Originally posted by benjikan Just shot upside down and it worked. One of the bodies was a little bit sharper.
...in the AF plate not being parallel to the sensor plane, causing the error. The error should appear with all lenses, but wide angle lenses or zooms at wide angle settings used at short distances should exhibit the error more clearly (similar to "focus-recompose" errors).
The solution: Pentax should be able to easily adjust the AF plate for you. FYI, there are three screws that are used to position the AF plate. You can take a look at this post here with the illustration (*istDS is depicted, K10D should be similar):
Re: Pentax DSLR AF accuracy: Pentax SLR Talk Forum: Digital Photography Review
I would recommend you to EXPLICITLY ASK them to adjust the AF plate position, not to simply give you a new body hoping the problem will go away. It may not, since there are variances between samples as you have already seen.
And the final note: the image quality, ergonomics, electronics, software and hardware in Pentax cameras are all excellent. But Pentax should really find out why simple final calibration and quality control are allowing for such a large tolerances in products hitting the market.
-= IVAN =-