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.


Bringing eyepieces inside from sub zero temps?

  • Please log in to reply
18 replies to this topic

#1 Sparky00


    Lift Off

  • -----
  • topic starter
  • Posts: 4
  • Joined: 14 Dec 2017

Posted 24 January 2018 - 12:25 AM

Hello all

New to the hobby. I was out tonight it was 5 degrees F. First partly clear night in the last couple of weeks. Anyway after bringing the gear in I noticed condensation on the outside of everything is there a way to keep my eyepieces dry

#2 jgs99v


    Explorer 1

  • *****
  • Posts: 63
  • Joined: 05 Jun 2012

Posted 24 January 2018 - 12:34 AM

Well - I'd like to hear what folks think about using a hair dryer for these conditions - to reduce dew and condensation.

#3 Aleko



  • *****
  • Posts: 1058
  • Joined: 01 Aug 2010
  • Loc: Georgia

Posted 24 January 2018 - 12:50 AM

Welcome Sparky,


What you want to do is prevent the warm moist air from hitting the icy cold eyepieces.  Before bringing them inside, wrap them in a plastic bag, or put inside an eyepiece case and keep closed until it has warmed up. Be sure to open the bag or the case after warmed up to let any residual moisture evaporate.  


I do use a hair dryer on LOW before storing the eyepieces.  

#4 michael_m


    Ranger 4

  • *****
  • Posts: 340
  • Joined: 16 Nov 2010
  • Loc: Mount Vernon, Wa

Posted 24 January 2018 - 12:56 AM

You might want to try allowing your eyepieces to slowly warm, rather than quickly warm up. I bring mine into my unheated garage, which is about midway in temperature from the outside air vs inside my house. I just place the eyepiece caps on the eyepieces to keep off dust, but I do not push the caps all the way down. I let the eyepiece glass breathe.

I don't wipe away what slight dew may form. I let it simply evaporate. Later after they warm fully, and what dew may have formed is evaporated, then I seal the caps. But the real idea here is to not let them heat up too quickly. Let them slowly warm back up, and this prevents a whole lot of dew from forming in the first place.
  • ShaulaB, Augustus and Defenderslideguitar like this

#5 t-ara-fan


    Ranger 4

  • -----
  • Posts: 309
  • Joined: 20 Sep 2017

Posted 24 January 2018 - 01:19 AM

When I am outside, I put them in a ziploc bag, squeeze all the air out, and seal the bag.  Hours later when it has warmed up, I open the bag so any trace of condensation can evaporate.   I do this with eyepieces, camera bodies, and camera lenses. 

  • ShaulaB likes this

#6 Tony Flanders

Tony Flanders


  • *****
  • Posts: 16490
  • Joined: 18 May 2006
  • Loc: Cambridge, MA, USA

Posted 24 January 2018 - 06:23 AM

I leave everything out overnight, then put it away in the morning after it has dried. My biggest problem is actually condensation on my charts.


Condensation on the outside is irrelevant, but you do want to avoid condensation on optical surfaces. Sealing them tight before bringing them inside will do that. If condensation does form on an optical surface, it can be removed easily with a hair drier or an electric space heater.

Edited by Tony Flanders, 24 January 2018 - 06:23 AM.

#7 aeajr


    Voyager 1

  • *****
  • Moderators
  • Posts: 11104
  • Joined: 26 Jun 2015
  • Loc: Long Island, New York, USA

Posted 24 January 2018 - 06:29 AM

As noted by others it is the warm moist air of that house hitting the cold eyepieces and telescope that causes the condensation.  If the moist air can't get to the eyepieces or telescope then condensation can't form.  An eyepiece case, a telescope case can keep that moisture away from the equipment.


The zip lock back is probably the simplest approach for the eyepieces and other small items.


My stuff lives in my well ventilated, unheated garage so I don't have this problem.

#8 Sparky00


    Lift Off

  • -----
  • topic starter
  • Posts: 4
  • Joined: 14 Dec 2017

Posted 24 January 2018 - 12:26 PM

Thanks you for the responses, the ziplock sounds like a good idea.

#9 SteveG


    Fly Me to the Moon

  • *****
  • Posts: 7305
  • Joined: 27 Sep 2006
  • Loc: Seattle, WA

Posted 24 January 2018 - 02:06 PM

I simply put the lens caps on before bringing them in. The same with a refractor objective. There will be no condensation on the optics, just the outer barrel. I do leave them out of my case overnight to dry.

#10 star drop

star drop

    contra contrail

  • *****
  • Moderators
  • Posts: 107579
  • Joined: 02 Feb 2008
  • Loc: Snow Plop, NY

Posted 24 January 2018 - 07:06 PM

Welcome to Cloudy Nights, Sparky00!


Thanks you for the responses, the ziplock sounds like a good idea.

Yes indeed.

#11 kfiscus


    Baltic Birch Dob Bases

  • *****
  • Vendors
  • Posts: 6380
  • Joined: 09 Jul 2012
  • Loc: Albert Lea, MN, USA

Posted 24 January 2018 - 07:09 PM

I leave mine outside in their case in an unheated garage. Cold will not hurt them.  I realize that this may not be an option for the OP but it saves lots of condensation/evaporation cycles.  Hiding them in a small case in your locked vehicle trunk would be another "leave-them-outside" option.

#12 Luna-tic


    Viking 1

  • -----
  • Posts: 930
  • Joined: 26 Jul 2017
  • Loc: Foothills North Carolina

Posted 25 January 2018 - 10:12 PM

When I bring my gear in from a cold night out, I remove all the lens/corrector covers and let things acclimate. Whatever moisture forms evaporates quickly as things return to inside temperature, usually within 15-20 minutes. I've had no issues with water spotting on EP glass or mirrors or corrector. Warm air can hold more moisture than cold air; it takes less water vapor to attain a high relative humidity (causing dew/condensation) in cold air, so bringing the cold objects into a warmer environment creates a new relative humidity environment that requires more moisture to create the same dew/condensation  circumstance. The transient time as the cold objects begin to warm changes the dew point of the surface moisture, so you see condensation, but it quickly disappears as the warmer air absorbs the moisture. Once I see my corrector is clear, and no 'fog' on the EP's, I close everything up.


Using a hair dryer to warm things is just speeding up the process.

Edited by Luna-tic, 25 January 2018 - 10:15 PM.

#13 VNA


    Ranger 4

  • -----
  • Posts: 301
  • Joined: 13 Nov 2009
  • Loc: Northern California

Posted 25 January 2018 - 10:29 PM

Like tonight I bring everything in the basement and keep everything open overnight to dry out slowly.

Don't think a hair dryer is a good idea because you may force some humidity go inside the various parts and layers.

For sure don't enclose or cover anything until fully dry otherwise humidity will be locked in.

Edited by VNA, 25 January 2018 - 10:30 PM.

#14 Jim_V


    Fly Me to the Moon

  • -----
  • Posts: 7237
  • Joined: 20 Jan 2018
  • Loc: Iron Range Lake Ontario

Posted 26 January 2018 - 07:04 PM

I have been doing a lot of observing, in lower than -10F temps as of late. For me I place the EP cap covers on, while still outside before bring them in ( sometimes I just leave the EP's outside, if I know I will be using them the next night), same goes for the OTA. Dust covers on outside, before bring it in.

#15 Tim Campbell

Tim Campbell

    Lift Off

  • -----
  • Posts: 15
  • Joined: 12 Mar 2011

Posted 26 January 2018 - 08:21 PM

I put the dust-caps on and I have a gear-case that holds my eyepieces, filters, and other bits of gear.  As long as you put them away while still in the cold-dry air, you can bring them inside and they’ll just slowly acclimate without moist air being able to get in and condense on cold surfaces.  


This is even true of my scope, cameras, etc.  Everythis is capped, covered, and put in cases before coming inside to warmer air that can hold more moisture.

#16 infamousnation


    Ranger 4

  • *****
  • Posts: 348
  • Joined: 10 May 2017
  • Loc: Woodstock IL

Posted 26 January 2018 - 09:50 PM

Small cloth bags are good for preventing condensation. The last ep I bought from explore scientific came with a nice one, and its waterproof so no need to worry at all. Putting the caps on also should do the trick.

#17 infamousnation


    Ranger 4

  • *****
  • Posts: 348
  • Joined: 10 May 2017
  • Loc: Woodstock IL

Posted 26 January 2018 - 09:54 PM

And obviously put your scope in the case outside, as soon as you take it off the mount.

#18 drneilmb


    Viking 1

  • *****
  • Posts: 911
  • Joined: 05 Jan 2017
  • Loc: Decorah, IA, USA

Posted 28 January 2018 - 04:48 PM

I too use the eyepiece caps put on outside before coming in. My epiphany recently was that when you're done observing and getting ready to go inside, you can just turn on the porch light! That makes it really easy to get all the right caps in the right place. :)

#19 Szumi


    Ranger 4

  • -----
  • Posts: 329
  • Joined: 01 Oct 2016
  • Loc: NLP, Michigan

Posted 28 January 2018 - 05:06 PM

My imaging equipment is a dslr and a telephoto lens.  If it is really cold I'll put it in a camera bag and bring it inside and then put a blanket over it.  I pull the flash card before I come inside.  Alternatively, I put it in the trunk of my car and bring it in later in the day.

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