Unit 4: Optics

Question 1

Polycarbonate lens index

Answer 1

1.586

Question 2

Trivex lens index

Answer 2

1.53

Question 3

CR 39 lens index

Answer 3

1.498

Question 4

Equation for sagittal depth

Answer 4

Sag = r -  √ (r^2 - (d/2)^2)
Sag = (radius) - (square root of (radius squared) - (diameter/2) squared)

Question 5

How to find radius of curvature in the sagittal depth equation

Answer 5

r = (n-1)/D
r = (index - 1) / (power of lens)

r WILL COME OUT IN METERS AND NEEDS TO BE CONVERTED TO mm!!!

Question 6

Approximate sagittal depth formula

Answer 6

Sag= ((d/2)^2)(D)/ 2000(n-1)
Sag= (diameter/2)squared x (Power) / 2000(index -1)

Question 7

Convex lens produces real or virtual image

Answer 7

Real image

Question 8

Concave lens produces real or virtual image

Answer 8

Virtual image

Question 9

Nominal power formula

Answer 9

F(total) = F(front) + F(back)

Data can be obtained by using a lens clock to measure front and back

Question 10

Prentice’s rule

Answer 10

P=cD

Prism = (decentration IN CENTEMETERS) x (Power in diopters)

Question 11

Approximate formula

Answer 11

F(theta) = F(cyl) (sin(theta))^2 + F(sph)

(New cyl power) = (current cyl) x (sin of difference to desired axis)squared + (current sph)

Question 12

What effect does an increase in the base curve of a lens have on a minus lens

Answer 12

Decreases minification

Question 13

What size wavelengths make up the visible light spectrum

Answer 13

400-750nm

Question 14

How to calculate index of refraction

Answer 14

n = (speed of light in air) / (speed of light in substance)

Question 15

Regular (crown) glass index

Answer 15

1.523

Question 16

Snells law

Answer 16

n(1)(sinangle1) = n(2)(sinangle2)

Question 17

In vergence equations a negative number is this in relation to the lens

Answer 17

In front of

Question 18

In vergence equations a positive number is located here in relation to the lens

Answer 18

Behind

Question 19

Focal length equation

Answer 19

P = 1/f

(Power)=1/(focal length IN METERS)

Question 20

Surface power formula

Answer 20

D= n-1 / r

Power= (index) - (other index usually air) / (radius)