How To Clean Your Telescope Mirror or Lens

Telescope optics become dirty with use, just like any other items.

This can be disheartening because you want to keep your telescope looking like it’s brand new and has just been unpacked. To restore its mirror or lens, you should clean it in the correct way.

What happens if you don’t clean your telescope mirror or lens?

When dirt accumulates on a lens or mirror, it causes the light to scatter. The result is that you end up seeing celestial objects that don’t look as clear as they should.

While it might seem like a daunting task to have to clean your telescope’s mirror or lens, it really doesn’t have to be. Follow this guide to ensure that it’s easy and doesn’t cause any damage to your telescope. 

How To Clean Your Refractor Telescope Lens

Be very careful when cleaning your telescope lens. Household detergents are dangerous as they can damage the lens and reduce its quality.

The best way to keep your lens clean is to use a brush that’s made with camel hair, which is soft so it won’t cause scratches on the lens. You can find these brushes in camera stores.

However, it’s been said (via Sky at Night ) that an air blower is an effective way to remove particles such as dust from the refractor telescope’s lens.

This provides a high-powered blast of air to remove dust and other particles, but it’s not enough – you’ll have to finish off the cleaning process with a special lens solution. 

Note: a high-powered bulb air blower is useful, but you should remove its brush attachment as that could transfer more dirt to the lens that you’re trying to clean.

The Best Cleaning Solution For Telescope Lenses

In the case of stubborn stains, the best way to clean your telescope lens is to use a lens cleaning solution that’s made up of pure isopropyl alcohol or methyl alcohol. You can also find lens pens that are very convenient to use.

These are soft solvent-doused cleaning pads that are retractable, so they’re perfect for removing tiny flecks and stains more accurately. 

However, when you want to clean the lens with a solution like the one listed above, you should never put it directly onto the lens.

If you do, the liquid can accumulate around the edges of the lens and this can cause stains in places you won’t be able to reach. Instead, always apply the solution to the cleaning pad. An effective cleaning pad to use is a pure cotton cloth.

How To Prevent Dirty Lenses In Future

The best way to prevent your telescope lens from becoming dirty in future is to ensure that you always keep its lens cap on when you’re not using the telescope! This will ensure that dust and dirt can’t reach the lens and cause distortions in what you see in the night sky. 

When you’re handling and using your telescope, it’s essential that you avoid touching the lens or mirror surface. This is because your skin’s oils can cause the optical coatings to degrade over time.

If it happens that you touch the surface and leave a fingerprint, make sure you wipe it off immediately – you can use the previously-mentioned solution.

It’s worth mentioning that you shouldn’t obsess over a few dust particles that are on your telescope lens, unless there are many of them. It’s better to leave them alone as they won’t get in the way of your sky views.

What Happens If Dirt Is Trapped Inside The Lens?

Now, this is a trickier situation and one that’s best left to a professional. While it’s tempting to take apart the telescope, this should not be undertaken.

The reason why is because you’ll have to cock the lens and if you do it too roughly it will cause the edge of the lens to crack.

How To Clean Your Reflector Telescope Mirror

We’ve looked at how you can effectively clean the lens of your telescope, but what about its mirror?

You’ll find mirrors in a type of telescope called reflectors. These use mirrors instead of lenses in order to focus the light. There are usually two mirrors in a reflector.

To clean the mirrors of your reflector telescope, you will have to disassemble it. This is something that you shouldn’t do lightly so only commit to it if your mirrors are really dirty. If you have to clean them, here are the steps to follow.

• First, you want to unscrew the screws that attach the main mirror’s cells to the end of the telescope tube.
• Carefully reach in the back and pull out the cell. You’ll see it has the mirror inside.
• Undo the clips that are keeping the mirror in place. Then, push the mirror out the back. Be careful not to touch its surface!
• Remove the holder that keeps the small, secondary, mirror in the front of the tube and take it out of its holder.
• Once you’ve removed the mirrors, you will need to head into the kitchen because you need to make use of your kitchen sink.
• Ensure that your kitchen sink is clean, then place a towel in it. 
• Put the first mirror on it. Make sure the mirror is facing up.
• Blast the mirror with warm water from the tap to remove any dust on its surface. This is important because you don’t want to rub the mirror as that can cause small cracks to form on its surface.
• Turn off the tap and wash the mirror with a bit of distilled water so that it won’t leave any mineral deposits on it once the mirror has dried.
• Put the mirror on a folded towel on its edge to let it air dry. 
• Repeat this with your second mirror if your telescope has one.

What Happens If The Mirror Is Still Dirty?

You’ll have to do a bit of a deeper clean!

Here’s what you’ll need

• Towel
• Sink
• Water
• Liquid detergent
• Cotton ball

Instructions

• Put the towel back into your kitchen sink and place the mirror on it, facing upwards.
• Fill half the sink with warm water.
• Put in a few squirts of gentle liquid deterrent and let the mirror sit in the water for up to 10 minutes.
• Afterwards, you want to hold it under the water and move it around a bit so that you can wash off any debris.
• With a wad of cotton, gently swab the mirror in one direction and without putting too much pressure on it. Always use wet cotton as it will be much less abrasive than if it’s dry.
• Then, you can drain your sink but do one last blast of water on the mirror: run it under warm water for 60 seconds.
• Rinse it with distilled water, then place it on a towel to dry.
• You can go ahead and follow the same steps with your secondary mirror.

Notes:

• Always make sure you clean your telescope mirror separately to prevent them from touching or scuffing each other.
• Never rub the wet cotton wool across the mirror’s surface, as that can scratch it.
• When you reinstall the mirrors, you’ll have to collimate your telescope again. This is another good reason why you should only clean it when you really need to.
• To prevent the mirrors from being damaged when they are air-drying, you should place a towel over your dish rack and then prop the mirrors in it so that they will stay upright.

Related Questions

What happens if your eyepiece coatings have been discolored?

This can happen from fingerprints and eyelash oil, but the good news is that they don’t decrease the eyepiece’s performance.

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

You can make your own with a shower cap, dishcloth, or plastic bag. To protect the front of the telescope tube, cover it with one of these and secure it with a rubber band.

Conclusion

The sight of dust on your telescope lens or mirror is enough to make you worry that its quality is decreasing.

But, as we’ve seen in this article, you shouldn’t worry too much about a little bit of dust. If you have more than a bit of dust or other marks on your lens/mirror, then you should clean it by following the steps we outlined in this article.

The most important thing to do is take your time and work slowly. When it comes to how to clean your telescope mirror and lenses, it’s important to treat them with the utmost care!