Hi Markus
I did see a video on Planetary astro that covered a lot of ground and spoke specifically also about focus. I will have a look through my history and see if I can recall it to post it here.
EDIT (that was quick, found it)..... Longish Video Presentation 55min - Wonderful jupiter Image at ~12:20 onwards followed by camera/focusing discussion, a few years old now also lovely animation of Jupiter at ~41min
https://www.youtube.com/watch?v=puoh1ikzonA&t=836s
Best
JA