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Cleaning Optics

  • Author: Scott Roberts at Explore Scientific
  • Create Time: 07/23/2012 14:04:44
  • Last Update Time: 07/23/2012 14:09:57

How To Clean Optics

It never hurts to use filtered, compressed air on your optics, or to use a photographic-grade camel hair brush. Indeed you will find that most professional photographers will double check the optical surfaces and give them a quick dusting before using their cameras, you can do the same when you use your telescope or eyepieces.

You can use canned, compressed air as found in office supply and camera stores. Be careful not to tip the can, because frozen propellant will come out and leave a layer on your optics that will then require cleaning with fluid and tissues or cotton balls. Start by giving a few quick bursts on your hand to make sure that only air is coming out, then with the can held vertical give a few quick bursts of air to remove dust.  If you have an air compressor, use two in-line filters to prevent spraying oil on your optics. Another alternative is to use an ear syringe (available from a local pharmacy) to blow off dust. The ear syringe does not have the force of compressed air, but it doesn't have the problems of compressed air, and it never requires to be refilled. 
Stubborn dust particles can be removed with a photographic-grade camel hair brush. They come in different sizes, depending on the size of the optics that you will want to clean. Only use very gentle brush strokes on the optics and follow up by blowing off the dust with compressed air or the ear syringe. 
If brushing and blowing off the dust on your optics does not clean them, then it is time to use cleaning fluids. You will know that the optics will require further cleaning, if they appear to be hazy, have fingerprints, or other buildup of pollens, tree resins, grease, makeup, food, etc. 
Explore Scientific offers a professional cleaning and collimation service if you wish, but it is helpful to know how to clean the optics yourself.  In this instruction, we give you all of the cleaning agents that we use in regular optics production, how to prepare them, and how to use them. Below is a list of materials that you will need to get started:
 4 Spray Bottles
 White, Unscented, Lotion-Free Facial Tissue, or White Cotton Balls (avoid cleaning cloths)
 Pure Cotton Swabs
 Distilled Water
 Pure Isopropyl Alcohol (94% or better)
 Dishwashing Liquid Detergent Free of Phosphates with Biodegradable Anionic Surfactants
 Acetone

Prepare the Spray Bottles and Label Them Accordingly:
 Straight Distilled Water Only (for suspending stubborn dust and dirt, and rinsing after using cleaning mixture)
 Straight Pure Isopropyl Alcohol Only (a solvent that can dissolve some contaminants, alcohol will not affect paint or plastic surfaces)
 Straight Acetone Only (a more effective solvent that will dissolve almost any contaminant on the glass)
 Cleaning Mixture (for cutting through grease, fingerprints, etc.)

Cleaning Mixture Formula:
Mix three parts of distilled water to one part of pure isopropyl alcohol. Then add a single drop of biodegradable dishwashing liquid detergent per half liter (or pint) of mixture. 

Some Notes:
Before attempting to clean an optical surface with a liquid solution, it is very important that as much dust as possible is removed by using forced air and/or gentle strokes with a photographic grade camel hair brush. This is done to try to eliminate the problem of grinding the optical surface with grits of dust as you start cleaning with the tissues or cotton balls and liquids. 

Be careful of using so called optical lens cleaning tissues as many of them contain fiberglass to reduce the problems of lint. The fiberglass fibers can be abrasive to optics. You can always remove lint, but you can't remove abrasions. When using tissue or cotton, use short, gentle strokes. Don't apply pressure, just let it touch the surface and wipe in a straight line, don't make circular motions. After each stroke replace the piece of tissue or cotton, or use an unused surface with each stroke. This way you are removing contaminants instead of just spreading them over the optical surfaces. 
If you are cleaning small optical surfaces, you can roll the tissue into a small wand, use a cotton swab alone, or use a tissue wrapped cotton swab, depending on the need and your preference. For cleaning large optical surfaces with distilled water, isopropyl alcohol, or the cleaning mixture, tissues can be made into pillows by opening a sheet, then placing a crumpled sheet in the center, then pulling the four corners of the opened sheet 
around the crumpled one. This gives you a smooth pillow surface that you can vary in size depending upon the surface to be wiped. For cleaning edges, or when using acetone, fold the tissue into points, or squares as needed. 

When using liquids (with the exception of acetone), it is important that you apply enough solution to wet the optical surface, but not so much that it can seep around the edges and run in between lens elements, such as on multi-element optics (e.g. refractors and eyepieces). An important advantage of waterproof Explore Scientific eyepieces that there is no danger of liquid seeping in between the lens elements, in fact they can be submerged under water for cleaning. In all cases, the cotton balls or the tissue that you are wiping with should have the liquid applied first to wet its wiping surface. 
CAUTION: Alcohol and acetone are poisonous and flammable, so take appropriate safeguards when using, handling, or storing these liquids. Do not eat, drink, or smoke when in using these materials, and wear protective gloves and eyewear (do not wear contact lenses). Always use in a ventilated area. Dispose of the used tissues and/or cotton balls appropriately.

Acetone will remove paint, melt plastic, and erase silkscreened labels. Be careful to only apply acetone to the optics themselves. And after a single wipe, use a new or different wiping surface (e.g. tissue, cotton ball, or cotton swab). This will make the cleanest optical surface.
Children should never attempt to prepare, handle, or use these materials without informed adult supervision.  For more information and material safety data sheets (MSDS) data visit http://harzard.com/msds.

Cleaning Procedure:
1. Once you have removed as much dust and dirt from the optics as possible with forced air and the camel hair brush, apply Straight Distilled Water to the optical surface and the cotton balls or tissue pillow to help lift off  stubborn dust and dirt particles. Apply no pressure to the wiping surface and use a new wiping surface with each wipe. With the optics still wet follow step 2. 
2. Use Straight Isopropyl Alcohol using the same technique as above. If there are no other contaminants on the optical surfaces, you will see the optics come clean and dry. If you see streaks or smudges, then follow steps 3 and 4.
3. Use the Cleaning Mixture with the same wiping technique as in step 1, then follow up with step 2, then to step 4.
4. Use the tissue squares and spray Acetone on the wiping surface. ​
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2 piece(s) of feedback were found. 2 were marked helpful.
Marc   10/12/2013 15:39:05  
[Helpful]    Excellent article and initiative. So many (idiot) things are said all over the web around cleaning procedures.i however would have appreciated that you highlight the risk of using acetone on your eyepiece lenses.... as plastic or rubber would more than probably melt down from this very efficient and recognized disolvent.
Jason   08/01/2012 11:40:59  
[Helpful]