I just realized something, should I even use a filter if I can white balance? What's the best way to do this, bring a small slate down and wb off of that? Do you white balance when using a filter?
Billy
If you can MWB without the filter, go that route first. The reason for this is that the filter is taking away available light. Unfortanetly, that will probably only be an option down to about 20'/6 meters (depending on your camera, the ambient light conditions etc.) I can usually white balance with the red flip filter in my Gates Housing with the Sony HC7 above 20', but if there is a lot of sunlight or I am really shallow, I must remove the filter and MWB without it. If I am using my HID lights, I usually MWB without the filter.
As far as the can of worms "how to white balance" question - great question, I think there are as many approaches as there are people on this board. There's some good responses to that question here, and on other forums as well (wetpixel). I think a lot of it is personal preference, but a summary of the approaches I am aware of are:
1) MWB on Sun (shooting up directly into sunlight)
2) MWB on white slate (great if your subject is never more then an arm length's away from you)
3) MWB on specialized U/W slate (these are usually gray or lt. blue to try to solve the distance issue with #2)
4) MWB on your subject/scene, or as close as possible to your subject/scene.
5) MWB on your (or someone else's) white or gray fin
6) MWB on white sand (similar to #4)
7) MWB on the palm of your hand
I'm sure I left some out. I think it would be good to compile a list of approaches, and see what works best for you. I generally use #4 now, but have had to revert to other approaches, especially when the frame contains little or biased color variation.
Good luck - and strive to not have to use CC!
Some links:
Perfect White Balance - Wetpixel :: Underwater Photography Forums
http://www.scubaboard.com/forums/underwater-videography/112770-white-balance-vs-filter.html