Hi ianmarsh, this is in reply of your message to kkfok about the stability of the Nikonos with Nauticam NA A7. First time user of the lens might find it "unsafe" as although the lens is securely fitted onto the Nauticam adaptor, one can easily have it tilted/moved by 0.5-1mm when attached onto the housing. This is because there are actually four tiny springs built in the lens itself, I am not sure of the purpose of these springs but once UW, the apprehension will be gone coz water pressure will have the lens securely fitted onto the housing, rendering a safe, compact and easily maneuvered set up. I had a great time with my Nikonos 15mm - the only lens I have from the Nikonos family. I usually set my focus to 3m-infinity and adjust the aperture on the Nikonos instead depending on my strobe output and the surrounding environment, and with the A7R peaking function.