Thin
Lenses
High-index
Aspheric
Polycarbonate
High-index
= Lenses that are thinner & lighter in weight because the material
is denser.
Standard plastic (Cr-39) is the material of choice with low to moderately
strong prescriptions. It is relatively inexpensive, lighter than
glass and scratch resistant. From moderately strong to severe, different
"high-index" materials are called for. The term "high-index"
refers to any lens material with an index of refraction greater
than the 1.49 of Cr-39.
All lens materials being denser than air have higher refractive
indices ranging from the 1.49 of CR-39 through 1.60 through 166/7
to finally 1.71, corresponding to progressively denser and thinner
high-index lenses. 1.60 lenses are about 30-35% thinner than CR-39,
and 1.66 lenses are about 40-50% thinner.
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