Looking my U/W GH4 menu now. I can't say what would be different on the GH3 I'm afraid:
AFS/AFF = AFS
Continuous AF = ON
AF/AEE Lock = AF LOCK
AF/AE Lock Hold = ON
Shutter AF = ON
Quick AF = OFF
Eye Sensor AF = OFF
Pinpoint AF Time = MID
Direct Focus Area = ON
Focus/Release Priority = FOCUS
AF+MF = ON
MF Assist = Use the AF mode button
MF Guide = ON
So many blummin' focus options on this thing. It does my head in! Took me about 100 dives to find a way of working with it that suited me and I still have to relearn it at the start of trips.
Hahaha. Same here!
I haven't my camera here now but as far as I can remember, except some "exotic" option like "Eye Sensor AF" and "Pinpoint..." I have more or less the same on both GH2 and GH3. (Thanks to Panasonic, if I will upgrade to GH4 I will feel at home, more or less...).
In AFS mode, with my general medium/macro lens (Oly 12-50), I change the size and position of the square focus box a lot while I'm diving, depending what's in front of me, using the 4 cursor buttons on the back and the thumb dial. It's quick to do. Usually I keep the box large and central between encounters to cover whatever might show up. I reset it with the DISP button. With the thumb lever on the housing I operate the AF/AE Lock button which switches between AFS and AFL (see the current mode with the tiny text top right of screen that I definitely need my prescription mask for!). With a macro encounter where I have TIME, I shift and size the yellow box onto the critter's eye (for example) then do a back-button-focus with that lever so it's locked into AFL mode.
Same approach as you. Most of the time I focus with the rear lever/button that I set to AF Lock.
With an encounter where I don't have time, I just start recording in AFS. But then the focus will continue moving, often nasty little micro-shifts, even if it doesn't look like it on your little monitor, so as soon as I can I lock the focus manually by physically moving the rotating focus control to AFS/AFF to MF. You can do that in the middle of at shot (or before) when you know focus is right and it will keep recording. This will usually wobble your camera a little and leave a clear audio trace in your recorded file, which can actually be useful in post-production to know when you locked focus. Also MF mode then displays peaking which is useful.
With this lens I badly long for a proper manual focus knob that works with peaking. All these fancy features and it's missing that hugely important feature. Crazy really.
Hummm... Of course, GH2 and GH3 doesn't have focus peaking but once I press the shutter release button or movie button (being in AFS) I get a completely different behaviour: the camera acts exactly like being in AFL. It focus while starting th recording and then the focus remain locked. It works exactly like shooting photos. I would kill myself if the focus would continue moving. Is it something peculiar to GH4 or some nasty combination of the above options? IMHO the main culprit would be that
"Continuous AF = ON"
However glad to know that we work in the same way. I remember a good post of Peter on GH4 AF use: http://wetpixel.com/...showtopic=55392
Sounds unusual. I would expect the image to not be sharp all the way across into the corners so check that. Might not be too bad.
Yesterday i was speaking with the Nauticam Italy's representative and he confirmed that it should be good enough.
Few years ago, I mad some test in a pool for fun placing the pana 20mm pancake in the same 4.33" dome. Distance from the glass is grater but the image was tack and sharp. Now the 45mm has an even narrower FOV so I guess it should be better. Maybe you already saw it. I have a small video on Vimeo of those tests: