1、Materials and Categories
In terms of material, it can be divided into four types: glass, PC, resin and natural lenses. The most widely used is resin.
Spherical and aspherical: mainly talk about aspherical lenses, the advantage of aspherical lenses is that the lens edge distortion is relatively small.
In this way, the lens has a good image, no aberration, and a clear field of view.
And under the same material and degree, aspherical lenses are flatter and thinner than spherical lenses.
Degrees and Refractive Index
Generally speaking, it is recommended to choose a lens with a high refractive index. The higher the refractive index, the thinner the lens.
But pay attention to a problem, that is, the higher the refractive index, the impact on the Abbe number, do not blindly pursue the refractive index, specific analysis of specific problems.
2、Abbe number and coating
The so-called Abbe coefficient, also known as the dispersion coefficient, is more commonly referred to as the edge of the glasses to see the object closer to the human eye without the purple edge, the yellow edge and the blue edge. Generally speaking, the greater the refractive index of the medium, the more serious the dispersion, that is, the lower the Abbe number. This also answers the reason why it is said above that the refractive index should not be blindly pursued.
(Knock on the blackboard: The same optical medium has different refractive indices for different wavelengths of light. For example, the refraction of sunlight through a prism will show seven colors of light, which is the phenomenon of dispersion.)
Next, let’s talk about the coating of the lens. A good lens will have several layers of coating.
The top mold is waterproof and oil-proof; the anti-reflection film lets more light in:
The electrostatic discharge film makes the dust not easy to absorb; the hard film can protect the lens and make it not easy to be scratched and so on.
3、Functional lens
Frankly speaking, about the functionality of the lenses.
I also thought it was inexplicable before, the lens is not to help the myopia see things clearly, where do so many functions come from? At most, I only know that there are lenses with anti-blue light, until after I checked a lot of information (Master, I realized!)
It turns out that it has so many categories! (Although I can’t remember it after reading it)
However, for the comprehensiveness of the article, it was decided to sort it out.
A Anti-blue light lens： This does not need to be introduced too much. As the name suggests, it can play the role of anti-blue light. It is more suitable for friends who often look at mobile phones and computers.
B Progressive multifocal lens: This kind of lens means that there are multiple focal points on one lens, and objects at different distances can be seen clearly with the conversion of sight distance. That is to say, this lens can have different luminosity required to see long distance, medium distance and close distance at the same time.
- It has three categories:
- a Middle-aged and elderly progressive film (reading glasses): This should be the most common one. Suitable for both myopia and presbyopia.
- Adolescent myopia control lenses – used to reduce visual fatigue and control the speed of myopia development. The “good student” lens is one such.
- b Adult anti-fatigue lenses – for programmers and other friends who often face computers. In other words, most of the feelings are only for psychological comfort. The most important thing is to combine work and rest, and take appropriate rest.
- c Smart color-changing lenses. When encountering strong ultraviolet light, it will automatically become darker and block the strong ultraviolet light outside. When returning to a darker environment such as indoors, it will automatically brighten to ensure the clarity of vision.
Post time: Jan-17-2022