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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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Visual Products

Rig Wheels Passport

Media Blackout - Custom Cables and AKS

NIBL

ORCA Bags

rebotnix Technologies

Paralinx LLC

CineLab

Abel Cine

PLC Electronics

CineTape

Robert Starling

Cinelicious

Tai Audio

K5600 Lighting

MustHD Monitors

The Slider

Zylight

Pro 8mm

Ritter Battery

Aerial Filmworks