Hi! Welcome to the Pentax Forums!
The first question I always ask in regards to this sort of thread is whether you have tested the AF against a
simple flat target with the camera tripod mounted. A sheet of newsprint taped to a wall at about 50X the lens focal length distance is a good choice. A resolution target works well too. Do your test with fixed center AF focus point. Use natural daylight if possible.
1. Do your best-effort try using focus peaking in Live view. This is your standard.
2. Using focus confirm (green hexagon) and manual focus mode you can see if the PDAF system matches what you determined using focus peaking.
The above is a rude version of a more involved flow detailed in the video below. Note that all testing is done using a flat target and single focus point. You are testing and calibrating the bias in the AF system, not the ability of the system to magically pick a point out of space to focus on.
Steve
---------- Post added 02-23-14 at 09:57 PM ----------
Originally posted by "Student" Does anybody have any suggestions or similar experiences? Is it possible that I just got a defective camera or am not using it right?
A defective camera is always a possibility. If your camera cannot consistently acquire focus on a flat stationary subject in a timely manner or if precision is poor when attempting to calibrate, it is probably time to talk with the dealer to arrange a replacement unit.
Remember that the industry standard for serious defect with dSLR cameras is about 3-4% of all makes and models. Yep, more than one out of every 30 cameras that go out the door need to go back.
Steve