Hello, I've just received the [url="http://www.metabones.com/buy-speed-booster"]Speed Booster adapter from Metabones[/url]. Autofocus works fairly well, not as fast as on an a real EOS camera, but usable and better than the adapter shown on that video.
But the real bonus, is that you get the same full-frame coverage on the Nex APS-C sensor! The optical element in the adapter acts as a 0.71x focal reducer. so a lens made for the FF sensor will be able to project its entire FOV on the APS-C sensor.
And, with this process (the same amount of gathered light is spread on a smaller area) you gain ONE f STOP! An f/4.0 lens will act as a f/2,8 and an f1,4 will work like an f/1.0.
There's no decrease in quality in can see, the optical part has been designed by Caldwell Photografic, very well regarded for their Coastal Optics 60mm f/4 UV-VIS-IR APO macro, a 4495$ beast used in forensics.
I've posted a very quick first impression images on my Blog:
No decrease in quality I can see (in fact, images with the adapter looks a bit sharper), but now I can use a very nice 17-40L at 2,8 on my Nex-7! I'll order the EF 50 f1,4 USM soon, can't wait to use a real 50mm at f/1.0
Image stabilization works too, EXIF data works so my f/4.0 reads as an f/2,8 both in the camera and in the EXIF data and even the MF/AF switch on the lens is properly recognized, so if I select MF, the Nex switches into Manual focus mode with peaking+magnification, then it goes back to AF mode when the lens is switched back to AF.