I followed Robin’s method of capturing a series of Miles stars just for practice and instrument response/calibration.
It works well. (Unless, like i did on one occasion, you misidentify a comparison Miles star. That leads to some head scratching! But reinforces Kevin’s point).
i particularly like the Miles database excel spreadsheet for finding suitable Miles stars. Very useful.
Kevin, I don’t know if I understand your description above correctly but are you guiding through a guide-scope/camera separate to the Alpy guide module?
If so, I managed to do this down to (above) mag 12 target but only with a fixed setup and considerable patience. It was also prone to wind, bumps, etc. A QHY5LII through a 50mm finder/guider would plate solve in SG Pro. But I then had to manually point to the target for the last few pixels. I couldn’t get SG Pro to be that accurate.
I now follow accepted practice. A Lodestar or G3 on the Alpy module. Can’t plate solve but the field is big and bright enough to find a star. Actually, I’m at the point where I can find/see far fainter than I can capture usable spectra. I use the QHY/Finder as a rough ‘first-pass’.