There is a 10” Carl Zeiss Refractor for sale on Ebay. I would like to know if anyone knows about the possibility to make a flourite 4" lens that is mounted about 3 feet from the tailpiece to produce Apochromat quality images? The owner says this scope has one made by Roland Christen.
The objective is F/16, but if I understand correctly with the correcting lens it is about F/13, Any possibility of such, and any designs would be appreciated as I have a 9.5" Achromat blanks set, which would be better than the triple folded F20 I have been contemplating.
Many thanks from Old Will