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Old February 10th, 2005, 12:39 PM   #1
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Fluorescent Light Fluxuations

I just recently shot a 'special effects' scene on a PD-170. The shot in question is an OTS of actress in a mirror, cheated so there is nothing in the mirror. After the lines are delivered, actress is cheated over to be the image in the mirror and supply the response lines. The idea is to mask between the shots in post and create a conversation with a mirror image.

Here's the problem I encountered in the test shoot; as I was going through the lights (all fluorscent, 1 key @ 200w and 2 small battery operated kickers) appeared to be cycling between a blue hue and a green hue. The effect is subtle and actually pretty cool, but there is no way to sync the phases while shooting, so 1/4 of the time the mask is almost visible.

Is there any way to eliminate this effect on set? My only other idea is to keyframe some color correction in post to dull the effect...
Tom Koerner
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Old February 10th, 2005, 07:57 PM   #2
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1- There might be a plug-in that does auto white balance. Which editing program are you using?

If your program doesn't have a AWB filter, you can export a quicktime image sequence to Photoshop (full, not elements) for batch processing. I'm fairly sure Photoshop has such a filter.

The problem with this is that the filter needs the brightest thing in the image to be pure white.

2- An alternate approach is to keyframe the color correction. You can speed things up by copy keyframes over and over.

3- Yet another approach is to desaturate the image completely. You can add color back in via the 3-way color corrector (any CC plug with 3 color wheels). Drag the wheels to 3 different colors. The same effect can be achieved with color curves.

4- Can you reshoot this? Is this what your original question is asking? (Reshoot this and fix the problem on set)
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Old February 11th, 2005, 08:54 PM   #3
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Interesting suggestion about the desaturation... I might have to try that just for fun. I guess this is my real question; is there any way to prevent the fluxes on set? The change is subtle enough that it is almost impossible to notice on an LCD - and the nature of the effect doesn't lend itself to having anything attached to the camera that might cause movement (ie a coax to a monitor).
Tom Koerner
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Old February 11th, 2005, 09:14 PM   #4
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I would do a little testing to identify the cause.
I'm thinking possible causes are 1/ voltage fluctuations(line or battery)
2/ bulbs and/or ballast that may be on their way out or of poor quality
3/ interference from another electrical source
to test..... a/ try individually b/try a different location
if 1 light is the culprit then try in a different set( for testing)
if ok there try a line conditioner if ac powered and look for a source of interference
if its same in different set, swap out the bulb(s) and/ ballast
you might be able to fix it if you know the cause.
ps What shutter speeds are you using? It's been said that some flourscents will fluctuate with higher shutter speeds
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