Careful friends may notice that the lens of mobile phones has colors, and different mobile phone lenses have different colors, some are red, some are blue, and some are gold. For example, the lens of the iPhone 4S is blue, the lens of the Nexus 4 is red, and the lens of the ONE X+is green. So why does the lens of the phone have different colors?

In fact, in addition to mobile phone lenses, the lenses of digital cameras, telescopes, glasses, etc. we usually use are colored. These colors are mainly due to the thin coating on the lens surface, and the different colors on the lens surface are also due to the different coating. The coating of various colors of the lens is not intended to please users. These coatings play a very important role in lens imaging.

The coating has two main functions: 1. antireflection; 2 Color correction

Antireflection

When the light passes through the lens, about 4% - 10% of the light will be reflected by the lens (the reflectivity of plastic lens will be higher). You may think that 90% of the light transmittance is actually good, but generally the lens is composed of several lenses. For example, Meizu MX2 and OPPO Find 5 released a while ago both said that their lens is composed of five lenses, so if you calculate, only 59% of the light finally reaches the sensor. In addition, the light reflected inside the lens will be repeatedly reflected inside the lens, which will eventually form glare or ghost on the sensor.

Therefore, how to increase the transmittance is a very important issue, and the commonly used method is to add a layer of coating on the lens surface, which can greatly increase the transmittance of a certain section of spectrum.

However, the light we need to antireflect is often not monochromatic, but has a certain bandwidth. Single layer antireflection film can only completely antireflect monochromatic light of a certain wavelength. Therefore, we need multi-layer coating technology to improve the coverage of antireflective light. In addition, the different reflectivity of each coating layer can also improve the light throughput.

When observing the lens surface, the color seen by the lock is the reflected light. Generally speaking, the less light reflected back, the more effective this coating will be.

Color correction

The material or some components in the lens may lead to the high absorption rate of the lens to some colors, resulting in the final image color deviation. In order to eliminate this color difference, lens manufacturers will add coatings of other colors, such as amber, cyan, purple or blue, on the basis that the lens does not produce additional glare and ghost. These coatings can balance the final image color of the lens.