Originally posted by Serkevan If the optical formula is similar, the lens will focus by extension... Not sure anything other than a ring-type SDM (like the one in the DFA* 50 and 85) would have the torque to be suitably fast. For all its issues, screwdrive is actually a pretty powerful system.
Yes, screwdrive does work and for things like my 35mm 2.4 it makes for a light lens that still focuses okay.
But other SLR macro lenses have quiet and fast focusing motors. Why shouldn’t Pentax? I certainly use my Tamron 90 for macro work but I also use it because it is a great focal length for head shots.
A modern lens design with at least a decent motor at “slightly more expensive” (which I would take to mean anything up to maybe $900) could be a product that would appeal to a lot of people that like that length and/or macro work.
If it is a modern design with a motor and “slightly more expensive” it will probably be something I will get at some point.