I had some lenses that cant focus correctly with my k-5II. I do many corrections, test shots, etc, but with no succes.
So, I call to our local Pentax repair centre - they told me, that it can be camera fault - So I take five my most used lens and camera and take it to repair centre. They test it and - yes - camera has slight missfocus - nothing to notice with f-stop 3.5 and higher. They send my 5 lenses and body to France to racalibration (body is under warranty, some lenses are, some not - but all brand Pentax) - and now it is razor accurate. Nice. Even my 100 Macro is even better then before
The very helpfull srvicemen told me, that people usually do they af callibration wrong way - and make it worse. And often it is camera problem - and with calibrated camera it turns to no (or verry little) need to calibrate lenses.
Also, I have DA 50 1.8 with no excessive hunting problem. Problem is that center AF point is 2.8 accuracy and lens is 1.8...
But, in the other hand, some my lenses (that are calibrated) need more that -10 coorection on my K-r body (need to acces service menu)! And my DA40 dont focus correctly anyway... Then I realized, that my DA40, when focusing really close - is focusing slightly off. And I tested and calibrate it in close distance. - So, I calibrate my camera with my razor sharp DFA100, then put on it back DA40 - and voila! Focus is right!
BTW: I have allways problems with sigma lenses on my Pentax cameras - must return 18-35 and 30 1.4 C becouse focusing issues. But, to be honest, I must return DA20-40ltd due to decentring issue, so even in Pentax high grade lens arent everything ok.
So my advice - send to calibration all your Pentax lenses, which is for you importatnt, with your body. In Europe must be in warranty only body, if lenses are brand Pentax.