« on: April 29, 2014, 04:23:09 PM »
I agree. I've never understood people's fascination with using a FF sensor in an M-mount camera. It always seemed more reasonable to just shorten the flange-sensor distance and use the EF mount. Just getting rid of the mirror box will allow significant size and weight reductions. I don't see how the M-mount would make that much of a difference.
EF (and EF-S) lenses are designed with a 44mm flange focal distance. If Canon makes a FF mirrorless with that same flange focal distance, they'll use the same mount. If they make one with a shorter flange focal distance (it's 18mm for EF-M lenses, for example), they'll make a new mount for the same reason they designed the system so EF-S lenses don't mount on FF bodies - to avoid confusion and unexpected results. They might try squeezing the FF mount into the EF-M size, so that the new FF-mirrorless lenses could be used directly on EOS M or other APS-C mirrorless, in the same way that EF lenses can be used on APS-C dSLRs. In particular, it the whole ecosystem does shift to mirrorless, longer lenses don't really benefit from a smaller image circle, so having a mount compatible with larger and smaller sensors makes sense.
I thought the reason that EF-S lenses can't mount on FF bodies is because EF-S lenses may extend further into the body, and there was the risk that the mirror in the FF body would hit the rear of the lens. Nikon and third party manufacturers don't seem worried about confusing the customer. Their APS-C lenses fit onto FF bodies just fine. Also, given that the M-mount and EF-mount aren't all that different in size, your last point seems to argue that the M-mount shouldn't have been invented at all. The SL1 would seem to support that argument.
However, for whatever reason, the M-mount was invented. If Canon shortens the flange distance to create a mirrorless EF mount, they could shorten it to something longer than the 18mm used for the M-mount, perhaps 24mm. That way, they could introduce an adapter allowing FF mirrorless lenses to be used on an M-system body. Furthermore, Canon could (and should) introduce their answer to the Metabones Speed Booster, allowing EF lenses to be used on an M-body. Because of the 1.6X crop factor, Canon's speed booster could provide a 1-1/3 stop advantage, although the device would probably have to be very high quality and consequently very expensive to provide good image quality in the corners.