RE: my ist D AF problem

[Alan Chan]

I believe it was due to the fact that as the lens approach infinity 
(especially for non-tele lenses), the subject and the amount of lens travel 
are so small the system is unable to differentiate the difference. Just try 
to manual focus and notice how the AF indicator behaves. The acceptable 
focus of AF is actually a range, not an exact point.

Alan Chan
http://www.pbase.com/wlachan
The problems relate to focussing on distant objects and shooting wide
open - this is not something which is called for, so normally goes
unnoticed until or unless tested specifically.  Compare with manual
focus on a distant object and you will probably find that the AF has
focussed in front of the object.  Well documented on dpreview and I
think pretty much everyone found to their surprise that it was evident,
but the conclusion was that under normal shooting conditions it is not
that significant.
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