MICHAEL ZHANG, PETAPIXEL:
"Having trouble nailing tack-sharp autofocus with your camera? Aside from technical proficiency, there are a number of other issues that could be causing you AF grief. [Watch] a 14-minute video on 8 common AF problems and their solutions.
"Photographer Steve Perry of Backcountry Gallery touches on: lens calibration, dirty AF sensors, wrong AF modes, AF guide inaccuracy, heat refraction, using the wrong AF point, dirty lens contacts, and poor technique."
Read more, from here.