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Mak Cass Cool Down time differences

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#1 stevereecy

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Posted 03 April 2020 - 12:37 AM

Is there a big difference in cool down time between a 100mm and a 127mm Mak?

#2 stevereecy

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Posted 03 April 2020 - 12:48 AM

Follow up question: What will it cost to insulate a 127mm? Thanks in advance.

#3 luxo II

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Posted 03 April 2020 - 01:34 AM

Not really, no, and it shouldn't be an issue with maks under 6". Are you really sure you need to ?

 

You can buy a sheet of Coreflute  from hardware stores under $10 and enough to do your scopes 4X over. Or cannibalise a car sunshade from auto accessory places. You may need some adhesive Velcro tabs or a Velcro strap (wrap around) to hold it in place.


Edited by luxo II, 03 April 2020 - 03:47 AM.

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#4 Bean614

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Posted 03 April 2020 - 04:48 AM

Reflectix is about $20 per Roll (a roll will do quite a few SCT's/MCT's).  DO IT!  Visit the HUNDREDS of threads here on CN about insulation.  You won't regret it, and you'll get the best views possible from your MCT.


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#5 markb

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Posted 03 April 2020 - 04:49 AM

Reflectrix is the commonly used solution in the US. 

 

Posts on cloudy nights abound, I believe a small roll is under $25, providing enough material for several scopes.

 

Big box building supply stores like Lowes remain open in many stay-at-home States, but I would absolutely avoid going to them until after the crisis passes.


Edited by markb, 03 April 2020 - 04:51 AM.


#6 stevereecy

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Posted 03 April 2020 - 08:36 AM

Not really, no, and it shouldn't be an issue with maks under 6". Are you really sure you need to ?

 

You can buy a sheet of Coreflute  from hardware stores under $10 and enough to do your scopes 4X over. Or cannibalise a car sunshade from auto accessory places. You may need some adhesive Velcro tabs or a Velcro strap (wrap around) to hold it in place.

Thanks.  Yes, I was using a 4-inch Mak as a grab and go.  It seemed to cool down almost instantly.  But I upgraded to a 5-inch Mak and seems to take long enough to be noticeable (to me) because I literally just pull it outside into my front yard for a 5-minute viewing session of something interesting.  That probably wouldn't annoy most people.  Perhaps the insulation will help me avoid the wait.


Edited by stevereecy, 03 April 2020 - 08:39 AM.


#7 Hesiod

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Posted 03 April 2020 - 10:12 AM

IMHO there is a noticeable difference between my 5" and 3.5" ones, but this is also enhanced by the better resolution offered by the 5".

I could see hints of the heat plume after roughly 45' in the 5" with a gradient of roughly 15° C, even if could split Eta Or or Epsilon Hya after roughly 20'.

With the 3.5" remember that views peaked after about 20' with similar gradients; however it was much easier to disrupt the image by heating accidentally the telescope


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#8 SeattleScott

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Posted 03 April 2020 - 11:26 AM

I got a roll of Reflectix for $10 and self adhesive Velcro for $4. Did my 6” Mak, a buddies 8” SCT with plenty left over for another buddies TEC6, but I think he doesn’t want to cover up the logo.

Scott
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#9 markb

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Posted 03 April 2020 - 12:59 PM

I agree on the cool-down issues, I was able to use an ETX 125 without great difficulty, but my Intes  150 had severe cool down issues. My ETX90 seem to have no obvious issues at all.

 

I prefer a larger apertures. If I still had the Intes I would absolutely have put reflectix on it and made all attempts to keep it. The 90 had a rare, perfect, figure but was too darned dim for me.


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#10 stevereecy

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Posted 03 April 2020 - 02:53 PM

I agree on the cool-down issues, I was able to use an ETX 125 without great difficulty, but my Intes  150 had severe cool down issues. My ETX90 seem to have no obvious issues at all.

 

I prefer a larger apertures. If I still had the Intes I would absolutely have put reflectix on it and made all attempts to keep it. The 90 had a rare, perfect, figure but was too darned dim for me.

I agree.  The 5-inch Mak seems to best fit in the sweet spot between usability on a lightweight mount, cool down time, and reasonable aperture for brighter DSOs. Interestingly, it’s also the largest size before the price for a used one goes geometric.   It was enough to make me upgrade from a 100mm, but barely and I’m experiencing some sellers remorse.  My 5-inch still has a touch of mount vibration that isn’t worth addressing  and is just slow enough thermally to justify wrapping.  I think if someone made a 4.5 inch Mak it would be perfect for me. 


Edited by stevereecy, 03 April 2020 - 02:55 PM.


#11 Classic8

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Posted 03 April 2020 - 04:17 PM

I agree.  The 5-inch Mak seems to best fit in the sweet spot between usability on a lightweight mount, cool down time, and reasonable aperture for brighter DSOs. Interestingly, it’s also the largest size before the price for a used one goes geometric.   It was enough to make me upgrade from a 100mm, but barely and I’m experiencing some sellers remorse.  My 5-inch still has a touch of mount vibration that isn’t worth addressing  and is just slow enough thermally to justify wrapping.  I think if someone made a 4.5 inch Mak it would be perfect for me. 

I was wondering about this myself. I have a 4" mak and haven't noticed cooldown issues much and wondered if a 5" would be a lot different.



#12 Erik Bakker

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Posted 04 April 2020 - 03:12 AM

A 5" MCT is the start of the big boy issues and benefits, even if it seems only a small step up from a 3.5-4" MCT. Go to a 7" MCT and you are definitely in big boy territory. Adding insulation will quickly and cheaply show you how that affects image quality and cool down time in your situation. My Questar 7 could take up to 2 hours to fully acclimatize without insulation of the OTA.

 

On an SCT cool down is friendlier, but they dew up much quicker. than a MCT. On most nights in my mild sea climate, the flexible and padded AstroZap dewcap, attached around the cell that holds the Schmidt corrector, does an amazing job at preventing dew from forming and keeping cool down issues low on my Super C5. A few days ago, on Match 31st, that allowed me to observe cloud details on Venus, the Pup of Sirius and an absolutely stunningly detailed moon at 80-120x. Seeing was at least 9/10, transparency 7/10 and temperature around freezing, with the scope showing full performance within half an our after being brought outside from my room.

 

For that set up, see the picture below:

 

IMG_2233.jpg


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#13 luxo II

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Posted 04 April 2020 - 07:13 AM

Sorry I’ll take back what I said and agree with Erik. Took my 6” M615 out tonight - and what a superb night it turned out to be too. It did show a thermal plume for a little while maybe 30-45 mins, but only a tad obvious at 200X. At 100X I wouldn’t have noticed.

So yes you might see this in a 5” as well, but not badly.

Edited by luxo II, 04 April 2020 - 07:13 AM.


#14 kjkrum

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Posted 05 April 2020 - 10:28 PM

Why do Maks take longer to cool than SCTs? I keep reading that they do, but never an explanation why. Thicker mirrors? Or something about the design that makes the same tube currents more visible?

#15 gene 4181

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Posted 05 April 2020 - 10:39 PM

  the thicker meniscus  up front   ,   



#16 stevereecy

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Posted 06 April 2020 - 07:39 AM

  the thicker meniscus  up front   ,   

Exactly.  There's a youtube video where a guy takes one apart.  I was shocked by how thick the glass is.  It's more like a glass paperweight.


Edited by stevereecy, 06 April 2020 - 07:40 AM.


#17 luxo II

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Posted 06 April 2020 - 08:27 AM

The corrector in the Santel MK91 is 23mm thick, and in my 10" about 25mm. That's a LOT of thermal mass - roughly 4X that of an SCT corrector. Enough that on most nights they don't dew over without a heater.

 

What's even more insane is the volume of glass ground away to make these correctors - they aren't slumped.


Edited by luxo II, 06 April 2020 - 08:29 AM.


#18 SeattleScott

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Posted 06 April 2020 - 03:30 PM

For most Maks the cooldown is very similar to a SCT. Granted this might be different at 8”-9” aperture. But in general the meniscus is exposed and cools down much faster than the mirror. Granted this can be different if you have cooling fans. But generally there is no functional difference in cooling time between a Mak or SCT because the mirror takes longer to cool than the corrector. Again, unless you use fans for the mirror.

The MYTH that Maks take longer to cool is because of usage differences. People typically use SCT for medium power DSO viewing and Maks for high power planetary viewing. Obviously you need to be near ambient (or well insulated) for high power planetary viewing so Maks seem to take longer, as opposed to a SCT that you can start using right away on low power targets like the double cluster.

Scott
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#19 luxo II

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Posted 06 April 2020 - 05:11 PM

I don't encourage one to cool - at all. Insulate them properly and ready to use from the start.

 

The myth is that it's necessary or even desirable to cool them - and then applying heater straps to keep dew off is a clear clue that was a myth.


Edited by luxo II, 06 April 2020 - 05:12 PM.

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#20 olivier737

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Posted 07 April 2020 - 07:08 AM

  the thicker meniscus  up front   ,   

This is definitely not correct! I own a 300mm aperture Mak. I let you imagine how thick and heavy the meniscus can be. If you manage to properly cool down your Mak, it will not take longer than a classical Schmidt-Cassegrain to reach thermal equilibrium. As explained by SeattleScott, the meniscus is exposed and cools down much faster than a mirror. However after approximately one hour cooling time, you need to insulate the OTA and the dewshield to avoid them to cool lower than the outside air temperature! 

 

Have a look at these very interesting advises from Roland Christen (Astro-Physics) :

 

https://groups.io/g/...ted,,,20,2,20,0

 

Find in attachment a picture of my Mak with and without insulating foam rollers. When using the insulation I have never had any colling issue :

Attached Thumbnails

  • IMG_3542.jpg
  • IMG_3530.jpg

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#21 gene 4181

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Posted 07 April 2020 - 12:53 PM

       127 Orion  mak  bare 8.6 lbs  , SW  127 w/accessories  9.7 lbs ,  5inch SCT w/accessories   6 lbs .  150 mak , bare 11.5  lbs,  SW  150 w/ accessories  14 lbs , 150 / 6in SCT  w/ accessories  10 lbs .   180 mak , bare ota, 15.9 lbs, SW 180  w/ accessories  19 lbs    and  200 mm / 8in SCT / Orange SE  12.5 lbs  with accessories 1.25 inch diagonal / red dot finder and 25 mm plossl   .   There are weight differences  and it can't just be slightly longer tube lengths   , 


Edited by gene 4181, 07 April 2020 - 02:02 PM.


#22 SeattleScott

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Posted 07 April 2020 - 05:10 PM

Yes no one is disputing Maks having considerably thicker correctors. That is true and well documented. It absolutely impacts weight. But it doesn’t necessarily mean anything regarding cooling.

Basically if you DON’T insulate, and you DO have cooling fans for the mirror, then the thicker corrector slows cooling. Otherwise, not really a factor.

Scott

Edited by SeattleScott, 07 April 2020 - 05:28 PM.

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