The right way of how to clean telescope mirror surface

Over some time, dust and other particles can gather on the surface of a telescope mirror, leading to a decrease in the quality of the observing image.

To ensure the telescope is functioning at its best, it is crucial to clean the mirror regularly.

However, it is important to use proper cleaning techniques and tools to avoid damaging the delicate mirror surface.

Caring for your telescope and making an effort to keep it clean may seem like a minor detail, but it can have a significant impact on the performance and longevity of your telescope.

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While minor dust accumulation or a few drops on the primary mirror and secondary mirror may not cause any major issues, it is significant to take precautions to prevent the buildup from getting out of hand.

When it comes to removing dust and other debris, it is essential to avoid any actions that could scratch or damage delicate mirror surfaces.

While you may be tempted to frequently clean your telescope, it’s best to take a hands-off approach and only clean when necessary to avoid any unnecessary damage.

Why should you clean your telescope mirror?

A dirty telescope mirror can affect the telescope’s performance and image quality.

The primary mirror and secondary mirror collect dust, dirt, and other debris that can block or scatter incoming light.

This can result in a hazy or fuzzy image, reducing the telescope’s ability to produce clear and sharp views.

Cleaning the primary mirror and secondary mirror removes the accumulated dust and dirt, allowing for more light to enter the telescope and produce a clearer, brighter, and sharper image.

It is recommended that you clean your telescope’s primary mirror and secondary mirror regularly to maintain optimal performance.

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Take away the primary mirror and secondary mirror

Locate the mirror cell: The mirror cell is the part of the telescope that holds the mirror in place.

It is usually located at the bottom of the telescope tube.

Unscrew any retaining screws: The mirror may be held in place by screws.

If this is the case, use a screwdriver to remove them.

Lift the mirror: Carefully lift the mirror out of its cell.

Hold it by the edges to avoid touching the reflective surface.

Inspect the mirror: Check the mirror for any dirt or dust.

If necessary, clean it using appropriate cleaning materials and techniques.

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To clean the telescope’s mirrors

Before cleaning the telescope’s mirrors, a shower cap should be worn to prevent hair from falling on clean mirrors. Prepare a place where you will wash mirrors, it should not be a kitchen sink.

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Then be the mirror safely out of the telescope and use lens pens.

Use a new brush from a plastic bag to carefully eliminate dust or debris from the mirror’s surface with its gentle bristles.

Create a solution by combining distilled water and isopropyl alcohol in the same proportions. Don’t use soapy water.

Soak a gentle, non-fibrous fabric with the mixture.

Maybe a final rinse for the mirror surface. Don’t use tap water for cleaning mirrors.

Using a moistened cloth, carefully clean the surface of the mirror by beginning at the center and moving in a circular motion toward the edges.

Employ a distinct cloth that does not contain lint to carefully dry the reflective facade.

Check the surface of the mirror for any streaks or spots that may still be present, and redo the cleaning procedure if needed.

Make sure your hands are clean and refrain from touching the surface of the mirror with any objects or fingers when handling it.

It is recommended to refrain from utilizing household cleaning items that have ammonia, bleach, or other strong chemicals as they may harm the mirror’s coating.

After the cleaning process, replace the mirror. Once the mirror has been cleaned or replaced, carefully put it back in place in the mirror cell. Ensure it is securely fastened with mirror clips and aligned correctly with the telescope’s optics.

Test the telescope: With the mirror back in place, test the telescope to ensure everything is working correctly and that the image produced is clear and focused.

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Additional methods for cleaning telescope’s mirrors

Blowing the dust off: Using a can of compressed air can help blow off any loose dust particles that may be on the mirror’s surface.

Hold the can upright and use short blasts to avoid any over-spraying.

RO distilled water rinse: Rinsing the mirror with Reverse-Osmosis (RO) distilled water can help remove any mineral deposits or stains that may remain after cleaning. Don’t use tap water for cleaning mirrors.

RO water is pure and contains no dissolved minerals that leave spots or stains, unlike tap water. Very suitable for the final rinse.

Microfiber cloth: A microfiber cloth is a gentle method of removing dirt and grime from the mirror’s surface without leaving any scratches. Always use a clean microfiber cloth for optimal results.

Warm water soak: For stubborn stains or grime on the mirror surface, try soaking the mirror in warm water for five to ten minutes.

This can help loosen any dirt or grime before applying a cleaner.

Ultrasonic cleaning: An ultrasonic cleaner uses high-frequency vibrations to remove dirt and grime from delicate surfaces without scrubbing.

This method can be used for small mirrors or eyepieces.

Dry ice cleaning: Dry ice cleaning is a quick and effective way to remove stubborn dirt and grime from the mirror’s surface without leaving any residue behind.

Using cotton balls to clean the telescope’s mirrors is not recommended as cotton balls can leave lint and fibers which can scratch the surface of the mirror. It is recommended to use cotton balls or a lens cleaner specifically designed for telescope optics.

It involves blasting dry ice pellets at high pressure onto the mirror surface.

Remember to always check with the manufacturer for recommended cleaning methods for a reflector telescope and never touch the mirror surface with your fingers, as the oils can leave permanent marks behind.

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What is the frequency of cleaning my telescope mirrors?

There is a heated discussion in the astronomy community regarding how often to clean optical mirrors. In my opinion, the issue is sometimes exaggerated.

Generally, telescope mirrors should be cleaned at least once a year, or more frequently if necessary.

Proper cleaning techniques will not cause any damage to the mirror, but neglecting to clean it can lead to degradation of the reflective coating due to exposure to harmful chemicals.

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Additionally, when the reflector telescope is brought outside, it takes time for the mirror to adjust to the temperature and during this time, moisture from the air can accumulate on the mirror as dew.

This dew can contain minerals and debris that are left on the mirror’s surface when it evaporates.

Astronomers who are located near the coast or in areas with heavy pollution may experience dew-containing compounds such as salt and sulfur, leading to the gradual accumulation of these substances on their mirror surfaces.

To prevent this from shortening the lifespan of their mirrors, regular cleaning is necessary.

If you observe your mirror during daylight and notice no apparent dust or grime, then there is no need to clean it.

Shining a flashlight into your telescope will inevitably make your mirrors appear unpleasant, prompting you to clean them more often than is required.

Therefore, it is better to avoid doing this unless necessary.

It is important to maintain a healthy balance between being cautious and overly concerned.

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Vigilance when cleaning mirrors in a telescope

Here are some of the guidelines to keep in mind when cleaning mirrors in a telescope.

Either use specialized cleaning materials that are specifically made for telescopes or choose a soft, lint-free cloth, such as a paper towel.

Avoid using ordinary household cleaning agents or paper towels, as they can cause scratches on the mirror’s surface.

Be gentle when wiping the mirror, using light pressure and circular motions to avoid damaging it.

Do not apply excessive force, as this can lead to deformation and loss of reflectivity of the mirror.

Clean the mirror only when necessary, as frequent cleaning can cause more harm than good.

If the mirror is very dirty, consider getting it professionally cleaned to avoid damaging it.

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Can you clean the telescope mirror with alcohol?

Using alcohol to clean a telescope’s mirror is generally discouraged since it has the potential to strip off the mirror’s reflective coating.

Instead of using harsh chemicals, opt for a mild cleaner made specifically for telescope mirrors, or gently wipe them with a paper towel and distilled water.
It is best to consult the manufacturer’s instructions for proper cleaning techniques.

Make sure to use a gentle and clean cloth or a tool designed for this purpose when cleaning dirt from the mirror.

To prevent damage to the reflective coating, it’s important to steer clear of harsh chemicals and abrasive materials.

By cleaning and maintaining your telescope, you can guarantee years of clear, high-quality views of the nighttime sky.

How often should you clean a telescope mirror?

The telescope’s mirror ought to be cleaned solely when it is required.

The maintenance schedule for the telescope will differ depending on how frequently it’s used, the environment in which it’s used, and the amount of dirt and dust that collects on its mirror.

When you can see dirt on the mirror or when the quality of the image starts to decline, it suggests that the mirror requires cleaning.

Here are a few basic suggestions on how to clean a mirror on a telescope.

Take it easy. Don’t rush to clean the mirror just before observing. Take your time to complete the process.

Eliminate loose dust and dirt using compressed air or a brush. Avoid blowing air onto the mirror or using your breath to remove dust, as it may cause moisture to accumulate.

All remaining dirt and dust can be removed with a lint-free cloth or soft camel hairbrush. Note that paper towels may scratch the mirror. In case a cleaning solution is necessary, ensure it is specially formulated for telescope mirrors.

To clean the mirror, use the cleaner in small amounts and apply it in a circular motion gently. Avoid rubbing hard, as it may cause damage to the mirror coating.
Rinse the mirror with distilled water and then dry it with a clean cloth or towel, making sure not to touch it with your fingers. Check the mirror under good lighting to confirm it’s clean. If there are streaks or residues, repeat the cleaning process.

To prevent dust and dirt from accumulating on the surface, store the mirror in a clean, dry place and cover it.

How do you remove fungus from a telescope mirror?

Here are some suggestions that might assist you.

Initially, delicately eliminate any detached fragments or dirt from the mirror using a gentle brush, pure cotton cloth, or compressed air.

Afterward, make a mixture that contains the same amount of distilled water and isopropyl alcohol.

Moisten a soft, tidy fabric or cleaning pad with the mixture and delicately clean the mirror in circular movements, being careful not to use excessive force.

If the fungus is stubborn, you can use a mixture of hydrogen peroxide and ammonia (1:1) to remove it. But use this solution with extreme caution as it can damage the mirror coatings, and, after the application, rinse the mirror with water and dry it with a clean cloth.

When you finish cleaning the optical coatings, either allow it to air dry or use a soft, lint-free cloth to dry it. You must avoid using abrasive materials or paper towels to dry the mirror.

It is better to prevent an issue than to deal with it later. Keep your telescope in a place that is well-ventilated and dry to prevent moisture or dampness.

Additionally, regular cleaning of the primary mirror and secondary mirrors in the optical tube can stop the fungus from accumulating.

Can you clean a telescope lens with Windex?

Using Windex or other general cleaning products to clean a telescope’s dirty lenses is not advisable, as they may include harmful substances that can harm the coatings and scratch the lens.

Custom-made lens cleaning solutions and microfiber cleaning clothes are suggested for telescope cleaning. It is also recommended to use dust caps.


Telescope mirrors need to be clean to ensure that they reflect light accurately and effectively, without any impurities or distortions.

Any dirt or dust on the mirror can cause scattering and absorption of the light, leading to a decrease in image quality, brightness, and contrast.

It can also create unwanted glare, halos, or other optical aberrations that can hinder the telescope’s ability to reveal fine details or faint objects in the night sky.

Therefore, regular maintenance and cleaning of telescope mirrors are important to keep them in optimal condition for observing the universe.

Ida Stewart

I have had the incredible opportunity to work as a tour guide at the planetarium for over 5 years. Ever since I was a child, astronomy has held a special place in my heart, and I have nurtured a deep passion for exploring the wonders of the universe. Among all the celestial bodies, Mars has always fascinated me the most, captivating my imagination with its mysterious allure.

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