Nikon F4 Instruction Manual page 52

1. Set lens to its minimum aperture (largest I·number).
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With AF Nikkor lenses, lock lens aperture ring at its mini-
mum setting. (See lens instruction manual.)
2. Lightly press
shutter release button and confirm exposure in
the viewfinder.
Shutter speed is controlled steplessly from 30 to 1/8000
second. Controlled aperture value and shutter speed are
steplessly selected. They are indicated in the viewfinder LCD
in 1/2 EV steps.