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Archive 2012 · D800 Left AF inconsistent
  
 
Alan321
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p.2 #1 · D800 Left AF inconsistent


The "left-side AF issue" was one in which the left-side AF sensors caused the lens to focus at a consistently different distance from the where the central and right-side AF sensors focused. Emphasise "consistent". If you are getting variability then something else is happening to cause that. It could be a different type of fault with the AF system, or the lens symmetry, or your technique, or maybe the focus target just needs to be a bit flatter and have a bit more ink or toner on it

I can see by the shadows that the focus target sheet is not flat. There is enough curvature to be seen by the focus system, and together with a possible field curvature of the lens you might get some inconsistency.

You might get some variability depending on whether the correct focus is approached from the camera side or from the infinity side. The distance itself could make a difference (e.g. more consistent at longer distances than at shorter distances).

The lighting could make a difference too. Be sure to avoid intense reflections from the focus target (e.g. glossy paper or glossy ink/toner) or anything around the target.

I agree with others that focus fine tuning makes a difference but be sure to use only one setting for the lens during your tests - i.e. do not try different settings for each AF sensor as that would defeat the purpose of the test. Unfortunately, any zoom lens may need different fine tune settings at different focal lengths and at different focus distances, and yet only one setting can be used for all.

Also avoid shooting targets at 45-degrees unless they present only one straight contrast line parallel to the tilt axis to focus on or else the AF system will be trying to decide which of several contrast lines at different distances is the one to focus on.

- Alan



Dec 12, 2012 at 03:18 AM
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