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Crown Lenses Material (B270) ( Helpful:4 ) Back »

*Refractive index (nd): 1.52288
*Abbe value (Vd): 58.5
*Density: 2.55 g/cm3 (the heaviest corrective lens material in common use, today)
*UV cutoff: 320 nm

Glass has historically been the material of choice for ophthalmic lenses. Glass is most stable, scratch-resistant, and provides the best optical quality of all lens materials. However, since glass is more brittle than most materials, lenses made of glass must be tempered or heat-treated to give them more strength and make them safer to wear. Glass is available in a number of indices of refraction. As mentioned above, the higher the index, the thinner a lens will be for a given power. However, the specific gravity also increases dramatically with the index making high-index glass lenses much heavier. Chromatic aberration is also more pronounced in high-index glass. Index: Crown 1.52; High index 1.60, 1.70, 1.80

Pros

Superior optics
Stable material
Scratch resistant

Cons

Does not accept tint
Not impact resistant
Heavy

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