I checked the 6" mirror in a sun test, and it was about f/7, f/7.5, f/8. I think it's f/8. What focal ratio U should choose? - - - - - - - - - - - - - - - - - - Looking for a webmaster? E-mail me. Asaf Shtull-Trauring, asafs@ibm.net http://www.maxnm.com/asaf/ http://www.maxnm.com/asaf/nsc/