Thanks for the compliments everyone
Mirko, no reason why you wouldn't also insulate a refractor. While a refractor does not have a primary mirror or baffle tube, it will also benefit from insulating as it will also forego the need of a cooling period. As with SCT's and Maks, insulation will only slow down the dewing up of the optics, not stop it. That's were fans come in to stop its formation. That's the whole premise of the use of fans, to get away from using heat.
We need to change our mindset about the need to use heat. You DON'T NEED HEAT. You shouldn't.
Last night was a very dewy one for me here in Sydney. I set up my 9" Mak at sunset, with its wrap. After two hours I started to notice dew forming on the mount and dampening the wrap. So I installed the fan and flicked it on, with all the juice it could take. By the time I finished up at 4:30am, EVERYTHING was soaking wet, including the wrap, but the corrector was nice and dry
What did fog up was my eyepieces, but that's easy enough to deal with. With only the insulating wrap, the corrector would have started dewing up after a couple of hours, and I would have had to give it a shot from a hair drier every little while over and over again, if not put an end to the session altogether.
Bob, the thing to look out for with fans is the amount of air they they push through. That fan that your put a link to, it depends on the dew conditions of any given night and the scope. In light conditions, that fan may be enough for refractors and SCT's & Maks. But in heavy dew conditions, like it was for me last night, that small fan may still be ok for a
small refractor, but it won't be enough for an SCT or Mak or possibly larger refractors.
The PWM unit gives me the versatility with my Mak and refractors, and the conditions of whatever each night throws up.
Alex.