Thanks for the response and the advice Ryan. Yes, in future I will shoot flats with this camera. It will be interesting to see what difference it makes with such a tiny sensor so I'll give them a go next time I use it. No CC used either, I thought the tiny sensor would not include any of the peripheral aberrations of the 6 inch mirror but it is an f5 scope and has obviously shown a CC is needed for this
uncropped image.
