I have not tried insulation - but I have indeed posted images of the Airy pattern that compare measurement of a star in-situ and compare it with theory - and it is essentially perfect. I have also posted numerous thermal studies and so forth. I am way ahead of the insulation folks in terms of posting actual results to demonstrate that my approach works well. And there is nothing contrarian about my approach - whereas insulation goes against over 100 years of progress in professional observatory design, where ventilation is critical.
That doesn't mean insulation is bad or doesn't work. But I have never seen compelling results to show it is a good idea - and the various interpretations of why it should work are fairly simplified. My main point is that the results are backed by anecdotal evidence and subjective assessments. If you take such evidence as proof you will find that most everything works and is backed by someone who tried it and liked the results.
There are plenty of top rate planetary imagers in the planetary-solar imaging forum who go to great lengths, such as ice packs on their tubes, to get their SCT 11s and 14s to ambient temp. and never mention Reflectix. But few in these threads seem to read or follow what the really good SCT planetary imagers do to get their sub arc second details on every night of good seeing. Instead, in thread after thread I only read anecdotal arguments against well known principles of physics with "common sense" and a cheap fix. And I thought astronomy and those who practice it, was all about science. Was I wrong.
Good grief - I was not going to make any comments in this thread because as I see it there is a large dose of the proverbial "faith" in many things that AA'ers prescribe to...
I freely admit I'm driven by practicality...if it appears to work with sufficient testing it gets the nod...if not - the flick!
With my old C11 I did insulate the entire scope...& I thought the pattern-making of the rear-casting assembly & the creation of said insulative cap would've just about qualified me as a bespoke tailor!
Not this seemingly marvellous Reflectix...but a double layer of 5mm thick natural cork, which I reckon provided pretty good insulative qualities...the ota was also sheathed in the same btw.
I collimate on a star before every imaging session & have what I consider to be a very intimate awareness of the collimating process in all sorts of seeing etc, but also the characteristics of many of the effects of various parameters on star pattern appearances...both in & out of focus.
Our results are well-known in the Solar System Imaging forum & elsewhere...some of our achievments can be read in my signature & a visit to our website should attest to the quality & resolution we regularly achieve on just about every planetary target. (well, with the exception of Venus & Mercury!)
Insulation per se was of almost no benefit, whether that was imaging with whatever the scope's ambient temperature was within - or aiming for a specific value...we could switch on a rather sophisticated cooling system I derived myself using multiple TEC's with cowled heatsinks & fans blowing the heated air away from the scope's rear...internal fans also inside the rear casing & under the primary mirror with brass cold-plates acting as additional internal cooling cowls...
I had multiple temperature sensors on the primary, at the front of the corrector, inside the ota & also at several positions outside the scope itself...I must have logged literally hundreds of hours with data, graphs & also diffraction ring patterns & of course the planetary results themselves.
Without making this post one of my (often longer usually!) tomes, we are now using a C14 - & "yes" I think I have refrained completely from posting in any of those threads that go along the lines of "are C14's any good" - "has anyone ever found a C14 that has decent optics" - "why are all SCT's ****" etc, etc...
What do we believe..?!?
If an SCT (or in particular a C14) can have the mirror cooled to air/ambient temperature you will notice the most stable set of diffraction rings or Airy Disk that seeing allows...once collimated to the best degree possible the results will be outstanding. (the nexus between seeing, primary at ambient & collimation quality implicit here...)
We don't try to retard the primary's temperature changes once we achieve the desired value...at certain times of the year the temperature literally "drops like a stone" after Sunset & whilst I admit we don't get the freezing temperatures of many Northern folks, we have often had temperatures of -4°C to -6°C in Winter in the Oz bush, where the scope ends up covered in a sheath of ice.
We also regularly encounter a mirror at 40°C+ at this time of the year before Sunset & with our practice need to lower it to around 8°C or less in time for the start of an imaging session.
I'm not overly interested in whether deep space/the sky has a temperature of -60° or whatever - I want the primary mirror to be about 2°C below the predicted temperature for the start of the imaging session knowing that only in exceptional circumstances will the primary not track the ambient air temp over the course of 4 to 8 hours...
All corrector plate defogging is done with a hair-dryer...I've seen what dew heaters do at 10,000mm focal length/image scale & it's not too much better than what a quick blast of the hair-dryer does...except the effects of the hair dryer settle down with a minute or 2..!
A long dew shield when imaging Neptune or Uranus in conditions where fogging occurs fairly rapidly is very helpful for the 500" to 800" durations of these captures btw.
After all the experimenting & faffing around with all sorts of ideas & apparatus where our sole objective is to achieve the highest resolution on a regular basis, in whatever the seeing etc dishes up anytime over the last decade or so, we are convinced that our method of attaining ambience between primary & air clearly delivers the best outcomes.
I'll humbly suggest our results over that time make this point not only indisputable...but are clearly also a tangible/evidence-based proof of the "workability" of said...
Nowadays it is the simplest modus operandi for effecting this objective: a double-bagging (for leak safety) of 5Kgm of crushed ice mixed with 1Kgm of common table salt...placed on the rear-casing of the C14 with Moonlite focuser in situ & ice evenly arranged in the bag...pointing face down on the mount with a doona wrapped around ice bag & ota...
We wait till our gauges display the primary temperature is around -2°C below what is predicted for when we begin imaging, take off the ice & doona etc...point the scope straight up skyward with corrector uncovered & wait about 1/2 an hour or so for the primary to "relax" & its' temperature to become uniform throughout et -c then set the rest of the cables & gear etc up & start the collimation process...collimation is always done "in camera" at the sorts of f/l's I have mentioned.
I'll finish by saying that "YMMV" but we want what we get...& get what we want, weather permitting - everyone is free to believe what they like & think differently but for us the only thing that matters is "primary temperature = ambient air" for maximum outcomes that can be quantified!
Edited by Kokatha man, 04 December 2018 - 06:25 AM.