Originally Posted by
slawecki
by the way what does this mean? "The M mount has FLB of about 18 mm as opposed to the 44 mm of the EF and EF lenses."
First of all it means I managed to make a typo. FLB is nonsense, it should be FBL, meaning Flange Back Length. This is the distance from the flange, i.e. where the camera and the lens meet to the sensor. This distance with the M mount is 18 millimeters and with the EF and EF-S 44 millimeters. Consequently, the M mount allows for a much thinner body and smaller lenses.
Cheers,
T.