How to Clean Telescope Mirror: 11-Step Quick Guide

Chris Klein, Amateur Astronomy Advisor

By Chris Klein

Updated:

Cleaning your telescope mirror can seem daunting, especially if you’ve never done it.

It’s scary to be taking apart your telescope. You also want to avoid causing any damage to the mirrors just by cleaning them.

The good news is it’s a relatively straightforward process, but there are a few things you need to consider.

This article shows you 11 easy steps to clean your telescope’s primary and secondary mirrors.

In this article, you get

A complete list of the required materials

An easy-to-follow 11-step guide

Tips and tricks for protecting your mirror

By the end of this article, you’ll have the confidence to clean your telescope mirror.

Let’s dive right in.

HOW TO KNOW WHEN TO CLEAN

Assuming you have a Newtonian reflector telescope, there are a few things to look for before you decide your mirror needs cleaning.

First, take a look at the surface of your mirror. If you see any dust or fingerprints, it’s time to clean the mirror.

Another way to tell if your mirror needs cleaning is by checking the performance of your telescope. If you notice that your images are not as crisp and clear as they used to be, it’s likely that your mirror is dirty and needs cleaning.

If you still need to figure out whether or not your mirror needs cleaning, here’s a simple test you can do:

Take a look at a bright star or planet through your telescope. Then, cover half of the lens with a piece of paper.

Your mirror doesn’t need cleaning if the image is still clear and sharp.

If the image becomes fuzzy or distorted when you cover half of the lens, it’s time to clean your mirror.

HOW OFTEN SHOULD I CLEAN MY TELESCOPE MIRROR?

Checking if your optics are clean regularly is a good idea, especially if you live in an area with a lot of dust or pollen. You’re good to go if your mirrors are clean and free of smudges, fingerprints, or other dirt!

If not, you can follow the step-by-step guide below.

Before doing so, however, it’s essential to realize why you may want to avoid cleaning your telescope mirror.

WHY SHOULDN’T I CLEAN MY TELESCOPE MIRROR?

There are a few reasons why you shouldn’t clean your telescope mirror.

  • It’s unnecessary – unless the mirror is significantly dirty, there’s no need to clean it.
  • It’s risky – cleaning the mirror can damage it if done incorrectly.
  • It’s time-consuming – depending on the size of the mirror, cleaning can take anywhere from a few minutes to a few hours.
  • It’s messy – dealing with soapy water, towels, and cotton swabs can be annoying.

PRECAUTIONS TO TAKE BEFORE CLEANING

If your telescope mirror needs cleaning, you may still want to take precautions.

You’ll want to pay attention to whether or not the coating on the mirror is damaged.

HOW CAN I TELL IF MY COATING IS DAMAGED?

It’s essential to inspect whether or not your mirror coating is damaged.

Below are a few things you should watch out for as you perform the cleaning.

  • Look at the surface of the mirror. If you see significant scratches or haze, the coating is damaged.
  • Look at the reflection of the light off of the mirror. If the reflection is very dim or fuzzy, the coating is damaged.
  • Look at the water during cleaning. The coating is intact if the water beads on the mirror’s surface. However, the coating is damaged if the water soaks into the mirror or leaves streaks behind.

CAN I GET MY TELESCOPE MIRRORS RECOATED?

Yes, you can get your telescope mirrors recoated.

The process is called re-aluminizing, which involves stripping the old coating off the mirror and applying a new one.

Recoating is a fairly involved process and should only be attempted by someone with experience. It would be best if you used a company specializing in this service.

10 REQUIRED Materials FOR CLEANING

1. WORK AREA

A good work area is one of the critical things you’ll need to clean your telescope mirror safely. I highly recommend you clean off your kitchen countertop and use that as your work area.

2. LUKEWARM TAP WATER

One of the tools you’ll be using is lukewarm tap water, so setting up your work area near your kitchen sink is ideal. A spray nozzle attachment on your kitchen faucet is perfect.

3. DISTILLED WATER

You’ll need a gallon of distilled water to prevent water stains on the mirror surface.

4. BASIC TOOLS

Check your telescope’s operating manual, or look at it directly to see what essential tools you need. You’ll need a few tools like a screwdriver or hex key to remove the mirrors from your telescope. Grab some tape or a pen so you can mark the orientation of the primary mirror.

5. CLEAN LINT-FREE TOWELS

You’ll want to place a few clean towels on the kitchen countertop to avoid chipping your mirror.

6. BULB BLOWER

I recommend using a projectile-free clean-air blower. Avoid using a can of compressed air because due to chemicals that may be present.

7. LENS CLEANING BRUSH

These brushes are static-free and contain no abrasives or silicones.

8. LIQUID DISH SOAP

Regular liquid soap used to clean dishes is ideal for loosening grime or grease that may be on your mirror.

9. ISOPROPYL ALCOHOL OR METHYL ALCOHOL (METHANOL)

Pure Isopropyl or Methyl alcohol is suitable for removing tough dirt. Avoid diluted rubbing alcohol or any other cleaning solution. It’s best to use pure alcohol.

10. SMALL SOFT, LINT-FREE CLOTH (OR COTTON WOOL)

These cloths absorb moisture well and don’t leave behind any lint. These remove excess water and any hard-to-remove dirt from the mirror’s surface.

HOW TO CLEAN TELESCOPE MIRROR: STEP-BY-STEP GUIDE

You should now be ready to clean your telescope mirror.

I’ve put together the below 11-step process to make it easier for you to follow. You may not need to perform each step.

I recommend you read the whole process through before starting with the first step.

STEP 1: PREPARE THE WORK AREA

One of the first things you should do is to prepare your work area.

Your work area will be from the left of your kitchen sink to the right side.

Place some of your lint-free folded towels on either side of the sink. Use several towels so that you have a work area that’s large enough to accommodate both your primary mirror and your secondary mirror.

Move anything away that you don’t need for cleaning the mirror.

Placing a clean towel or soft padding inside your sink would ensure a soft footing for the mirror.

STEP 2: REMOVE THE PRIMARY MIRROR

The next step involves removing the primary mirror cell from the telescope itself.

Do so now if you wish to place a mark to indicate the mirror’s orientation.

Remove the screws around the telescope base. Your mirror may also be held in place using some mirror clips. Remove any bolts from these clips to release the mirror.

Gently place the primary mirror on one of the towels on the left side of your sink.

Avoid bumping the mirror into anything to eliminate the chance of chipping the coating.

STEP 3: REMOVE THE SECONDARY MIRROR (OPTIONAL)

This next step is optional because you may not want to or need to clean your secondary mirror.

My general advice is that you don’t need to clean it.

If you are going to clean your secondary mirror, then carefully remove it now from the spider assembly holding it in place.

Gently place the secondary mirror on a separate towel to the left of your kitchen sink.

STEP 4: REMOVE THE GRIT

Use the bulb blower to force air onto your mirror (or mirrors). The forced air is the best way to remove much of the larger loose dust particles and grit on your mirror.

You may also use a soft brush to remove any little dust during this step.

Removing the dust particles before you wash the mirror minimizes the chance of scratching.

STEP 5: WASH THE MIRROR

Turn on your tap water and adjust the temperature until it’s lukewarm.

Gently place the mirror inside your sink on the towel or soft padding. Let the water hit the mirror for a few minutes to wash away any dust or particles.

Using only water is your first pass at cleaning the mirror. You may or may not need a second pass, which is a future step.

Turn off the tap water.

STEP 6: RINSE THE MIRROR

Rinse the mirror using a bottle of distilled water.

The distilled water rinse removes any minerals that may have been present in your tap water.

STEP 7: DRY THE MIRROR

Gently move the mirror from the sink to one of the clean towels on the right side of the sink.

Prop the mirror up upright to allow the water to naturally run off the mirror’s surface for the drying process.

Avoid touching the mirror’s surface and avoid causing any chips along the vertical edge of the mirror by gently placing it on the towel.

STEP 8: INSPECT YOUR FIRST PASS

This next step is an inspection to see if you have finished or need to continue cleaning.

Suppose there is still a lot of dirt or grime visible, or you can see finger prints on the mirror’s surface. In that case, I recommend continuing the cleaning process.

If the mirror looks much cleaner than before and you’re happy with the results, consider stopping here.

STEP 9: SOAK THE MIRROR

Gently place the mirror back into the sink. Fill the sink with enough lukewarm water to submerge the entire surface of the mirror.

Add a few squirts of liquid detergent and let the mirror soak in the soapy water mixture for up to 10 minutes.

You may gently move the mirror around underwater to remove any stubborn dirt.

STEP 10: SWAB THE MIRROR

This next step is again optional and somewhat risky. This step is the first time you will contact the mirror’s optical surface.

Avoid applying any pressure beyond simply making contact with the mirror.

Using a small soft, lint-free cloth or several cotton swabs, gently swab the mirror underwater. This step is the gentlest cleaning possible.

Avoid scratching the mirror’s coating by being extraordinarily gentle and using a different part of the cloth or a new cotton ball for subsequent swabbing.

In extreme cases, you may have stubborn dirt. If so, it will require slightly more aggressive cleaning. You may use alcohol with a cloth or cotton balls.

Apply the alcohol to the cloth or cotton balls, not directly to the telescope mirror surface. Allow the alcohol to do its job to lift the dirt.

Again, be extremely gentle as you swab the mirror to remove any stubborn dirt.

STEP 11: RINSE AND DRY THE MIRROR

The final rinse with distilled water will wash away any minerals from the tap water, liquid detergent, and any alcohol you may have used.

If you see a water mark, once the mirror has air-dried, you can dab off any minor spots using a new lint-free cloth.

If you also decided to clean the secondary mirror, go through steps 4-11 again with the secondary mirror.

When done with both mirrors, reassemble the telescope by reversing steps 2 and 3 above.

Once it’s reassembled, it will need to be collimated. Read my article How to Tell if Telescope Needs Collimation for 3 easy ways to collimate.

CONCLUSION

Your telescope mirror (or mirrors) should now be clean!

Cleaning telescope optics seemed like a daunting task, but now it’s an easy-to-follow 11-step telescope mirror cleaning process.

The most important thing to keep your telescope’s mirror clean is protecting it from dirt and dust by installing its protective cap.

Looking up at the night sky and peering into deep space is a humbling experience. The sky’s stars seem so limitless, yet, if you have a telescope, you can bring them closer to home.

And with a clean mirror, you’ll see them closer and brighter than ever.

Clear Skies!

FREQUENTLY ASKED QUESTIONS

CAN YOU CLEAN A TELESCOPE MIRROR WITH WINDEX?

No, I would not recommend cleaning your telescope mirror with Windex. It’s best to use pure alcohol, like Isopropyl or Methyl alcohol. Pure alcohol is suitable for removing tough dirt.

WHY IS EVERYTHING BLURRY IN MY TELESCOPE?

One of the reasons everything is blurry in your telescope is that the mirror is dirty. Dust, grime, and maybe even fingerprints have gotten on the mirror. Cleaning your telescope mirror seems daunting, but it’s pretty simple.

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About the Author

Chris Klein, Amateur Astronomy Advisor

Chris Klein is an amateur astronomy advisor, astrophotographer, and entrepreneur. Go here to read his incredible story "From $50,000 in Debt to Award-Winning Photographer Living in Switzerland". If you want to send Chris a quick message, then visit his contact page here.

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