How Slow Can I Go....

[Brock Burwell]

I'm shooting football games at 60fps and I am slowing it down in post, but I was wondering if there is a general rule of thumb for how slow I can actually make this footage before it starts to look jittery. I currently have it at 40% in FCPX and it looks nice, but I didn't know if there is a general rule for these things. What about 96fps?

[Jon Fairhurst]

In general, slow it down to 24 fps or 30 fps. With 30, there's no "judder" as you're just repeating frames. With 24, you get a film like judder with 2, then 3 frames repeating. Any slower than 24 and it gets to be too slow. (And yes, 24fps is 40% of 60.) The faster you shoot, the stronger the slow motion effect. If you target 24, 30, of 60 fps as the end result, you're golden.

[Mike Watson]

What John said.

If you want to go slower, go in even fractions of your framerate. If you're going to 24fps, get it to 12 (20%), if you're going to 30fps, get it to 15 (25%). I don't know if this is acceptable anymore, but up until maybe 5 years ago, cameras that shot higher than 30fps were basically unheard of, and folks were used to the 15 or 7.5 fps flicker for slomo.

[Bruce Watson]

Originally Posted by Brock Burwell

I'm shooting football games at 60fps and I am slowing it down in post, but I was wondering if there is a general rule of thumb for how slow I can actually make this footage before it starts to look jittery.

The human visual system is... interesting. Some people are more sensitive to flicker than others. So... it depends.

The 24fps "standard" (we've ALWAYS done it that way, except of course, we haven't) was a limitation of audio, back when audio was recorded on the film strip right beside the individual frames. You had to push up to 24 fps to get acceptable sound. Before that, in the silent era, the "standard" was around (yes, it varied) 18 fps. Ask someone who's familiar with silent films, like a curator of films at a museum. Probably tell you more than you could ever want to know.

Anyway, it's more or less a moot point. Our current standard is either 24 fps or 25 fps depending on where you happen to live in the world. That's effectively your lower limit. To get slower motion, you either need to capture at a higher frame rate, or resort to interpolation software like Twixtor.

[Roger Shore]

Originally Posted by Brock Burwell

... how slow I can actually make this footage before it starts to look jittery..

The suggestions above are of course absolutely correct when considering 'standard' frame interpolation techniques...... You can go a lot slower than that - and still without any 'judder' - if you utilise software that uses 'optical flow' for frame interpolation...

The most famous tool for doing that is probably 'Twixtor', mentioned by Bruce in the post above, which is available as a plug in for most editors......Often thought to be a bit expensive though.....

You can achieve the same sort of thing for free, using an application like MVTools - although there is a bit of a 'learning curve' attached to that!

I made the clip here: http://www.jp137.com/lvs/boat.slox.mp4 using that freebie. Slowed the clip down 10x , and still no judder....(clip is about 30MB)

I also made some notes here: http://bit.do/SLOMO-Home on how to use MVtools if you're not familiar with the technique. ...I wrote the notes for my rather 'non-techie' brother, hence the 'left click here', 'right click there' type of approach......I hope that's not too distracting?....

Setting it all up is bit long winded..... using it after that is relatively simple...