The refractive index of the lens is determined by the material used in the lens.In the case of the same thickness of the center, the same degree of lens of the same type, the higher the refractive index, the thinner the edge of the lens; when the brand is the same, the refractive index means the difference in the material used, and can also determine the price of the lens. The higher the refractive index, the higher the price, and vice versa.
2. Wear resistance coefficient
The reason why the wear resistance coefficient is mentioned is that the resin lens is not wear-resistant when it enters the market, and it is basically worn after wearing the lens for half a year. However, with the continuous iterative updating of the technology, the surface hardness of the ordinary resin lens is 2-3H, and after hardening, the hardness reaches 4-5H, and the hardness of the resin lens has now exceeded 6-7H, and then the surface plating is performed. The addition of a hard film solves the disadvantage that the lens is not wear resistant. Although the hardness can not be compared with the glass sheet, most of the glass sheets have been withdrawn from the market at present, and the only remaining ones are mainly high refractive index, such as: 1.8, 1.9, the refractive index.
3. Spherical and aspherical
Cutting a part of a lens with a convex or concave shape from a sphere is called a spherical lens.
Since the spherical lens is difficult to avoid aberrations (especially astigmatic aberrations, such as bending aberrations), there are lenses that correct the disadvantages of spherical lenses, that is, aspherical surfaces (usually referred to as single-sided aspherical lenses). Aspherical lens: refers to a rotating surface (such as a parabola) with the same non-circular cross section on all meridians. The biggest advantage is that there is no object distortion in the edge field of view, and the edge of the lens is about 1/3 thinner than the ordinary spherical lens. Therefore, the price will be relatively higher, and there are also double-sided aspherical lenses on the market. The wearing of the field of view is clearer and the imaging effect is better. Of course, the price is also very expensive.
4. Anti-fouling ability
In recent years, the research and development direction of many brand lenses has shifted from increasing hardness and increasing light transmittance to increasing the smoothness of the lens to improve its water and oil resistance. The most representative lens is the Zeiss lotus film series. Test Method – We can wipe the lens clean and drop a drop of water and move it back and forth on the lens. If the lens is always a water droplet, it proves that it is waterproof. If the water droplets are all spread out on the surface of the lens, the function is relatively poor.
5. Anti-UV ability
Anti-UV lenses are UV resistant lenses. It can completely absorb or reflect the most harmful ultraviolet rays to the human eye to protect the eyes. The UV resistance coefficient is expressed by the UV value: the most preferred is UV400, which is generally UV375. Optical shops generally have instrument testing. However, it should be noted that the optical lenses of regular lens manufacturers all contain UV protection (more than or equal to UV375), and should not be blinded by many market gimmicks.
6. Radiation resistance
Nowadays, almost all lenses on the market have anti-radiation coatings. However, the radiation protection effect of the lens is only the lens range, and the electromagnetic wave is not completely linear. Therefore, the lens used as the gimmick should be treated with caution.
7. Anti-blue light ability
Blu-ray prevention is the most sought-after lens function in recent years. For people who use computers or electronic display devices for a long time, the role of anti-blue lenses can certainly prevent some harmful blue light from harming the eyes, making the eyes more comfortable when working in front of the computer screen. However, there is no further evidence that anti-blue lenses can effectively improve eye soreness, dry eyes, decreased vision, and fundus lesions.