Nikon D100 Manual page 190

Optional Accessories
For the D100, Nikon recommends CPU lenses, particularly types G and D, as it
is only with type G and D lenses that you can use such features as 3D-matrix
metering and 3D multi sensor balanced fill flash for digital SLR. CPU lenses
can be identified by the presence of CPU contacts. Type G lenses are marked
with a "G" on the lens barrel, type D lenses with a "D."
CPU lens Type G lens Type D lens
Type G lenses are not equipped with a lens aperture ring. Unlike other CPU
lenses, there is no need to lock the aperture ring at the minimum aperture
setting (maximum f/-number) when using a type G lens.
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