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This topic comprises 3 pages: 1 2 3
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Author
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Topic: Projector speed issues
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John Hawkinson
Film God
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Posts: 2273
From: Cambridge, MA, USA
Registered: Feb 2002
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posted 02-08-2004 01:55 AM
I'm a bit confused -- why is it hard to reach 24.0fps with your system? Insufficient resolution in the frequency adjustment? or lack of a strobe/photocell/oscope?
(I think that hitting it to 3 significant figures is proably what you want to shoot for; in an optimal world).
Probably a better way to look at it, though, is what your maximum frequency error is. Some quick googling suggests that an average human can detect approx. a 2 Hz difference around 400 Hz. So shooting for 1 Hz accuracy sounds good. 402Hz/400Hz is 0.5%, though 4002/4000Hz is 0.05%. If we assume the former is good enough (i.e. absolute Hz difference a human can detect falls off with frequency), then 0.5% of 24fps is 0.12fps.
In short, your 24.1fps is probably good enough for 2 Hz accuracy, but not for 1 Hz accuracy.
If you get to 24.0fps (i.e. as much as 0.05fps off), that's 0.2%, or 0.9Hz at 400Hz and 9Hz at 4000Hz.
So, again, I would shoot for 24.0fps, which is barely under 1Hz error, but anything +- 1.2fps is probably good enough for most people.
--jhawk
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