The soon-to-be-released Lumix S Series full frame mirrorless cameras sound mightily impressive on paper, and we've been itching to see how they stack up in the flesh. We recently had that chance at a Panasonic launch event in and around the picturesque port city of Hobart, Australia, where we got to drive the new Lumix flagship in a variety of shooting situations.

Stepping in above the micro four-thirds video powerhouse, the Lumix GH-5, the S Series is made up of two models – the S1 and S1R – and is aimed at professionals, though it will no doubt grab the attention of serious amateur enthusiasts, too. Both models look and feel the same and share many features, including an excellent OLED viewfinder that almost convinces you you're looking through the lens, a high-res display that tilts up and down, along with dual memory card slots (XQD and SD).

The S1R is optimized for stills with a massive 47.3-megapixel CMOS sensor and a high resolution mode, where the sensor shifts during an eight-shot burst that is then stitched together in-camera to produce an incredible 187-megapixel equivalent image – that's 16,736 x 11,168-pixels for those of you measuring up for new wallpaper.

The S1 is geared towards video making, with a 24.2-megapixel full-frame CMOS sensor optimized for shooting in low-light (ISO 51,200 extendable to 204,800). It shares high res mode (though in this case you "only" get a 96-megapixel equivalent image), records full frame 4K 24/25/30p with no time limit and 4K HLG (Hybrid Log Gamma) internally, plus 4K 50/60p cropped to APS-C for around 30 minutes. A paid software update later this year will open up a range of other options, including the V-Log picture profile found on Panasonic's broadcast-quality Varicam rigs. During our test we used the S1R, so we'll dig deeper into the video capabilities of the S-Series in a full review down the track.

Before you even pick up this camera you know it's a serious piece of kit, the sharp edges and chunky design give it a solid look, and in the hand it's a hefty unit – the magnesium alloy body weighs in at around 1,021 g (2.25 lb) with a battery on board. So, while it's not going to slip into your your pocket while on vacation, it's well balanced and comfortable to hold for extended periods. It's also weather-sealed, designed to take on the elements and survive the odd knock and scrape.

While it's a complex beast, everything is there at your fingertips, and with time and a little muscle memory you can learn to make adjustments on the fly quickly. There's a rotating switch beneath the standard mode wheel that gives you access to continuous shooting and a 4K/6K high speed burst function; a focus zoom button on the front; a lock switch; a switch for quickly swapping between single shot, continuous and manual AF; and a toggle button for scrolling through things like autofocus menus. The list goes on, but essentially it's well set up to allow you to unlock much of the camera's capabilities without having to pull back from the camera and delve into the menus.

When you do need to go digging, the menus are refreshingly easy to navigate – the groupings makes sense, and you can see all the options in each sub menu without having to scroll to a second page.

The 225-point auto focus system on the S1 is particularly impressive. Hit the button on top of the unit and you can easily scroll through the various AF modes using the toggle switch on the back, which also lets you control focus area position or re-center your focus point by pushing it down. Alternatively, you can use the articulated touchscreen to do the same job.

The facial tracking function, which I've never really trusted, won me over. When you're shooting portraits, the system is so finely tuned that you can switch between which eye you want to focus on with a simple push of the toggle button, and the camera's ability to identify and track faces (or animals) while shooting in continuous auto-focus at 6 fps is pretty astounding. The burst rate jumps to 9 fps in single AF mode.

This is where one of the very few issues with the S1 crops up. While the 5,760k OLED viewfinder is brilliant, when in continuous AF mode the image sometimes softens slightly in the viewfinder, though the results are still sharp, suggesting the viewfinder isn't quite keeping up with what's going on in the rest of the camera.

This brings home the fact that shooting with a mirrorless camera is a very different ballgame. I'm used to shooting on DSLRs, so I'm in the habit of pulling back and reviewing images after each shot. On a mirrorless camera there's no need – what you see on the viewfinder is what you get in the file – and it takes a while to get used to that. Once you do, making adjustments in camera that you might otherwise leave for post seems to make sense, and making the photo you are after becomes a more seamless process. The upshot is that a great viewfinder is critical, and this is definitely the best I've ever used.

On top of the beautifully detailed images delivered by the massive sensor, razor sharp autofocus and quality lenses, the S1R also has outstanding dynamic range capabilities and great low light performance (ISO 25,600 extendable to 51,200). The two auto white balance modes are also useful – AWBw for warmer skin tones and AWBc for a cooler cast when shooting landscapes.

Helped by an anti-reflective coating on the sensor, none of the three new Lumix L-mount lenses we used (24-105 mm F4, 70-200 mm F4, and the awesome 50 mm F1.4) showed any hint of flare or chromatic aberration.

While the L-mount system is new, Panasonic's partnership with Leica and Sigma will mean that early adopters won't be left with a lack of options. The three lenses above are available at launch, but around 42 native lenses will be available by the end of 2020, and Sigma will also have an adapter for EF mount lenses.

Dual image stabilization, up to six stops worth according to Panasonic, also plays its part in delivering crisp images. It combines the in-body system with optical stabilization in some lenses (the 24-105 mm and 70-200 mm both have it) to help when shooting without a tripod, though you'll still need one for the high resolution mode. This system is aided by a "Status Scope" that shows you how much the camera is shaking in the viewfinder and allows you to compensate.

All of these features mean the S1 chews through batteries, even if you're only shooting stills. It's a very decent-size at 3,050 mAh, but you wouldn't want to venture out for a day-long shoot without at least two fully charged batteries in tow.

This is a definitely a camera built for pros, but enthusiasts with a hankering to venture into full-frame mirrorless territory will find it hard not to be tempted. It's outstanding in low light and its image stabilization capabilities, sophisticated facial tracking, and the incredible detail offered by the large sensor and high res mode will make it appealing to landscape and portrait photographers in particular. Its not exactly super portable, which was one of the big selling points for mirrorless cameras when they first came on the scene, but that isn't necessarily a downside – instead it shows how the technology has evolved to make mirrorless cameras a serious alternative even at the higher end of the scale. After a taste of what the S1R can do, it's hard not to see DSLRs going the way of the dinosaur.

And despite its formidable capabilities, the S1R manages to be approachable – it's feels like the sort of camera that can help you push your boundaries as a photographer ... though, not surprisingly for professional-grade gear, it isn't cheap.

The Lumix S1 and S1R will hit shelves in April. The S1 (body only) is priced at US$2,499/AU$$3,599, or US$3,399/AU$5,199 bundled with the 24-105 mm lens. The S1R costs US$3,699/AU$5,299 for the body or US$4,599/AU$$6,899 for the kit, which puts it in similar territory to Sony's a9.

Head to the gallery to check out some sample shots from the Panasonic Lumix S1R.

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