Understanding the Limits of Autofocus on Digital Cameras – PictureCorrect: "
Automatic focus (AF) has come a long way in modern cameras. Leica came out with some of the first patents for AF back in the mid-1970s and some of the early attempts to implement the feature on a wide basis were less than stellar. Most used either infrared light or sound to measure the distance to the subject and were easily confused by glass, rain and other obstructions. You could actually hear the motors whirring as a set of gears in the camera manually turned the lens focus and the old cameras had a tendency to hunt around for focus, a process that could take quite a long time."
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