Alright fellow Pentaxians, there has been a lot of discussion lately about "AF problems" with the K20D (and probably covering the K10D as well). The following information may be old news to some of you, if so then please humor me! (And hey I'm still off work from my surgery so I had to do -something- to kill the time!
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A while back I had thought there was something wrong with the AF system in my K20D, and people like Marc Sabatella were gracious enough to point out that the actual center AF zone in spot-focus mode is quite a bit larger than the little flashing red box we see in the center. How much larger?
Well, another contributor (sorry I forgot the name) mentioned an easy test to find out. So what I did was run a strip of black electrical tape across a sheet of printer paper, about 2/3 of the way up. I taped it to a wall, then put the camera on a tripod and aimed at the white zone underneath the black bar. Then all I had to do was attempt to AF, elevate the camera a bit, try again, repeating this procedure until the camera would reliably autofocus on the black line. I then rotated the paper 180 degrees and started from the top, working my way down until focus would consistenty lock. I also checked the zone from side to side.
The result: The center AF point in spot focus mode corresponds almost exactly with the semi-circular outline in the center of the viewfinder. I repeated the test with a couple of different zoom lenses, at varying focal lengths, and the results were consistent.
Perhaps this information will help some of you who (myself included) are/were scratching your heads trying to diagnose an "AF problem". Personally I think now knowing the actual size of the AF zone will help eliminate some of the problems I was having with inconsistent focus.
Paul