7 - Magnification

Question 1

Relative distance magnification (RDM)

• describe
• equation

Answer 1

If an object is closer, it appears relatively larger bc it subtends a larger angle

RDM = r/d (old distance/new distance)

Question 2

Relative distance magnification (RDM)

• the magnification produced vs change in viewing distance
• an object moved to half the original distance

Answer 2

Inversely proportional

Half distance = twice mag

Question 3

Relative size magnification (RSM)

• describe
• equation

Answer 3

Same as RDM, but for print sizes

RSM = new size/old size

Question 4

Angular magnification

• results from
• what’s NOT changed (2)
• what is changed

Answer 4

Apparent incr in agular subtense

Object size + viewind distance UNCHANGED

Angular subtense of light rays changed by an optical system

Question 5

Maximum angular magnification (MAM)

• equation
• for this relationship to hold true, __

Answer 5

M = 1 + hF

Where h = distance from lens -> eye (m)
F = dioptric strength of lens

Lens must be one focal length from the object

Question 6

YAY MATH!

What is the Maximum Angular Magnification for an object 40cm from the eye using a +10D lens?

Answer 6

MAM = 1 +hF

h = distance from eye->lens = eye-object distance minus focal length of lens
h = (0.4 - 0.1)

F = 10

MAM = 4x

Question 7

Total magnification

-equation

Answer 7

M = rF

Where r = object distance * dioptric strength of lens

(Object distance aka reference distance)

Question 8

YAY MATH!
What is the total magnification if we measured our reference acuity at 40cm, and now we use a +10D lens at its focal length to view the same object at 20cm?

Answer 8

M = rF

r = 0.4m
F = 10

M = 4x

Question 9

Magnification from multiple sources

Answer 9

Multiplicative

M(total) = M1 * M2 * M3, etc.

Question 10

Labeled magnification (aka rated mag)

• determined using an arbitrary reference distance chosen by manufacturer, usually __
• labeled magnification =

Answer 10

25cm

Labeled = F * 0.25 => F/4

Question 11

YAY MATH!

What is the expected expected power of a magnifier labelled 4x?

Answer 11

+16D

Labelled = F/4 -> F = 4 * 4 = 16

Question 12

Additional concerns

-magnification is not/does not (3)

Answer 12

Is not clarification

Does not improve contrast

Does not eliminate scotomas

Question 13

Magnification required

-equation

Answer 13

Required = reference size/ goal size

Aka (what you got)/(what you need)