How to Clean Binoculars
More binoculars have been ruined by improper cleaning than by being dropped.
You've probably watched someone degrade their binoculars. They breathe on the binocular's eyepiece and then rub the glass with the corner of a shirt. Poor birder, they never knew they just dulled every image they would ever see with that binocular again.
The totally WRONG way
The breathe-and-rub method is really just a way to frost the glass — like a shower door. A primary ingredient of dust is silica. In other words, tiny rocks. Silica is harder than glass. If you rub dust across your eyepiece, you gouge microscopic scratches into the glass and the ultra-thin coatings on the lenses.
You may not see the scratches individually, at least right away, because they're so small. But they scatter light. And so over time your binocular begins to give a cloudy image.
The RIGHT way
However, it's easy to clean your binocular the right way, and keep your binoculars bright for many years.
Step 1 ~ Remove all the loose dust from the binocular's lenses.
Use the brush end of a lens cleaning pen, specially made for cleaning optics. The brush is soft and won't harm the glass or coatings. It helps to hold the binocular upside down so the dust falls away.
Or blow away the dust with a can of air (from photographic supply store).
Don't use your breath. The air coming out of your lungs has tiny droplets of water in it. Those drops will leave waterspots on your lens.
Step 2 ~ Moisten a Q-tip with water or lens cleaning solution and float off any remaining dust.
If your binocular is waterproof, you can actually run it under the tap. Just don't squirt it hard. You don't want to force the seals with undue pressure.
Do not use fluid designed for cleaning eyeglasses or windows, as it may attack the coatings. It is OK to use lens cleaning fluid designed for cameras and optics.
Step 3 ~ Now that the dust is gone, you can wipe the lens with lens tissue, a special micro fiber lens cloth, or a very soft cotton cloth (like a piece of a clean old cotton undershirt).
Do not use paper towels or facial tissue, as these are too rough. They may feel soft to your hand, but they usually include wood fiber that will scratch your lenses or its coating.
Easy does it
Don't be a clean freak. Often even when there are waterspots or dust on the objective lenses, you can still see amazingly well through your binocular. If possible, try to tolerate a bit of dust or imperfection until you get to a place when you can clean your binoculars safely.
Even after you've cleaned them, you don't have to polish them absolutely perfect up to the edges of the eyepiece glass. Generally, it's better as much as possible to avoid rubbing the optical surfaces.