Lens Materials & Coatings
Lens Parameters

Material	Refractive Index	V-Value	Specific Gravity
Opthamalic Crown	1.523	59	2.55
Photogrey Extra	1.523	59	2.41
CR-39	1.498	58	1.32
High-Index Plastic	1.595	36	1.36
Dense Flint	1.690	30	4.04
Barium	1.60	42	3.71
Titanium Glass	1.701	31	2.99
Flint 1.8	1.805	25	3.37
Polycarbonate	1.586	30	1.20

Specific Gravity: The weight in grams of one cubic centimeter of any given mat-erial. The higher the specific gravity of the material from which a lens is made, the more it will weigh.

V-Value, or Abbe number: A relative measure of the dispersion or color distortion of a lens. Through the optical center of any lens, regardless of material, color distortion is virtually non-existent. As the eye turns behind a powered lens, prism is induced which causes dispersion. Dependent on the V-value, more or less dispersion is induced.

Materials made from dense flint or barium glass are commonly used for the segments in fused glass bifocals. We will be covering bifocal design in the next session.

Although a wide variety of spectacle lens materials are available for use, most lenses sold today are made of either CR-39 plastic, clear crown glass, photochromic glass, or polycarbonate.