ahsanford said:
Canon can't reasonably support 4 mounts. They have tough decisions to make by the time FF mirrorless arrives.
They have to go through exactly the same burning hoops Sony has been and is jumping through.
At the end of the day, I see 2 Canon mounts, one for APS-C, one for FF - just as in the DSLR times.
APS-C: EF-S -> will be superseded by EF-M
FF: EF -> superdeded by native short-flangeback EF-X [or whatever they call it]
I don't believe Canon will use the EF-M mount for FF mirrorless. As opposed to Nikon they werre always using generously wide mounts -> EF easily allows for all sorts of UWA and f/1.2 lenses for FF image circle.
, EF-S is designed generously large for APS-C image circle. I fully expect them to do the same.
Transition is practically painless. Like EF-M adapter there will be an "EF-X" adapter. With enough CPU power and smart mount protocol, there will be no hit in functionality, AF-speed, IS operation, flash-metering info, etc. etc. Canon may actually see the move as another opportunity to make life more difficult for third party lens makers and owners. Those Sigma Arts may be in for a tough time, if they are not (adequately) supported by new EF-X adapter while Canon EF glass will work just fine - within the scope of physics of course (USM lenses will not behave like STM lenses and so on).
And even if such an adaptir is included "free of charge" with every FF MILC (knowing Canon and their greed ... Highly unlikely), there will still be more than enough incentive to buy new, native EF-X glass - new lens formulas, better optical performance, unheard-of tracking-AF-performance, and/or same performance, but a lot smaller/lighter WA lenses ... everything in sync with rollout of new Canon FF MILC cameras.
I don't see major issues or obstacles in the way. Except that Canon let Sony get unneccessarily big with FF MILCs - so they'll face much tougher competition once they come to market with their FF MILC system. That's the price they pay for milking their DSLR/EF customer base longer than they should have and for not leading the industry.