I bought a UR Pro green water filter when I first got the camera (46mm). With flash, you get a very red shot. In natural light, between the dark water and the filter, your camera is going to drop to something like f2.8@1/30 unless you crank the ISO way up. I haven't tried it since I've practiced more with the camera settings, but if you look at my gallery, the emerald green shots at 70 feet at Hopkins by the Monterey aquarium were all done with the green filter. They'll be the Metridium, sea stars and anemones toward the end of the gallery. I had a lot of problems with blur due to heavy surge that day and the slow shutter speed due to low light. I might try it again now that I know what I'm doing. I'd certainly stay above 40 feet if you want decent shots.