Shocking insight: AF is not a closed feedback loop!

Started Jul 18, 2003 | Discussions thread
DavidP Forum Pro • Posts: 29,088
but how do it know?

As Mishkin described it, he said the body tells the lens "go 20 steps thata way", and the lens goes 20 steps that away, and it's done. No feedback at all? No double-check? As in, "OK, I went 20 steps, now waddya think, big boy?"

If it's only a single step, the body would have to know what size steps the lens takes, right? That would mean the lens has to know that info, and tell it to the body somehow, right?

Jason Hutchinson wrote:

Loop stability is the most likely one, but what about the response
time of the older motors? They're clearly not designed as well as
modern USM motors for the small repetitive motions that'd be
required for that. Who knows.

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