for your ISO values, just open/import the file in the free PHOTOfun software that comes with the cam. There's useful info available if you just right-click on the thumbnail, including ISO, shutter, aperture etc.
"AFL hold" is buried in one of the menus somewhere. Switch it to "on" and you're good to go. Point at something a couple of metres away, e.g., press AFL once, and that's it. No need to re-focus between shots, unless you want to.
Before I went on the trip, I thought that I would be using 1080, 50fps 10-bit. However, the advantage of 10-bit seems to be above all in "extreme" grading. I couldn't see any difference on any of the (not very modern) screens in my house. 4k gives you the advantage of being able to zoom in a little at least in post, and provided your shutter speed is twice the frame rate, i.e. 180 degrees, then the slo mo from slowing down 50 fps is really useful. Things like shots that just lasted 2-3 seconds in real time can be made to stand out a bit more. If you want to go to less than 42% slo mo however, then you have to use 1080. I just put these different options in my custom pre-sets, so it's easy to switch. Variable frame rate is only available with manual focus of course....
One bizarre problem I had was that the camera completely froze at the start of a dive. I had just pressed AFL. Nothing I could do underwater would unfreeze it, including turning it off, pressing any of the buttons, etc. Only after the dive when I could take the battery out and re-insert it did the camera work again. I noticed that there were loads of "this video file cannot be played" on the card in the slot I'd been using. I realised that after a few days' use and transferring my shots every day to the hard drive, the card would probably need re-formatting. It seemed to do the trick, and the problem didn't occur again.
@Pajjpen - I'll post some clips after I get back. It's not feasible where we are now. I think the low light performance is significantly better than the GH2, but I don't know the GH4. Actually, I found that the test shots I did at 26m were a bit overexposed with auto ISO and exp compensation at 0. Of course, Palau on a sunny day is really seriously bright, not like a Belgian quarry....
Hey Davide, I think there's still a video on my vimeo page from a few years ago. Have a look (link in my signature).
The white balance on this cam is so good it's like my old 3-chip Sony,.... for which I paid about 1700 euros 12 years ago. Exactly what I paid for the GH5!
Right now the biggest challenge with the GH5 is deciding which settings to go for...
Re: "... manual WB works really well when shooting ambient light. "
I did my first ocean dives with the GH5 in the Nauticam housing yesterday, here in Palau. MWB does work very well indeed, BUT don't forget the red filter. Below about 10m I found it to be essential. However, even in the very murky vis at the site known as Buoy 6, at about 4pm, the colours, including the reds, really popped even at 26m. I'm still using the same method as with my GH2, which works a lot better for me than a card. It's a piece of grey-white/translucent detergent bottle, held over the port, and pointed to the brightest part of the surface. It's like an expo-disc.
I'll post a clip after I get back.
@Rollin, I see what you mean about switching to MF, but doesn't the AF-L button work just as well? I haven't tested my new setup yet, so I don't have practical experience underwater. I was thinking a single small AF point, aperture f5.6 or higher, then AF-L would do. I have the Pana PZ 14-42, and there's no MF control with the NA-GH5.
I had a week of pretty awful weather in Palau at the beginning of this year. As someone who relies a lot on ambient light, this wasn't ideal, but as always in Palau there were some great dives. Highlights here: