Properties Of Lens Materials

Question 0

Index of refraction (n)

Answer 0

Speed of light in a vacuum compared to its speed in an optical material

velocity of light in vacuum / velocity of light in material

Question 1

What is a lens?

Answer 1

Transparent material between two polished surfaces

Question 2

What wavelength is yellow helium line?

Answer 2

587.6 nm

Question 3

What is considered normal index?

Answer 3

> 1.48 but < 1.54

Question 4

What is dispersion (dispersive power)?

Answer 4

Chromatic aberration of an optical material

Spread of white light as it’s passed through material

Question 5

Equation for dispersion (w)

Answer 5

(w) = (nf - nc) / (nd -1)

Question 6

Blue light

Answer 6

nf

486 nam

Question 7

Red light

Answer 7

nc

656 nm

Question 8

High dispersion =

Answer 8

= High chromatic aberration

Question 9

What is the Abbé number?

Answer 9

Constringence
V = 1 / w
Usually around 30-60

Question 10

What is axial/longitudinal chromatic aberration?

Answer 10

Aberration occurs on the optical axis

Inherent in lens material

Question 11

Equation for axial chromatic aberration

Answer 11

ACA = F / V

Question 12

What is transverse/lateral chromatic aberration?

Answer 12

Measures differences in chromatic aberration via prismatic differences

Question 13

Equation for transverse chromatic aberration

Answer 13

TCA = (Fd) / V

Question 14

What is specific gravity?

Answer 14

Weight of a given volume of material compared to the weight of the same volume of water

Depends on density

Question 15

Higher specific gravity =

Answer 15

= heavier material

Question 16

Glass =

Answer 16

= Mineral

Question 17

What material is in glass?

Answer 17

Lead

Higher index -> heavier glass

Question 18

What is glass?

Answer 18

Amorphous, supercooled liquid with high viscosity and no discrete melting point

Question 19

What are the basic ingredients for crown glass?

Answer 19

Silica (sand)
Sodium oxide (soda)
Calcium oxide (lime)

Question 20

What is ophthalmic crown glass made of?

Answer 20

Potassium
Borax
Antimony
Arsenic

Question 21

What is absorptive glass?

Answer 21

Non-visible radiation absorption

Photochromatic

Question 22

What makes photochromatic lenses change from light to dark?

Answer 22

Silver halide crystals

Question 23

Which glass material is the most optically superior and stable?

Answer 23

Crown glass

Question 24

Reasons why crown glass is the best glass:

Answer 24

``` Lowest chromatic aberration High Abbé number Least warpage Good optics Difficult to scratch ``` High specific gravity and low refractive index

Question 25

What is the refractive index of crown glass?

Answer 25

1.523

Question 26

What is the Abbé number of crown glass?

Answer 26

59

Question 27

What is the specific gravity of crown glass?

Answer 27

2.54

Question 28

Plastic =

Answer 28

= Organic

Question 29

What is plastic?

Answer 29

Polymeric material of large molecular weight Synthetic material formed by combining organic with inorganic materials

Question 30

What are the two main groups of plastic material?

Answer 30

Thermoplastic | Thermosetting

Question 31

What is an example of thermoplastic material?

Answer 31

Polycarbonate

Question 32

What is an example of thermosetting plastic material?

Answer 32

CR-39

Question 33

What is thermoplastic material?

Answer 33

Softens when heated Can be stretched, pressed, or molded Plastic memory Not stable, susceptible to heat deformation

Question 34

Explain the thermosetting process.

Answer 34

Granules of raw material are melted. | The molten material is injected into mold.

Question 35

What are thermosetting materials?

Answer 35

Once hardened, can't be softened | Stable, rigid, flame resistant, insensitive to heat

Question 36

Explain the thermosetting process.

Answer 36

Liquid monomer is mixed with a catalyst and placed in molds then cured.

Question 37

What does CR-39 stand for?

Answer 37

Colombian Resin, 39th lab formation

Question 38

How did CR-39 come about?

Answer 38

At the end of WWII, Pittsburg Plate Glass had a railroad tank full of CR-39 monomer without a buyer.

Question 39

The original CR-39

Answer 39

Slightly yellowish tinge | Soft surface, easily scratched

Question 40

Characteristics of CR-39:

Answer 40

Better impact-resistant than untreated | Lower specific gravity than glass

Question 41

Characteristics of polycarbonate:

Answer 41

Greatest impact resistance Higher refractive index, low specific gravity, More dispersion than glass

Question 42

What material has the best impact resistance?

Answer 42

Polycarbonate

Question 43

What is the refractive index for CR-39?

Answer 43

1.499

Question 44

What is the Abbé number for CR-39?

Answer 44

58

Question 45

What is the specific gravity for CR-39?

Answer 45

1.32

Question 46

What is the refractive index for polycarbonate?

Answer 46

1.586

Question 47

What is the Abbé number for polycarbonate?

Answer 47

30

Question 48

What is the specific gravity for polycarbonate?

Answer 48

1.20