Rocky said:
I respectfully disagree. Canon may be using EOS-M as a learning tool for the mirrorless. It is doing well in the Asian market. There is no reason why Canon cannot have a new mount for the FF mirrorless.
Here's the problem: Because of their shortsighted EF-M design, it is physically impossible for Canon to design any EF system in which lenses are interchangeable between crop bodies and full-frame cameras. The reason EF-S kind of worked was that they used the same mount diameter. Without that, compatibility between EF-M and this theoretical mirrorless full-frame mount is basically impossible.
If they build it so that crop body lenses can work with full-frame, that will mean that they would have to use a shorter flange focal distance on full-frame bodies to accommodate the adapter, which means the full-frame lenses won't work on EF-M crop (short of a wide converter, with a significant loss in IQ).
Alternatively, if they build it so that full-frame lenses can work with crop bodies, then they've stupidly limited the smallest lenses (the crop lenses) to only crop bodies for no good reason, and worse, they'll have to use a longer flange focal distance for the full-frame bodies, which eliminates a lot of the fun advantages of mirrorless designs in the first place, because you'll have to have room for an adapter if you ever want to use those new full-frame lenses on the mirrorless crop bodies. Either approach is a
terrible design decision. At that point, they'll basically be using EF, so they might as well just use EF. And if you're using EF anyway, the full-frame mirrorless cameras have very little to no advantage over existing DSLRs, so there's basically no reason to ever build them. (Okay, so I suppose they could shove the back element farther back and gain a little advantage within a narrow range of focal lengths, but....)
I mean, ostensibly they could build a camera with an interchangeable mount, or maybe use a slightly longer flange focal distance for the full-frame version, make the EF-M mount slide in from the side in two pieces, and provide a very thin adapter ring with contacts for EF-M users who want to use full-frame, but... every option is a hack.
IMO, Canon will be *much* better off if they switch their existing mirrorless crop bodies to the new mount, and shoot EF-M in the head. Completely. Sell replacement mounting plates for the existing lenses so you can upgrade them with two screws, then write it off the EF-M mount as a serious design mistake and move on.