Originally posted by rRnt Has anyone experienced something similar with this lens or any other Pentax lens? Seems odd for a star-series lens to perform like this.
Your lens may have a defect, it's possible. However, after doing a lot of AF precision and accuracy measurements, I found that the Pentax factory calibration is a pretty good compromise for minimum focus distance to infinity and from the minimum focal length to the maximum focal length.
When people look at AF accuracy, they usually use one subject at one distance using one focal length at one aperture value and also ignore the precision impact on accuracy from run to run. Consequently, they may set +10 AF fine correct for a subject at 2 meters distance, and actually worsen the AF accuracy at infinity and at apertures values different from the one used for AF fine tuning. In some cases, AF fine tune other than 0 is dialed in for one lens setting/subject distance, making the overall AF accuracy worse for all shooting conditions.