What is the basic knowledge of sunglasses？
Classification of sunglasses lenses
What makes ideal sunglasses：
96% of ultraviolet rays must be filtered
The color of the left and right lenses is uniform, and the difference cannot be more than 5%, the scene cannot be bent and deformed through the lens
Lightweight and comfortable to wear
Not easy to break
The frame should be tightened and comfortably on the bridge of the nose and ears, and eyelashes should not touch the lens. Even if the frame is slightly bent, the lens will not fall off.
What are the sunglasses lens materials :
1. PC LENS 2. GLASS LENS 3. RESIN LENS 4. NYLON LENS (Tr-90) 5. AC LENS 6. POLARIZED LENS 7. ECCENTRIC LENS 8. COLOR CHANGING LENS
POLYCARBONATE LENSES(Carbonated polyester lens) are tough, not easy to crack, and impact resistant. It is a specially designated lens material for sports glasses, and the price is higher than that of acrylic lenses.
How to distinguish PC lenses?
After removing the lens, you will see small particles clearly.
Clarity is slightly higher than resin, and not easy to wear. But it is heavy and easily broken (even-tempered glass), in addition, the ability of the glass sheet to absorb ultraviolet rays is relatively weak, unless it has been specially processed.
Glass lenses are also divided into three types:
Coquille Glass Lens, Polished Ground & Polished Glass Lens, Impact-resistant Glass Lens
3.CR-39, Hard Resin lens
Resin is a chemical substance with a phenolic structure.
It is characterized by lightweight, high-temperature resistance (the lighter is not transparent), and strong impact resistance, which can effectively block ultraviolet rays.
How to distinguish CR-39?
There will be a white powdery thing when the lens is taken off.
4. Nylon lens
It is made of nylon.
Features: It has very high elasticity, excellent optical quality, and strong impact resistance. It is usually used as a protective article. It is rich in color, ultra-lightweight, not easily broken, has good optical performance (comparable to glass lenses), and has 100% UV protection.
It is currently the best lens on the market and is mostly used in high-end sunglasses.
5. ACRYLIC LENS
It has excellent toughness, is lightweight, high perspective rate, and has good anti-fogging properties.
6. POLARIZED LENS
It is a Polaroid film, its function is to only accept light from one direction and block light from other directions. It uses the principle of blinds to filter stray light so that we can see things more clearly.
The polarizer principle, in order to filter the sun shining on the water, land, or snow in equal directions, adds a special vertical coating to the lens, which is called a polarized lens. The polarized lens has a total of 7 layers. The outer two layers are super hard wear-resistant layers, the second layer and the sixth layer are anti-shatter strengthened layers, the third layer and the fifth layer are ultraviolet filter layers, and the middle layer is a polarized light filter. The overall structure is compact and unique. Tests show that it can remove 99% of dazzling and chaotic reflected light, 96% of harmful ultraviolet rays, and has special functions of anti-shatter and anti-wear.
The quality of the polarizer is determined by two parts: one is the quality of the intermediate layer of the polarizing film, and the other is the thickness of the polarized lens. (In order to enhance the quality, it is usually thickened to 1.5 or 2.2)
In the previous article How to distinguish the differences between polarized and non-polarized sunglasses? we introduced the functions and advantages of the polarizer in detail, as well as the identification method.
Because polarized lenses are generally thin, manufacturers will not make the lenses too large when they produce sunglasses. If the lenses are too large, the frame will squeeze the lenses, which will cause the lenses to arch, produce extra luminosity, and affect vision. If the lens is not too large, it will often be too small. If the lens is too small, the problem of film drop and shrapnel is easy to occur. In addition, the polarizer is easy to shrink, so the factory will make the film a bit bigger when it is produced, so as to avoid problems such as lens drop and light leakage caused by shrinkage. However, if it is transported by air, the customer will find that the curvature of the lens is incorrect during the inspection, and this production method cannot be used. If the goods are shipped by sea, this method can be used.
7. Eccentric lens
The eccentric lens makes the curved surface of the lens into a non-parallel curved surface，The purpose is to make the refractive index of light within the acceptable range of our eyes so that our vision is clear and not dizzy while pursuing fashion, it also protects our eyes.
How to distinguish Eccentric lens?
The closer the lens is to the middle of the nose, the thicker the lens. The eccentricity principle is similar to the prism effect, and its optical center is not equal to the geometric center.
8. PHOTOCHROMIC LENS
This is a kind of lens that reacts differently under different light.
Attention: The plate is acidic, so PC and AC plates are usually not used for the plate frame, because the lens is prone to a chemical reaction, which can cause the lens to break.
What are the shapes of sunglasses lenses？
The thickness of the spherical lens is the same,It will produce a myopia effect of 8°-17°, which is different from the polarizer.
The left and right arcs are inconsistent with the upper and lower arcs, for example, 4C*8C
3. Cylinder lens.
This kind of lens only has a curvature on the left and right, no curvature on the top and bottom
4. Double Sphere Lens
5. Two-fold Sphere Lens
7. Bifocal lens
There is still a lot of knowledge about sunglasses lenses, such as the coloring principle of the lens, the depth of the lens color and the light transmittance, etc. We will talk about it in the next article.
Thank you for reading.