[JA]

Hi Terry,

I mucked about with selectively masking the comet and adjusting the exposure of the background and ended up with a darker background for sure, but it ended up a little washed out (version NOT shown).

The version below does not use selective masking and achieves a better result than the selective masking version I tried. I used a grey point and white point adjustment and hey presto... most of the tail retained on a darker contrasty background. With more effort one could even kill the dust dots in the lower left, but they're also greatly reduced with the above adjustments. Another bonus, with the darkened background the star colour is a little more evident - See the large bluish star on the left side of the comet versus the large orangish star on the right side of the comet. Less really is more !

If it were me, I'd be happy with that as a result, given the conditions you imaged under and the starting point (I used your smallish 85.6kB JPEG above).

Best
JA