[frompdx]

For what it's worth virtually every medium format rangefinder uses a leaf shutter integrated in the lens. Many are simply fixed lens cameras (Fujifilm). Even kits with interchangeable lenses like the Bronica RF645 and Mamiya 6/7 integrated leaf shutters in the lenses.

To get a sense for what is required to have a focal-plane shutter on a medium format camera look at the Pentax 67. It's huge and heavy. Even with the mirror locked up there is a significant amount of inertia from the shutter transferred to the user requiring the use of a tripod in many settings.