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Insulating my SW 180 Mak.

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#101 Joe1950

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Posted 16 September 2018 - 06:39 PM

So, JB, what is your assessment of the entire insulation idea? Is it something that works as some report, or simply a partial remedy?

 

If the temperature is changing, due to heat escape via the corrector, there will be some air currents formed. And, with the changing temperature tha shape of the optical elements will be affected.

 

I do feel that the insulated can experiment should have had a glass barrier at the open end to more simulate the structure of the scope. Plus the corrector in a Mak is rather thick and I would think have insulating characteristics that are much better than thin sheet metal.

 

Thanks.



#102 elwaine

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Posted 16 September 2018 - 06:50 PM

Joe, from his original post:

 

Just to be clear, I'm totally on board with the insulation jacket idea.  I started using Reflectix wrapped around my OTA and part of the dew shield with some wall-hanging 3M velcro strips last year.  The velcro strips let me use the original packaging foam in my transport and storage solution, since I can just take off the jacket when it goes in the box.  It works great on the Colorado plains, where we can see a 40F temperature change over the night.

He wasn't questioning the efficacy of using insulation jackets. He was questioning my plan for a jacket that did not have the reflective layer in direct contact with the atmosphere that surrounds the OTA. I finally understand why his concept is the better choice. My only question now is whether or not my "sandwich" jacket will work satisfactorily in my environment. If I lived in a cold climate with rapidly dropping temps during my observing session, I would abandon the idea of making the Mak look nice and I would use a single layer of foam against the OTA and two layers of Reflectix (or, Prodex, in my case) as the outer coverings. 

 

As an aside, the white rubber foam I'm using is more resistant to tearing than the thin aluminum sheets that encase the air cells in both Reflectix and Prodex... which is another reason I hope the rubber foam works as planned,


Edited by elwaine, 16 September 2018 - 06:59 PM.

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#103 Joe1950

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Posted 16 September 2018 - 07:03 PM

Thanks, Elwaine! I appreciate that clarification. 

 

Where I am and with the smaller scope I'll use a layer of the foam, or maybe two since it is so thin and one layer of Reflectix, the aluminum on both sides. 

 

Anyway, if the temperature swings too much, I don't go out. lol.gif  And the planets are not positioned well in the real cold months this year. Though it's better when they are since there is much more altitude.

 

Winter viewing is primarily confined to the moon and maybe a few interesting doubles. 

 

Thanks again.



#104 jbrandmeyer

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Posted 16 September 2018 - 10:58 PM

Most nights I'm using insulation to control the tube currents.  On the Colorado plains, many good observing nights are also bone dry.  Instead of the temperature falling for a few hours and leveling off, it will keep falling all the way to sunrise.  True equilibrium is impossible.  I'm just trying to deal with the unending transient as best I can.

 

Setup time is maybe 15 min before sunset.  I start off with my C11's tempest fans running, jacket off.  After the first hour or so, I put on the insulation jacket and leave the fans running all night.  I'm trying to minimize thermals everywhere, including the corrector plate.  The function of the insulation jacket on these nights is to minimize thermals rolling off the tube.  Without the reflective jacket, the fans would be have to heat up the metal tube as the tube otherwise would radiatively cool well below the ground-level air temperature.  Adding the jacket means that the little tempest fans can follow the air's 3-4 F/hr unrelenting cooldown rate as the night progresses.

 

Does it work in this mode?  To be perfectly honest, I'm not entirely sure.  Certainly the telltale mirror plume in a defocused star isn't there (and was everpresent before I adopted this strategy).  Similarly, the radial waving threads/spikes disappear and don't come back.  But living just east of the Rockies means that seeing conditions are generally poor.  Looking at the moon is surreal; as if the moon was at the bottom of a swimming pool.  Planetary viewing is an act of patience, as the image phases back and forth through both sides of focus.  In the naked eye, the planets can twinkle just as much as the stars do.  I've never seen the Airy disc's first ring in my telescope without an artificial star.

 

Although much less common, dewing or frosting can be a threat even up here on the high plains.  On humid nights (like last Saturday) I turn the fans off after the first 45 min or so when I put on the insulation jacket.  In this case, I'm trading off a little more thermals around my corrector plate to get some more dewing resistance, but I still want to get somewhat closer to ground-level temperature.  When I started packing things up last weekend the status was:

 

- Telescope OTA plastic crate: dewy

- Observing notebook: wet

- Car roof: wet

- Eyepiece pelican case: damp

- Car windshield: fogged

- Telescope insulation jacket: dry

- Telescope corrector plate: dry

- Astrophoto refractor guy on the next pad: Grumbling about dew-ruined subs

- Open-truss dob guy on the next pad over the other direction ... still happily observing with his boundary-layer fans :)

 

I don't even own a dew heater.  Just a dew shield and single-layer reflectix insulation jacket.  I'd've stayed out longer, if it wasn't for the fact that my observing buddy was passed out in the car secure in the promise that daddy was gonna take her home Real Soon Now :)

 

 

Elwain's strategy is different.  He's starting the night off with a robust insulation jacket and zero fans for grab-n-go use.  He's accepting a little more corrector plate thermals in exchange for low (negligible?) mirror and tube thermals right away.  He's also aiming for maximum dewing resistance in a humid climate.  I don't do much grab-n-go in the Denver suburbs, but I think the basic strategy is totally legit and I'll be doing the same thing on my smaller scopes in the future.


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#105 elwaine

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Posted 17 September 2018 - 11:00 AM

One more thing to consider is that during discussions like this one, we often fail to take variables into account. Even in the same climate, an insulating jacket that woks well for a 6" Mak or an 8" SCT may not work for a C11. And a jacket that works in warm, humid climates may not work in cold, dry climates. As with houses, the insulation requirements for a closed tube MCT or SCT will depend on the climate it's used in.


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#106 cuivienor

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Posted 18 September 2018 - 09:21 AM

Following advice on this thread and others, I have wrapped my LX200 8 inch OTA in two layers of insulating material (using stuff that is used in Japan to keep the bath warm - two layers of reflective material sandwiching some foam. It seems to be working great!

 

Next will be my 150mm Mak, and my EdgeHD800 :)

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#107 Joe1950

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Posted 18 September 2018 - 09:49 AM

Looks good, Cuivienor! Very nice job. Thanks for the report.



#108 elwaine

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Posted 19 September 2018 - 01:46 PM

Finally finished making the 3-layer insulating jacket for my TEC 7" Mak. The inside and outside layer on the OTA and on the dew shield is 2mm thick, white rubber-foam. Sandwiched in-between the rubber-foam layers is a 5mm layer of Prodex (similar to double reflective Reflectix). The back of the Mak is covered with 2 sheets of Prodex, which I painted flat black on the outside.

 

The black band between the dew shield and the OTA is not there for decoration. The dew shield simply slip-fits on to the OTA. It's a poor design, IMO, because it doesn't take much force to dislodge the dew shield. The 1.5" wide self-adhering Velcro strap adds a lot of support and helps keep the dew shield from falling off the scope.

 

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Edited by elwaine, 19 September 2018 - 01:55 PM.

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#109 Joe1950

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Posted 19 September 2018 - 01:50 PM

Nice job on that, Elwaine!


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#110 elwaine

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Posted 19 September 2018 - 01:51 PM

The other design flaw (again, IMO), is that the protective metal meniscus cover doesn’t fit the dew shield opening very well. While the metal cover attaches securely to the front of the OTA, it fits very loosely in the front opening of the dew shield. It rattles and it can eventually chip the paint. So I found a silicon rubber cover that fits perfectly.

 

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I won't know how effective my jacket is, in all respects, until the mid-winter months. So it will be a while until I can report back... although I should know how it works to prevent dew in just another month or two.

 

_Larry


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#111 Joe1950

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Posted 19 September 2018 - 02:30 PM

I’d place a wager it is super efficient. 



#112 GUS.K

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Posted 04 October 2018 - 02:39 AM

It’s been over a month since I first tried the insulation jacket on the 180 Mak. All told, about a dozen outings now and the scope has been useable straight away, no issue with tube thermals, with seeing conditions being the only limiting factor. The other morning I was up before dawn, set up the scope with jacket and was viewing the moon with an 8.8mm (307x) eyepiece straight off, in excellent seeing, with a temperature difference of 15 degrees C. One thing I have noticed is the insulation cap on the back of the scope can be left off and doesn’t seem to cause any visible issues. I was initially sceptical, but now see for myself the benefits of insulating my Mak, especially when there is a large temp differential. 


Edited by GUS.K, 04 October 2018 - 02:40 AM.

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#113 elwaine

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Posted 04 October 2018 - 07:26 AM

waytogo.gif waytogo.gif

 

Great report, Gus. Thank you. 

 

(And yet we still read posts that talk about the prolonged cool down times of midsized Maks and SCTs.)

 

-Larry 


Edited by elwaine, 04 October 2018 - 07:26 AM.

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