I got my a7s3 and Nauticam gear just before a big dive trip in the Caribbean in late November. Shot three Sony Profiles settings, sLog3/SGamut3.Cine, HGL3 and No profile. File format:XAVC S 4K at 60fps10 bit 4:2:2 for all profiles. Customize the C4 function for white balance (So I could execute WB in right hand UW and hold Grey slate and later chip chart with left hand). I used official Sony LUTs and Leeming LUTs in post for evaluation of clips. Will edit in FCP and finish color in Resolve.
It was a well balanced neutrally buoyant rig with Keldan 4x Lights, red and blue filters were consistently used. I was hoping because of the lowlight capability of this sensor to shoot with no lights so as to not scare off fish. In field evaluation I sensed that just a bit of light made a huge difference in color accuracy and saturation. So after a 3 dive and no lights I shot the remaining 20+ dive with light.
1- Love the setup, would choose sLog3 if time in post permits CC, If not post time then I would go with no profile. You lose 1 maybe 1.5 stops of latitude but generally clips were nicely saturated and accurate. I understand some people think the sony color science is to be avoided but I saw no issues. In also I preferred Sonys LUTs over Leeming LUTs for 90% of the shots. Whats my experience in Video color science? 40Plus years surface shooting and a successful life doing so. UW shooting is just my hobby,
2- I used SDHD cards for the XAVC s 4K file format and they bogged down a Late 2013 Mac Pro with 32GB Ram and top end graphics cards. Had to use proxy's to not go crazy in post. I did buy and have tested the new Sony CFExpress Tough card and "I think" it performs well enough to be able to avoid proxies in post. This is because the CPU has to do less calculations than with a codec that has more compression. I did a surface shoot yesterday (Birds in Flight) using sLog3 S&Q settings for 120fps with XAVC S I 4K and I filled a 160GB card in well, not very long. Luckily I had a laptop to download to continue shooting. Take Away 2.1 if you want 120FPS you better mean it! Or have lotsa expensive cards. Moving them into post and seeing performance will take place in a couple days (I hope).
Apologies on long post, but a couple further observations. Cost, yea I'd say camera "May" be a1/3 of the get in the water costs. so, lights and floats, buy the best you can. Housings often are sacrificed if you go for a new camera, but odd note here, I have an a7R4 and it goes in the a7s3 housing. Most of the buttons on the top work but the only button on the back at seemed to work was the Disp button.
I am exceptionally happy with this my 3rd rig. Should be able to last the rest of my life. Knock on wood!