When light enters different transmission materials (such as from air into glass), about 5% will be reflected off. There are many lenses and refractors in the optical sight, which can make the incident light loss up to 30% to 40%. . Modern optical lenses are usually coated with single-layer or multilayer magnesium fluoride anti-reflection coating. A single-layer anti-reflection coating can reduce reflection to 1.5%, and a multi-layer anti-reflection coating can reduce reflection to 0.25%, so the whole aim is If the mirror is properly coated, the light penetration rate can reach 95%. Lenses coated with a single-layer anti-reflection coating are usually blue-violet or red, while lenses coated with a multi-layer anti-reflection coating are light green or dark purple.
The main purpose of coating is to reduce reflections. In order to improve the transmittance of the lens and the quality of the image, the lens must be coated in the modern lens manufacturing process. The coating of the lens is based on the principle of optical interference. The surface of the lens is coated with a quarter-wavelength substance (usually fluoride) to minimize the reflection of the colored light of this wavelength. Obviously, one layer of film only works on one color light, while multi-layer coating can work on multiple colors. Multilayer coatings usually use different materials to repeatedly coat the surface of the lens with different thicknesses. Multi-layer coating can greatly increase the light transmittance of the lens. For example, the reflectivity of each surface of an uncoated lens is 5%, which is reduced to 2% after single-layer coating, while multi-layer coating can be reduced to 0.2%. In this way, the diffuse reflection between the lenses of the lens can be greatly reduced, thereby improving the contrast and sharpness of the image.