I am having problems generating V-Curves in SGPro for my (fast) F/3.8 Astro-Physics Riccardi-Honders Astrograph using the Starlight Express Focus Boss II electronic focuser. I have also noticed that there is no consistency in the focus point between different nights. Sometimes the focus point (tested with a Bhatinov mask) is 12,000 steps, others 16,500 etc. From examining the Half Flux Radius (HFR) manually through the RH305, to reach the CFZ I need between 10 and 20 steps to start seeing differences. I have no problems controlling the focuser from SGPro in temperature compensation mode where the delta is c. -25 steps each 1 degree (F) drop. I previously used exactly the same Focus Boss II on an F/7 refractor and had no problems generating V-Curves.
On a 7-step auto-focus run I expect the focuser to rack out 3 steps and work its way back in past the focus point. The first exposure sample is correct, but successive samples start going all over the place. My graphs look more like a W than a V. I have tried all sorts of combinations of step and sample size with no luck. The Astro-Physics 3.5” rack and pinion focuser cannot slip, so I am trying to eliminate other variables.
On the Astro-Physics User Group a comment was made that auto focussing in SGPro can be problematic at fast focal ratios and that a new beta is taking another approach. Does what I am describing seem familiar to anyone?