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Eyepieces fogging up.

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#1 ColdFront


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Posted 28 November 2010 - 01:24 PM

Greetings. I've been having problems with my ep's fogging up.

I'm using 12" Lightbridge, TMB Planetary 8, generic 17mm 65fov.
The scope also has an Astrozap light shield, and secondary dew heater.
I'm setting up outdoors in sub freezing temps. I keep the scope and ep's in an unheated garage (about 10 degrees last week)
I set scope out for at least an hour b4 viewing. Is the fogging normal, or am I missing something to prevent it?

Any help appreciated.

#2 FLYcrash



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Posted 28 November 2010 - 01:26 PM

Welcome, Derek! :)

Try keeping the eyepieces inside the house where it's warm and keeping them in your pockets when they aren't in the focuser. If the EPs stay warmer than the ambient air, they will fog/frost over less.

#3 hfjacinto


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Posted 28 November 2010 - 01:27 PM

When its cold the EP's tend to fog up. I use a dew heater strip turned up all the way, that helps a lot. Shorter Eye Relief ep's are really bad for fogging up.

#4 johnnyha


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Posted 28 November 2010 - 02:01 PM

Fold down the rubber eyeguard that helps a lot. Back away from the EP and wave your gloves around, a little circulation of air will usually do the trick. I'll take the EP out and wave it around sometimes. Be aware of where your breathe is when viewing, keep it away from the eyepiece if you can.

#5 dan_h



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Posted 28 November 2010 - 02:11 PM

It is almost human nature to exhale as you settle in and approach the eyepiece with your eye. It is all part of the get relaxed and get ready to view ritual. You can learn not to exale as you approach the eyepiece in the focuser. For some folks this takes more learning. Some take to it easily.

Eyepieces with tight eye relief, and binoculars, will fog up just because your eye is so close to them when viewing. These require that the eyepieces be kept warm before use and while in the focuser. You can get heater strips just the right size for your eyepieces. They work.


#6 UmaDog



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Posted 28 November 2010 - 02:27 PM

Keeping the eyepieces in a box when not in use helps. The cool very quickly when left on the holder attached to the Dob's base.

#7 ColdFront


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Posted 28 November 2010 - 02:34 PM

Thank all Of You who replied. I was assuming one had to keep ep's cold. (Doh!) I was aware of breath and was wearing a scarf. I'm sure that keeping the ep's warm will do the trick.


#8 blb



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Posted 28 November 2010 - 02:55 PM

Yes, I usualy only use three eyepieces when observing. I keep one in each coat pocket and the other one on the telescope. All the rest stay in the eyepiece box. Humidity from your breath is a problem you must watch out for but getting to close with your eye can fog up the eyepiece also. Changing out the eyepieces for different magnifications, when I take them from my pockets, seems to be the hot ticket. When I do that every once in a while they do not fog up unless I breath on them.

#9 Doc Bob

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Posted 28 November 2010 - 03:58 PM

Hi Derek,
I discovered that breathing was a major problem for me during our "cold" (not nearly as cold as your area!!) nights - I needed to be exhaling in some other direction than onto the eyepiece; so I started to exhale downwards (towards my chin) through pursed lips, and avoiding any bundling against the cold that would redirect warm, moist breath onto the eyepiece. This seems to work for a while . . . but then there's the radiant heat from our eyes, lids, cheeks, etc. Haven't figured that one out yet but long eye relief eyepieces do tend not to fog-up quite so fast, at least for me.

Like Buddy I only use a couple of eyepieces during the coldest months, and I keep them in a vest pocket to keep warm . . . this; however is a little tough when using Axiom LX or equivalently large & heavy equipment.

Best of viewing,

#10 FerK


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Posted 28 November 2010 - 04:08 PM

In cold nights I wear a neck tube and a beanie. Keeps my balding head, face and neck warm, and the tube absorb my breath. It also holds some of that facial warmth from further fogging the EPs I guess. Never really thought about that.

I also like many people posted here prefer to keep the EP in my pockets. It's not only to keep them warmer, but also because I don't like to fumble in the dark, trying to find out which one's which. I keep my (only) 2" in the holder when not in use (it's the 30mm that came with the scope), whatever 1.25" is in the focuser, and one 1.25" EP in each pocket. That way I know exactly what I have where, and most of them stay warm.

#11 Radiostar


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Posted 28 November 2010 - 07:47 PM

A handwarmer in the pocket with the eyepiece certainly helps. Another one gets thrown into the case. And one for the hand controller too.
Eddy B

#12 ColdFront


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Posted 28 November 2010 - 08:01 PM

Great idea on the hand warmers! Thanks Eddy!
I just got in from a quick looksee. Bringing a warm ep from the house straight to the scope worked perfectly.
I can't believe that didn't dawn on me!! I guess I figured I needed to cool down ep's just like my scope.


#13 sixela


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Posted 29 November 2010 - 12:55 PM

Is the fogging normal, or am I missing something to prevent it?

Rule #1: never expose the lenses at either end to the night sky. Those eyepiece racks that they sometimes include on Dobsonian rocker boxes look like a good idea, but they're not unless you put the caps on the eyepieces.

#14 hbanich



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Posted 29 November 2010 - 01:04 PM

One more technique to keep your eyepieces from fogging over is to keep them covered while you're not looking through them, like when you're writing notes or checking your charts. I've used a spare wool cap, a thick sock and a neoprene coffee mug sleeve to good effect. I'll reinforce that keeping eyepieces in your pocket (or an eyepiece vest) with a handwarmer works quite nicely. Even so, there are nights when having an hair dryer really comes in handy.

#15 mountain monk

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Posted 29 November 2010 - 01:19 PM

Tactics here at down to-20 below zero:

Lenses in clean pockets
Old, well-washed towel over lens when not in use--enough weight not to blow off
Hot water bottle (cheap/pink) or a chemical hand warmer in lens case
Dew buster and Firefly straps

...in some combination. Whatever works.

Good luck

Dark skies


#16 Matt2003



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Posted 29 November 2010 - 01:55 PM

I learned to be aware of my breathing last year, when EPs fogging up constantly ended several viewing sessions.
I also encountered this in early Fall, when Dewpoints were still high. I have yet to find a good solution to it, except to keep caps on the ones not in use..
I do control my breathing at the scope these days, and leave the EP kit inside when the OT is outside cooling down..

Clear Skies,

#17 condensermike



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Posted 17 November 2012 - 01:29 AM

Thanks to everyone who posted on here. Great info for a newbie like me.

#18 Achernar



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Posted 17 November 2012 - 10:14 AM

I use heater strips on my eyepieces because otherwise they will fog up here in coastal Alabama. Also, I keep my case closed and when it's very dewy, I put one of those heat packs in the case. That keeps the interior warm and thus discourages dewing inside the case. Putting the eyepices in your pockets helps too, as long as there is nothing else that can scratch the lenses in your pockets.


#19 mich_al



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Posted 17 November 2012 - 02:20 PM

Something I'm just trying out : A bag of raw rice, heated in the microwave for a minute or two, in the EP case. Actually double zip lock bagged in case of a spill. It's quite a bit of thermal mass and lasts quite a while. Like I said I'm just experimenting with it and there are things to learn, no doubt.


#20 spongebob@55



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Posted 19 November 2012 - 11:23 PM

What kind of hand warmers are you guys talking about? I've tried those chemical toe warmers in my pockets and they're now warm enough or my pockets are not thick enough.

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