Nikon Autofocus Speedlight SB-22 Instruction Manual page 18

2_ Set aperture.
With Nikon F-401/N4004, use camera's aperture dial.
Don't forget to lock lens at minimum position.
For programmed TTL operation, set to smallest lens
aperture (largest f-number) and lock the lens aperture.
(For details, see the lens instruction manual).
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