Thanks very much for the focus images. I think there is one missing in the 1x1 set (10 and I was expecting 11). It doesn't really matter - I duplicated point 6 and use it as the 11th (in focus) frame.
So here is more or less what you get with bin 1x1...
Here, I've played around with the SEP settings...
What I've done is increase the noise threshold and increase the number of pixels that need to be above the threshold in order for star extraction to consider a group of pixels as a star. So, the effect of this is that I'm identifying less stars and the ones I'm identifying are bigger and as a consequence I'm excluding more noise.
I believe that by binning 3x3 its achieving the same thing; its boosting the S/N so you get less stars but also less noise masquerading as stars, which gives you better results. Here are my changed SEP parameters run on 3x3 bin data...
It works OK, but the number of stars is too low IMHO (<10 on most datapoints) so I would suggest that you match the SEP parameters to the bining level.
I'm not saying that these settings are necessarily the best as I've only got 1 set of bin 1x1 focus data to play with but it should point you in the right direction.
There is one other adjustment I would like to play with (it may or may not make much difference) but I need to know your image scale (have many arc seconds per pixel). If you don't know this just tell me your camera and telescope (and reducer if you have one) and I can look it up.
Hope this helps.