Wearing eyes of friends will find that the glasses shop lens has a lot of weight, one of the main difference is the coating is different. The telescope is the same, according to the quality, material and other differences in different coating. A lot of friends outside will feel, from the lens inside, is the red lens, will feel infrared, can night vision, many small traders on the street is also such a reason to deceive consumers. In fact, this is a mistake. Red reflective, only red coating or use a very low-level means to deceive consumers, that is, in the mirror tube wall coated with red material. When the light is on the surface of the lens, some light will be reflected off, the general telescope has more than 10 reflectors, even if each reflector reflects only a few percent of light, coupled with the absorption of light inside the lens, the final entry into the eye may lose most of the light, not only imaging dim, and reflected light in the telescope multiple reflection, partly through the eyepiece into the eye, forming glare, interference observation, reducing the contrast of the image. The coating is generally needed to change this. The more common blue film, is one of the simplest antireflection film, the general high-grade mirror will use multilayer film, can enhance the optical transmittance of the whole system. The most simple way to judge a mirror is to look at the reflective lens, the smaller the reflection, the more transparent the lens, the better the coating.