Magnetic HMI ballasts and 23.98fps

[Bryce Lansing]

I got my Arri 1.2k HMI Par with magnetic ballasr, fully aware of the flicker issues. But now I'm a little confused...

 

I read that 24fps at 180 degree shutter (1/48th) was flicker free, but that 23.98 at 180 degree shutter was unsafe..

 

So first I test the Canon 7d at 24p (which is really 23.98 right?) at 1/50th, and sure enough, rolling bars. 1/30th, 1/40th, and 1/60th looked fine.

 

Then I tested my HVX200a, 24p (23.98 as well right?) at 180 degree shutter, and it from what I could see it looked completely fine. I know it has a global shutter so I wasn't expecting rolling bars, but it wasn't flickering at all either.

 

Why is this? Is 1/48th a flicker free shutterspeed with the HVX? Or am I not seeing a very subtle flicker?

[timHealy]

where are you and what kind of electricity are u juic'in this baby with?

[David Winters]

I got burned with rolling bars on a Red One M shoot. 23.98 1/48th, shooting 2 passes of a scene to be compt'ed together. In the end we cleaned it up in post, but now I shoot a test, wide lens on a even light surface to verify. If I don't have time to test I shoot at 1/40th or 1/60th. Some cameras appear to be more sensitive vs others. I've never personally experienced rolling bar issues on 3-CDD systems at 23.98 1/48th, but I have had problems with rolling shutter CMOS cameras. However, most of the time it's so subtle that it's not an issue.

 

Hope this helps.