I just returned from a trip to Palau, and I was able to experiment a bit more with the FS100/Genesis setup. I think that at least a big part of the color reproduction issues, as well as the rings and halo effects, are due to problems within the 16mm pancake lens. I left that lens in my bag this trip, and decided to try the stock 18-55mm e mount lens with an equinox blue water color correction filter. I was very happy with the results. I'm now convinced that with a decent lens, the right filer, a few tweaks to the picture profile, and adding a housing for my Ninja2 deck, it is possible to consistantly get very good quality images with this rig.
I just posted a few unedited clips on vimeo....
I tried to pick clips with more color, so these are not neccesarily my best shots. All of the clips I've posted were shot with natural light, at depths between 40 and 80 feet, with the 18-55mm lens, and equinox filter. I did manual white balance on a white slate with exsisting light at around 20 feet on my way down (with no further adjustments), or in some cases I was able to get a decent manual white balance using my 2 sola 1200 lights on the white slate, and then switching the lights off. I set the gain to 9db on some of the deeper shots, which doesn't seem to have any noticeable ill effects (to me anyway). I also saw no signs of the halos or rings. Proper exposure is definitely neccesary, although I personally like the look of the slightly underexposed shots. There seems to be planty of detail left, so I'm sure bumping them up in post a bit will result in a good look.
I hope there are still others that still haven't given up on this camera for underwater use. It will be a while before I can afford another set up, and my next camera will undoubtably be a 4k model. Please keep posting your experiences.