Nikon L28 - Manual (Page 146)

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Autofocus Mode
You can select how the camera focuses in movie mode.
Enter shooting mode M d button M D menu icon M Autofocus mode M k button
Option Description
A Single AF
(default setting)
Focus is locked when the b (e movie-record) button is pressed to
start recording.
Select this option when the distance between the camera and the
subject remains fairly consistent.
B Full-time AF
Camera focuses continuously.
Select this option when the distance between the camera and
subject changes significantly during recording. The sound of the
camera focusing may be heard in the recorded movie. Use of Single
AF is recommended to prevent the sound of the camera focusing
from interfering with recording.