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Author
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Topic: Perforated tape
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Martin Jones
Phenomenal Film Handler
Posts: 1269
From: Thetford , Norfolk,England
Registered: May 2008
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posted September 17, 2011 06:19 AM
I've put this on General Yak, as it is not related to any specific gauge of film.
I have 2 Spools of Recording Tape made to be used on a Craven Syncrodek. They are made by Ampex, are Unused and on 7 inch standard spools. I do not know the length (and I'm not going to measure it!) but I would assume it's Standard play tape and the spools are full.
The interesting thing is that the tape is PERFORATED with 18 perforations every 3.75 inches, and is designed to run in sync with a projector at 18 fps. Actually the other way round as the perforations produced 18 pulses per second when the tape is played at 3.75 in/sec, using a photocell to read them. The Syncrodek compared these with the pulses from a reed switch operated by a magnet mounted on the projector main shaft, and controlled the projector speed to obtain synchronization. The perforations occupy track 3(or 2) on the tape; tracks 1,2(or 3) and 4 can be used for recording.
I've actually got a Syncrodek unit and a modified Eumig 824 HQS, but I've never used the unit for this purpose. I actually used it as a fine speed control for the Eumig when transferring to Video "on the fly".
I am considering putting the tapes, and possibly the unit, ( but not the Eumig!) on EBay, but I thought they may be of interest on the Forums first.
So, is anyone interested in making an offer or offers? Happy to answer questions.
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Retired TV Service Engineer
Ongoing interest in Telecine....
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Martin Jones
Phenomenal Film Handler
Posts: 1269
From: Thetford , Norfolk,England
Registered: May 2008
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posted September 19, 2011 03:10 AM
Good Morning, Paul,
There were two types of Syncrodek, the original mechanical one, which was connected to the projector by a flexible drive and one electrical cable, and the later electronic one, connected by two electrical cables.
From your post, I get the impression that yours is the Mechanical version, am I right?
The mechanical one compared the speed of a capstan driven by the tape with the speed of the projector via the flexible drive. Any error (detected by a simple differential gear) varied a resistor connected to the projector motor, thus correcting the speed. That one used conventional tape (No perforations).
The holes in the tape for the Electronic version served no mechanical purpose; the tape is too fragile to either be driven by, or turn, any sprocketed device. They are simply to detect the tape speed by optical means, so a projector running at 16 fps is synchronised to a tape running at 3.75 inches per second using a tape with 16 perforations in each 3.75 inches. Tapes running at other speeds and projectors running at other speeds had their own perforation pitch (18 every 7.5 ins, 24 every 1.875 ins, etc). At the time these units were in production you simply ordered tape for the combination you required, and the same unit would work with all of them. The other item to be specified was the projector make and model; the manufacturer supplied the correct mechanical/ electrical version for your machine. Simple, but effective.
The "tapes" you refer to (reg 8, Super 8 etc) are actually magnetic coatings on an acetate or polyester FILM base, used on sound recording/playback gear where the can either be driven by,or drive, a sprocket as they are strong enough for the purpose. Such Recording/Playback is know as "sepmag" (Separate Magnetic),commonly used by professionals as a replacement for the original separate optical recording systems.
So I don't think my tapes would be of much use to you, unless your Unit IS the Electronic one, and you can find a projector modified for (or capable of being modified for)it. The Elmo is not suitable.
The Synchrodek was made by Craven, by the way; the CRESTA units are an entirely different story... albeit a very successful one!
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Retired TV Service Engineer
Ongoing interest in Telecine....
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