One of the worst kept secrets in the camera business was finally confirmed today with the announcement of Sony's A7 and A7R full-frame interchangeable lens cameras. These cameras, which are designed and sized closer to Sony's full-frame (but fixed lens) RX1 than its NEX line, are the first mirrorless cameras to have a 35mm equivalent sensor. The two models are physically and feature-wise very similar: the A7 having a 24.3MP sensor with optical low-pass filter (to reduce moire) and more expensive A7R having a 36.3MP sensor with no low-pass filter. (DPreview says that the A7R's sensor is likely the same one that Nikon puts inside its D800E.) Without an aliasing filter, photos on the A7R should be sharper, but are more susceptible to moire distortions.
The other technical difference between the models is auto-focusing ability: the A7 uses a hybrid autofocus model (both phase and contrast-detect), while the A7R only uses contrast-detect. Sony claims that the contrast-detect autofocus on the A7R is 40% faster than performance on the NEX-7, thanks to the new Bionz X processor running the camera. Both cameras also have built-in OLED electronic viewfinders with a resolution of 1024x768 (2.4M dots, same as other Sony EVFs), and 3-inch tilting LCDs.
Even though this new line of full-frame cameras uses Sony's E-mount, they won't be fully compatible with existing E-Mount lenses released for the NEX cameras, which are designed for APS-C sensors. It's the same reason that Canon EF-S lenses won't work on Canon's full-frame DSLRs. You can technically attach an existing E-mount lens to these new cameras, but the image will be cropped (with an option to uncrop for severe vignetting). Sony is launching these cameras with five FE-series full-frame lenses over the next six months, along with an adapter for Sony's A-mount lenses. The Metabones speed booster will likely work with Canon EF-lenses on these cameras, too.
These look like really nice cameras and you can't deny the appeal of a full-frame camera that weighs just one pound, but adopting a whole new ecosystem of expensive lenses and accessories isn't going to be practical for existing full-frame DSLR users. This however does give new photographers more options when buying their first MILC in the entry-level NEX line if they know they can invest in a platform that will scale to full-frame. Sony's A7 will retail for $1700 (body only) and $2000 (with 28-70mm f/3.5-5.6), while the A7R is priced at $2300 for the body only. Both will ship in December.