What Should We Pay Attention To When Choosing Lenses?
Many people are confused about how to choose lenses.
Don't worry, Xiao Xin from the following five aspects to teach you some ways to choose lenses, I hope to help you.
No.1 Refractive index
Refractive index reflects the ability of a lens to refract light. Under the same conditions, the larger the refractive index value, the thinner the lens, the more beautiful it is, and of course the more expensive it is.
But remember that thinner is not better when choosing lenses. Because there's something very closely related to refractive index called the Abbe number.
Abbe number refers to the dispersion coefficient, which is an important index to measure the clarity of lens imaging. The higher the value, the clearer the lens image; The lower the value, the blurrier the lens will be.
Abbe number and refractive index are relative and in an opposite trend. As shown above, in this figure, the blue lines represent the refractive index and the green lines represent the Abbe number.
In general, the higher the refractive index of the lens, the lower the Abbe number. So high light and high clarity is a relationship you can't have your cake and eat it.
Therefore, it is generally recommended that you select the lens with the corresponding refractive index according to your own degree.
It is generally recommended to choose 1.56 degrees below 200 degrees; Choose 1.6 from 200 to 400; 1.67 for 400 ~ 700; Over 700 choose 1.74; More than 1000 choose glass lens or high refractive index resin sheet, please consult optometrist.
No.2 Choose a sphere or an aspheric surface
A lens cut from a sphere with a convex or concave shape is called a spherical lens. As spherical lenses will inevitably appear aberration, so the appearance of a lens to correct the shortcomings of spherical lenses, namely aspheric lenses.
An aspheric lens is a surface of rotation (such as a parabola) with the same non-circular cross-section on all meridians.
Its biggest advantage is that there is no distortion of the image in the peripheral field of vision, and the visual deformation is less. At the same time, the lens edges are about 1/3 thinner than ordinary spherical lenses.
Now on the market to promote the basic aspheric lens, this basic pit is not big, if you want to choose, directly choose aspheric lens is good.
No.3 Selective coating
Lens price from dozens to thousands or even tens of thousands of pieces, expensive lenses are expensive where? Brand, material, process and other aspects may have differences, and one of the biggest differences is: film layer.
Lens film is mainly to reduce the reflection, improve the clarity of the lens, waterproof, and UV protection ability. The main optical film with hard film, anti-reflection film (anti-reflection film), anti-fouling film (waterproof film), anti-radiation film, polarization film, anti-fog film and polarizing film.
It is because of the existence of these membranes that the clarity and comfort of different lenses are different. For example, the lens with waterproof anti-fouling film, every time with water, only a few drops of water will be left on the lens, and then with the glasses cloth suction is very clean, there will not be how to wipe is not clean phenomenon.
You can choose lenses with different film layers according to your own needs.
No.4 Choose the material
Glass sheet: the clarity is slightly higher than resin, than other materials of the lens scratch resistance, wear resistance, thin lenses, good optical performance, but due to heavy and fragile characteristics, the use of low, and the factory is mainly made of high refractive index, such as: 1.8, 1.9 refractive index.
Resin sheet: is currently the most mainstream material for myopic people with glasses, light weight, high temperature resistance, impact resistance is not easy to break, safe to use, and can effectively block UV.
PC tablet: also known as "space tablet", "universe tablet", with strong, not easy to break, impact resistance and other advantages, is currently used for glasses lens the lightest material.
No.5 Choose the brand
After determining the above points, you can choose the corresponding 2 ~ 3 brands of lenses according to your budget for detailed comparison.
Now take the popular lens brand on the market as an example, to briefly introduce:
German Zeiss lenses - the biggest feature is the image quality is good, so in the field of camera lenses also occupies a high market rate, the technical aspect is impeccable, but the price is very expensive.
French Essilor -- the time-honored big brand, stable quality, wear-resistant and easy to clean, strong anti-fouling ability, is currently the lens field of the highest market share of the brand.
