What do folks do to stop their breathe fogging eye pieces whilst observing?

[g__day (Matthew)]

I have been away from visual astronomy for a while now, but with the purchase of some APOs recently I have delighted to return to some visual enjoyment at the scope. I'd forgotten a problem that use to annoy me - my own breathe I supposed fogging up the eye piece whilst I am observing.

Whilst I was observing Saturn - I noticed a light fog form on the centre of the eyepiece after I had placed my eye near it and commenced viewing for a few seconds. If I moved away from the eye piece the fog would evapourate after 10 - 20 seconds. So I imagine this is water vapour coming from my breathe, traveling around my face and body and some condensing on the eyepiece lens.

I could wear a scarf - to try and trap my breathe - but does anyone else have this challenge and how do they best solve it?

Many thanks,

Matthew

[Steffen]

I suppose an eyepiece dew heater would help, but I haven't got one, so it's scarf/balaclava for me.

Cheers
Steffen.

[Ric]

Hi Matthew

I usually find a scarf works quite well.

[MattT]

Towel for me, never thought about a balaclava, good idea Steffen.

[AG Hybrid (Adrian)]

Put the fogged up eyepieces in your pants pockets. The warmth of your pants clears the fog up fast. Repeat as necessary.

[ZeroID (Brent)]

Originally Posted by AG Hybrid

Put the fogged up eyepieces in your pants pockets. The warmth of your pants clears the fog up fast. Repeat as necessary.

The view becomes quite restrictive I find, no stars in ya pockets .... to my knowledge.

It's not even necessarily your breathe that does it, just the wetness of your eye can be sufficient to create a small vapour cloud which fogs it. Pocket is best, keep your pockets clean to prevent dust 'n dirt contamination.

[Steffen]

Originally Posted by ZeroID

The view becomes quite restrictive I find, no stars in ya pockets .... to my knowledge.

Is that an Ethos in your pocket, or are you just happy to see me?

Cheers
Steffen.

[Wavytone]

Originally Posted by g__day

I noticed a light fog form on the centre of the eyepiece after I had placed my eye near it and commenced viewing for a few seconds. If I moved away from the eye piece the fog would evapourate

Nothing to do with breath, or heavy breathing.

Your eye is warm, the eye lens is cooler.

The water at the surface of your eye (it's wet, remember) evaporates and, close to the eyepiece, this water vapour in close proximity to the eyelens has a relative humidity that exceeds the level sustainable at the temperature of the eyepiece. The result is that it condenses on the eye lens, forming the fog you saw. As you move away from the eyepiece the surrounding air has lower humidity and the fog thus evaporates off the eyepiece back into the air.

The easiest solution is to keep the eyepiece warm, e.g. use a heatpad around the eyepiece to keep it warm, or warm it beforehand in an inside jacket pocket, or to use a heated eyepiece case, or blowing warm air on it (hair dryer).

Another solution is to wear spectacles (which i do most of the time). Awkward, but they prevent this happening.

[Nico13 (Ken)]

A small dew heater strap is what I use on a very low setting as it only needs to raise the temp just above the dew point so it doesn't need much. Just runs on the 12v at the scope. Mine is all home made and costs very little.

[niko]

what's an eyepiece?

[multiweb (Marc)]

Originally Posted by g__day

I could wear a scarf - to try and trap my breathe - but does anyone else have this challenge and how do they best solve it?

Bintel mouth wash solution
Seriously do you use any dew heater around the eyepiece. That should do it. If the glass is warm breathing on it shouldn't matter as much.

[Weltevreden SA (Dana)]

Hi everybody . . . I live in a semi-desert region that even so has moist air from distant cold ocean currents. Dewing is frequent and quick. I bought a small card table, on which I first put a heavy dark blue bath towel twice the size of the table. On top of the towel I lay a single-bed electric blanket, also about twice the size of the table. The electric blanket is pale creme like most such items. I position the long end the towel-under-blanket combo so it folds over and completely covers the table with a pocket in the middle, The dark towel is now on top so you can't even see the table under dark conditions. You can't believe what a night-vision wrecker a large expanse of pale creme can be. I put all my equipment in between the folded-over blanket—eyepieces, laser pointers, Telrad, and charts. Medium is the best setting to keep everything warm while adding no local thermal plume. By the time the scopes are set up, everything under the blanket is slightly warm to the touch. The only items not under the blanket are the ones I'm actually using. Take a bit of extra time when switching eyepieces, but they never dew. Every time a laser pointer goes flat, I switch it for a warm one. My hands go under there as well when the fingers get stiff. Only real drawback is my cat, who thinks a warm dark fuzzy table is the greatest idea in the world as a mouse-spotting platform.

[CJ (Chris)]

Originally Posted by Weltevreden SA

You can't believe what a night-vision wrecker a large expanse of pale creme can be.

I've often wondered, for the same reason, why so many scopes are white.

[andyc (Andy)]

An interesting question (dew in general) after a I had dewy night at the ASV Heathcote site last night (otherwise absolutely perfect conditions towards and after moonset). I don't have very expensive eyepieces, so I didn't feel too concerned about keeping my main eyepieces in my pockets, swapping them in and out as needed. Saves touching the elemets too much, and very effective if your pockets are not too dusty. The cheap 30mm finder was dewing up every 5 mins but that just got a wipe with loo roll.

The main scope optics survived pretty well, but the secondary finally succumbed after about 2 hours. As there was nobody else at the site that night (lights would be an issue if others were there), I took the secondary housing off the scope, put in in the car , started the engine and warmed the whole housing up with the blowers. 10 minutes later, my secondary was back in working order! I had to do that once more in a 5 hour session. The primary finally succumbed to dew about 3:30am, which was probbly as well because I needed to get to bed, but conditions were just too good! Whether it was the extra shielding from open sky afforded by the light shroud, or whether running the cooling fan much of the session was what kept the primary from dewing, I'm still not quite sure. My money's on the fan helping a bit, but not sure how the thermodynamics go for that one as the fan is on the back of the mirror!

Until I get really precious bits of glass (ie naglers or whatever), I think the pockets idea works pretty well.

[Gem (Grant)]

Originally Posted by CJ

I've often wondered, for the same reason, why so many scopes are white.

Because they are expensive to knock over???

[mental4astro (Alexander)]

I too have an EP dew heater strap on my big scope. But I don't rely on this small bit of kit to warm my eyepieces. I give the strap a head start by keeping my EPs warm. Some folks make themselves electrically heated cases. Me, my solution isn't so high tech. My EP warmer is a hot water bottle placed over my EPs with a big fat towel over the whole lot. The case too is heavily lined with a thick amount of foam to help insulate.

To me is seems counter productive to expect a heater strap to warm a 1kg lump of glass when it is at an ambient temperature of 0deg. I suggest that the best way to keep your EPs from fogging up is to have them warm from the start. A heater strap then just maintains the heat gradient from dropping too far. Heating straps are designed to stop DEW forming, not from being fogged up by our breath.

In the field, when I find I'm swapping between EPs, my pockets are most convenient. Selecting a new jacket is a pain to find one with pockets that are both sufficiently lined and large enough. On occasions I can find four large EPs knocking around in my pockets until I settle on the one I'll use for the next while. I then pop the loose EPs back in the heated case.

I'm not too high tech minded with my approach to astro. It's my escape from high tech. To power my half dozen heater straps I now tow along two car batteries. I've found out the hard way that the worst enemy of batteries that are used to keep our gear warm is the very cold itself. My lesson was learnt when I found my secondary mirror had frosted over even though by my calculations the battery I had powering the heating straps should have not run out of juice until well after sunrise - five hours away from when the secondary was frosted. Thus the reason for the two batteries now. But I'm also trying to work out a small portable insulated case to keep the batteries in when out in the field so I don't need to pull out the reserve until I stuff up somehow else.

[dannat (Daniel)]

one of the cheap iso-thermic heat pack hand warmers works well without need for power -some are re-usable after boiling - or settling
get them from camp stores or big pharmacy