Originally posted by mee
Is it physically possible to reduce the size of lenses for mirrorless platforms or are we at the limits of physics?
Not as long as the sensors in mirrorless are the same size as in a DSLR.
In theory, lenses with a focal length at or less than the registration distance can be made quite small - they can do without the retrofocal group at the back normally designed to put light back past the mirror box.
In practice, such small lenses very close to the sensor can have real problems with light reaching the edges at oblique angles - vignetting and discoloration can be the result, as people found putting Leica rangefinder lenses on Sonys found.
So a decent wide angle *should* be much the same size, no matter what kind of ILC. They often aren't, so m43 and Fuji and so on are accused of cooking the RAW files. The lenses have chips containing corrections for the camera, so it shouldn't be possible for DxO style tests to be replicated by traditional measurements on an optical workbench.
With teles, there's no advantage either way, so a good long lens will always be big, heavy and expensive no matter what kind of camera it's put in front of. The Sony 300mm f2.8 weighs more than five pounds and costs more than $7000.