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Variable Frame Rates


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#1 Curtis Bouvier

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Posted 13 February 2007 - 01:57 PM

It seems the majority of scenes in movies are reduced in speed to some degree, obviously some more than others. but for the most part it feels as if this is one of the bigger tricks as to what makes a movie LOOK like a movie.

Any footage that I see filmed with interlaced tape, If i reduce this speed by about 25% so its playing at 75% instead of 100%, it Instantly starts looking more like a film. its a little choppier in frame rate and everything is so much smoother looking, speaking in terms of movement.

Since film cameras can shoot 1-75 frames per second, this is clearly a must for film making, as different degrees of speed bring out your artistic touch to certain shots.

can anybody with alot of experience in this please embelish?

thanks.

Edited by Curtis Bouvier, 13 February 2007 - 01:58 PM.

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#2 David Mullen ASC

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Posted 13 February 2007 - 02:37 PM

Just depends on the type of movie. A dialogue-heavy movie shot on film is probably going to mainly stick to 24 fps sync-sound. An action movie may vary frame rates and shutter speeds more often for effect.

I haven't played much with off-speed shooting myself though. I once did a fight scene where I shot someone hitting the ground at 20 fps (I think) to make it look like a faster, harder land.

But you're describing a different effect altogether, taking interlaced-scan footage (normally shot at much higher motion sampling rates like 60 versus 24 like with film) and altering the speed, causing some jumpiness in motion that is more like the look of 24 fps / 24P.
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#3 Michael Nash

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Posted 13 February 2007 - 09:48 PM

Any footage that I see filmed with interlaced tape, If i reduce this speed by about 25% so its playing at 75% instead of 100%, it Instantly starts looking more like a film. its a little choppier in frame rate and everything is so much smoother looking, speaking in terms of movement.


Interlace video is 30 fps (60 fields), and movies are filmed at 24fps for normal speed. Slowing 30fps down by 75% would yield 22.5 fps, much closer to 24 -- so that's a lot of the difference right there. And the interlaced nature of fields gives it that "jumpy" quality when played back at 75%. So what you're noticing is the difference in motion rendering between 24 progressively captured frames, and 60 interlaced fields.

As for off-speed photography, it's true it's done far more often with film than with video, since video hasn't been able to shoot alternative frames rates, at least not very easily, until recently (there have been high frame rate video systems used in sports for some time, but you rarely saw it anywhere else). Now you have cameras like the Panasonic Varicam and HVX200 which can shoot varaiable frame rates, progressively captured. They too look much more like film than video.

But most movies still stick to 24fps for a majority of the scenes, and usually only go off-speed for creative effect. For one thing, you can't shoot synch-sound at anything other than 24fps, at least when making theatrical prints. If a scene has dialogue in it, you can pretty much bet it's 24fps.
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