Originally posted by Parallax Focus is achieved when the lens elements are brought into a precise relationship to one another. Whether that relationship is achieved manually or automatically has no effect on the IQ. Focused is focused.
The issue is, how do you reach that focused state?
For MF, the user is part of the system,
and a long, smooth focus throw helps the user bring the lens elements into that precise relationship.
OTOH, optimizing for MF makes for bad (slow) AF.
Pentax Limited primes offer a fair compromise,
but not at the level of the MF on a Takumar or a ZK lens.