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Canon C300 slow motion and frame rates issue

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Andy Jarvis
Canon C300 slow motion and frame rates issue
on May 16, 2015 at 6:29:33 pm

Hello. I shot some footage of some people dancing with 2 x C300 cameras. I had one recording as normal at 1920x1080 25fps and the other at 720 and 50fps using Special Recording > Slow Motion. The plan was to have the second camera footage available in slow motion for a certain section of the film but also to double the speed of it in post to be able use it in sync with the other camera in normal speed.

The slow motion footage looks great, as expected. But when I double the speed of it, it looks a bit weird, a bit jittery, almost like it was shot at a very high shutter speed. It turns out that the C300, whilst filming at 50fps, recorded the data to the card at 25fps. So I guess what I'm seeing is 50 frames squeezed into a 25 frame sequence.

My editor is using Avid.

Is there anything I can do to make the second camera footage match the first, i.e. look normal?

Any suggestions greatly appreciated.


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Todd Terry
Re: Canon C300 slow motion and frame rates issue
on May 16, 2015 at 11:43:56 pm

Is it possible for you to post a clip so we can see exactly what it looks like?

You say that it "almost like it was shot at a very high shutter speed." So it has the strobby "narrow shutter" look?

Well... you have to remember that it was shot at a much-higher-than-normal shutter speed compared to a "regular" fps setting. So... it looks like a higher shutter speed because it is a higher shutter speed.

Let's say I usually shoot at 24fps, which here in the colonies, I do. At that rate, my "normal" shutter speed that I'd usually choose would be 1/48th of a second ("normal" being one over twice the frame rate, emulating a 180° shutter in a film camera). Then, I shoot some overcranked footage for slow-motion work, at, say 60fps. For that footage my shutter speed would be 1/120th. The slow-mo footage would look great. But lets say I want to present this footage at "normal" speed, not slow-mo. I can easily do that, yes. BUT, even though the footage now has the framerate appearance of being shot at 24fps rather than 60fps, the shutter speed is still 1/120th. Ergo, there is much less motion blur than if I had shot the footage at 24p, and we have that strobby staccato look... the "narrow shutter look" (i.e., "Gladiator" or "Saving Private Ryan").

I'm not saying that this is what you did, but I've heard numerous people in the past say "I might want to slow-mo some of this footage so I'll shoot everything at a faster framerate, because I can always return it to normal speed in post." Bad BAD idea, because you are always locked in to footage with the higher shutter speed, no matter what the framerate is. These days in post we can do almost any kind of image manipulation imaginable, but shutter speed is one of the things that you are locked into and can't change... once it's shot.

It's a much better idea to always shoot at whatever fps your project is (24p, 25p, 30p, whatever), and only overcrank just for the shots you want to slow-mo. You'll get infinitely better results that way.

OR... your issue could be something completely different and I'm talking out of my ear. If we could see a sample that might clear things up.

T2

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



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Andy Jarvis
Re: Canon C300 slow motion and frame rates issue
on May 17, 2015 at 11:50:25 am

Hello Todd, thanks very much for your very constructive comments.

Here are a couple of quick clips. This is 50fps footage at 200% speed. Weirdly, the effect I'm talking about is much less pronounced on the second clip.

https://vimeo.com/128055886
https://vimeo.com/128055887
password: c300

I've just checked with my camera guy and yes the shutter speed was cranked up to 1/100 for the 50fps shots. So it looks like I'm stuck with it. Which is all very well as a creative choice but not so much when cutting with 25fps clips which don't have that staccato effect. But do have a look at the clips and I'd appreciate any more comments.

Cheers...


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Todd Terry
Re: Canon C300 slow motion and frame rates issue
on May 17, 2015 at 3:43:56 pm

Ah... yeah. The shutter speed is definitely your issue. What you are seeing is exactly as if you were shooting at 25fps, but with a shutter speed of 1/100th.

Stop the footage on any of the action and look at a still frame, as you'll see there is very little (if any) motion blur in the frame, much less than 25fps footage shot at 1/50th would have had. Your brain needs that motion blur to interpret it as smooth motion, without it you get that staccato look.

And sadly that's really one of those things you can't do much about. If it had been something like a constant pan you might could judiciously add some directional blur that might help... but in this scene you have all kinds of things going in all kinds of directions (and some things like people's faces not moving much), so you can't do it that way... you'd have to do hours and hours of painstaking rotoscoping to add appropriate blur.

MAYBE there is some kind of high-end voodoo that has the ability to mesh the two frames (remember you are only seeing half of the frames) and interpolate what the motion should like like (sort of a "reverse Twixtor"), but I've never heard of such a thing. Maybe it exists, but if so I don't know about it.

Unfortunately shutter speed is pretty much a "baked in" setting... once you've got it, you've got it.

T2

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



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Blaise Douros
Re: Canon C300 slow motion and frame rates issue
on May 18, 2015 at 11:04:29 pm

In Adobe CC apps, there are a few settings that can mitigate the worst of this--one of them is a checkbox for frame-blending, which is basically the interpolation software that Todd was mentioning. I don't know Avid at all, but if there's a frame-blending option, you (or your editor) might consider using it.


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