Originally posted by nah ...
It's just probably my lens, but the sharpness at infinity focus is terrible. Focus overall is kind of all over the place too...
That was my initial experience with that lens too (mounted on K-7). The problem is that the lens can focus past infinity and if you have back-focusing issue the lens will try to focus "farer" than infinity resulting in soft images. Somewhat later I re-calibrated it. Even +10 in AF microadjastment was not enough so I had to get into debug menu and enter +140 there (and reset microadjustmen value in non-debug menu). After that I was able to get very sharp pictures at all focusing distances. The above issue was with K-7 but for K-5 I just had to make +2 AF micro adjustment. If you have a K-5 then I suggest you to mount your camera on a tripod, turn on Live View and focus on some distant object using contrast-detection AF, take note on distance scale on your lens and then turn off the Live View and focus using phase-detectaion AF to see the difference.