Nikon D300 User Manual page 656

Command dials to change aperture or shutter speed in 1/3 EV
steps. If you'd like, you can set b2 to 1/2 or 1 EV step instead.
When you are metering your subject, a bar will extend from
the zero in the center toward the plus side to indicate
overexposure or toward the minus side to indicate
underexposure (see Figure 9-12). You can gauge the amount
of over- or underexposure by the number of dots and lines the
bar passes as it heads toward one side or the other. The goal
in Manual mode is to make the bar disappear. In Figure 9-12,
the bar indicates 2⅓ EV steps (stops) overexposure.
Figure 9-12. Control panel with M-Manual mode
You'll adjust the aperture with the Sub-command dial and the
shutter speed with the Main command dial.
Note on Lens Types – With newer G lenses, you can control
the aperture from maximum to minimum by using the
Sub-command dial on the D300(S). If you use an older AF
lens with an aperture ring, set it to the smallest aperture on the
lens, then use the Sub-command dial, instead of the ring on
the lens, to change aperture. If you have an older non-CPU
lens, you'll have to use the aperture ring on the lens to control
the aperture.
656