Cleaning Optics

Before deciding if you actually need to clean your optics, read these instructions ALL of the way through first.  Here are two very informative articles on how to clean mirrors, eyepieces and filters. These are in the "Must Read" category if you are thinking about cleaning your optics!!

UNDER NO CIRCUMSTANCES SHALL ANY USER OF THESE INSTRUCTIONS HOLD ASTRO-TOM.COM OR THE MANUFACTURERS OF ANY PRODUCT MENTIONED HERE LIABLE FOR ANY DAMAGE THAT MAY OCCUR, DIRECTLY or INCONSEQUENTIALLY, WHATSOEVER.

[This means that you can really screw up, BIG TIME, and it'll be your fault, if you're not VERY careful...]

GENERAL GUIDELINES FOR CLEANING OPTICS AND MIRRORS

More On Cleaning Optics from Astralnomicon Observatory Systems: 

NOTE: These guidelines have been synthesized from several different sources from experienced astronomers to optics manufacturers. Although no one cleaning method or cleaning solution works for all surfaces, optical coatings or types of contamination, these guidelines apply to most commercially available optical surfaces and contaminates.

Since these guidelines are highly dependent your actual application to your optics, the purity and type of materials used or type of contamination present so...

UNDER NO CIRCUMSTANCES SHALL ANY USER OF THESE INSTRUCTIONS HOLD ASTRALNOMICON OR THE MANUFACTURERS OF ANY PRODUCT MENTIONED HERE LIABLE FOR ANY DAMAGE THAT MAY OCCUR, DIRECTLY or INCONSEQUENTIALLY, WHATSOEVER.

Most of the components cited here are generally available from your local drugstore, pharmacy or optical supply company. Some of the more advanced solvents must be obtained from chemical supply houses.

WARNING: When in doubt as to whether to clean your optics or if you are unsure of the quality and purity of your cleaning components or your cleaning technique, DO NOT PROCEED! 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 that can not be repaired. Yet, if a telescope is to perform at its greatest potential, cleaning must be done time to time. First you must realize that usually the best advice on cleaning mirrors and lenses is this: DON'T DO IT unless absolutely necessary!

With this said, let's proceed.

DUST

Most dust that you see on your objective lenses, mirrors, correcting plates, eyepieces or filters is harmless and generally does not effect the quality of your optics or effect image quality, whatsoever. This dust should be left-alone or simply blown-off with high-quality compressed air product that uses dry nitrogen as its propellant. DO NOT use compressed air products that contain solvents as their propellants! Most compressed air products designed for blowing off electronics or computers contain such solvents. Do not use any other type of aerosol product that claims to clean glass of any type no matter what the claim of the manufacturer. If dry nitrogen propelled air is not available, the use of a compressed air product sold at photography stores such as Dust-Off may be used if your are careful not to tilt the can, thereby releasing the propellant onto your optical surface. Alternatively, you may obtain a rubber syringe bulb (found in the baby supply section of your local grocery store or pharmacy) or a blower bulb/camel hair brush combination from a local photography supply store. Blow the dust off starting at the center of lens or mirrors working your outward towards the outer edge. Stubborn dust particles can be ever so gently brushed outward using the same method only using a soft camel hair brush. If you observe anything other than dust (sand particles or eyelashes, for instance) DO NOT BRUSH THEM for they will scratch your optics!

DIRT, FINGERPRINTS, BUGS and other CONTAMINATES

Dirt, sand particles, grease, fingerprints, bugs or other contaminates that adhere 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. Certain organic residue or oils from fingerprints or bugs or cigarette smoke may eventually damage delicate coatings and must be cleaned. Removing dirt without allowing it to rub against the underlying optical surface is what makes cleaning such a critical task. If your mirrors and lenses are so dirty that they must be cleaned, then proceed carefully as instructed.

PREPARE CLEANING SOLUTION

Many types of powerful commercial solvents are available including methyl ethyl ketone (MEK), methylene chloride (MEC), acetone or pure isopropyl alcohol, but these products should only be used by professionals in the correct dilution on the appropriate optical surface.

However, most professional observatory operators say the simplest solution is the best! Click here to see what they say at the Gemini Observatory in Hawaii.  

For personal use, you should prepare a solution that can be used safely on all optical surfaces based upon commonly available ingredients as follows:

1. Distilled Water. The basis of this solution is the most commonly available solvent on the planet (which also happens to also be responsible for life on earth): water. In our case, pure distilled, de-ionized water. Do not use tap water or bottled water for this purpose because they both contain minerals and other contaminates that defeat the purpose of what we are trying to accomplish: PURITY.

2. 99%-97% Isopropyl Alcohol. You may have to ask your pharmacist for this or look around your drugstore. Most off-the-shelf "isopropyl" alcohol is usually in the 70%-90% with the other 30%-10% containing regular water or other contaminates. Avoid this. Methyl hydrate (methanol) may be substituted for isopropyl alcohol.

3. Mild Detergent. Liquid dish detergent that is fragrance-free, color-free works best such as Dawn or other similar product (hint: the folks at Gemini say use horse shampoo!).

4. New plastic spray bottle. These can usually be found in the garden supply section of your local Wal-Mart or garden supply store. Do not be tempted to use a used bottle that previously contained some other solution such as glass cleaner, buy a new bottle; it only cost a couple of bucks. A one time solution can be mixed in a clean drinking glass, in a pinch, that has been adequately rinsed in distilled water.

Now the recipe. If you are cleaning a Newtonian type reflector you will be cleaning your primary and secondary mirrors. If they are aluminized mirrors (most are) do NOT add the isopropyl alcohol in step 3, below because alcohol reacts with aluminum. If you are cleaning a refractor or SCT you will be primarily cleaning your objective lens or front corrector plate, do add the alcohol in step 3. On occasion, SCT and other catadioptric telescope owners will want clean their primary or secondary mirrors, these are usually aluminized as well. You will need to mix two solutions, one with alcohol and one without, carefully marking each bottle as required with an "M" for mirror and a "G" for glass.

1. First start by rinsing your new, unused spray bottle with the distilled water. Fill and vigorously shake the water in the bottle at least three times to remove any inadvertent particles or residue that may be present in the bottle as a result of manufacturing.

2. Next, fill 3/4 of the bottle with the distilled, de-ionized water.

3. For glass cleaning only add 1/8 of the bottle with 99% isopropyl alcohol. Too much alcohol will leave streaks. This should leave the bottle 1/8th empty. For mirror cleaning omit the alcohol or any other solvent besides the mild liquid soap.

4. Finally, very carefully add 2-3 drops of the mild dish detergent. If your detergent bottle dispenses too much use an eye dropper. Too much soap will leave a cloudy residue.

Screw on the pump spray top immediately to avoid dust or other particulate material from entering the solution. Always keep it covered, in a cool dark place when not in use. Do not refrigerate.

WARNING: Care should be taken not to inadvertently get this solution on any other part of your telescope except the optical surfaces. Lens cells and corrector plates are often held in place by cork or rubber seals and gaskets to which this solution could damage. Always blot or wipe excess solution and prevent it from running down in these areas or entering the optical tube assembly.

CLEANING MATERIALS

You will need to obtain several different cleaning materials depending on whether you are cleaning mirrors, lenses or eyepieces. First and foremost, never use prepackaged bulk "cotton" balls, they always contain other miscellaneous fibers that can scratch delicate coatings and secondly they are not very absorbent. Additionally, also never use tissues, toilet paper, paper towels or lens cleaning paper that you may find at the photo store. All of these products may scratch coated optics or leave more dust than they remove. For lenses and mirrors, we recommend the use of precision quality optical wipes such as Opto-Alignment Technologies Inc.'s OPTO-WIPES(tm) available from AOS. Additionally, wearing OPTO-GLOVES(tm), also made by the same manufacturer, will prevent recontamination from fingerprints and body oils. If OPTO-WIPES are not available, obtain Johnson & Johnson's Sterile Surgical Cotton, (U.S.P.) which is sold in bulk pads at your local pharmacy. The pro's say to use a Natural Sponge! You will also need pure cotton swabs (Q-tips), that are mounted on the plastic sticks rather than the wood or paper sticks to clean your eyepieces and filters.

DISASSEMBLING YOUR TELESCOPE

Many factors must be considered before attempting to disassemble your telescope. Always consult your manufacturer or your operating manual prior to disassembling any telescope. Disassembly may also void your warranty, check to be sure. Additionally, disassembling your scope can also cause it to be permanently out of alignment (collimation) requiring it to be returned to the factory for correction. This can be both time-consuming and expensive! Some types of scopes, such as Newtonian reflectors, require special tools or collimation devices to re-align the optics, make sure you have these on-hand prior to disassembly. In general, avoid disassembling your scope unless absolutely necessary! There are many user groups and experienced amateur astronomers that can give you good advice in this area for your particular scope, so we will not go into specific details regarding this process in these guidelines. In general, consider the following:

1. Refractor. Most refractor telescopes have multiple objective lens systems that are permanently mounted in cells or are permanently attached to the optical tube assembly (OTA). Because of their closed optic