FujiFilm X-E3 Owner's Manual page 108

Quick Focus
To use autofocus to focus on the subject in the selected fo-
cus area, press the button to which focus lock or AF-ON has
been assigned (the size of the focus area can be chosen with
the rear command dial). In manual focus mode, you can use
this feature to quickly focus on a chosen subject using either
single or continuous AF according to the option chosen for
G AF/MF SETTING > INSTANT AF SETTING.
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