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Step by Step: How to Clean a Reflector Telescope

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» Telescopes » Step by Step: How to Clean a Reflector Telescope

A reflector telescope is an optical instrument for observing astronomical objects. The main parts of the telescope are the tube, inside which are located lens, mirror, focusing device and eyepiece. The telescope tube is installed on the mount, which serves to point the telescope to the celestial object.

Cleaning of optics is one of the most delicate topics for the owner of a telescope. As a rule, this problem often concerns owners of reflectors telescopes: dust gets on mirrors and should be carefully washed off. Let’s look at a few options for cleaning a reflector telescope.

You have to understand that cleaning telescopes at home is a really dangerous move – you should do it if there are no other options left. If you’re sure about your decision, I will tell you how to clean a reflector telescope.


Cleaning a Reflector Telescope: Detailed Instruction

Many fans of observing the sky often purchase telescopes in order to view beautiful stars and sometimes even planets. However, not everyone understands how to properly care for a telescope and how to clean it. A telescope is usually a very expensive item, so the cleaning of this instrument should be approached responsibly and with care.

Telescope cleaning kit: basic supplies

Please keep in mind that it is virtually impossible to repeat the actions of a professional reflector telescope cleaning service at home. However, if you already have the spirit to go to this page, here is the minimum cleaning kit:

  • cotton disks, ear sticks;
  • a can of compressed air or a special cleaning pen;
  • cleaner (dishwashing detergent);
  • special wet wipes for lens cleaning.

cotton discs on table

How to clean reflector telescope mirrors?

First of all, mechanical influences of mirrors are highly not recommended – you may easily erase the aluminum layer, as it is already hanging on by a thread. Mirrors have to be cleaned. Any dust and dirt that has settled on the mirrors and stuck to them should be blown off with a can of compressed air. It is not recommended to shake the can during this operation. Before blowing air on optical surfaces, deflate a little air. This way you can make sure that no liquids are escaping from the can together with the air.

  1. Prepare a very diluted solution of any liquid mild detergent (like dishwashing liquid).
  2. Rinse the mirror under a stream of water at a moderate pressure. The water should be warm but not too hot.
  3. Roll several balls of sterile surgical absorbent cotton taken from the newly opened package. Soak 2-3 cotton balls in the detergent solution. Wipe the surface of an already wet mirror with them. Do not apply any force, the ball should slide as if it were moving by its own gravity.
  4. Throw away the used cotton balls.
  5. Repeat the procedure again, applying less pressure to the mirror.
  6. Rinse the mirror thoroughly under the faucet, which should be turned on beforehand.
  7. Rinse the mirror with plenty of distilled water (it is necessary to do this, no matter how good the tap water seems to you).
  8. Place the mirror so that the water flows freely from it. Use paper towels to collect the water that runs off the bottom of the mirror. Change the towels as needed.
  9. If any water droplets are left on the surface of the mirror, blow them off with a can of compressed air.
  10. Put the mirror in its place, making sure that the screws and clamps are not tightened too much and the mirror rattles slightly when swinging (the amount of play should be 0.5-1 mm).

You should be ready to spend the next month aligning the telescope. If you overdo it – there will be a risk of damaging the mirror coating and maybe the glass itself.

How to clean a telescope lens?

Under any circumstances, you should not remove lenses from their frames or the frame from the telescope tube. This means that the procedure described above requires correction. Only the outer surface of the lens can be cleaned. If you take the lens and frame out of the tube, you are in big trouble. Very few people in the world can effectively collimate a refractor.

Don’t forget to wear medical gloves before washing the lens, otherwise, you will just transfer the grease from your hands to the lens while washing (or wiping, to be more exact).

  1. Blow off the settled dust with a can of compressed air. All precautions mentioned above must be observed.
  2. Moisten cotton balls with glass cleaner half diluted in water. Squeeze them slightly to prevent water from dripping off.
  3. Wipe the surface of the lens with the moist cotton balls. Then immediately blot with dry absorbent cotton. Do not rub the surface of the glass and do not put any pressure on it.
  4. Repeat the procedure, applying even less pressure.
  5. If absorbent cotton fibers remain on the surface of the lens, blow them off with a can of compressed air.
  6. Repeat this procedure if the lens surface does not appear clean.

Examine the lenses carefully to make sure that the cleaning fluid has not seeped under the lens barrel or into the telescope tube. If this happens, do not cover the lens caps and leave the telescope in a warm room until it dries.

How to clean telescope eyepiece?

To clean eyepieces, you should use the same technique as for lenses, only with plastic ear buds instead of cotton balls. Eyepieces can be cleaned on both surfaces. It is possible that sweat on the eyepiece lens may not be removed the first time. In this case, there will be no harm in repeating the procedure.

How to clean a telescope body?

Fortunately, there is nothing special about cleaning a corpus of a reflector telescope. You can use a regular rag for this procedure.

What you should not do:

  • No aerosols of any kind should be used, no matter who made them or what the manufacturer claims.
  • Do not use cloth wipes or paper. They will scratch the surface of the glass.
  • Do not use cotton balls from store-bought packages. Often they are not made of cotton at all.
  • Do not use any alcohol-based liquids.
  • Do not use tap water.
  • Do not use glass cleaning liquids made by companies nobody knows about.


Let’s consolidate the information and answer the most popular questions:

What can you use if you don’t have a telescope cap?

The telescope cap is designed to protect against moisture and dust, which can completely destroy the entire functionality of the telescope. If you lose this cover in any way, the best option is to buy a new one or simply print a prototype on a 3D printer. Otherwise, you can use any tool at hand to create a new telescope cap.

How do you polish a mirror on a telescope?

As written above, you should use compressed air cans and cotton disks. You can also use a special cleaning pen for deeper cleaning, but such a device is quite expensive.

When should I clean my telescope mirror?

As for the number of times to clean the telescope, a general cleaning will be enough once in an observation season. Local contaminants should be removed as they are applied. Eyepieces, on the other hand, need to be cleaned more frequently.

Is it dangerous to clean optics with compressed gas?

Sometimes a can with compressed gas can be defective, so it releases not only air but also water. If you’re too afraid, you can simply pour a diluted detergent solution into a basin and leave the lens there until all the grease and dust have detached from the optics.

Can lenses be cleaned with regular wet wipes?

It is never recommended to use personal care wipes to clean your optics. Special wipes for glasses contain completely different substances, and only they can help in cleaning in the most effective way.

How to Clean a Reflector Telescope?

Observe all precautions when cleaning the reflector telescope optics. Even the smallest precaution can lead to irreparable consequences.

Share your thoughts about the topic in the comments below. What other ways of cleaning optics besides with a can of compressed gas do you know? Do you use a special cleaning pen to clean the eyepiece?

About Michael Oliver Barlow

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