December 9, 2015 at 5:28PM

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You voted '+1'.

Speed ramping HELP!

I want to shoot a video where I can be able to play with the speed ramping. By this I mean, the subject moves in full speed, slows down for a few seconds (VERY SMOOTHLY) and then goes back to normal speed. I own a GH4, I've been heard I should shoot at 60 fps so I can slow down the clip, I've ran some tests (with Twixtor) and the results have not been quite as I expected. Can anyone help me out with this? At what speed should I set my shutter? Should I film at 60fps? Which software should I use to slow, how should I do it? I would be FOREVER grateful for a complete answer to this question that is driving me nuts. Cheers.

8 Comments

Not sure as I haven't used it before but I do know that the shot has to be set up very carefully and filmed in a special way... better ask YouTube...

December 9, 2015 at 5:45PM

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Clark McCauley
Spaceman
1797

Thanks Clark, I've searched in Youtube but haven't found anything REALLY helpful tbh.

Tommy Plesky

December 9, 2015 at 6:47PM

I've seen some great work done with Twixtor, so it sounds like you are definitely on the right track.

As far as shooting goes normally you set your shutter speed to be...

1 / frame-rate x 2

So if your maximum Twixtor FPS is 250, then you would shoot with a shutter speed of 1/ 250 x 2 = 1/500 sec. Slower than this may cause blur issues when Twixtor manipulates the image.

I would also be careful about rolling-shutter, as that's a different problem that Twixtor will have to deal with, and may screw up your final result.

December 10, 2015 at 10:58AM

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Guy McLoughlin
Video Producer
33037

So if Im at 60 fps, my shutter should be 120 or more? Btw, thanks for the answer.

Tommy Plesky

December 10, 2015 at 11:28AM

>>>So if Im at 60 fps, my shutter should be 120 or more?

Yes, if that's the frame rate you are going use with Twixtor.

If you shoot at 60 fps, but are going to use it at 300 fps in Twixtor then you want to shoot your 60 fps footage with a shutter speed of 1/600 sec.

It doesn't matter what fps speed you shot the footage at, what matters is the frame-rate you are going to use the footage in Twixtor.

December 10, 2015 at 7:22PM, Edited December 10, 7:23PM

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Guy McLoughlin
Video Producer
33037

Thanks, Guy, aprecciate it, Im gonna run some tests with a higher shutter speed then!

Tommy Plesky

December 11, 2015 at 2:16PM

We can only offer theoretical advice if you don't show or at least describe how the footage didn't tun out as expected. Slowig footage down can create all kind of different problems and artifacts caused be all kind of various factors: background vs foreground, patterns and textures, the type of movement (lineair vs 'bouncy-organic'), direction of movement (to/from camera or sideways).
Shutterspeed is also a factor, indeed.

December 11, 2015 at 3:27AM

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WalterBrokx
Director, DOP, Writer, Editor, Producer
9766

I tested/used twixtor quite a lot once, but it's long time ago by now..

Guy is probably onto the right track with the shutterspeed. As far as i remember it though, i found twixtor to work best with really high shutter speeds (like 1/2500) and as high fps as your camera can go.

The reason why Twixtor most of the time screws footage up is shooting your subject on a to complicated background. Twixtor works by creating/guessing/interpolating all the frames in between the "real" frames.
If the shot is complicated twixtor can't figure out what is moving and what is not. The distance to the subject also matters as relativity makes subject "move" slower (or what you would call it ;) )

Philip Bloom wrote a pretty good post about it: http://philipbloom.net/blog/twixtor/

December 12, 2015 at 1:59PM

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