How to Clean A Telescope: Step By Step Guide

By Chris Cook & Brian Fulda

 

Cleaning a telescope depends on which type of telescope you have, but usually involves removing dust & debris with a brush or blower and then cleaning the optics. The steps to clean a telescope are different for telescopes with lenses vs. telescopes with mirrors. In this guide, we’ll go over how to clean both, along with some other tips to keep your telescope in tip-top shape for observing. Jump to the following sections:

Important Note Before Cleaning

If your telescope is only a little dusty, it likely doesn’t need to be cleaned at all! Most telescopes can function perfectly fine even with a moderate layer of dust or debris on the front lens. In many cases, we recommend leaving your telescope alone as accidents and damage can occur while cleaning a telescope if you’re not careful. Only if your telescope has a thick layer of dust or grit should you proceed carefully with the steps below.

 

 


How to Clean A Telescope Lens

For Refractor, Schmidt Cassegrain, & Maksutov Telescopes

You will need a few items to properly clean your telescope’s lenses. If you’d like to skip buying each one individually, we highly recommend this Celestron Lens Cleaning Kit. Here is the full list of items you will need:

  • Microfiber brush or rocket air blower
  • Lens cleaning tissues or 100% cotton balls
  • Optical cleaning solution

Note for Schmidt Cassegrain, Maksutov, and RASA telescope owners: Do not remove the corrector lens on the front of your telescope for cleaning or any reason unless absolutely necessary. Each corrector lens is rotationally positioned at the factory for best performance. This is sometimes marked with an indicator line, allowing you to line it up again in case it is removed, but not always. Improperly positioning the rotation of the corrector lens can ruin the telescope's performance. For this reason, we don't recommend doing this unless you have prior experience. Just focus on cleaning the front of the corrector lens without removing it, and you won't experience any issues. If you feel you must remove the corrector lens, please contact your telescope's manufacturer first.

Step 1: Remove dust and debris

You can do this using a microfiber brush or air blower bulb. Just let the weight of the brush glide over the surface or blow off the dust. This should remove any larger loose debris. We don’t recommend using compressed air as it can permanently damage optical coatings.

Step 2: Clean the front lens

With the lens pointed upwards, spray the surface with an optical cleaning solution several times so it is evenly coated. Let the solution soak for about 30 seconds. With a soft lens tissue or cotton ball, gently wipe the surface in one direction and then discard. You will want to use a new clean tissue or cotton ball for each pass. Doing this ensures that any removed dirt is not reapplied to the lens. 

Step 3: Make multiple passes until the lens is clean

Make several passes to ensure all of the solution has been removed. Check the lens for any remaining dust, dirt or contaminants. Repeat the process until the lens is clean. Remove all cleaning solution before covering the lens and storing the telescope in its case.


How to Clean A Telescope Mirror

For Newtonian, Dobsonian, & Ritchey Chretien Telescopes

Cleaning the primary mirror on a telescope is a bit more challenging as it requires you to remove the mirror and its cell from the optical tube. This will require you to remove the clips that hold the mirror in place and recollimate the telescope once complete. For these reasons, we don’t recommend cleaning telescope mirrors unless you absolutely have to. As previously mentioned, a minor coating of dust will not impede a telescope's performance at all. Only proceed if there is a thick coating of dust or grime you cannot remove with an air blower. Never use compressed air to clean a telescope.

To clean a telescope with mirrors, you will need:

  • Access to a large sink
  • Plastic dish rack
  • Soft hand towel
  • Non-abrasive dish soap
  • Distilled water
  • 100% cotton balls
  • 91% isopropyl alcohol (optional)

 

Step 1: Rinse the mirror

First, remove your telescope's primary and/or secondary mirror by removing the mirror clips and/or screws. Next, bring all of your materials, including the mirror(s), over to your large sink. Turn your sink's faucet on and let it adjust to room temperature water.

Place the dish rack or towel at the bottom of a sink to hold the mirror. Grab the mirror and angle it diagonally upwards towards the faucet, either by holding it or letting it rest in the dish rack. Using a dish rack is preferred as it will help keep the mirror angled upward.

Then, turn on the faucet for several minutes or use a cup and pour room temperature water run over the mirror. This will help loosen and remove any larger pieces of dirt or debris on the surface.

Step 2: Clean the mirror with soapy water

Next, mix a bowl of soapy water at room temperature with 1-2 drops of non-abrasive dish soap. Holding the sides of the mirror, pour the soapy water onto the surface of the mirror and soak it for several minutes, then rinse with room temperature faucet water.

Step 3: Clean the mirror with a cotton ball

Next, gently drag a soapy wet cotton ball across the mirror’s surface. Use a new cotton ball for each pass and discard the used cotton balls as you go. Once the entire mirror has been cleaned, rinse it one more time with distilled water.

One optional step is to use 91% isopropyl alcohol and rinse the entire surface of the mirror. This will remove any remaining water drops and prevent water spots from forming.

Step 4: Let the mirror dry

Set the mirror vertically on its edge to air dry for a few hours on a soft, clean towel placed on a dish rack. Once dry, reinstall the mirror into your telescope and recollimate it using collimation tools.


How to Clean A Telescope Eyepiece

Telescope eyepieces are quite easy to clean. Like an objective lens or corrector plate, modern eyepieces almost always have durable multi-layer coatings. Make sure these coatings are not damaged before cleaning.

To begin, use an air blower bulb or soft camel hair brush to remove any large loose deposits on the lens. Next, spray a small amount of optical cleaning solution to a lens tissue or microfiber cloth. Gently rub the lens, rotating the tissue or cloth to a clean damp section as you go. If the lens looks clean, you’re done! Repeat the process if there are still specks of dirt or smudges. If the lens is still not clean, it could have a fair amount of microscopic oil residue on the surface. This oil can come from the environment or your eyelashes and skin as you observe. In this case, use a ROR solution (Residual Oil Remover) and continue the cleaning process as described above. Once your optics are clean, you are now ready to explore the cosmos with your telescope while also enjoying clear crisp views.

 


Tips to Keep Your Telescope Clean

Most telescopes and eyepieces become dirty from neglect or improper storage. We strongly recommend using the dust covers and dust plugs that came with your telescope to cover the optics after use. If you don’t have these, you can shop for replacement dust plugs and end caps on our website.

We also strongly recommend purchasing a telescope case to keep it protected when not in use or when traveling. Cases not only keep your telescope clean from dust, but they protect the delicate optics inside from bumps or slight drops. 

 

 

Disclaimer: Telescopes are very fragile, and caution must be taken while following these steps carefully. If you're stuck and unsure how to proceed, the best action is no action until you identify a solution. Agena Astro is not responsible for any damage caused to telescopes or optics from following the steps in this article.