How do you prevent fogging of eyepieces?

Hi

I have a somewhat newbie question here. In cold weather, typically, there is a lot of condensation whenever you exhale. So I end up fogging the eyepiece as I breath while observing. How do you prevent that? Crazy idea -- do you put some sort of a conical baffling on your nose to direct the humid air away from the eyepiece?

In fact, every time I hood myself, I need to hold my breath at the eyepiece, and I've noticed that this renders the views fainter because of the oxygen supply or something. Essentially, doesn't work.

Regards
Akarsh

In our climate here in the Appalachia it is a rare night - any time of the year - when one can observe without a big dew heater strip wrapped around the ocular and set to "medium" at least. Dew heater strips and controllers just live somewhere behind the seats in my car; I am not sure which ones I use at present (since it is only the dark) but the Canadian company Kendrick here across the border makes some reasonably well-made and reliable stuff that I think I prefer over others. They do eventually fail too though if you use them a lot. Even with a heater, if you don't want to completely bake your eyepiece (probably not advisable), I need to be considerate how I block the light from entering my eyes so as not to create a too humid microenvironment. Normally I only wear a eye patch on the other eye.

Hi Akarsh,

Along with Ivan's suggestion to use a dew heater strip on your eyepieces, I've found that exhaling through my mouth and directing the air down and to one side also helps minimize eyepiece fogging. It takes practice, but after awhile it becomes second nature. Along with that, covering the eyepiece with an end cap when not looking through it also helps reduce fogging. I use a neoprene beverage insulator sleeve that I put a couple of chemical hand warmers in to help keep the eye lends warm. It's a rare night indeed when my scope isn't covered with dew - or frost this time of year - and these measure work 90% of the time. When they fail, I resort to a small "hair dryer" device to warm up my eyepieces, like this one: http://tinyurl.com/yktjj55 . It's a temporary solution on a night wet enough to have to use it, but it does let you keep observing.

An alternative to the full-blown dew heater approach is to attach a chemical hand/toe warmer to the side of the eyepiece. If you're only combating breath fog, not heavy dew, a chemical warmer is likely to be sufficient. I used to deploy them for this purpose, but decided that training myself to exhale away from the eyepiece was a lot less trouble than fiddling with warmers.

Jim

I have to second the comments above. Its helps to breathe in a certain direction away from the eyepiece. It isn't foolproof, but it sure does help.

I also like to keep my eyepieces in the pockets of my vest. Keeping them there helps to keep them ever so slightly warmer. This won't guard against the wettest nights where everything is dripping wet. Only a real heater will help that. But for those nights where you get a little fog on the eye lens, some body warmth and careful breathing seems to help out.

Hi Akarsh,

this is a common problem when using a hood. My hood is open and very wide at the bottom. By breathing "downwards" the moist air is kept away from the eyepiece.

During very cold nights, the eyepieces may fog up even without using a hood. For those nights, I have a small insulated box equipped with two heatpacks (actually heated icepacs) where I keep the three to four eyepieces I use most.

I put the dew heater straps like from Orion Telescope on two favorite eyepieces (they oem them I am sure) .
Here in California I cannot say I get this much but generally many winter nights a year I have light dew and certainly fog from close eyeball or breath risk, rarely heavy dew.

Here is a warning: Inspect them from time to time, I had one short and spark and smoke which was 'rather exciting' as it was not fused and went right to 12V gell cell.

I have learned my lesson and all my 12V connections are fused these days.

My other eyepieces stay in the back of my van in my eyepiece box.

I have heated secondary and I have many times been 'last man standing' only to thank the secondary heater. That only strikes in winter here from October on to Feb and only gets bad enough to fog secondary maybe 2-3 nights a winter out of maybe 10 nights.

I also have a unique heated Telrad finder where I have wired it with 4 resistors that sit at the side of the glass and fire that up on dew risk nights. That too is a piece that will always due up and I hate those Telrad covers even though I have one, I prefer always ready telrad.

Mark

I don't use dew heater straps for my eyepieces. Years ago I switched over to the Pentax XW eyepieces. The XW's only fog up in the most extreme conditions.
And I keep my equipment such as books, eyepieces, atlases, computer, tablets etc. in a small observing tent.

As I do 97%+ of my observing from my backyard, I use a good old fashioned Connair 1600 plug-in hair dryer, run on an extension cord from the side of the house. Short blast on eyepiece(s) or secondary and I’m usually good for an hour or so. If your remote site has electric plugs at the pads, this is a possible solution. In a pinch, you can also try using your car heater to toast your eyepieces; if you’re lucky, you might only have to do this a couple of times a night; car has to be warmed up for a few minutes before the heater does any good. The chemical hand warmers are also a good solution.

I too use dew heaters. I live in Alabama and dew is a fact of life. However one other thing to consider, if you can observe somewhere with some elevation. With elevation here in Alabama usually means there is a breeze. A little wind helps with keeping dew at bay. Not sure what the science is behind it but it does work.

I used to use these battery type felt and nico. wire eyepiece heaters, but I gave up using them, it's just too much bother. I will leave an eyepiece cap on the finder eyepiece before it starts reaching dew point and replace the cap as soon as I am done using the finderscope. But I have rubber eyepiece guards on all my eyepieces for the main scopes which helps against dew. And I am also changing eyepieces of different focal lengths so often that dew doesn't get much time to accumulate. Another thing is I keep different FL ep that I will need in coat pockets which adds enough warmth that dewing is rarely a problem. I keep them sideways in the pockets to avoid touching a lens. Usually the only cleaning needed is some dust on the lenses. In the warmer months instead of a coat I will use a fly fishing vest instead with lots of pockets to keep eyepieces. It even has an extra large pocket I can keep my Barlow in.

I suggest the following:
1) When fogging or dewing is likely (high dew point and cold weather), remove the eyecups from your eyepieces. It will allow more air to circulate between the eyepiece and your warm, moist, eye.
2) If viewing with, say, the right eye, breathe through the left corner of your mouth and always blow away from the eyepiece when exhaling.
3) If fogging is really tough to avoid, rotate your head and view with your head at such an angle that the exhalation from the opposite corner of your mouth is at or above the eyepiece height (because warm air rises). Never, therefore, breathe through your nose or exhale UNDER the eyepiece--it will guarantee fogging.
4) Don't use an observing hood in the winter. It will just guarantee fogging.
5) If it's just a little fogging, wave your hand or mitten at the eyepiece to circulate some cold dry air around the lens and the fog will evaporate. If that fails, or it happens to be frost because of a high humidity, then a small 12V hair dryer will work. This isn't a bad thing to have handy, anyway, because many secondary mirrors are too close to the upper end of the UTA and may themselves dew up.

I can't see keeping eyepieces in a vest, because in cold weather that vest would be on the outside of 3 down parkas and my body wouldn't keep them warm at all. Plus, my eyepieces weigh at least 12-13 lbs, and I can't see keeping that much weight in pockets.

Quote:

---

Originally Posted by Don Pensack

I suggest the following:
4) Don't use an observing hood in the winter. It will just guarantee fogging.

---

Using a hood in winter is just fine. I do it all the time. Takes a little practice but using a hood doesn't necessarily guarantee your eyepieces fogging over. Besides, just the heat of your eye and face can be enough to fog things over. What do you do then? Not observe?

The trick is to keep the eyepieces warm just enough and there are options to do that.

Quote:

---

Originally Posted by Don Pensack

I can't see keeping eyepieces in a vest, because in cold weather that vest would be on the outside of 3 down parkas and my body wouldn't keep them warm at all. Plus, my eyepieces weigh at least 12-13 lbs, and I can't see keeping that much weight in pockets.

---

The stitching can handle it just fine so don't get hung up on weight. You're only placing one eyepiece in one pocket at a time (I would hope). The heaviest Televue EP (21E) is 2.25 pounds. That's well within reason for a pocket to handle. Its a static load so there is no issue whatsoever. With 3000 vests in the field, we have yet to have a stitching fail. Not one. That should say something. Load em up. Just don't do any handstands and you'll be fine.

Depending on air temperature, I'll sometimes where my vest underneath my outer garment. There is plenty of body heat to keep all your eyepieces toasty. Yes you have to zip and unzip each time but that's a small sacrifice pay to ensure warm eyepieces.

If that isn't to your liking, a handwarmer in the bottom of each pocket is plenty to help keep things warm.

Just takes some forethought to ensure fog free eyepieces.

Perhaps I should have said, "It will just guarantee fogging if your eyepieces aren't heated. Not allowing heat from your face, breath, and warm moist eye to fog the eyepiece usually, in my experience, requires allowing ventilation between the eyepiece and your eye and that is the opposite of a hood that extends forward on either side of the eyepiece. I very rarely ever observe at a place that is warm enough at night to allow the use of a black cloth over the head or an observer's hood. With either, one breath would cause instant fogging of a cold eyepiece. I don't have a problem with fogging because I don't breathe on the eyepieces and I have sufficient eye relief that my eye doesn't cause fogging.

I have used an occasional eyepiece that required complete blockage of peripheral light to prevent visible reflections off the eye lens (one example: 9mm 120 degree ES). A hood or black cloth would work great on an eyepiece like that (easier than cupping one's hands on either side), but I would expect the eyepiece to fog up. You can always use heater cords on the eyepieces, but I prefer not to do that. I'm fortunate enough to observe in arid, non-humid, environments.

An observer's vest to hold eyepieces sounds just great, but I have about 12+ pounds of eyepieces and PowerMate in my case, and I just couldn't see carrying that in pockets, even if the stitching were strong enough. But, then again, I don't use a ladder with my scope. A vest for eyepieces would be quite practical in that environment.

A winter coat with lined pockets has always kept my ep's and barlow from fogging. In summer a fly fisherman's vest is enough to prevent fogging. I am usually only using three 1 1/4" eps and a barlow which fit fine in either vest or coat pockets. Each ep and barlow has its own individual pocket. If dew or frost seems to be coming on I will cover the finders eyepiece and the main eyepiece with caps. Once I was showing a pair of galaxies to a couple of other people and I think one of them breathed on the eyepiece. I was using one of these Thermocell's (which in my opinion are worthless for bugs), but it provided enough heat that when I held it close to the fogged eyepiece for a moment it did the job and no more fogging.