Since I use a coma corrector in my F5 dobson I try to mantain collimation as perfect as I can, but I was noticing some tube flexure (not focuser flexure) when the focuser was loaded with the corrector and heavy eyepieces. It wasn't too much but enough to be readible at the autocollimator unstacking reflections just a bit.
Instead of reinforce the tube with an inside metal ring I decided to try another cheaper and lighter way trying to not compromise the tube balance. I have used 3 embroidery circles to aply press to the tube and now I can add 1.5 kg to the focuser and autocollimator reflections stay stacked.
Edited by cloudypatio, 27 February 2021 - 11:56 AM.