Cleaning Optics - Part 1
Glass Surfaces

Mike Swanson

You should first note that it takes a LOT of contaminants before your optical views will be compromised.  And, cleaning always runs the risk of putting small "micro-scratches" on the surface of the optics.  Under normal use most people should not clean their optics more than once a year.  Exceptions do exist though.  If the optics have collected any contaminants more harmful than just dew and dust, it is best not to leave this sitting for too long.  Some things can damage the anti-reflective coatings - for example, some pollens, mold and heavy pollutants (in industrial areas).  Also, eyepieces pick up "eye gunk" and fingerprints in a short period of time and should be cleaned more frequently.

Something you should do regularly though, is to use a large blower bulb to knock off loose dust.  Some use canned air, but I've seen this condense humidity out of the air and deposit a harsh haze onto optics.  Large blower bulbs are widely available at well-stocked camera shops and do a fine job although they require a bit more work on your part.  I recommend blowing off dust after each use of your telescope or binoculars.

When you do finally decide to clean, always keep one thing in mind - BE GENTLE.  First start with a large blower bulb to remove any loose dust.  Then gently brush any other visible dust loose with a camelhair brush, followed again by the blower bulb.  Any dust left on the surface increases the possibility of scratching when you proceed with the next cleaning steps. 

Next, prepare the cleaning fluid (well, actually you will want to read through all this and have everything ready in advance) - 50% isopropyl alcohol and 50% distilled water with a couple of drops of plain dishwashing liquid.  I've looked all over this island where I live for the usually recommended 90% (or higher) isopropyl alcohol but haven't had any luck finding it.  So, I have settled for rubbing alcohol, but I am certain to select a bottle that indicates only isopropyl alcohol and water - some rubbing alcohol includes fragrance and other ingredients.  As the mixture is 70% alcohol, I empty one small bottle of rubbing alcohol into a large bowl and add a little less than a half bottle of distilled water to produce the 50/50 mix.  After adding the dishwashing liquid (really, just a couple of drops), the final result is a great solution that leaves absolutely no residue on glass surfaces.

Next you will need some sort of lint-free tissues.  Many recommend plain, white Kleenex® (be sure it doesn't have any lotions or scents), but the last box of Kleenex® I purchased wasn't suitable for use.  The box I got deposited terrible amounts of lint.  Fortunately I have found a brand of Japanese tissues that had almost no lint - Nepia.  Another possibility in the USA is a product known as Kimwipes.  Part of the reason I prefer plain tissues to specialized lens cleaning tissues is their weight.  After you dip them in the cleaning fluid, you can simply drag them over the optics and the weight of tissue is sufficient to lift all the contaminants from the surface.  Most specialized lens tissues are too light for this.  Also, most specialized lens tissue is not absorbent enough for the drying phase as described below.  Fold the tissue 4 times to present the best working size and wet the last folded edge.

Drag a wetted tissue from the center of the lens out towards the edge and immediately follow the wet tissue with a dry one to absorb the fluid - again, just dragging it over the surface, although in this case I simply crumple it a bit rather than fold it.  Then both tissues go in the waste pile along with any scratch-inducing-particles collected - never reuse the tissues.  The other reason I prefer tissues is the number that I use - for an 11" corrector plate I use about 60 tissues.  That would be quite expensive with lens tissues.  It always amazes me to see this method in action - it is almost magic the way it leaves the surface absolutely clean and yet there is no rubbing involved.

Occasionally there are very small spots of oily residue that require a repeat with the wet and dry tissues.  Rarely even that will not remove a very stubborn oily spot.  For those final spots, I use a Lens Pen with very light pressure.  The Mini Lens Pen is best and is available at most Astronomy dealers.  The larger-sized Lens Pen is widely available in camera shops but not as useful as it is too large for eyepieces.

Speaking of eyepieces, this method works great for all but the smallest optical surfaces, like medium to small eyepieces.  In this case, I use tissues and cleaning fluid as much as possible, but a good deal of the cleaning is left to the Lens Pen.  First, use the blower bulb and camelhair brush (one end of the Lens Pen contains such a brush) to remove all visible particles.  Then drag a wetted corner of tissue across the eyepiece lens followed immediately by a dry corner to absorb the liquid.  After this, follow with the Lens Pen using very light pressure.

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