Ritchey-Chretien optical sets from GSO seem to be of reasonable quality and not too expensive. For instance, APM sells currently a 16" f/8 optical set for €2,990.
I am wondering whether the hyperbolic primary (which is f/3 I believe) could be used also at primary focus or Newtonian focus with a Ross-type corrector, preferably made with off-the-shelf lens? I don't know if the conic constant imposed by the RC formula works also in such configuration. For the 16" version it seems that k=-1.1 (using that primary to secondary distance is 900mm), while for the 8" version k=-1.2 was found there.
It would be a way to get a larger version of the Tak Epsilon astrographs at a reasonable price...
Edited by Dan_I, 30 November 2023 - 06:46 AM.