Very nice blog Bobu! I am amazed that you can shoot at f/16. Most of my available light shots are at f/8 at ISO 1600 and frequently have relatively long shutter speeds, e.g., 1/20s. Often I have to toss out shots due to fish movement. Short shutter speeds are pretty much limited to within ~1 month of the summer solstice on clear sunny days. I can do long shutter speeds mainly because the camera is on the bottom (sometimes on a tripod). Hand-holding like you do at the surface is much more challenging!