Thanks for all the comments folks. I did not use any autoguiding. I just let the mount run. The longest exposures were eight minutes. The astigmatism can be explained by the rather large thermostat shielding one side of the base of the lens.
See here
http://www.iceinspace.com.au/forum/s...ad.php?t=44558
I have been testing the new thermostat and it is really working well. The whole lens is being maintained at 20C with the fridge at -5C. This thermostat has two relays that can be individually set to respond to different settings from the same temperature sensor. This allows two heaters to be controlled to manage the heat distribution far better.
What this really means for me is that I can set the system to take 20x16 min exposures and I can go to sleep. As I do not need to adjust focus with any ambient temperature change.
Bert
below are a few quick pictures