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Magnetic HMI ballasts and 23.98fps


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#1 Bryce Lansing

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Posted 28 May 2010 - 10:02 PM

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?
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#2 timHealy

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Posted 29 May 2010 - 04:52 PM

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

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Posted 20 June 2010 - 09:51 PM

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.
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