SCT AutoFocus


I broke out my 11" Edge SCT the other night after a long break where I was using my refractor only. I decided to image at F/10 with 2x2 binning (KAF 8300), just to see what kind of results I could get.

At some point in time I did have SCT focusing dialed in pretty well – the key for me was keeping the step sized constrained to avoid donuts, and ensuring there was backlash compensation. But I ran into some troubles the other night - my AF runs were more or less zig-zag patterns. When I switched to pinpoint/FWHM, I got a pretty tight v curve.

Part of the problem was that only a few stars were found. I think I can tweak this with appropriate nebulosity rejection and dark frame subtraction. I kept the AF packages, but is there a way to have SGP recalculate the HFR as the AF routine would? (That is, with nebulosity rejection / dark subtraction?) This would allow me to tinker to see if I can fine tune my settings.

I did load the image in SGP, right click and calculate the HFR, but it’s picking up a lot of noise that I think the AF routine avoided…