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HMI ballast and camera setting for non flicker


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#1 igus mikler

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Posted 06 August 2006 - 09:28 AM

Hey there!
I am having a 1.2K HMI on the set today and the sony FX1, shooting 1080i 30fps. I am unsure about the ballast, if its flicker free or Magnetic. If it turns out to be Magnetic, do I set the shutter speed to 1/60 or what is the process? and if its the flicker free ballast I dont got nothing to worry about right? my intendend shutter speed is 1/48.
appreciate any help!
thanks!

/mikus
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#2 peter kantor

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Posted 06 August 2006 - 10:05 AM

here's what i've learned

magnetic ballast contain a copper coil so tend to be heavier. Flicker free ballast achieve the electronic equivalent using solid state devices which weigh much less.

there are frame rates that are safe to shoot with, and others that are not with a magnetic ballast. they have less buttons/controls on them ..usually just the ignite(red) off(black) and a circuit breaker

electronic ballasts usually have a silent mode and a flicker-free mode. thus flicker-free makes some noise and silent mode does not ensure flicker-free. they may have a type of dimmer other settings and many models have a detachable power cable (the male edison ended power cable)

since your medium is digital, you can use a monitor in good faith because wysiwyg
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#3 Brian Drysdale

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Posted 06 August 2006 - 10:33 AM

Hey there!
I am having a 1.2K HMI on the set today and the sony FX1, shooting 1080i 30fps. I am unsure about the ballast, if its flicker free or Magnetic. If it turns out to be Magnetic, do I set the shutter speed to 1/60 or what is the process? and if its the flicker free ballast I dont got nothing to worry about right? my intendend shutter speed is 1/48.
appreciate any help!
thanks!

/mikus


At 30 fps you'll be safe with a shutter speed of 1/60th sec - assuming your mains frequency is 60 Hz.

With a flicker free ballast you'll be safe, however, if you disengage flicker free use the above setting.

You'll see any flickering on your monitor, it's a good idea to keep an eye out.
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#4 David Mullen ASC

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Posted 06 August 2006 - 10:57 AM

You should be safe even at 1/48th because it's within the margin of tolerance, but you'd be even safer at 1/60th for 60 Hz lighting / power. Besides, if you are shooting at 60i, there's no real reason to prefer 1/48th over 1/60th except for the slight increase in exposure.

It might not even be an option since in theory, the longest exposure time at 60i is 1/60th (if you're capturing 60 fields per second, i.e. 30 fps in interlaced, then you can have a per-field exposure longer than 1/60th of a second without actually dropping the field capture rate.) Some cameras lose vertical resolution when shooting at shutter speeds longer than the capture rate. Remember that 1080i at 30 fps is actually 60i/1080.
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#5 Matt Workman

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Posted 06 August 2006 - 09:25 PM

I have a Lee HMI and Visual Products after some heavy debugging (some adjustments) found out that my G&E HMI bulb flickers. They swapped it for an Osram and it worked flicker free.

Something I wish someone told me before I bougth two G&E bulbs, ouch.
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