[olwick]

Think of the Pentax 67. It's mirror is larger and heavier, with greater inertia and momentum, but it illustrates the concept of image degrading mirror induced vibration.

The Pentax 67's problems are also due to the shutter curtain. See the illustration, even with the mirror locked up, here:
http://www.luminous-landscape.com/re...ntax67ii.shtml