if you have mixed lighting, the AF system can be absolutely useless. i had large windows letting in daylight and mixed cfl track lighting in this large room i was taking pictures of cars in. white balance hell aside, autofocus was next to impossible. i had to continuously stop after each photo, check preview to confirm focus, then switch between AWB and tungsten, retake the photo and sometimes neither would even work. i ran this by pentax a few days ago and was told to use manual focus.
Quote: In the type of mixed light shooting conditions you described the only practical solution might be to use manual focus.
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Sincerely,
Randall S.
Pentax Imaging Technical Support