It is really nice Chris, lovely FOV. Feeling like a mosaic to match Andy?
Are you using the Vixen 0.67x FR? What I am thinking is that even if you have the spacing correct it'll probably not look crash hot around the edges as it is designed for a F/7.7 system. As it isn't made for telescope it may be over or under correcting at the edges, changing the focal spacing may help but it could simply be an artefact of using that FR on that scope.
The seagulls in lens are a combination of uncorrected field curvature and astigmatism (my Nikon 50mm F/1.8D has it BAAAAAAAAAD).
https://dl.dropboxusercontent.com/u/...of%20stars.jpg