Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Dew Prevention for RC 6" Telescope

  • Please log in to reply
15 replies to this topic

#1 svsalako

svsalako

    Vostok 1

  • *****
  • topic starter
  • Posts: 143
  • Joined: 25 Feb 2018
  • Loc: Vermont

Posted 23 July 2021 - 01:17 PM

Hi All --

 

I am awaiting delivery of a GSO RC 6" telescope and I am trying to pull all the accessory bits together for it. Specifically, I am looking for recommendations for a dew heater system. I've seen Astrozap Flexi-Heat products that are combination dew shields and heaters that go on the front to the telescope, but it seems like it would be useful to have a heater band around the base of the telescope where the primary mirror is located. What are other folks doing? I'd love some suggestions from folks that have already solved this problem!

 

Thanks in advance

 

Cheers,

 

Grey



#2 Scott Badger

Scott Badger

    Sputnik

  • -----
  • Posts: 44
  • Joined: 13 Apr 2021

Posted 23 July 2021 - 01:34 PM

I wanted something simple without having to deal with the converters, control units etc. that all the astro units I could find required, so I went with this:

https://www.northern...77769_200577769

 

Fits my C9.25 perfectly but they also have some shorter heating blankets that have an adhesive backing:

https://www.northern...87804_200587804

 

Note that I've only tested it one night, and that was a cloudy night so I wasn't doing any imaging, just testing the heater. It was plenty humid, and no dew issues, but I haven't yet seen how it might impact seeing and will probably still need to dial in the setting.

 

I also have a dew shield and used that before getting the heater, and maybe it helped, but I still had issues.

 

Cheers,
Scott



#3 Dan Crowson

Dan Crowson

    Gemini

  • *****
  • Moderators
  • Posts: 3,079
  • Joined: 08 Oct 2010
  • Loc: Dardenne Prairie, MO

Posted 23 July 2021 - 01:57 PM

Grey,
 
I owned an AT6RC for several years in the Saint Louis area. I would image with it all night ever clear night. It was not uncommon to have humidity levels over 90%. I never had any kind of issue with dew as the scope is more or less a mirror with a big dew shield. The only thing that would dew up was the guide scope. I fixed that with just a solo cup on it.
 
You might find that you don't need anything for dew.

Dan


  • SkipW likes this

#4 nic35

nic35

    Apollo

  • *****
  • Posts: 1,251
  • Joined: 08 Sep 2007

Posted 23 July 2021 - 02:04 PM

+1 on Dan's comments.  Never had a dew issue with tubed RC like you are getting.

 


  • SkipW likes this

#5 SkipW

SkipW

    Viking 1

  • -----
  • Posts: 999
  • Joined: 03 Feb 2011
  • Loc: Oklahoma, USA

Posted 23 July 2021 - 03:43 PM

Agree with the last two comments. Try it first. You will probably find you don't need it at all.

 

Dew isn't typically a big problem where I live, but after a few hours at a Green Bank Star Quest (West Virginia), the outside of my AT6RC (AstroTec 6" RC) - and just about everything else exposed to the open sky - was dripping wet. There was no dew at all on the RC's optics.



#6 svsalako

svsalako

    Vostok 1

  • *****
  • topic starter
  • Posts: 143
  • Joined: 25 Feb 2018
  • Loc: Vermont

Posted 23 July 2021 - 04:04 PM

Ok -- I will take your advice and give it try. Vermont in the summer can get pretty humid, but I'm sure W. Va., and St. Louis Mo. are similar.

 

And Scott -- thanks for the suggestion -- I'll keep it in reserve if I have a problem.

 

Cheers,

 

Grey



#7 jgraham

jgraham

    ISS

  • *****
  • Posts: 22,359
  • Joined: 02 Dec 2004
  • Loc: Miami Valley Astronomical Society

Posted 23 July 2021 - 04:27 PM

My imaging sessions go all night long from dusk to dawn and I have had dew reach the mirror on my RC8. I fixed this by adding a dew heater around the lower end of the tube about 6” above the primary.

 

Problem solved.

 

Enjoy!



#8 Scott Badger

Scott Badger

    Sputnik

  • -----
  • Posts: 44
  • Joined: 13 Apr 2021

Posted 24 July 2021 - 01:05 PM

hey Grey, I live over in NH, so the same summer humidity. Like skip related everything metal and glass exposed is dripping wet in no time…..but my scenario is different with the schmidt cassegrain where the corrector plate is the issue.

cheers,
Scott

#9 licho52

licho52

    Vostok 1

  • -----
  • Posts: 131
  • Joined: 15 Dec 2020

Posted 24 July 2021 - 10:13 PM

Contrary to some reports in this thread you will get dew on the secondary (I got it just 2 days ago when I thought I was safe). To prevent you need to have some type of collar, I use a foam collar protruding about 10 inches past which I found is enough.  Got lazy 2 nights ago and it bit me.



#10 SkipW

SkipW

    Viking 1

  • -----
  • Posts: 999
  • Joined: 03 Feb 2011
  • Loc: Oklahoma, USA

Posted 25 July 2021 - 03:38 PM

Contrary to some reports in this thread you will get dew on the secondary (I got it just 2 days ago when I thought I was safe). To prevent you need to have some type of collar, I use a foam collar protruding about 10 inches past which I found is enough.  Got lazy 2 nights ago and it bit me.

It seems like that situation is pretty rare; I think I've heard a similar report one other time. I still recommend the OP check it out first unless he's in a situation where any loss of observing time would be significant.



#11 Migwan

Migwan

    Mercury-Atlas

  • *****
  • Posts: 2,790
  • Joined: 24 Jul 2017
  • Loc: Meeechigan

Posted 25 July 2021 - 07:54 PM

If Vermont is anything like Michigan, dew points are reached early more nights than not.   Half of those not nights, will still manage to reach 100% RH by 3 or 4 AM.  There's not many mornings that you don't need waterproof shoes to walk across the grass.

 

I'd be hesitant to put heat around the primary mirror and would try a dew shield without heat first.  Then with heat.   A dew strip near the primary would be my last choice and only if absolutely necessary.



#12 licho52

licho52

    Vostok 1

  • -----
  • Posts: 131
  • Joined: 15 Dec 2020

Posted 26 July 2021 - 03:29 PM

When the temperature drop is significant this will happen all the time.  Primary mirror is fine, it will never fog up but the secondary needs to be kept in a dew shield, 10 inches is enough and it can be wider than the scope.  It doesn't take much to prevent it but if you don't you're done for the night.



#13 svsalako

svsalako

    Vostok 1

  • *****
  • topic starter
  • Posts: 143
  • Joined: 25 Feb 2018
  • Loc: Vermont

Posted 26 July 2021 - 05:57 PM

Hmmmm. All good advice I think. I know Vermont gets really wet in the summer time. I think I'll start with a passive dew shield and see how that works. Thanks for all the replies.

 

Cheers,

 

Grey


  • Migwan likes this

#14 Scott Badger

Scott Badger

    Sputnik

  • -----
  • Posts: 44
  • Joined: 13 Apr 2021

Posted 05 August 2021 - 02:29 PM

Just wanted to follow up and add to this thread that the Briskheat drum/bucket heater I got finally saw real action and worked great. Last time imaging, when my alarm sent me out at 4am to start darks and otherwise pack up, everything was covered in dew....the outside of the OTA & dew shield, the mount & tripod, my plastic gear totes (that I stupidly left open...), the grass, my laptop......but not the corrector plate or internal optics.

 

Cheers,
Scott



#15 Nippon

Nippon

    Aurora

  • *****
  • Posts: 4,582
  • Joined: 22 Oct 2009
  • Loc: Central Florida

Posted 05 August 2021 - 03:48 PM

It gets very wet here in Florida. I would get a little dewing on my Mewlon 180 secondary on long damp nights but not the primary. A 6" long dew shield solved the problem. I have gone long nights where everything gets wet but my Mewlon's secondary and primary mirrors stay dry.



#16 Scott Badger

Scott Badger

    Sputnik

  • -----
  • Posts: 44
  • Joined: 13 Apr 2021

Posted 06 August 2021 - 10:09 AM

Unfortunately, for my SCT, a dew shield alone wasn’t sufficient so I had to add a heat blanket too. Maybe part of the issue for me is being in the north east where we have hot humid days followed by much cooler nights e.g. the day before yesterday was in the 80’s but dropped to 48 that night.

Cheers,
Scott


CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics