Well, I like to shoot reef tanks and other saltwater aquariums. Typically reef tanks have a very high amount of blue spectrum light (actinic) on them. Now, that I have my my D70s I use raw and set WB to Shade -3 to filter some of the blueness out. Anyway, even after I compensate in PS or NC I am still not happy with the colors in my pics. They still seem off a little bit. Soooo - I get this bright idea to get a color correcting filter and put some of the burden of color correction before the camera processes the pic. My initial thought is that I need a blue filter of some sort. My color theory sucks I suppose. As I searched around on the net and found some info on diving pics and color correction, it turns out the filter I need is more of red filter. So I have found at B&H and Adorama this nifty underwater filters. Here is a link. Underwater Color Correction Filter for Blue Water So now here are my questions for those that are divers or understand the color thing better than I do. 1) Since, I am shooting in digital is it worth buying the filter? Can I simply do better in post processing and get better pics? 2) If I do get the filter I have 2 lenses I would like to use it on. My 105 Micro and my 24-120 VR. So, should I buy the 72mm size or the 52mm size and use step up/down rings? Do step up/down rings effect the edges of a picture. Never used one so I do not know if going up lens->filter or going down lens->filter has any positive or negatives about them. 3) I do know the 52mm filter is half of the price of the 72mm filter. 4) And I am not sure I want to invest $150 bucks to find out that this did not improve anything for me. Hey-Gregory "GHO" - You out there? I bet you can shed light on this for sure! Thanks for everyone's help.