So in our previous entry we talked about what not to do when cleaning sensitive optics such as telescope lenses and binoculars. Now it is time for a better explanation of how to properly clean those optical lenses. Note that everything mentioned here can be applied to binocular lenses, telescope lenses, and even camera lenses.
Before we discuss specific cleaning methods let me state the first rule of lens cleaning, similar to Hypocratic Oath:
DO NO HARM!
If your lenses are not dirty, don’t clean them for the sake of cleaning them. If a tiny smudge is on your lens but isn’t showing any effect on viewing, just let it be. All too many lenses have been damaged or destroyed by unneeded cleaning. So consider carefully before starting the cleaning process.
We are going to discuss two methods of cleaning optics: using a cleaner and lens tissue and using a Lens Cleaning Pen. Let’s start with the latter.
Method 1: Lens Cleaning Pen
Lens cleaning pens are sold under a variety of names but they mostly have the same features: A soft dusting brush and a flat cleaning end. The first thing you will do is brush the lens gently with the brush end.
Here you are trying to get the various dust particles and grit off of the lens. So use short, gentle strokes of the brush. Do not do anything that will grind the particles into the glass or coatings.
Once you have the lens clear of loose dust activate the flat tip (the method varies from pen to pen) and start cleaning by pressing the tip and making small circles on the lens.
Be patient with this tool and make certain not to make circles too big or move too fast. Start at the center of the lens and work your way out towards the outside. Lens cleaning pens can work wonders I have seen them remove a coating of tree sap from the objective lens with no harm to the optics or coatings. It took a while, however.
Method 2: Cleaning Liquid and Tissue:
You will need some things for this method of cleaning:
1) Multicoated optics cleaning fluid (NOT window cleaner), in a pinch Reagent grade Isopropyl alcohol (99.8% or better) can be used.
2) Lens cleaning tissues
3) Compressed air, a blower bulb, or a camel hair brush.
Step 1 is a lot like the first part with the lens pen – first you must get the loose dirt, dust and other particles off the lens. Use the compressed air, a blower bulb, or the camel hair brush to remove them. Otherwise they will get caught under the cleaning tissues when you clean and scratch the optics or coatings.
Step 2 is to coat one of the tissues with the lens cleaner and gently rub the lens in a small circular pattern., moving from the center towards the outside.
Do not press excessively, try to let the cleaning fluid do as much of the work as possible.
Sometimes the lens dirtiness is cause by some kind of oil (skin oil is quite common) and the cleaning process only pushes the oil around rather than removing it you mind try a very small quantity of mild soap to remove it. Remember the primary rule, however.
Note about Reflecting Telescopes.
Reflecting telescopes don’t have glass objective lenses like refracting telescopes (although the eyepieces do) but instead have large primary mirrors. Instructions on cleaning the mirrors is somewhat different. You can see our blog post on cleaning a telescope mirror here
Good luck and take care.