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1. Refractive index

The refractive index of the lens is determined by the material used in the lens. In the case of the same type of lenses with the same center thickness and the same power, 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 materials 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 for mentioning the coefficient of wear resistance is that resin lenses are not wear-resistant when they first entered the market, and they wear out after half a year. However, with the continuous iteration and update of technology, the surface hardness of ordinary resin lenses is 2-3H, and the hardness after hardening reaches 4-5H. Now the hardness of resin lenses has exceeded 6-7H, and then the surface is electroplated. Adding a hard film solves the shortcomings of the lens that is not wear-resistant. Although the hardness cannot be compared with glass plates, most of the glass plates have been withdrawn from the market at present, and the only ones left are mainly high refractive indexes, such as 1.8 and 1.9 refractive indexes.

3. Spherical and aspherical surfaces

A part of a lens with a convex or concave shape cut from a spherical surface is called a spherical lens.

Because spherical lenses are difficult to avoid aberrations (especially astigmatic aberrations, such as bending aberrations), there are lenses that correct the shortcomings of spherical lenses, namely aspheric lenses (usually called single-sided aspheric lenses). Aspheric 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 high, and there are also double-sided aspheric lenses on the market. The field of vision is clearer and the imaging effect is better. Of course, the price is also very expensive.

4. Antifouling ability

In recent years, the research and development direction of many brand lenses has shifted from increasing the hardness and increasing the light transmittance to increasing the smoothness of the lenses to improve their water and oil resistance. The most representative lens is the Zeiss lotus film series. Test method-we can wipe the lens clean, drop a drop of water on the lens and move it back and forth. If the lens always drops water, it proves that it is waterproof. If all the water droplets are scattered on the surface of the lens, the function is relatively poor.

5. Anti-ultraviolet ability

The anti-ultraviolet lens is an anti-ultraviolet lens. It can completely absorb or reflect the most harmful ultraviolet rays to human eyes and protect the eyes. The anti-ultraviolet coefficient is expressed by the UV value: UV400 is most preferred, and UV375 is generally. Optical shops generally have equipment for testing. However, it should be noted that the optical lenses of regular lens manufacturers contain UV protection (more than or equal to UV375), so don't be blinded by many market gimmicks.

6. Radiation resistance

Almost all lenses on the market now have anti-radiation coatings. However, the radiation protection effect of the lens is only the range of the lens, and the electromagnetic wave is not completely linear. Therefore, the lens as a gimmick should be treated with caution.

7. Anti-blue light ability

Anti-blue light is the most sought-after lens feature 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 light lenses can effectively improve sore eyes, dry eyes, decreased vision and fundus diseases.