Sam, I've yet to put grit to glass for any sort of lens, but I've done a fair amount of preperations. Design wise my thinking has focused on the chromatic issues. Since a 6" doublet must be f/24 or there abouts to be diffraction limited, minus vilote filters and/or designs tuned for green to orange look good to me. Some day (soon I hope) I'll get going on the 3" doublet. Anthony