Today I have a follow up to my original note declaring that the C11 Edge, at f7 or f10,?is not suitable for guide scope tracking for anything over 100 seconds or so. The question I had, that?remained unanswered, is?what is it about the OTA that?is causing the?star drift, in an otherwise?Very well?guided mount.
I now have the answer. The main mirror is shifting within the OT.
Evidence I'd collected,?indicated?that this?was?a?leading suspect, though?there were too many other possibilities and?unknowns to say so for sure. To put the question to bed, I finally decided to?drill and tap 5 of 1/4-20 holes in the OT, around the circumference, 72deg apart, in line with the outside edge of the main mirror. I then?turned?5 nylon screws in until?each?slightly snugged against?the edge?of the main?mirror. End result,?300 sec (5 min) images,?with a?standard guide?scope?setup, now?track "perfectly". By around 10 min,?some elongation is regularly?noticeable, but whether acceptable being a matter of taste.
