Jump to content


Photo

HMI + Alexa


  • Please log in to reply
4 replies to this topic

#1 Marie Davignon

Marie Davignon

    New

  • Basic Members
  • Pip
  • 9 posts
  • Cinematographer
  • Montreal, Quebec, Canada

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!
  • 0

#2 David Mullen ASC

David Mullen ASC
  • Sustaining Members
  • 16064 posts
  • Cinematographer
  • Los Angeles

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.
  • 0

#3 Marie Davignon

Marie Davignon

    New

  • Basic Members
  • Pip
  • 9 posts
  • Cinematographer
  • Montreal, Quebec, Canada

Posted 19 June 2011 - 03:20 PM

Thanks!
  • 0

#4 Phil Rhodes

Phil Rhodes
  • Sustaining Members
  • 9609 posts
  • Other

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
  • 0

#5 Gregory Middleton

Gregory Middleton
  • Basic Members
  • PipPip
  • 78 posts
  • Cinematographer
  • Vancouver BC

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!


  • 0


K5600 Lighting

Robert Starling

Zylight

The Slider

Glidecam

Cinelicious

Paralinx LLC

Visual Products

rebotnix Technologies

NIBL

CineLab

CineTape

Rig Wheels Passport

Cadrage Directors Viewfinder

Aerial Filmworks

Abel Cine

Pro 8mm

Media Blackout - Custom Cables and AKS

Ritter Battery

Robert Starling

Visual Products

Abel Cine

NIBL

CineTape

Cinelicious

The Slider

rebotnix Technologies

Paralinx LLC

Rig Wheels Passport

Pro 8mm

K5600 Lighting

CineLab

Media Blackout - Custom Cables and AKS

Cadrage Directors Viewfinder

Zylight

Ritter Battery

Glidecam

Aerial Filmworks