Optical Coatings

Q: What is the difference in binocular and scope lens coatings, and how can you tell if the glass is coated?

A: One way to check a riflescope, spotting scope or binocular for coated lenses is to hold it under a common ceiling light, objective lens up, and look at the reflections of the light bouncing off the various lens surfaces inside. Each reflection (usually three to seven) represents one air-to-glass surface. If this lens surface has been coated, its reflection should be colored, usually purple, green or yellow, depending on the proprietary coating recipe the manufacturer used. White reflections indicate an uncoated lens or, in a binocular, the prism.

Unfortunately, colored reflections don't tell you how many layers have been applied or how effective they are. Determine effectiveness by comparing scopes side-by-side in low light. The best test is to look at some type of lettering or a series of black-and-white bars set in shadows with the sun setting behind.