Astronomy
Eyepieces If you take a look at the eyepieces pictured on these pages, you will notice the lenses used in them have multiple elements. These elements are cemented together with the resin from Canadian Balsam trees, which is very clear, and has an extremely low refractive index.
All of them are coated and some of them have every air to glass surface within coated as well. This internal coating cuts down internal reflections by as much as 30%.  When more than one coat is applied these surfaces, you get multicoated lenses that cut down internal reflections by 95%,- drastically improving the eyepiece's over all contrast.
The Nagler eyepiece on this page is but one example of a premium eyepiece. It has an Apparent Field of View of 82 degrees, and corrects for every type of aberration known to lens makers.