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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Shooting 72fps for 24fps.

J

Jase

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Hi.

My question is, if you shoot 72fps in camera, but bring that back to 24fps in post, is there any issues or reason you might not want to do that? Heres why I ask...

I'm shooting a low budget show with a big action sequence. We have limited time to get the sequence done and we have 2 Red cameras. My plan is to shoot from 3 set ups, each set up running both cameras almost side by side, yet on different focal lengths. Say camera A is in 2K shooting 72fps with a 18mm lens (35mm lens) and camera B is in 2K shooting 72fps with a 50mm lens (35mm lens), then I would have the option in post to use either focal length at 72fos or at 48fps or 24fps. But of course if I shoot one at 24fps and the other at 72fps, then I am only able to use whats in camera. And if I did that, I would want to switch lenses so each focal length is captured at both 24 and 72fps. Technically, this would take twice as long to shoot as we would need to nail it for both before we move to the next set up where we do it all over again.

If anyone can give their advice and shed some light on this that would be great. I hope I didn't write it to confusing. Thanks!
 
you could always speed up the 72 in post so that yo can use that as high speed and normal speed and then you would not need a second setup to capute regular 24fps
 
Jase said:
Hi.

My question is, if you shoot 72fps in camera, but bring that back to 24fps in post, is there any issues or reason you might not want to do that?
Click to expand...

In a low-budget production it's more important than ever to test, because you don't have the money to re-shoot.

With that out of the way... It might work really well, but the 72 fps camera will have a different shutter speed than the 24 fps camera. When you return it to 24 fps, (throwing out 2 of each 3 frames) it will look different, because each frame will be sharper. In an action sequence, that might be a look you like, so you might want to set the 24fps camera's shutter to match. So test it. Shoot a rehearsal, cut it together, and see what you like and what you don't.
 
Extracting 24fps out of 72fps with RED is not a great idea and I would reccomend against it.

Shoot 24 frame material at 24 and 72 frame material at 72fps. All of this happens in a 23.98 time base.

The RED records film style slow motion so it captures 72 frames per second (overclocking the sensor). it then plays that material back in a 23.98 time base.

So you are capturing all of those frames and actually seeing "inbetween" the action.

It is not the same as recording 24fps and making 24fps play back 72 fps. This method (as you might do in FCP or AVID relies on "frame interpolation". That means it is building frames to achieve 24 fps.

SO I recommend the following tests:

1. Set the camera to 23.98 time base.
2. shoot 24P material of a scene.
3. set the camera to 72FPS in varispeed mode and shoot a scene.
4. Play back both in a 23.98 sequence.
5. Duplicate the sequence.
6. Set the speed of the 24P material at 33% speed (72fps) and you will see how different the slomo is.

7. Try to get your 72fps material to 24fps (and we will be answering questions from your editor who will posting here to try to FIX the big problem that was created when you assumed it would all work).


Get a primer on film slo-motion and understand that RED works the same way. Like a FILM camera, not one of these faker slomo video camera's.

David


]
 
As to your lens problem.

Put the 24fps takes on a 50mm and the 72FPS takes on a 24mm.
or use zooms to make your life easier.

IE 17-35 zoom is easy to switch from 35mm on the 24fps to 17mm on the 72fps in 2K.

David
 
This seems like a bad idea, but theoretically it should work if you communicate carefully with your post house.

You can use After Effects (or probably even Cinema Tools) to tell your 72fps footage, which will appear natively as 23.976fps footage slowed down, to actually play back at 72fps (technically, 71.928fps), in which case if you put it in in a 23.976 composition with frame blending turned off and then export it...it should turn into "legit" 23.976 footage.

Of course (assuming you shoot with a 180º shutter), your footage will look like it was shot with a 60º shutter when played back at 24fps. So your slow motion will look normal and your regular motion will look choppy even once you get past the weird workflow quirks (and inherent loss of resolution from shooting 2k, which may be okay on the MX but is extremely soft on the original red due to an over-aggressive anti-moire filter). You can use a motion blur plug in to fix the choppiness and maybe unsharp mask to correct for softness, but that's all unreliable--and now it's getting more complicated/expensive on the post side.

It seems like an idea that's cleverer than it is practical. But for a one-off shot or something where I knew I could finesse it in post, sure I'd try it. For an involved sequence...probably not.
 
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Thanks for the replies. In regards to what Matt W. said, is there a shutter angle we could shoot the 72fps at that, when played back at real time (300%) would look similar to a 180 degree shutter shot at 24fps?

Thanks!
 
If you used a 360º shutter at 72fps, it would look close (it would look like a 120º shutter). But then your 72fps footage would look a bit "video." It's a trade-off; either way slow and normal motion look different, it's just a choice of "too smooth" slow motion or choppy regular motion. For the 300 when they did speed ramps, they shot with a 180º shutter at high frame rates--but they treated it in post (with Nuke, likely, but you can do it in After Effects) so it didn't look too choppy at regular speed. So I'd take that approach if I chose to do it in post but...it's a pain.

I'd just shoot it once normal, once in slow motion. Assuming you're not shooting in 24fps wide open, you can compensate for the light loss (1.3 stops, I think?) by opening up your aperture, which will make the DOF seem more consistent between slow motion takes and normal takes (due to cropping, etc.)
 
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