I recently bought a Tamron 17-50/2.8 from KEH (in LN- condition) and was very pleased with it for the first few weeks. Yesterday, I used it in manual focus (on my K-5) for the first time - for a period of a few hours - and now I'm seeing something that I can't figure out at all. I set the camera back to AF-S, and for the first few seconds it behaves normally. Then - while I'm focusing on a subject - all of a sudden, the MF indicator comes on in the viewfinder, the green "in focus" indicator starts flashing on and off as I move from one subject to another, and the focus confirmation beep is sounding every few seconds (presumably when it finds focus). While all this is happening, the MF indicator is lit steadily. It's as if the camera thinks that the lens has an AF/MF switch and that it's in the MF position, but this lens doesn't have such a switch. I've tried turning the camera off and back on again, taking the battery out for a couple minutes and then reinstalling it, recharging the battery, wiping the contacts, and turning the focus ring back and forth between stops a couple times. Nothing makes any difference -- when I turn it back on, everything's normal for the first few seconds, then it goes wacko again. With a Pentax lens on, everything works normally.
Has anyone else seen anything like this? I like this lens otherwise and, as I say, it worked fine in autofocus for the first few weeks. This didn't start until after I had used it in manual focus for a few hours.
Last edited by dshombert; 03-31-2013 at 01:58 PM.