Thanks for the extra info guys. I like the grounded nature of these replies, so many of the CN replies seem to encourage people to buy things for the sake of it.
I'm going to wait for a night of good seeing over Sydney and then tease out what this optical artifact is.
Some research shows it might be astigmatism. If so, given the effect is distributed radially about the center of the field of view, that indicates that it would be eyepiece astigmatism. Yet I perceive it in my Tele Vue eyepieces, which should be well corrected for that.
So another culprit would be field curvature, which would explain the radial distribution and the abberations presence in both. I wear glasses but do not observe with them on, as I only suffer from spherical abberation (no astigmatism) and can tune the focus wheel to compensate for it. However, I might be lacking the ability to focus on the stars at the centre and edge of the FOV at the same time.
So it's not an easy diagnosis, but my suspicions are now more directed at field curvature than coma. This is going to take some detective work, if it is field curvature I should be able to tune the focuser to get the edge stars sharp and the centre of the FOV blurry.
I found this website handy by the way:
http://umich.edu/~lowbrows/reflectio...scobel.27.html
Cheers,
Richard