29 replies to this topic

[gezak22]

Hi all,

 

Always learning new things, this time I was educated on thermal management of SCTs. Rather than install fans and wait for it to acclimate, people are now recommending insulating it to avoid temperature gradients and thus tube currents. Perhaps people have known this for a long time, I don't know, I still spend most of my time on the refractor forum. *shame on me*

 

At any rate, the local store only had the single layer reflectix, so I ordered the double layer version online. To my surprise, it arrived 24 hours later. Also to my surprise rather than buying 48 in. x 100 in., I ordered 48 in. x 100 ft. Well, I guess it will do.

 

In order to avoid as much work as possible while still keeping it functional, I ended up insulating the scope the following way. I did not want to cut out pieces between the dovetail and the scope. Also, I wanted to put two layers on, just because.

I was surprised that the film is thin enough that I can actually get it between the dovetail and the scope with the original screws still screwing in properly.

 

The front and back look like this:

 

I still need to trim things a bit so I can install the dew shield (and insulate it if needed [I sure have more than enough material]) and perhaps insulate the back.

 

First light will hopefully follow sometime this week.

[Peter Besenbruch]

I clamped a layer of Reflectix with my dovetail plate. I used a double layer on the main tube. I also insulated my dew shield. In Hawaii, I have not insulated the back, but a layer of Reflectix sticks over the back casting. Had I lived in a colder climate, I would have put a layer over the back.

 

Looks good.

[elwaine]

Good job, Geza. You are going to like the way your insulating jacket works. 

 

Did you extend the insulation in front of the OTA to form a dew shield, or will you use a standard dew shield that you cover with reflectix? Either one will work well. No dew will build up on the corrector plate when an insulated dew shield is used.

[WadeH237]

No dew will build up on the corrector plate when an insulated dew shield is used.

I've made a (single layer) Reflectix insulation blanket for my C14 this spring and have had a chance to use it a number of times now.  It makes a *huge* difference in the performance of the scope in the early evening.  We were observing Jupiter at the onset of dusk at GSSP earlier this month and were getting great views right from the start.  Normally, it would be after midnight before planetary views in the C14 really settle down.

 

Regarding dew, I have a flexible AstroZap dew shield for the C14 and I made the insulation blanket long enough to cover the scope and dew shield in one piece.  I will agree that the scope is much more resistant to dew than it is with just the dew shield alone.  And the Reflectix blanket makes the dew shield quite a bit more sturdy.  But at Brothers Star Party in June, it was accumulating dew in the early morning and I needed to turn on the dew heater to clear it.

 

So don't leave the dew heater at home until you know for sure that you won't need it.

[gezak22]

Good job, Geza. You are going to like the way your insulating jacket works. 

 

Did you extend the insulation in front of the OTA to form a dew shield, or will you use a standard dew shield that you cover with reflectix? Either one will work well. No dew will build up on the corrector plate when an insulated dew shield is used.

I did extend the insulation by ~2 inches, but I am planning on trying it out with a dew shield as well, which I have already insulated. I'll cover the back of the scope too.

 

It is such as shame that I found out about this so late in the season. Jupiter is going to be so poor over the next couple of years. I'll just have to make do with using the moon and double stars as a playground.

[David P]

I've found it to help with my C8.  Fits under the dovetails real nice like.

 

Edited by David P, 24 July 2018 - 08:23 PM.

[David P]

Another view.

 

[David P]

 

At any rate, the local store only had the single layer reflectix, so I ordered the double layer version online. To my surprise, it arrived 24 hours later. Also to my surprise rather than buying 48 in. x 100 in., I ordered 48 in. x 100 ft. Well, I guess it will do.

 

 

 

 

 

 

Maybe you could sell some of the excess to NASA for the James Webb Telescope.  The roll I purchased is 16" x 25' and I have enough remaining to wrap a lot of C8s.

[gezak22]

Maybe you could sell some of the excess to NASA for the James Webb Telescope.  The roll I purchased is 16" x 25' and I have enough remaining to wrap a lot of C8s.

I was thinking of just putting the left-over material in the classifieds. Of course NASA can have it too if they browses the classifieds, but they better have positive ratings from previous transactions.

[jhayes_tucson]

I would be very concerned about clamping Reflectix between the tube and the dovetail plate.  That might work for visual but it's no good for imaging since it will interfere with a rigid mechanical connection between the scope and the mount.  Furthermore, there is absolutely no need to clamp the Reflectix with the dovetail.  The whole reason that you put Reflectix on the tube is to minimize radiative heat transfer between the tube and the sky--and that doesn't require a full multi-wrap conductive blanket.  You simply need to wrap a single layer over the parts of the tube exposed to the sky (and that applies to the dew shield as well.)  To minimize thermals in the tube, it is better to very gently circulate air at the ambient outside air temperature so that everything equalizes at the ambient air temperature; otherwise, you will spend a very long period of time trying to get the system to stabilize.  The Reflectix is there to prevent the temperature of the tube from falling below the ambient air temperature, which may cause internal thermals and/or internal dew (or frost.)

 

John

[gezak22]

These are all perfectly valid points, but (1) I don't do imaging any more and (2) I wanted to be lazy (not cut out a template for the contact between the dovetail and the tube) and it approach worked so I didn't bother with the more elaborate approach.

[David P]

I would be very concerned about clamping Reflectix between the tube and the dovetail plate.  That might work for visual but it's no good for imaging since it will interfere with a rigid mechanical connection between the scope and the mount.  Furthermore, there is absolutely no need to clamp the Reflectix with the dovetail. 

With my C8 the Reflectix slid between the OTA and dovetails. No clamping.  Taped the seam with aluminum tape and rotated it under one of the dovetails.

[jhayes_tucson]

With my C8 the Reflectix slid between the OTA and dovetails. No clamping.  Taped the seam with aluminum tape and rotated it under one of the dovetails.

 

Agreed...that's true for all of the models.  Frankly, it is much easier to wrap the tube and tape it than it is to A) remove the telescope from the mount, B) remove the dovetail from the telescope, C) wrap the telescope with multiple layers of Reflectix, C) try to fish screws through the dovetail and the stack of Reflectix to engage the threaded holes in the tube, and then D) try to tighten this whole mess together so that you end up with a wobbly mess  I dunno who's lazier--one who just wraps the tube or one who goes through all of this rigmarole. 

 

John

[Cotts]

My C11 has Parallax rings which I much prefer to attaching a dovetail straight to the tube...stability, accessories....

 

If I wanted to use Reflectix on my scope should I just cut carefully around the rings or should I put the Reflectix all over and squash it down with the rings?  The latter would certainly hold the stuff in place...

 

Dave 

[jhayes_tucson]

My C11 has Parallax rings which I much prefer to attaching a dovetail straight to the tube...stability, accessories....

 

If I wanted to use Reflectix on my scope should I just cut carefully around the rings or should I put the Reflectix all over and squash it down with the rings?  The latter would certainly hold the stuff in place...

 

Dave 

 

Dave,

If it were me, I think that I'd cut around the rings to wrap it.  Reflectix is actually pretty thick and you might have trouble closing the rings around it.

 

John

[coopman]

I recently wrapped my OTA just as David P shows above. Haven't been able to test the results yet - it's been cloudy here and hot & humid too. I am not all that concerned about the looks of my equipment, but that reflectix stuff sure makes a nice scope look cheap....garage sale cheap.

[gezak22]

I recently wrapped my OTA just as David P shows above. Haven't been able to test the results yet - it's been cloudy here and hot & humid too. I am not all that concerned about the looks of my equipment, but that reflectix stuff sure makes a nice scope look cheap....garage sale cheap.

If you ask me, the film makes it look like the Hubble telescope.

 

Clouds here too, and I have family visiting next week. If it's not clear Friday or Saturday, first light will have to wait.

[Jeff B]

Here are my C11 and TEC 7 mak in full metal jacket.  I used two layers for each scope.

 

This stuff does work and made a huge difference in the usability of the scope when taken outside.  Save for a single, weak, narrow heat plume from either the mirror or the  primary baffle I could basically use them immediately.  The plumes then dissipated slowly over the next hour of so.  I wrapped the dew shield too.  The real big bonus was that lack of dew formation on the C11 corrector.  It will be interesting to see how well the stuff works going from a cold basement to a hot outdoors.

 

First the TEC 7

 

Jeff

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[Jeff B]

Next the C11.  The stuff is really easy to work with and surprisingly strong and tear resistant.

 

Jeff

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[gezak22]

Do you keep the fans on the back running?

[Jeff B]

Do you keep the fans on the back running?

Nope.  Nor do I want to.  Pushing cold air in defeats the purpose of the insulation by providing cool air around the primary which causes it to shed heat quicker, giving rise to bad thermal effects, which is exactly what I want to avoid by using the insulation.  

[gezak22]

Nope.  Nor do I want to.  Pushing cold air in defeats the purpose of the insulation by providing cool air around the primary which causes it to shed heat quicker, giving rise to bad thermal effects, which is exactly what I want to avoid by using the insulation.  

So then why not remove them and cover up the holes with insulating material as well?

[Exnihilo]

Next the C11.  The stuff is really easy to work with and surprisingly strong and tear resistant.
 
Jeff

Those are great scopes! Great job with the insulation. Please let us know the results. I have fans on my 11" Edge, but still unsure if I want/need to do the insulation thing.

[punk35]

I put a single layer on my CPC11, and also made a dew shield with it that slides all the way to the forks. That left about 14 inches beyond the corrector. I believe I bought the 24”x50’ roll and have plenty left over. I think it made a huge difference. Thermals we’re almost nil, and I was getting nice views immediately after setting it out. Here’s some photos. In one photo you can see the dew shield standing on the grass while I took the shot. I’m very pleased with the results of this mod.

 

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[Ty Williams]

A few years back after learning how important thermal control was in my Newtonian, it became something I was thinking about all the time. I noticed my EdgeHD800 would drip with dew while the chromed legs of the mount stayed dry. I bought some reflectix and, lo and behold, the scope stays dry as a bone even when the dew is dripping off everything else. Everyone treats me like I'm crazy for having a shiny silver scope but you all are crazy right along with me.

 

Combined with the Starizona hair dryer thingy that blows air in the front (with the secondary removed, obviously before observing only) and the TempEST fans, the EdgeHD800 never shows evidence of thermal problems. The payoff is that every single other person who looks through the scope is absolutely shocked at the sharpness and contrast and can't believe it's a small, consumer-level scope. I just take it to mean that thermal control and collimation actually do matter.