whites changing color?!?!
 

hey guys,
i just got back from filming a buddy in his surfboard shaping studio and came across what i think is a problem w/ my gl2. we shot some white boards against a white wall and periodically changed the white boards out w/ a painted board (kind of a michel gondry effect) - anyways, i began to notice that the white wall which i white balanced and had looked really vibrant and white, would 'dissolve' to a yellow orange for a second and then back to white. it did this all night, for about an hour.
you should know we were filming under flourescent light in total manual mode with a flourescent filter


any ideas as to what this could be?

I don't think your camera has a way to deal with the frequency differences between the flourescent light cycle and the shutter speed. I've observed similar oscillations, especially when vtaping under flourescent lights with shutter speeds at 1/180 and above.
My problems were reduced when I dropped that speed down to
1/60, but then my sports frame grabs were blurry.

Gints is correct. What you saw is likely a common artifact of using higher shutter speeds with discharge type lighting; e.g., flourescent lighting. Using 1/60 or 1/120 should be OK. The reasonis the the actual color balance of the light varies during the electrical cycle, and fast shutters only see part of a cycle. The part they see varies over time because frame rate is a bit slower then line frquency (in the USA).

wow what a great explanation gints and don! I am really happy to have learned that, although I wish i knew yesterday.
So 'discharge' lights are like flourescent lights... what other kind of lighting could give this problem?

The mercury and sodium vapor lights, often seen in parking lots and large buildings like warehouses and gyms may have a similar issue.

Note that some specialized lighting systems using flourescents may also use 3-phase power or high frequency ballasts that will tend to minimize this sort of effect.

Would a flourescent filter prevent this all together so you could shoot at higher speeds, or would you still notice a difference?

Not likely it would fix it given that the filter is fixed - i.e., does not change its color. over time. It just would improve the 'average" accuracy of the color if you are using the color lamps for which the filter is intended.