And here's some more white balance discussion in case you haven't had enough ha! I sent this email to some friends a while back after buying my first gray card, it really is a great little tool. While not directly related to aquarium photography, it does give you a little more insight as to how white balance in cameras and post processing works:
Just wanted to share a nice little tool that I just bought. I had heard about them for the longest time but I always thought I could fix it on my own. A Gray Card, a photographer's best friend. Even more so if you shoot Nikon and like to shoot RAW files, since Photoshop screws with the color settings. I find it hard to get the right white balance on skin tones. Landscapes any other object is easy, but I always have a hard time getting the perfect white balance with skin tones.
I finally bit the bullet and bought this ingenious little device. The best $13 I ever spent! This 'gray card' is made to be 18% gray, the standard neutral tone between black and white. This does two very important things:
1) Gives you an excellent reference point for setting white balance, either in post processing or a custom white balance in your camera settings as your shooting (I prefer to adjust in post processing).So of course I just had to test it out. I took 3 pictures in different lighting; one under tungsten/incandescent lighting, fluorescent lighting, and outdoors. In each shot I purposely set a funky preset white balance setting, like 'cloudy', 'shade', 'tungsten' etc to give me some weird colors. Sometimes the 'Auto' setting will get it right, others times it won't. White balance is my biggest pet peeve when shooting people as it can ruin the shot, and it's difficult to get it right. I'm of the opinion that white balance is just as important as exposure.
2) A great place to spot meter and set your exposure for those that like to shoot manual. Most DSLR meters are built to render everything as middle gray. By pointing your spot meter on the gray block and zeroing your camera meter out, you'll have the perfect exposure based on your lighting. No fudging around with exposure comp or tweaking your settings. Just aim, zero out your meter on the gray spot, and shoot away. If you move to a difference scene, just put the gray card back in, take another exposure reading and you're set. [NOTE: some cameras are set to 13% gray, while this is an 18% gray card. These will require a 1/2 stop of additional exposure. On my D90, I find that it worked best when zeroed out completely with no adjustment]
These photos were shot as RAW files and I worked on them in Adobe Photoshop using the 'Camera RAW' converter. I have screenshots of the before and after. All you do is select the white balance dropper tool and click on the gray spot. It's that easy! The 18% gray shade gives a perfect white balance at the click of a button, I did nothing to the photos afterwards.
This is really a great tool. If you're doing a set of portraits, just take one test shot and have the person hold the gray card. That is your reference shot for all the others to follow, and you can process them as a batch in Photoshop. If you move somewhere else and have different lighting, again, have the person hold the card, take a test shot, and resume shooting.
Here's where I got it. Gray cards come in tons of different styles and sizes, but I liked the durability and price of this one. Can't go wrong!