VI. Types and functions of lenses  (introduction of film)

1. Choose the type of lens according to the needs of life:

Single vision lens

There is no special vision requirement, sufficient to meet  the daily vision correction.

Multifocal lens

The lens has multiple focal points, and the upgraded  version of the bifocals has no obvious dividing line,  making the appearance more beautiful. It is suitable for  the elderly who have different needs for degrees of the  upper and lower end of the lens. It is also especially  suitable for students to prevent the rapid increase in the  degree of myopia. However, compared with single vision  lenses, the processing process of bifocals is cumbersome  and expensive, and users need to adapt for a long time.

2. Choose the type of lens according to lens material:

Currently used lenses are classified by materials as follows:

Glass lens

Glass lenses are heavy, fragile and most of them are  spherical lenses, but their refractive index is stable and not  easy to wear. Nowadays, glass lenses are rarely used, and  only custom-made glass lenses with high refractive index are  available. The target customer group is people with myopia  of more than 1000 degrees.

PC lens

PC lens is also called space lens, universe lens, a kind of  ultra-light lens. For myopia lenses, PC is widely used in  lenses with a refractive index of 1.60.PC lenses are more  impact resistant than lenses of other materials, but the  biggest problem of PC lenses is that the surface is very easy  to be scratched, easily deformed by force, and has a low  Abbe number.It is not suitable for plastic and rimless frames.  If it is only for impact resistance, it is very suitable for  children and people who need to ensure safety, such as  sports and windproof glasses.

Resin lens (CR39)

Resin is currently the most common lens material on the  market. Plastic and resin sheet are half lighter than glass  sheets, more impact resistant, have high light transmittance,  are safe, and not easy to break, but the surface is easy to  scratch and wear.

3. Spherical and aspheric

Spherical lens

A spherical lens is one in which both the inside and outside  of the lens are spherical, or one is spherical and the other is  flat. Spherical lens, suitable for people with low degree.  With small thickness gap, its imaging will not be distorted,  and the price is lower than the same type of aspheric lens,  and more cost-effective. But the spherical lens with a high  degree distorts the view of the object, limiting the wearer's  view.

Aspheric lens

The design of aspheric surface can solve the distortion of the  view to the greatest extent.In particular, the high-degree  lens is lighter, thinner, flatter, with a minimized edge  aberration and wide field of view.The object is clear and  natural, and still maintain excellent impact resistance  performance, to ensure the safety of the wearers.

4. Refractive index and Abbe number

The refractive index of the lens depends on the material used.  The refractive index of the lens: 1.499, 1.56, 1.60, 1.67, 1.71,  1.74.

The higher the refractive index, the flatter the front and  back surfaces of the lens are, and the thinner the lens is.  High refractive index lenses cost more than low refractive  index lenses.Abbe number is also known as the "dispersion  coefficient". Generally speaking, the larger the refractive  index of the lens, the more serious the dispersion and the  smaller the Abbe number.

Degree of glassesRecommended lens      refractive index
Within 200 degrees1.499
0-400 degrees1.56
300-600 degrees1.60
400-800 degrees1.67
600-1200 degrees1.71
More than 800 degrees1.74

5. Choose according to the film layer

The main functions of the lens are realized by coating  different types of functional film on the surface of the lens.  The main functions of the film layer include hard protection,  reducing reflection, anti-blue light, anti-radiation, improving  the clarity of the lens, waterproof, anti-fouling, anti-UV and  other functions.

Hard film(Wear-resistant film)

Harden lens, make it not easy to scratch, effectively  protect the surface of the lens from wear, but also can resist  the damage of hard objects, prolong the life of the lens.

Top film (waterproof film, anti-fogging film)

The top film makes the surface of the lens more clean,  waterproof, anti-fog, dustproof and anti-pollution.

Anti-UV film

The main function is to prevent ultraviolet radiation,  infrared radiation and a variety of harmful glare which can  damage the eyes.

Blue film

It has the function of preventing electromagnetic radiation  from computer, TV, mobile phone and so on. It is the main  film color of anti-blue lens.  Green film (emerald film): the most commonly used film  color for radiation-proof and blue-proof lenses. It can  prevent ultraviolet radiation, has the excellent light  transmittance. With it you can see the thing clear, and it  wears comfortably.

According to different film layers, common functional  lenses are:

Radiation proof lens

It has the function of anti-ultraviolet, anti-electromagnetic  radiation from computer, TV, mobile phone and so on.

Anti-blue lens

On the basis of anti-radiation lens, adding anti-blue light film  can not only prevent electromagnetic radiation, but also  prevent the damage of blue light to eyes.

Anti-fog lens

Coat the surface of the lens with a film to prevent moisture.

Photochromic lens

A photochromic film is coated on the surface of the lens,  which turns dark in the light.

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