The lenses which are used by the binoculars namely the objective lens as well as the eyepiece lens have antireflection material coated on them. These binocular lens coatings are only on the surface which comes in contact with the air.
Before buying the binoculars you will have to make sure that you understand what all the terms which you keep hearing like the “fully coated” or “multi coated” mean.
Why does the lens need coatings?
The answer lies in the light transmission as most of the lenses if not coated can lose up to 4% of the light when it enters the lens. You will say that it is merely 4% but the fact is that that there are so many surfaces that a light transmits through that it is an established fact that the light will lose about 50% percent of its original brightness if all the lenses are uncoated.
What is the material of the lens coating?
The basic material which is coated on the lens surface is Magnesium Fluoride.
Coated – In the binocular market coated will mean that at least one air to glass surface has the antireflective coating on it.
Fully Coated – This means that lenses or air-glass surfaces are coated with the material.
Multi coated – This means that at least on lens has the up to 15 thin layers of the coating material on it.
Fully multicoated – This will mean that all lenses or air-glass surfaces will have multiple coating of the antireflection material on their surface.
Tip: Always check for the specifications before buying the binoculars. You can easily tell if the lens is coated or not as you can see a green or a purple tint on the lens.
Be careful while cleaning the lens as these chemical layers are very soft and can easily be scratched while you are busy cleaning the lens.
The new trend is ruby red coatings which are not much better than the normal coated lenses apart from the fact that these are mostly available in lower end binoculars.