Hmmmm.... Have you thought about sending your camera in for a check up? I sent my K10D back because of a back-focus issue. I bought a *istDL for a backup and the 31 is phenominal and phantastic! :-) Anyway... I sent a Pentax 14mm lens back, and it turned out to be my camera.
Bottom line: the 31mm is very, very, very sharp!!! (after you have a camera that will focus!)
edit: The problem I had showed up only on 35mm and shorter lenses - fixed (prime) only!
Last edited by TomInJax; 03-20-2008 at 04:50 PM.
Reason: clarification