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Dew/Frost Shield for C8

Cassegrain Catadioptric Celestron
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#1 brunza

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Posted 11 December 2023 - 01:35 PM

Hey Everyone,

 

I was out stargazing the other night and the corrector lens frosted up on me. I looked into dew shields and found a few options, but I was hoping to get some feedback before making the purchase. I live in Colorado, dew wasn't an issue for me this fall as it's rather dry here. We do get frosty in the winters.

 

The first option is just a plastic shield from Celestron with a velvet lined interior to prevent glare from external light sources. It's very basic. Will this prevent my corrector from frosting up on me in the winter?

https://www.celestro...ld-dx-for-c6-c8

 

The second option is the heater ring from Celestron, it runs at full amperage unless controlled. Instead of paying and additional $250 for the controller, I found the Astro Zap Pegasus for $90. I know it's just a manual controller. Do I need this to prevent frost or this overkill?

https://www.celestro...heater-ring-8in

https://www.highpoin...ller-peg-dewzap

 

Thanks,

 

 


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#2 daveco2

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Posted 11 December 2023 - 02:04 PM

I have the Celestron heater ring, dew shield and controller.   I got this system because the heater ring is pressed to the front of the corrector lens, which is the best place for heat transfer.  A wrap-around heater

has a much longer path, which may work, but I didn't try it.  In any case, the Celestron system is very efficient, which may be a problem because heating the corrector at full throttle induces artifacts in the stars

that look like vertical spikes.  This is a widely reported problem.  Turning down the power takes care of this problem, which is why I got the controller.  I think a manual controller would work just as well, considering

that achieving the right heat level to eliminate dew while avoiding star spikes is a trial and error process.

 

The dew shield alone without heater didn't work for me in Southern California, a few miles from the coast.


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#3 Mark Lovik

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Posted 11 December 2023 - 02:11 PM

I use a simple pwm controller on the Celestron Dew Ring.  It is so efficient that I set things to a very low power setting --  no frost or dew.

It has much better optical behavior at the lowest power setting you can manage.

 

.. returned to a dew shield at home ... now it is only used to handle local stray light conditions.  This is not needed at dark sky sites.


Edited by Mark Lovik, 11 December 2023 - 02:12 PM.

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#4 Mike G.

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Posted 11 December 2023 - 02:25 PM

I use the dew heater ring as well as with a dew shield.  We get lots of dewy nights here and frosting of the scope as well in the winter.  I built a simple PWM controller for the dew heater ring and it works perfectly at very low settings. The dew shield helps with giving you better contrast by cutting down on stray light entering the tube.  Even on very dry nights when no dew is expected, I always use a dew shield.

You can buy simple DIY PWM controllers on A-zon for just a few $.


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#5 Notdarkenough

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Posted 11 December 2023 - 11:30 PM

I, too, use the Heated Ring for my 8" EdgeHD. Wonderful. As for the dew shield, I previously used the AstroZap Flexi Shield but didn't love it. I now use the Celestron Aluminum Dew Shield and absolutely love it. It is very stable, longer than the AstroZap, can support a light box, has special cutouts for the Heated Ring and/or HyperStar cables and the aluminum cap fits very securely. My climate is very similar to yours, and had I purchased the dew shield first, I might not have bothered with the Heated Ring. Regarding the Controller, I had problems utilizing it and sold it. It did work the heated Ring very efficiently. If I had a Celestron mount (Evo just for temporary uses) I think it would have worked well.

 

In short, the aluminum dew shield is expensive, but absolutely the bees knees. The Heated Ring is very efficient and very effective. The combination is, honestly, too much for my ultra-dry winter air. Ymmv


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#6 Sacred Heart

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Posted 11 December 2023 - 11:55 PM

I use dew shield extensions on all my scopes.  Two refractors and a 7" Maksutov.  No problems here in Tennessee.

 

Made from EVA foam, depending on the aperture, either 5mm or 10mm thick material. The foam is from Hobby Lobby. Simply wrap the scope, overlap the foam by 2 inches, glue it together using duct tape to hold together while the glue dries. Length of the extension is from where the scope bolts on to the dovetail plate to about 3 - 8 inches past the existing dew shield.  Depending on aperture.

 

https://www.hobbylob...10mm/p/80982131

 

Joe

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#7 brunza

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Posted 12 December 2023 - 08:39 AM

I, too, use the Heated Ring for my 8" EdgeHD. Wonderful. As for the dew shield, I previously used the AstroZap Flexi Shield but didn't love it. I now use the Celestron Aluminum Dew Shield and absolutely love it. It is very stable, longer than the AstroZap, can support a light box, has special cutouts for the Heated Ring and/or HyperStar cables and the aluminum cap fits very securely. My climate is very similar to yours, and had I purchased the dew shield first, I might not have bothered with the Heated Ring. Regarding the Controller, I had problems utilizing it and sold it. It did work the heated Ring very efficiently. If I had a Celestron mount (Evo just for temporary uses) I think it would have worked well.

 

In short, the aluminum dew shield is expensive, but absolutely the bees knees. The Heated Ring is very efficient and very effective. The combination is, honestly, too much for my ultra-dry winter air. Ymmv

Notdarkenough,

 

I think I looked at that dew shield as well, is it this one: https://www.highpoin...-with-cap-94021

 

Just curious, why didn't you like the astro zap dew shield?

 

You mention if you would have bought the aluminum dew shield first, you may not have bothered with the heated ring. Have you had your telescope out with just the dew shield on without the ring powered up with no frost issues? If all I need is the aluminum dew shield, and not the ring and controller to keep the frost off in Northern Colorado. that's great news for me. 

 

Thanks,



#8 rjacks

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Posted 12 December 2023 - 10:02 AM

You should read one of the many threads on reflectix insulation for cats. In many cases, reflectix insulation combined with a simple dew shield will solve dew problems on most dewy nights. I don't think anything can solve dew issues on super dewy nights - those nights when it seems like a ghost is throwing buckets of water on your equipment. 



#9 brunza

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Posted 12 December 2023 - 10:37 AM

I use dew shield extensions on all my scopes.  Two refractors and a 7" Maksutov.  No problems here in Tennessee.

 

Made from EVA foam, depending on the aperture, either 5mm or 10mm thick material. The foam is from Hobby Lobby. Simply wrap the scope, overlap the foam by 2 inches, glue it together using duct tape to hold together while the glue dries. Length of the extension is from where the scope bolts on to the dovetail plate to about 3 - 8 inches past the existing dew shield.  Depending on aperture.

 

https://www.hobbylob...10mm/p/80982131

 

Joe

Joe,

 

Are you using the 10mm thick stuff? Either way, it's fairly cheap and might be worth a try.


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#10 Sacred Heart

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Posted 12 December 2023 - 12:25 PM

Joe,

 

Are you using the 10mm thick stuff? Either way, it's fairly cheap and might be worth a try.

brunza,

 

Yes, in the pictures is 10mm.  On my 7" maksutov it is full width, 24" long  wrapped around the tube.  It is 9 inches on the tube and 15 inches overhang.   If you want you can insulate the C8 tube with it too.  The 10mm material is stiff enough to hold / slide on and grip good.   I have this stuff on my refractors too.  Was out last night trying for the Rosette Nebula till tranist, about 1:15 AM.  No frost on the lenses. Everywhere else.

 

Just overlap by two inches or more, I used the clear Gorilla Glue and strips of duct tape to hold it until the glue dried.  Wrap it and glue it while on the tube, let the glue dry before sliding off the tube.

 

The 5mm is good for making Bahtinov masks for focusing.

 

If you try it, let me know how it went.

 

Good luck,  Joe


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#11 Notdarkenough

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Posted 12 December 2023 - 06:32 PM

Notdarkenough,

 

I think I looked at that dew shield as well, is it this one: https://www.highpoin...-with-cap-94021

 

Just curious, why didn't you like the astro zap dew shield?

 

You mention if you would have bought the aluminum dew shield first, you may not have bothered with the heated ring. Have you had your telescope out with just the dew shield on without the ring powered up with no frost issues? If all I need is the aluminum dew shield, and not the ring and controller to keep the frost off in Northern Colorado. that's great news for me. 

 

Thanks,

Yes, that link is the dew shield I love. I didn't like the AstoZap as it was too short to block a neighbor light, didn't have any cap (I leave my rig set up year around), and was prone to wiggling in the wind. For me, I do short-exposure EAA imaging; I haven't had any frosting with the dew shield yet. However, if you leave it out all night for AP techniques, it may be different. I have rigged up the Heated Ring to work off my ASIAir+, but haven't needed it at all. I would certainly try the just the dew shield alone before adding kit. I am in Northern Utah, so similar climate and viewing angles.

 

Regarding the other comment about adding insulation to your SCT, this may well be an excellent choice if you set-up and tear down each session. It will certainly reduce the acclimation period required before using. If you are going to rig up insulation, having it long enough to work as dew shield is very popular and effective. For me, the Heated Ring is just too cheap to not buy; I spend too much on Astro crap anyway and $50 was an easy choice. But, again, leaving a rig setup semi permanently does have different pros and cons. The Celestron Aluminum Dew Shield is stable enough I leave it in place and cover with a Telegizmos 365, and it stays put with snow, hard rain (very rare) and some wind. If you have strong local winds, that too will require some additional thought.

 

Hope that helps-



#12 brunza

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Posted 13 December 2023 - 10:51 AM

Yes, that link is the dew shield I love. I didn't like the AstoZap as it was too short to block a neighbor light, didn't have any cap (I leave my rig set up year around), and was prone to wiggling in the wind. For me, I do short-exposure EAA imaging; I haven't had any frosting with the dew shield yet. However, if you leave it out all night for AP techniques, it may be different. I have rigged up the Heated Ring to work off my ASIAir+, but haven't needed it at all. I would certainly try the just the dew shield alone before adding kit. I am in Northern Utah, so similar climate and viewing angles.

 

Regarding the other comment about adding insulation to your SCT, this may well be an excellent choice if you set-up and tear down each session. It will certainly reduce the acclimation period required before using. If you are going to rig up insulation, having it long enough to work as dew shield is very popular and effective. For me, the Heated Ring is just too cheap to not buy; I spend too much on Astro crap anyway and $50 was an easy choice. But, again, leaving a rig setup semi permanently does have different pros and cons. The Celestron Aluminum Dew Shield is stable enough I leave it in place and cover with a Telegizmos 365, and it stays put with snow, hard rain (very rare) and some wind. If you have strong local winds, that too will require some additional thought.

 

Hope that helps-

Notdarkenough or Joe,

 

I have my C8 in the basement and I will set it up 1-2 hours before I plan to start observing. I leave the factory cap on the corrector lens and caps on the eyepieces. When I'm done I deconstruct it and haul it back down into my basement. How would the insulation benefit me? Wouldn't it prolong the cool down time?

 

Thanks,


Edited by brunza, 13 December 2023 - 10:54 AM.


#13 Sacred Heart

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Posted 13 December 2023 - 12:47 PM

brunza,

 

This is my take on insulation.

 

Insulation does not stop cool down it just slows it down to a gradual level.  Meaning cool down is less noticeable.  Takes longer so you change focus at a slower pace.  The image is supposed to be more stable at the beginning and throughout the cool down process.

 

Me I have small refractors, 76mm and 92mm, they cool down fast.  30 - 45 minutes tops.  I set up just before sundown.

 

I would look in CN, I think in Cats and Cass's, people show how they insulate. The main body of the scope is always insulated, so in that case if  I were to put the insulation on just leave room for the dew shield to slip on.

 

You may want to contact a reflectix / insulation user, but I'm thinking in 1 hour of sundown you are well on your way to a cool telescope, in 2 hours it should be stable, very stable.  This is my opinion.   What does your personal experience tell you??  Is the view good or still a little wonky.

 

When I image, like I said I set up right at sundown, my set up is on wheels so it takes ten minutes to set up. I focus at 75mm on the draw tube, iIt seems at every ten degrees drop in temperature I need to refocus.  NINA software measures HFR, half flux ratio,  say at start my HFR number is 2.6, I will refocus at a constant 2.9.  HFR varies between shots, atmosphere.  I need to start using the auto focus.  

 

My 7" Maksutov is not insulated, I use it for planetary viewing and imaging as well as double stars and some deep sly objects, mainly viewing.  Cool down not an issue for me.  The cold outside temperatures is the bigger deal with me, I don't stay out too long.

 

Joe



#14 brunza

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Posted 13 December 2023 - 05:46 PM

Hey Joe,

 

In 1.5 to 2 hours I feel like the views are great, if it's been less than an hour they're wonky. Just to make sure I have this straight, insulating my telescope will essentially slow the cooling process resulting in stabile views and slows the need to refocus?

 

I'm not doing any EAA or any imaging, I'm solely just observing. When I am out observing I will last about 1-2 hours out there until I turn into a block of ice. All I'm trying to do is delay the frosting of my corrector lens for those 2 hours of observing as I leave the cap on the corrector until I am ready to observe. I think insulating the body of my C8 is probably overkill for a guy like me. What do you think?  

 

Thanks,



#15 Sacred Heart

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Posted 13 December 2023 - 07:37 PM

Hey Joe,

 

In 1.5 to 2 hours I feel like the views are great, if it's been less than an hour they're wonky. Just to make sure I have this straight, insulating my telescope will essentially slow the cooling process resulting in stabile views and slows the need to refocus?

 

I'm not doing any EAA or any imaging, I'm solely just observing. When I am out observing I will last about 1-2 hours out there until I turn into a block of ice. All I'm trying to do is delay the frosting of my corrector lens for those 2 hours of observing as I leave the cap on the corrector until I am ready to observe. I think insulating the body of my C8 is probably overkill for a guy like me. What do you think?  

 

Thanks,

brunza,

 

Insulation, reflectix / cardboard / foam / whatever, only delays getting cold. Much like you wearing a jacket in the cold, unless you have a lot of insulation - that tube is cooling down. How fast or slow I do not know.

 

If your normal practice is setting up 1 - 2 hours ahead then viewing for another 2 hours,  then no I would not insulate, you are achieving your desired result naturally - why slow the process down.

 

As for dew prevention, those dew shield extensions work for me here in Tennessee.  Two nights ago it was cold, at 3:30 AM when I brought it all in the garage - I'm on wheels so it is easy and fast - 10 minutes -  just about everything was covered in frost, mount, dew shield extensions.  The optics were clean.

 

Advice, cool down like you normally do, when you view, then put the dew shield on and have fun.

 

Joe 



#16 brunza

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Posted 21 December 2023 - 09:44 AM

Hey Guys,

 

I appreciate all of your tips and advice on this! I went the route that Joe mentioned and picked up some foam from Hobby Lobby last Friday, built and tested it the same night. That foam is actually rather thick! It worked out really well. I'll attach a photo of the setup the next time I get it out, probably when the moon starts to wane. It's ugly, but it's very functional and does improve the contrast a little. I'm fairly lucky, it's rather dark in my backyard, but when I setup in my front yard, I'd probably really notice a difference then. There was enough foam left over to make my kids a couple of swords to play with!

 

Thanks,

Brunza


Edited by brunza, 21 December 2023 - 09:46 AM.

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#17 Sacred Heart

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Posted 24 December 2023 - 03:31 AM

Hey Guys,

 

I appreciate all of your tips and advice on this! I went the route that Joe mentioned and picked up some foam from Hobby Lobby last Friday, built and tested it the same night. That foam is actually rather thick! It worked out really well. I'll attach a photo of the setup the next time I get it out, probably when the moon starts to wane. It's ugly, but it's very functional and does improve the contrast a little. I'm fairly lucky, it's rather dark in my backyard, but when I setup in my front yard, I'd probably really notice a difference then. There was enough foam left over to make my kids a couple of swords to play with!

 

Thanks,

Brunza

Brunza,

 

Out of curiosity, what are the dimensions of the shield??    Ugly,  for sure, but it does work.

 

Joe



#18 brunza

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Posted 28 December 2023 - 10:42 PM

Brunza,

Out of curiosity, what are the dimensions of the shield?? Ugly, for sure, but it does work.

Joe


Hey Joe,

Ugly, absolutely haha! The dimensions are 24" long 35" wide (or circumference) with 2.25" of overlap to glue the thing together and 3/8" thick. It covers approximately 11" of the C8 and 13" past the corrector lense.

#19 Sacred Heart

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Posted 28 December 2023 - 11:02 PM

Hey Joe,

Ugly, absolutely haha! The dimensions are 24" long 35" wide (or circumference) with 2.25" of overlap to glue the thing together and 3/8" thick. It covers approximately 11" of the C8 and 13" past the corrector lense.

Does the job pretty good??

 

Joe



#20 brunza

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Posted 29 December 2023 - 09:50 AM

Does the job pretty good??

Joe

I've only had it out once so far, but yes it worked perfectly and the price was right! I probably won't be out star gazing with the C8 until we get closer to a new moon and I'll get you a pic of it then and how it does, but thank you for the advice!

Edited by brunza, 29 December 2023 - 09:50 AM.

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#21 Sacred Heart

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Posted 29 December 2023 - 03:29 PM

I've only had it out once so far, but yes it worked perfectly and the price was right! I probably won't be out star gazing with the C8 until we get closer to a new moon and I'll get you a pic of it then and how it does, but thank you for the advice!

I'm a huge fan of effective, cheap and easy.   Glad to help, glad it works well for you.

 

Joe




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