fstop, As you see from the quote, I was aware of the purpose of this idiot proof feature. Of course, anyone unaware of how a covered lens would affect aperture priority has already missed the point so why implement it?

Of course in Nikon's final manual focus SLR - the FM3A, they smartly left this feature out of it. They also smartly left the extra locking mechanism need to open the film back . . .