Help! Lens with back-focus?!

Yes Drew, thanks, I had already seen the link you gave and my DS's firmware (1.0).

The problem happens only with the Tokina. None of my other lenses exhibit this behavior, so there is nothing wrong with my DS.

Oh, and something I didn't clarify earlier: when I said the Tokina was sharp, I didn't mean to say it is very sharp in a general sense (although this is exactly what I said), but that it is sharper than I was expecting of a 59 Euro 28-105 lens.

Actually, it is very consistent in sharpness from wide open to F8. Most of my other lenses are a lot sharper stopped down than wide open. The Tokina doesn't have too much CA as well, but I don't like it's color reproduction much... I simply love Pentax's color.

All of my Pentax lenses beat it in sharpness stopped down a bit. And when it comes to veiling and flare, there simply is *NO* comparison.

just browsing and spotted this back focus discussion - i can confirm that the tokina atx pro 80-200 2.8 lens most certainly focusses wrongly in af mode, i use this lens to shoot motorcycle racing (wsb and bsb) and was puzzled as to why some shots were in and some out of focus - took a while to suss out because i was using af on fixed point on trackside and switching off af to lock focus into manual so never thought to blame lens ,however when lens is focussed manually but 2 or 3 feet nearer to me i get consistent depth of field and much more consistancy - i am now delighted with the results and also relieved because replacing a 200 f2.8 lens is not cheap
to follow other threads - how good is it that pentax stuck to tradition and made their digitals accept all old lenses - recently put my old pentacon 300mm f4 on ist ds ( using adapter as lens is screw thread) and recorded some astounding results - punchy colours and sharp images - so glad i didn`t switch to nikon as i was tempted to or follow the sheep and buy canon 300d