<p>Since you haven't mentioned what eyepiece you are using, I will go with the common scenario. Fog, fungus or dirt on outer part of the lens are easy to clean, air then a brush or a microfiber cloth is enough to do some good job. While getting inside of eyepiece, most eyepieces come with screw type lens mount, you can find some grooves in the eyepiece's lens mount that will help you figure out whether you can remove the lens to clean. You can distinguish between &quot;fog&quot; (haze) and fungus, fungus usually appear like small &quot;streaks&quot; or &quot;scratches&quot; or a patch in a particular area, where as in haze the eyepiece would become translucent. Haze is caused by several reasons. Best way to clean optics of eyepieces is to use some compressed air, then take a microfiber cloth give the lenses a little clean then clean the lenses with solution of distilled water and isopropyl alcohol (100%) with 1:2 concentration respectively, this solution do not erode any of the coatings on the eyepiece. (note: only a drop on the microfiber cloth, in case if your eyepiece lenses are plastic, use only distilled water to clean). I don't recommend using brush for inner part of the lens.</p>
<p>In case if you need help in removing the eyepiece. Here is a demo what to do</p>
<p>Take your lens. here I marked the barrel</p>
<p><a href="https://i.sstatic.net/YlaW5m.jpg" rel="noreferrer"><img src="https://i.sstatic.net/YlaW5m.jpg" alt="enter image description here" /></a></p>
<p>Mostly you will be able to unscrew the barrel or the barrel will be held by two clips. after removing it. you will see two grooves to unscrew the mount to remove one of the two lenses in the eyepiece. I have marked the two grooves in the picture below.</p>
<p><a href="https://i.sstatic.net/hU2Mem.jpg" rel="noreferrer"><img src="https://i.sstatic.net/hU2Mem.jpg" alt="enter image description here" /></a></p>
<p><a href="https://i.sstatic.net/CUCwxm.jpg" rel="noreferrer"><img src="https://i.sstatic.net/CUCwxm.jpg" alt="enter image description here" /></a></p>
<p>Then keep the lens on your palm  (will the opening tightly closed) a little bit of shake will get the lens(es) detached from the assembly</p>
<p><a href="https://i.sstatic.net/QOik5m.jpg" rel="noreferrer"><img src="https://i.sstatic.net/QOik5m.jpg" alt="enter image description here" /></a></p>
<p>you will get the lens in hand for better cleaning. The ring next to the lens is used to separate the two lenses. Not all eyepieces have this. (Please keep the lenses on a soft towel even when cleaning, I don't don't keep it on other surfaces, I have kept it on my laptop's palm rest since I don't have soft towel right now)</p>
<p>In case if you the top lens doesn't detach, then you can use a brush and an earbud with drop of the solution</p>

CC BY-SA 4.0
2022-06-01T05:54:30.900Z
2022-06-01T06:45:49.307Z
2022-06-01T06:45:49.307Z
Kavin Ishwaran
<p>I wonder if you're seeing condensation?</p>
<p>I ride a bike and wear glasses. In winter there's frequently fog issues when warm breathy air hits a cold lens surface, or a warm surface goes into a cold environment.</p>
<p>Is it possible your kit is not acclimated to the ambient temperature?</p>

CC BY-SA 4.0
2022-05-31T05:27:37.003Z
2022-05-31T05:27:37.003Z
Criggie
<p>I'm wondering what the procedure would be to clean the eyepiece of a telescope when it looks foggy or there's dirt either on the outside or inside it.</p>
<p>I can get rid of loose dirt with a camel hair brush or air. But how can I clear foggy eypieces?
Or what should I do if somehow anything got into the eyepiece?</p>

CC BY-SA 4.0
2022-05-25T15:15:53.330Z
Can you post a photo of the eyepiece? How old is it? "Foggy" could be fungal growth, or maybe the coatings have disintegrated, or maybe even condensation (unlikely). When I clean my eyepieces I first use air, then a brush, and finally the Baader "Optical Wonder" lens cleaner on a cloth.
Aaron F
CC BY-SA 4.0
2022-05-25T16:56:20.383Z
@AaronF OK thanks. It's not really the case for my eyepiece, I was just wondering what I should do if it were to be. It's related to another question I posted (that my telescope looks blurry for some eyepieces) and people said it could be that the eyepieces dirty/foggy. But I don't think that's the case. But someone asked me anyways to ask that question seperately (how to clean an eyepiece).
299792458
CC BY-SA 4.0
2022-05-25T18:15:03.777Z
ah I see, it's this one: https://astronomy.stackexchange.com/questions/49410/telescopes-eyepieces-got-blurry-over-time 
As well as checking the collimation, another thing to check is the 'seeing': https://www.meteoblue.com/en/weather/outdoorsports/seeing/ 
If the value for seeing (in arc seconds) at your location is too high (over ~1.5) then things won't appear sharp. Try again when the seeing is <1.0.
Aaron F
CC BY-SA 4.0
2022-05-27T00:43:21.560Z
@299792458 If you've had some success (or not) please feel free to leave an informative answer.
uhoh
CC BY-SA 4.0
2022-05-27T16:11:24.450Z
The cleaning method is going to rely quite heavily on what's causing the "fog".  Trying to detemine what it is and a method of removing it without affecting the coatings on the lens would likely cost more than the eyepiece.  We had some success using an ultrasonic cleaner, but not 100%, and not really cost effective if you don't have one already.  Unless it's a really pricey eyepiece, I think your best bet is to grab a cloth and hope for the best.
Greg Miller
<telescope><amateur-observing><eyepiece>
How do you clean a foggy or dirty eyepiece of a telescope?
299792458
# How do you clean a foggy or dirty eyepiece of a telescope?

(Asked by: username_0 on 2022-05-24)

I'm wondering what the procedure would be to clean the eyepiece of a telescope when it looks foggy or there's dirt either on the outside or inside it.

I can get rid of loose dirt with a camel hair brush or air. But how can I clear foggy eypieces?
Or what should I do if somehow anything got into the eyepiece?

**Tags:** telescope, amateur-observing, eyepiece
> **Comments:**
> **username_1**: Can you post a photo of the eyepiece? How old is it? "Foggy" could be fungal growth, or maybe the coatings have disintegrated, or maybe even condensation (unlikely). When I clean my eyepieces I first use air, then a brush, and finally the Baader "Optical Wonder" lens cleaner on a cloth.  
> **username_0**: @AaronF OK thanks. It's not really the case for my eyepiece, I was just wondering what I should do if it were to be. It's related to another question I posted (that my telescope looks blurry for some eyepieces) and people said it could be that the eyepieces dirty/foggy. But I don't think that's the case. But someone asked me anyways to ask that question seperately (how to clean an eyepiece).  
> **username_1**: ah I see, it's this one: https://astronomy.stackexchange.com/questions/49410/telescopes-eyepieces-got-blurry-over-time  As well as checking the collimation, another thing to check is the 'seeing': https://www.meteoblue.com/en/weather/outdoorsports/seeing/  If the value for seeing (in arc seconds) at your location is too high (over ~1.5) then things won't appear sharp. Try again when the seeing is <1.0.  
> **username_2**: @299792458 If you've had some success (or not) please feel free to leave an informative answer.  
> **username_3**: The cleaning method is going to rely quite heavily on what's causing the "fog".  Trying to detemine what it is and a method of removing it without affecting the coatings on the lens would likely cost more than the eyepiece.  We had some success using an ultrasonic cleaner, but not 100%, and not really cost effective if you don't have one already.  Unless it's a really pricey eyepiece, I think your best bet is to grab a cloth and hope for the best.  

---

## 2 answers

### Answer by username_4 on 2022-06-01. Score: 5

Since you haven't mentioned what eyepiece you are using, I will go with the common scenario. Fog, fungus or dirt on outer part of the lens are easy to clean, air then a brush or a microfiber cloth is enough to do some good job. While getting inside of eyepiece, most eyepieces come with screw type lens mount, you can find some grooves in the eyepiece's lens mount that will help you figure out whether you can remove the lens to clean. You can distinguish between "fog" (haze) and fungus, fungus usually appear like small "streaks" or "scratches" or a patch in a particular area, where as in haze the eyepiece would become translucent. Haze is caused by several reasons. Best way to clean optics of eyepieces is to use some compressed air, then take a microfiber cloth give the lenses a little clean then clean the lenses with solution of distilled water and isopropyl alcohol (100%) with 1:2 concentration respectively, this solution do not erode any of the coatings on the eyepiece. (note: only a drop on the microfiber cloth, in case if your eyepiece lenses are plastic, use only distilled water to clean). I don't recommend using brush for inner part of the lens.

In case if you need help in removing the eyepiece. Here is a demo what to do

Take your lens. here I marked the barrel

[![enter image description here](https://i.sstatic.net/YlaW5m.jpg)](https://i.sstatic.net/YlaW5m.jpg)

Mostly you will be able to unscrew the barrel or the barrel will be held by two clips. after removing it. you will see two grooves to unscrew the mount to remove one of the two lenses in the eyepiece. I have marked the two grooves in the picture below.

[![enter image description here](https://i.sstatic.net/hU2Mem.jpg)](https://i.sstatic.net/hU2Mem.jpg)

[![enter image description here](https://i.sstatic.net/CUCwxm.jpg)](https://i.sstatic.net/CUCwxm.jpg)

Then keep the lens on your palm (will the opening tightly closed) a little bit of shake will get the lens(es) detached from the assembly

[![enter image description here](https://i.sstatic.net/QOik5m.jpg)](https://i.sstatic.net/QOik5m.jpg)

you will get the lens in hand for better cleaning. The ring next to the lens is used to separate the two lenses. Not all eyepieces have this. (Please keep the lenses on a soft towel even when cleaning, I don't don't keep it on other surfaces, I have kept it on my laptop's palm rest since I don't have soft towel right now)

In case if you the top lens doesn't detach, then you can use a brush and an earbud with drop of the solution


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### Answer by username_5 on 2022-05-31. Score: 0

I wonder if you're seeing condensation?

I ride a bike and wear glasses. In winter there's frequently fog issues when warm breathy air hits a cold lens surface, or a warm surface goes into a cold environment.

Is it possible your kit is not acclimated to the ambient temperature?


---

