I have the Pentax 645n and it is delightful. The 645nii adds mirror lockup, unnecessary according to The Luminous Landscape, and I think imprints the lens used in addition to fstop and shutter. The lens imprinting would be nice.
The 645n also imprints focal length, but only if you are using an FA series autofocus lens. With the A series manual focus lenses you don't get any focal length info.
Originally Posted by GRHazelton
Oddly the 645 yields 15 exposures on 120, the 645n 16.
Actually, not odd at all. Virtually all 645 cameras yielded 15 frames until recently. ETR, Mamiya 645, etc...