Why do lenses need AF calibration?

Started Oct 15, 2003 | Discussions thread
Frank Nichols Senior Member • Posts: 1,814
Yes - maybe...

It is not known for certain how Canon AF works, they do not publish the information, but some have researched their patents and come to the conculsion that teh Canon design is NOT closed loop.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.


Radu Tenenbaum wrote:
If that's really true, then it becomes susceptible to tolerance
stack-up problems.

Is this the state of the art, or are there any closed loop AF
systems out there?


mskad wrote:

Radu Tenenbaum wrote:

I've read lots of threads about needing to send body AND lens to
Canon for AF calibration, but I don't understand how the lens could
be out of calibration. After all, isn't the AF system a closed
loop system where the focus is adjusted until the body detects
optimum sharpness?

Also, can someone explain what is involved in performing the body's
AF calibration? Is it firmware or mechanical?

Sorry if this information has already been posted, but there are so
many posts on this topic that it's hard to do a specific enough
search to get me these specific answers.


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