Why do lenses need AF calibration?

Started Oct 15, 2003 | Discussions thread
Derek Hawkins Senior Member • Posts: 2,049
Re: a simple design change

All that's needed is for the camera/lens to do a few more "sighting
shots" along the way, especially right at the end.

I see this happening quite often....Hunting around optimum focus, you hear it as a click-click-click as the lens "rocks" in the correct area and imagine each click amounts to a single pulse/count operation. In low light situations each click coincides with a flash from the assist lamp (D60). I'm not convinced that the last few movements are open loop at all.

DavidP wrote:
I would think that Canon could add a simple design change (maybe
even in firmware) that would make the camera much closer to a true
closed-loop design.

All that's needed is for the camera/lens to do a few more "sighting
shots" along the way, especially right at the end.

Ideally, you'd make this a custom function. That way you could
choose between a very fast focus (at the expense of a bit of
accuracy), or a super-accurate focus (at the expensive of a bit of
speed).

FrancisCF wrote:

The problem is the degree of turning and the distance relation is
not linear and different for different lens (we heard some
complaints about incorrect focus at certain distance), this makes
high accuracy hard to achieve. Since the last movement is an open
loop there is a great chance of missing focus.

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