How to Clean Your Telescope Mirror

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Based on what I have learned over the last few years, I will show you a quick and easy way to clean your telescope mirror. Before I get into that here’s a quick answer to the question summarized for you.

You can clean a telescope mirror by immersing it in slightly soapy water or by spraying it with water and detergent and then wiping it very carefully with a lint-free cloth. The final step is to rinse the mirror with distilled water and let it dry in a vertical position.

However, if your telescope mirror has not been cleaned before or if it is very dirty you should do the following:

To clean a telescope mirror, first, make sure the mirror is cool and not exposed to sunlight or any other source of heat. Gently blow any loose dust off the mirror, then carefully moisten a soft, lint-free cloth with a mixture of warm water and a mild, alcohol-free detergent. Wipe the mirror in a circular motion, starting from the center and working your way outward. Avoid pressing too hard or using too much liquid, as this can damage the mirror. Once you have finished cleaning the mirror, use a clean, dry cloth to carefully remove any excess moisture. Allow the mirror to air dry before using the telescope again.

There is more detailed information and guidance on this page at sky and telescope.

If your telescope has a mirror that is not very dirty, I’ve got a much simpler method for you to try. It worked for me.

First, let’s check a couple of important points because you don’t want to do this unnecessarily nor do you want to damage your precious telescope.

Disclaimer: Please use caution when attempting to clean your telescope mirror. The method described worked for me, but it may not work for everyone and there is no guarantee that it will be safe for use with your specific equipment. Attempting to clean your telescope mirror can potentially cause damage if not done properly. I take no responsibility for any damage that may occur as a result of following the method described. It is important to carefully read and follow all instructions provided by the manufacturer of your telescope and to use caution and good judgment when attempting any maintenance or cleaning tasks.

Is it safe to clean the telescope mirror myself, or should I take it to a professional?

Yes, it is absolutely safe to do it yourself, (if you are careful not to drop anything and take precautions against any possibility of scratching the glass surface of your telescope mirror). How do I know? because I have done it a couple of times on my telescope the Celestron 130slt. At first, I was worried but it is easy to take out the mirror and is just a matter of removing three screws and taking out the mirror housing.

Many videos I have seen and articles that are written on this topic advise you to remove the mirror completely but in my opinion, this is not necessary and could risk you damaging either the mirror mountings, losing screws, or scratching the mirror.

My method is fast and easy and minimizes any risks of damage. First does your mirror actually need cleaning? Mirrors can actually continue to work well even though dusty.

dirty telescope mirror
A dirty telescope mirror in its housing

How often should a telescope mirror be cleaned?

I have looked at a number of videos and read many online articles that tell you your mirror may not need cleaning for years. One person I watched even stated that he hadn’t cleaned his telescope in ten years and that this is not a problem. Wrong!

Why do I say this is wrong? Based on my own experience. The best research anyone can do is to actually try different methods and learn by experience. So, here’s what I have found…

How often you need to clean your mirror depends on how often you use your telescope and where you use it. For example, I live in a place where I can use my telescope for astrophotography almost every night during the summer months which covers a period of about 5-6 months of the year. What’s more, it is generally dry here and tends to be windy and a bit dusty as I am close to the sea.

Sometimes I image the whole night long and over the whole year, (taking into account how often I find the time to do astrophotography), I would say I can image about 2 times a week which is more than 100 times a year. Maybe this might be an overestimate because the Moon is sometimes too bright for astrophotography, but it’s a good estimation.

I have found it necessary to clean the mirror twice in the last two years. Most recently, I cleaned it because I had started to see some light circular motes on my images.

Therefore, in a dusty environment when you use your telescope often 80-100 times a year it will need cleaning each year. Better though not to clean it often and wait until you see a problem with your images or if you inspect the mirror and find patches of dirt on it.

Prevention is better than cure: how to protect your mirrors from getting dirty

A little bit of attention to detail can go a long way to maintaining the cleanliness of your telescope and its optics. Here are a few simple steps you can take to minimize the need for cleaning:

  1. Keep everything capped when not in use, unless the optics have fogged over after a session (in which case, allow them to dry out before capping).
  2. When swapping eyepieces or filters, be sure to put the caps back on the previous one.
  3. Keep your equipment packed away when not in use, rather than leaving it out in the open.
  4. Use a bulb blower before and after using all optics, this includes mirrors, and be sure to bulb blow eyepieces after every use (your eye/eyelashes contain gunk!).
  5. Proper dew management is essential to keeping your optics clean. Invest in a dew heater strip and use it on nights when dew is a concern. After a session, allow your equipment to warm up slowly in a dry environment. If your optics have fogged over, keep the dew heaters on until all moisture has evaporated, and only cap when dry. If your scope has a front corrector plate, consider getting a portable hair dryer to help remove moisture.
  6. Silica gel packets are a must-have for any astronomer. Use them liberally and replace or replenish them regularly.
  7. When selecting an observing site, be mindful of the potential for pollen and other debris to stick to your optics. Choose a site that is free of plants and trees that may produce pollen.
  8. If there is wind, make sure you do not set up anywhere too close to a dusty area. Grass is best.

By following these simple steps, you can help to keep your telescope optics clean and in top condition.

Can I use household cleaning products to clean my telescope mirror?

Not really a good idea. You should avoid, at any cost, any abrasive cleaning products as a scratched mirror is ruined. Often detergent is recommended but again I don’t use it and don’t like the idea, only use it for really dirty mirrors!

How can I remove stubborn dirt or stains from my telescope mirror?

Stubborn dirt or stains should not be on your mirror but in the exceptional cases where you have such dirt on your mirror do not think of rubbing your mirror even lightly. In this case, my method should work but you may need to leave the liquid on the mirror for a short while to remove these kinds of marks.

How do I clean my telescope mirror?

Now, my method for cleaning a telescope mirror is what I have done the last two times without any problems and I managed to do this very quickly in 5-10 minutes maximum. Here’s what I do:

Magic Clean cleaning fluid bottle

I spray the mirror finely with a cleaning fluid such as that in the image. The type of spray I use is the same as I use for cleaning my laptop screen. It is the clear kind of fluid rather than the frothy one as this is easier and quicker to use and doesn’t leave anything behind.

I saw marks on my mirror a few months back and after a spray with this, I waited a few minutes and wiped it off very gently with a lint-free cloth, and done!

This has worked for me. The dust motes in my image were gone and my mirror was clean.

If your mirror is extremely dirty then a different method can be used as suggested in other videos, such as this one by Small Optics, but the above method works on any telescope which you have used from a new and have cleaned regularly.

I hope this has helped you and the views you’ll get from a cleaned mirror will reward you many times over for the small amount of effort of cleaning it! Clear skies to all!