Fujifilm is skipping the full frame and moving straight from the APS-C X-Trans mirrorless to into the world of medium format sensors with remarkable detail, color and low light performance -- and with a price that's actually rather reasonable considering the feature list.
The Fujifilm GFX 50S uses a medium format sensor that's about 1.7x larger than full frame. Larger sensors mean more resolution, better low light performance and better bokeh. Unlike most of Fujifilm's mirrorless cameras, however, Fujifilm didn't label this sensor as an X-Trans, which means it likely still has the optical low pass filter -- though with a larger sensor, theoretically you don't need that detail boost anyway.
While the GFX 50S is large for a mirrorless, it's small for a medium format camera. The 50S uses a similar format to the X series with plenty of physical controls and dials, but adds a secondary screen at the top displaying shooting data. The camera's touchscreen also tilts and the electronic viewfinder can be completely removed from the camera as a sort of modular system. The camera is made with magnesium alloy and weather-sealed for enhanced durability.
The GFX 50S looks impressive and will likely turn out exceptional images that build on the strong colors and details of the X-Trans sensor -- but with big sensors come big files. The camera shoots at just 3 fps, which is nothing unexpected giving the size of the files the 50S is handling. The video, just plain old 1080p HD, also has a fairly slow 30 fps -- which is more common for the higher resolution 4K.
Medium format cameras often retail between $25K and $50K -- the Fujifilm GFX 50S is expected out at an impressive $6,500 list price. That's closer to Nikon and Canon's flagship DSLRs than it is to medium format. While the GFX 50S doesn't have the speed of those flagships, image quality should be impressive with that medium format sensor. For high-end professionals shooting portraits, weddings, fashion and pretty much anything that doesn't require a ton of speed, the GFX 50S should be an excellent, though luxury shooter.