Understanding about anti rfelection coating.

1. Refractions, Reflections and Caustics :
Basic Concepts
Lecture #15
Thanks to Henrik Jensen, John Hart, Ron Fedkiw, Pat Hanrahan, Rahul Swaminathan, Ko Nishino

2. Reflection and Refraction
Water
Air
Vertex Normal N
α
α
β
Reflection
Refraction

3. Snell’s Law
• α Incoming = α Reflected
• sin(α)/sin(β) = Refractive Index (material dependent)
• Refractive index inversely proportional to speed of light
(Huygens Principle)
Material Refractive Index
Air 1.0003
Water 1.333
Glycerin 1.473
Immersion Oil 1.515
Glass (Crown) 1.520
Glass (Flint) 1.656
Zircon 1.920
Diamond 2.417
Lead Sulfide 3.910

8. Reflection

13. Really starts to be noticeable at less than 10-15° from the surface.

15. Fresnel Term
• Fresnel Term as found in text books is
F = ½ (sin²(α-β)/sin²(α+β)) + tan²(α-β)*tan²(α+β)
• Returns good results for strong reflecting water surfaces

16. Approximated Fresnel Term
• F0 = (N-1)2/(N+1)2 is a minimum of incoming light
parallel to the normal of the surface.
• Fα = F0+(1- cos(α))5 * (1- F0) is a value between 0 and 1
depending on the angle between the incoming ray and
the surface normal.
• e.g. F90 = 1, if the incoming ray is parallel to the surface,
all light is reflected.

17. Designed to reflect all light eventually to Observer.

18. Anti-reflective Coatings
“One of the most significant advances made in modern lens design,
whether for microscopes, cameras, or other optical devices,
is the improvement in antireflection coating technology.”
• Reduce unwanted, stray reflections
• Use material coatings on glass to reduce
reflection and maximize transmission.
• Take advantage of destructive light interference.

19. Anti-reflective Coatings
Magnesium fluoride very commonly used on Lenses, Microscopes

20. Refractions or Reflections?

21. Refractions or Reflections Confusion
Why do you see shiny roads when
they are diffuse and are not wet?
Why do you see apparent reflections in deserts?
Where else do you see apparent reflections?
Do you see reflections above objects???

25. Used in Endoscopy, Communications

26. Water Drops : Refractions + Reflections

27. A Drop and its Environment.
World in a drop

28. Shapes of falling drop
Shapes of falling drop

29. Refraction and Reflection
(r)
(s)
^
n
^
^
Le
Le
i
i
s
^
r
^
i
v
^
n
^
qn
z
a
A
B
a
Pin hole
r
Image
plane
q
q
q
i
p
^
q
z
^

30. Refraction

31. Geometric mapping
fov=165 degrees

32. Experiments: Refraction
Experimental setup Calculated corners are in green

33. Photometry of Refraction

34. Plot of Transmitted Radiance

35. Experiment: Photometry of
Refraction
Experimental Setup
Rendered actual image difference image

36. Reflection

37. Photometry of Reflection

38. Reflection vs. Refraction
0 0.2 0.4 0.6 0.8 1
0 0.2 0.4 0.6 0.8 1
0
0.2
0.4
0.6
0.8
1
refraction
reflection
internal reflection
distance from the center
radiance L
radi
ance
L

39. Rendering a Rain drop
(a) Environmental Illumination
(b) Rendering a Drop



40. World in a Rain Drop
Low Library Pupin Hall

41. Tired of water drops?
Wait, there’s more…

42. Rainbows : Refractions + Reflections
+ Wavelength of Light

44. Visible Light Wavelength Dispersion

45. Can you see rainbows during midday?

46. Why are there two rainbows?
Are there only two rainbows?

47. Why the color pattern?

48. Bright Sky under and Dark above the Rainbow
Photo by Ben Lanterman taken immediately after
a heavy rainstorm when the air was quite saturated at 4PM.

50. Caustics: Bunching up
Reflections or Refractions

51. • What is wrong with this rendering?

52. • With caustics

54. Looking at Water
• Light is reflected and refracted at the same time
• There is a light pattern on the ground (Caustics)

55. • Shafts of light and caustics:
– http://nis-lab.is.s.u-tokyo.ac.jp/~nis/cdrom/pg/pg2001_iwa.pdf

56. Caustics by Refraction
• Light is refracted by the water surface
• Some spots are stronger illuminated then others

57. Light rays through a water surface
Bright areas caused by bunching
of refracted rays
dark

58. Water-filled glass spheres to focus or condense candlelight onto small areas
( 1800s )

60. Graphics Definition
 Create nice pictures with translucent objects and
render nice effects on diffuse surfaces.

61. Caustics in Cornell Box

62. Modeling and Animating Water Surfaces

63. Caustics by Reflections

64. Reflections and Caustics :
Catadioptric Imaging
+
Refractions/Reflections and Caustics:
Photon Mapping
Lecture #16
Thanks to Henrik Jensen, John Hart, Ron Fedkiw, Pat Hanrahan, Rahul Swaminathan, Ko Nishino