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.