When it comes to keeping your telescope clean, prevention is better than cure. Stopping your telescope becoming grubby in the first place is preferable to sorting out the consequences afterwards. It’s impossible to keep a scope in perfect condition forever, unless you’re guilty of the worst crime against astronomy and have never unwrapped it!
Over time, dust and grime will build up on the surfaces of your telescope’s optics and some gentle care will be needed to bring them back to full glory. This is a particular problem with Newtonian scopes and the large Dobsonians with open tube, or truss, designs.
However, you should only clean the optics when it’s really necessary. After all, a small amount of dust doesn’t do much harm to the view, whereas physically cleaning the mirror or lens can do far more damage.
For more on telescope and equipment cleaning, read our guide on how to prepare for the new astronomy season.
Complete cleaning guides:
How to protect your telescope
When not in use, all optics should be protected with lens, eyepiece and finderscope caps or hoods. If you can, store your telescope in a dust and dirt-free environment.
A garage or garden shed may be practical, but not necessarily the best for your scope. An indoor cupboard that can be kept clean is the best option.
Even with the lens cap on, dust within the scope can fall down. So store your scope with the reflective side of the main mirror facing down to avoid this.
As for accessories like eyepieces, they’ll stay in tip-top condition if they’re kept in sealable plastic boxes or bags.
A spray such as WD-40 shifts old grease from your telescope mount and protects parts from moisture. Credit: Anton Vamplew
How to clean your telescope
Even after following all this advice, there’ll come a time when you feel a clean is in order. First, make sure that the area in which you clean is clean itself.
Don’t do it outside at night and never use a red lamp, as you will not be able to see the dust. A clean kitchen table under a bright lamp for uniform lighting is a good place to do it.
The following equipment is useful for cleaning a telescope:
- Microfibre lens cleaning cloth
- Air-blowing bulb (without the brush)
- Alcohol-based cleaning fluid
With regard to the final item, acetone cleaning fluid is not recommended as this can dissolve paint and plastic from around the edge of the lens. And never use nail-polish remover.
Cleaning a mirror in a reflecting telescope is quite simple – it can be cleaned in a washing-up bowl filled with warm tap water and a few drops of washing-up liquid.
After cleaning, rinse with distilled water (available from chemists) and leave to dry.
Don’t forget the mount. Many people use a spray, such as WD-40, to get rid of old grease on the gears and protect the parts from moisture.
Replace any grease you take out with white lithium grease available from cycle shops.
A different procedure is used to clean a lens in a refractor or a telescope with both mirrors and lenses – see the steps above.
With ultra-clean optics in your telescope, you’ll enjoy perfect views for a long time.
How to clean a telescope lens
Remove dust particles
If your lens is dirty, you need to get any particles of dust off before cleaning. Use an air-blowing bulb to gently puff away the loosest particles.
Do not use an air canister or your breath, as these will blow moisture onto the lens, which can cause the remaining particles to stick to it.
All the dust must be cleared before cleaning, or you’ll simply spread the dust around the lens, making it more difficult to clean. You also run the risk of scratching the lens as you wipe.
Wipe with alcohol cleaning fluid
Now dampen a tissue with alcohol cleaning fluid. Gently wipe the lens slowly in a circular motion from the centre to the edge, with as little pressure as possible.
After wiping the lens with a tissue throw the tissue away and select a fresh, clean one for your next sweep – you do not want to wipe any particles over the lens.
Try and avoid accidentally touching the lens during this process, but carefully clean away the finger marks as soon as possible if you do.
Protect the edges
The edge of the lens is an area to be wary of. Don’t use too much fluid here as it could creep inside the lens elements by capillary action.
You also may find that, because of dew or atmospheric condensation, there are water spots on the lens.
At this stage only, they can be removed by breathing gently on them and wiping with a clean tissue.
This is because pure alcohol cleaning fluid won’t dissolve water spots without moisture, which comes from your breath in this case.
How to store your telescope
Telescopes are precision bits of kit, and the aim of the ‘happy telescope’ game is to find a safe home that avoids dampness and moisture, knocks and bangs, dust and dirt, high temperature swings, spiders and insects.
You may consider the loft, a spare bedroom, a shed or maybe the garage. These are all common places used by amateur astronomers around the world.
Wherever you keep yours, you should also be thinking about what precautions to take to keep your scope in top working condition.
One of the easiest safeguards is covering the scope with a sheet (or even better, a scope coat) followed by something waterproof to keep the moisture out. This is especially important if you keep it fully assembled between observing sessions, rather than returning it to a storage case.
With a bit of string, you may even be able to keep out any insects intent on building a home inside your scope as well.
When your scope’s not in use, make sure that all its caps and covers are securely in place.
Make sure you also replace all scope covers and caps, as they will keep the optics and insides free from moisture and dust.
All things considered, a dry indoor cupboard is a good location. You’ll still need to cover your scope with a sheet and put on the caps, but the atmosphere is not as corrosive as anywhere else.
This, of course, may not be practical – for example, if your scope is heavy and you keep it upstairs, the prospect of getting it outside may be enough to put you off. The only thing worse than a ruined scope is one that’s stored so well it’s never used.
One place where you should definitely not keep your kit is a conservatory. Telescopes do not like places with a lot of moisture, nor do the temperature extremes that can be found here suit them well.
Alternatively, if you have the space, the time and the budget, you could always become the talk of your neighbourhood and build a dedicated space for your scope: your own observatory.
A clean, dry cupboard is a much better home for your scope than a humid conservatory.
Hazards to avoid when storing your telescope
At best, dew on the optics can ruin a night’s observing by fogging up the view. At worst, it’s likely to bring all sorts of nasties that can damage lens coatings.
Simply leaving a scope undisturbed for a long time can cause problems. Among other things, it can allow gravity to redistribute the grease that sits all over the gears. This leaves moving parts prone to excessive wear and damage.
People and pets
Of all the things that can seriously shorten a telescope’s life, your nearest and dearest are the worst offenders. Never leave a telescope anywhere that it can be knocked over, banged against a wall, used as a coat stand or climbed on by the cat.
Warmer isn’t necessarily better – high temperatures can damage your scope, evaporating the grease on gears or weakening the glue that holds the lenses.
Wet or damp storage conditions do your scope no good: you will soon find rust beginning to form on all the joints. Even if you simply pack your scope away in its case without fully drying it first, you’re asking for a fungus attack on the lenses.
Make your own telescope storage
BBC Sky at Night Magazine
If you find the storage case that came with your scope is too flimsy (or indeed, if it didn’t come with one), consider making a custom one. You can create a marvel that fits your scope – or your storage space – exactly, and add extra sections for your accessories, too. The only downside is that you need to take your scope apart after each session.
Read our full guide on how to build a telescope case.
Wheeled telescope tripod
Some tripods can be remarkably heavy bits of kit, and carrying them can be quite awkward, with a chance of banging into things or even hurting your back. So, how about easing the problems by having a tripod with retractable wheels? As long as the ground is not too bumpy, you can now glide along with ease.
Read our full guide on how to build a wheeled telescope tripod.
This guide originally appeared in the October 2010 and September 2012 issues of BBC Sky at Night Magazine.