Originally posted by cyberjunkie Portraits with a super fast lens wide open aren't for AF either.
DOF is paper thin, if the subject isn't jumping around, MF allows to focus to the right spot (closest pupil).
Well Contrast AF is as accurate as manual focussing and some new lenses have corrective system that make phase AF as precise as MF. I remember reading a test from lens rental I think about it with some modern Canon or Nikon lens, They explained that even it is written nowhere the latest high end lenses had very accurate phase AF and performed as precisely as a careful manual focus. The old AF lens where noticably less precise.
Anyway I agree that with a K5-II and the stock OVF it is pretty difficult, even for MF. K3 make focussing on off center point very precise and AFC keep the subject in focus if they move slightly. For paper thin dof, this help.
As the Zeiss is for mirrorless you might complain for sport/action performance of the AF (also depending of the camera model) but you would always manage to get very precise AF whatever the dof. I am not sure I would find a 55mm f/1.8 on FF the best case. It more suited to larger portraitures with more body in the frame and so having the subject in focus is no challenge. For a tight portrait, on FF I would think more on a 135mm...