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FLickering HMI's at high speed.


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#1 Jase Ryan

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Posted 21 May 2009 - 05:12 PM

Hi there... I'm wondering if HMI's run at a different frequency than Tungsten lights. If I'm shooting high speeds that don't match with HMI's, will the same be for Tungsten lights? I know HMI's run at 50Hz.. do Tungsten? will this cause both lights to flicker at say 50fps?

Thanks.
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#2 Tom Jensen

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Posted 21 May 2009 - 05:29 PM

Harry says.....http://books.google.com/books?id=EfUlyxSlBYMC&pg=PA82&lpg=PA82&dq=flicker+free+frame+rates+for+HMI&source=bl&ots=gv8l8uhHLg&sig=psgNqp_yzkMoBk88YlgT9Cf7WfU&hl=en&ei=WtUVSu7cH52stgei97HjDA&sa=X&oi=book_result&ct=result&resnum=2

Edited by Tom Jensen, 21 May 2009 - 05:33 PM.

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#3 John Sprung

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Posted 21 May 2009 - 07:31 PM

Some HMI's run at the line frequency, 50 or 60 Hz depending where you are. That gives you 100 or 120 clearly defined pulses of light per second. Others have high frequency square wave ballasts to solve the flicker problem.

Tungsten lights pulsate at twice the line frequency, but not by a large enough amount to matter in most cases. Big ones, 5K and up, are especially good because the massive filaments take longer to cool, and thus smooth out the flicker even better than with little inkys.




-- J.S.
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#4 Jase Ryan

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Posted 22 May 2009 - 06:07 AM

I shot a scene that had a 1.2K HMI and a 1K Baby. We were shooting at 54fps and the HMI was flickering a lot but the Baby wasn't. But being at 54fps I thought would have been a safe frame rate. What rates are?
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