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HMI + Alexa


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#1 Marie Davignon

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Posted 16 June 2011 - 07:49 PM

I have an important question :

Do I need to use flicker free HMI ballasts when shooting with the Alexa at 24 fps? 23,97?
Does it work like the RED, with a rolling shutter that can make some lines moving through the frame?

Thanks!
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#2 David Mullen ASC

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Posted 16 June 2011 - 07:57 PM

I haven't had problems with older HMI's on either the Red or Alexa. Yes, the Alexa has CMOS sensor with a rolling shutter.

At 23.98 fps, you are on the edge of flicker but usually it's not noticeable unless you look at a waveform monitor.
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#3 Marie Davignon

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Posted 19 June 2011 - 03:20 PM

Thanks!
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#4 Phil Rhodes

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Posted 19 June 2011 - 05:09 PM

I have seen a 60Hz HMI flicker on a 7D at 1/60 shutter.

There appear to be no rules.

P
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#5 Gregory Middleton

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Posted 28 June 2011 - 06:03 PM

Its always safer to shoot flicker free. You should be able to see any issues on the waveform however. Sometimes it will only show up from 1 light or at a particular angle depending on conditions as a very slow pulsing density shift.
Flicker free will make sure however of no issues at 23.98
Beware fluorescents in locations with magnetic ballasts however.

I have an important question :

Do I need to use flicker free HMI ballasts when shooting with the Alexa at 24 fps? 23,97?
Does it work like the RED, with a rolling shutter that can make some lines moving through the frame?

Thanks!


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Pro 8mm

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Rig Wheels Passport

Tai Audio

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CineTape

CineLab

Cinelicious

Media Blackout - Custom Cables and AKS

Aerial Filmworks

Paralinx LLC