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Normal-to-Slow Motion Shutter Speed and Frame Playback Rate

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Rob Jennings
Normal-to-Slow Motion Shutter Speed and Frame Playback Rate
on Jan 7, 2015 at 9:43:30 pm

I'm planning to shoot basketball footage and would like to play with time remapping in post. Most footage will play back at normal speed but spectacular highlights will slow down using time remapping. I want to avoid using Twixtor if possible to avoid possible warping against irregular backgrounds in the crowd. I'm fine slowing native 60fps footage but I'm concerned about shutter speed and frame rate for playback.

If I shoot 60fps @ 1/1000 (it will be a fairly dark so I can't push it much faster than that) I'm concerned that I will have a staccato effect on normal playback. On the other hand, I don't want slow motion footage to be to blurry. Should I shoot closer to a natural blur at something like 1/250 or 1/500? What would you recommend for the sequence settings? I'm thinking keep the sequence at 60fps and slow it down to half speed rather than play 60fps footage @ 30fps just for the sake of having cleaner slow motion.

Thoughts? Thanks in advance.


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Todd Terry
Re: Normal-to-Slow Motion Shutter Speed and Frame Playback Rate
on Jan 7, 2015 at 10:07:22 pm

It's a little bit of a "I want my cake and eat it, too" situation, as you simultaneously two things that are very different.

It's not quite "I can only have one thing, so I'll have a pork chop and a piece of cake," but it's similar.

The simple fact is, that the best shutter speed for slow-mo and the best shutter speed for normal footage are going to be two very different things.

The best you can do there is find a happy medium that doesn't compromise it too much.

Firstly though, 1/1000th is way overkill for a basketball game... you likely don't have to shoot nearly that fast to give you sharp enough action for decent slow-mo. It depends on how much you are going to slow it. If you are shooting 60fps for slow-mo (I'm assuming for a 24p project) to get a 40% slow-mo... then the "normal" shutter speed for the 60fps footage (which would be 1/120) should be absolutely fine. Any faster than that and you risk getting choppy staccato motion in your slow-mo as well as your normal speed footage.

Even at 1/120th though, you still will get some of that staccato look in your normal-speed footage... but it really can't be helped. It will be there, but on the bright side (if there is one) it shouldn't be as bad as your 1/1000th footage. Not quite like "Gladiator," heaven forbid.

There simply is no single shutter speed that works perfectly for both scenarios, each has the one that works best for them. Find a happy medium.

If you notice how this speed-ramp effect is done in movies (or more commonly, commercials), they tend to use higher shutter speeds so the slow-mo looks good and just live with (or maybe even desire) the staccato look for the normal footage

Best thing to do is grab a camera and run some tests... just don't bother with anything nearly that fast because it is unnecessary.

T2

__________________________________
Todd Terry
Creative Director
Fantastic Plastic Entertainment, Inc.
fantasticplastic.com



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Richard Herd
Re: Normal-to-Slow Motion Shutter Speed and Frame Playback Rate
on Jan 10, 2015 at 12:01:50 am

Motion Shutter Speed is calculated as follows: Frame Rate * Shutter Angle. dSLRs do not have an option to control the shutter angle, the next step up in camera pricing allows the shutter angle to be controlled. If your camera does that, it might be called something else, like syncro scan.

In normal motion photography, regular sync sound at 24fps, with a 180-degree shutter angle, the shutter SPEED is 1/48. When shooting overcranked, say at 60fps, with a 180-degree shutter angle, the shutter speed is 1/120. Halving everything again, means the shutter angle of 90-degrees, at 60fps, gives you a shutter speed of 1/240. Check my math, but a 1/1000 shutter speed at 60fps is a shutter angle of 16-degrees. At those fast shutter speeds, you run the risk of creating funky-jerky-feeling footage. I call it "feeling" because, as an audience, we are used to seeing the motion blur of 1/48 and 1/240 shutter speeds.

You might try them all and vary the ISO as you go. See what happens, being sure to get your required shots, of course.


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