AF

Question

From reading reviews, I know that some recent DSLRs, like my Pentax K-7, include an Autofocus Adjustment function that allows for modifying the AF system for more accurate focus with certain lenses. Is this function necessary? If so, how does it work? R. Webber

Answer

Yes, an increasing number of high-end DSLRs of several brands include a feature of this type. It allows for instructing the camera to focus slightly more closely, or to a slightly greater distance, than it would do at default. This function would be useful for an older AF lens-especially one that has been banged around-if it is no longer focusing accurately. You may find that it focuses slightly ahead of the subject, or slightly behind it; these issues are called “front focus” and “back focus” and they call for AF Adjustment.

Before using this in-camera feature however, be absolutely certain of the lens’s exact focusing tendencies. (more…)