I cannot talk about the C11 but I think the RASA is missing resolution for smaller galaxies. I am not talking about M31/33/LMc/SMC, of course, and I think M81 is very large still, but those smaller fuzzies from the NGC. Its spot size as published is 4.6 microns which limits resolution to 1.6“. To realize this you also have to put in considerable work on each setup to get spacing, tilt and collimation perfect. It is a wonderful widefield instrument, though, and I have great fun using mine.
I looked at a lot of APO images of smaller galaxies and found that all taken with apertures smaller than 6“ are lacking in detail as compared to larger optics. So I think for small, detailed galaxy images you will need 6“ unobstructed apertures minimum.
On the other hand, seeing will probably limit the benefits of aperture for resolution beyond 8“. So something in the 8-10“ range is, I think, the sweet spot, and smaller means a smaller mount can handle it.
I think none of the „cheaper“ scopes (RC or SCT) are really great mechanically which is why I opted for a CFF 10“ RC (these are no longer made, but maybe some with (from my experience very good) GSO optics are still available).
I you have the space (I do not) I would recommend a nicely made 8 or 10“ imaging newtonian with a high-quality coma corrector. TS ONTC and the Lacerta Carbon Imaging are European ones that look very well made. I saw an advertisement recently for an 8“ American truss design that looked excellent, too. I can only share my research, though, and have no personal imaging newton experience. If I had the space, I would have gotten one instead of the RC.
Edited by Rasfahan, 27 February 2021 - 04:58 AM.