Many photographers will be happy with this basic understanding of autofocus, but depending on the type of photography you’re about, you may want to understand the different forms and modes of focus to make informed purchasing decisions. Here’s a brief description of the common AF jargon:
Simple and effective, this system looks for contrast at the edges of a subject and adjusts the focal point until the contrast is sharpest.
With this system in cameras like the Olympus OM-D E-M5 Mark III, light coming off a subject is measured to determine the distance, and the lens adjusts accordingly.
Within the frame there are points for the camera to focus, so your subject will need to be at one of these points for the autofocus to work. Modern cameras, like the Canon EOS 90D, have a high number of points making it easier to achieve this. The points can be in vertical or horizontal lines, or cross-type points which result in the most accurate autofocus.