In terms of lightweight, aesthetics, and usability, nonspherical surfaces are superior to spherical surfaces; In terms of price, nonspherical surfaces are generally higher than spherical surfaces. In addition, nonspherical lenses have many functions and a wide range of applications.
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When you don't know how to choose the cheapest eyeglasses online, choosing a nonspherical surface usually won't go wrong. To exaggerate, if you're going to get spherical lenses, why don't you cut a glass ball and wear it on your eyes?
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Generally, a new type of glass is ultra-thin, ultra-thin, or ultra-thin, but when you look at it, the price is ultra-high, ultra-high, or ultra-high. At this point, I will think about the principle of ultra-thin lenses and why they become ultra-thin.
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Let's talk about thickness first. Generally speaking, the refractive index is used to describe thickness, and the higher the refractive index number, the thinner it is. Will there be a significant difference in thickness or price?
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Is it better for lenses to be thinner and more expensive? We usually think that expensive ones are better, but when it comes to choosing lenses, is that the case?
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I followed this idea and searched around, and I found some things that eyewear store staff usually wouldn't be able to tell us. Of course, I think it's also something we must understand when purchasing discount eyeglasses online.
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Later, I found my previous optometrist and told him about what I found, and he admitted that the Abbe number of my lenses was not higher than before.
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What is Abbe's number? Abbe number is a very strange name, right? But anyway, all you need to know is that it is a physical academic concept.