The DK-17A Anti-Fog Eyepiece from Nikon is
a replacement viewfinder eyepiece that uses specially surface-coated
transparent plastic to reduce condensation or fogging. Designed for use
in humid or cold weather, when fogging is most likely to occur. The
DK-17A is compatible with Nikon D2 series, D3 series, D4, D700, D800,
D800E and F6 cameras.