Compatible with F-501/401/s/x/301 FG D60 D300 D3100. The Nikon DK-5 eyepiece cap is a shield that prevents interference during long exposures from stray light when your eye is not behind the viewfinder.
When using the self timer or remote release, it is recommended to remove the viewfinder eyepiece cup and attach the DK-5 eyepiece cap. This will prevent light entering the viewfinder from affecting the exposure in auto exposure modes. Additionally, they are also claimed to protect Nikon camera's viewfinder from dust, dirt and moisture.