Nikon F4 - Manual (Page 88)

Aperture-Priority Auto Exposure Mode (A)
This mode operates with all Nikon lenses. When used with any
optical system such as Reflex lens, microscope, telescope,
bellows, etc., the F4’s microcomputer automatically selects the
correct shutter speed to match the aperture you set. This is the
recommended mode when depth of field is your prime con­
sideration. For less distinct backgrounds, as in portraiture, use
larger apertures to obtain a shallow depth of field. For overall
sharp, clear pictures, as in scenic photography, use smaller
apertures.