I use an ST7E with built in guide chip so my set up is a little different, but here are my general settings for what it's worth.
- I have the capability of being able to calibrate on any star on the guide chip, and the advice is not to saturate the guide star as it may cause false guiding corrections to be made.
- I have read that 3s to 10s is the optimum guide star exposure range. Less than 3sec exposures can result in you “chasing the seeing”, more than 10s may not correct guide star excursions, resulting in trailing. I like to use 5 secs whenever I am able.
- For focal lengths under say, 800mm, correcting at x1 sidereal rate is okay.
- Imaging at 800mm to 2000mm, set the correction speed to x0.7
- For over 2000mm I reduce corrections to x0.5 sidereal rate.
You are right – this is not easy but persevere and you will succeed as I understand that the Vixen Sphinx is a well engineered mount.
I personally find that I can “easily” auto guide at 1000mm and less; anything over tends to take a bit of tweaking and is not as straightforward.
Good luck!
Dennis