There are two main types of optical coatings:
1. Anti-Reflection Coating
That means coating multiple transparent materials with different refractive indexes and different thicknesses on the front surface of the lens, and then using the principle of light interference to reduce the excess reflected light on the surface. After adding the anti-reflective coating to the lens, the permeability of the light will increase. And the wearer will feel less glares, and the vision will be more real and bright.
2. Hard Coating
It is mainly used for resin lenses. The hard coating is generally added to the front surface of the lens to enhance the abrasion resistance of the resin lens, while the light permeability is also enhanced. When the user is cleaning the hard-coated lens, the front and back surfaces of the lens should be washed with clean water first, and then dry with a clean soft cloth. Do not to wipe the lens when it is dry.
If ordinary lenses can help users see clearly, it is not necessary to add a coating. If it needs coating, the anti-reflection film or a hard film can be added for the resin lenses, and the glass lens generally use anti-reflection film only. When light enters into different transmission materials (such as from air into the glass), about 5% lights will be reflected off. There are many lenses and refractors in the optical sighting lens, and the total incident light loss is up to 30% to 40%. Modern optical lenses are usually coated with a single-layer or multi-layer magnesium fluoride antireflection film. The single-layer antireflection film can reduce the reflection to 1.5%, and the multi-layer antireflection film can reduce the reflection by 0.25%, so if the mirror is properly coated, the light transmittance can reach 95%. Single-coated anti-reflection coated lenses are usually blue-purple or red, and multi-layer anti-reflection coated lenses are light green or dark purple.
Vacuum coating is commonly used on cameras, telescopes, microscope eyepieces, objective lenses and prisms to increase image illumination.