How to Clean Telescope Mirror

Keeping your telescope in good condition is essential for ensuring you get the best quality images of the night sky, and for prolonging the lifespan of your telescope.  

In particular, your telescope mirror will be exposed to dust particles, and these have silica in them that is very abrasive and can cause damage to your mirror. However, it’s not as simple as just picking up a cloth and wiping the mirror clean, as tempting as this may be.  

A regular cloth may scratch the surface of the mirror, which is very delicate, so it’s best to use a soft fabric to clean your telescope components.  

Ensuring your telescopic mirror is kept as clean as possible is essential for ensuring you get the best view possible. Experts suggest that the total dirt on the mirror surface should amount to about 1/1000th of the entire area

 If you have dust on the mirror, it may disseminate the light particles inappropriately, causing your images to become blurry and dark. 

Of course, it’s not possible to keep your mirror 100% spotless all of the time, and getting some dust on there is inevitable. The main thing is that you know the correct way to clean your telescope’s mirror.  

Keen to find out how to clean your telescope's mirror? Keep reading to find out how...

Cleaning the Mirror

Use compressed air to blow off the dust from your telescope. The mirror must be left in the tube with both ends of the tube facing downwards.

You should also maintain a 1-foot distance as you blow the mirror, and let the telescope tube face downwards for 15 minutes after blowing. This allows any excess dust to fall out of the tube. 

However, you should avoid regular cleaning of the mirror as this can cause it to wear out, which will reduce the collimation effect. You should also use distilled water, as it is free of any impurities that may corrode your mirror. 

Limited Aperture Cleaning

This is the best way to clean your telescope if you need to clean a specific spot or stain. 

You Will Need:

  • a facial tissue or cotton cloth, as well as one quart of fresh acetone or propanol solution.

Procedure for Cleaning

  1. You should fold the soft tissue twice and ensure it’s thick enough not to break when wet. 
  2. Blow warm air on the area of concern and then get rid of the stain by wiping with the tissue in one direction. 
  3. Next, dampen an additional tissue with the solvent and lightly wipe the area of concern. This will remove any remnants left over from the initial wipe. 
  4. Repeat this process until you are satisfied that no visible remnants are remaining. 
  5. Finally, blow on the mirror again to check whether it’s clean - monitor the vapor as it escapes from the mirror to inspect the cleanliness of the mirror.

Full Aperture Cleaning

This technique will help clean your secondary mirror and is also useful for those with large telescopes.

It’s worth considering that if your telescope is significantly big, you’ll need the hands of an extra person to help you tip it.

You Will Need:

  • A high-pressure duster, 2 gallons of distilled water, 2 quarts of fresh acetone or propanol, sodium lauryl sulfate soap, a 4-quart pan, and lens tissue or cotton.

Procedure for Cleaning

  1. Mix approximately one teaspoon of soap with two quarts of deionized water in the pan. Place the mirror on a flat surface, lift one side, and blow off any dust that has settled on it, then repeat the process with distilled water to get rid of any contaminants that may scratch the surface during cleaning.
  2. Next, place the mirror on a flat surface and wash it with the soap solution and tissue without allowing the surface to dry up. We say not to allow the surface to dry up because if it dries up too quickly, stains may be formed by the soap solution. 
  3. Leave the mirror on an even surface and rinse it with water to get rid of the soapy solution. Then lift the mirror slightly and blow the solvent from the surface in a back and forth motion. Finally, dry the edges of the mirror with cotton to remove any streaks.

Tips for Keeping Your Telescope Clean

  • Avoid touching the mirror and lenses. If you handle these your skin may leave marks on the surface, but it can also cause long-term corrosion, as your skin contains acidic oil.
  • Your telescope’s eyepieces should have a cap on both ends for protection. Alternatively, they can be stored in plastic containers, or, if yours is missing, you can use a shower cap as an alternative.
  • Always store your reflectors with all the mirrors facing downwards. This prevents them from accumulating dust. 
  • Like we said earlier, you should always use soft cloths to clean the lenses and mirrors of your telescope. Solid and fibrous materials are too harsh and can scratch the surface of the mirror and cause damage and corrosion. 
  • When you are not using your telescope, keep it covered up with a plastic bag, as this minimizes the accumulation of dust on the device.
  • Always store the telescope away from direct sunlight, and keep it in a horizontal position to avoid the settling of dust on the mirror.
  • When not in use, plug the hole of your focuser with a plastic 35mm canister.
  • Avoid cleaning the telescope regularly, as over-cleaning the telescope causes corrosion of the mirror surface.
  • When using compressed air to clean your telescope, always regulate the pressure. Too much air can loosen the components of the gadget.

How Do I Know the Mirror Needs Cleaning?

Over time your telescope’s mirrors will inevitably accumulate dirt and dust when stored without use. To minimize the impacts of this, routinely clean your mirrors even when they appear clean. The regular cleaning and maintenance of your telescope will ensure you get the most out of it and that you prolong its lifespan.

In Summary

Cleaning something as valuable as a telescope may seem daunting, but when handled with care, and cleaned with the right materials, this is a pretty simple task.

While you should avoid cleaning your telescope too often, it’s still important to schedule routine maintenance even if your lenses or mirrors do not appear to be dirty.

You can’t ever fully prevent dust from settling on the surfaces of these, however, capping the ends and ensuring your telescope is stored correctly is a simple way of minimizing the amount of dust that gets into the device.

Gordon Watts
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