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Cool Cats and Careless Claims

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#1 Deepskyclusterstruck

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Posted 11 December 2018 - 08:14 AM

I received an Orion 180mm Maksutov-Cassegrain yesterday. The inside of the lens cap had dust and debris but a casual glance seemed to indicate no debris anywhere else. The box looked pretty banged up but the scope seemed uscathed. No sctatchmarks , nothing problematic that I can see. Looked through the front in good light..seems ok.

When I ordered this scope I knew one of its drawbacks would be that cooling would take a long time. I think I saw an estimate of two hours and even then depending on the weather maybe not completely on a given night. I was ok with that. A compromise I was willing to make.

But I open the instruction manual and what do I find? "Take your telescope out at dusk and let it acclimate to the outside temperature; this usually takes 30-60 minutes." Im guessing they don't mean in subzero temperatures but what kind of conditions are they thinking of and have I been mistaken in my previous understanding about cool down time taking much longer?


Everything Ive read previously would indicate that claim is optimistic at best.

I don't want to make careless claims but I'd say they might be stretching things. But what do I know afterall...Ive never taken a Cat that large out before.

Edited by Deepskyclusterstruck, 11 December 2018 - 08:18 AM.


#2 Asbytec

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Posted 11 December 2018 - 08:29 AM

Oh, I dunno, in modest tropical climates that's about right as I recall. It's been a while cuz I always cool my MCT prior to observing and have not seen a heat plume in years. Others have their preferred method, I chill mine with a frozen medical gel pack. Local conditions intuitively and from all accounts seem to matter and differ. YMMV.

#3 bobhen

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Posted 11 December 2018 - 08:37 AM

They are not addressing the acclimation issue with Maks they are thinking of selling telescopes.

 

Sure, if you live in a very mild climate with little temperature difference then that advice is fine but with a 10, 20, 30-degree or more temperature difference you will need to take aggressive steps so that your scope is acclimated and STAYS acclimated in falling temperatures. Initial acclimation is just part of the problem because if temperaturs fall rapidly the scope might not keep up and heat plumes will reform and distort the image.

 

Some wrap their scopes in insulation
Some install fans in the rear plate
Some use Cat Coolers that insert into the tube and force air out of the tube
Some start but leaving their scopes in unheated rooms like garages or sheds

 

All the above have advantages and disadvantages but you will need to take cooling seriously if you want the best high power views out of your Mak. And high power viewing is one reason to get a Mak in the first place.

 

Bob


Edited by bobhen, 11 December 2018 - 08:38 AM.

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#4 Hugh Peck

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Posted 11 December 2018 - 09:31 AM

Actually, if your observing where Orion is located that probably is plenty of time. In fact, my experience has been that's been plenty of time for most of the year. I've owned 4, 5, 6, and 8" S-Cs and 3.5, 5 and 7" Maks. On the other hand I've had a C-5 never reach equilibrium on occasion during the summer.


Edited by Hugh Peck, 11 December 2018 - 09:32 AM.


#5 Eddgie

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Posted 11 December 2018 - 09:37 AM

Everything Ive read previously would indicate that claim is optimistic at best.
 

If you live in California near one of the Orion stores, this is probably right about 80% of the time.

 

If you live in Canada, this would probably be the case 20% of the time.

 

So, correct some of the time, optimistic for others. 
 

Apparently you already were aware that cool down would be long, so what is the big deal?   Most consumers these days would not buy something like a 180mm MCT without doing some research on it.

 

Is Orion bad for being about right for some of the population some of the time?  Yeah, I think they could have done better, but like I said, you already had the correct knowledge and the vast majority of people that buy this model scope will likewise already know that cool-down is dependent on temperature differential. 


Edited by Eddgie, 11 December 2018 - 09:41 AM.

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#6 Deepskyclusterstruck

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Posted 11 December 2018 - 04:38 PM

Not bashing anyone...Orion has by and large been extremely helpful in my experience especialy in regards to customer service. Didn't mean to sound petty. Its not such a big deal in the grand scheme of things but it does matter and its easy to blow anything out of context. I learned some things I didnt know though so thank you.

#7 gfstallin

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Posted 12 December 2018 - 02:22 PM

If you are able, keeping in a space that is not climate-controlled could allow for very quick acclimatization. I've read some people who keep them in Tuperware containers with lids on caps on in unheated garages and sheds. When I lived in a high rise building, I would place my scopes on the balcony before dinner and afterwards they would usually be ready to use or almost there. 

 

George


Edited by gfstallin, 12 December 2018 - 10:53 PM.

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#8 dscarpa

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Posted 12 December 2018 - 03:46 PM

 I live in southern California but we can have 30* drop in the winter. I've got a IM715D and put my scope out a half hour before sunset which does the trick. It's got a fan but I never use it unless I'm putting it outside at night. Cool down with out fan is not longer than with my C9.25 about an hour. If either is not cooled down image quality is really bad. David  


Edited by dscarpa, 12 December 2018 - 03:49 PM.


#9 Deepskyclusterstruck

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Posted 12 December 2018 - 05:12 PM

I live in an area with high humidity and temperatures regularly below 32 Fahrenheit(often low 20's and teens) this time of year. If I place the Mak in a soft telescope case made of nylon and polyester(padded or not)and sit it outdoors for a few hours would that be sufficient cooling time? Ive read that bubble wrap can help but am assuming(though not certain)there is no usefullness from the normal bubble wrap that telescopes are often shipped in. When people say reflective bubble wrap Im not certain what they mean. For people using frozen medical gel packs where on the scope do they apply them and how? The fan solution sounds involved. So do cat coolers but Im intrigued. If sitting the scope outside isnt sufficient by itself maybe Ill try to work with the other suggested methods as well or any others suggested. Maybe my Mak needs a vacation to a more hospitable environment and of course Id be compelled to come along.

#10 bobhen

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Posted 12 December 2018 - 06:16 PM

I live in an area with high humidity and temperatures regularly below 32 Fahrenheit(often low 20's and teens) this time of year. If I place the Mak in a soft telescope case made of nylon and polyester(padded or not)and sit it outdoors for a few hours would that be sufficient cooling time? Ive read that bubble wrap can help but am assuming(though not certain)there is no usefullness from the normal bubble wrap that telescopes are often shipped in. When people say reflective bubble wrap Im not certain what they mean. For people using frozen medical gel packs where on the scope do they apply them and how? The fan solution sounds involved. So do cat coolers but Im intrigued. If sitting the scope outside isnt sufficient by itself maybe Ill try to work with the other suggested methods as well or any others suggested. Maybe my Mak needs a vacation to a more hospitable environment and of course Id be compelled to come along.

I live in PA and have owned 8, 10 and 11” SCTs and a 7” Mak and currently own a Mewlon 210. They ALL needed aggressive cooling on most autumn, winter and spring nights.

 

There are 2 issues. The first problem is initial acclimation. The second problem is that on nights of falling temperatures, even after initial acclimation, if the primary can’t keep up with the falling temperatures heat plumes will reform and distort the light path.

 

With your sever temperature differences you might want to…

 

1. Leave the tube outside without any case or dew shield and let it cool. This can take hours and there is no guarantee that heat plumes will not reform if temperatures drop.

 

2. The cat coolers are fine for aiding with initial acclimation but on nights of falling temperatures you need to keep reinserting them to remove heat plumes. This, of course, interrupts observing or imaging.

 

3. With your sever conditions, a frozen gel pack (placed on the back plate) will probably have little impact. The gel packs do not come in direct contact with the primary so their cooling ability is marginalized.

 

4. People are having some success with insolation and there are a few threads about that solution. The idea is to keep the temperature inside of the tube stable (warm) so acclimation is not needed. You will have to wrap your scope before you take it out. And how long that insolation keeps the air in your tube stable can depend on many factors.

 

5. Fans on the back plate that blow cool outside air on primary is a solution used by many high-end Cassigran, Mewlon and Mak makers. The advantage is that fans will help with acclimation but they can be left running and can chase heat plume if temperatures fall. Of course, instillation can be a hurdle. The New Celestron Edge SCTs have fan ports and fan instillation is somewhat easy.

 

I have tried all the above except the insolation solution (which won’t work on my Mewlon) and personally like the fan solution the best. I believe Deep Space Products still does custom fan instillations. Even though my Mewlon 210 has an open tube, it still needed a cooling solution. I added 4 fans on the rear plate and they really help.

 

Try one of the easier solutions above first and if that works for you great. If not, just try another.

 

Bob


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#11 Asbytec

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Posted 12 December 2018 - 08:08 PM

I live in PA and have owned 8, 10 and 11” SCTs and a 7” Mak and currently own a Mewlon 210. They ALL needed aggressive cooling on most autumn, winter and spring nights.

 

There are 2 issues. The first problem is initial acclimation. The second problem is that on nights of falling temperatures, even after initial acclimation, if the primary can’t keep up with the falling temperatures heat plumes will reform and distort the light path.

 

With your sever temperature differences you might want to…

 

1. Leave the tube outside without any case or dew shield and let it cool. This can take hours and there is no guarantee that heat plumes will not reform if temperatures drop.

 

2. The cat coolers are fine for aiding with initial acclimation but on nights of falling temperatures you need to keep reinserting them to remove heat plumes. This, of course, interrupts observing or imaging.

 

3. With your sever conditions, a frozen gel pack (placed on the back plate) will probably have little impact. The gel packs do not come in direct contact with the primary so their cooling ability is marginalized.

 

4. People are having some success with insolation and there are a few threads about that solution. The idea is to keep the temperature inside of the tube stable (warm) so acclimation is not needed. You will have to wrap your scope before you take it out. And how long that insolation keeps the air in your tube stable can depend on many factors.

 

<snip>

 

Try one of the easier solutions above first and if that works for you great. If not, just try another.

 

Bob

Bob, totally agree with the need to aggressively cool any scope really in more extreme climates during winter. I did not go with a CAT cooler for the very reason you mentioned. Plus, air is more of an insulator than a conductor, so I question the efficiency of cooling with air. A fan may be the best choice, however, in many cases. 

 

What caught my attention was the idea gel packs do not come into direct contact with the primary. That's true, not directly. It's also very true they will very likely have marginal utility at more extreme temperatures. I am sure you will not cool a scope to freezing ambient with a gel pack. But, the one thing that are, in my experience, is very efficient at dampening residual heat. When my gel pack is spent (during dinner), the entire OTA is cool to the touch as if it had been sitting out all night. One thing a gel pack might do is give a scope a good head start with the cooling process, but I have not heard anyone having tried it in more extreme climates. 

 

Insulation is very interesting if not unsightly. It does seem effective, though, at least on scope designs that benefit from it. 

 

I agree with you, also, the OP can try a variety of methods and pick one that gives the best results and is not too burdensome. But, the point is, it has to be done for best results. Maybe hit it with a gel pack prior to dinner, set up near dust and let it cool some more during dinner, then hit it with a fan for a bit. I've even toyed with putting it in the freezer, but never had to resort to that. 


Edited by Asbytec, 12 December 2018 - 08:11 PM.


#12 Deepskyclusterstruck

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Posted 12 December 2018 - 11:19 PM

The freezer? You want me to turn my beautiful new telescope into a popcycle? Do you suppose it would get freezer burn? Seriously though this is all very helpful. I fear though that for all but the simplest of these methods the devil is in the details (and experience).In an ideal universe Id ask you for even more detailed steps on the fan and cooler but Im afraid of stretching the limits of your time and energy.

Edited by Deepskyclusterstruck, 12 December 2018 - 11:20 PM.


#13 Asbytec

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Posted 13 December 2018 - 12:51 AM

Yea, no experience with installing fans. Just think it through and try different things or a combination of things.

When contemplating the issue, I realized the problem is the scope is too warm. So logic seemed to dictate making it cold. And do it easily and cheaply. But how? The light came on for a gel pack. Worked perfectly every time for me.

That logic is flawed, though. The problem really is thermal stability. So how to make it stable at whatever temp delta? This is where insulation comes into play. Folks reporting great success.

There may not be a any one thing, other than insulation, that works for you. You may need to cool it progressively over a series of steps. If cooling is the objective.

Needless to say, over time you'll develop a method that works, that is efficient, and hopefully is simple and repeatable.

Bob's list about covers methods we've all had some success with. Try them.

Edited by Asbytec, 13 December 2018 - 12:53 AM.


#14 Kokatha man

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Posted 13 December 2018 - 02:23 AM

 

What caught my attention was the idea gel packs do not come into direct contact with the primary. That's true, not directly. It's also very true they will very likely have marginal utility at more extreme temperatures. I am sure you will not cool a scope to freezing ambient with a gel pack. But, the one thing that are, in my experience, is very efficient at dampening residual heat. When my gel pack is spent (during dinner), the entire OTA is cool to the touch as if it had been sitting out all night. One thing a gel pack might do is give a scope a good head start with the cooling process, but I have not heard anyone having tried it in more extreme climates. 

 

 

...I've posted a couple of times in that "Reflectix" thread & really said enough there imo, but this topic & post caught my eye...& without wanting to quibble too much about the difference between "gel packs" & "a large bag of salted ice" you really need to see what the latter does to the primary mirror's temperature in a large SCT (C14) to appreciate just how effective encompassing the rear & sides of said mirror within the scope's ota rear-casing is using this approach - especially when it has been cooled to way below 0°C after a couple of hours..! bigshock.gif lol.gif

 

Even when daytime temperatures are around 40°C not too long before Sunset, 2.5+ hours can pull the primary mirror down to around 0°C & even lower.....targeting your imaging session's start-time (allowing for approx. 1/2 hour or so to allow for the mirror to reach equilibrium throughout) is something that becomes fairly easy to do once you get the hang of how different seasons & temperature falls present themselves - but "woe betide!" if you make the mistake of being distracted for 10 to 15 minutes at the critical stage! shocked.gif mad.gif

 

Temperature drop is initially slow, then begins to speed up about 45+ minutes into the application...but sometime around the 1.25 to 1.5 hour mark the primary mirror's temperature drop begins to speed up markedly. (a rough & simple figure suffice for this explanation)

 

Later still (closing on 2 hours, again roughly for this explanation) the drop enters what I'd term the "cascade" period where 10 minutes can cause alarming drops in the primary's temperature...I've been distracted a few times over the years to find my target has been left way behind by virtue of this cascading effect...& certainly found my primary at -1°C or lower when my target was (say) around 5°C or so...

 

Incidentally, you need to be aware that upon removing the ice the primary will still fall a degree or more, depending upon conditions. 


Edited by Kokatha man, 13 December 2018 - 02:24 AM.

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#15 Deepskyclusterstruck

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Posted 13 December 2018 - 11:54 AM

Yea, no experience with installing fans. Just think it through and try different things or a combination of things.

When contemplating the issue, I realized the problem is the scope is too warm. So logic seemed to dictate making it cold. And do it easily and cheaply. But how? The light came on for a gel pack. Worked perfectly every time for me.

That logic is flawed, though. The problem really is thermal stability. So how to make it stable at whatever temp delta? This is where insulation comes into play. Folks reporting great success.

There may not be a any one thing, other than insulation, that works for you. You may need to cool it progressively over a series of steps. If cooling is the objective.

Needless to say, over time you'll develop a method that works, that is efficient, and hopefully is simple and repeatable.

Bob's list about covers methods we've all had some success with. Try them.



#16 Deepskyclusterstruck

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Posted 13 December 2018 - 11:54 AM

Yea, no experience with installing fans. Just think it through and try different things or a combination of things.

When contemplating the issue, I realized the problem is the scope is too warm. So logic seemed to dictate making it cold. And do it easily and cheaply. But how? The light came on for a gel pack. Worked perfectly every time for me.

That logic is flawed, though. The problem really is thermal stability. So how to make it stable at whatever temp delta? This is where insulation comes into play. Folks reporting great success.

There may not be a any one thing, other than insulation, that works for you. You may need to cool it progressively over a series of steps. If cooling is the objective.

Needless to say, over time you'll develop a method that works, that is efficient, and hopefully is simple and repeatable.

Bob's list about covers methods we've all had some success with. Try them.



#17 JeffreyAK

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Posted 13 December 2018 - 01:11 PM

Well it's all about delta-T, really.  If you take your scope outside from a toasty living room to a snowy 20F patio, it will take many hours for the scope to equilibrate, so 30-60 minutes is not realistic.  If the temperature continues to drop rapidly, it may never equilibrate, and you might have been better off leaving the scope in the living room. ;)  There are calculations backing this up that you can find on websites (as well as lots of empirical data and anecdotes), and it's mostly the glass thickness that matters.  There's no way Orion or anyone else can toss out a number and expect it to cover all possibilities, but probably for casual observers who aren't too demanding and who are viewing in summer, their numbers aren't way off.  My Mewlon is relatively quick to cool, with an open front and no thick corrector plate, but even in summer - and waiting to take the scope out until the outdoor temperature reaches the indoor temperature - I still need to wait a couple hours if I want the sharpest views, say for planets.  Part of this is because the temperature here typically continues to drop for about that long, so it's a moving target.



#18 dscarpa

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Posted 13 December 2018 - 03:35 PM

 On the plus side of the ledger my IM715D is much  less prone to dewing up than my C9.25 because the thick corrector.    David



#19 Asbytec

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Posted 13 December 2018 - 06:20 PM

...I've posted a couple of times in that "Reflectix" thread & really said enough there imo, but this topic & post caught my eye...& without wanting to quibble too much about the difference between "gel packs" & "a large bag of salted ice" you really need to see what the latter does to the primary mirror's temperature in a large SCT (C14) to appreciate just how effective encompassing the rear & sides of said mirror within the scope's ota rear-casing is using this approach - especially when it has been cooled to way below 0°C after a couple of hours..! bigshock.gif lol.gif

 

Kokatha, that's amazing really to think you can get down to 0 degrees Celsius. I suspected the "ice" method is very efficient. One night I forgot to recharge my gel pack, so a grabbed a pack of frozen hot dogs (oxymoron?) and applied it to the metal primary mirror casing of my CAT. Immediately I could observe cold plumes. Three of them descending through the light column which was interesting in and of itself. Over twenty minutes, give or take, each time I checked for the heat plume it was visibly diminished until it was gone. But, that's in a mild climate.

 

Jeff seems to be right, it is about the delta when cooling is the objective. I have not tried insulation, but the concept of stability seems a good one. And he is right to suggest we cannot put a number on all cases in terms of cooling time. In the past, I have seen heat plumes well into the night in my CATs (SCTs at the time.) And that was in a warmer tropical climate long before cooling became all the rage and well known prior to the internet and forums like this. 

 

I agree with David, too, my MCT has dew up only once in the 7 years I've been using it. It may just be the climate, or maybe not. My C11 would dew over more frequently in the same climate. Maybe the thicker meniscus retains just enough heat for long periods, even though it its pointed skyward and radiating heat to the sky. 



#20 SeattleScott

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Posted 14 December 2018 - 12:48 AM

Insulation is the obvious choice to me. $10 of Reflectix and $3 of self adhesive Velcro. About half an hour of cutting time. No more cooling problems or dew problems, since the corrector doesn’t cool down to the dew point. Kill two birds with one stone. Haven’t convinced my buddy to cover up the TEC logo on his Mak with Reflectix though...

Scott

#21 Traveler

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Posted 14 December 2018 - 01:06 AM

Mmm seems your buddy doesnt have a big dew problem but more an Ego issue lol.gif


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#22 Deepskyclusterstruck

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Posted 14 December 2018 - 01:30 AM

So much of worth here including previous threads noted.

I wonder what the comparative value of various materials would be for insulation if one were to rank in order.

Edited by Deepskyclusterstruck, 14 December 2018 - 01:50 AM.


#23 Kokatha man

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Posted 14 December 2018 - 03:09 AM

Salt (common NaCl) added to the ice makes an enormous difference when compared to simply ice: we mix 1Kgm of salt with 5Kgm of crushed ice.

 

As I said in the "Reflectix" thread, I've trialled the insulative approach: I made a complete jacket for the C11 out of a double layer of 5mm thick natural cork, silver-spray finished on the outside: folks are free to make any claim they wish about this or other approaches...but for us there is only one "proof of the pudding" that we pay any attention to - ie, consistent, palpably hi-res image outcomes - which for us are delivered by no other means than an SCT that has the primary mirror temperature as close to the ambient air temperature as possible... wink.gif

 

Whatever the real mechanics of "why?" it is actually achieved (ie, radiative, conductive/convective etc) the major issue is not any inability of the primary to track any falls in the ambient/outside air temperature over the course of any night...this it does very well, even when there might be a 10°C or more difference at the start of an imaging session to that near the end: it is the (often large) initial temperature differences that are the stumbling block to maximum optical efficiency. (sorry, I don't "do" deltas, "changes" or "variations" works fine for me & doesn't make me sound as if I'm trying to impress anyone! lol.gif )

 

Without wanting to sound rude I know of no other hi-res planetary imager anywhere who achieves their results via that insulative approach: many attempt to acclimatise there scope relatively passively if the climate they operate in requires such...others utilise some sort of "active" cooling of the primary...whilst some resort to keeping there scopes in air-conditioned rooms...or even as mentioned by someone in that other thread, ice chests! shocked.gif

 

For us, where there can be in Australia enormous drops both in the short term after Sunset...&/or during the night's imaging session(s) we have moved through experimentation over the years to the method I've detailed, which we standardised on quite a few years ago: dewing on the outside of the corrector might be exacerbated at times, depending upon the humidity etc...& this "might" mean the hair-dryer could be called upon every 6-10 minutes when it is "bad" - but that is a small price to pay & such applications mean a loss of only a few minutes at most between capture sets. smile.gif

 

 


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#24 Ed D

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Posted 14 December 2018 - 07:39 AM

The freezer? You want me to turn my beautiful new telescope into a popcycle?

I once had the brilliant idea of putting my Mak in the freezer for a few minutes, then letting it sit outside for a little while so the temperature would stabilize.  idea.gif

 

I got busy with something else and forgot about the scope.  About 45 minutes later my wife asked me if the scope wasn't going to dew over when I took it outside.  OH, SH.........!!!!!  bigshock.gif   shocked.gif

 

That night I ended up with one of the largest frosted beer mugs on earth.  foreheadslap.gif

 

True story.  gramps.gif

 

Ed D


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#25 Sarkikos

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Posted 14 December 2018 - 11:01 AM

Salt (common NaCl) added to the ice makes an enormous difference when compared to simply ice: we mix 1Kgm of salt with 5Kgm of crushed ice.

Would dry ice (solid CO2) be more efficient?  Probably a lot more difficult to acquire, set up and maintain than salted H2O ice.

 

Mike


Edited by Sarkikos, 14 December 2018 - 11:02 AM.



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