[tornado33]

Thanks all
Alchemy, I use Iris to do both the dark subtraction/flatfielding and aligning/stacking. It has several ways of aligning, the simplest is one star align wher I draw a box around a single star, it will then attempt to align on that star in all the images, however it needs to not have other bright stars in the box I draw. In this case I drew the box round the centre of the comet, the stellarlike core was what Iris aligned on, ignoring the background stars.

Here is a shot from last night, using the 300mmf2.8 flourite lens from Bert. Conditions nowhere near as good as the pervious night, but the CLS filter and fast f ratio helped
5x3mins ISO1600, Houghys cooled camera and CLS filter
Theres a gap in the trailed stars as I had to stop for a bit when cloud came through
Scott