Robin - I was looking at an extender for my 102 (and another for the 90), but bought a photographic teleconverter - a good one. I bought a Nikon TC-300 from Zane Hammond a while back, and it gives me better results than any barlow I've tried. It ain't a Tak extender matched to the scope, but it's a lot better than anything else I've tried.
http://www.mir.com.my/rb/photography...ter/index2.htm