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Author
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Topic: Video Hum on Camcorder Capturing 16mm?
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John Hermes
Expert Film Handler
Posts: 139
From: La Mesa, CA, USA
Registered: Nov 2008
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posted July 07, 2011 12:59 AM
A ground loop will usually move more slowly than that. Is this a factory modified projector with a sync motor and timing gears and belts, such as the Elmo ETC 24 model? Usually, shutter bars moving up that quickly mean the projector is running too fast. Just putting a five-blade shutter in a projector won't make it necessarily free of picture artifacts. A sync motor is locked to the AC line frequency, ensuring correct, stable speed. In addition, I've had some cameras (usually old tube models) that will show a moving bar even on some factory telecine projectors. A fully professional projector, such as an RCA TP-66, with true 3-2 pulldown, will sync with any camera I ever tried.
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John Hermes
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Martin Jones
Phenomenal Film Handler
Posts: 1269
From: Thetford , Norfolk,England
Registered: May 2008
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posted July 08, 2011 02:28 AM
The symptom you show is typical of the speed difference between the projector flicker frequency (speed x 5 = 120hz approx.) and Camera field rate x 2 = 120 hz approx.
The clue is in the "approx". An NTSC camera field rate is CRYSTAL controlled at a fraction less than 60 per second. The bars will disappear if the projector speed is the SAME fraction below 24 fps. You therefore need to be able to adjust the projector speed to match EXACTLY and keep it there, either manually or by some kind of electronic locking. The amount of deviation from 24 fps is very small, and the difference in sound pitch should not be detectable.
BUT, the speeds must match EXACTLY.You need to determine how the projector speed is controlled, and work accordingly. If the projector speed is determined by a synchronous or asynchronous motor controlled by the mains frequency (60hz) the speed will vary dependant on that frequency, which could be in error up or down, which does not guarantee "correct and stable speed".. But if the ELMO is controlled electronically it may be possible to bring the speed adjustment trimmer out on leads to provide a manual control.
My advice.... do not spend countless dollars buying equipment that may or may not do what you want, investigate the above notes; it could save you a fortune!
[ July 08, 2011, 04:04 AM: Message edited by: Martin Jones ]
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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 July 09, 2011 03:07 AM
Regardless of whether the USA uses the world-wide practice of reducing mains frequency by small amounts at times of heavy demand in order to reduce transmission losses, and subsequent raising of frequency at times of low demand to compensate, or not... the fact remains that in order to eliminate "flicker bars" when using a consumer video camera with a projector of any type the speeds must match exactly.
Highly sophisticated transfer machines will have some means of locking the projector speed to the video camera field rate (which is NOT the same frequency as the NOMINAL mains frequency). Such machines are, by virtue of that sophistication, expensive. I do not know if Craig has a bottomless pocket or not; he certainly does not already own such machines, so he is faced with either considerable outlay (if he can afford it) or with doing what the rest of us without unlimited means have had to do... find a method that not only works, but also costs as little as possible.My remarks(and advice) address that eventuality.At least he already has a machine that could be capable of good transfers.. so no great outlay there.
Perhaps Craig would like to comment? After all, this is a discussion Forum.
Martin
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Retired TV Service Engineer
Ongoing interest in Telecine....
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