laxx wrote in post #4220042
I was looking into this a few months back, but kept reading about how the image quality is pretty bad with the Nikon eyepiece. Care to share your experience?
With the DK-21M on my 30D, looking through the new eyepiece did slightly help on the magnification part, I didnt notice any cropping at all but I found that the lens on the DK-21M to be smaller than my 30D VF. This meant I had to stick my eye right into it. Looked great - didn't even notice any contrast loss maybe very very slightly but nothing to worry about. So the eye piece lens is probably closer to the size of the VF on an XT/Xti.
The fit on the DK-21M eye piece onto the 30D was almost snug... but not a perfect tight fit. A slight annoyance but acceptable.
So I decided that I wanted a larger eye piece opening so looked into getting the MEA-17M/DK-17M combo with 21% magnification and the eyepiece lens is alot bigger.
I went to this site http://www.ircube.jp/main/product/mea/eng_kd.html
and found MEA-17KD, an adapter that accepted the DK-17M and fit perfectly onto my 30D - ordered it, got in about a week.
It's definitely better than the DK-21M but there is some loss of contrast.
Overall it performs pretty good, magnification is great, I keep it on 100% and my nose no longer greases up the LCD screen 
Cost for DK-21M $35 at a local store
Cost for DK-17M + all the adapters necessary $90 shipped
For a 30D I would not go anything less than the 17M.
For the XT/Xti, choosing DK-21M is not bad.