1. Check whether the light transmittance is good or not, and see if there are bubbles or impurities in it.
2. Looking at the hardness of the lens, the resin lens itself must undergo strict surface hardening treatment before leaving the factory due to its low hardness to meet the wear resistance requirements, otherwise it is generally After two or three months of wearing, the 'scratches' on the surface of the lens will be more serious, and it can not even be worn. The abrasion resistance of resin lenses with qualified hardness is much better, and there are only a few scratches after wearing for a few months. Do not affect the wearing.
3. Look at the color, high-quality resin lenses do not have any background color (if it is a coated lens film with color), and the background color of inferior lenses is slightly blue and matching It is easy to turn yellow after wearing for a period of time.
4. Inferior resin lenses have a thinner center thickness, and the edges look thinner than lenses with the same refractive index. This sacrifices the center thickness to make the lens become The thin approach is wrong, because resin lenses are different from glass lenses and are called 'safety lenses'. The minimum thickness of the center is required. Wearing such lenses is at the expense of the safety of your eyes.
If you can’t accurately identify inferior resin lenses, you'd better go to a large-scale optical shop with a good reputation Go with resin lenses.
Optical properties are the basic properties of materials. The optical properties of the material are consistent with the various optical phenomena encountered in the daily life of the spectacle lens, mainly including the refraction and reflection of light on the two surfaces of the spectacle lens, the absorption of the lens itself, the scattering phenomenon and the diffraction phenomenon. When light passes through the surface of the lens and is refracted, it will follow the law of refraction.
The refractive index is A parameter that reflects the refractive power of the lens material. The greater the refractive index value, the farther the light enters the lens and deviates. In general, the larger the refractive index value, the smaller the thickness of the lens, and the lighter the weight of the lens.
(2) Dispersion coefficient
The chromatic dispersion phenomenon refers to the different colors of light with different wavelengths and different refractive indexes , When the white light is refracted, the resulting color aberration is called chromatic dispersion. The dispersion capability of a material can be described by the Abbe number. The size of the Abbe number is inversely proportional to the dispersion of the material, that is, the larger the Abbe number, the smaller the dispersion of the material. Under normal circumstances, the Abbe number of spectacle lens materials is 30-60. Generally, the higher the refractive index of the spectacle lens, the greater the dispersion, and the lower the number of Abbe focusing lenses.
Although all spectacle lenses have dispersion, this factor can be ignored in the center of the lens. Only lenses made of high-dispersion materials are prone to chromatic dispersion, such as colored fringes on the edges of lenses that are relatively far from the optical axis.
When light is refracted on the surface of the lens, it also reflects. When light reflects off the surface of the lens, it will also follow the law of reflection. The reflection of light has a certain impact on the imaging of the spectacle lens, such as affecting the clarity of the lens and reducing its light transmission performance; the surface of the lens will produce interference reflected light, that is, forming a virtual image; glare. Generally, the higher the refractive index of the lens material, the more light is lost due to reflection. Of course, the anti-reflection coating on the surface of the lens and the aspheric mirror with multi-layer anti-reflection coating will be improved.
(3) Absorption of light
The light absorption of spectacle lenses usually refers to the absorption of light inside the lens material. It is expressed as the percentage of light absorbed by the front and back surfaces of the lens. For example, 30% light absorption means that 30% of the luminous flux is reduced inside the lens.
The light absorption of material follows Lambert's Law, which shows that light absorption changes exponentially with the thickness of the lens. The absorption of light by the lens material will reduce the light transmittance. For ordinary lenses, this part of the light loss can be ignored, but if the lens is a colored lens, such as a tinted lens, a color-changing lens, etc., the amount of light absorption will be large. This requires the amount of light absorption to meet our design requirements.