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Insulation (airspace) layer for under Reflectix

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#1 precaud

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Posted 08 December 2018 - 12:22 PM

Now that the Reflectix controversy has settled down somewhat, I've decided to stick with my original idea and insulate the SW180 Mak OTA using a two-layer approach; a 1/4"-1/2" thick porous insulating layer bonded to an outer layer of Reflectix.

The dew shield can also be made from it, though the insulating layer gets replaced with something thinner, black, and nonreflective at grazing angles of incidence.

For the OTA insulating layer, something like low-density wool felt would be awesome, but it is unobtainium around here.

Fiberglass is out of the question for obvious reasons.

So I may have to revert to the typical polyester felt sold in crafts stores.

 

Any other clever ideas before I go get the stuff?

 


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#2 Richard O'Neill

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Posted 08 December 2018 - 12:36 PM

I recommend Thinsulate.  https://en.wikipedia...wiki/Thinsulate

 

https://www.voguefab...ning-cs150.html


Edited by Richard O'Neill, 08 December 2018 - 12:39 PM.

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#3 precaud

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Posted 08 December 2018 - 12:46 PM

Ah, good one, thanks. I'll see if any of the local stores have it. EDIT: Unfortunately noone has it here.


Edited by precaud, 08 December 2018 - 12:53 PM.


#4 Richard O'Neill

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Posted 08 December 2018 - 01:43 PM

Same here. Since one layer of Reflectix and two internal fans work well with my TEC Mak I haven't tried this product. You may want to examine a small swatch before ordering a yard or two. Good luck.



#5 precaud

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Posted 08 December 2018 - 04:14 PM

JoAnn Fabrics to the rescue again. On the phone, they couldn't suggest anything they had like Thinsulate... but in-store, I found a box of this stuff in 1/2" thickness

https://www.joann.co...k/14195788.html

 

They market it as "Nu-Foam" but its really densified polyester batting, 27" wide and sold by the yard. Exactly what I had in mind. And on sale at 50% off this weekend.

 

And then a few sheets of black felt to line the inside of the dew shield.


Edited by precaud, 08 December 2018 - 04:15 PM.


#6 gene 4181

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Posted 08 December 2018 - 04:54 PM

 1/2 in or 5/8 inch neopreme insulation blanket  ,   smile.gif .    A good pipe fitting / plumbing shop will have it .  They use it on refrigeration systems  ,  no sweating or dew problems ,(scope) going back in either .



#7 precaud

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Posted 08 December 2018 - 05:27 PM

 1/2 in or 5/8 inch neopreme insulation blanket  ,  

 

aka neoprene foam sheet. I've made light shields for my dobs out of it before. Denser than what's needed here, but it would probably work, you could use the 1/4" thick stuff. Can also be bought with self-adhesive backing. Amazon has several types.


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#8 Richard O'Neill

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Posted 08 December 2018 - 08:42 PM

It seems you've found what you want but looking further I also found Primaloft.

 

https://www.seattlef...tions_c_59.html



#9 precaud

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Posted 09 December 2018 - 10:14 AM

The appearance ans description is exactly like the stuff I got.



#10 luxo II

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Posted 09 December 2018 - 04:45 PM

Precaud,

I used a material called ‘coreflute’ - rather like corrugated cardboard, 6mm thick. Plenty of airspace in the flutes. It’s also available in 2.5mm thickness.

Details https://www.cloudyni...s/?fromsearch=1

The other material readily available are the reflective automotive sunshades, that stuff can be cut to size and makes an excellent dew cap and insulation, in one.

Edited by luxo II, 09 December 2018 - 04:47 PM.


#11 precaud

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Posted 09 December 2018 - 07:39 PM

Well since Reflectix has about the same R value as cardboard, that might be a good combo  :)

I'll read through your thread, thanks.



#12 Paradoxdb3

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Posted 13 December 2018 - 09:29 PM

I'd like to follow this thread and hopefully get some advice/help. I recently insulated my 7" SkyWatcher Mak-Cass with two layers of Reflectix, perhaps expecting more than I should have, because either I did something wrong, or the seeing was SO BAD that everything looked just as it did before I insulated. I duct taped the Reflectix directly to the outside of the OTA. Did anyone do this and see major improvements? I live in Saskatchewan, so winters can be very cold, although it's quite mild this year.

#13 Paradoxdb3

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Posted 13 December 2018 - 09:56 PM

By the way, I took my SkyWatcher out this evening and defocused on Mars. The tube currents looked like a pot of boiling water! At first, I wasn't sure if it was the poor seeing conditions, or actual tube currents. After an hour, I defocused again, and the "boiling water" was a "gentle steam". I feel like I can conclude it was definitely turbulence inside the tube. Question is, why am *I* not seeing these immediate results everyone keeps talking about? I used two layers of Reflectix. Did a pretty good job, I think, and even made a dew shield and insulated it with Reflectix, too. Still had to wait an hour, and even then, there was still some turbulence.

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#14 precaud

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Posted 13 December 2018 - 10:50 PM

I'll take a shot at this.

: If you took your SW180 from indoor house temps to outside (Google says its 26ºF there now) and only waited an hour, I doubt that is long enough for a 40+-degree swing to settle and normalize.

: IMO two layers of Reflectix are little better than one. You need a non-conductive insulating layer, such as polyester batting, between it and the OTA.

: Mars is a poor target to for judging just about anything, IMO.

: Some of the guys that were posting good results live in very temperate places.



#15 TomK1

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Posted 14 December 2018 - 12:40 AM

Maybe because the corrector plate and secondary are exposed to the outside cold air.  The heat loss is then conducting through the glass and secondary.  Inside your tube you have the room temp air next to the cold surfaces ( your corrector plate glass and the mirrored secondary).   Because of the temperature difference, convection is taking place and right next to those surfaces you have air movement and a temperature gradient.......hence air density difference.......bending your light all over the place, until you reach equilibrium.   I suppose the temperature gradient is much smaller at the primary, so light is bent less through the lower air density difference.   The greater the temperature difference, the longer the mass takes to reach equilibrium.   



#16 Traveler

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Posted 14 December 2018 - 12:47 AM

By the way, I took my SkyWatcher out this evening and defocused on Mars. The tube currents looked like a pot of boiling water! At first, I wasn't sure if it was the poor seeing conditions, or actual tube currents. After an hour, I defocused again, and the "boiling water" was a "gentle steam". I feel like I can conclude it was definitely turbulence inside the tube. Question is, why am *I* not seeing these immediate results everyone keeps talking about? I used two layers of Reflectix. Did a pretty good job, I think, and even made a dew shield and insulated it with Reflectix, too. Still had to wait an hour, and even then, there was still some turbulence.

Always nice to see the use of DuctTape in the amateur astronomy world...I am a big user as well grin.gif


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#17 Steve D.

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Posted 14 December 2018 - 05:38 AM

I would try the experiment again but this time look at a star higher in the sky instead of Mars.  This would help eliminate seeing as a factor.  I’m having trouble getting a steady image of Mars in my 85mm refractor due to the low viewing angle.  I’ve been able to see the Airy disk in my C8 immediately with a 30 degree difference.



#18 luxo II

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Posted 14 December 2018 - 05:52 AM

: If you took your SW180 from indoor house temps to outside (Google says its 26ºF there now) and only waited an hour, I doubt that is long enough for a 40+-degree swing to settle and normalize.

Agree that's a really tough scenario. I'd suggest keep the scope in a colder place like a garden shed or garage, if you have one - not in your house.

 

Here in temperate Sydney the typical difference between indoors and outside at night is perhaps 10 degrees C (ie much less than what you have to deal with).

 

When we do venture to our dark sky site (and in winter that can be below 0C) its a two-hour drive. My scope is in a padded bag so it has a chance to cool in the car en-route, plus another 45 minutes by the time its set up to observe.

 

I still have vivd memories of living in a country town where winter temps could drop to -10C - great seeing - but one night the cornea of my eye froze on an eyepiece (a horrible nasty one with next to no eye relief). Painful is an understatement - and I had to remain motionless for a few minutes till it thawed and parted from the eyepiece.


Edited by luxo II, 14 December 2018 - 06:00 AM.


#19 Paradoxdb3

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Posted 14 December 2018 - 06:58 AM

Okay, I super appreciate the feedback! I'll quickly address the replies above and hopefully get a better understanding of what I need to do.

I'd really hate to have to undo all the insulation and toss on a nonconductive layer of insulation, like polyester or possibly felt lining. But let's say I did take off the Reflectix and put it back on over top a layer of felt.

"I did take off the Reflectix and put it back on over top a layer of felt."

(Sorry, I have clearly watched too many Leslie Neilson movies!)

But seriously, if I redid the insulating job, would this actually make a difference, given my environment?

And I will try again, but look at something above 45° and see what results I get. Like I said, the turbulence did settle after an hour, so I think it wasn't just poor seeing, but you're right, I need to completely rule out atmospheric distortion.

I live in an apartment, so I don't have an outside storage, but what I usually do is set the scope in the trunk of my car an hour or so before viewing. It cools pretty well in there. Maybe given my weather conditions, there is no "magic cure" to the tube currents. And I do sometimes travel an hour out of town, as well.

Anyway, thanks again. I'm still getting tons of flack for insulating my OTA, and being told all the harm I'm doing to it, including holding moisture in, which is encouraging mold buildup. I may actually take off the insulation, take it for a test run, and the next similar-in-temp day, take it out exactly the same way, and run the exact same test, but insulated. Take a video, as an example, and show the difference. That would prove to me, as well, that there is something to this insulation idea!

#20 precaud

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Posted 14 December 2018 - 09:38 AM

One thing to consider is, the scope will come to equilibrium with ambient temps faster without the insulation. The insulation material slows down that process. So, for large temp differences like you have, you will probably be better off leaving the insulation off until you're ready to observe.


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#21 Paradoxdb3

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Posted 14 December 2018 - 10:03 AM

I was under the impression that slowing the cooling was what I wanted to do. Slow and steady wins the race, as they say! But if someone who has experience with insulating their OTA can chime in and confirm that this is indeed the goal of insulation, that would help. And if 8m wrong, let me know. I also thought that insulation helped with frost issues. Again, correct me if I am wrong.

#22 precaud

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Posted 14 December 2018 - 10:20 AM

It's simple, really: think about it. Insulation slows down what we call "heat transfer", which moves from hot to cold. Let's say your scope is stored in a 70ºF environment and taken out into a 26ºF space. And for now let's assume that outside temps don't drop further. The scope will take longer to reach 26ºF with the insulation on. So for large Tdelta, the insulation prolongs a large, necessary adjustment.

 

Now lets add in the fact that temps are still dropping while you observe, we'll say at 4ºF per hour. And we'll assume the scope starts out somewhere close to outside temp. The scope body and other metal parts will cool faster than the glass. In this case, it helps to insulate the body so that the entire mass of the scope can cool down in sync.

 

So insulation helps for the slower, more gradual adjustments, but not the big one...


Edited by precaud, 14 December 2018 - 10:26 AM.


#23 Sarkikos

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Posted 14 December 2018 - 10:22 AM

Now that the Reflectix controversy has settled down somewhat, I've decided to stick with my original idea and insulate the SW180 Mak OTA using a two-layer approach; a 1/4"-1/2" thick porous insulating layer bonded to an outer layer of Reflectix.

The dew shield can also be made from it, though the insulating layer gets replaced with something thinner, black, and nonreflective at grazing angles of incidence.

I'd like to stick with a good, stiff and sturdy dew shield with decent flocking.  Most anything you make with Reflectix and a second insulating layer is going to be somewhat floppy and prone to shifting by the wind and gravity.  

 

So far I think the best are Astrozap.  It stays securely on the OTA and the flocking inside is excellent.  You can cover the outside of the dew shield with Reflectix.  I wouldn't bother with an extra insulating layer between the dew shield and the Reflectix.  Would it really be necessary?  The dew shield is mostly over air above the corrector, not directly on the OTA.

 

Two of my dew shields have a warming strip built in.  I would probably continue to use the warming strip even with the Reflectix.

 

Mike


Edited by Sarkikos, 14 December 2018 - 10:25 AM.


#24 Sarkikos

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Posted 14 December 2018 - 10:28 AM

Always nice to see the use of DuctTape in the amateur astronomy world...I am a big user as well grin.gif

My preference is Velcro.

 

:grin:

Mike


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#25 Sarkikos

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Posted 14 December 2018 - 10:33 AM

Agree that's a really tough scenario. I'd suggest keep the scope in a colder place like a garden shed or garage, if you have one - not in your house.

The problem is many people don't have an outdoor building like a shed and don't have a garage.  I don't even have a yard.  I would be reluctant to store a telescope even temporarily in the back of my Forester.  No trunk.  

 

I have a porch I can set a telescope on for an hour or so before I observe.  Then I carry the telescope back behind my building.  But that's it.  Any scenario that involves storing the telescope outside is out of the question.

 

Mike


Edited by Sarkikos, 14 December 2018 - 10:39 AM.



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