Filter Cleaning Nightmare.

Is the dust staying in the same place or are you just seeing new dust every time you clean?

Gürkan Erkula · Aug 10, 2026, 04:04 PM

I am fairly new to astrophotograhy. My problem is with my filters. No matter how hard I tried, there would always be dust motes on them. Blowing, using special solutions (commercially available), using special dusters and cloths would not help at all. A guy proposed isopropyl alcohol bathing, but I am not sure about the technique of that and will it destroy the filter integrity over time? How do you clean your filters? Any suggestions will be welcome.

Thanks

How are you determining there is dust etc on the filter?

They might (for example) be on your sensor glass, depending on how you are coming to this conclusion ;)

I use a lens pen, old used airbrush compressor and old airbrush to clean my lens filters etc

As a start - as much as it will feel ‘funny’ to do so, make yourself a mini-clean room anytime you’re intending on doing filter cleaning. You want no dust in the air, because that will invariably end up on your clean filters.

go into the smallest bathroom in your house, block off any areas where air can enter the room (like the under-door gap) turn on the hot water and leave any exahust fans off. Allow the room to fill with steam, then turn off the hot water, and wait for the steam to settle.

Doing this will capture most of the dust in the room in the moisture of the steam, which will then settle to the ground. This is the best way to ensure the least possible dust in the air, and thus, the least possible contamination of the clean filters.

If, however, you’re realising that the dust stays in exactly the same place when you replace your filters, then it is far more likely that your dust is on your sensor window, or the sensor itself, or potentially on the corrector lens (if one is in use).

If you can show us all a flat frame, and provide details of the optical system, I can calculate the likely distance from the sensor that the dust exists in the light path, and by doing so, you can identify where the dust is based on how far it is from the sensor.

Alex Nicholas · Aug 11, 2026, 12:35 AM

As a start - as much as it will feel ‘funny’ to do so, make yourself a mini-clean room anytime you’re intending on doing filter cleaning. You want no dust in the air, because that will invariably end up on your clean filters.

go into the smallest bathroom in your house, block off any areas where air can enter the room (like the under-door gap) turn on the hot water and leave any exahust fans off. Allow the room to fill with steam, then turn off the hot water, and wait for the steam to settle.

Doing this will capture most of the dust in the room in the moisture of the steam, which will then settle to the ground. This is the best way to ensure the least possible dust in the air, and thus, the least possible contamination of the clean filters.

If, however, you’re realising that the dust stays in exactly the same place when you replace your filters, then it is far more likely that your dust is on your sensor window, or the sensor itself, or potentially on the corrector lens (if one is in use).

If you can show us all a flat frame, and provide details of the optical system, I can calculate the likely distance from the sensor that the dust exists in the light path, and by doing so, you can identify where the dust is based on how far it is from the sensor.

That is very interesting and scientific; I will definitely try that. I am much obliged.

In a perfect world every surface would be absolutely clean but as we all know, perfection is hard to achieve. Still, anything on an optical surface that shouldn’t be there is a loss. Light is scattered, diffraction is added and though you can fix the most horrendous cases of dust motes with flats, doing so has a cost. It’s a fine line and it’s up to you as to where that line is. It also depends on what you are doing. Your average deep sky image with a reasonably bright target is going to be less effected than if you are doing planetary or solar work where that last shred of contrast matters.

Dust motes are easy to rectify if its fresh dust as long as you keep a blower handy at all times, just blow right before you seal and inspect with a BRIGHT flashlight in a dark room. Once the dust goes through a couple humidity cycles it welds on there. Then it’s impossible to blow off.

First Id remove the filter glass from the housing/thread or whatever it’s on if you can, makes things a lot easier.

I have used IPA on a lot of things at this point, I have never had it kill a coating on a filter, but most of my filters are modern and hard coated. I have had it kill plastics when its pure and the last thing you want is it to dissolve some nearby plastic and then evaporate it onto the glass.

However, I agree with what others have posted with regards to soap and water. It’s usually pretty harmless. If I don’t want whatever im cleaning to get wet or absolutely need it to be immaculate, I have a technique for that with IPA.

The thing about water is it steaks, as does IPA or anything wet in my experience. Under a bright light, it really is hard to leave anything streak free.

But there is a solution to that if you are interested (it was groundbreaking for me).

I had tried every single product under the sun, including first contact polymer (do not use this near plastic or anything fuzzy, it’s a disaster) to get a streak free finish. It always, always left streaks. Only way I could get a clean finish was to wipe dry, and we are told to NEVER wipe dry because it’ll scratch the optics, but I did. Probably got away with more than I should.

One day I had to clean an irreplaceable $20,000 sensor. I had no other choice because of its condition and what I wanted to use it for. It was a nightmare surrounded by small exposed electrical components.

I had to get it things right with wet swabs on a single or close to single pass and I could not just keep swabbing, or dry swab the thing. There were no do overs.

I spent an entire day practicing with cleanroom swabs and kim wipes and a bottle of 99.99% IPA on a piece of black glass under a bright light. It was the purest cleaning solution I could create. And it STILL LEFT RESIDUE. No matter how pure, it always left residue.

Frustrated, I started trying to play with my technique, I blotted, I soaked, I went fast, nothing, then I went really slow, like 1mm a second slow. Even pressure.

I was absolutely blown away by the difference: the surface behind the swab, when I went slow, was absolute IMMACULATE.

You could hold a spotlight to the thing and wouldn’t show a single mote of dust or streak. In fact, that’s my standard now. I hold a spotlight to the thing. It’s the sort of test you don’t see people do often because most every product out there streaks… unless you go slow.

Turns out if you go slow, like really slow, it doesnt matter what purity of IPA you use, it comes out immaculate every time. Now I use Zeiss prepackaged wet wipes. They are cheap and always come clean.

My technique is:

Blow the surface free of what I can with a bulb. Blot it with a wet wipe to remove the big pieces of dust, then go again (if needed) with a new wipe lightly pushing what’s still there off to the side of the lens.

Finally, I take a cleanroom swab and wrap a fresh wipe around its end so there is a soft knife like edge. Press that edge lightly against your surface and try to get a swab thats bigger than the glass because the sides of the swab will leave a tiny amount of residue if they are smaller, as will any edge (like a lose end of the wipe)

I slowly (1mm a second) drag the swab from one end to the other. Immaculate. Every time.

Changed my life. I no longer fear cleaning the optics because when I do, I barely touch them. Well, except for diffraction gratings, those you never touch.

Tim Patton · Aug 11, 2026, 07:44 PM

I do agree with a lot of the recommendations, I found that while cleaning the filters I also clean the sensor window . I use Sensor cleaning Swabs and Pec Pads . The solution I use is Eclipse Optic Cleaning Fluid. I use a Rocket dust bulb as well. I also use a seldom used room with no airflow to cut down on the airborne dust. Let’s face it. No one way is perfect and after all of that you may still have a few dust motes. Since I change up my equipment every now and then it does allow for the collection of dust motes. At that point I clean it. I find some of the dust or pollen becomes hard to remove so it may take a few tries. Just don’t let it drive you crazy.

As a side note if you really want to go down the rabbit hole there is always this.

https://www.photoniccleaning.com/Store-s/101.htm

Thanks Tim; for the sensor, I use the Eclipse also. Not perfect, but gets the job done mostly. Thanks.

Question about the Astrodon filters, did the coatings flake off or visibly scratch? Or did they just change color?

I accidentally got too close to a first surface dielectric coating on an Astronomik on chip h-alpha filter for my Sony A7s.

I didn’t touch it, I just got a tiny patch of fog on it that condensed from my sweaty finger nearby. Tragic.

The smallest patch of fog stained it. It was noticeably a different color. It didn’t go away on its own and I thought there was no way I could clean it if fog stains it.

For 10 years it sat like that. Then this year I had this epiphany that maybe the coatings weren’t damaged at all. Perhaps whatever residue remained was changing the refractive index at the surface and therefore changing the passband/coating color.

so I did the IPA and swab trick I mentioned earlier. It’s now immaculate.

I’ve also now legitimately seen damaged coatings with scratches and others that flaked off.

Flaking ive only seen on very old optics. One case was a custom 1300nm shortpass filter that someone I knew deposited themselves long ago, not production quality. The other an old Tamron lens (very old!) and reportedly stored in a humid environment. Finally, some old germanium IR optics (probably 90’s or 80’s era).

So im not saying it’s impossible to damage coatings, especially old ones.

But if you have nothing to lose (I figured I didn’t) it might be worth the risk to investigate. I truly didn’t realize my coatings were fine for 10 years. Old school Astrodon filters are collectibles at this point.

Basic rules, never rub with anything, lens cloth, microfiber, lens pen, anything. Also, never use canned air even if you’re careful. Lastly, never blow on a surface even lightly with your breath. These are rules that a lot of use learned in the old chemical photography days when we were dealing with the first surface mirror found in all SLR’s.

Not really a cleaning tip but since suggestions are welcome... I'm pretty new to this myself and was struggling with the same thing for the first few months, until I caved and got an electronic filter wheel. The filters are all sealed inside now so once I cleaned them and put them in I haven't had to touch them again. Fingers crossed it stays that way.