Part of the light that passes through the lens is reflected by the front (incident light) and rear (exiting light) surfaces. This reduces the amount of light passing through the lens, so the image appears to be dark. Also, the reflected light may cause ghosting and flare, affecting image contrast. To minimize reflection on the lens surfaces and ensure clear, sharp images, anti-reflective coating is applied.

Coating is applied to both surfaces of the lens. There are two main types of coating: a single layer and multilayer (usually 3-5 layers). A multilayer coating effectively reduces reflected light that cannot be eliminated with a single-layer coating, and increases the transmittance of light.