I been testing 16-35mm f4 topside with f2.8 II. New f4 is sharper corner and have better lens coating (better sunball).
I couldn't try it behind dome but still if I don't have f2.8 then I would buy f4. IMHO, both lens will give you better sharpness and contrast then 17-40.
Wow that is not something I could afford to do on a regular basis but then I suppose you could shoot another fan lol. Maybe a less powerful diopter would be fine too and if you need some clear image zoom or whatever panasonic calls it loose bit of quality but keep working distance reasonable
I have some footage with less powerful wet lens. I'll try to post GH4 highlight video (WA + Macro) when I'll be back from Indonesia.
BTW, Ex Tele mode (in-camera zooming effect?) not working when 4K mode.
Marine life of the Southern Atolls in Maldives.
Shot on Canon 70D in Nauticam housing.
Lens using Canon 10-22mm, Sigma 8-16mm behind 9' dome.
Most of time I was using continuous AF and it's works well. The 70D is probably the first Canon DSLR with a usable continuous aufo focus system on video mode, it's smooth and doesn't jerk or hunt.
Shot 1080P, All-I, Standard profile (1,-3,-2,0). No color grading or sharpening in post.