Outcome 1 Describe Properties of Lens Materials

Question 1

Index of Refraction

Answer 1

Refers to the speed of light by which light travels through a lens material. As the index of refraction increases the lens thickness decreases

Question 2

Specific Gravity

Answer 2

Refers to the ratio of weight or mass of a given volume of a substance to that an equal volume of another substance that is used as a standard

Question 3

Abbe Value

Answer 3

Indicates the amount of chromatic aberration within a lens

Question 4

Transmission

Answer 4

Is the amount of visible light that can pass through an opthalmic or sunglasses lens

Question 5

Additional Characteristics of Crown Glass Lenses

Answer 5

• They fog more than plastic
• Can be heat or chemically tempered , only 1.7 high index

Question 6

Additional Characteristic of Plastic Lenses

Answer 6

• Can be manufactured and sold with no coatings
• Easier to scratch compared to a glass lenses
• Anti-reflective coating should be added for high index lenses

Question 7

Additional Characteristics of Polycarbonate Plastic Lenses

Answer 7

• Plastic lenses that are coated with scratch resistant , scratches easier than a CR39 thats not coated

Question 8

Additional Characteristics of High Index Plastic Lenses

Answer 8

High-index plastic lenses are about 1.0 mm thinner than polycarbonate plastic lenses. This reduced thickness produces thinner and lighter lenses that are easier to break than polycarbonate lenses.

High-index plastic lenses are also about 10-25% lighter and 15-25% thinner than CR39 plastic lenses. They are about as easy to break, as lenses made of CR39 plastic.