Thanks for your offer Greg - have PM'd you. And to Gary & Mike, thanks very much for the information. IIS is a great forum, because there's so much knowledge out there that people are happy to share. And yes Mike, I did get the info off the filters!
Anyway, as you suggested I did a search - your term "mirror lens" was invaluable, and opened up a wealth of information. The brand is MTO, and this company was the first to bring mirror lenses onto the market. Russian mirror lenses are looked upon as a bit 'down market' in some quarters, but other people swear by their quality.
Anyway, the interesting news is that 1.25" visual backs are available for MTO mirror lenses, meaning that for a few extra bob my son could have a nice little Mak Cass telescope if all else failed! Link is:
http://www.telescope-service.com/mak...O1000Zubehoehr
Still used in telephoto photography, although 500mm/f8 seems the most popular. Even found a site with MTO 1000mm/f10 photography, mostly lunar, some terrestrial etc:
http://api.flickr.com/services/feeds...format=rss_200
So there you go! Seek and ye shall find!
Thanks again -
Cheers -
Rob