The A7 III, with its compact and ergonomic design, has been a very popular camera for video recording. The battery life is drastically improved compared to the previous A7 Series cameras, which was a primary complaint of Sony Alpha users and is particularly beneficial for underwater video, as it allows you to shoot for much longer without the need to open the housing. The A7 III also has dual SD card slots, which play an additional role in the maximum allotted time you can record underwater without having to open the housing. The auto-focus during video works very well.
Panasonic is the latest manufacturer to release their line of mirrorless full frame cameras. They released the Panasonic S-series in March of 2019 and swept the photo world of its feet with these impressive new mirrorless cameras. The Panasonic S1 is the S-series camera designed for video, as it incorporates fewer, larger pixels that yield impressive low-light capabilities. The Panasonic S1 incorporates a 24MP, full frame sensor with a new Leica-L lens mount. The S-series cameras bested all other full-frame mirrorless lines in many categories. The Panasonic S1 (and S1R) is the first full frame mirrorless camera to shoot 4K at 60fps -- a feature that full frame mirrorless shooters have been waiting for for years. Not only that but with the latest firmware update, the Panasonic S1 can record 4:2:2 10-bit footage internally, making it an absolute workhorse for color science and post-processing workflow.
The Nauticam Panasonic S1/S1R housing offers an M28 bulkhead, designed to be used with the HDMI 2.0 cable with the Atomos Ninja V monitor/recorder. When shooting the Panasonic S1 with the Atomos Ninja V monitor/recorder, you will immediately be able to record 10-bit 4:2:2 HDR footage direct to Apple ProRes or Avid DNx. This is highly advantageous and the Nauticam housing for both the Panasonic S1 and the Atomos Ninja V work hand in hand to provide a particularly user friendly system.
The next most immediate specification to consider would be the frame rate that your video camera allows you to record in. Top-of-the-line video cameras record at 4K resolution and 60 frames per second (fps), giving your footage that smooth, slow-motion cinema look that everybody loves. This is a highly sought-after capability and only a select few cameras on the market (excluding high-end cinema systems) provide this feature.
Then there's resolution and video quality. You'll want a camera that can record in 4K for sure. The top-end models from DJI and GoPro offer 60fps 4K with digital stabilization that's absolutely incredible. They're also not limited to ultra-wide views; you can set a narrower angle to remove lens distortion, making them solid choices for vlogging and travel logs.