Working with 120 fps Footage

I think for some reason the little Sony ( a very nice camera ) is a little prone to being sensitive. I don't have one. I got some footage from a friend so I could test my computer using 4k S log, so he sent me stuff on a memory stick straight from his camera.

This is 2 minutes and if you look carefully you can see some lights strobing.

TOM FINISHED on Vimeo

To me this is complicated cause one would think that 30fps at 180 would be the only safe U.S. combination.

This video sample is the U.S. on 60hz grid, so 23.976 ( or 24) fps should be fine with a 180 deg shutter.  In the UK, France, you'd have to be at around 171 deg shutter I think ( or 25 fps at 180 ) cause they are on a 50hz grid.

The shutter and fps combination is really important ( boils down to fps and shutter SPEED).

Some LED's are further confusing things due to some strobing on some of those ( and of course fluorescent and sodium vapor are fun too )… but basically what comes out of the camera is the main thing to start with.

So if you are getting strobing from lights, or from sunlight, double check your shutter ANGLE ( there are charts that will give you equiv angles to 'speeds' settings...  ( e.g. 180 at 24 fps would be 1/48th of a second ).

Interesting. Unlike incandescent light sources which are simply a glowing filament providing constant light (similar to a candle flame), other sources like flourescent and LED actually flick the light source on and off very rapidly. Looks like a steady light to our eyes, but cameras can pick up the flicker due to shutter opening and closing and catching the light when it is OFF/cycling. Looks to me like this is the issue - if the light source on tree was constant, there would be no dark frames in playback, because the light would always be on.

I believe the problem is inherent in the footage as shot and nothing to do with slow-motion in Premiere. There are third-party plugins available to repair. search web for "flicker fixer".

Try this - open a 60p project. Import the 120p clip, and interpret as 120fps. This should double the length when clip is put on timeline. Now play the footage frame by frame using arrow key. You should be seeing every single frame you shot. Bet you have frames with lights on, and frames with lights off. You don't notice flicker when playing the footage realtime in 24p sequence because you are not seeing all the frames, or they blend together.

Thanks

Jeff

EDIT: remember watching old Westerns and the wagon wheels seem to turn backwards? Due to how the shutter freeze-frames the spokes at various positions in time. I am now seeing this same phenomenon on the aluminum-spoke wheels of cars driving next to me on the expressway! Now, my eyes don't have shutters in them, so the only explanation is that the new type of highway lighting being used is flickering, so the wheel spokes are not constantly lit and like the old film camera shutters, light up the wheel spokes with such timing that causes them to appear to spin in reverse. Wild. With steady (incandescent) lighting, the wheel spokes should be a blur at 70mph, but I can see the spokes due to flickering lights. Like a strobe light. Any old-time mechanics here that have used a timing light? Then you know exactly what I am referring to!

Thanks, Jeff. I think what we've described is two ways of achieving slow motion - interpreting high frame rate as lower or dropping high frame rate into a lower frame rate sequence and changing clip speed. You don't lose the frames when reinterpreting - the clip becomes longer.

In either situation the strobing is still there. Tried both.

It's very similar to shooting a monitor or under fluorescent lights that have refresh rates that cause flicker at certain shutter speeds and frame rates.

I was able to eliminate the flicker by converting 120 fps to 60 fps. Still able to get slow motion slowing down to 23.98 but not as much as going from 120 to 23.98.

Thanks,

James