225 replies to this topic

[eklf]

Very interesting post and calculations, speedster. 

 

 

......

 

Heat loss rates:

 

Stock SCT = 258 Btuh

With Reflectix covering all the tube = 227 Btuh

1" polyurethane foam covering all the tube = 194 Btuh

 

..........

 

If reports of the success of reflectrix are to be believed, then I wonder if one way to reconcile that with the calculations above may be to consider that the air *inside* the tube is acting as the "dead air space" required for reflectrix to perform as a good radiant barrier.

Edited by eklf, 05 December 2018 - 08:46 AM.

[whizbang]

Forget reflectix.  My wife is going to knit a wool sweater for my C8.

[eklf]

Very interesting post and calculations, speedster. 

 

 

If reports of the success of reflectrix are to be believed, then I wonder if one way to reconcile that with the calculations above may be to consider that the air *inside* the tube is acting as the "dead air space" required for reflectrix to perform as a good radiant barrier.

On further thought my proposal is wrong, because for this to happen, the reflectrix would have to be "inside" the tube not outside.

 

Since the conductive property (R-value) has little bearing on the radiant barrier function, perhaps calculations using R value as a stand-in for  "emmisivity" value may be flawed.  

 

In other words, reflectrix works as a radiant barrier because it has an appropriate emmisivity value.    Maybe?

Edited by eklf, 05 December 2018 - 10:25 AM.

[Jimmy462]

>snip<

 

Jimmy G: - occasionally we experience internal dewing issues...this year we've probably gone out well over a hundred nights & perhaps encountered said on 2 or 3 of those nights...

 

The worst (very occasionally) is fogging of the secondary because it can be difficult to detect at times & even harder to actually see by looking into the scope's front - if this occurs I pull out the imaging train, stick the neck of the hair dryer (a nice fit) into the 2" focuser opening & give it a 10 second blast or so, turn the scope facing directly up & the warmed air rises & defogs the secondary...same with fogging on the inside of the corrector plate but longer hair-drying from the front surface will also remove this underside fogging...it takes longer & then longer still to cool down naturally.

 

Remember that dew/fog usually occurs on the coldest surfaces: should the primary itself actually fog up (rarer but not unknown) you shove the hair dryer up the focuser spout but with the scope pointing downwards such that the introduced warm air rises up to the primary & very quickly dissipates the fogging.

 

I have never had to do any of the internal defoggings more than once in a night btw - once internal fog (wherever that might be) is dissipated it does not come back again that session...

 

>snip<

Hi Kokatha man,

 

Thanks for sharing those experiences with your icing-down procedures, certainly fascinating to read but I'm left wondering if this practice would yield different results in more dew-prone locales. Living here in the northeast United States I'm apparently in good company with folks who have to keep an eye on the dew point year-round and I'm thinking that any procedure (such as yours) that more-rapidly gets my scope to dew-forming ambient temperatures is not the way to go. But I'd be curious to hear yours or others thoughts in those regards if I'm "getting" this wrong.

 

Thanks again,

Jimmy G

[Sarkikos]

First, this thread started off about dew and became thermals. 

Yes and no.  The topic is Questions About Insulating SCT's with Reflectix.  My first three posts contained my initial questions about insulating SCT's with Reflectix.  I didn't want to jam everything into the opening post. Only the first of these three posts asked about dew.  In fact, it asked about dew and thermals.  I am concerned about both.  

 

But any and all questions and answers about insulating SCT's with Reflectix are welcome.  Both dew and thermals are pertinent issues.  Keeping the topic focused on either dew or thermals alone would not make sense and would not be productive.

 

Mike

Edited by Sarkikos, 05 December 2018 - 10:49 AM.

[John Vogt]

What has the experience been of those who have tried wrapping their Nexstar 11 GPS with Reflectix?

I had not much success searching the various Reflectix threads about this.

BTW, I Googled thermal conductivity of carbon fibre and, if I'm interpreting it correctly, the graphs that were

returned showed the carbon fibre to have much greater conductivity than aluminum. I realize it can vary

quite a bit depending on the type of carbon fibre but thought aluminum would have had much greater

conductivity.

 

Thanks!

John

[Spikey131]

Forget reflectix.  My wife is going to knit a wool sweater for my C8.

No good.  Won’t work for reflective heat loss. 

 

Unless she can add some tinsel to the wool.......

[Jimmy462]

Yes and no.  The topic is Questions About Insulating SCT's with Reflectix.  My first three posts contained my initial questions about insulating SCT's with Reflectix.  I didn't want to jam everything into the opening post. Only the first of these three posts asked about dew.  In fact, it asked about dew and thermals.  I am concerned about both.  

 

But any and all questions and answers about insulating SCT's with Reflectix are welcome.  Both dew and thermals are pertinent issues.  Keeping the topic focused on either dew or thermals alone would not make sense and would not be productive.

 

Mike

Hi Mike,

 

At the risk of becoming, um, non-productive...I keep revisiting "ventilation as the seemingly logical solution" in my mind as dew will evaporate faster in the presence of wind. Quite by chance I stumbled upon this fellow's video this morning where he incorporates the use of an oscillating fan to keep his imaging gear dry throughout his night-long sessions, and thought I'd share it here (queued to the time) for everyone's considerations...

 

DSLR Astrophotography - Let's Photograph the Trifid Nebula - YouTube:

https://www.youtube....khh7GsQek&t=500 ...or, for mobile...

https://youtu.be/7Lkhh7GsQek?t=500

 

...not that this method would resolve internal OTA thermal issues. However, it does lead me to consider that a combination of full internal OTA ventilation and the use an external fan might be an alternate solution to both problems. Maybe not-so-fun on a cold winter's night, but it could help alleviate the mosquito-problem in the depths of summer!

 

Just food for thought,

Jimmy G

Edited by Jimmy462, 06 December 2018 - 10:31 AM.

[Sarkikos]

Large fans would not work for me.  I don't have an observatory.  I'm not lugging out a large fan behind my building or to the dark site. 

 

I have a small fan hanging under the primary of my 10" Dob.  And two smaller fans in the OTA of my EdgeHD 8".  But beyond small fans like those, I don't see fans as a viable solution to mitigate any problems for most observers.

 

Mike

Edited by Sarkikos, 06 December 2018 - 10:48 AM.

[TG]

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

This is fairly cheap experiment to do. A can of spray Rustoleum Chalkboard paint and a piece of Refectix is all it'll take (and maybe a thermometer if you want to take measurements).

Tanveer

[Kokatha man]

<"Ron359, on 04 Dec 2018 - 5:52 PM, said:

There are plenty of top rate planetary imagers in the planetary-solar imaging forum who go to great lengths, such as ice packs on their tubes, to get their SCT 11s and 14s to ambient temp. and never mention Reflectix. But few in these threads seem to read or follow what the really good SCT planetary imagers do to get their sub arc second details on every night of good seeing. Instead, in thread after thread I only read anecdotal arguments against well known principles of physics with "common sense" and a cheap fix. And I thought astronomy and those who practice it, was all about science. Was I wrong.">

 

JimmyG & speedster: I commented about the dew issues in my Post #173 with special attention to internal dewing, which is the only real worry...but this is an extremely rare occurrence! The only other concern is if there is a lengthy wait (1+ hours) between imaging targets - & I cover our method of dealing with that in the same post.

 

I don't think our climate is terribly different apropos dew...we've imaged in temperate, tropical & arid climates across Oz...even in the arid bush, some might be surprised by the fact that days could have extremely high temperatures for the season but as night approaches it's not unusual that temperatures really do drop like the proverbial stone...I understand US deserts can be very similar...the relative humidity is the salient factor in determining dew-points of course.

 

Btw, we live 50kms South of Adelaide which is where we have been obliged to do much more imaging this year instead of our normal "field trips." A description of Adelaide's climate is Quote: "Adelaide has a Mediterranean climate (Köppen climate classification Csa), with cool to mild winters with moderate rainfall and warm to hot, generally dry summers."

 

I've included Ron's comments above from earlier because *ahem* we always aim for "sub arc second seeing" & I think evidential outcomes are what really counts tbh - & apart from another SSI forum member trying the ice packs out this year after some of my comments, I'm unaware of anyone else who resorts to this tactic...although that doesn't of course mean others haven't - it's just that in the several years we've used ice I haven't come across anyone else anywhere.

 

I'm going through old files on stored HD's in a casual way to try & find a few pikkies of the cork gasket & other stuff I've either mentioned in earlier postings here...this is a decade or more old in places so it ain't easy - but I did find an image of the rear-casting's insulated cap. (but not of the entire "suit" unfortunately )

 

I omitted to mention earlier that the outside of this double layer of 5mm cork was sprayed silver* - & apart from (now most likely) lost temperature graphs etc I can tell you we personally ditched the "insulative approach" eons ago...as I said, the diffraction ring patterns & Airy Disk during the collimation procedure we carry out each night tells you precisely how your optics are running at the moment.

 

Viewers will note the non-matching soft drink caps pressed into service as part of an early primary mirror lock setup on the C11  - another pikky of our take on "Tempest" fans for the C14 in an earlier incarnation (superseded by the "Blizzard Blower" I made from an auto aircon turbo fan) - both these causing internal dewing frequently by bringing in external air, hence the ice bags now.....a tad more sophistication on mirror-locking also nowadays btw!

 

*EDIT: the insides also if I remember correctly.

 

 

Edited by Kokatha man, 06 December 2018 - 06:13 PM.

[Ron359]

<"Ron359, on 04 Dec 2018 - 5:52 PM, said:

There are plenty of top rate planetary imagers in the planetary-solar imaging forum who go to great lengths, such as ice packs on their tubes, to get their SCT 11s and 14s to ambient temp. and never mention Reflectix. But few in these threads seem to read or follow what the really good SCT planetary imagers do to get their sub arc second details on every night of good seeing. Instead, in thread after thread I only read anecdotal arguments against well known principles of physics with "common sense" and a cheap fix. And I thought astronomy and those who practice it, was all about science. Was I wrong.">

 

 

 

I've included Ron's comments above from earlier because *ahem* we always aim for "sub arc second seeing" & I think evidential outcomes are what really counts tbh - & apart from another SSI forum member trying the ice packs out this year after some of my comments, I'm unaware of anyone else who resorts to this tactic...although that doesn't of course mean others haven't - it's just that in the several years we've used ice I haven't come across anyone else anywhere.

 

 

 

TestFire2.jpg

 

C14-modifications.jpg

Kokatha man,   Its been great to read your contributions on this subject of which there have been several lengthy debates.  Just to comment on your comment of my comment.... ; )  I mentioned sub arc second details in planetary images, not knowing for sure if how frequent or if you seeing is always great.   Your raw video image of Jupiter on your tutorial has more detail than I get from processed video under our typically 2,3, or 4 arc sec. seeing here under turbulent mountain wave skies.  I greatly envy your 'upside down sky' where Mars and other planets are overhead instead of barely 25 deg. up this past summer for dwellers up North, knowing this was likely the last, closest opposition in my lifetime.  Another to me -unbelievable 'myth' I've seen posted in this SCT forum is that some think those great planetary images you and others get, are essentially faked by photoshop type processing adding details that are not really there in the raw images!   But when you're seeing is always fair to less than poor it can be hard believe anyone can get such degree of details.

 

  I hope all agree, quality of seeing rules all our attempts to capture planetary details so if your tightly collimated scope never reaches equilibrium with its ambient environment, it will never live up to its optical potential even on a night of excellent seeing and 100 thousand frames of video. Some observers may believe that SCTs are poor designs or that they just have a poorly made one that produce "mush".  Thats why understanding empirical and analytical art & science of cooling (or maybe even warming up in some cases) the scope is critical to achieve the best visual or imaging performance of the scope.  Your dedication to following the evidence, hard work and persistence in achieving the best, shows in your results.   

[bikerdib]

I have a fairly large sealed chest in which I installed a peltier cooler system and also a warming system.  I used to brew beer and used it to control the temperature while fermenting.  I was thinking a while back that since I no longer brew beer, I could set this up a few hours before a viewing session and put the scope inside.  I could check what the outside temperature was predicted to be at session time and set the chest to that temperature.

[Jaimo!]

I have a fairly large sealed chest in which I installed a peltier cooler system and also a warming system.  I used to brew beer and used it to control the temperature while fermenting.  I was thinking a while back that since I no longer brew beer, I could set this up a few hours before a viewing session and put the scope inside.  I could check what the outside temperature was predicted to be at session time and set the chest to that temperature.

Or, perhaps, you could just set you scope outside for the same amount of time.

 

Jaimo!

[Jimmy462]

>snip<

 

JimmyG & speedster: I commented about the dew issues in my Post #173 with special attention to internal dewing, which is the only real worry...but this is an extremely rare occurrence! The only other concern is if there is a lengthy wait (1+ hours) between imaging targets - & I cover our method of dealing with that in the same post.

 

I don't think our climate is terribly different apropos dew...we've imaged in temperate, tropical & arid climates across Oz...even in the arid bush, some might be surprised by the fact that days could have extremely high temperatures for the season but as night approaches it's not unusual that temperatures really do drop like the proverbial stone...I understand US deserts can be very similar...the relative humidity is the salient factor in determining dew-points of course.

 

Btw, we live 50kms South of Adelaide which is where we have been obliged to do much more imaging this year instead of our normal "field trips." A description of Adelaide's climate is Quote: "Adelaide has a Mediterranean climate (Köppen climate classification Csa), with cool to mild winters with moderate rainfall and warm to hot, generally dry summers."

 

I've included Ron's comments above from earlier because *ahem* we always aim for "sub arc second seeing" & I think evidential outcomes are what really counts tbh - & apart from another SSI forum member trying the ice packs out this year after some of my comments, I'm unaware of anyone else who resorts to this tactic...although that doesn't of course mean others haven't - it's just that in the several years we've used ice I haven't come across anyone else anywhere.

 

I'm going through old files on stored HD's in a casual way to try & find a few pikkies of the cork gasket & other stuff I've either mentioned in earlier postings here...this is a decade or more old in places so it ain't easy - but I did find an image of the rear-casting's insulated cap. (but not of the entire "suit" unfortunately )

 

>snip<

 

TestFire2.jpg

 

C14-modifications.jpg

Hi Kokatha man,

 

First off, "hats off to you" for all of those experiments and mods in those pictures, wowee! As for my next move I guess it comes down to "ice it down" or "trap the heat inside with reflectix". Thanks again for sharing all of your insights and experiences!

 

Jimmy G

[bikerdib]

Or, perhaps, you could just set you scope outside for the same amount of time.

 

Jaimo!

I do, but in southeast Texas the temperature can drop substantially after the sun sets.  The 14" Edge can be a bear to acclimate, even with the Tempest fans.

 

But, with the temperature controlled box, I could have the scope at the predicted evening temperature for much longer, giving the scope much more time to acclimate.

Edited by bikerdib, 07 December 2018 - 09:27 AM.

[Adun]

I'm late to the party, but I find myself asking the same question as the OP:

 

So if I wrap the OTA in Reflectix, will I still need the warming strips to prevent dew/frost?  If there is a choice between no thermals and no dew/frost, I'd rather do without the dew/frost. 

 

My SCT is a 6" EVO OTA, which is my "grab and go" for planetary visual at home. I live in a city in the tropics, where the temperature drop overnight is small, and there's no such thing as dew.

 

But after making arrangements for a vacation trip by car, that'll end with several nights in a small town by the mountains, right next to a big nature reserve, I came to realize I need a dew solution if I hope to bring the C6 with me to take advantage of the dark skies for visual of DSOs at low/med powers.

 

I'm not worried about currents, plumes, focus shift, imaging concerns, or any of that, only condensation, and the fact that I don't own heating strips nor dewshields, and there's not enough time for me to buy them before the trip.

 

So I've made an insulator + dew/light shield for my 6" SCT, using a thermal material that is meant for campers, consisting of some ~5mm black matte foam, with mylar on one side:

 

 

 

 

 

It's a little long, but I understand that will help delay the appearance of condensation. I'm not sure about the effect of it also being a full body cover (the "insulator" part) but I'm hoping that will help the tube retain heat longer and afford me more observing time before dew shows up. The place I'm going has 85% humidity, and dew point at 18°C, which is reached at just 8pm, with temperatures dropping further to 14°C at 1am. I only intend to observe for a couple hours (from 7:30 to 9:30pm maybe) so there's hope this might be enough despite the lack of a heater.

 

If I find something interesting I'll post it here. 

Edited by Adun, 08 January 2019 - 06:51 PM.

[Ryan555_1]

Hello everyone,

 

This is a great thread. I am glad Mike so persistently asked questions. I was thinking the same ones as I was reading along just to get clarity. Thanks to all who responded. The thread pushed me over the edge of trying reflectix out again (last time I tried this I used very thin, almost tin-foil-like stuff. No good!). 

 

The reason I am reconsidering is that, living in the desert, there are times the temperature drops too fast for my TEMPest fans to keep up. Sure, I live in a nice, warm environment, but during winters and summers I am dealing with too much thermals due to my unstable CPC 1100 Edge. Don't get me wrong: This drastically improved after I installed the TEMPest fans, but I still note the instability on those more tumultuous nights. Given John's experience above, it seems doing both reflectix and TEMPest fans is the best idea. (Thanks John. Your comments were very helpful.)

 

On some nights, my airy, donut pattern is a bit astigmatic. It is usually not too bad, but it is sometimes the case that the pattern is elliptical in one direction (horizontal) and then in the other direction (vertical) after I move past in-focus and onto the other side of the donut pattern. This astigmatic issue goes away when the scope is stable, but that sometimes never happens when temperature drop more than 3 degrees per hour or so. (I'm sure I am not using the correct terminology here.) Anyway, this is what got me thinking about reflectix again.

 

Anyway, I am purchasing this stuff soon. Which would you all recommend:

1. https://www.amazon.c...PTCFP432DY15WZ9
2. https://www.amazon.c...words=reflectix

I'm leaning on 1., but I thought I'd ask. 

 

Thanks!

Ryan

[Kokatha man]

Ryan, if you've read any of my own posts in various "Reflectix" threads you'd appreciate that I have a poor estimation of its merits...but for this post I just want to state that your <"living in the desert, there are times the temperature drops too fast for my TEMPest fans to keep up. Sure, I live in a nice, warm environment, but during winters and summers I am dealing with too much thermals"> is entirely consistent with what we experience much of the time here in Oz.

 

The "tempest-style" fans you see in the first image in my Post #186 above had similar issues. Btw, what you don't "see" is the micro-mesh filters underneath the fans...the fans being the largest air volume units in 12v that could be accessed on the internet.

 

This is why the "salted-ice bag" cooling method was developed - I've mentioned several times that after removing these bags (when the primary reaches a determined temperature) we wait for 30-40 minutes for the primary to "relax" & its temperature to become uniform throughout because its deep internal temperature will be different to that nearer the surfaces, being the material it is (thick glass) - it is during this period that you will notice that the Diffraction Rings appear distorted (along with other aberrations) & one such distortion <"is a bit astigmatic"> as you put it...or perhaps better to state as "definitely not circular."

 

This is more marked in "crash-cooling" via salted ice in comparison to internal air ventilation methods (Tempest etc) but nonetheless the same phenomenon, & it does disappear as the mirror temperature evens out throughout - & naturally does not impose itself to any noticeable degree when any change in temperature occurs more slowly. ( the gradient) 

 

But just to clarify, this is more a "Diffraction Ring" description rather than an "Airy Disk" one, although the Airy Disk will manifest the same distortion on a much smaller scale... & not so obvious to many...

[Ryan555_1]

Ryan, if you've read any of my own posts in various "Reflectix" threads you'd appreciate that I have a poor estimation of its merits...but for this post I just want to state that your <"living in the desert, there are times the temperature drops too fast for my TEMPest fans to keep up. Sure, I live in a nice, warm environment, but during winters and summers I am dealing with too much thermals"> is entirely consistent with what we experience much of the time here in Oz.

 

The "tempest-style" fans you see in the first image in my Post #186 above had similar issues. Btw, what you don't "see" is the micro-mesh filters underneath the fans...the fans being the largest air volume units in 12v that could be accessed on the internet.

 

This is why the "salted-ice bag" cooling method was developed - I've mentioned several times that after removing these bags (when the primary reaches a determined temperature) we wait for 30-40 minutes for the primary to "relax" & its temperature to become uniform throughout because its deep internal temperature will be different to that nearer the surfaces, being the material it is (thick glass) - it is during this period that you will notice that the Diffraction Rings appear distorted (along with other aberrations) & one such distortion <"is a bit astigmatic"> as you put it...or perhaps better to state as "definitely not circular."

 

This is more marked in "crash-cooling" via salted ice in comparison to internal air ventilation methods (Tempest etc) but nonetheless the same phenomenon, & it does disappear as the mirror temperature evens out throughout - & naturally does not impose itself to any noticeable degree when any change in temperature occurs more slowly. ( the gradient) 

 

But just to clarify, this is more a "Diffraction Ring" description rather than an "Airy Disk" one, although the Airy Disk will manifest the same distortion on a much smaller scale... & not so obvious to many...

Thanks for all this and for taking the time to respond. Diffraction ring is what I was looking for. 

 

I am going to try your ice/salt method on the colder nights. Thanks! Are there any pictures that show how you do it specifically? I think I can visualize it adequately if not.

 

I am going to still try reflectix, only because it is so cheap and no hassle. The main reason I think it might work for me is that my average session outside is 2-3 hours at home and 4-5 hours at the dark site. That is quicker than the average around these forums, it seems, so I was wondering if slowing the cooling would work on some nights. I'll give it a try. If it doesn't work, I'll just remove it. No harm done. 

[Kokatha man]

 

I am going to try your ice/salt method on the colder nights. Thanks! Are there any pictures that show how you do it specifically? I think I can visualize it adequately if not.

 

...probably - but I've had a devil of a time trying to find any pikkies etc, such as those in Post#186: I would've liked to have been able to chronicle all the various approaches I've experimented with on both the C11 & C14 over the years...including the copious amount of related graphs; but unfortunately I cannot find them anywhere & I don't think there are many HD's floating around that I haven't searched yet - but darn infuriating 'cos I feel certain they are still around somewhere..!  

 

What I do know is that I have posted a few images on CN but the archive images appear to have been removed on stuff I've looked at...& with so many posts I've made it's likely be a mammoth task even if I bothered searching here.   

 

Whatever I do find I'll probably post in a new thread here sometime...

[yellobeard]

The logic is obvious if you don't make the wrong assumption that fans are for cooling.

The furnace in your house puts out heat and in forced air systems, or with ceiling fans, their purpose is to redistribute the heat, not cool your house. Insulation is used to retain that heat! Have you ever observed over the roof of house on cold night? Thermals or "bad seeing" is all you see despite the insulation which only slows the release of heat from your warm house if insulation wasn't there at all.

That probably is the most important detail that most still seem to overlook !

Lets go somewhat deeper into 'your house': Heaters produce heat, fan's (or natural circulation) redistribute the heat, insulation keeps that heat inside your house..

In that situation, there is an important detail: The fan's only purpose is to circulate, NOT ! to blow outside air inside, or blow inside air out, as they do in many scopes!
Only when you have a optically closed scope, big or tiny, insulation does work best. And adding (low power) fan's inside, for circulation, can in many cases contribute
somewhat, in better thermal homogenity of the air inside your scope. But still, the biggest 'win' comes from the insulation itself

When your insulated scope is inside your warm house, all optics inside have the same temperature. When you put your scope in the colder outside air,
the insulation and IR reflectivity of the Reflectrix slow down the cooling of the inside in such way, that even the most massive optic (primary mirror) can 'follow' the cooling
process without the creation of thermal deformations. And when the primary has no thermal issues, the remaining optics definitely will not have thermal issues!

But: If your house is not insulated properly, you immediately will be confronted with those nasty cold drafts, turbulence !! Which exactly is the same with telescopes.
So be sure that you insulate properly, before posting a verdict about insulation! You probably notice me using the words 'Proper insulation' quite often.. That's because
it is important to do this properly, or else you still end up with thermal issues. (Edit:) More importantly, you will probably end up with the conclusion that insulating a scope will not ever work, which is not fair towards a new insight which is not yet tested fully in all situations! (End of edit..)

Of course, there is thermal loss through that thin schmidt corrector plate if we talk SCT, but that is much, much less than the thermal issues you encounter when
you don't insulate your scope! Don't forget that glass still has quite some insulation capacity, and the deformations caused in the schmidt corrector plate, by the
warm air inside, working against the colder air outside, never were big enough to spoil even the first 10 minutes of my stargazing night!

My 16inch SCT has a extremely thin corrector plate for its size: only 5.7 millimetres (0.22 inch).. But with its proper insulation, that 16" scope still gives immediate sharp
images, right after put in a 15 degree colder outside temperature. I think that most here who tried it will agree: "The proof of the pudding is in the eating!"
My 16" has no internal fan's, but right next to it, I have two modified C11's (also insulated of course) that do have internal circulation fan's, and although I have a tiny bit
more that feeling of stability with those C11's, looking at the differences in a 'objective' way, makes me conclude that there is no difference.. So from that point of view,
I think that internal circulation fan's are not very much needed when your scope is insulated in a proper way.

Some think that they have the right (theoretical) answers, without even having tried this fairly new insight in a proper way, but trying to read those posts with theoretical
views, mostly takes more time than buying some insulation stuff, and try this yourself in the field !!

......My 2 cents...

Edited by yellobeard, 12 January 2019 - 12:47 AM.

[Ron359]

That probably is the most important detail that most still seem to overlook !

 

 

Some think that they have the right (theoretical) answers, without even having tried this fairly new insight in a proper way, but trying to read those posts with theoretical

views, mostly takes more time than buying some insulation stuff, and try this in the field !!

 

......My 2 cents...

 

Also often overlooked:   Because you are at or below sea level in the Netherlands, how much differential drop per hour do you have of air temperature and increase in humidity when observing on a clear night?  

[yellobeard]

In my country, there is no 'stable' or reliable situation as it comes to changes in temperature and humidity during the night.
However, I think that many know that during 'clear sky' situations, the temperature significantly drops, and that dewpoint issues are reached easily, unless you live in a very dry area, like a dessert..

[Kokatha man]

<"Of course, there is thermal loss through that thin schmidt corrector plate if we talk SCT, but that is much, much less than the thermal issues you encounter when
you don't insulate your scope! Don't forget that glass still has quite some insulation capacity, and the deformations caused in the schmidt corrector plate, by the
warm air inside, working against the colder air outside, never were big enough to spoil even the first 10 minutes of my stargazing night!

My 16inch SCT has a extremely thin corrector plate for its size: only 5.7 millimetres (0.22 inch).. But with its proper insulation, that 16" scope still gives immediate sharp
images, right after put in a 15 degree colder outside temperature. I think that most here who tried it will agree: "The proof of the pudding is in the eating!">

 

Well, the C14 possesses a 5.35mm thick corrector according to figures (I've never actually measured it but that seems right) although a 16" corrector 5.7mm thick would be nominally thinner from a relative area versus thickness perspective...whatever that might mean.

 

What I can say is that using the hair-dryer method of removing dew/condensation on the outside of the C14 corrector - something we regularly do between imaging runs, which might be anything from 3 minutes up to 10 minutes, there is a noticeable degradation of the onscreen image whilst the corrector gives up this heat, usually around 3 to 4 minutes. (the 10 minutes is for Neptune, where a long dew-shield helps noticeably at keeping condensation at bay over this 10 minute period when the night is prone to said...)

 

I can speed up this "cooling" of the corrector by waving a magazine in front of it for about a minute...but the release of heat from the corrector is something palpably evident on the onscreen image - as it cools the image becomes more stable (relevant to the seeing conditions) & more & more detail is seen until it returns to that of when I started the last imaging run before this. (naturally I refocus after the image stabilises & of course the image might not be as good - or be better - than the previous recording depending upon seeing fluctuations...)

 

One of my concerns is that a warm tube inside the ota as per the insulation adherents' situations is always going to be liberating heat through the corrector - not precisely the same as the hair-dryer scenario but perhaps somewhat similarly, or to that from a dew heater which in the few times I employed one many years ago now, image degradation could be clearly seen onscreen whilst it was operating.

 

Heat transfer both from a radiative as well as thin glass properties aspect, I suspect...as I've stated several times there is occasionally condensation on the corrector's inner surface - it does not take much extra hair-dryer application to remove this if it isn't to heavy...evidence that the thin glass is pretty effective at allowing heat transfer despite being an insulative medium, whatever the mode of heat transfer. 

 

That is only one concern I have, but yellobeard's post that I've quoted reminded me of these facts: without personally addressing yellobeard but rather all insulation promoters <"the proof of the pudding is in the eating"> - no matter how many verbal testimonies might be uttered by such folks, show me some instances of hi-res imaging using large image scales (eg, 6 - 10 metres, preferably planetary ) that do provide actual proof, ie "tangible evidence" rather than "testimonial evidence" - someone do so & I'll happily revisit old ground with renewed interest...I'm always trying to improve our results but have long since learnt to be very circumspect about anything which cannot provide tangible supporting evidence..!

 

...just posting in a spare moment & trying to keep some balance in something that seems to have spread around the world of AA forum advice - but still without anything other than "verbal testimony" from anything I have looked at..!