[JohnH]

After about a week or so of trial and error I think I am getting a good result. My findings have been:

1. Gemini PEC does not yield significant improvement without adjustments which are hard to make with just the controller - curve smoothing, drift compensation and phase adjustments may make it work but it is not easy.

2. PEMpro or equivalent software lets you see what is going on and therfore give far better contol of PE - in theory however my results have be inconclusive as to the merits of PEC on the G11.

3. Guide parameters and alignment are FAR more important to get right than PEC. For a mid range mount like the G11 corrections should be small and a dead band should be set to prevent chasing the seeing. How you do this varies dependanty on the software you use but in may case I find exposures of 0.5 to 1s, slews limited to 250ms max at 0.5x and a min move of 0.5" for RA and 1" for DEC works well. Do not think you can compensate for bad seeing with longer exposures - I did and it does not work, reduce the exposure/gain to get a good guidestar (point) that is not saturated. Measure your PE and make sure the sware cannot send corrections bigger than the max PE possible in the guide/exposure cycle. Finally adjust aggressiveness (if you have to) so corrections do not cause overshoot.

Now having said all that my result in not perfect - I seem to have round stars only in a pert of the image - I think the remaing distortions are as a result of a combination of field curvature combined with lack of rigidity in the focuser (127mm ED scope with the stock focuser) but I would value other views. Basically I am happy if I am beginning to see other sources of error than the mount.