Focus is rapid (though not as rapid as Sony's A7 III), with a lock-on time of just 0.08 seconds, and you can shoot up to 9 fps with single autofocus (AF-S) and 6 fps in continuous (AF-C) modes. The buffer can handle up to 40 RAW shots, or 90 if you use the faster XQD slots.

Panasonic set up a few shooting scenarios, including several bar scenarios, static food and some studio scenes complete with lights. While it locked on to focus most of the time, it occasionally lost track of faces, eyes and bodies, though once it had locked on to a subject, it tended to stay with it persistently.

As for video, autofocus seemed slower than on Panasonic's GH5 Micro Four Thirds cameras, though hunting was minimal to non-existent. Video face-tracking was again not quite as quick and accurate as on the GH5. Overall, the system was not bad, but lagging behind Sony's powerful eye AF system. However, these cameras aren't final production models and don't have final firmware, so we'll reserve judgment for a full review.

Video is where the S1 and S1R are most different from each other. The specifications of both cameras are a bit complicated, so bear with me here. Suffice to say, you'll get very powerful video capabilities, especially with the S1.

Both cameras can shoot 4K at up to 60 fps, and 1080p at 180 fps. That's almost to the level of the Sony A7 III and GH5, both of which can also shoot HD at 240 fps. The S1 can handle 30 fps 4K with no cropping and a full pixel readout. However, you'll have to settle for an APS-C crop when shooting 4K at 60 fps on that model.

On the S1R, you can shoot all the way up to 4K 60p with no cropping. However, both video modes introduce line skipping, so 4K video is not quite as sharp as the S1. To get a full pixel readout, you'll need to use APS-C cropping for all 4K modes.

The S1R is limited to 8-bit video, both internally and externally, and always will be. However, the S1 can handle V-log and 10-bit video, thanks to the sensor's superior noise and color handling. You can shoot 4:2:0 10-bit video internally and 4:2:2 10-bit via the HDMI port.

Panasonic has promised it'll eventually shoot 4:2:2 10-bit video internally via a firmware update like the GH5 can. That update will reportedly not be free, but there's no word yet how much it'll cost. Unfortunately, the cameras won't get ProRes RAW recording, a feature that offers much higher video quality and recently came to Nikon's Z-Mount cameras.

In my brief time with both cameras, I'm optimistic about their video capabilities. The video looks crisp with rich colors, especially on the S1 model, and is capable of very shallow depths of field thanks to the larger sensor. If Panasonic can bring the capabilities up to the level of the GH5 and GH5s, this camera could be the full-frame mirrorless camera to beat for video.

Alongside the cameras, Panasonic has introduced three lenses, and much like Canon's models, they're very expensive. The 50mm f/1.4 is $2,299, though Panasonic called it a "reference" model and claims it's the highest quality full-frame 50mm lens you can get, period. The other models are the $1,699 70-200mm f/4 pro, and the $1,299 24-105mm f/4 pro. Suffice to say, this glass is costly -- the 50mm f/1.4 is the same price as Canon's 50mm f/1.2 model, which is in another class, optically speaking.

With the S1 and S1R, Panasonic has gotten off to a better start than Canon and Nikon. They're loaded with features like in-body stabilization, dual card slots and 10-bit video, which are missing on rival models. Panasonic jammed as much tech as it could into them, and based on my limited first impression, they seem to perform just as well as they look.

However, at $2,499 ($3,399 with the 24-105mm f/4 lens), the S1 is a bit more expensive than the Nikon Z6, Canon EOS R and Sony A7 III. Given the impressive capabilities and huge sensor, though, it will be a no-brainer for many professional videographers. The lack of a fully articulating display is a bummer for vloggers, but otherwise, it's the most capable full-frame mirrorless camera for video.

The S1R is a bit more of a question mark. At $3,699 ($4,599 with the 24-105mm f/4 lens), it's a tough sell against the cheaper $3,199 Sony A7R III and $3,299 Nikon D850, its closest rivals. It has more resolution, no low-pass filter and a superior stabilization system, but the autofocus doesn't work as well so far.

Perhaps pricing is the main flaw with these new cameras. It's not that much higher than Sony, Canon and Nikon's devices, but when you add in the lenses, you're looking at a lot of cheddar. The full-frame mirrorless market is suddenly very saturated, and there are only so many folks with $3,000 or more to spend on a camera system. Both cameras go on pre-order today, with availability by early April.

Update 2/2/19 4:30 AM: The article originally said that the Panasonic S1 could shoot at 9fps in continuous autofocus mode, but it can only shoot at that speed in AF-S (single shot) mode. It can shoot at 6 fps in continuous autofocus mode. The post has been updated with the correct information. (Thanks, David!)