In my country, there are no discussions anymore about wether or not insulating is more effective than cooling with fan's.
The people who don't want to accept insulating, mostly are the ones that didn't try it (yet) in a proper way.
Some even think they already know in advance that insulation doesn't work, I wonder why.
I started insulating some 20 years ago, and will never stop.
C90 or 16" SCT, there is virtually no 'cooling time' anymore!
As already written here before: Insulation only works for 'closed' optical systems.
Edit: Insulating also solved another 'challenge': We always want glass with low termal expansion for our optics.
But with insulation, the cool down of the internal optics is slowed down in such a drastic way, that even my plate glass 16" mirror inside my SCT can keep up without the slightest deformations normally caused by temperature differences in the glass!
It means that because of insulation, simple cheap plate (float) glass suddenly is very usable for even the biggest mirrors.
Yes, it took quite some time and tests for me to accept that fact!
Back in 1992, I found my 8" Newtonian not performing well because of thermal issues, in that time we believed that primary's should be quite thick, but that made them a nasty radiator of warmth during the entire night!
I developed a watercool system on my 8" and later on my 12" newt (1995). Cooling that mirror solved the temperature problem completely, yes, the 12" needed some 40 minutes too cool from 21 degrees C towards 5, but I didn't know how much I would gain with a diffraction limited performance of a 12" newt!
Years and years of amazing images would follow, and it still is going strong!
So, in very short:
With optically closed scope's, insulating is the way to go, but of course, that is my own believe based on my experience..
With 'open' systems (newt), insulating is not the way to go, but there a lot is already won by the nowadays much thinner primary mirror.
Edited by yellobeard, 27 April 2019 - 02:11 AM.