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Insulation jacket for Mak?

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#76 Steve D.

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Posted 22 January 2018 - 02:58 PM

If I can get a clear night this week, I'll try to take the scope out with no preparation first to see how it behaves and then cool it down to see if it stays stable.


 

#77 MarkMittlesteadt

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Posted 22 January 2018 - 06:45 PM

For now, I'm just going to use this carpet runner. It's very lightweight, yet holds it's shape very well. It has a flat black rubberized underside (which is to the inside when around the OTA). 

 

It covers my OTA all the way up to my rings and it extends out about 8" beyond the corrector when in place. The rings are lined with felt and are very close together, so almost no part of the OTA except the rear mirror cell is left uncovered. I also have a dew heater strap under it right behind the corrector plate.

 

It will probably be a while before I get to try it out. Really cold temps, and though it's warmer now, we're under a winter weather advisory. That's what warm temps bring around here in winter. frown.gif

 

long-dew-shield-1.jpg

 

The inside of it is really much darker than this pic shows, and a very dull flat black...

 

long-dew-shield-2.jpg


Edited by MarkMittlesteadt, 22 January 2018 - 06:46 PM.

 

#78 yellobeard

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Posted 23 January 2018 - 02:15 AM

It still amazes me how many members at CN didn't read the threads about insulation yet.
So many remarks about 'cooling times' with bigger scopes, including pictures of their un-insulated setup's..

They really don't have a clou of what they're missing!
 

#79 Asbytec

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Posted 23 January 2018 - 05:10 AM

Now, I gotta try it.
 

#80 spongebob@55

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Posted 23 January 2018 - 08:22 AM

For now, I'm just going to use this carpet runner. It's very lightweight, yet holds it's shape very well. It has a flat black rubberized underside (which is to the inside when around the OTA). 

 

It covers my OTA all the way up to my rings and it extends out about 8" beyond the corrector when in place. The rings are lined with felt and are very close together, so almost no part of the OTA except the rear mirror cell is left uncovered. I also have a dew heater strap under it right behind the corrector plate.

 

It will probably be a while before I get to try it out. Really cold temps, and though it's warmer now, we're under a winter weather advisory. That's what warm temps bring around here in winter. frown.gif

 

long-dew-shield-1.jpg

 

The inside of it is really much darker than this pic shows, and a very dull flat black...

 

long-dew-shield-2.jpg

Mark,

Home Depot?  Lowes?

Let us know how it works.

Thanks

Bob


 

#81 DLuders

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Posted 23 January 2018 - 08:57 AM

If you don't want to go for the "industrial look" of aluminized insulation, consider some inexpensive Camping Pad that is used beneath sleeping bags:  https://www.walmart....h=sem#read-more


 

#82 MarkMittlesteadt

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Posted 23 January 2018 - 11:00 AM

 

For now, I'm just going to use this carpet runner. It's very lightweight, yet holds it's shape very well. It has a flat black rubberized underside (which is to the inside when around the OTA). 

 

It covers my OTA all the way up to my rings and it extends out about 8" beyond the corrector when in place. The rings are lined with felt and are very close together, so almost no part of the OTA except the rear mirror cell is left uncovered. I also have a dew heater strap under it right behind the corrector plate.

 

It will probably be a while before I get to try it out. Really cold temps, and though it's warmer now, we're under a winter weather advisory. That's what warm temps bring around here in winter. frown.gif

 

long-dew-shield-1.jpg

 

The inside of it is really much darker than this pic shows, and a very dull flat black...

 

long-dew-shield-2.jpg

Mark,

Home Depot?  Lowes?

Let us know how it works.

Thanks

Bob

 

I work at an Ace Hardware. We carry all kinds of things one could use. I found this carpet runner which is only $2.69 per foot, but I only pay half that. It's pretty light, and it has a thin, tight weave of almost like a textured indoor/outdoor carpet on the outside, with a thin rubber backing. While totally flexible, it's still stiff enough that when wrap into a cylinder it keeps it's shape perfectly. Also, velcro sticks to both sides very well. I spray painted the outside of it with gloss black (to seal the carpet fibers from moisture) but left the inside the nice flat black of the rubber. 

 

I have no doubt it does not insulate as well as Reflectix, but I would think anything wrapped around the metal tube of the OTA would suppress the fast loss of heat better than having the bare metal tube exposed. 

 

It will probably be a while before I can test it out. This has been a miserable winter. Bitter cold, and when it is warm enough to almost entice me to go out, that means clouds and snow. I just got done digging my vehicles out from under the glacier of frozen rain and snow they were trapped in and then shoveled and snowblowed from last nights storm. Ugh. Maybe another 4 weeks of this weather (crossing fingers).


 

#83 MarkMittlesteadt

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Posted 23 January 2018 - 11:06 AM

If you don't want to go for the "industrial look" of aluminized insulation, consider some inexpensive Camping Pad that is used beneath sleeping bags:  https://www.walmart....h=sem#read-more

I don't mind the Reflectix look too much, but unless it's wrapped around an existing dew shield (of some stiffer material) it bends out of shape too easily for me. One also has to line (or paint) the inside with something flat black to be effective in minimizing stray light reflections in the light path. I might try it again sometime in the future. I want to see how this carpet runner works for me first. 


 

#84 MarkMittlesteadt

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Posted 23 January 2018 - 11:08 AM

It still amazes me how many members at CN didn't read the threads about insulation yet.
So many remarks about 'cooling times' with bigger scopes, including pictures of their un-insulated setup's..

They really don't have a clou of what they're missing!

This makes sense to me because typically the night sky almost never stops cooling off, so trying to keep the OTA at ambient temps seems like a dog chasing it's tail. 


 

#85 TG

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Posted 23 January 2018 - 12:55 PM

 

It still amazes me how many members at CN didn't read the threads about insulation yet.
So many remarks about 'cooling times' with bigger scopes, including pictures of their un-insulated setup's..

They really don't have a clou of what they're missing!

This makes sense to me because typically the night sky almost never stops cooling off, so trying to keep the OTA at ambient temps seems like a dog chasing it's tail. 

 

^^^^^^^^^^^

This.

 

Radiative cooling is the enemy, especially the differential between the skyward and ground sides which causes convection currents in the tube. Newt guys have realized this ages ago. SCT folks seem to be catching up only now.

 

Tanveer.


 

#86 spongebob@55

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Posted 23 January 2018 - 02:30 PM

I've been using this closed cell foam for my home made dew shields.  Keeps a pretty good shape.  I just checked and can be slid under the rail on my 6 & 8" SCTs with just a bit of compression.  Its 1/4" thick and would wrap very nicely.  Inexpensive and very very light.   I've also spray painted the inside black after I sanded it down with super fine sandpaper to give it some tooth.  It'll stretch just a little bit.

 

https://www.ebay.com...0G9GS96s_7j6Phg

 

Assuming that the front cell, and OTA is covered, isn't there a problem with not covering the rear cell creating currents?  

 

Regards

Bob


Edited by spongebob@55, 23 January 2018 - 02:33 PM.

 

#87 MarkMittlesteadt

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Posted 23 January 2018 - 03:06 PM

Assuming that the front cell, and OTA is covered, isn't there a problem with not covering the rear cell creating currents?  

 

Regards

Bob

I'm going to hazard a guess (and perhaps I'm all wrong). Our scopes are most often pointing up and warm air rises. If the front half of the scope is heated (dew strap) and insulated (dew shield that covers the OTA and extending beyond) and the rear mirror cell is constantly cooling off, wouldn't the warm air rising from the mirror end and mixing with the warm air higher up, make it more stable? Wouldn't warm air + warm air = stability? 

 

Perhaps those who are forever trying to cool down their scopes (chasing the ever dropping outside air temps) are only allowing the warmer air in front of the mirror to rise into the (also) cooling down front end. Warm air mixing with the cooler air inside causing the turbulence? 

 

I would guess that completely insulating the entire OTA front to back would be ideal, but I think if the rear cell wasn't insulated and it was always cooling, the warmer air coming off the mirror end is rising into warmer air might still be more beneficial than simply trying to cool the entire OTA all night long. Again, just a guess on my part. 


 

#88 Mitrovarr

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Posted 23 January 2018 - 03:56 PM

I'm tempted to get some of that aluminized insulation and give it a try. I still don't quite get how the scope doesn't cool via the corrector plate and rear cell, though

On a side note, people did used to try to insulate newtonians. I have a 6" homemade newt I found at a yard sale that came with a insulating layer of cork spaced about half an inch from the outer tube wall. As I understand it, corking tubes used to be a thing.
 

#89 TG

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Posted 23 January 2018 - 04:35 PM

Re. keeping the dew shield out of the light path, I already provided a solution previously in the thread but here it is again:

 

https://www.cloudyni...sign/?p=5516704

 

Re. Reflectix vs. camping pads, I have used both and Reflectix is preferable by far for these reasons:

 

  • It's much lighter
  • It has a much higher ability to insulate due to the reflective aluminum layer

Previously, I used to stick black felt/flocking on the inside, This makes the shield heavier. I've since come to prefer painting with black chalkboard paint (posted earlier in the thread). With a lighter shield you only need a few spots of Velcro to secure it.

 

Tanveer.


 

#90 MarkMittlesteadt

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Posted 23 January 2018 - 04:45 PM

Re. keeping the dew shield out of the light path, I already provided a solution previously in the thread but here it is again:

 

https://www.cloudyni...sign/?p=5516704

 

Re. Reflectix vs. camping pads, I have used both and Reflectix is preferable by far for these reasons:

 

  • It's much lighter
  • It has a much higher ability to insulate due to the reflective aluminum layer

Previously, I used to stick black felt/flocking on the inside, This makes the shield heavier. I've since come to prefer painting with black chalkboard paint (posted earlier in the thread). With a lighter shield you only need a few spots of Velcro to secure it.

 

Tanveer.

My concern is storage. I know how Relfectix will end up down the line (for me anyway)...like something I pulled off the grill and tossed in the garbage. LOL. 

 

I could use aluminum tape (like the kind used around heating/cooling ductwork) and line only the part of my dew shield that is over the OTA. Granted, there still isn't the air pockets sandwiched in between the aluminum layers that Reflectix has, but the aluminum tape would reflect heat back towards the OTA tube more than the carpet runner alone. 

 

EDIT: I have this tape at home. 


Edited by MarkMittlesteadt, 23 January 2018 - 05:55 PM.

 

#91 yellobeard

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Posted 23 January 2018 - 04:46 PM

Insulating open systems like newtonians does not work very well.. When the inside of the scope stayes warmer than ambient, warm currents from inside the tube collide with the colder air that is waiting in front of the scope's opening.

Back in 1992, I solved this by designing a watercooling system at the back of the primary of my 8" newt, and deliberately not insulate the scope's tube. Its huge success made me complete a very similar setup, involving a 12,5" newt..

Edited by yellobeard, 23 January 2018 - 04:47 PM.

 

#92 Peter Besenbruch

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Posted 23 January 2018 - 06:21 PM

I'm tempted to get some of that aluminized insulation and give it a try. I still don't quite get how the scope doesn't cool via the corrector plate and rear cell, though

I think the answer in another thread went something like this: The corrector is made of glass, and glass is a decent insulator. Whether SCT or Maksutov the entire back portion of the scope tends to act as a large heat sink. If the rest of the scope cools more quickly (and it tends to), then the mirror assembly and primary baffle tube becomes a source of tube currents.


 

#93 James Ball

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Posted 23 January 2018 - 11:59 PM

 

 

 Would wrapping dew heaters around the tube then putting on the insulation and running at very low power to just maintain a constant temperature also work?  This would keep the entire tube and corrector at a nice constant temperature no matter what the outside temperature was, especially if a thermostat was rigged into the system. 

 

This might just be the next aftermarket accessory to sell like crazy smile.gif

 

And that is exactly the idea that I'm working on already for a year or so!! I didn't mention it earlier because I mostly want to be fully sure, and have a good image within myself on the advantages and disadvantages, before I post about it.

 

But its a big yes ! Up till this moment, I didn't find any good reason against it!

The thought behind it is quite simple:

With proper insulation, you can immediately use your scope after puting it out in a colder environment.

During that situation, the temperature of the inside of the scope definitely is higher than ambient, for a very long time. So already that fact, tells me that it should not give any problems to keep the inside of that scope warmer than ambient permanently.

 

And indeed, with proper insulation, the energy you'll need to put in to keep that inside temperature higher, will be not much.

 

But I would choose for putting an evenly heated blanket directly on the tube, under the insulation.

That way, even less energy is needed, as lots of energy is not radiated in the coldness of ambient. Which of course would be the case when putting the heater on top of the insulation.

 

 

Very interesting.  What about going the other direction?  How do you think the insulated scope would perform if you used a Lymax Cat cooler to cool down the entire inside close to ambient temp instead of trying to keep the temp higher by warming it?  It seems the scope would still always be slightly above the ambient temperature but perhaps the entire inside of the scope would cool at the same rate so that thermals wouldn't be a problem.   The Lymax Cat cooler always initially worked for me but continued falling temperatures and the aluminum tube always insured that the mirror was warmer than the rest of the tube.  Just wondering if insulation and a Cat cooler is the way to go.   I'm hoping to get some opportunities to test it soon. 

 

It might work, the goal is thermal stability either above, below, or at ambient.  The problem I see with below ambient would be increased chance of dew on the corrector.  If you are slightly above ambient then the corrector will be less likely to dew up. 

 

Thermal currents are caused by temperature differentials.  With an aluminum tube, which is a great conductor of heat, any change in temperature outside the tube is going to cause the air inside the tube next to the side of the tube become different than the air in the center of the tube, which will initiate an air current.  The spectrometers at work are usually set to 40C which is above room temperature( unless the hvac goes out like last summer) and holds everything in thermal equilibrium, or they are chilled with a peltier cooler to 0c or -20c, but those are also constantly purged with dry argon to prevent moisture from condensing inside.

 

An interesting idea I had would be to take something like a C8, wrap heat strips around it and place it inside an empty C11 or Meade 10" tube and fill the gap with expanding foam for insulation, using the larger tube to mount the smaller scope.  Could either be dovetail or fork mounted easily.  To go even further you could purge the tube with argon and seal the rear with a focal reducer to prevent moisture from building up.  But it might be better to use nitrogen to prevent refraction problems.


 

#94 yellobeard

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Posted 24 January 2018 - 12:28 AM

Well, don't think that I didn't go far in thinking on getting rid of internal tube currrents...

The best of the best is..: Total vacuum in your scope!!

But with my 16" SCT, there will be some 1100 kilogrammes of pressure on the schmidt corrector plate..
 

#95 spongebob@55

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Posted 24 January 2018 - 04:49 PM

So I guess I have to tape over the air vents in my one Edge SCT and not turn on the fans and tape over the vents on my other if I use this method?

Bob


 

#96 TG

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Posted 24 January 2018 - 06:32 PM

Well, don't think that I didn't go far in thinking on getting rid of internal tube currrents...

The best of the best is..: Total vacuum in your scope!!

But with my 16" SCT, there will be some 1100 kilogrammes of pressure on the schmidt corrector plate..

Is there going to be a difference in performance due to having a vacuum inside? If yes, have you booked a ride on Soyuz to figure the optics in outer space? :lol:

 

Tanveer.


 

#97 Asbytec

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Posted 24 January 2018 - 06:33 PM

So I guess I have to tape over the air vents in my one Edge SCT and not turn on the fans and tape over the vents on my other if I use this method?

Bob

I have no test results, just a hypothesis. I'd say you could probably use your active cooling system with a thermal shield to good effect. The insulation simply slows passive radiation to the sky providing thermal stability inside the OTA at whatever temperature it may be. 


 

#98 gfstallin

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Posted 24 January 2018 - 11:32 PM

So I guess I have to tape over the air vents in my one Edge SCT and not turn on the fans and tape over the vents on my other if I use this method?

Bob

Since this thread opened up, I've been wondering this as well. In particular, I had holes drilled into my standard C11 and fans installed by Deep Space Products. The thermal difference was night and day, though I cannot really compare it to results I could have obtained with Reflectix. It would be a hard lesson learned if $16 of Reflectix and 20 minutes of my time could have solved the thermal "issue" by tackling it from a completely different angle (or, not tackling it at all, as it were). I guess we would need a control - one Edge/ventilated SCT and one standard SCT with Reflectix, same aperture, same location and same night. We could call it the Reflectix Challenge. It might be a good experiment for club members. 

 

Considering the wife and I are in the process of buying a house right now (placed our bid tonight), I would be a perfect candidate to carry this experiment out with significant corporate sponsorship (ahem, Reflectix and Celestron). I've already reached a tentative conclusion. "These products are wonderful! This study was in no way influenced by the free installation of Reflectix on my new-to-me duct work and in my attic or my receipt of free C14 Edge and standard C14 SCTs. All three products work and stuff. You will not be disappointed. Please see the classifieds for further information on one of the C14s." 

 

More immediately, I could be part of a study testing the impact house down payments can have on scientific integrity, which should pay me enough cash to get a roll of Reflectix for my standard C9.25. grin.gif  

 

George


Edited by gfstallin, 24 January 2018 - 11:35 PM.

 

#99 divers

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Posted 25 January 2018 - 07:14 AM

All dressed up for a night on the town.  I have some industrial paint at work that I am going to,use on the outside to get rid of the silver color.

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#100 Asbytec

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Posted 25 January 2018 - 08:31 AM

"All dressed up for a night on the town."

 

Curious about performance. Report back? 


 


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