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Cleaning Your Telescope's Mirror The Safe And Easy Way
by: Thom Bemus



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Over the years I've helped dozens of club members clean their telescope mirrors for the first time. Many people are terrfied during their first attempt. But there is no reason to be scared if you follow this safe and easy procedure.

First, do you really need to clean your mirrors? If your mirrors are just dusty, at most, rinse them only. Every time you clean your mirrors, even if you use the safest methods, you will make some microscopic scratches on your mirrors which scatter light. These tiny scratches degrade your telescope's performance much more than a little dust. Since you can't scratch mirrors if you don't physically touch them, I rinse my mirrors about two out of every three times I do cleaning. In general, amateur astronomers physically clean (ie: rub them when cleaning, as opposed to just rinsing) their telescopes too often. The large telescopes at major observatories get incredibly dusty, dirty and even have bird-dirt on them before they are cleaned. Given reasonable care in keeping out dust and dirt, most people should only need to clean their telescope once a year, at most. However, when tree sap or other residues appear on your mirror it is time to clean!

You will need the following items: a clean sink (preferably with a sprayer), a few drops of Dawn (blue) dish washing detergent, distilled or deionized water, one soft towel, a bowl to mix your cleaning solution in, one pint of 91% or higher rubbing alcohol (with NO skin conditioners or other additives), one package of sterile surgical cotton, a blow dryer (be sure to wipe any dust off of the dryer before you use it).

READY! Here is the safest way I've found to clean the mirrors in your telescope, I would suggest you save this for future reference:

1) Carefully remove the mirror from the cell (the mirror can be left in the cell if the cell is waterproof, but getting rid of water spots around any mirror clips can be a problem) and place it face up on a soft towel in a clean sink (don't clog the drain). Be sure to remove anything that might fall on your mirror from the area and keep curious children and pets away.

2) Run LUKE WARM tap water at moderate pressure on the mirror for about 5 minutes, making sure the entire mirror surface remains wet at all times.

3) Remove mirror from water stream and make sure all dust and debris that might scratch the mirror are gone, if not let it go under the water for another 5 minutes. Use your sink sprayer to remove stubborn dirt.

4) If the mirror appears clean after this water rinsing proceed to step #7.

5) Using a solution of 1 drop of dawn dish washing detergent mixed in one quart of warm tap water, dip a wad of surgical roll cotton into the solution and drag it (apply NO pressure accept the weight of the wet cotton) in a circular motion from the center to the outside edge around the face of the mirror, repeat if absolutely necessary, do not allow the any of the surface of the mirror to dry.

6) Immediately rinse the mirror for 5 more minutes with LUKE WARM tap water at moderate pressure to ensure that all of the soap residue is rinsed away.

7) Immediately rinse the mirror with distilled or deionized water.

8) Immediately rinse the mirror off with the 91% or higher rubbing alcohol while keeping the mirror tilted, this will strip most of the water off the mirror.

9) Using a blow dryer at low heat, try to blow any remaining water droplets off the edge of the mirror. Any that remain, you may BLOT [not rub!] them away VERY GENTLY with surgical cotton or a Q-tip.

10) Admire yourself in your in now very clean mirror, which is now ready to reinstall in your telescope.

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Weston CSC:

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