Nikon D300 User Manual (en)

To choose a metering method, 
rotate the metering selector until 
the desired mode is displayed.
3D Color Matrix II Metering
In matrix metering, exposure is set using a 1,005-segment RGB sensor. 
Use a type G or D lens for results that include range information (3D color 
matrix metering II; see page 352 for information on lens types). With other 
CPU lenses, 3D range information is not included (color matrix metering 
II). Color matrix metering is available when focal length and maximum 
aperture of non-CPU lens are specified using [Non-CPU lens data] item in 
setup menu (see page 197; center-weighted metering is used if focal 
length or aperture is not specified).
See Also
For information on choosing the size of the area assigned the greatest 
weight in center-weighted metering, see Custom Setting b5 ([Center-
weighted area], pg. 277). For information on making separate 
adjustments to optimal exposure for each metering method, see Custom 
Setting b6 ([Fine tune optimal exposure], pg. 277).
Metering selector