[OrenMc]

I'm not the one to ask as you can see the trouble I was having trying to figure this out.
I would ask you a couple question before I answered first though.
You said you just received your K20D so I am wondering what camera you was using the 70-200 on before and if you had any problems with it before? If you had no FF issuse with the lens before it may be the camera.
Second, I would ask what kind of testing did you do? As you can see from this thread the difference of light does make a difference. The tests we use and how we use them is another question.

I don't think I really answered your question but I hope it helps.

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Last edited by OrenMc; 12-19-2008 at 07:54 PM.

[sholtzma]

I was using the K10D before and had the same results with that lens. The charts were the ones for the K20D that Yvon Bourque developed. Of course, whether I was using the right light, right angle, right distance, right mantra, right breathing, right posture, and right timing is another matter....

[tim71]

Same for me as KungPow. Test your camera in daylight or flourescent, tungsten has a tendency to confuse my K20D.

I made some repeated tests to compare the behaviour on AF in tungsten vs normal light with the same exposure levels. Then I repeated these with different focusing distances to get consistent results.

K20D with Tamron 17-50, Tamron 90 macro, FA31 Limited and DA* 50-135.

Results were actually... interesting.

Tungsten light had obvious effect on focusing with both Tamron lenses - AF adjustment had to be corrected by about 3 steps ( from -5 to -8 or from -3 to -6). After applying this "tungsten correction" both lenses focused fine in tungsten light.

I find more interesting, that both Pentax lenses were almost not affected by tungsten light - it was just between setting it from 0 to -1 or not. Maybe -0,5 would be ideal if possible (btw my FA31 would maybe need +0,5 in daylight for perfect AF).

It looks like the camera body and AF system itself are not the only issue here.

One solution can be just testing the equipment to find out this needed "tungsten correction factor" and then applying it when needed.