Thanks for the comments.
Interceptor121 - well, I've done about 450 dives with a fairly large and heavy video rig in my hands with full electronic controls. Losing the electronic controls and 1-push WB is a huge and regrettable change; a step backwards in fact. This means that when it comes to using the GH2 in my 10 Bar housing I'm basically a newbie. As a newbie, this is my radical/stupid* (*delete as appropriate!) answer to your question: I think interchangeable lenses are no big deal for underwater video!
My thinking is this. Currently, my Sony PDX10 has a 12x optical zoom and I attach a Sony x0.7 WA lens inside the housing (flat port). This is very useful for filming sharks, mantas and other fish in clear tropical waters. It also means I can get some decent macro shots. In addition, I can screw on diopters, although I can't change these during the dive. In my experience I've found that in a 25-minute DVD (which is very long for your average audience) I might be able to use maybe 1 minute's worth of macro footage at most. A video of a nudibranch is just not that interesting if it's not moving, and unlike our photo colleagues I find that I really need a tripod for macro filming, which is a PITA. Basically, I only use the macro lens for night dives, and I don't think that will change. I could get an external macro lens for the 10 Bar, but there's also room to slip on a +2 diopter inside the 14-42 power zoom port. Now, if I was filming deep wrecks in dark water with low vis., or if I was into muck diving, I would do things differently. It all depends - there's no single rule.
I have another heretical view too. If you're filming in 1920x1080 but burning to DVD (720x576) as I do, surely there's scope to use the digital zoom, a bit, in your NLE without noticeably degrading image quality? I think the BBC do something similar when they down-res from 4k to broadcast HD. I haven't made up my mind which setting to use yet on the GH2. I've hacked all the options to 42 Mbps and GOP 3, but with 1280x720 you get 50p, whereas with 1920x1080 you get 24p or 50i. 1280x720 50p would probably be better for doing slo-mo shots in Vegas, but with lower resolution (although still higher than DVD).
Hmm.........
Cheers,
Matthew
