1, refractive index
The refractive index of the lens depends on the material used in the lens. With the same center thickness, the higher the refractive index, the thinner the lens edge. In the case of the same brand, the refractive index means the different materials used, and the price of the lens can also be judged. The higher the refractive index, the higher the price, and vice versa.
Refractive index selection reference (for reference only, not mechanical comparison)
1.56:0 —400 (-4.00D)
1.60:300(-3.00d)-600(-6.00d)
1.67:400(-4.00d)-800(-8.00d)
Over 1.74: 800 (-8.00d)
1.74 double non: higher than 1000 (- 10.00d).
2. Spherical and aspherical surfaces
A part of a convex or concave lens cut from a spherical surface is called a spherical lens.
Because spherical lenses inevitably have aberrations (especially astigmatism and image bending aberrations), there are lenses that make up for the shortcomings of spherical lenses, that is, aspherical lenses (usually referred to as single-sided aspherical lenses).
Aspheric lens refers to a plane of rotation (such as parabola) with the same non-circular cross section on all meridians.
Its biggest advantage is that there is no object distortion in the edge field of view, and the lens edge is about 1/3 thinner than the ordinary spherical lens. Therefore, the price will be relatively high, and there are also double-sided aspherical lenses on the market, which makes the wearing field of vision clearer and the imaging effect better.
Of course, the price is also very expensive.
3. Abbe number
Abbe number, namely dispersion coefficient, is an important index to measure the imaging clarity of lens. Usually expressed by the reciprocal of dispersion coefficient, also known as Abbe number.
The larger the Abbe number, the smaller the dispersion. Conversely, the smaller the Abbe number, the greater the dispersion and the worse the imaging definition. Abbe number of lens has a certain relationship with refractive index. The larger the refractive index of the material, the more serious the dispersion, that is, the lower the Abbe number.
Therefore, as far as this single index is concerned, the lower the refractive index, the better. However, when matching glasses, it is necessary to judge according to the comprehensive situation of one's own vision. Fitness is the most important and cannot be mechanically limited to Abbe number.
4, antifouling ability
In recent years, the research and development direction of many brand lenses has shifted from improving hardness and light transmittance to increasing smoothness of lenses to improve their waterproof and oil-proof ability.
Among them, the most representative lenses are Zeiss Lotus Membrane Series and Essilor Diamond A3 Series.
Test method-we can wipe the lens clean and drop a drop of water and move it back and forth on the lens. If the lens is always a drop of water, it proves that it has a good waterproof function. If all the water drops are scattered on the lens surface, the function is relatively poor.
5. Anti-ultraviolet, anti-radiation and anti-blue light.
Let's talk about ultraviolet protection.
Anti-ultraviolet lens is anti-ultraviolet lens. It can completely absorb or reflect the ultraviolet rays that are most harmful to human eyes to protect them. UV protection coefficient is expressed by uv value: it is better to be UV400 and generally UV375. Optical shops generally have instrument testing.
However, it should be noted that the optical lenses of regular lens manufacturers all contain anti-ultraviolet function (greater than or equal to UV375), so don't be fooled by many market gimmicks.
Look at radiation resistance.
At present, almost all lenses on the market have anti-radiation films. However, the radiation protection effect of the lens is only within the scope of the lens, and the electromagnetic wave does not travel completely in a straight line. Therefore, the lens that uses this as a gimmick needs to be treated with caution.