One of the engineering feats of the Sony Alpha autofocus system is the face recognition. It tracks faces like a robot, and allows you to “register (memorize)” faces so that they are prioritized in an order you choose.
But what happens if you want to shoot a different face than the one automatically selected, or a non-face object (like a bouquet of flowers in front of the bride’s face, with the flowers in focus and the bride in the background?) You have to ‘override’ the face recognition, but it is too time consuming to disactivate it.
Gary Fong demonstrates a little-known shortcut for using “focus lock” as an alternative to disabling the face recognition. This requires button customization – all of which are explained on the premium Unleashing The Power Of Your Sony A6000 video.