Sunday night was going to be a wide-field night using my Sigma 10-20mm zoom attached to the QHY camera. Things didn’t go to plan. The issue was focusing again. I’d cracked this on the 75-300 zoom but the Sigma is very fussy about back focus. A 10mm extension tube put the focus point beyond infinity and a 5mm tube was equally unsuitable at the other end of the focus range. So, I need something between the two but ideally it needs to be adjustable as well. Back to the drawing board.
With that plan axed for the night I put the Zenithstar 70mm on the mount and in the time remaining before Orion disappeared behind a tree took 90 minutes worth of 3 minute exposures of the region around Alnitak.
