Mo' focal length, mo' problems. I'm using my Celestron C9.25 SCT (focal length - 2280 mm) with the NINA autofocus routine. So far, not so good. I've had great results with my refractors, but very poor results with the SCT. We take a look at NINA's Half-Flux Radius (HFR) and compare it to Astrophotography Tool's (APT's) Half-Flux Diameter (HFD) and Inverse Power method. APT's HFD wins! Will try the Hocus Focus NINA plugin next.
APT Inverse Power Paper:
https://drive.google.com/file/d/1LSuSElozryAOwzL-59rAyG2gzDn5ca_S/view?usp=sharing
Bahtinov Mask Focuser Characterization:
https://youtu.be/qXcZ3ZMMMco
https://youtu.be/3YLG2Qdzgk8