Get Pentax 645z and Pentax 645 lens at B&H Photo.
Medium format cameras have large shutters and a natural question to ask is whether the shutter can cause loss of image sharpness. The Pentax 645Z does not have an electronic first curtain shutter option (EFC shutter).
In my review of the Pentax 645Z:
Shutter Vibration: Landscape and Portrait Orientation, 90mm
Includes actual pixels crops from 2 seconds to 1/250 second in both landscape and portrait orientation, with analysis.
Two Really Right Stuff B645D plates were attached to the camera (one on bottom, the other on the side) for mounting into the Arca Swiss Cube head on the very substantial Really Right Stuff TVC-44.
Pentax 645Z + 90mm f/2.8 @ 1/250 sec @ f/4