Affected side of the flat lens light transmission has many causes. Mirror roughness will cause diffuse the incident light, reducing the lens transmittance. In addition, optical absorption of the material, can also cause some of the frequency of the incident light source, some of which disperse the particularly serious. For example, the material will absorb the red light looks green. However, these adverse factors can be processed to remove as much as possible.

    It is unfortunate that already exist in the nature of defects. When the incident light passes through different media, it will happen reflection and refraction problems. If our material at normal incidence, Zinc oxide we can define the reflection and penetration.

    Many people will be curious to ask: a perfect and transmittance of the coated glass-free should be the number? Since the non-coated glass transmittance is not good, then coated with several layers, the light transmission rate should be even worse is?

The refractive index coating

    In fact, these two issues are the same. Just understand the first question, the other naturally solved.

    According to the basic theory of electromagnetism, the reference for the different media of transmission and reflection. If the normal incidence to the medium n1 n2
Reflectivity = [(n2-n1) / (n1 + n2)] 2
Penetration = 4n1n2 / (n1 + n2) 2


    If the refractive index of air is 1.0, the refractive index coating nc (example: 1.5), the refractive index of glass n (for example: 1.8)

    (1) directly into the glass by the air

    Penetration = 4 × 1.0 × 1.8 / (1 +1.8) 2 = 91.84%

    (2) and then by air to enter into the glass coating

    Penetration = [4 × 1.0 × 1.5 / (1 +1.5) 2] × [4 × 1.5 × 1.8 / (1.5 +1.8) 2] = 95.2%
    Seen with the glass coating will increase light transmission. In addition this formula, we can calculate the light through the lens of both sides, found that even a perfect lens (refractive index 1.8), the transmittance of about 85%. If you add a layer of coating (refractive index 1.5), the light transmission of up to 91%. Shows the importance of optical coating.

    For example, if the thickness of the coating caused by the green light relative to consumption, the reflected light will show red. Market, many seemingly red telescope lenses are made using this principle. Nevertheless, the transmitted light reddish, Titanium dioxide but not the phenomenon. In many complex optical system, the reflected light of the suppression is very important lessons. Therefore, among a group of lenses, will make use of different coating thickness to eliminate the reflected light at different frequencies. So the more advanced optical system and found that the color of reflected light will be more.

    The same principle will be presented after the spectacle lens coating in different colors, common colors are red, emerald green, blue and so on. Although the lens looks show different colors, but when you see things through the lens, there will be no color. Different lenses and other optical applications is the use of glasses because of its special coating used only to increase the light transmittance of glasses after lens coating reduces light reflection on the part of the lens, to reduce this part of the light on line of sight interference. Uncoated glasses wearing people can often be seen in the night lights is due to multiple causes in this area.

Usually the general multi-coated lenses, the lens is mainly used to increase hardness, scratch-resistant ability, blocking UV rays and other functions. Some of the lens is also coated with a film can block electromagnetic waves, Magnesia electromagnetic waves used to reduce the harm to the human eye. There's the surface of the lens in the lens coating layer can reduce the increase of water surface tension of special coating, when moisture condenses on the lens surface, water droplets can not form, and thus can not reduce the transmittance of the lens effect, this lens is anti-fog lenses.
Coating thickness

    Finally, we want to explore the different coating thickness, will be affected? We already know that light transmission and coating of refractive index, Nickel oxide but hardly on its thickness. But if we can up and down in the coating thickness of effort, you will find the reflected light and reflected light B A difference between the nc × 2D optical path difference.
If nc × 2D = (N + 1 / 2) λ which N = 0,1,2,3,4,5 ..... λ is the wavelength of light in air will result in the specific wavelength of the reflected light have similar eliminate the effect, so the color of reflected light will change. Source: