Nikon f2 - Manual (Page 42)

For automatic diaphragm lenses with no coupling prong,
such as the Zoom-Nikkor 200-600mm f/9.5 lens and
super-telephoto lenses using Nikon focusing units, set
the camera to the desired shutter speed; then, depress
the depth-of-field preview button to stop-down the lens
diaphragm and, while holding the button depressed,
adjust the aperture ring until the center LED indicator
comes on. Be sure to release the depth-of-field button
prior to making the exposure.
For bellows units, extension rings and preset lenses, set
the camera to the desired shutter speed; then, stop down
the lens manually until the center LED indicator comes
on. Preset-type lenses include PC-Nikkor lenses.