Owain Glyndwr wrote in post #14789093
Is there any reason why they couldn't take an EF mount and a full-size sensor and put it in a mirrorless body? I have no idea of the tech or physics behind all this so it may be a dumb question, so sorry for that.
If you own a 5D2 or 5D3 (or 1Dx), press the button to get it into LiveView mode, and voila, you have what you asked for -- a camera with full-size sensor and EF mount, and no mirror-reflecting light into the optical viewfinder.
My point is: keeping the native EF mount will result in a bulky body not much smaller than current DSLRs, and for most people, that's defeating the purpose of going to a mirrorless body -- size saving.
The EF mount dictates a flange distance (distance between mount and sensor) of 44mm, so in a mirrorless body with EF mount, it still needs to keep the mount 44mm away from the sensor, even though there is no longer a mirror there. The resulting body will be as bulky as current FF DSLRs.
(You might be able to shave some height by removing the viewfinder bulge on top, but look at the EOS-M thread and you'll see the firestorm an absent viewfinder can generate.)
The same limitation applies to APS-C, that's why the EOS-M can be much smaller than a Rebel -- by abandoning the EF/EF-S mount, Canon can shorten the mount-to-sensor distance to only 12 mm (from 44 mm).