The Cardinal Rules of Cleaning your Optics : Telescopes and Binoculars
Photo : Orion Mak 150mm, Michael Gilmer (GalacticStone)
DIRT PREVENTION AND CLEANING YOUR OPTICS
There have been countless debates about the correct methods for cleaning the optics of your telescopes/binoculars. There have also been an endless chain of horror stories about cleanings gone wrong and damaged lenses/mirrors. Bearing this in mind, the very best way to keep your optics clean is to NEVER LET THEM GET DIRTY IN THE FIRST PLACE.
Don't ever ever ever touch your optics for any reason. A tiny speck of dust on a lens is preferable to a scratch caused by a well-meaning but incorrect cleaning method. The dust can always be removed in the proper manner, a scratch is permanent. So if in doubt, just leave it alone and don't touch it.
If there is a speck of dust, a tiny grain of sand or dirt, or something similar on your lens, then use a VERY SOFT, natural-hair brush to flick the offending particle up and away from the lens. Using a gentle flick of the wrist, "kick" the dirt or dust outward towards the rim of the lens. This should be combined with a simultaneous upward motion. Using this technique will ensure you do not rub or drag the dirt particle across the glass, forming a permanent scratch.
A stubborn grain of dirt may require additional motivation to vacate the lens surface. Do NOT blow on the lens using your mouth or breathe on the lens. Your telescopes or binoculars are not sunglasses, so don't even think about breathing on the lens to form a vapor and wipe it off. This is forbidden! And even though it may seem like a good idea, resist using cans of compressed air to blast dirt/dust from your lenses. Canned air uses propellants which can (and usually do) escape from the nozzle and land on your lenses. The propellants used are a variety of nasty substances that can and will damage the sensitive coatings on your optics. So what is one to do? Use a squeeze bulb, atomizer, or specially-made "blower brush" to gently direct a puff of air onto the offending dirt speck.
Beware of pre-moistened "lens cleaning cloths" that come packaged like disposable hand wipes. These are sold on drug store shelves and in checkout lines for use primarily on eyeglasses. A check of the package usually reveals a claim that the cloths are safe for use on coated optics, binoculars, camera lenses, etc. Do not trust this claim with your optics. If the exact cleaning agent used is not identified on the package then do NOT use it. Many of these cloths or wipes contain a cleaning solution that is oily in nature and is extremely difficult to completely remove. Some may contain a solvent or harsh chemical like ammonia. Again, don't use them.
Ok, so what does one do if these methods do not work or are not sufficient to clean the dirty lens in question? Honestly, I say don't do anything at all. Wait and ask someone who is an expert in the field or an authority on the subject. Some people recommend certain types of alcohol cleaning solutions, other swear by solutions made by optics manufacturers like Zeiss. I know nothing of these things, because honestly, I do not let my equipment get that dirty. If the brush or puff of air technique does not work for you, then you have already broken the cardinal rule I mentioned above : NEVER LET THEM GET DIRTY IN THE FIRST PLACE. If you find yourself with nagging doubts or questions regarding what to do in a particular cleaning scenario, then DO NOTHING.
Getting back to the cardinal rule, what are the other fundamental "rules" for keeping optics dirt-free?
Don't touch and don't let anyone else touch your optics.
Don't let anyone, and I mean ANYONE, use your equipment without your direct supervision. A fellow astronomer can usually be trusted (take a peek at their instruments and lenses to see how they treat their stuff), but never let a stranger touch or use your equipment without your specific guidance. If a person is one of those types who never takes anything seriously or appears flippant about your equipment, then don't let them anywhere near your stuff. Politely shoo them away. The one time you make an exception to this rule, you'll end up breaking rule #1 as well because the offender is going to stick a thumbprint on your eyepiece or objective.
Don't take your telescope or binoculars to the beach. Now matter how tempting it may seem, just don't do it. Think about the idea : setting up your equipment in a place with a nearly-infinite supply of abrasive sand grains. Combine the sand with wind and water, and one has a recipe for optical disaster. I set up my gear at the beach once, a few months ago, and I am still getting sand out of the nooks and crannies of my tripods. Common sporting-style binoculars and spotting scopes are fine for the beach, but keep your astronomical optics out of such minefields.
Never, ever, NEVER NEVER NEVER leave your equipment setup and walk away from it. You may get away with breaking this rule if, and only if, you are : alone, have no children in the area, no pets in the area, and no chance of anyone or anything coming into contact with your optics while you are away fetching a cold drink or having a smoke. The minute you walk away, a Bolivian Oily Moth (the nocturnal variety) is going to fly in and build a mucus-cocoon on your objective. If you must leave your stuff setup while you are absent for a moment, then make sure you put the lens caps and eyepiece covers back in place.
Don't smoke near your equipment or let smoke come in contact with your lenses. If you are a smoker like myself, then only smoke downwind and well away from your equipment (or anyone else's). Smoke is BAD for optics.
Don't eat or drink in close proximity to your lenses. Accidents happen. Drinks can splash and crumbs can land in places where they shouldn't be. Treat food and drink like smoking - do it away from the equipment.
NEVER rub your lenses with any kind of "lens cleaning cloth" - dry or otherwise. Your telescope or binocular lenses are not dime-store cameras or sunglasses, so don't use cleaning products designed for those types of inferior optics.
For goodness sakes, NEVER try to remove a scratch with a scratch-removing solution! These scratch removers were intended for use on windows and other non-optical quality glass. They work by using mild abrasives to "even out" the glass surface around the scratch, reducing it's APPEARANCE. In reality, if you use something like his on your scope optics, then you might as well hit the lens with a sledgehammer. You will only make matters worse.
Finally, don't freak out if you get a small scratch or blemish on your lenses. Chances are, it may be unsightly but it will have a minimal effect on the performance of your instrument. Freaking out over scratches leads to well-intentioned but tragic episodes of optics cleaning - which inevitably makes matters worse.
This has been my experience with optics. It is better to be accused of being "anal retentive" or "obsessed" than to have damaged or scratched optics. Remember, you cannot take back a scratch - it's permanent.
MikeG (GalacticStone)
Note : an earlier version of this article was previously posted on Cloudy Nights. I am the author.
thanks for very practical and informative article, I recently bought my first telescope
Enjoy your scope. It's a deep and fun rabbit hole to go down. It can be addictive. I hope you get clear dark skies with it. :)
These a are good words of advice. I tend to avoid cleaning optics unless they are really bad (I use my scopes regularly) and then it is done with a lot of care. The biggest point is to use techniques that reduce the chance of dragging fine debrii across the optics.
As I learned more about optics, I was surprised to learn that a typical small scratch does not adversely impact image quality or resolution to any noticeable degree - depending on where the scratch resides on the lens. The same can be said for dust and dirt - the coverage has to be pretty bad and ugly before it really starts to send the image downhill. Eventually I did learn to just leave my optics alone and not worry about the tiny smudges or motes of dust - it's better to have a lens that looks a little dirty than have a lens that is scratched up from ill-advised attempts at cleaning.