ronaldnc It seems that the guiding is confusing which star to track.
That is exactly why you need to understand what multi-star guiding is doing and not just take my word for it.
I have over the past few months descibed the process over and over, and tired of repeating myself, so you would just need to search the Forum archives.
Search (probably a few months ago) a posting that includes the bar chart showing the distritbuion of stars relative to their signal to noise ratio.
ASIAIR uses signal to noise ratio to weight the centroid averages, and when there are one or two really bright stars in the frame, this SNR weighting causes the equivalent of just one or two stars being used instead of 12 stars, even though you see it select 12 stars (i.e., the weights of the rest of the stars are miniscue).
When the brightest star scintillates so that the next star is now "brighter," (higher SNR) ASIAIR will suddenly place a huge weight on that other star, while redusong the weight on the previous star, and thus suddenly move the estimated centroid.
When you increase the gain (by a lot) so that the brightest stars are saturated (and thus ignored), and the remain stars have more evenly distributed SNR, then multi-centroid star averaging will work more like what you expect it to work.
Until you understand this previous paragraph, I would recommend not just randomly play with the gain. I never believe in telling people what to use. I prefer to tell them what is the underlying factors, and let the folks who are willing to spend time understanding the problem to come up with the solution themselves (... teach a person how to fish and you feed him for the rest of his life...).
Chen
