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Arri Lighting and Flickering with HD


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#1 anwar alyasri

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Posted 21 June 2006 - 07:50 AM

I am facing a problem witth my arri lighting setup (HMI) i am getting flickering in my picture when i am shooting high speed (50 or more) using HD cameras.

What is the cause and the solution please?

is it normal with high speed?

regards
Yasri
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#2 David Mullen ASC

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Posted 21 June 2006 - 12:14 PM

Are you using electronic ballasts in flicker-free mode or older magnetic ballasts on the HMI's? And are you shooting in a 50 HZ or 60 HZ country?
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#3 Gil Seltzer

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Posted 21 June 2006 - 11:20 PM

I was just about to post a similar question...

I'm shooting HD with HMIs


Do I need Square-Wave (flicker-free) ballasts if I go off speed?

Is it problematic to overcrank? At what speeds?
Is it problematic to undercrank? And at what speeds?

If I use the regular ballasts...am I only safe @ 24P?

Also, do most Square-Wave ballasts have a switch for turning off the square wave if you're shooting sound? (I think we're renting ARRIs)

I'll be shooting in the states - NYC to be exact.

Thanks - Gil

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Are you using electronic ballasts in flicker-free mode or older magnetic ballasts on the HMI's? And are you shooting in a 50 HZ or 60 HZ country?


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#4 David Mullen ASC

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Posted 22 June 2006 - 12:33 AM

If you don't have square-wave ballasts set to flicker-free mode, in film you have to shoot crystal-sync at HMI "safe" speeds for the older magnetic ballasts.

But I believe for 60 Hz lights, it should be enough on an HD camera to keep the shutter speed set to 1/60th of a second to avoid flicker at different frame rates (1/50th for 50 Hz countries). I could be wrong on that point.
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#5 Michael Nash

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Posted 22 June 2006 - 12:39 AM

I was just about to post a similar question...

I'm shooting HD with HMIs
Do I need Square-Wave (flicker-free) ballasts if I go off speed?

Is it problematic to overcrank? At what speeds?
Is it problematic to undercrank? And at what speeds?

If I use the regular ballasts...am I only safe @ 24P?

Also, do most Square-Wave ballasts have a switch for turning off the square wave if you're shooting sound? (I think we're renting ARRIs)


******************************


All the same HMI rules that apply to film apply to HD. The mathematics of light pulse vs. camera capture are the same.

24P HD should not flicker with 60hz. lighting (HMI's), regardless of shutterspeed (at least below 1/120 second). Off-speed frame rates follow the same rules as "HMI safe" speeds for film. If you need a "non-safe" frame rate, you may be able to dial in a scan frequency with the "clearscan" or "synchroscan" to eliminate flicker.

Many electronic ballasts are switchable. You'll have to take that up with your gaffer or rental house.
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