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Thanks Mirko.
It is not just the glass and localised seeing. These scopes are made out of materials for which the engineers know their precise expansion and contraction with temperature variations, and the equipment is designed to react to these predictable parameters. Add heat and these are no longer predictable as heat is not uniformly distributed. It also introduces IR to their equipment.
Thing with the use of fans is not to do with our scopes being less than 1m in diameter. It is that there is a way to control dew WITHOUT heat.
Amateur Newts and open tube OTAs have been using fans to great effect for many years now - how fans are used is critical though as incorrectly employing them actually induces thermal issues rather than avoid and prevent them. Certainly not my invention to use fans with scopes! I just worked out a way to use them with SCT's, Maks and fracs.
Alex.
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