These are some nice images Barry
I get blue halos with my ED doublet - I think RGB imaging through a refractor is probably best done with a triplet.
From my limited experience, surely large aperture helps when imaging, but faint details can also be successfully captured with small telescopes, and small telescopes are generally more 'user friendly', especially when starting off astroimaging adventures.
I might be bragging, but this image taken with a 4" doublet from a balcony only about 2km from Brisbane's CBD compares surprisingly well with those taken with 17" telescopes.
http://www.astrobin.com/full/148715/D/