Introduction.
Binocular anti-reflective lens coatings are often the least understood, yet are one of the most important features relative to the quality of the binoculars. Lens coatings determine how well you are going to see your image, the clarity of color, the resolution, and the contrast.
Background.
Realize that there are a series of internal glass surfaces within binoculars. As light enters through the front objective lens it travels through the binoculars. As it hits each series of uncoated glass surfaces approximately 5 percent is reflected (lost). Assuming ten internal sets of glass surfaces, times 5 percent reflective loss at each, equals a total of a 50 percent light loss as the image reaches the rear ocular lens. The result will be a dim, hazy, unclear image.
Anti-reflective lens coatings allow a greater percent of the light to pass through each series of glass surfaces. Instead of the 5 percent loss, coated lens may reduce that figure to less than 1 percent. A smaller percentage of the light is reflected and a greater amount continues on to the ocular lens. In better, high quality binoculars in excess of 95 percent of the light reaches the ocular lens and your eyes. This results in a sharp, clearly defined, and bright image.
Types of Lens Coatings.
Binocular anti-reflective lens coatings are rated in one of four categories.
1. Coated Lens. (C) Contains a single coating on at least one set of the internal series of glass surfaces. The first and last set of lens are probably coated, but the remaining sets probably are not:
Example: ____ || ____ | ____ | ____ | ____ | ____ ||
Note: Typically, coated lens have only the first and last lens of the binoculars coated. The first and last lens are the ones you can see (the front objective lens and the rear ocular lens).
2. Fully-Coated Lens. (MC) Contains a single coating on all sets of the internal series of glass surfaces. Each set of lens receive a single coating:
Example: ____ || ____ || ____ || ____ || ____ || ____ ||
3. Multi-Coated Lens. (FC) Contains multiple coatings on at least one set of the internal series of glass surfaces. Often the first and last lens are multi-coated, while the remaining lens may be single coated:
Example: ____ |||| ____ || ____ || ____ || ____ || ____ ||||
4. Fully Multi-Coated Lens. (FMC) Contains multiple coatings on all sets of the internal series of glass surfaces. Each series of lens are fully multi-coated:
Example: ____ |||| ____ |||| ____ |||| ____ |||| ____ |||| ____ ||||
As we have shown with our four categories, the Fully Multi-Coated models are vastly superior when compared to the other three categories.
The Coating Process.
Lens coating is a process where certain chemicals (such as metallic, silver, or aluminum) are physically applied to the glass lens of the binoculars to allow light to pass through and not be reflected. Generally, one coating may reduce light reflection from the 5 percent for untreated glass to 1 percent for a coated lens. Multi-coating commonly uses magnesium fluoride or calcium fluoride to further reduce reflection. Each glass is typically coated 3 to 5 times (and at times upwards of 10 times) to create a situation where near 100 percent of the light reaches your eyes.
A Closing Recap.
Listen closely to the salesperson, or understand what you are reading, when a reference is made to lens coatings. The type of lens coatings go a long way to determining the quality of the image you will be seeing.
o Fully Multi-Coated Lens produces the very best quality images.
o Multi-Coated Lens is a step below the best, but still produce quality images.
o Fully Coated Lens produce good images that are acceptable to most users.
o Coated Lens is usually found in the most inexpensive binoculars.
