-In theatres utilized a special type of intermittent that had a faster pulldown speed than standard intermittents. These "DI" intermittents pulled down the film quicker and then left it in the aperture for a longer interval. The shutters were then cut back so that the interval that closed off the light was short and the interval where the shutter was opened was long. This allowed alot more light to pass to the screen. The idea of course was to get every ounce of light they could onto those 150 foot screens. Is this an old wives tale or do such creatures exist? Seems like a cheaper alternative to bumping up lamphouse wattage if you just need an extra kick, even if you are only running an indoor. Anyone heard of this?
------------------ Frank Angel, Brooklyn Center Cinema www.BrooklynCenter.com
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Stefan Scholz
Expert Film Handler
Posts: 223
From: Schoenberg, Germany
Registered: Sep 1999
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posted 12-04-1999 03:01 PM
Correct, not only Simplex, but also Phillips (Norelco) was a supüplier of such gears. There are only two ways to get more light on screen, on is the optical way, the use of light sources, which offer a higher density of light (candelas per sq inch). This, is why rotating carbons wirth vent systems were used on larger arclamps. They were limited to a maximum of about 225 A or so. With Xenon, the maximum light efficiency is archiueved with 35 mm film with the 4200 W lamp, the 7k's gap is about 1/2", which is close to the heigh of film, and does not give any light effectivity. On the other hand the visible spectrum is intense enough to endanger the film. So, for large screen presentations, other measures must be taken. On is improved shutter design (XtraLight), and a shorter film travel time, thus archieved with accelerated intermittents. But there's another limit. The accelaration of film must stay within certain values, not to mechanically overload film. (No longer with polyester). As theese intermittens still used standard 4 wing maltese crosses, they had to use a gear train inbetween. Therefore registration stability was not as good as with a standard type, but the gain abiout 25% effectivity and the use in special venue type (sorry, drive in is considwered a special venue operation) this was acceptable.
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