why micro focus adjustment ?

Started Feb 25, 2013 | Questions thread
OldClicker
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Re: why micro focus adjustment ?
In reply to Chimere, Feb 25, 2013

I have never really read a good answer to this question.

You are right in that a for/back focus adjustment is to compensate for the difference in the length of the light path between the main sensor and the AF sensor.  This is entirerly in the camera body.  So why would the lens change this???

The best I can figure out is:  There are actually two light paths used in PDAF; hitting the AF sensor in two places.  It is the difference seen in these two that allows the PDAF to work.  If you were to slightly tilt the lens (or in some other way misalign the light exiting the lens), one of the light paths would be affected more than the other.  The micro focus adjustment can compensate for these lens specific errors.

Make sense?

TF

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Some would have you believe that having to adapt to new technology is a workaround, but having adapted to old technology is photography.

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