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Old March 8th, 2009, 05:14 PM   #1
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Shooting under fluorescent lights - shifting WB

Hey guys.

This is a problem I've had before and I'm not entirely sure how to ensure it doesn't happen again. A few weeks ago, I was shooting some badminton footage in a school gym. (Canon XHA1.) When I played the footage back at home, the white balance would cycle from orange to more of a blue. It would shift constantly in sort of a 5 second cycle. This footage is obviously not usable as it looks terrible.

I've heard this has to do with shutter speed when shooting under fluorescent lights. I don't even remember at what shutter speed I shot. I think it might have been 1/60. That footage wasn't critical but I'm shooting something next weekend that has to be perfect and I can't have this happen again. Can anyone give me the straight dope on how to avoid this problem? Thanks in advance!

J.
Jarrod Tully is offline   Reply With Quote
Old March 8th, 2009, 08:55 PM   #2
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Did you lock your white balance? In a situation like this where the lighting will not change, that's probably the best idea.

To be honest, I don't shoot under fluorescent so I've not experienced what you describe. Nor have I heard anything of the fluorescent issue you describe. Not saying it doesn't exist. Just unfamiliar with it.
Tripp Woelfel is offline   Reply With Quote
Old March 8th, 2009, 09:22 PM   #3
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Sounds like you were in auto mode.
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Old March 8th, 2009, 10:04 PM   #4
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I'm pretty sure I was in manual white balance mode. It's happened to me before and I've heard of other people having the same problem. Thought someone here might have dealt with this before but maybe it's not as common as I thought.
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Old March 8th, 2009, 11:54 PM   #5
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Hi Jarrod...........

Well, actually, it is as common as you thought.

If you do a search for "fluorescent lighting problem" or similar (see bottom of page) it will turn up quite a few hits.

The problem arises with old style choke type fluoro units running on 50/ 60 Hz mains supplies.

These units fire twice per mains cycle, so 100 or 120 times per second.

During that 1/100th or 1/120th of a second, the colour balance of the light produced changes dramatically.

Thus, if you shoot at say 1/400th of a second, you will only be seeing part of the spectrum emitted by the tubes.

As this shooting window shifts with respect to the mains frequency, the colour balance will drift also, thus giving rise to the billious colours.

The usual way around it is to shoot at 1/ 60 (for US mains) or even less, the lower the better to include as many full cycles as possible, thus minimising this colour shift.

Setting and locking the manual white balance is of course necessary as you won't in most cases know what colour temp any given set of tubes will be.


CS
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