I've got the Nikon Fieldscope MCII zoom eyepiece, which I believe is 7 - 21mm, although Nippon Kogaku seem to release remarkably few specs for their gear, even top of the range stuff like this. Nikon eyepieces use a non-standard screw mount for which Tomy make an adaptor to 1.25" in their Borg series of astronomical fittings (available through the excellent Hutech:
http://sciencecenter.net/hutech/borg.../html/7162.htm).
The zoom is primarily used in my PST, where its high contrast and very flexible focal length work brilliantly and the somewhat narrow field of view at lower magnification is not an issue. It is also a splendid planetary/lunar viewing eyepiece - if it wasn't for its dedicated PST usage, it could easily replace my fixed eyepieces for those applications.
In a previous life as an amateur photographer, I always understood that zooms suffered from low contrast and indifferent resolution - seems nobody told the wizards at Nikon!