Although my scope came with a fan, it isn't needed.
Home-built Newt: 10" f/4.5 Royce conical primary, Skywatcher NEQ6 (Astrotroniks tuned) iEQ45, Duo-T, 8" f/4 Skywatcher Quattro CF 120 ED f/7.5 Skywatcher Black Diamond 80ED Stellarvue
Jeff Morgan - Wile E. Coyote School of Telescope Making
Quote:You might be right. As a generalization, I am finding the conical mirror shape, and reduced mass, are functionally important. I did have the telescope in New York for two months in the spring and would run the fan for a few min. during initial cooldown, and then seal the back of the tube. From that point, I felt the mirror tracked the air temperature very well.