2. OBJECTIVES:
1. Discuss principles of pinhole imaging,
mirror and lenses.
2. Define object and image characteristics
3. Discuss principles of light propagation

3. GEOMETRICAL OPTICS
 Deals primarily with imaging
PHYSICAL OPTICS
Wave nature of light
QUANTUM OPTICS
Particle nature of light and interaction of
light and matter

4. DEFINITION OF TERMS
 CONJUGATE- correspondence between
object and image points
 RAY- the route that light follows as it
travels from an object point to the image
point
 PENCIL of light- small bundle of rays that
travel in the same direction

6. PINHOLE IMAGING

9. OBJECT CHARACTERISTICS
 REAL objects
◦ Can be felt, touched, located in front of the
optical system
 VIRTUAL objects
◦ Cannot be felt or touched, located behind an
imaging system
 LUMINOUS
◦ Objects that produces its own light (eg.
candle)

10. IMAGE CHARACTERISTICS
MAGNIFICATION
 Most important
 enlargement
 Making images smaller or larger than the
object
◦ Transverse = image height/ object height
◦ Axial
◦ angular

11. 4 cm
Object
Height
Image
2 cm height
Transverse magnification = 2/4 = -0.5

12.  AXIAL MAGNIFICATION
◦ Aka longitudinal magnification
◦ Axial magnification = ( transverse magnification) 2
 ANGULAR MAGNIFICATION
◦ The ratio of the angle subtended by an object
without the lens or magnifier

13. IMAGE LOCATION
 The distance between a reference point
and the image
 Reference point- back surface of the lens
 Positive- image is right to the reference
point

14. DEPTH OF FOCUS
Image appears
sharp within
this region

16. DEPTH OF FIELD

17. Object w/n this
region appear
sharp in the
DEPTH OF FIELD
image

18. IMAGE QUALITY
 Images are imperfect facsimiles.
 Each object point produces a 2- mm
diameter spot in the image= BLUR circles
 STIGMATIC IMAGE- a perfect point
image of an object point
 The smaller the blur circle- less image
details lost

19. BRIGHTNESS and IRRADIANCE
 BRIGHTNESS-
 A visual perception
 The response of the nervous system to
light entering the eye
 IRRADIANCE
 A purely physical measure of the amount
of light per unit of an image
 Important in calibration of perimeter

20. Wavelength
570 nm

21. LIGHT PROPAGATION

22. OPTICAL MEDIA AND
REFRACTIVE INDEX
 Medium- any material that transmits light
 Light travels at different speeds in
different media
 REFRACTIVE INDEX-
 N= speed of light in vacuum
speed of light in medium
◦ is always greater or equal to 1

23. REFRACTIVE INDEX FOR SOME
MATERIALS OF CLINICAL INTEREST
MATERIALS REFRACTIVE INDEX
AIR 1.0000
WATER 1.3333
CORNEA 1.376
AQUEOUS/VITREOUS 1.336
SPECTACLE CROWN 1.523
GLASS
PMMA 1.492

24.  Dispersion- short
wavelengths travel
slowly than long
wavelengths
 Leads to chromatic
abberation
 Eye- 0.5 D of
chromatic abberation

25. RED BLUE
BLUE RED
RED BLUE

26. LAW OF RECTILINEAR
PROPAGATION
 Light in a single medium travels along
straight- line paths called rays
 Pencil of light- a bundle of rays traveling
close to each other in the same direction

28. OPTICAL INTERFACE
 The boundary separating 2 different
optical media
 Smooth- light undergo specular reflection
and transmssion
 Rough- diffuse reflection and transmission

29. Smooth optical interface

32. SPECULAR REFLECTION:
LAW OF REFLECTION
 The direction of the reflected ray bears a
definite relationship to the direction of
the incident ray
 Reflected ray lies in the same plane as
the incident ray and the surface normal
and that θ i = θr

33. Smooth optical interface
θi
θr

35.  Reflection coefficient
 Used to calculate the amount of light
transmitted at an optical surface
R= n2-n1 2
n2+n1

36. How much more reflective is an acrylic IOL than a silicone
IOL? Assume that the index of refraction of acrylic is 1.55 and
the silicone is 1.43. ( aqueous= 1.33)
R acrylic = 1.55-1.33 2
1.55+1.33
0.0584 =0.584%
R silicone= 1.43 - 1.33 2
1.43 + 1.33
0.00131= 0.131%
 0.584/0.131= 4.46

37. SPECULAR TRANSMISSION: Law
of Refraction
 The transmitted ray’s direction bears a
definite relation to the incident’s ray
direction
 Snell’s law= the refracted or transmitted
ray lies in the same plane as the incident
ray and the surface normal
 Light- lower- higher refractive index–
bends toward the surface normal

38. N1<n2 optical interface
N1>n2
Incident ray
θi
θi
θ
Surface normal θt

39. TOTAL INTERNAL REFLECTION
 Occurs when light travels from a high-
index medium to a low –index medium
and the angle of incidence exceeds a
certain critical angle
 Critical angle- angle of incidence that
produces a transmitted ray 90° to the
surface normal

42. DISPERSION
Refractive indices are not fixed values
 Refractive indices- wavelengths

43. Fermat’s principle
 Light travels from one point to another along
the path requiring the least time
 Optical path length- distance light travels in a
given medium multiplied by the medium’s
refractive index
 e.g
 Light travels 5 cm in air (n= 1.000) and 10 cm in
glass ( n= 1.523)
 OPL= 5 cm x 1.000+ 10 cmx 1.523=
 20.2 cm

44. B
A air
glass

45. Path 1
O I
Path 2

47. “I have been a multitude of shapes, Before I assumed a consistent form”-
Taliesin