If you're looking for a 10 to 12 inch f/3 or thereabouts system that is fully corrected and has a flat field, which can also be made by an experienced mirror maker, I suggest a Busack or Honders-Riccardi type dialytes. Here's an example of one
All surfaces are spherical so the configuration can be readily scaled, the glass substrate used for the corrector, the primary Mangin mirror and the field flattener lens is the affordable N-BK7 (Schott) or BSC7 (Hoya), S-BSL7 (Ohara) or similar crown. The system has a flat, diffraction-limited, Schmidt-camera-like wide photographic field of view of 3∘, and is essentially color-free, better even than much slower APO objectives.The absence of aspheric surfaces greatly eases production and testing.
The convenience of being able to bring the focus outside the tube is a great advantage over the classic Schmidt camera. The added bonus is that such systems are visually excellent as well, save for the large central obstruction, which is unavoidable in very fast configurations.
Notice also that the corrector is almost a plano-convex lens. In fact, it can easily be designed as a pcx lens if needed. This is by far much easier to make than a Schmidt corrector. The field flattener ubaperture lens could even be an off-the shelf stock lens of commercial quality. What this lens does is flatten the field by a judicious redistribution of astigmatism as seen in the Wright telescope and the Linfoot camera configuration of the late 1930's and 1940's. http://adsabs.harvar...MNRAS.109..535L
A similarly well corrected all-spherical configuration can also be designed in a Cassegrain mode. Officina Stellare in Italy and AstroPhysics in the US have offered (or still offer) such instruments in sizes of 300 mm (12-inch) aperture operating at or near f/3 to f/3.5 photographic aperture. No Newtonian+Parracor will ever rival these configurations.
Unfortunately these solutions remain relatively unknown in the amateur world. Be the first to break the mold, and make one. You will surely get a Stellafane award. :o)
Very interesting !
First I will study to be able to evaluate the technical aspects.
A first analysis I had an excellent impression.
Thank you very much.