When light enters different transfer materials (such as air entering the glass), about 5% will be reflected off. There are many lenses and refracters in the optical collimator. The whole amount of simultaneous interpreting can cause the incident light loss to be 30% to 40%. Modern optical lenses are usually coated with a single or multi-layer antireflective coating of magnesium fluoride. The single layer antireflective coating can reduce the reflection to 1.5%, and the multi-layer antireflective coating can reduce the reflection to 0.25%. Therefore, if the whole sight is properly coated, the light transmittance can reach 95%. The lenses with single antireflection coating are usually blue purple or red, while the lenses with multi antireflection coating are light green or dark purple
