The Auto Focus Misconception

The Symptom:  When in the A/F (autofocus) mode and recording a subject
in the full tele position, you find the lens continually adjusting for proper focus. 
Please note this condition occurs only in certain situations.

The Reason:  In this position, the A/F circuit tries to compensate for the 
slightest movement of the subject.  The lens of the unit in full zoom is most 
sensitive to changes of depth and any movement of the subject causes a depth change.  
So the lens is always being mechanically corrected by the A/F drive circuit.  
This may be thought of as erratic lens movement leading the operator to believe 
there is a problem with the unit.  This is not a technical problem but an inherent 
trait of all lenses on the market.

The Cure:  To lessen the effect, back the lens slightly toward wide angle.  
This increases the depth of field making changes in depth less critical. 
To alleviate the effect, operate the lens manually.

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