1. Refractive index
2. Abbe number
When sunlight passes through a prism, it will be dispersed into seven-color light, which is also the theoretical origin of the dispersion coefficient. Generally speaking, the higher the Abbe number, the smaller the dispersion, and the lower the Abbe number, the higher the dispersion. The resolution of the image is lower.
Lenses with a low Abbe number are prone to edge iridescence, which affects visual effects. The reason why it is said that the refractive index is closely related to the Abbe number is because in fact, the higher the refractive index, the lower the Abbe number, and it is often difficult to have both lightness and clarity. But with the improvement of the production process, the high refractive index can also take into account the high Abbe number, but the price is just a step up.
3. Spherical surface
Spherical and aspherical lenses are also words that are often heard when dispensing glasses. Simply put, aspherical lenses are better. After the light passes through the spherical lens, the focus point is different, and aberration will occur. The wearer feels that the edge is distorted and deformed, and it is easy to get tired after wearing it for a long time. The aspheric lens is cut and transformed on the basis of the spherical lens to ensure that the focal point is the same when the light passes through the lens, and the image will not be deformed and distorted. Because of the cutting, the lens will be thinner and lighter.
4. Material
There are three most common materials for lenses: resin, PC, and glass. Nylon and the like are relatively rare in conventional glasses.
Let’s talk about resin first. This material is the mainstream lens material. It is light in weight, strong in impact resistance, good in light transmission, and easy to process. It used to have a disadvantage of low hardness. With the development of coating technology, this disadvantage has gradually disappeared. disappear.
PC lenses, PC lenses with a certain thickness can be used in the portholes of space shuttles, the masks of space suits, etc., also known as space films. It has good toughness, is not easy to break, and is relatively light in texture. It is also commonly used to make lenses for some sports glasses. However, the wear resistance of PC lenses is also relatively poor, and it also needs coating support. The strength is sufficient and the Abbe number is relatively low.
At present, glass lenses are generally required for specialized glasses. High hardness, wear resistance, and higher refractive index make it the mainstream of early lenses. However, the glass is heavy, fragile, and difficult to process, and most of them are spherical lenses, so it is basically not considered to be used when dispensing glasses. However, the high refractive index allows it to be applied to myopia users above 800 degrees, and people with high myopia can consider it.
5. Coating
So much has been said here and there, and the basic information about the lens is almost the same, but since the coating was mentioned just now, let's talk about the coating again.
The purpose of the coating is to make up for the defects of the material itself or to enhance the performance of a certain aspect. The improvement of the hardness of the resin mentioned above benefits from the coating. Some ski goggles are also coated on the surface to achieve better UV filtering and enhanced visibility.
The coating of a pair of glasses is not single, and there are often multiple coatings covered together.
Adding hard film is a widely used film. It is commonly used in resin lenses and PC lenses, which can significantly increase the wear resistance.
The anti-reflection film is aimed at the case of low light transmittance. Ordinary lenses generally cannot achieve 100% light transmission, and a considerable part of the light will be reflected by the surface. After being coated with anti-reflection film, it can reduce reflection, enhance light transmission effect, and increase clarity. Especially in taking pictures, the difference can be clearly felt.
