Cleaning Techniques for Optics 

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     Also: Fungus and/or Mildew Removal from Primary and Corrector --2 Parts


Subject: Lens Cleaning Solution Formula by Dr. Clay Sherrod  Top

From: John Duchek <> Date: June 2005

For cleaning your refractive glass and eyepieces, the best reference I have seen is by Dr. Clay Sherrod.
See: <>

He is a professional astronomer who has devised a cleaning system that he discusses (and uses when doing his telescope tune up) and tells you how to make it on his site. I am an organic chemist and found it so effective that I started making it and selling it: <>. There are a couple of other companies that also sell his formula and his style of glass wipes.

I would recommend that you go to the Arkansas Sky Observatory site (link above) and read the article (I can send you a pdf version if you have problems). Then either make your own or buy somebody's. As a chemist I say, Don't use turpentine and don't use windex (a small amount is in Dr.Sherrod's formula, but the pH is held at 8. Any higher and you will start to degrade coatings. Turpentine is distilled, but is a witch's brew of compounds. Batches from different areas and sources will not be consistent, and there are organic components that can hurt your glass.


Subject: Cleaning the Mirrors of the LX200 --part 1 of 5  Top

From: Randy Marsden <>

----- Original Message -----
From: Christian Molnar:
It seems that, as long as you don't grab a sledgehammer and pound it
because it won't come off, it has marks for aligning and, if you treat
it nicely, which in my case it would just be blowing the primary and
secondary with my compressor from a distance until the couple of
particles come off, I shouldn't even have to re-collimate.

Christian, I have pulled off my corrector to clean it and to do minor improvements to the secondary holder. Removing and replacing the secondary, carefully, has had no ill effects on my scope.

However, I caution you not to use air from an air compressor, even from a distance. Unless your compressor has a very sophisticated water vapor, oil droplet, and dust filter system, you are likely to spray under high pressure water, dirt and oil onto your primary and do more harm than good. Use only 'canned air' made for cleaning optics in conjunction with a soft brush explicitly made for cleaning fine optics - use the brush only if the particle is not removed by the air. You can obtain these products from most fine camera stores.


Subject: Cleaning the Mirrors of the LX200 --part 2

From: Bruce Johnston

I have a place on my website where I take the first-time person through how to remove the corrector from his/her SCT, and it just might help you in your first attempt at removing the corrector. (Especially if you've heard horror stories about how difficult it can be <g>). You might want to visit the site, just in case.

You'll find it at: <>

As a side point, if you're going to be cleaning the primary mirror ... it doesn't say if you're talking about the primary or just the secondary... I'd recommend that you completely remove it from the OTA instead of trying to clean it while still inside. This may seem obvious to most people, but it wasn't to me the first time I did it. The result was, I turned a small spot into a much larger spot... and also got enough extra moisture into the OTA that after it was all closed back up, the primary would regularly dew up!


Subject: Cleaning the Mirrors of the LX200 --part 3  Top

From: John Mahony <>

Go to: <>.

Instructions straight out of the LX200 manual for how to remove the corrector plate (Appendix E, at the end of section 1. The orientation is important, but not nearly as critical as some make it out to be.

And even the canned air has hazards (spitting liquid, etc.). I use it frequently for smaller optics, but a safer alternative is a bulb syringe.


Subject: Cleaning the Mirrors of the LX200 --part 4

From: Richard Emerson <>

There are alcohols with oil of wintergreen added for scent. At least in this area (Phila, PA), they're the predominant type found on drug store shelves. Finding simple, dilute alcohol took three tries the last time I went shopping for alcohol. Maybe the scent doesn't hurt optics but why bet your lenses on finding out the answer to that question?

You wrote:
>I've used both 70% and 91% successfully.
>I think the concern about alcohol with additives is over-rated. Someone
>posted on one of these lists a year or so ago about that. I can
>understand why a rubbing alcohol manufacturer might want to put
>moisturizers in it, but I've never seen it. The only alcohol I see is
>straight pharmacy quality alcohol, the stuff in the generic-looking bottles.


Subject: Cleaning the Mirrors of the LX200 --part 5 of 5  Top

From: Rod Mollise <>

Joe Shuster writes: You mentioned original blue Windex and Clay Sherrod and others have, too. All I can find is "Original Windex with Ammonia". That's an ambiguous description. Does it mean "Original Windex with its original ingredient Ammonia"? Or does it mean "Original Windex with its new ingredient Ammonia?"

Hi Joe: My bottle, a fresh one just purchased and already used on a scope, says: "Windex Original, Streak Free Shine! Glass Cleaner with Ammonia D"

Windex, I believe has had ammonia (or "Ammonia D," whatever the fitz that is, and which I remember hearing in their commercials back in the 1960s! ;-)) in it since day one, and, at least in the concentration used in this product, seems completely benign for use with Celestron's Starbright and Meade's MCOG coatings. I can't speak for the Meade UHTC or Celestron's new coatings. That does not mean Windex would be harmful to them, just that I haven't tested it on them, and that I have not heard of others doing so either.

What would I avoid? Any of the non-blue Windexes. I don't know that they would be harmful, but why fool with something that's had some kind of funky scent added for no reason?


Submitted by various authors--  Top

Subject: Cleaning Optics 

I don't recomend cleaning optics that are gasketed, with anything other than distilled water with *2* drops of Dawn detergent to a quart of the distilled water, in a spray bottle. Using sterile cotton, push the soap/water in circular motions, flush with distilled water liberaly, dry with the sterile cotton, then buff with your breath and Klenex brand *Softique non-scented* tisues, by rolling one up and wrapping another around it to make a pillow.

I've never had as good luck with alcohol, just too "sleeky" for my taste.


I used tap water/methyl hydrate/tapwater/distilled water just yesterday to clean a very dirty corrector plate and it came out as clean as when new. Your idea, Colin, to chase the drops away with an air can worked beautifully. That last part (getting rid of the last few drops of water) has always been a problem.


Subject: Cleaning Optics  Top

From: Steve Berganini <>

Barry, I have recently had the same problem, but only on the outside surface. Seems everything I tried on my LX50 10" corrector left smears and smudges. But, I found the solution. You'll need 98% pure isopropyl alcohol (not the 70% or 90% variety). You can get it at your pharmacy. Also, pure 100% cotton balls and distilled water. Use a combination of half alcohol, half water, moisten a cotton ball and very softly sweep from the center to the edge of the corrector plate and IMMEDIATELY follow the sweep with a dry cotton ball.

You may have to work your way around the surface more than once, but the result is a completely immaculate surface with no residual stains or marks. By the way, this solution is also great for cleaning dirty eyepiece lense surfaces.


Subject: Cleaning Optics/Filters  Top

From: Colin Haig <>

In short, you can clean anything that is not reactive, petrochemical in original, or (generally) anything that is not organic. So, stuff like glass, aluminum, silver, Magnesium Fluoride, SiO2, etc. is generally no problem - all inorganic chemicals. Beware of specialty filters (gels, wratten, etc.), plastics, and particularly rubbers.

The alcohol will attack any of these organic substances. The rubber one is particularly nasty, because it will come clean, but will then start to break down over months afterward, or after exposure to UV (in daylight for example).

If the filter is something like a piece of glass that has been dielectrically coated, you are probably fine. WATCH OUT (don't use it) if it is a sandwich arrangement (as are many nebula filters) etc. Lastly, Isopropyl is technically 2-propanol. The Drug Store variety is often 70% 2-propanol, and the balance water (not distilled) and light oils. Very bad idea. Try for 90% isopropyl, or use an alternative like methanol (methyl hydrate).


Subject: Lens Cleaner

From:  Ric Ecker <>

  Betelguese Lens Cleaning Solution:

  • 8 oz. of DeIonized water
  • 2 oz. of pure Isopropl Alcohol 99%
  • 3 drops of 409 detergent cleaner


Subject: Cleaning Optics   Top

From: Thomas Wideman <>


by Lenny Abbey, <>

The cleaning of optical surfaces, especially those of first-surface mirrors, is the most delicate and exacting task which the astronomer is called upon to perform. At the time of cleaning, a lens is most vulnerable to damage; damage which cannot be re paired. Yet if a telescope is to perform at its greatest potential, cleaning must be done time to time.

I have used the following method for over twenty-five years without adding a single scratch to the surface of my mirrors and lenses. It has the advantage of requiring only materials which are readily available at the neighborhood pharmacy or grocery store. The cost is less than twenty-five cents per cleaning.

First you must realize that usually the best advice on cleaning mirrors and lenses is.........DON'T DO IT. Dirt and grease which are adhering to the surface of mirrors and lenses may degrade image quality, but they will not damage the delicate optical surface until they are moved against it. Removing dirt without allowing it to rub against the underlying optical surface is what makes cleaning such a tricky task. If your mirrors and lenses are so dirty that they must be cleaned, then this is the way to do it:


  1. Blow all loose dirt off with "Dust Off" or another canned clean air product. (Available in camera stores.) Take care not to shake the can while you are using it, and be sure to release a little air before using it on the optical surface. This will assure that no liquid is dispensed to make things worse! You can use a rubber bulb for this purpose, but it is not nearly as effective.
  2. Prepare a VERY dilute solution of mild liquid detergent (e.g., Dawn). Use about 2 - 4 drops per liter (quart).
  3. Rinse the mirror off under a moderate stream of luke-warm water for two or three minutes. Test the temperature of the water with your wrist, just as you would when warming a baby's bottle.
  4. Make a number of cotton balls from a newly opened package of Johnson & Johnson sterile surgical cotton, U.S.P. Soak 2 or 3 balls in the detergent solution. Wipe the surface of the wet mirror with a circular motion, going first around the circumference, and then working your way towards the center. The only pressure on the cotton should be its own weight. For this first "wipe" you should use several fresh sets of cotton balls.
  5. Throw cotton balls away.
  6. Repeat process with new cotton balls, using a LITTLE more pressure.
  7. Rinse mirror thoroughly under tap, which has been kept running for this step.
  8. Rinse mirror with copious amounts of distilled water (do this no matter how clean or "hard" your tap water is).
  9. Set mirror on edge to dry, using paper towels to absorb the water which will all run to bottom of mirror. Keep replacing the paper towels as the mirror dries.
  10. If any beads of water do not run to bottom, blow them off with Dust Off, or the rubber bulb.
  11. Replace the mirror in its cell, being careful to keep all clips and supports so loose that the mirror can rattle in the cell if it is shook. (Perhaps .5 to l mm clearance).
  12. Spend the next month realigning your scope.
  13. If you do anything more than this, you will damage the coating, and maybe the glass.
  14. You should not have to clean an aluminized mirror more often than once per year. Do NOT over clean your optics.


This restriction means that the above procedure must be modified. Only the front surface can be cleaned. If you remove the cell from the telescope, you will be in big trouble. There are probably not more than 25 people in the United State s who can effectively collimate a refractor!

  1. Blow loose dirt off with Dust-Off or a rubber bulb, using the above precautions.
  2. Soak the cotton balls in a 50:50 solution of Windex (commercial glass cleaner containing ammonia) and water. Squeeze slightly so that the balls are not dripping wet.
  3. Wipe front lens surfaces with the wet cotton, using only the pressure of the weight of the cotton balls. Follow immediately with dry cotton, using little or no pressure.
  4. Repeat procedure, using slightly more pressure.
  5. If some cotton lint remains on surface, blow off with Dust-Off or rubber bulb.
  6. Repeat procedure if lens is not clean, but if one repeat does not do it give up and leave it as is.
  7. Inspect lens to make sure that no cleaning solution has found its way into the lens cell, or between the elements. If this has happened, leave the telescope with the lens uncovered in a warm room until it is dry.


Follow the procedure given for objective lenses, but use Q-Tips (cotton on plastic sticks) instead of cotton balls. You may, of course, clean both surfaces. The eyebrow juice on the eye lens of eyepieces may require repeated applications. I think that this is OK in this case.


  1. Do not use any aerosol spray product, no matter who sells it, or what their claims are.
  2. Do not use lens tissue or paper. It DOES scratch.
  3. Do not use pre-packaged cotton balls, they frequently are not cotton.
  4. Do not use any kind of alcohol, especially on aluminized surfaces.
  5. Do not use plain water.
  6. Do not use any lens cleaning solution marketed by funny companies, like Focal, Jason, or Swift. Dawn and Windex (or their equivalents in other countries) are cheap and commonly available.


Subject: Cleaning Debris off of Corrector Plate Top

From: Nigel Puttick <>

Jim Williams wrote:
>The other day I happened to notice that the secondary mirror has
>several large black fibers and a large speck of something on it. Is it
>safe to remove the corrector plate in order to debride the secondary?
>Is there anything I should take into consideration before attempting
>this action?

Don't do it! It is NOT necessary to remove the corrector for this. I had some specks of debris on the secondary of my 8". I taped together two drinking straws, and taped them to the nozzle of a vacuum cleaner. Carefully introduced same through the threaded aperture (diagonal removed, obviously) while sighting down the baffle tube. Whoosh! No specks. Much easier than disassembly. Try it. BTW I have also used the same technique to remove a dead insect from the inside of a 5" Celestron SCT.


Subject: Optics Cleaning, Lens Pens, & Other Ruminations Top

From: Gordon W. Stanley <>

I made my living as a professional medical photographer for years. I had access to all kinds of cool reagents. I had to regularly clean lens, microscope slides that were going to be photographed under oil-immersion techniques at 1200X... read one spot of dust looks like a Sequoia tree.

Anyway after all my years of experience, here are a few thoughts:

  1. Don't clean until you are absolutely persuaded you need to and even then think again.
  2. Cleaning finger prints and eyelash grease early is good because they are acidic and will etch the lens overtime. I used to use ether because it didn't leave any residue, except for a sleepy photographer ... or a blown up photographer if I wasn't careful. I DO NOT RECOMMEND THIS!
  3. Leave the dust alone for a long time. Dust is usually either dead skin or desert sand. The sand is worse ...because quartz is a lot harder than glass and makes ugly scratches.

When you finally convince yourself that cleaning is necessary, try these steps:

  1. Use a very clean and very soft blower brush to remove ALL loose dust and dirt. Breathing works if you can control your spit but the brush is better. Compressed air cans work as long as you are very careful to keep them level so they don't spew compression gasses and/or freeze the optics. Be gentle, take your time. Just barely let the brush touch the glass if at all to move larger particles. And be prepared to wash or replace the brush. By the way, the brush should be stored in a clean container so it doesn't get contaminated.
  2. Say to yourself several times "gentle is better." I have tried acetone, ether, alcohol in several variations, ammonia and many others ... often they have contaminants and they are all too strong. Pure water with a little help is best.
  3. When the optic is really clean, no visible dust, just some finger prints, I have a special brew that I make, for liquid cleaning. Note, if dusting gets the optics mostly clean, STOP, because the next step risks scratches.
  4. Mix this brew. 1/2 cup of really distilled water. Rinse the cup once or twice so there is no loose dirt in the cup to be dissolved into the water. Then one small squirt of Windex window cleaner with ammonia. Note the highly scientific description of the amount (that's for you Doc). It seems to be about 1 teaspoon. Save this mix in a very clean container, previously rinsed. If you don't have a clean container, mix it fresh.
  5. Now that you have 1/2 cup of this mix, you are going to use drops.
  6. Next take Kodak lens cleaning tissue and roll up like a cigarette and tear in half. Combine the two halves to they look like cigarette butts with one ragged end. Make a half dozen or so of these devices. An alternate is really clean pure cotton, not that poly ... stuff they have in drug stores today. You are going to use the ragged end like a gentle brush with a drop of the liquid.
  7. Now ... check again to see if you really have the dust off the optic. Then taking one or two of these butts at a time. Get a drop of two of the specially brewed GENTLE cleaning fluid and begin working the smear off the lens. Note I say smear, not dirt. If you are working dirt off, you will scratch the optics.
  8. When you are satisfied that the smear is being removed, start another butt until it is clean. Do this with an extremely gentle wiping motion. DISCARD the butts often, that's why I said to start with 6 or so. In my experience it takes two or three to gently remove a finger print from an eyepiece. It takes 4 or 5 to clean a camera lens like a 85 mm F1.8 and it takes about a dozen to clean a 10" LX200 corrector plate.

Here are some guidelines on cleaning:

  1. I clean camera optics after trips to the beach, more for the salt, and I am usually cleaning the skylight filters that I can ditch if I scratch.
  2. I have cleaned my LX200 corrector 2x in 2 years and I mostly spend nights in San Diego or out at Tierra Del Sol ... slightly dusty desert conditions. Is the corrector dusty, a little, but I blow it off, and I don't scratch the corrector.
  3. I clean my eye glasses about 2x daily. I clean them wet with the same solution, I am not quite as gentle. I replace my glasses about 1 each year and they typically have about 200 microscratches on the surface. About one per cleaning... See why I say gentle. These are hard coated lenses so imaging what this kind of diligent cleaning would do to your nice scope optics.


Subject: Fungus and/or Mildew Removal from Primary and Corrector --Part 1 of 2 Top

From: Les Watkins <> Date: Oct 2002

>From: Al Brockman <>
>On inspection of the primary mirror surface and the inside of the
>corrector lens of the OTA, I am dismayed to find that there are about 15
>small areas of fungal or mildew growth, each approx. 5mm in diameter. The tell tale
>spidery filaments are apparent and there is no doubt that having the LX200
>live through three long rainy seasons over the last 3 years has had its
>toll on the optics here in the tropics. Would UV light kill the fungus?

First off all, using UV light to kill the fungus or mildew will not accomplish what you hope to achieve. You will not be able to expose it to sufficient light to kill the fungus completely and in the end what is killed will remain as inert dead fungus which will decay and cause further damage and optical degradation. Additional moisture will only reactivate the fungus and will result in regrowth. Both the primary and secondary mirrors have to be treated differently from the corrector plate and any lenses/filter that have been affected. In any case all of the optical components must be removed from the OTA in order to accomplish eradication of the fungus. I will let those more experienced with dissecting the OTA provide this advice but will concentrate only on the cleaning process.

Under any circumstances do NOT follow the advice of soaking your mirrors or any aluminized optical surface in alcohol. You must first kill the fungus then safely remove it without damaging the optical surfaces. This should be accomplished by creating a diluted solution of distilled water and an antifungal solution. These are commonly marketed as bathroom or swimming pool cleaning products and should not affect your optical coatings if used in the proper dilution. While antifungal solutions may not be available in your location pour a copious amount of quality HORSE SHAMPOO (yes you heard me right, horse shampoo which usually contains mild antifungal ingredients) directly on the optical surface. Do not rub or swath it, just pour it right on. (This is what is used by professional observatories such as Keck and Gemini)

Additionally a weak solution of methyl ethyl ketone (MEK), methylene chloride (MEC) or acetone should also work. In the absence of any of these chemicals, use pure unscented bleach that you have filtered several times though several coffee filters. The solution required should be no more that a 1:10 solution of one of the above mentioned chemicals to distilled water. Again, you must use distilled water. Completely immerse the mirrors in the solution for 1 day, then rinse completely with distilled water. Next very carefully follow the optical cleaning instructions that you will find at this page

Which provides detailed instruction for cleaning each optical surface. There is no simple solution for keeping the fungus away except by eliminating moisture. Since it may be impractical to completely dehumidify an entire observatory, increasing the interior heat to evaporate the moisture may be answer. This can be accomplished by installing some of the those infrared heat lamps you find in the nicer hotels. Additionally placing some additional Kendrick (or other) dew straps around the OTA a the mirror base, center and corrector plate and keeping them turned up on high 24/7 may keep the OTA warm enough to keep the moisture out. Also, placing a neutral density filter on at the eyepiece end of the OTA will effectively seal out the OTA and reduce the introduction of moisture and couldn't hurt.


Subject: Fungus Removal from Primary and Corrector --Part 2 of 2 Top

From: Roland Smith <>

With all the discussion on fungus, it would seem appropriate to suggest a Stanford University website that contains several papers on the topic with information on prevention and removal.
   Go to: <>


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