We all know that glasses are composed of two parts, one is the frame and the other is the lens, and often, we will spend a lot of thought on the lens. Because there are many types of lenses, and there are many lens materials, many people don't know how to choose lenses, but don't worry, if you master these points, you can definitely choose a good lens. 1. How to choose glasses lenses? 1. Clarity The refractive index not only determines the thickness of the lens, but also affects the Abbe number. The larger the Abbe number, the smaller the dispersion. Conversely, the smaller the Abbe number, the greater the dispersion and the worse the image clarity. . But generally speaking, the higher the refractive index, the greater the dispersion, so often the lightness and clarity of the lens cannot be balanced. Therefore, when choosing a lens, the first thing to observe is the clarity of the lens. 2. Light transmittance Only when the light comes in can we see things, so the light transmittance is also one of the factors that affect the quality of the lens. If the light is too dark, seeing things for too long will cause visual fatigue, which is not conducive to eye health. Good materials can effectively reduce light loss, have good light transmission, clear and transparent, and provide you with bright vision. 3. UV protection Ultraviolet rays are light with a wavelength of 10nm-380nm. Excessive ultraviolet rays can cause harm to the human body, especially the eyes. In severe cases, it can even cause blindness. At this time, the anti-ultraviolet function of the lens is particularly important. It can effectively block the ultraviolet rays without affecting the passage of visible light, and protect the eyesight without affecting the visual effect. 4. Thin and light Many people who wear glasses always need to hold their glasses from time to time to prevent them from falling. There are even many people who wear glasses for work, which will become a burden. At this time, what we can do is probably to change a pair of lighter lenses. NS. The material determines the refractive index of the lens. Common refractive indexes are: 1.56, 1.60, 1.67, 1.71, 1.74. With the same power, the higher the refractive index of the lens, the stronger the ability to refract incident light, the thinner the lens, the lighter the weight, and the more comfortable to wear. 2. What are the types and characteristics of lenses? 1. Glass lens The main raw material of glass lenses is optical glass, which can be divided into white film and red film. Advantages: high surface hardness, high refractive index, strong scratch resistance, good optical properties, good light transmittance and mechanochemical properties. Disadvantages: heavy weight and fragile mirror surface, which seriously affects the wearing comfort and comfort. 2. PC lens PC lens, also known as cosmic lens, is an environmentally friendly engineering plastic and is currently the lightest lens material. Advantages: PC lens is strong, not easy to break, can effectively prevent the lens from cracking during strenuous exercise, is light in weight, and can prevent ultraviolet rays. Disadvantages: The processing is cumbersome and the dispersion control is not ideal, and the price is high. 3. Lenses made of nylon The material of the nylon lens is transparent polyamide. Advantages: very high elasticity, excellent optical quality, and strong impact resistance. Disadvantages: wear resistance is worse than glass, and production cost is high. 4. Resin lens The resin comes from the hydrocarbon secretions of plants. Resin lenses are chemically synthesized and polished lenses. It is a very popular lens among myopia. Advantages: lighter weight, more wear-resistant, strong impact resistance, not easy to break, safer, and good light transmission. Disadvantages: not resistant to wear, poor thermal conductivity, and easy to deform. 2. How to distinguish the quality of spectacle lenses? 1. A pair of qualified spectacle lenses is composed of a substrate and a film. The substrate is composed of various materials, such as glass, tree branches, PC, etc. There are also many kinds of films, such as hard film and anti-reflection film. , Anti-fog film, anti-radiation film, etc. Generally speaking, there are more problems in the film layer of spectacle lenses, such as film cracking and film peeling. 2. There are generally two types of spectacle lens release: chemical and physical. To know whether the lens has chemical peeling, you can wash the lens with a neutral detergent, and then drop a few drops of tap water on the surface of the dried lens, such as water drops rolling on the surface of the lens like water drops on a lotus leaf, indicating that the lens is waterproof The performance is good; if the water droplets have tails, it indicates that the lens has been corroded by water or weak acid liquids, and chemical peeling will occur. 3. The method to check the physical peeling is to clean and wipe the lens, stick it tightly to the surface of the film with transparent office tape, and then quickly lift the tape to observe whether there are bright reflective spots on the surface of the lens. If there are reflective spots, it means that the surface of the lens is peeling off or has a tendency to peel off; otherwise, it means that the film is good.