I've had my K10D for almost a year now. After getting the 31mm Limited lens, I thought that I had a bad copy of this lens. Not so. I tried my 35mm and another wide lens and found that the point of focus was pretty far behind the target.
At 35mm, wide open, it is noticable. With the 31mm, wide open, it is bad. The reason that I hadn't noticed it sooner, was that in order to see this problem, the lens had to have a narrow DOF to make it obvious. At f/4 or f/5.6 the DOF was masking it.
Another thing that I noticed is that it gets worse, as the lens gets wider. It is fine at 50, bad at 35, really bad at 31, and I thought that I had a bad copy of a 14mm last month and sent it back!! All the time it was my K10D.
I read somewhere that this is a software calibration issue. That the K10D can be calibrated at several focal lengths for autofocus.
I am thankful that I found this out before the warranty ran out!
I cannot afford the K20D for a while, but now I know why they added the "lens self-calibration" feature in it. I would bet that this is a "known" issue, and that Pentax has a lot of cameras coming back under warranty for mis-calibration.
I am sending my K10D back on Monday. I purchased a used *isd DL to get me by until the K10D gets back from Colorado.
Does anyone use the *ist DL as a primary or backup? How do you like it?
Sample "back-focus" photo:
The point of focus is on the bird feeder. I have also done the paper test at 45 degrees. This photo isn't an anomaly.