Nikon DK-19 Rubber Eyecup
The DK-19 flaring rubber eyepiece mounts over the DK-17M or similar on the Nikon D3/D3s/D3x/D700, and possibly others.
The DK-19 is very helpful in blocking side-light (eg sunlight) while composing or focusing. This allows your eye to relax and see through the viewfinder more easily. It also helps for regular viewing, simply by letting your eye relax.
Reader Peter G reports the following when using the DK-19 with the DK-17M:
One thing that has caused problems in the past, is that the little steel retaining ring that slips over the DK19 rubber eye cup often comes loose, and the rubber eye cup falls off.
I have not experienced this in my use so far. However, I find that one can omit the retaining ring with the DK-19, and ironically this yields a more secure attachment, because the DK-19 slips inwards past the outer lip of the DK-17M, and thus must be deliberately stretched to be removed. With the retaining ring, the DK-19 is wrapped on the outer lip, which is why it can easily come off. The downside to omitting the retaining ring is the loss of 1-2mm of “depth”, but I did not find this to be an issue.
See my hand-picked Nikon list.