Nikon D300 - Manual (Page 134)

108
Z
3
Frame a photograph, focus, and shoot.
A
Non-CPU Lenses
If the maximum aperture of the lens has been
specified using the [Non-CPU lens data] item in
setup menu (pg. 197) when a non-CPU lens is
attached, the current f-number will be displayed
in the viewfinder and control panel, rounded to
the nearest full stop. Otherwise the aperture
displays will show only the number of stops (
F,
with maximum aperture displayed as FA) and the f-number must be read
from the lens aperture ring.