David Busch's Canon EOS 90D Guide to Digital Photography

Mastering the Mysteries of Focus

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How far we’ve come! My first professional job was as a reporter/sportswriter/photographer for a daily newspaper (back when a backslash really meant something), and focusing to achieve a sharp image was a manual process accomplished by turning a ring or knob on the camera or lens until, in one’s highly trained professional judgment, the image was satisfactorily in focus. Manual focus was particularly challenging when shooting sports.

Today, modern digital cameras like the EOS 90D can identify potential subject matter, lock in on human faces, if present, and automatically focus faster than the blink of an eye. Usually. Of course, sometimes a camera’s AF will zero in on the wrong subject, become confused ...