How do I clean my telescope optics – primary mirrors, lenses, eyepieces, corrector plates?
February 20, 2005
Cleaning telescope optics should only be done when necessary. It is not necessary to clean the lens or mirror of your scope if it just has a few visible specks of dust. Overly frequent or aggressive cleaning can actually damage and prematurely age the special coatings on mirrors and lenses–permanently degrading their performance.
When optics are truly dusty or dirty, that’s when they need to be cleaned. The best philosophy is progressive: clean only as much as you need to clean, starting with the gentlest cleaning and then progress to more thorough cleaning using more force. Clean outside optical surfaces first before even considering disassembly and cleaning inner surfaces.
Note: These techniques are for normally dusty optics or those with minor fingerprint or eyelash smudges. Optics with films, fungus, oil or grease needs special techniques for cleaning. We recommend contacting Celestron factory service in these cases for cleaning services. However, some tips for really dirty optics are covered in another knowledgebase article.
For basic cleaning:
1. Use compressed gas or compressed air to blow off loose dust and large particles. This greatly reduces your chances of scratching the lens or mirror in successive steps and may be all that’s needed. Canned gases like Dust-Off contain bitterants and other compounds that can plate out or leave deposits unless proper precautions are taken. Never shake a can of compressed gas before using it and always first vent a jet of gas away from any optics. Use the can in an upright position and move it slowly or move the optics instead. Compressed air should be filtered and also first be jetted away from any optics to blow out any dust in the line.
2. Use a cleaning solution to gently lift off any remaining dirt or smudges. The recommended solvent is alcohol. You can make a mix from pure alcohol and distilled water or buy off-the-shelf dilutions from your local drugstore. Dilutions of 50 to 70 percent alcohol work best. Higher percentages evaporate too fast and have a greater chance of dissolving optical cements, non-metallic parts and lacquers on mechanical parts if the solution accidentally gets into the wrong parts of the optics or telescope. Lower percentage dilutions won’t evaporate readily but may still cause problems if the solution accidentally gets into the wrong parts of the optics or telescope. The alcohol can be used straight or you can add one or two drops of clear liquid dish-type soap (non-waxy) per quart to help lift off dirt and finger oils. (Adding too much soap will leave visible residues on your optics.)
3. Use the solution to wet soft, plain tissue or cotton balls for larger optical surfaces or cotton swabs for small parts like eyepiece lenses. Don’t use too much solution, as you don’t want excess fluid to run off the surface you’re cleaning.
For eyepieces and filters, use the swab and wipe with little to no downward pressure in straight strokes across the eyepiece surfaces while rotating the swab to lift the dust off the lens. Repeat as needed to remove any remaining oils or dust.
For the primary main lens or mirror, use a wet cotton ball or tissue and gently drag it across the surface in straight strokes. Simply dragging it is the lowest force possible and the least chance of scratching from any remaining dust. Repeat with new balls/tissues. If you must use force (on a localized deposit), use as little as you can, just enough to remove the deposit, no more, without damaging the optical surface.
The same process can be used for corrector plates on Schmidt-Cassegrain scopes. Use radial strokes from the secondary mirror outwards. Repeat as needed. Again, any rubbing should be as gentle as possible.
Minor spot cleaning of any optics can be done much the same way (your corrector plate or refractor lens if it has a minor fingerprint). Blow it off first. Then use the swab/ball/tissue, and if necessary, gently wipe the affected area.
We do not recommend removing the corrector plate or disassembling optics to do cleaning. Removal or disassembly may void your warranty. If the inside of your optics are dirty, call Celestron factory service.
Please see these links for some additional tips: