Why do lenses need AF calibration?

Started Oct 15, 2003 | Discussions thread
Derek Hawkins Senior Member • Posts: 2,049
Has to be closed loop....

Where did this open loop nonsense originate other than Mishkin's post where he apparently calls what represents an operational amplifier a comparator? The hunting alone when movement/focus over/undershoot occurs should tell you that this is a closed loop system. Don't get me wrong, I'm not satisfied with Canon's AF at all but being not closed loop has to be ludicrous and isn’t the issue IMO.

DavidP wrote:
From what I've seen, I tend to believe that it's really an open
loop, but that a FEW "updates" are made along the way to guide the
AF. Maybe one or two. Three max.

My understanding is that Nikon has a closed loop system.

Why Canon can't give an option to use either an open-loop system
(for raw speed) and a closed-loop system (for greater accuracy) is
beyond me. Sounds like a great idea for a custom function.

Frank Nichols wrote:

It is not known for certain how Canon AF works, they do not publish
the information, but some have researched their patents and come to
the conculsion that teh Canon design is NOT closed loop. It appears
teh reason is that the closed loop system would be slower, and
Canon opt'ed for a faster open loop system.

I think I read that Nikon was closed loop, but I am not sure.

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