Shocking insight: AF is not a closed feedback loop!

Started Jul 18, 2003 | Discussions thread
DavidP Forum Pro • Posts: 29,088
one question

The 24-70/2.8 is a brand new lens. Post-DSLRs.

So why would Canon put out a lens now that needs to be "tightened"?

Mishkin2 wrote:

That also explains why some lenses jump so much when trying AF many
times on the same subject. Their "Drive quantity detector" does not
have steps fine enough to match the signal from AF processor
precisely and consistently. When two steps are equidistant from the
desired position, the lens will focus one time at one position,
another time at another position. That explains why several of my
24-70's are focusing so inconsistently especially in the 24-35mm
range. It's focusing group moves too little in this range to have
fine steps. A small miscalibration of my camera (not noticeable
with other 4 lenses, which have different optical construction)
might be "helping" this, too.

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