Collimation or mechanics..?

[lukepower]

Hi guys,

 

somethimes I feel like I am running around a pot of food like a hungry dog... I checked today - abusing of the "nice" weather with clouds in every direction you look - a few of the latest frames with CCDInspector, and noticed an unexpected difference in the last days:

 

Alright, sunday:

 

ANd monday:

 

Sure, CCDInspector has its limits, but it's using plenty of stars. I just wonder what the heck is going on there. It's the same target near zenith, so even tube flexure shouldn't be the problem. Just looking at the latest curvature map I was thinking about a miscollimation of the primary, or the secondary not being perfectly centered (mechanically) on the optical axis. But counting the quite good result the night before it doesn't make sense.

 

Now, if I consider FWHM's of 3" and more, I still feel I am off with the secondary and causing some astigmatism and/or coma. I did had lots of trouble with my scope prior to getting this - quite good in relative terms - collimation done, so it is absolutely plausible that I am still away from optimum here...