What is the significance of binocular optical coatings?

Optical coatings reduce internal light loss and glare and ensure even light transmission, resulting in greater image sharpness and contrast. Binoculars may have 10-18 glass surfaces, each one contributing to scattered light, so coatings make a big difference in what you see. Coated optics will have a less shiny, even dark appearance when looking into the barrel or tube; you may see a greenish, bluish, or brownish tint as well. Most coatings are magnesium fluoride or calcium fluoride and work by destructively interfering with certain colors or wavelengths of light, eliminating their reflection. Therefore, more light enters your binoculars and is able to pass through to your eyes. Almost all modern consumer optics have some kind of coating on most of the optical elements. However, there are different levels and qualities of coatings.

Coated optics means that at least one of the major optical elements has a coating on at least one surface. Fully-coated means that all lenses and glass surfaces have a coating layer. Multicoated means that at least one of the major optical elements in a fully-coated binocular has multiple coatings of anti-reflective compounds on at least one surface. Fully-multicoated means all glass surfaces have multiple coatings and it is the best kind, resulting in light transmission of 90-95% for bright, sharp and contrasty images.

Some roof prism binoculars feature phase coatings. Because the light travelling through the prisms in these binoculars takes a slightly different path in one prism, it's shifted by one-half its wavelength and contrast is lowered. By applying a special coating that compensates for this shift, the contrast loss is eliminated, giving phase-coated binoculars brighter and more vivid images.

Updated 10/21/13