Nikon Zfc Mirrorless Camera with 28mm Lens - Manual (Page 115)

Focus
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A
Focus peaking
･ If an option other than [Off] is selected for Custom Setting d9 [Focus
peaking], objects that are in focus will be indicated by colored outlines
that appear when focus is adjusted manually (focus peaking).
･ Note that focus peaking may not be displayed if the camera is unable to
detect outlines. Check focus in the shooting display.