I wish it was smaller because I often need to lug gear around trade shows and on the streets. But the size has some advantages, and when you see the technology Panasonic packed in there, the extra pound or so is worth it.

It has a weather-sealed body that feels very rugged and a huge grip that makes it comfortable to hold for long periods. The S1 is covered with buttons and manual dials, letting you set things like the autofocus and burst shooting modes without diving into menus. It has a better control layout than any other mirrorless camera I've tried recently, including Fujifilm's excellent X-T3. Controls like the ISO and joystick toggle are even textured so you can find them by feel. It's just very easy to operate this camera without taking your eye from the viewfinder.

Speaking of, the Panasonic S1 has the best electronic viewfinder of any mirrorless camera, period. It's an OLED model with a 5.76-million dot resolution, 120 fps refresh rate and .005-second lag rating. It's brilliantly sharp and quick, making it possible to judge focus and accurately preview photos and video. For me, this nullifies any argument for an optical viewfinder, putting the S1 on an equal footing with DSLRs.

The rear touch display lets you control not only focus and other camera functions but the entire menu system, as well. It's sharp, responsive and reasonably bright, though it gets washed out a bit in sunny conditions, much like the display on the GH5. Both Canon and Nikon, I found, have brighter displays on the EOS R and Z6/Z7.

Camera menus are typically the worst part of many camera systems, but Panasonic has done a great job here. They're arranged logically, making it easy to find a given function, and are fully controllable via the touchscreen. Once you set up the customizable Q menu and buttons the way you want, you should be able to operate the camera without even touching the menus.

Unfortunately, the display only tilts up and down and at a 60-degree angle to the right, and not all the way around. I can't quite understand why Panasonic did this, as the GH5/GH5s both have fully articulating displays. The S1 will therefore never make a great vlogging camera, though you could argue that it's too heavy for that purpose anyway.

One of the main reasons for the extra size and weight is the 5-axis in-body stabilization (IBS). Alone, it offers an impressive 5.5 stops of shake reduction, compared to 5 on the Sony A7 III and Nikon Z6, and zero on the Canon EOS R. That means you can shoot -- conditions and luck permitting -- at 1/8th of a second and lower and still get a blur-free photos. In concert with stabilized lenses, you get up to 6 stops. Panasonic's goal was to match the IBS capabilities of the GH5, and it succeeded. Because the S1's sensor is so much larger, however, the IBS system needed to be very large and heavy. That's one of the reasons the camera is so big.

The S1 has two card slots, one SD UHS II and the other XQD. At first, I wondered why Panasonic would use different, incompatible systems, but it makes sense considering the dual use of the camera. Photographers who need a reliable backup can use both slots at once, while videographers can shoot on XQD. The latter is significantly faster, running at up to 440 MB/s, and will hit a blistering 1,700 MB/s when Panasonic brings CFexpress support via a future firmware update. That will make video recording more reliable and large file transfers faster.

As for ports, Panasonic hasn't skimped there, either. The S1 packs both headphone and microphone ports, and it will support XLR via a dedicated hotshoe, just like the GH5. You also get a fast USB Type C port and HDMI output to external recorders or monitors. The S1 supports both Bluetooth and WiFi remote control, and the new Lumix Sync app for remote shooting and photo transmission is actually pretty good.

Performance

Panasonic has stuck with its contrast-detect "depth-from-defocus" AF system (DFD) for the S1, rather than using phase-detect like all its other rivals. It does that, it said, to retain image quality, because phase detect pixels can add banding and other artifacts to photos in some (fairly extreme) shooting conditions.

The slight boost in image quality isn't worth the downsides of contrast detect, though. The S1 does feature a rapid .08 second focus lock-down time, and burst speeds of 9 fps in single AF mode, or 6 fps in continuous AF mode. That's not bad, but doesn't compare favorably with Sony's A7 III, which can handle 10 fps in continuous AF mode, even with eye AF turned on. On the plus side, using a high-speed XQD card you can shoot 90 RAW images without stopping and infinity ("999", according to Panasonic) JPEG photos continuously.

The S1 is also less reliable than Sony's A7 III, failing to lock autofocus at times. That results in a relatively low "hit" rate of usable shots, particularly during continuous shooting. The system tends to pulse, or hunt back and forth, to try to nail focus. That's particularly disconcerting when shooting video, as it can render some shots unusable. By comparison, Canon's excellent Dual Pixel system usually locks focus without any hunting, making it much more useful for video.

On the plus side, I found that Panasonic's subject-, face- and eye-tracking system works extremely well. Powered by deep-learning AI, it locks onto your subjects' eyes nearly instantly and can follow multiple people at once. I also tested it on animals, including chickens and dogs, and it had no problem tracking them, even when they went behind shrubs and plants.