Controls In Detail; Film Speed Dial - Nikon F4 Instruction Manual

CONTROLS IN D E T A I L - - - - - - - - - - - - - - - - -
FILM SPEED DIAL
The F4 offers two ways to set film speed, depending on film in use.
OX-Coded Film
While pressing the lock release, set the film speed dial to OX.
Camera automatically senses film speed (ISO 25 to 5000) of
installed OX-coded film.
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With dial set to OX, use only OX-coded film. If non-OX-coded
fi lm or film with a defective OX code is loaded, or no film is
loaded, lightly pressing the shutter release button causes the
red alert LEO to blink, and the shutler locks.