Hey Ron,

that's great to hear! And makes me wonder: Do you use a color camera?
I did have comparable issues (with star detection) when using a color camera as guider, and everything started working when switching to LUMA mode, or bin 2x2.....

And a short remark again to that different-stars issue: On first hand, seeing and defocus determine the point spread function for the image, and in theory this PSF is the same everywhere. So the shape (and thus things like FWHM etc.) are the same for all stars, and it doesn't really matter which of them you use.
In praxis, especially for short exposures, seeing will vary over the FOV, and averaging over many stars will give you a much better estimate of the seeing than a single star. The same is the case for the instrumental PSF, that can vary across the image: Collimation errors, as mentioned already, curvature of the focal plane (mainly for refractors) etc. Also there you usually want to get the best field-averaged focus. And again, the errors there do not depend on the star, only on position in FOV, and as long as your star ensemble is spread uniformly across the FOV it doesn't matter which ones are used....

Read More...