I had a question the other day about different lenses, so I thought I post a little bit of information about the subject.
Lenses are either made of plastic or glass - most lenses sold today are plastic. Usually it's only when extremely thin lenses are required for very high prescriptions that glass may be the better option. Otherwise plastic is the more practical and lighter choice.
The different lens numbers (1.49, 1.56, 1.61, etc.) refer to the refractive index of a lens - it's a measure of how the lens bends light.
The higher the number; the thinner the lens. This is because lenses that bend light more than others have a higher refractive index and need less material to achieve the same eyesight correction (hence are thinner).
So 1.49 index does not mean 1.49mm. It refers to the lens refractive index.
However, less material in thinner lenses doesn't make them cheaper - the thinner you go, the more expensive the lenses are!
I'll post again soon about the different indexes you can get at Focalise.
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