F: controls, F1: illuminator switch, F2: ok button (shooting mode) – Nikon D90 User Manual
Page 216: F1: d switch

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f: Controls
f1:
D Switch
Choose the function performed by rotating the power switch to the
D position. This
option is available in all shooting modes.
f2: OK Button (Shooting Mode)
This option (available in all shooting modes) determines what operations can be
performed by pressing the
J button in shooting mode.
Option
Description
f LCD backlight (D) (default) Control panel backlight illuminates for 6 s.
g Both
Control panel backlight illuminates and shooting
information is displayed in monitor.
Option
Description
Select center focus point
(default)
Pressing the
J button in shooting mode selects the center focus
point.
Highlight active focus
point
Pressing the
J button in shooting mode highlights the active
focus point.
Not used
Pressing the
J button has no effect when the camera is in
shooting mode.