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 p.1 #5 · Shooting in gym question | |
Light cycling.
Most gyms have a WB of around 4000 - give or take, depending on age of the bulbs - and can vary at different parts of the gym. Maybe they have newer, updated bulbs to get you around 5000? If you want get a custom WB, make sure you expose at 1/60th of a sec.
The reason for your varying lighting is due to the lights cycling with the AC line. You'll possibly notice different lighting at different parts of the gym - even in the same frame. But the bulk of what you are experiencing is due to your shutter speed being able to capture the lights during their cycle.
What we see as normal light - is actually a fluxuation in sync with the current - going from bright white (with an almost green tinge) down to a deep red hue every 1/120th of a second (1/60th to complete a full cycle - hence getting custom WB when you have the full spectrum available) When you shoot from 1/120th to about 1/640th, you'll capture a portion of the cycle. No way to determine which part of the cycle you'll get.
The best you can do is set a WB to match the lights 'designated' color, and deal with the cycling - expect it. The only real way around it is to shoot less than 1/60th of sec - so you always get a full cycle of light. Otherwise, if you shoot 1/800th or faster, you'll minimize the gradient in your photos - but you'll still be at the mercy of where the lights where at the time of exposure.
Older Nikons and the Canon 1D were capable of this all the time because the exposure was controlled by the CCD - not by the shutter as is the case in all film cameras and newer (CMOS and LBCAST) sensors.
Here is what the lights cycling look like to a fast shutter:
http://public.fotki.com/Hammy/gym_lights/
You'll get the same result shooting under similar lights in outdoor fields at night.
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