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How to choose optical lenses and factors affecting refractive function
When buying optical lenses, how to choose the right lens? It is very important to choose the lens that suits you. The following is a detailed introduction to how to choose a lens.
Here are the standards for 4 kinds of lenses:
1, glass lens
Glass lens is more scratch-resistant than other materials, but its weight is relatively heavy, and its refractive index is relatively high: ordinary The slice is 1.523, the ultra-thin slice is: 1.72 or more, and the highest is 2.0. Polymer resin lens: Polymer resin lens is lighter than glass lens, and it is not easy to break due to impact resistance. However, because of its lower hardness, it is more prone to scratches than glass.
2, PC lens
There is another material that is more resistant to impact than polymer resin, and is often used in aviation. The transparent windows of the equipment, the police masks, and the masks on the helmets of astronauts are only about one-tenth the weight of glass, and only half the weight of traditional resin lenses.
Generally, PC lenses need to be coated with a scratch-resistant protective film, which will be sufficient to obtain better timeliness in use. Most of them are used in children’s eyeglass lenses or athletes Eye protection. PC lens also has an important feature, that is, PC lens has the effect of blocking harmful ultraviolet rays, but its shortcomings also include easy scratches on the surface.
3, bifocal lens
bifocal lens can correct both the vision of far and near at the same time, mainly for presbyopia Needed for correction. Optical lenses are generally assigned to bifocal lenses: the upper part of the lens is used to see the distance, and the lower part of the lens is used to see near points. As for the size of the near-use range, it is determined by the nature of the near-use work.
Generally flat-top bifocals have the highest probability of being used. They only have a small area at the bottom of the lens for near-point work. As for the periphery and upper part of the lens, Used to look into the distance and provide a good peripheral vision. The traditional bifocal lens is a first-line bifocal lens. The lens is divided into upper and lower parts from the middle, that is, all the less than half of the lens is used as the near point distance. They provide a better wide near point field of view, and are aimed at a longer time Workers at close points have better results. Architects, accountants, artists and other workers focus on mirrors with similar properties. This kind of lens can reduce the chance of head swinging. Bifocal lenses can also be used for people who only need to correct near-point reading, but it is inconvenient to take the glasses up and down when working at near-points.
4, trifocal lens
For those who need middle distance vision ( Generally from 18 inches to six feet), as far and near, the use of trifocal lenses can meet this kind of needs. Those who work in front of a computer or cash register have special eyesight at this medium distance. This kind of lens can meet his vision needs at work.
The corrective effect of these lenses also includes multiple ranges. The difference is that the dividing line between each aspherical lens with different distances is not obvious. These multifocal lenses The dividing line of may need to be very close before it can be seen or felt by the touch of the hand. However, when the user switches from near to far, the eyes will still feel a big sudden Variety.
The main factors affecting the refractive effect of spectacle lenses
1, geometric characteristicsp>
The geometric characteristics of the lens mainly include the radius of curvature and the surface shape of the lens.
2, physical and chemical properties
The physical and chemical properties of lenses mainly include the refractive index and Abbe number of the lens. The research and development of spectacles is to design and control the above influencing factors reasonably, so as to continuously improve the optical correction effect of spectacle lenses.