The coating is mainly to reduce reflection. In order to improve the lens transmittance and image quality, in modern lens manufacturing process should be coated with the lens. The lens coating is based on the optical interference principle, on the lens surface coated with a thickness of one-fourth wavelengths of substances (usually fluoride), so that the lens of the wavelength of the shade to minimize reflection. Obviously, a layer of film only works for a shade, while multi-layer coatings can work on a variety of shade. Multilayer coatings usually use different materials repeatedly to coat different thicknesses on the lens surface. Multilayer coating can greatly improve the lens transmittance, for example, the lens of non-coated film each surface reflectivity of 5%, single-layer coating to 2%, while the multilayer coating can reduce to 0. 2%, in this way, can greatly reduce the lens between the diffuse reflection, thus improving the image contrast and sharp degree.