Nikon F 4 Instruction Manual page 19

If the shutter does not operate and display does not appear in the viewfinder,
batteries are exhausted or improperly loaded.
•The batteries operate both auto-
focus function and camera
motor; when operation becomes
noticeably slower, change
batteries.
•To conserve battery power when
not using the camera, be sure to
turn film advance mode selector
to L.