I was perusing the new book from Willman Bell, Telescopes Eyepieces Astrographs, and see the authors have proposed a fairly simple field flattener that would improve Meade's ACF design for astrophotography. The corrector is a cemented doublet using N-SK5 and N-K5 glasses. It produces a coma and astigmatism free flat field about one degree in diameter, but with ~ 25 micron spot size.
Jim McSheehy
