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It's hard to find information on it - but from what little I can find out it is a doublet BK7 lens, with the rear end of the second lens aluminised to make it a mirror. In a riccardi-honders you then go to a lens group to make an astrograph (you can buy them atm, A&M sells a 300mm F3 astrograph), so a riccardi-honders cassegrain would have much shallower curves going to a mirror secondary then to a second lens group then through the rear of the scope. You can make it at F8 with a small obstruction (26%).
Last edited by Kal; 03-04-2009 at 08:17 PM.
Reason: correction
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