[blende8]

But do note that Benjamin did have got 4 copies (IIRC) of the DA21 and he was only satisfied after several exchanges, even that was arranged by Pentax France. So, it seems that the DA 21 does have some kind of mis-focusing problem when used on Pentax DSLRs but at least Ben finally was able to get one which is accurate.

The DA21 has a strange "characteristic", about which you can read here:

DA 21 focussing error K10D: Pentax SLR Talk Forum: Digital Photography Review

[RiceHigh]

The DA21 has a strange "characteristic", about which you can read here:

DA 21 focussing error K10D: Pentax SLR Talk Forum: Digital Photography Review

Your findings sound very strange to me. As the AF is measured with lens wide opened TTL-ly, I cannot see why the Av setting in the camera can affect the final achieved focus unless this Av value is *also* used as one of the correction factors (as a parameter) in the calculation / adjustment of the final AF point. But this looks rather illogical, technically.

Even if this is true, the outcome proves that this algorithm is just a failure, as the lens focus wrongly at wider apertures..