Film-Tech Forum ARCHIVE: Sprocket holes on picture area

This is topic Sprocket holes on picture area in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Thomas Pitt (Member # 4322) on 07-27-2007, 01:55 AM:

I've noticed in showings where the projector aperture gate is misaligned, you can sometimes see the edges of the sprocket holes on the side of the film. The effect is more pronounced during the short black film segments between commercials, as if the sprocket holes have actually been exposed in the picture area. One particular showing was so bad that I could see some of the real sprocket holes, and an 'echo' of the holes to the left of them.

Anyone know what causes that effect? Is it perhaps caused by the negative or other intermediate being out of line when making the print? I'm sure it would be easier to notice by looking at the film directly [Wink]

Posted by Jeremy Weigel (Member # 4208) on 07-27-2007, 02:24 AM:

Is this something that you have noticed with several prints or just on the current print. It sounds like your apeture plate isn't fully seated in the horizontal.

Posted by Robert E. Allen (Member # 1351) on 07-27-2007, 02:31 AM:

Are these "short black segments" spliced in by staff at your theatre? If so, it's possible they spliced them backwards (with the soundtrack area "inboard"). Double check your splices. That is the most common cause of what you describe (especially the "motorboating" effect in the sound system).

Posted by Thomas Pitt (Member # 4322) on 07-27-2007, 02:54 AM:

I'm guessing the black segments are spliced in by the theater to make it obvious when one commercial ends and another starts. As I've mentioned in another thread, they often cut off the few seconds from the beginning of the trailer (the bit that shows the trailer certificate), leading to the sound suddenly cutting in after the trailer starts.

I've seen the 'Following trailers are appropriate' card spliced in backwards and upside down on more than one occasion, but never heard a 'motorboating' effect. Do you mean the effect that you get if the ending cue fails and the film tails out with the projector/sound reader still running?

The aperture gate on these projectors moves horizontally, not vertically, when the lens changes over from flat to scope. The motorized system is also prone to failure, and often has to be moved over manually by the projectionist after a lens changeover - otherwise you get a 'letterbox' effect on the scope screen! I assume they're not pushing the gate back over fully in some cases.

Posted by Chris Slycord (Member # 4239) on 07-27-2007, 05:47 AM:

quote: Thomas Pitt
I've seen the 'Following trailers are appropriate' card spliced in backwards and upside down on more than one occasion, but never heard a 'motorboating' effect. Do you mean the effect that you get if the ending cue fails and the film tails out with the projector/sound reader still running?

No. Motorboating is where you literally get sound that sounds like a motor going in water. He mentioned splicing black leader incorrectly because many times the non-soundtrack side of black leaders has numbers/info that get read by a soundtrack reader and played back as this kind of effect. So if you hear some sort of buzz/hum during a section of black; that's what he's meaning.

He was trying to say that if someone really screwed up the splice you could see the sprockets and that screwing up the splice also can cause motorboating.

edit: Though I guess tailing out could be seen as similar to motorboating but the effect is much different. When the film tails out you get a pretty random bunch of sounds where with a mis-spliced black film you tend to get a pretty consistent, repeating effect.

[ 07-27-2007, 01:42 PM: Message edited by: Chris Slycord ]

Posted by Robert E. Allen (Member # 1351) on 08-01-2007, 01:53 PM:

"Motorboating" is the sound caused by the sproket holes passing in front of the scanner when the film is spliced with the soundtrack inboard instead of outboard.

Posted by Stephen Furley (Member # 1277) on 08-01-2007, 03:56 PM:

Surely that would result in soundtrack on screen, and picture frames abd framelines being scanned by the soundhead. Since the sprocket holes are the same distance from each edge of the film lacing up the wrong way round shouldn't change the position of them, and they shouldn't be scanned any more than they would be if the film was laced correctly. About the only thing that you can easily scan sprocket holes on is double perf 16mm.

Posted by Kenneth Wuepper (Member # 1174) on 08-01-2007, 04:11 PM:

Perhaps the "black" is a threading leader material where the image and soundtrack are black but there are "clear" framing lines for loading into the projector. Reversing this leader material can cause the clear frame lines to be read by the sound scanner and would be 24Hz pulses of in phase sound information.

If the film is imaged, then the frame line 24Hz would be included in random picture information. The combination would be random noise with 24Hz pulses.

If the film is running at a different frame rate, the pulses would be that frequency.

A method for telling the speed of a machine is to feed the frame line scanned pulses into a frequency counter and read the frame rate directly from that counter. Flutter and wow will effect the accuracy of this measurement. It is a possible way to tell frame rate on a variable speed drive if the projector has a sound scanner that operates. (Most variable speed machines are used for silent film presentations)

KEN