If I have a Cokin FLW (to kill green under flourescent) should I white balance with the filter on, or manually white balance then put on the filter ?

White balance with the filter on the camera. What the camera "sees" as white should be wilth all filters (and lights) in place.

P.S. How far off is the color temp if the lights? The PDX10 should be able to do a manual white balance all by itself.

White balancing with the filter in place will negate the point of using the filter. Any color correction filter that is in front of the lens when white balancing will be rendered ineffective.

When you white balance a camera, you are telling the camera that the reference point you are giving it is white. If a color correction filter is in between the camera and the referrence point, the camera will read the color of the filter as a color that needs to be balanced out.

The FLW and similiar filters are designed to correct the color temperature without white balancing. Specifically if you are shooting with a format that can't electronicly change color temperatures, such as film.

Furthermore, if you are manually white balancing the camera under flourescent lights, then the camera should adjust the color temperature to match the flourescents, and not require a filter to compensate. I say should, because not all cameras have the same range of white balancing capability. And not all flourescent sources have a color temperature that can be balanced out effectively. Not to mention that many flourescent sources vary widely and if you're shooting in a room full of flo's you could have a dozen different flo bulbs with completely different output temp's.

I would suggest that you white balance without the filter in place and then evaluate the image on a properly calibrated monitor. If you feel like color is still too green, then add the filter. OR you could use one of the WB presets and use the filter only, to supress the green.

The same applies to gelling lights. If you gel a light with CTO and then WB to that light as your main source for the referrence point, the camera will match that color rendering the filter ineffective.

You should manually white balance the camera to the source you desire to be white and then light, gel, and filter around that setting.

Jon
Thanks for the detailed reply, I was playing with it a little yesterday and your method seems to work best, although like you say it will probably be rarely used.
Thats the nice thing about the Cokin system, if I dont use it i've only wasted a few dollars.