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25 fps and 60 Hz HMI


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#1 Sam Nolan

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Posted 13 October 2008 - 08:59 PM

Last week we did a shot using an HMI as our only source, and after it was done realized the camera had been accidentally set to 25fps.

We thought it was fine since there was no dialogue and it was a quick shot. But now I realized - the HMI ballast was not set to flicker-free, and we were on 60Hz lighting. Shutter was at 180. Can anyone give me an idea as to how likely flicker will be, and/or what it will look like (fast, slow, etc.)?

Thanks.
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#2 timHealy

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Posted 13 October 2008 - 09:37 PM

I have worked so hard not to be in that situation I have never seen it happen.

However, as explained to me by an HMI technician at a rental house a few years ago, electronic ballasts are flicker free even in the "silent" 24 fps setting for a small range like 20 to 30 fps. When switched to the "flicker free" setting, the light is flicker free for everything else (up to the manufacturers ratings).

There is absolutely no guarantee here, but there is a small chance you may be OK.

If you were using magnetic I would say you will have flicker.

But please by all means, post your results when you see your dailies.

Good luck and looking forward to hearing from you.

Best

Tim
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#3 timHealy

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Posted 13 October 2008 - 09:44 PM

always helpful

http://www.cinematog...lickerfree.html

but I believe these are for magnetic ballasts and safe settings in the non "flicker free" all the time mode.

best

Tim

Edited by timHealy, 13 October 2008 - 09:46 PM.

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#4 Martin Solvang

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Posted 25 October 2008 - 06:43 PM

Hey..
I live and work in Norway, and we do most of our stuff in 25 fps.
Shooting with HMI in 60 hz is no prob.
Shooting 50 fps without switching on flicker free is dangerous ..(worked on a commercial in my
early days as a gaffer..and learned the hard way..)
still...let us know..
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