Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Questions About Insulating SCT's with Reflectix

catadioptric DIY equipment SCT
  • Please log in to reply
225 replies to this topic

#26 starman876

starman876

    Hubble

  • *****
  • Posts: 18500
  • Joined: 28 Apr 2008
  • Loc: VA

Posted 26 November 2018 - 05:53 PM

I hate it when I see that plume coming from the baffle tube. Tells me it will not be very good images until that settles down.  Does wrapping the OTA in a thermal blanket slow that down?   seems now with these 100 degree eyepieces that they will need to cool before use otherwise there is another mass in the baffle tube that would create currents.  On the other hand the newer Celestron edge HD's have a lens at the end of that tube and would that slow down the plume coming out of the baffle tube?


  • Ryan555_1 likes this

#27 555aaa

555aaa

    Vendor (Xerxes Scientific)

  • *****
  • Vendors
  • Posts: 1211
  • Joined: 09 Aug 2016
  • Loc: Lynnwood, WA, USA

Posted 26 November 2018 - 05:59 PM

As alternates to reflectrix, you might consider this stuff:  https://www.joann.co...ht/7145857.html or this stuff which is what I used I think:

 

 https://www.joann.co...35.html#start=1

 

or this stuff.

 

 https://www.joann.co..._14898621a.html

 

I like the quilted gold "Aluminor" thermal fabric above. They also make it in silver.


  • Sarkikos, okiestarman56 and spongebob@55 like this

#28 punk35

punk35

    Viking 1

  • *****
  • Posts: 854
  • Joined: 26 Jan 2005
  • Loc: Adrian Michigan

Posted 26 November 2018 - 06:10 PM

Interesting thoughts starman876. 

Now I have to put a Reflectix jacket on my 2” diagonal and bigger ep’s. lol.gif lol.gif foreheadslap.gif


  • okiestarman56 likes this

#29 Reid W

Reid W

    Viking 1

  • *****
  • Posts: 706
  • Joined: 06 Oct 2010
  • Loc: Shreveport, LA

Posted 26 November 2018 - 06:19 PM

Wade is on track.  

 

Since I "reflexed" my C11, it has become the quick view tube.   


  • Skywatchr and Sarkikos like this

#30 Peter Besenbruch

Peter Besenbruch

    Fly Me to the Moon

  • *****
  • Posts: 6760
  • Joined: 21 Aug 2014
  • Loc: Oahu

Posted 26 November 2018 - 09:30 PM

I hate it when I see that plume coming from the baffle tube. Tells me it will not be very good images until that settles down.  Does wrapping the OTA in a thermal blanket slow that down?   seems now with these 100 degree eyepieces that they will need to cool before use otherwise there is another mass in the baffle tube that would create currents.  On the other hand the newer Celestron edge HD's have a lens at the end of that tube and would that slow down the plume coming out of the baffle tube?

I have seen plenty of baffle tube currents rising off the outside of the primary baffle. Yes, Reflectix stops those. They simply don't form. As a result, I have had some very nice planetary views (OK, Mars wasn't as good as I had hoped).


  • Sarkikos likes this

#31 Bean614

Bean614

    Viking 1

  • *****
  • Posts: 545
  • Joined: 05 Nov 2015
  • Loc: Mass.

Posted 26 November 2018 - 10:19 PM

It's encouraging to see how many folks are discovering, and discussing, Insulation for Maks and SCT'S.  Now, for those of you for whom this is all brand new, and may have questions that aren't covered in this thread, just Search INSULATION in "Forums", and you will find a few hundred more threads!  They will explain, in even greater detail, the science of the concept.  Those of us who have been using Insulation for the past year, and posting about it,  are glad to see this concept finally being accepted by the "general population".  

It has transformed SCT observing.


  • Traveler, Sarkikos, okiestarman56 and 1 other like this

#32 jhayes_tucson

jhayes_tucson

    Fly Me to the Moon

  • *****
  • Posts: 6616
  • Joined: 26 Aug 2012
  • Loc: Bend, OR

Posted 27 November 2018 - 02:08 AM

I've heard that the reflective nature of the Reflectix is a major factor in why it works to retain heat.  It works by reflecting heat.  I can understand how reflecting heat coming up from the OTA back into the OTA would make sense. 

 

But why would reflecting away heat coming onto the OTA from the environment - the sky, the grass, the trees, whatever -  help the OTA retain heat?  That doesn't make sense to me.  So why does the outer surface of the Reflectix need to be shiny?  Why can't we just blacken it with paint?  Why would that affect the Reflectix' ability to help the OTA retain heat?  It's the inner surfaces of the Reflectix that face the OTA which are important as heat retaining surfaces.  The OTA never "sees" the outer surface of the Reflectix.

 

Mike

 

Mike,

OK, first read post #23 in this thread:

https://www.cloudyni...th-dew-heaters/

It's a good intro to dew, where it comes from, the importance of radiative heat transfer, and how to combat dew.

 

Second, read post #15 in this thread:

https://www.cloudyni...-dew-heater-go/

It will further explain the effectiveness of various anti-dew strategies.

 

I am currently working on a much more comprehensive article on the physics of dew prevention but it will be another month or two before I get it posted in the "articles" section.  It's a pretty big subject.

 

John

 

 

PS  Here's a tip:  The advanced search function on CN is actually pretty good if you know what to look for.  Searching for "dew", "Reflectix", "dew-heaters", etc. will pull up a wealth of information on this topic.  The downside is that CN is full of an almost equal mix of both good and bad information so you have to be a bit circumspect about what you find.


Edited by jhayes_tucson, 27 November 2018 - 02:11 AM.

  • MortonH, Jaimo!, Sarkikos and 4 others like this

#33 Sarkikos

Sarkikos

    ISS

  • *****
  • topic starter
  • Posts: 29157
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 27 November 2018 - 07:23 AM

Now, why should I bother to search when I can have nice people like you post the links for me? poke.gif

 

Thanks. grin.gif

 

What I see from the threads is that there is no consensus of opinion on how best to combat thermals and prevent dew, and exactly how Reflectix should be used.  

 

Will painting the outer surface of the Reflectix black affect its efficiency?  (I'm skeptical about colors having any significant affect at night.  Besides, it's how well a surface transfers or reflects infrared, not visible light, that is important here.)

 

Should fans be used or not?

 

No stare decisis.  All is in flux.  Or at least some of it.

 

Mike


Edited by Sarkikos, 27 November 2018 - 08:57 AM.


#34 Sarkikos

Sarkikos

    ISS

  • *****
  • topic starter
  • Posts: 29157
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 27 November 2018 - 07:51 AM

I've been using a Reflectix wrap on my C14 since this spring.

 

My setup is a single layer that is wrapped around most of the OTA.  The dovetail is exposed and the back of the telescope is exposed.  The Reflectix wrap is significantly longer than the OTA, so it extends well past the corrector plate.  Before wrapping the scope, I attach an AstroZap flexible dew shield which is about 1/2 longer than the Reflectix wrap.  So I have no bare reflectix exposed to the optics on the inside, so it cannot produce reflections visible in the eyepiece.  I also install a dew strap on the corrector end of the OTA, just behind the retaining ring that holds the corrector in place.

I would probably set up Reflectix wrap around my EdgeHD 8" the same way.  I'd definitely attach my AstroZap dew shield.  The flocking is excellent in the AstroZap.  The AstroZap is also very sturdy, stays in place, will not sag.  I wouldn't go to the bother of making a dew shield out of Reflectix and then having to flock it when I already have a perfectly good dew shield with superior flocking. 

 

I'll just have the Reflectix cover about half the dew shield, as you say.  The AstroZap has a built-in warming strip which is positioned about at the corrector.  I've heard that some observers have cut the warming strip out and repositioned it behind the corrector.  I want to avoid doing that.  Instead, I'll use it as is.  The warming strip should retain more heat, last longer and use less power since it is below the Reflectix.  That is good enough.

 

Mike


Edited by Sarkikos, 27 November 2018 - 08:09 AM.

  • Skywatchr likes this

#35 Sarkikos

Sarkikos

    ISS

  • *****
  • topic starter
  • Posts: 29157
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 27 November 2018 - 08:01 AM

 

As for visible light reflections, I don't have any Reflectix exposed to the scope's optics, as I mentioned above.  And since I observe at dark sky sites, there has not been any problems with reflections off the external, exposed Reflectix.  I have to say, however, that I don't think that covering or painting the exterior of the Reflectix would hurt it's performance at all in this application (but I've never tested it to be sure).  We're trying to keep heat from radiating out of the aluminum OTA, and there is no significant source of radiant heat trying to enter the scope at night.  I would say, though, that if you painted the Reflectix flat black and then exposed the scope to direct sunlight, you would probably make it heat up quicker than being unwrapped.

 

Those are my thoughts and experiences.  My suggestion is that you try it for yourself.  Reflectix is really cheap, and it's easy to wrap the scope.  There's no significant cost in trying different variations to see what works best for you.

This all makes sense to me.  Why should painting or covering the outer surface of the Reflectix alter its capacity to retain heat coming up from the OTA?  The night sky is cold.  Concerns about the outer surface of the Reflectix are irrelevant.  All that matters is that the Reflectix is reflecting back and retaining the heat trying to escape from the sides of the OTA.

 

When I go to dark sites, I don't set up the telescope until soon before sunset.  If I stay more than one night, I rent a cabin that is some distance from the observing field.  I keep the equipment in the cabin during the day.  So whatever color I paint the outer surface of the Reflectix, or whatever I cover it with, shouldn't matter.

 

Mike


Edited by Sarkikos, 27 November 2018 - 09:00 AM.


#36 Sarkikos

Sarkikos

    ISS

  • *****
  • topic starter
  • Posts: 29157
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 27 November 2018 - 08:15 AM

As alternates to reflectrix, you might consider this stuff:  https://www.joann.co...ht/7145857.html or this stuff which is what I used I think:

 

 https://www.joann.co...35.html#start=1

 

or this stuff.

 

 https://www.joann.co..._14898621a.html

 

I like the quilted gold "Aluminor" thermal fabric above. They also make it in silver.

Interesting.  I'd like to see comparative tests between these materials and Reflectix.

 

mike


  • spongebob@55 likes this

#37 starman876

starman876

    Hubble

  • *****
  • Posts: 18500
  • Joined: 28 Apr 2008
  • Loc: VA

Posted 27 November 2018 - 08:23 AM

I have seen plenty of baffle tube currents rising off the outside of the primary baffle. Yes, Reflectix stops those. They simply don't form. As a result, I have had some very nice planetary views (OK, Mars wasn't as good as I had hoped).

This is all great news.   However,  if one keeps the scope outside and let it settle to ambient temps would a thermal blanket still be needed?  Or are we insulating the scope from out body heat.   I would think if it was that cold out we would be wrapped pretty good also.  


  • Sarkikos likes this

#38 Sarkikos

Sarkikos

    ISS

  • *****
  • topic starter
  • Posts: 29157
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 27 November 2018 - 08:24 AM

I have several Cats that need Reflectix sweaters.  grin.gif  

 

Three SCTs:  EdgeHD 8", C6, C5.

 

Two Maks:  Bosma Rumak 150, C90.

 

For years the 6" Rumak has been on my list of scopes to sell.   It is a built like a tank.  The images are great, but only after a long wait for the thermals to settle.  Maybe a Reflectix cover will keep it out of the Swap and Shop Forum.

 

Even the little C90 shows heat plumes.  I like it as a grab-n-go for double stars, but until it acclimates, all the stars look like doubles!

 

Mike


Edited by Sarkikos, 27 November 2018 - 08:25 AM.

  • Skywatchr likes this

#39 Sarkikos

Sarkikos

    ISS

  • *****
  • topic starter
  • Posts: 29157
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 27 November 2018 - 08:26 AM

This is all great news.   However,  if one keeps the scope outside and let it settle to ambient temps would a thermal blanket still be needed?  Or are we insulating the scope from out body heat.   I would think if it was that cold out we would be wrapped pretty good also.  

When it's cold out, I have trouble keeping myself warm.  I don't think my body is a big source of heat to any telescope I'm around.

 

YMMV

 

Mike


  • Dynan likes this

#40 WadeH237

WadeH237

    Soyuz

  • *****
  • Posts: 3853
  • Joined: 24 Feb 2007
  • Loc: Snohomish, WA

Posted 27 November 2018 - 08:37 AM

When it's cold out, I have trouble keeping myself warm.  I don't think my body is a big source of heat to any telescope I'm around.

 

YMMV

 

Mike

I think that the reason you have trouble keeping warm is that your body is radiating its heat to the cold air :)



#41 Sarkikos

Sarkikos

    ISS

  • *****
  • topic starter
  • Posts: 29157
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 27 November 2018 - 08:40 AM

I don't have that much heat to radiate in the first place!  I'm only 5'6", 140 lbs.   coldday.gif

Maybe I need to wrap myself with Reflectix!

 

grin.gif

Mike


Edited by Sarkikos, 27 November 2018 - 08:44 AM.

  • 555aaa and Dynan like this

#42 cytan299

cytan299

    Messenger

  • *****
  • Posts: 474
  • Joined: 24 Nov 2014

Posted 27 November 2018 - 09:11 AM

Yes, so it only matters that the Reflectix is wrapped around the OTA, to reflect back the heat coming from the OTA.  It doesn't matter if the outer surface of the Reflectix is painted black to prevent light glare.  It doesn't matter if the inner surface of a Reflectix dew shield is covered with black flocking to deaden ambient light.

 

Mike

Hi Mike,

   I have to disagree with what you wrote: the key to reflectix is the the shiny outer layer because it reduces radiative cooling. If you paint it black, radiative cooling *increases* (c.f. black body radiation and the reason why emergency blankets used by EMTs are silver and reflective), which means that the reflectix is less effective as an insulation when black. As for the inner surface of the reflectix that touches the OTA, heat transfer is via conduction -- this means that the shininess of the surface is not important. What reflectix does here is to increase conduction resistance having an air layer. Air is a very bad heat conductor.

 

  The bottom line: if you want an effective insulation of the OTA, keep the reflectix silver on the outside and try to keep the reflectix tightly wrapped onto the OTA.

 

cytan



#43 Sarkikos

Sarkikos

    ISS

  • *****
  • topic starter
  • Posts: 29157
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 27 November 2018 - 09:21 AM

Doesn't the OTA radiate heat?  Won't the metal surfaces of the Reflectix facing the OTA - as well as the inner air layer - retain that heat?  That is what is important, not the shiny outer surface.

 

At night the outer color of the object doesn't matter.  Once heat reaches the outer surface, it will be lost from the object at the same rate, no matter what the outer color is.

 

mike


Edited by Sarkikos, 27 November 2018 - 09:27 AM.


#44 Dynan

Dynan

    Vanguard

  • *****
  • Posts: 2083
  • Joined: 11 Mar 2018
  • Loc: NOLA

Posted 27 November 2018 - 09:23 AM

It WILL slow the transfer down, thus keeping the currents slow, which is the aim of insulating. Don't think in absolutes, since no insulation is perfect.



#45 Sarkikos

Sarkikos

    ISS

  • *****
  • topic starter
  • Posts: 29157
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 27 November 2018 - 09:31 AM

It WILL slow the transfer down, thus keeping the currents slow, which is the aim of insulating. Don't think in absolutes, since no insulation is perfect.

What exactly will slow the transfer down?  There are several balls being tossed in the air here. 

 

:grin:

Mike



#46 Dynan

Dynan

    Vanguard

  • *****
  • Posts: 2083
  • Joined: 11 Mar 2018
  • Loc: NOLA

Posted 27 November 2018 - 09:48 AM

Please keep track of your questions: Won't the metal surfaces of the Reflectix facing the OTA - as well as the inner air layer - retain that heat?

 

It WILL slow the transfer down, thus keeping the currents slow, which is the aim of insulating. Don't think in absolutes, since no insulation is perfect.


Edited by Dynan, 27 November 2018 - 09:49 AM.


#47 cytan299

cytan299

    Messenger

  • *****
  • Posts: 474
  • Joined: 24 Nov 2014

Posted 27 November 2018 - 09:50 AM

Doesn't the OTA radiate heat?  Won't the metal surfaces of the Reflectix facing the OTA - as well as the inner air layer - retain that heat?  That is what is important, not the shiny outer surface.

 

At night the outer color of the object doesn't matter.  Once heat reaches the outer surface, it will be lost from the object at the same rate, no matter what the outer color is.

 

mike

 

The amount of radiation depends on the shininess of the surface. However, the dominant mode of heat transfer when there is *contact* is conduction and not radiation. After heat is conducted (poorly with an intervening layer of air) from the OTA to the outer surface of the reflectix, heat loss is minimized by having a shiny surface. 

 

Finally, your last statement "it will be lost from the object at the same rate, no matter what the outer color is." is absolutely wrong. Here are links to radiative cooling and how the color of the surfaces affect it:

 

http://www.hk-phy.or.../radia02_e.html

 

or for those who love watching videos: 

 

https://www.youtube....h?v=iPufr7PHC8s

 

Conclusion: black radiates a lot more heat than silver. QED.

 

cytan


Edited by cytan299, 27 November 2018 - 09:58 AM.


#48 Sarkikos

Sarkikos

    ISS

  • *****
  • topic starter
  • Posts: 29157
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 27 November 2018 - 09:51 AM

Keep track of your questions: Won't the metal surfaces of the Reflectix facing the OTA - as well as the inner air layer - retain that heat?

Yes, of course.  The question I pose is:  Does the outer color of the Reflectix really matter at night?  I don't think it does.  But some people act as if the outer color is the most important factor!

 

Mike



#49 Sarkikos

Sarkikos

    ISS

  • *****
  • topic starter
  • Posts: 29157
  • Joined: 18 Dec 2007
  • Loc: Per sylvam ad astra

Posted 27 November 2018 - 09:57 AM

The amount of radiation depends on the shininess of the surface. However, the dominant mode of heat transfer when there is *contact* is conduction and not radiation. After heat is conducted (poorly with an intervening layer of air) from the OTA to the outer surface of the reflective, heat loss is minimized by having a shiny surface. 

 

Finally, your last statement "it will be lost from the object at the same rate, no matter what the outer color is." is absolutely wrong. Here are links to radiative cooling and how the color of the surfaces affect it:

 

http://www.hk-phy.or.../radia02_e.html

 

or for those who love watching videos:

 

https://www.youtube....h?v=iPufr7PHC8s

 

cytan

 

The Good Year blimp is shown during the day.  The Hubble Space Telescope is in sunlight.  Amateur astronomers observe at night ... usually.  Sure, white or shiny surfaces would minimize heat loss during the day, or in any case when the object is in view of the Sun.  But during the night?  

 

The second video does indicate that black is a better emitter of infrared than white or shiny.  But in the case of the Reflectix, the metal surfaces and the interior air layer will retain the heat radiating from the OTA.  How big of a factor will the color of the outer surface be at night?  Some act as if the outer color is THE major factor in retaining heat.

 

Mike


Edited by Sarkikos, 27 November 2018 - 10:07 AM.


#50 precaud

precaud

    Aurora

  • *****
  • Posts: 4520
  • Joined: 05 Dec 2012
  • Loc: north central New Mexico

Posted 27 November 2018 - 10:04 AM

I think it is better to just fuggedabout the "reflective" aspect of the material. which, in my experience, is mostly hyped in significance. The basic event is a relatively high-mass metallic item (the OTA) immersed in a cold air mass that is declining in temperature. This is convective heat loss. Radiated heat does not play much of a role in this event.  ANY insulation material, reflective or not, slows down the "heat loss" of the OTA to the air. The higher the R value, the slower the transfer.

 

If you place the reflective side against the OTA, to "stop" the radiated heat loss, you now have conductive heat transfer into the insulation material, swamping any meager benefit of trying to block the radiated loss. The honeycomb structure of Reflectix is only isulative where the enclosed air bubbles exist. The solid part of the material is a "thermal bridge" for conductive heat transfer.

 

A few years ago I tried Reflectix and some other materials to insulate the air feeds from a solar heater to/from a house. Used by itself, Reflectix most underperformed its R value rating. But it worked well as the outer layer of a two-part insulator, because it stops the insulated air mass from mixing with the insulated one. This assumes that the object being insulated is covered completely. Any gaps in the insulation (in our case, at either end of the OTA) lower the R value dramatically.

 

So a less-conductive material (more fibrous) under a layer of Reflectix will give better results.


  • Sarkikos and Dynan like this


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics





Also tagged with one or more of these keywords: catadioptric, DIY, equipment, SCT



Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics