Shocking insight: AF is not a closed feedback loop!

Started Jul 18, 2003 | Discussions thread
Pekka Saarinen Senior Member • Posts: 1,826
Re: Shocking insight: AF is not a closed feedback loop!

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.

You should be able to prove this theory:

When you are on subject distance that makes lens choose between two lockpoints on every new lock attempt, moving slightly back or forth should make the lens lock all the time to same position with one attempt, right?

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