HVX 200(PAL) + 60Hz Fluorescents + ?

P

paulydc

New member
I'm shooting in DV 576/50i and I'm going to encounter a lot of fuorescents. The lights are running off of a North American 60 Hz power grid whereas the camera's a European HVX200E with 25 or 50 frame options---can I correct through synchro scan or shutter angle (film mode) to prevent flicker, or am I in trouble? Or is this not a problem?
Thanks for your help.
Paul Williams
 
First of all, you may have no problem at all with more modern fluorescent fixtures with electronic ballasts which refresh the output at 20,000 to 40,000 times per second. However, if you have some older fixtures or newer cheap ones, there is a formula for figuring out all this with 50 or 60hz low frequency lighting and is applicable to both HMI and fluorescent (magnetic ballasts usually but there are actually electronic ballasts that operate at this lower frequency too):

Safe camera speeds with 60hz lighting :

Camera speed in fps = shutter angle / 3 / LPEP

Where LPEP = number of light peaks that you want to capture per exposure
period (typically 2 per cycle, or hz).

Safe shutter angles with 60hz lighting :

Shutter angle = speed in fps * 3 * LPEP

For 50hz power replace 3 with 3.6 in both formulas.

What all this means is that if you don't capture at least two cycles of light output during your exposure then you start to get flicker.

So for example in 50hz situations and assuming you want 30fps it would be as follows to figure out shutter adjustment:

30*3.6*2 = 216

Many may think its better to run at a faster shutter speed but it's the opposite. Think about it like this: Each shutter moment is a moment where we're capturing light. If you're light is flickering that means that its not refreshing at a very high rate. 50 to 60 times per second is not that much. You are practically guaranteed to see flickering if you're shutter is open at a moment the light is refreshing and not fully lit. The faster your shutter the more likely you are to be open at such a moment. Many feel that you need at least two refreshes of your light per shutter moment to be safe and not see flicker. Hope this helps.
 
Dear Richard Andrewski (Cool Lights USA):

Many, many thanks, I think I can relax a bit now! Just landed after 13 hour flight, going to use your formulas and figure this all out when I get my bearings. Cheers,
Paul W.
 
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