Hello!! It's Joseph

  cassegrain telescope on cloudynights , which is also on S&T Oct 2006 from mike lockwood : given: R2(sec ROC) = 47.35" secondary distance to primary focal point p (circled in orange) = 15.72" conic of primary = -1 (parabola) conic of secondary = -4 (hyperbola)   appendix on CassDesign: Unvignetted Field Width at Cass focus is the dimension in the user-chosen units. P = distance of secondary vertex inside primary focus P' = distance from secondary vertex to final Cass focus The back working distance (BWD) is from the primary mirror vertex to Cass focus. It is also P' - SEP, where SEP is the vertex-to-vertex mirror separation. BWD must be personally chosen to include enough distance for the primary mirror thickness, the primary support system, the back plate thickness, the optical path length through any fold optics, the height of the focuser, and the desired distance from the top of the focuser (maybe at midpoint travel setting) to the focal plane. BWD is entirel...

This is a spot diagram of what an e.g. 8 inch F8 Ritchey Chretien is supposed to perform like off axis. It's from page 68 of Telescope Optics by Rutten and Venrooij.  I see no coma at all but there is the strongest Field Curvature of any Cassegrain design, (without the ACF coating), plus some astigmatism, but the star images are pretty round a long way off axis (that's why professional astronomers use RC's, since they like to measure the Star images and round images are easier to measure).   cloudynights Chungblog  

 there is discussion from Cloudynights For lunar/planet viewing, I would choose the C11. In most locations, the usual mediocre or poor seeing compromises scopes above 6-inches or so. Combine the seeing with objects that are not always positioned perfectly high in the sky and both of these scopes will be affected. The Mak might produce a very slightly sharper image compared to the C11. The C11 will produce a brighter image and will have more resolving power when the conditions are good. The C11 will be better for deep-sky viewing and imaging. There is a comparison here on CN between a high-end, 9-inch Mak and a C11. The C11 came close in most observations so it should deliver better performance against a commercially produced 7-inch Mak. (meaning C8 is inferior to a Mak7?)  Things to consider for best performance: Collimation, Thermal Management, Dew/light shield (some of the best nights are moisture heavy), A good aftermarket focuser, a good aftermarket high-end diagonal, good...