Lens Material

Question 1

Index

Answer 1

Thickness of material (high index = thinner material)

Question 2

Specific gravity

Answer 2

Refers to the weight

Question 3

Abbe

Answer 3

Hardness of material

Question 4

CR-39

Answer 4

High Abbe w/ standard index

Question 5

Polycarbonate

Answer 5

Low Abbe
Easily scratched
High index = impact resistance

Question 6

Hi-Index Plastic

Answer 6

High index

Indices of 1.60, 1.66 and 1.71, 1.74

Question 7

Trivex/Phoenix/trilogy

Answer 7

High Abbe
Excellent quality
Lightest lens available
Impact resistance

Question 8

Crown Glass

Answer 8

High Abbe
1.52 index
Standard by which all material are measured

Question 9

Photochromatic glass

Answer 9

Very hard
Changes colour when exposed to light
Available in plastic or glass