Unit 1

Question 1

Other methods of obtaining PUPIL measurments

Answer 1

-Pen ligth and ruler
-Ruler alone
-Using the lens to dot then measure

Question 2

What are the refrences if we dont have a penlight to measure PD

Answer 2

Outside of canthus to inside of other canthus
or
Inside of canthus to outside of canthus

Question 3

When and why do we use the frame wrap compass?

Answer 3

-Measures the amount of wrap a frame has (degrees)
-Good tool to match a pxs old pair and adjust new ones to it

Question 4

Base curve formula

Answer 4

F1 + F2 = FT

Question 5

What does the lens clock take ?

Answer 5

-Base curve in dioptric value for the surface power

Question 6

What are most lens clocks calibrated for ?

Answer 6

1.53

Question 7

Lens clock compensating formula?

Answer 7

Dt = R [(n-1) / (n2 - 1 )]
DT= true dipotric power of the lens (front curve)
R= reading on the lens clock
n= the index of material
n2= the index of the calibration of the lens clock

Question 8

When do you use lens clock compensating formula?

Answer 8

If the pair of lenses is a different index compared to the index on the lens clock

Question 9

What does the thickness need to be in a safety lens

Answer 9

minimum of 2mm

Question 10

What is the purpose of neutralizing / duplicating gls?

Answer 10

-Determine the RX
-Derterime sphere power
-Deterime cyl power
-Determine cyl axis
-Mark the optic centre
-Measure amount of prism
-Used for laying out uncut lenses

Question 11

What is focal length

Answer 11

The measure in which a lens converges of diverges light

Question 12

Why do we need focal length ?

Answer 12

It tells us the angle of view and how large an image will be

Question 13

Focal length formula in air

Answer 13

D= 1/f (meters)
D= power in diopters
f= the focal length of the lens in meters, cm, mm, or inch

Question 14

Dioptric power when not in air

Answer 14

D= n/f (meters)

Question 15

Index of refraction for air >?

Answer 15

1.00

Question 16

What is prism?

Answer 16

light entering a prism bends towards the base

Question 17

what do we calculate with snells law?

Answer 17

we can calculate the angle at which the rainbow will emerge from the prism

Question 18

calculating index of refraction formula

Answer 18

n = c / v
n= index of refraction
c= speed of light in a vacuum (3x10^8m/s)
v= speed of light in the material

Question 19

snells law formula

Answer 19

ni (sin0i) = nr (sin0r)

Question 20

what is refracting?

Answer 20

the bending of light when it enters a medium where its speed is different.
When light strikes a medium straight at 90 it slows down but stays in the same direction.
-But when light strikes a new substance at a angle, the slowing down/ change in speed causes the light to change direction.

Question 21

Mm to m

Answer 21

Divide by 1000

Question 22

Cm to m

Answer 22

Divide by 100

Question 23

M to cm

Answer 23

Multiple by 100

Question 24

Mm to cm

Answer 24

Divide by 10

Question 25

Lens aberration

Answer 25

-when light from a point of surface goes through a correctly powered spectacle lens yet fails to create a perfect image

Question 26

chromatic aberration

Answer 26

distortion of the image due to the inability of the lens to focus all colors onto the same focal point. This leads to the perception of undesirable color fringes

Question 27

monochromatic abberation

Answer 27

occurs when the light source contains only one wavelength (one color)

Question 28

what is better a lens with a higher or lower ABBE value

Answer 28

higher abbe value because it will have lower dispersion

Question 29

what is abbe value ?

Answer 29

• it is a measure of the degree to which light is dispersed or seperated when passing through a lens