Cleaning A Telescope Lens
If you're wondering how to clean a telescope lens, I'm willing to bet you're a little worried about doing it, right?
Well, don't be, it's more straightforward than you think!
If, like me, your scope has been gathering dust in the attic for years, or in the garage over summer, then one of the best ways to improve its performance and bring it back to life is to clean your telescope's lenses.
In this article, I'm going to walk you through the safest and most effective way of cleaning lenses on any optical equipment, (you can clean a camera lens the same way) but please pay attention to the safety warning below:
DO NOT CLEAN THE MIRROR(S) IN A REFLECTOR TELESCOPE!
Mirrors are a different beast, and I would recommend having them professionally cleaned.
Cleaning your telescope lenses is still a job that demands time, care and a decent, inexpensive cleaning kit, (like this one from Orion) but it can be done thoroughly and safely at home.
OK, with warnings over, let's answer the question: How do I clean my telescope's lenses?
How to Clean Telescope Lenses
The lens is most important part of your telescope and, for that reason, it's vital to make sure that you treat it well and do not damage it whilst cleaning.
Follow the five simple steps below in order to get perfectly clean telescope lenses and eyepieces.
A quick word of warning though:
Only go as far through the steps as you need for success.
For example: if your lens is really clean after step three, then stop there. You shouldn't carry on through steps 4 and 5 just for the sake of it.
Following this advice means you'll get a clean telescope lens but you'll minimise the risk of damaging it.
There's a short video at the bottom of this article which shows you each of the following steps for cleaning your telescope lens in action.
Step 1 - Protecting your Telescope Lenses
Because even gentle cleaning can cause minute scratches to the lens or its coating, the first step for cleaning a telescope lens is to prevent them getting dirty in the first place.
Always make sure to use the lens cap (if you don't have one, improvise: a shower cap or even saran wrap will do the job) when you're not peering at the night sky.
The lenses of your eyepieces need similar care, so make sure they are in a protective case (or even a resealable sandwich bag if you don't have a case) when not in use.
Ironically, using the eyepiece is most likely to make it dirty, especially if your eye gets too close. Believe it or not, oil off your eyelashes gets left on the surface of the lens.
If you find this happens a lot, you might find an eyepiece with better eye relief (i.e. you can look through it from further away) keeps clean for longer.
Step 2 - Removing Telescope Lens Dust with Air
When there is no choice, the dirt has been left and you have to clean your telescope's glass lens, your first pass is to remove loose dust from its surface.
It's vital to remove loose particles first as even those tiny bits of dust can be enough to put small scratches into your lens or its coating if you jump straight into to scrubbing and wiping.
Your temptation will be to just blow the dust off, but...
Don't do it!!
Your breath contains a lot of water and getting spittle (frankly) on your telescope lens will do it no good at all.
The one thing you can do with your lungs (if you really want to) is to suck the dust off.
Yes, I did say 'suck'!
Cover the end of your telescope above the lens with your fingers and suck in air from one side.
This will pull air across the surface of the lens and suck some of the dust off (and into your lungs) with no moisture being deposited.
You may be pleased to learn there are a couple of better techniques which do not involve using your lungs.
Any decent optical cleaning kit, like this very popular one from Orion on Amazon.com, will come with an air blower. Use this mechanical device to blow the dust off your telescope lens.
It works by sucking in clean air at one end and then, when you squeeze the bulb, blowing it out as a jet through the nozzle end.
You can also use compressed air (professional sellers of telescopes, binoculars and cameras will be able to sell you this) but I wouldn't take the risk.
For me, the air bulb is more than adequate.
Step 3 - Removing Telescope Lens Dust with a Brush
Working your way through these steps very deliberately will make sure you get the most effective clean for the least risk of damage.
If you are satisfied with how clean the lens is now the dust has been blown off, stop here. If not, it's time to remove the more stubborn grime!
For this, you should use a very soft brush, like the one included in our very own telescope cleaning kit.
The brush should be kept in a bag when not in use, so that it doesn't collect its own dust. As an added precaution, use the air blower to clear dust off the brush after you've used it.
Use the brush to gently flick off the dust from the lens, there is definitely no drama required here - just gentle, light brush strokes from the centre of the lens to its outside.
It can be helpful to combine this brushing step with using the air bulb from step two to get rid of all the dust from your lens.
Step 4 - Using a Microfibre Cloth to Clean your Scope
By this stage, all the surface dust and dirt should be gone - and it may well be time for you to stop cleaning altogether.
Only continue lens cleaning with lens cleaner and lens cleaning wipes if there is evidence of fingerprint or eyelash oil on your lenses.
Firstly, take the microfibre cloth from your telescope cleaning kit and use that to gently rub the surface of your lens.
Do this dry - you do not need to add lens cleaning fluid at this stage.
If there's still oil on there, or a water spot, then move to a clean piece of the cloth, fog the lens with your breath and repeat the same gentle rubbing again.
You could well discover that this has left your lens looking perfectly clean and, if it has, then you should stop there and be pleased with a job well done.
If, however, there is just a stubborn piece of grease that will not be moved with gentle rubbing (never rub your telescope lenses harshly), then it is time to introduce a bit of lens cleaning fluid to your telescope eyepiece.
Step 5 - Using Lens Cleaning Fluid
This is the final phase of cleaning your telescope lens and should only be completed if you have a smear which gentle rubbing with a microfibre cloth will not remove.
Take your microfibre cloth and drop just one or two drops of the lens cleaner (which is isopropyl alcohol) onto it.
Whatever you do, don't drop the lens cleaning fluid directly on the lens, as it may work its way around the edges of the lens and pull grime inside your telescope or eyepiece.
Use either a gentle circular motion, or move from the centre of the lens to the edge to clean the glass.
Next, use a dry part of the cloth and following the path you have just taken, remove any excess lens cleaning fluid from the glass.
If you have any grime that is particularly stubborn to remove, then put a drop of the lens cleaner fluid onto one end of a Q-tip and use that to directly get at it.
Remember to be firm but gentle, you really don't want to scratch your lens glass.
And that's it - five simple steps to a very clean telescope lens!
Telescope Lens Cleaning - a Recap
You now know all you need to about how to clean a telescope lens.
Telescope lens cleaning is not to be taken lightly, so here are some notes of caution:
- Don't use this technique for cleaning the mirror(s) of a reflector
- Don't take your lenses out of the scope or eyepiece to clean them (putting them back together is hard and liable to go wrong... and isn't required anyway)
- Only clean your telescope when you need to - once a year for the main lens is probably fine, telescope eyepieces tend to gather more oil so may need to be done more frequently
- But, some contaminants can be harmful to the coating of a lens, such as some pollens and molds, so you should clean those off more regularly if they're a problem in your area
- Regularly using an air bulb to clean the lens (e.g. after every viewing) will reduce the need for a full-on telescope cleaning session.
Orion's Telescope Cleaning Kit is on Amazon is specifically designed for telescope lens cleaning.
Keep aware of how clean your lenses are, but remember that they need a lot of dust and grime to build up on them to reduce their effectiveness, so please spend more time looking through them than cleaning them.
Telescope Lens Cleaning Video
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Product images sourced from Amazon.com