He's wrong but so are you AFAICT:
Originally posted by photoptimist You remind me of the president of the scanner engineering company I once worked for. Everything was easy to him. But:
1. Semiconductor sensors are thicker and bigger than film: that pushes the shutter toward the lens, intruding into the space required for the focusing screen and mirror box
Quite dubious. It pushes electronics behind the sensor (toward the screen on the back). No way the other way around. IMO.
Originally posted by photoptimist 2. Even if there is an off-the-shelf 645-size focal plane shutter, it's almost certainly a different shape which likely changes the mirror box design (the old 645N shutter is obsolete with a 1/60 sec synch speed)
Why would anyone even think about keeping every little piece of the 645N is beyond me. That's your point I know.
Of course it should be changed. I see no real difficulties but of course it should fit and and such imposes redesign. Agreed (basically).
Originally posted by photoptimist 3. The 645N had only a 3-point AF system: if that's not good enough, the new camera needs a redesigned secondary mirror and mirror reflex mechanism.
Hum, Pentax proved 2 times already that the re-used APS AF modules. So no, no redesign needed (would be nice though).
Originally posted by photoptimist 4. Is the 645N's 6-segment light meter competitive: if not, then parts of the prism need redesigning
See AF point.
Originally posted by photoptimist 5. Is the 645N's viewfinder information display competitive: if not, then parts of the prism need redesigning
See AF point. Again.
Originally posted by photoptimist Maybe the outward shape of the 645FF might look like the 645N but almost everything inside it will need to be designed from the ground up. That's especially true if the 645FF needs to offer competitive features in AF, metering, and OVF information displays.
No, not from the ground up. In the end though, just taking a 645N and changing a few bits here and there is not gonna happen (that was your point I think). But no, everything does not need to be a complete redesign.