[Guest]

Not even that. There are just two mounts: A and E.

 

For lenses there are two image circle sizes: A/FE and A DT/E. Think EF and EF-S, with just one mount: EOS.

 

That is not exactly true. You cannot mount EF-S lenses on a full-frame EOS camera without modifications and risking damage of the mirror. Thus you should definitely consider EF and EF-S as different mounts.

 

There were rumors -- and I am not sure if these are confirmed now -- that you will not be able to mount Sony FE lenses onto the E-mount of APS-C (NEX) cameras. This would be the opposite of the EF/EF-S restriction.