Obtaining a good view of an astronomical phenomenon requires you to get several things right. Predicting local weather, reading sky charts and ephemerides, correctly aligning your equatorial mount, selecting the right filter, collimating and focusing…
If you get just one of these things wrong, your viewing time may just as well be spent in Dreamland.
There are plenty of resources online that cover all of these topics in detail. There are also telescopes that take some of the hard work away from you, like the NexStar SE and others with a go-to drive.
With all of this complex technical talk floating around, though, you may be forgetting about something a lot more mundane. If you don’t know how to clean a telescope lens, the clarity of your view is bound to get degraded over time.
How to Clean a Telescope Lens Safely
A high-quality telescope is a pretty substantial investment. The last thing you want, therefore, is to damage it by cleaning the lens or mirror improperly.
The first thing to understand in this regard is that lenses aren’t made only of glass. Almost all have optical films or coatings that serve a variety of purposes. Apart from abrasion and scratching, these can also be damaged by using the wrong detergents on a lens – the stuff you use to clean windows should probably not go anywhere near your telescope.
Similarly, it’s not necessary to clean a telescope lens or mirror just because there are a few specks of dust visible (unless you plan to take photographs). The less you do to it, the less can go wrong.
You’ll also want to steer clear of cleaning a telescope that’s contaminated with substances like oil or fungus growth (something that happens more often than you’d think!). In this case, or if any major disassembly is required, it’s probably worth it to contact a professional.
DIY Telescope Lens Cleaning
Assuming that all you have to contend with are dust and minor smudges, you can try the following steps to restoring your telescope to as-new condition:
- Go with Compressed Air. Blowing loose debris off the lens is the safest way of removing it. Note that some canned gasses contain chemical compounds that may end up on your lens: don’t shake the can before use and let it spray away from your telescope for a few seconds before using it in order to clear the nozzle. Alternatively, you could turn to the hand-powered air blower found in most telescope cleaning kits, or use your mouth to suck air (do not blow) from under a thumb partially covering an eyepiece. Here’s a video for this:
- Softly Brush the Lens. In case a stream of air can’t dislodge any offending particles, use a brush with very soft bristles as gently as you can, from the center of the lens outward. Celestron’s LensPen works beautifully.
- Use a Cleaning Solution. The safest and most effective cleaning solution is a 50% alcohol solution. This can be used to lightly dampen lint-free cotton balls, swabs or soft microfiber cloths; wipe these across the surface to be cleaned in straight strokes with almost no downward pressure. Afterward, use a dry cloth or swab to soak up any remaining liquid.
- Clean the Primary Mirror. If you’re not sure whether or not you need to clean this part of a reflecting telescope…you don’t! Newtonians and similar designs can actually tolerate quite a bit of dirt on their mirrors before the image in the eyepiece is at all affected. If it is indeed soiled enough to affect your viewing pleasure, the best policy is probably to take it to your local camera or telescope shop.
If you do want to try yourself, the easiest way to clean it is to (very carefully and without touching the reflective side) remove the mirror from its cell and place it in a spotlessly clean sink atop a folded towel. Running lukewarm water over it for a few minutes should remove most gunk, after which you can use alcohol and a soft cloth to get rid of any remaining stains.
The Bottom Line
Though the effect may not be noticeable at first, dirty optics can eventually degrade your telescope’s contrast and resolving power. If you’re continually on the hunt for fainter objects or clearer photographs, knowing how to clean a telescope lens becomes an important part of amateur astronomy.
The best policy, however, is still to keep your telescope clean in the first place.
Dobsonian telescopes like the Skyquest XT, for instance, are prone to collecting dust. If this is what you use, getting a tarp and some poles to create a windbreak around your scope may save you a lot of trouble.
Also keep lens caps on whenever you’re not actually looking through your telescope, and make sure that anyone using it besides you knows what parts they can and cannot touch.