Tonight in the observatory has been a real lesson to me.  When I first setup the observatory, I put a steel pier in, and levelled it thoroughly.  Unfortunately, over the last 2 years, it has shifted, and I have been having increasing problems with accurate tracking.

Once I realised what the problem was, I re-levelled the pier and mount, rebalanced and drift-aligned using the excellent WCS software.  If you haven't used it - give it a try - it just requires a webcam and you can accurately drift align your mount within about 30 minutes.

Anyway, the good news is that it worked.  The bad news is that I experienced a blue-screen of death right afterwards, and it corrupted my EQMOD configuration file.  The behaviour was very strange - EQMOD would reach a particular area of the sky (around my target annoyingly - how did it know??!) in Cygnus, and would then convince itself that it was in the southern hemisphere.  Most strange.  It took around 2 hours to troubleshoot that problem!

I did manage to get a few more Sii subs for my NGC6888 Crescent Nebula - here is the result so far:

Full version and capture details available here