According to some of the notes in this article, the lowest dispersion glass grade that can be manufactured up to 32cm across without issues in Ohara's line is S-FPL51Y. For this project, pure CaF was too expensive. Raises interesting questions about the fabrication of large amateur apo refractors. Such as where do they get high-grade FPL-53 or its equivalent?
Unfortunately, most of the images I think were left out of the .pdf.
Edited by RichA, 31 May 2020 - 11:29 PM.