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 fighting tips

  • Please log in to reply
7 replies to this topic

#1 alexvh

alexvh

    Messenger

  • -----
  • topic starter
  • Posts: 494
  • Joined: 29 Jul 2007

Posted 23 September 2021 - 04:32 AM

Guys,

after 2 hours of great viewing in the UK, my dob was covered in dew. actually dripping. What strategies do you guys use? I have a secondary heater that runs off AA batteries, but nothing else.

My binotron looked like Id dropped it in water!



#2 Kunama

Kunama

    Aussie at large

  • *****
  • Posts: 6,164
  • Joined: 22 Oct 2012
  • Loc: Canberra, Australia

Posted 23 September 2021 - 04:38 AM

I’ve had a few nights where the heavy dew hits early, I use a  couple of old bath towels and hand towels and drape them over the scope.  They soak up the dew beautifully…



#3 wrvond

wrvond

    Gemini

  • *****
  • Posts: 3,498
  • Joined: 25 Sep 2014
  • Loc: West Virginia

Posted 23 September 2021 - 04:56 AM

I have a heater on the secondary, eyepiece, Telrad and around the base of the tube (primary end). I also have a Noctua fan that I keep running.


  • George N and havasman like this

#4 Starman47

Starman47

    Viking 1

  • -----
  • Posts: 859
  • Joined: 10 Jun 2018
  • Loc: West of OZ

Posted 23 September 2021 - 05:38 AM

Perhaps moving to the desert southwest would work. grin.gif That is west Texas, New Mexico and Arizona. shocked.gif


  • lphilpot likes this

#5 Dan_I

Dan_I

    Mariner 2

  • -----
  • Posts: 296
  • Joined: 22 Sep 2010
  • Loc: France

Posted 23 September 2021 - 06:13 AM

Is your dobsonian solid or truss tube?  I live in France, west of Paris so I believe our respective weather conditions are kind of similar.

 

I have plenty of condensation on the outside of my solid tube OTA (I guess the black carbon tube doesn't help), but I don't care.

 

So far I managed to keep dew away from the optics with only passive measures, i.e. without heating: a felt-lined dew shield and, for the secondary, I replaced the metal holder by one made wood/carbon composite (with good thermal isolation characteristics).

 

I can image till dawn without issues (well I have currently dew issues on the camera window but it is not the telescope fault wink.gif ).


Edited by Dan_I, 23 September 2021 - 06:16 AM.

  • davejlec likes this

#6 George N

George N

    Fly Me to the Moon

  • *****
  • Posts: 6,506
  • Joined: 19 May 2006
  • Loc: Binghamton & Indian Lake NY

Posted 23 September 2021 - 11:33 AM

I have a heater on the secondary, eyepiece, Telrad and around the base of the tube (primary end). I also have a Noctua fan that I keep running.

I've had the same set-up for my old Obsession 20 Dob (except the primary heater) - including double heat straps for my bino-viewer. The one thing I missed - but have seen on other big Dobs - a special heated version of a filter slider (used to hold and slide in place things like O-III filter - which will dew up if left unheated and exposed to the air.)

 

It had a DigiFire 7 dew controller and a 17 Ah battery that rode on the outside of the rocker box. I intend to add that to my new Dob.

 

I live in a very 'moist' area - and have had scopes dew/frost up before it was dark enough to collimate! However, with all that dew control on the Obsession 20 I've used it on nights with it looking like it was hosed down - or so frosted up that the scope was pure white in color. Most others on the observing field with those conditions were shut-down. Without primary heating - I have had the primary dew/frost up after the air temp starts going back up - typically after 3 AM - and I'm mostly ready to call it a night by then. Still - all that acid dew/frost on the primary is not a good idea.

 

BTW - on dewy nights like that I wear my rain-suit pants - to keep the body parts dry when sitting on a dewed-up chair or needing to kneel down on dew-soaked grass.


Edited by George N, 23 September 2021 - 11:36 AM.

  • wrvond likes this

#7 havasman

havasman

    Voyager 1

  • *****
  • Posts: 13,187
  • Joined: 04 Aug 2013
  • Loc: Dallas, Texas

Posted 23 September 2021 - 01:36 PM

Active dew control works. A power supply, controller and dew strips appropriately configured will keep dew from forming on the secondary, eyepieces and finder(s). Dew is of no concern on the outside of the scope, finders or optics. Apart from the critical function of keeping the primary mirror at or very near ambient temp all night a fan behind the primary and blowing on it will also help keep the mirrors clear by providing air flow up a solid tube Dob.

 

For everything but the optical surfaces, carry towels and dry off the exterior at the end of your sessions. But don't worry about dew formation on the tube or accessory exteriors. 


Edited by havasman, 23 September 2021 - 01:37 PM.


#8 George N

George N

    Fly Me to the Moon

  • *****
  • Posts: 6,506
  • Joined: 19 May 2006
  • Loc: Binghamton & Indian Lake NY

Posted 23 September 2021 - 02:07 PM

Active dew control works. A power supply, controller and dew strips appropriately configured will keep dew from forming on the secondary, eyepieces and finder(s). Dew is of no concern on the outside of the scope, finders or optics. Apart from the critical function of keeping the primary mirror at or very near ambient temp all night a fan behind the primary and blowing on it will also help keep the mirrors clear by providing air flow up a solid tube Dob.

 

For everything but the optical surfaces, carry towels and dry off the exterior at the end of your sessions. But don't worry about dew formation on the tube or accessory exteriors. 

Mostly agree - but about a half dozen times over the last 18 years I've had my Obsession 20 so dewed up water was dripping off the soaked shrowd onto the primary!

 

Also - there's the issue of electronics getting wet - things like Nexus, tablets running Sky Safari, encoders - the dew heater controller itself ( saw a 16-inch Dob one very dewy night start smoking - destroyed the dew control and damaged the plastic of the UTA ).   --- and then there's the "fun" of having your notes, observering table, and star atlas all dewed up (in June of 2019 I had the dew all turn to ice at 2 AM -- in mid June!).

Oh -- and frost -- not fun taking a big Dob down with scope and ladder completely frosted up! I dropped the fully frosted up UTA of my 20-inch one night - thunk -- but no damage to scope or me. However -- none of it ever stopped me from observing - including the night I shorted out the dew controler and did not have an extra fuze -- back to rubber bands and hand warmers! Worked. ( I now have a life-time supply of fuzes in my observing kit!! )




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