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Old June 6th, 2005, 10:40 AM   #1
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Undercranking

Okay, so slow motion has been discussed to death. One of the best methods for slow motion is shooting interlaced at, say, 1/100 shutter, then slowing down in post usingthe alternate interlaced lines to produce really smooth half speed slow mo.

However, not a lot has ever been said about undercranking. Does anyone know of any decent method to get a 10 or 20 percent increase in footage speed without horrible motion blur or a jerky motion every few frames or so?

Reelviz is said to do undercranking but I can't find any examples that have been produced with it.
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Old June 6th, 2005, 03:20 PM   #2
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do it in after effects
capture your footage
de-interlace
import your new 30p footage
time scale to 500%
render with frame blending off
re-import your footage
adjust your footage back down (in negative %)
re-render with no frame blending

taadaa. instant kerky cam undercrank effect!
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Old June 7th, 2005, 01:23 PM   #3
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Simon, yeh, good question. There not much call for that effect, but it would be good to know how to do.

Does anyone know if they actually decrease the shutter speed when overcranking? Say shoot 15 frames a second, but use a 1/30 shutted speed so the ratio of frames to shutter speed is the same as 24 & 1/48?

For starters, have you seen the shutter tools over at http://www.de-interlaced.net? Unfortunately, it looks like the site is down right now, but he's got some great tools for AE that simulate long and short shutters, especially for use with slow-mo, fast-mo effects. His demo footage will blow your mind.

OK, that may not exactly be what you are looking for, but I have another idea. As with slow-mo, the trick to getting smooth looking motion for undercrank will probably be the ratio you use. If you increase the speed by 2, so that half the frames are dropped (I'm assuming progressive frames, but the same would apply to fields), it should probably be smooth. Increase by 20 or 30% and you get into a situation where it will use a strange pattern of frames of fields and result in jerky motion. I have done this myself without realizing it before.

So, you should easily be able to double the speed. I have another idea, though, if you are into 24p.

Say you shoot 60i. Deinterlace to 30p (I use DVFilm Maker). Speed up 200% without belnding so that half the frames are dropped. Finally, interpret the footage to 24p. This will turn one second of 30p into 1 second and 8 frames of 24p. So, you sped it up, now you slow it down, but the motion should still be fine, because the pattern of frames used remains the same.

So, how fast is it? Two seconds of 60i become 1.3 seconds of 24p. That's a 65% increase, instead of a straight doubling for 100%. So, there are a few options.

Hey, low-fi option. Have your actors move really fast!
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Old June 7th, 2005, 01:52 PM   #4
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Very few digital camcorders allow for over and under cranking (i.e. variable frame rates) unfortunately - the new HVX200 will apparently do so, however, so that might sort you out. It is a film camera technique, primarily.

BTW, to get slow motion you need to overcrank the camera, not undercrank it - 15fps shooting speed will give you a 100% *increase* in speed (assuming NTSC system).
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Old June 12th, 2005, 05:24 AM   #5
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Isn't the term overcranking? Ie, on a film camera overcranking should speed
up the film, which, when played back at normal speed, produces slow motion.
I'd say undercranking would produce fast motion, not slow.

I could be wrong on this though....
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Old June 12th, 2005, 06:00 AM   #6
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You are correct. Thats why I started this thread. Speeding up video to different degrees, say a 110% speed increase, without inducing horrible motion blur or motion stuttering, is harder than creating slow motion. So I wanted to know if there were any good ways to speed footage up by small amounts thereby replicating undercranking on film cameras.
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Old June 12th, 2005, 06:16 AM   #7
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I see I misread the content indeed, heh. I only did a speed up once (classic
POV from within a car) and it looked fine. Used Vegas 5 for that. This was
done in interlaced by the way. That's all I can say about this I'm afraid.

Good luck!
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Old June 13th, 2005, 06:36 PM   #8
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My only "real" film experience is Super8, but my understanding is that when you under-crank in a "real" film camera, your shutter speed decreases proportionally. So, if you're running the camera at 12fps, rather than 24, the shutter is open for twice as long per frame. When you speed up video, you'd have a hard time duplicating this effect, Perhaps you could blend adjacent frames (I think it's called "temporal blur" in VirtualDub) to achieve an approximation...

My old Panasonic DA-1 (single CCD MiniDV - circa 1998 ish) has a "gain up" mode which seems to achieve its effect by some sort of additive frame-blending approach. It really gives you that slightly smeary temporal effect, and I've used it to great effect when I've shot something with the intention of speeding it up later. Pretty much useless for "regular" shooting though.

I don't know if any of that helps...?
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Old June 13th, 2005, 09:45 PM   #9
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yeah... real undercranking gives a proportionally slower shutter speed. although some movie cameras (like bolexes) have adjustable shutter angles to compensate. (if you adjust from a 180 deg shutter to a 90 deg, you keep the same shutter speed at 12 fps as you had at 24, which is 1/48th.)
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