Unable to find a valid set of star pair matches

[Diane Miller]

I've gotten this error on the last 2 runs I've tried.  I only have an Astrotrac but I have gotten decent PA both times.  There was poor seeing and some wind, so the stars were not completely round, although focus was good.  I eliminated the worst frames before starting.  Just wondering if I'm doing something wrong.  Is there some parameter to loosen the tolerance a little?  If I reduce the number of stars from 500 I get more frames that give matches. 

Is this just a function of the files not being good enough?  Is there any fix up front for bad stars?  I was going for some nebulosity (the Lagoon) and did blow out the brightest stars.  Could that be part of the problem?

Thanks!

[pfile]

what's the focal length? if there are a billion stars you could have problems. i suggest the "detected stars" mode of StarAlignment to see what SA is considering stars. could also be picking up on noise...

rob

[Diane Miller]

Thanks Rob, I haven't used that one but will give it a try.  I was using the Canon 7 Mk II with the Canon 400 DO II + 1.4X III teleconverter, 560mm focal length, very sharp optics in good conditions.  There were quite a few dim stars, showing some color.  Brightest ones blown out.

Here's one of the raw files exported from Lightroom, and a crop to show detail:
https://dianemiller.smugmug.com/Photography/Files-for-PI-forum-2/n-BBs62B/i-gNfwV76

[pfile]

hmm, yeah this FL should work OK i think, though of course it's a very busy part of the sky

anyway in the star detection tab of star alignment, there are some relevant controls... if you hover your mouse over peak response and maximum distortion you'll see some tooltips that should guide you. the detected stars mode is really useful for tuning these parameters.

rob