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SPEED RAMPS in POST


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#1 James Mann

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Posted 19 November 2007 - 12:58 AM

Friends,

A quick question on the topic of speed ramps...

Getting ready to shoot an action film. We will have lots of off-speed stuff. Under crank. Over crank...

The director and I have carefully choosen our moments for the off speed work but want to reserve the right to change our minds down the road AKA after the film has been shot.

So I ask you:

Can we shoot at 60fps on the VARICAM, import the footage into FINAL CUT as 60fps and then
decide that we want to play the footage at 24fps instead? Will this look strange. Or will it play normally?

Yes, we could shoot it both ways (at 24fps and at 60fps) but I am wondering if that is neccesary.

Thanks,

James
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#2 Michael Nash

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Posted 19 November 2007 - 01:13 AM

You can change frame rates in post, but it's harder to change the motion sampling and motion blur captured by the camera.

Footage acquired at 60fps will use a shutterspeed of 1/120 second to appear "normal" as slow-motion footage. Dropping frames for normal-speed playback at 24fps will still have that fast-shutter look.

Similarly, footage shot at 24fps will have the motion blur of 1/48 second not 1/120, as well as having the motion sampling of 24fps (which means the playback will "step" because there weren't enough frames sampled for smooth playback at that speed).

There are software solutions that can create "tweener" frames to create smooth slow-motion from 24fps material, as well as add motion blur to fast-shutter material. But it takes finesse and experience with the software to make a convincing illusion of real slow-motion footage.
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#3 Stephen Price

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Posted 19 November 2007 - 04:02 PM

so is it right that you canot shoot all your non-sound sync shots at 60fps and decide later what speeds to play them back at? The motion will look different between the speeds?
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#4 Michael Nash

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Posted 19 November 2007 - 04:49 PM

so is it right that you canot shoot all your non-sound sync shots at 60fps and decide later what speeds to play them back at? The motion will look different between the speeds?


That's correct. 60fps material with a shutterspeed of 1/120 second will have motion that looks very "stroby," like that fast-shutter Saving Private Ryan or Gladiator look when you drop frames to make normal speed 24fps playback.

If you shoot with a longer shutterspeed (1/60 second is the maximum at 60fps), that motion will have a lot of video-ish motion blur when you use it for slow motion playback.

It's both frame rate AND motion blur that make a convincing slow-motion look.
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#5 Bob Hayes

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Posted 19 November 2007 - 07:44 PM

When shooting action footage for television series I got into the habit of just shooting everything at 48 fps. If I needed a speed ramp or slow mo I have the frames. If I wanted regular speed with a slightly narrow shutter I had that also.
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Aerial Filmworks

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CineTape

Media Blackout - Custom Cables and AKS

Visual Products

Gamma Ray Digital Inc

Willys Widgets

Technodolly

Paralinx LLC

Rig Wheels Passport

Broadcast Solutions Inc

rebotnix Technologies

Wooden Camera

Metropolis Post

FJS International, LLC