How Do You Clean Dirty Telescope Lenses?

No matter whether you’ve recently purchased your first telescope for astronomy and want to learn how to properly care for it, or your trusted favorite has started to look a little worse for wear, one of the most important aspects of maintaining a telescope is to properly clean its optics.

How Do You Clean Dirty Telescope Lenses

At some point or another, it’s only to be expected that your telescope is likely to get a little bit dirty, especially if you’re using it in an outdoor environment.

Dirt that is present across the lenses of your telescope can cause the light to become distorted, causing dark skies to appear lighter than they actually are, and causing objects in the sky to appear blurry and out of focus. 

Prevention is nearly always better than correction, so one of the first steps you should take to ensure that your telescope’s optics remain optimal is to reduce the chances of any dirt getting stuck in the lenses of your telescope in the first place.

With that being said, you should make sure that you always keep the cap of each lens firmly on whenever possible, and that goes for when you’re traveling with it, storing when not in use, and even taking a break from using it to grab a drink or take a break while admiring the night sky. 

If you do need to clean your telescope lenses, then one of the first things you should do is to gently blow on the surface. Form a cup shape with your hand and hold it over the lens, and then gently blow on it for a few seconds.

This will help to get rid of any surface dirt and dust particles without actually touching the surface.

Failing that, then the next best thing that you can do is to take either a cotton swab soaked in detergent or a lens cleaning tissue, and gently wipe in one swift motion to remove residue and stains. 

While cleaning, try your best to avoid touching the lens with your fingers, or adopting a rubbing motion, as both of these things can cause your lenses to become damaged.

What can I use to clean my telescope lens?

If you want to clean your telescope lens, then there are a variety of different options available to you to choose from. Prior to cleaning your lens, you should first decide whether or not it really needs to be cleaned.

Most dust particles or finger smudges do not cause any changes to the visuals when using it, and cleaning almost always comes with the risk of scratches and other types of damage.

Nevertheless, you’re going to need to clean your lenses and mirrors sooner or later (especially if you like to observe outdoors, or frequently travel to different observing spots) so you’ll need to make sure that you know what to do!

Below, let’s take a look at some ways that you can clean the lenses of your telescope:

  • Blowing method: This method is the most non-invasive, and consists of blowing air across the surface of your lens or mirror, to rid it of any surface debris.
  • Water method: You can place both telescope’s mirrors and lenses under a running tap of water for around two minutes, and this will lift away grime and dirt. 
  • Wipe method: This is most suitable for very dirty lenses and mirrors, as well as the diagonal mirror, and consists of gently wiping a telescope cleaning wipe across the surface, which will pick up any residue without causing any damage or scratches.

How do you clean the diagonal of a telescope?

If you need to clean your telescope’s diagonal mirror, then you won’t be able to clean it in the way you would the other lenses and mirrors of your telescope, as the diagonal is very easy to scratch and damage due to it being so delicate.

A little bit of dirt or dust across the lens of your diagonal shouldn’t affect the visual quality of your telescope, so it’s important to keep in mind that you should only ever clean your diagonal mirror if it is absolutely necessary.

  1. The first step is to try and remove as much dust and dirt from the surface as possible without actually touching it. Take a rubber ear syringe and gently hold it over the surface of the diagonal, before proceeding to then blow off all of the surface dirt particles. 
  1. Then, take a cleaning pad or tissue that has been specifically designed to be used on a telescope lens (such as these), and then gently wipe across the surface. While wiping across the surface, make sure that you are not applying any pressure from your fingers, while also ensuring that you do not rub the wipe at any point, as this could cause the diagonal to become scratched up.
  1. Carefully remove the cleaning tissue from the surface of the diagonal mirror, and allow the surface to dry completely.

As a side note, it’s very important to keep in mind that the diagonal mirror is very delicate and prone to damage, which means that you won’t be able to use any water-based cleaning products as they will only end up leaving a watery residue on the surface which will affect the visuals while observing.

How do you polish a mirror on a telescope?

If you wish to clean and polish the mirrors on your reflector telescope, then you’ll first need to decide if you feel you are confident enough to be able to disassemble the telescope, and then put it back together/realign it again. 

First, you’ll need to undo all of the screws that attach the main mirror to the back of the telescope’s tube.

Then, carefully take out the cell that contains the mirror inside of it, take out all of the remaining screws currently holding the mirror in place, and then pop the mirror out of its frame.

While doing this, be extremely careful to not let anything touch the surface of the mirror.

Place the mirror upright on a towel, and place it directly into a sink. Ensuring that the drain is not covered, blast the mirror for a minute or two, and this will effectively remove all of the dirt and dust to return your mirror back to its original, shiny appearance.

Then, take a lens cleaning tissue and gently wipe it across the surface of the mirror to get rid of any leftover stains. 

Keep in mind that these instructions are merely a guide to help give you an idea of what you’ll need to do to clean polish your telescope’s mirrors.

We also recommend that you refer to the owner’s manual when assembling your telescope, as you’ll have access to instructions tailored specifically to your model of telescope. 

Gordon Watts
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