gels & filter questions

[M DeM]

I've read some articles on gels on your strobes for wide angles to get a bluer blue. However, I'm wondering if doing that with strobes will warm your foreground waaaaaaay too much.

I'm shooting a 7D with the tonkina 10-17... and I"ll be doing some shallow/shallowish (15 - 40') photography and may go ambient.

Do I just keep white balancing off my slate every 10 feet or so? Or are there some loose guidelines where i can just dial the numbers in as I change depth.

I'm shooting raw, but I notice in some of my ambient light, there's almost NOTHING in the red channel.

 

[kelemvor]

I've never used a gel underwater, but when I use them on land I do exactly as you suggest. White balance off a grey card (or your slate perhaps). The slate might be too white though. If it's beyond the sensor's range (i.e. too white) it might not balance correct. I could be wrong about that, I've never tried to use a white card for white balancing.

You could always shoot raw and white balance after the fact, but that's an extra step in post. I've done that too, it's a pain if you've got a lot of images unless you're using bridge.

 

[Chris Ross]

The point of gelling strobes is that when you balance your shots properly they look neutral and if you do that when shooting with the gel this means it pushes the blues towards cooler colours. So if you auto white balance your shots when shooting with strobes the camera adjusts things to look like they were shot at 5000K (daylight) to make this happen when your strobes are at something like 4600K it shifts the balance bluer because the water is not illuminated by the strobes it's bluer than it otherwise would be as the whole image is shifted bluer to get the subject/foreground neutral. I know you are shooting raw, but most raw converters will use the AWB chosen as your starting point so less adjustments needed. I have INON Z-240s and they have an optional 4600K diffuser, I use this for all my shooting and it works well.

As far as white balancing goes, I leave things on auto white balance and strobes on all the time, deep or shallow. I can then concentrate on the subject not the white balance. The strobes also act to fill shadows which can be nandy for shots which otherwise look OK shot as ambient. RAW shooting cam only go so far until you eventually run out of red light when you get deep enough. Having the strobes on supplies this red light even if the strobe exposure is under exposed a little.

 

[Interceptor121]

I have used 4600K and 4900K diffuser filters. The first thing I can say is only use them when there is water in the column otherwise your shots will have too wam tinge
The idea of this technique is to make the water color look nicer when it is more on the greenish washed out side. Really only use it in those circumstances
Between the 4600K and 4900K the 4900K blendes better with the rest and is likely to produce a subtle pleasing improvement. The 4600K is only working with washed out water and in semi normal circumstances I tend to avoid it