Nikon DK-17M and DK-21M Magnifying Eyepieces
One common critique of the smaller DX-sized sensors used in Nikon digital SLR cameras has been that the viewfinder was correspondingly smaller, making critical use harder than it was with film. Nikon engineers have already compensated for the size differential some in the design of the camera, but there is still a noticeable difference when using the stock eyepiece.
But there is an easy fix.
Nikon took heed of their customer's feedback and came up with a magnifying eyepiece dubbed the DK-17M. Not only was it in scarce supply when first released in 2005, information about it was scarce too. After spending an evening searching the internet for details, I ordered one for my D2x. On backorder, it took three months before I finally received it.
The DK-17M fits Nikon bodies that accept round screw-on eyepiece accessories, replacing the standard eyepiece on the camera. All you have to do is unscrew the stock eyepiece and screw on the DK-17M in its place. It provides a 1.2x magnification factor giving you the big, beautiful viewfinder image you've always wanted. It is slightly thicker than the stock eyepiece, but not unduly so given the benefits it provides. You should get used to the change quickly.
It will fit on film bodies that use round eyepiece accessories too, with varying degrees of success. Reports are that you may just be able to see the entire display on some while it may vignette slightly on others. If you're doing macro photography, the increased size may be worth it, but most film users won't really need it.
Not all Nikon digital shooters will find the DK-17M as easy of a fit as I did either. For some reason, Nikon makes camera bodies with two different styles of eyepieces. Users of bodies such as the D2x and D1x that use round screw-on eyepieces will find the DK-17M will fit, but those who have a D200/D80/D70/D50 will have a harder time of things since their cameras use rectangular eyepiece accessories.
You might assume that the standard Nikon #2370 adapter will solve this, but it doesn't. Annoyingly, the DK-17M is slightly too big to fit the #2370. Some people have forced a #2370 to work, gluing things together after enlarging the hole using a wooden dowel wrapped in sand paper or other means. I have also seen a badly translated webpage from is a company in Japan called IRCUBE Co. Ltd. offering an adapter they call the MEA-17M that together with the #2370 will do the trick, but there's a better solution now.
Earlier this year, Nikon released the DK-21M that directly fits bodies with rectangular eyepieces. It slides over the "flanges" exposed after pulling off the stock rubber covering that comes on Nikon's rectangular viewfinders. So, if you use a D200, D100, D80, D70, or D50 you can now get a DK-21M rather than being forced to make a DK-17M fit. Nikon says it provides 1.17x magnification so it's not quite as strong as the DK-21M, but its close. If you go this route, no #2170 adapter required.
And just so you Canon shooters don't feel left out, here's a picture of an EOS 5D fitted with a Nikon DK-17M. No word on how they did it.