oh, sorry, didnt look in this thread for a while and somehow propably turned off notifications for that one. So, sorry for the Late answer to this. Yes, 0,58x and 0,64x from Metabones will fit, but the C-Mount Ring needs to be removed, but there is enough clearance there, i own and tested both. Make sure to screw the small screw all the way out and drop the small brass bar out on the bottom of the Camera, to avoid it dropping onto the Sensor later when the C-Mount ring is removed later. 0,58x will work very well for the 1.4, but will show serious vignetting on the 2.1 Sensor. For 720p Resolution the 0,58x is however also useable on the 2.1. the 0,64x works pretty well on the 2.1, but will still vignett at around 18mm and Shorter and on like 150mm and longer. Between 20 and 140mm its not too noticeable, but still a little bit visible if you are looking for it. The 0.64x is very useable on the 2.1 for most focal length. Keep in mind that maximal usefull input Apperture on all the Metabones speedboosters is f/1.2, so even if you for some reason managed to mount an f/0,95 Lens on there, you wont gain any more Light over a f/1.2 Lens.