I was just browsing the eyepieces entry in Wikipedia. Really well written piece for someone who still marvels at the quality and variety of astronomical products available these days compared to the very early 80s.
http://en.wikipedia.org/wiki/Eyepiece
The diagrams of the various eyepiece designs very informative. Can still remember reading Patrick Moore textbook descriptions of Kellners etc and wondering what they'd be like. Now we've got Ethos, Pentax, etc etc.
Happy time to be a visual or photographic astronomer.