So say you have a nice pair of binoculars or a good refracting telescope (or spotting scope). One day you are about to use it and you discover some kind of smear on the front lens. Perhaps it was a droplet of water from the day you were viewing and a small rainstorm brewed up? Doesn’t matter, you need to clean that lens or otherwise your view will be very diminished. So you grab a tissue from the bathroom and some window cleaner and….
OK, let’s talk about glass and the things we put on it to see better. Glass is a fairly hard material but it can be scratched, but a greater concern for your nice binoculars is the coatings on the lenses. You might notice that purple/green/blue coloring in the reflection if you look at the lenses at an angle. These coating are very important to the binocular/telescope’s optical quality and you cannot just use anything to clean them.
Well let’s start with the tissue. What is that tissue made of? Paper! What is paper made of? Wood pulp! Although the tissue might seem nice and soft to you to the glass and its coating that tissue might as well be rubbing it with a block of wood. If you need to clean the glass use either a multifiber fabric cloth (most binoculars come with one) or use lens tissue (your optometrist or local drug store should have some).
OK, but what about the window cleaner? That’s for cleaning up your windows nice and clean but your windows don’t have sensitive optical coatings. If your binocular and telescope’s lenses didn’t have those coatings you could get away with using window cleaner but they do have them, and window cleaner is very harsh on optical coatings.
If you end up using a lens cleaner made certain it says it is safe for multi-coated optics. If it does not say that do not assume it is safe. Many eyeglass cleaners are not actually safe for multi-coated optics and, while better for your lenses than straight window cleaner can still be fairly harsh on coatings. Be sure to find a proper cleaner.
Another option is to use a Lenspen. Sold under various brands these are carbon-tipped pens with soft surfaces designed to gently clean delicate optics.
But how do you go about cleaning your lenses? That is for the next entry.