57 replies to this topic

[Peter Besenbruch]

I wraped a thin sheet of a white rubber foam material over a Reflectix-like insulating material. I did that for aesthetic reasons only. Reflectix alone will do the job.

Reflectix imparts a sleek, professional, plastic baggy sort of look to your scope. It makes members of the public to keep their distance, and ask questions like, "What is THAT!" "What did you do to the poor telescope?" "Did the scope COME that way?"

[luxo II]

If it's good enough to wrap the the Hubble in a space blanket, it's good enough for me.

 

(and yes I do know what its wrapped with, and it's no ordinary space blanket).

Edited by luxo II, 24 August 2020 - 08:59 AM.

[jagg3d]

Any advantage on using Reflectix on open tube OTA's?

[Bean614]

Any advantage on using Reflectix on open tube OTA's?

Such as...???

 

Several years ago I had a truss Dob that was bothered by issues of my body heat, and close by building heat.  Reflectix,  in the form of one of those Windshield Sun Reflectors,  did the trick!  And, for this particular scope, it was a perfect fit, around the poles,  between the top and bottom tube assemblies. 

Edited by Bean614, 02 September 2020 - 07:49 PM.

[SeattleScott]

I'm going to try this but instead of Reflectix, out of curiosity would an aerogel blanket be even better or overkill? (waterproof and much better R value)

How long does the Reflectix work for per night?

Any insulating material will work. One approach is put your OTA in a five gallon bucket, spray foam all around it, then cut it out of the bucket. The insulation will work all night in terms of stabilizing temperature and moderating thermals, but at some point it could dip below the dew point and allow dew to form.

Scott

[SeattleScott]

Any advantage on using Reflectix on open tube OTA's?

Obviously it isn’t the same as closed tubes because you will get mixing with warm air rising up and out of the OTA. But I have heard some people claim success, or at least some degree of success. Logically it would reduce the thermals considerably, but it would take much longer to actually reach ambient and eliminate thermals. Whether it reduces thermals enough for high power planetary viewing idk.

[SeattleScott]

Reflectix imparts a sleek, professional, plastic baggy sort of look to your scope. It makes members of the public to keep their distance, and ask questions like, "What is THAT!" "What did you do to the poor telescope?" "Did the scope COME that way?"

It is perfect for blind shootouts. See if the general public can tell the difference between a TEC6 and an iOptron.

Scott

[Rustler46]

There's an extensive discussion of this subject on the following thread:

 

Questions About Insulating SCT's with Reflectix

[sanbai]

A happy user of reflectix here. I have it sorrounding my C8edge OTA and also around the dew shield. I store the the scope outside in a coverd area, then move it onto the grass when I want to observe. I'm in Baton Rouge, humid and warm. I don't see the need for a dew heater at the moment. However, I've observed a bit of dew formation if I don't have the shield on. My big question is, will I need a heater when I move back to the cold germany?...

[Regulus 1.36]

Ok there's an older thread that contains the detailed explanation but I'll spare you 17 pages as it caused quite a kerfuffle when this was first described.

 

What started it all was the old mantra of "must cool the scope", while true to reduce thermal currents in open-tube scopes (newtonians, RC and classical cassegrains), for scopes with closed tubes (SCT and maks) it creates another problem - the corrector dews quickly. So people then apply heat (dewstraps) in the hope of warming the corrector, which begs the question - was cooling it really the smartest thing to do ?

 

There is, however, an alternative solution, and the clue lies in identifying the source of the thermal plume seen in SCT's and maksutovs - the central baffle tube. When the scope is taken outside a metal OTA exposed to the night air cools rapidly by both convection and radiative cooling (to the dark sky) creating a temperature gradient with the internal air circulating between the cold OTA and the warmer baffle inside. It is this thermal gradient that drives the thermal plume. What's more, the primary mirror holds a lot of heat that is also being dissipated, mostly into the central baffle.

 

If insulation is applied to the OTA to reduce the rate it loses heat, the result is the thermal plume inside is likewise reduced and the result is visible in minutes.

 

There are two side benefits - retaining heat means the corrector doesn't cool so fast and will stay dew-free for longer and the insulation can be extended out the front to form a dew-cap. You could even put a heater strap inside the insulation and its effectiveness will be increased.

 

Win-win-win.

This sounds awesome. I'm going to give it a try. 

[quilty]

No. 35 tells correctly.

My view: It's all about avoiding or reducing thermals inside the tube (by huge temperature gradients).
Old access: let it acclimatise (this most times does never happen, see below)
Reflectix access: Acclimatisation (coolin down) is no point just insulation prevents the tube from huge temperature gradients thus thermals

In this regard Mak-casses with aluminium tubes do best, second SC scopes. The thick glass corrector and the aluminium tube keep warmth and distribute it better than steel tin or carbon.
Even after cooling down the primary mirror in a Newt or CC, the tube needs to be radiation shielded in order to avoid thermal drop from under to upper side of the tube. Without there'll always be a delta of 4-7 K
This is the second benefit of that insulation. In addition an isulated dewtube is a must have.

Edited by quilty, 19 July 2023 - 05:02 AM.

[mayhem13]

Even better than reflectix is Neoprene……much higher R value, easy to install and looks much better IMO. It is more expensive though.

[quilty]

Reflectix© is a tradename for all insulation measures.
And insulation must be just sufficient to make sure that heat dissipation in the tube runs faster than heat loss by radiation. So, nothing wrong when in the morning the tube really has reached ambient air temperature

Edited by quilty, 19 July 2023 - 07:36 AM.

[Winks]

Well, it looks like I need a Reflectix blanket for my 9.25 SCT then. My routine is to keep it inside around 80F, but outside this time of year is at least 95F what I step outside after dark.

 

And frankly, I was always curious if thermals are generated as strongly by a mirror coming up to temp versus coming down to temp.

How do you manage the night heat for yourself. I'm out 10 minutes and I am done in. Maybe I need to cover ME in reflectix.

[markmanner]

Even better than reflectix is Neoprene……much higher R value, easy to install and looks much better IMO. It is more expensive though.

Hi, I think the only potential issue with something that isn't silver, is that you may get better thermal insulation, but you start to lose the benefit of having a silver surface that has very low emissivity. I think that part or much of what the reflectix or other silvery surface is doing is reducing the surface cooling of the top of the tube vs the bottom due by reducing differential radiation, which reduces internal thermals. Silver has really low emissivity, but other things that you might think would too, like white, aren't nearly as low. Maybe put whatever you like for good insulation on and then cover it with a silver space blanket, for the best of all worlds?

Edited by markmanner, 19 July 2023 - 05:50 PM.

[mayhem13]

A reflective barrier is effective when you can’t establish full surface contact or such contact isn’t desireable as it promotes moisture, rot, etc. Neoprene is the material of choice for wetsuits which isn’t designed to keep the cold water out but instead, to create a warm water barrier of minimal volume that the body can maintain. When wrapped tightly around the tube, neoprene will in effect perform the same function……if you were to remove it after a night with a high dew point, you would find a barrier layer of dampness on the material and the tube surface. Since the tube is powder coated, there’s little to no long term harm. 
 

But as i mentioned, it ain’t exactly cheap and it is heavy. Does protect the tube against unintended bangs and scuffs though…..don’t ask me how I know this……

 

Application is easy….cut to size, lightly secure the lateral seam with 3M command strips and then fully secure by re attaching the CGE/CGX rail over the seam.

 

Reflectix ain’t bad stuff…..cheap, readily available, easy to install too…..just not nearly the most effective choice.

[maroubra_boy]

I don't use Reflectix.  This is only one material that can be used to make insulation wraps.

 

I make my insulation wraps out of Coreflute.  And I have also made insulation wraps out of light coloured EVA foam yoga mats.  What is critical here is not the material as such, but that the material actually provides an insulation property.  We are not using these materials for what they have been originally designed for so you cannot be so stuck in "technical properties" because we are not using them in a house as we would for Reflectix.  EVA/Neoprene has excellent insulation properties, which is why it is used in wetsuits.  Coreflute is typically used to make signs, but it too has excellent insulation properties for our scopes.

 

What is important here is the colour of the material.  DON'T use black or other dark colours.  This has a major impact on how it reacts to temperatures are night and it will cool to a lower temp than ambient, attracting dew long before lighter colours as well as altering the insulation/thermal properties we seek from the insulation wraps.

 

Below are three pics, one showing the C8 I had with the yoga mat wrap I made for it (the insulation wrap only needs to cover 2/3 of the tube to be effective) and my 9" Mak with its Coreflute wrap.  The third shows the wrap I made for my 127mm Mak with its war-paint livery to stir up the neighbours... .  The forth pic shows how tightly these wraps can be rolled up for storage.

 

Coreflute does take more care and time to turn into a wrap (every second cell is cut down its entire length in order for it to adapt to the tight radius of the OTA), but it can be easily designed and made to fit around the various "bits" that hang off on OTA and is the most robust material that easily handles the installation and removal every session.  In the pics of the Coreflute wraps you can see how each wrap has been cut to fit around different bits on the OTA, such as finderscope shoes and handles.

 

One BIG advantage of a Coreflute wrap is it can be easily made to have small fans fitted to its dewshield section as a means of dew control WITHOUT heat.  Very effective, far more efficient, way less power and no thermal compromising of the corrector or OTA.  Vibrations?  Fans have been used for YEARS with other scope designs and you never hear anything about vibrations, so no vibrations.  I started a thread about this:

 

CN link ->  Dew-free SCT's and Maks WITHOUT heat - it is possible.  Refractors too.

 

NOTE:  there are other spin off benefits to making a wrap for your scope, even if you don't believe in the insulation aspect:

*  These wraps will extend the dew-free period for the corrector.  Depending on the design of the wrap and conditions of any given night it may be enough to keep the corrector dry all night long when on other nights it would have dewed over.

*  Protects the OTA from getting wet and prevents this water from finding its way into the various nooks and crannies that scopes have - THIS is the water that is most difficult to have dry off out of the scope, NOT what you think that you can see that has dried off.

*  Making the wrap removeable also helps with the drying off and long term preservation of the scope.  It is not a good idea to keep the wrap permanently fitted to the scope - it works against the advantage of keeping dew off the scope in the first place.

 

Alex.

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Edited by maroubra_boy, 19 July 2023 - 06:09 PM.

[markmanner]

I don't use Reflectix.  This is only one material that can be used to make insulation wraps.

 

I make my insulation wraps out of Coreflute. 

 

Alex.

Hi Alex, do you think that my comment about emissivity isn't as important? I'm still experimenting, so I'm interested to see your white colored covering. 

[maroubra_boy]

There is a lot of confused talk about various aspects of colour, insulation properties, yada, yada, yada.  Much of this talk is confused because the technical properties of some materials is out of context because those properties relate to a SPECIFIC way of using that material, and our use of these materials is NOT the orthodoxy.  I refuse to talk about these "technicalities" exactly because we are not using these materials in the way that they are normally used.  Reflectix is a household insulator, not designed to be wrapped around scopes.  And Coreflute???  Instead I talk about my experience with different materials.

 

Yes, colour is important.  You can see this for yourself.  Take a board of plywood, or a sheet of metal or whatever, paint one half black and the other white.  The substrate is the same.  Now, put the plywood outside on a dewy night and look at how dew and even frost forms on the two different painted surfaces.  The black will form dew far sooner and by a larger quantity than the white.  Dew might not even form on the white.  And if the temp is close to freezing, frost will form on the black surface but not on the white.  With my scopes, I always find all the black surfaces forming dew while other lighter colour surfaces even staying dry all night long.  And hey, not just my experience, but something that has been noted in my own astro Club during our sessions and a topic of much discussion among our members.

 

You do not make an insulating wrap, or dewshield, from a material that is black in colour.  This will work against you.  It is absurd to have dewshields made black in colour!  A dewshield that actually ATTRACTS dew!!!!  And many people then go and stick a heating element to these or their black coloured scopes.  Talk about pushing the proverbial up hill.  And these black dewshields are sold because in this colour, one, they "look good", and two, because of a complete lack of understanding of thermodynamics and the roll of colour in this.

 

So you know, I do have a material science and engineering background.

Edited by maroubra_boy, 19 July 2023 - 06:29 PM.

[markmanner]

Thanks, I'll give Coreflute a try. I don't want to focus too much on looks, but if it works ok, I'd prefer that look to reflectix!

Hope all is well with you,
Best regards,

Mark

[luxo II]

Hi Mark, it was me that made the first Coreflute version for the MK91, on the basis it creates an air gap. It might not be as good as Reflectix in a north american winter, but here in our climate it works well enough especially with a little fan. With lengthwise slits, it rolls up to a tight bundle, and is sufficiently robust that it wont disintegrate with repeated use.

 

A reflective layer inside would probably be even better, but so far Alex never found the need for that.

 

On my 10" I cannibalised a spare reflective sunshade from my car; 5 minutes cutting with scissors and some velcro tabs.

https://www.cloudyni...th-70mm-on-top/ Over the years I tried a few experiments and have concluded I don't need to wrap the backend on this scope to stop the internal thermal plume, though this scope has a quartz primary with a very open backend (many holes, like a cheese grater) so the mirror will cool, fast.

 

Which was why IMHO the thermal source of heat that drives the internal plume is the heat stored in the primary mirror - on scopes that have a fully closed-back end, the primary mirror sheds heat via the central baffle, and hence the plume.

 

As always YMMV and some experiementation is worthwhile to see what works for you.

Edited by luxo II, 19 July 2023 - 07:05 PM.

[markmanner]

 

"As always YMMV and some experimentation is worthwhile to see what works for you."

 

 

Thanks, I'll play around with it. One thing that my children have said about my TEC mak with reflectix on it is that it looks like some James Bond villain mass destruction device.  I think I may put a layer of gold space blanket mylar on top of the reflectix or coreflute to see how that looks. Maybe it will then look like what you see on spacecraft .

[luxo II]

Ha call it “Hubble jr” …

Edited by luxo II, 19 July 2023 - 08:20 PM.

[quilty]

Hi, I think the only potential issue with something that isn't silver, is that you may get better thermal insulation, but you start to lose the benefit of having a silver surface that has very low emissivity. I think that part or much of what the reflectix or other silvery surface is doing is reducing the surface cooling of the top of the tube vs the bottom due by reducing differential radiation, which reduces internal thermals. Silver has really low emissivity, but other things that you might think would too, like white, aren't nearly as low. Maybe put whatever you like for good insulation on and then cover it with a silver space blanket, for the best of all worlds?

That dilemma is not a necessary one. No problem to properly insulate the tube and cover it with a topmost antireflection layer. Quite sure tha anti reflection layer must be the very surface.

[BKSo]

How about multi layered insulation. I use a clear plastic sheet base layer, followed by foam (neoprene?) with adhesive on both sides, then a layer of aluminum foil, and lastly, duct tape for protection.

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