 Colored photons (pigment versus light)
 Rainbows
 Astigmatism
 Visual Acuity
 CRT
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© 2010 Pearson Education, Inc.
Pigments
 Absorb certain wavelengths and reflect/scatter
others
 Pigments do not produce any new light.
© 2010 Pearson Education, Inc.
© 2010 Pearson Education, Inc.
Pigments
 Absorb certain wavelengths and reflect/scatter
others
 Pigments do not produce any new light.
 Florescent and phosphorescent materials emit light
 Absorb certain wavelengths and emit another.
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Florescence
 Absorb certain wavelengths and reflect/scatter
others
 Flourescent and phosphorescent materials emit
light
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Phosphorescence
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Photons come in a range of colors. Which
color(s) is not found as an individual
photon?
A. Red
B. Purple
C. White
D. Black
E. Violet
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Photons come in a range of colors. Which
color(s) is not found as an individual
photon?
A. Red
B. Purple
C. White
D. Black
E. Violet
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How can someone to become invisible?
A. They need to reflect all light off of them.
B. They need to absorb all light
C. They need to have the same index of refraction as
air
D. They need to refract all light.
E. Something else
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How can someone to become invisible?
A. They need to reflect all light off of them.
B. They need to absorb all light
C. They need to have the same index of refraction as
air
D. They need to refract all light.
E. Something else
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If you have the same index of refraction
as air, can you see?
A. Yes, perfectly fine
B. Yes but blurry
C. No not at all
D. I think this is a stupid question
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If you have the same index of refraction
as air, can you see?
A. Yes, perfectly fine
B. Yes but blurry
C. No not at all
D. I think this is a stupid question
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Speed of light in a material depends on
the color of the light
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Dispersion
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© 2010 Pearson Education, Inc.
Rainbows
When you see a rainbow, is red on top or the bottom?
A. Top
B. Bottom
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Rainbows
© 2010 Pearson Education, Inc.
Why can you never find the end of a
rainbow?
A. It doesn’t reach the ground
B. The rainbow doesn’t last long enough to get there
C. It’s magic
D. The angle changes as you move closer to the
rainbow
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Why can you never find the end of a
rainbow?
A. It doesn’t reach the ground
B. The rainbow doesn’t last long enough to get there
C. It’s magic
D. The angle changes as you move closer to the
rainbow
© 2010 Pearson Education, Inc.
© 2010 Pearson Education, Inc.
Astigmatism
Farsighted
Nearsighted
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Apparent Size
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© 2010 Pearson Education, Inc.
Lens Aberrations: Spherical Aberration
The Hubble space
telescope originally
suffered from
spherical aberration.
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Lens Aberrations: Spherical Aberration
The Eye – no problem!
 The Crystalline lens has
different indices of
refraction
 1.41 at the center and
1.39 at the soft outer
layers
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Chromatic Aberration
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Chromatic Aberration
The eye – it’s a problem
On the Fovea (most sensitive part of the retina) the eye
does not sense blue light (which helps)
2 mm pupil has an acuity of 5 mm
4 mm pupil has an acuity of 10 mm
pupil smaller or eye longer would help
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Eyes need to move quickly
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Foveal Cone size
To identify 2 separate objects, alternating cones have to be
stimulated
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Diffraction
2 point sources of light
through a circular aperture
Rayleigh’s Criterion
Two objects are resolvable if their
angular separation is greater than
1.22
 1=
D
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Clearly resolved images
for a person?
Barely resolved:
1.22
 1=
D
 = o/n
Vitreous humor index of refraction = 1.34
Center of the visible spectrum in air is 550 nm
= 550 nm/1.34 = 410 nm
min = 1.22 (410 nm)/3 mm
= 0.0001667 radians
Clearly resolved = 2 x min = 0.00033 rads
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Clearly resolved images
for a person?
Angle for clearly resolved images = 0.00033 rad
So what?

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h = 16mm  = 5 x 10-6 m = 5.3 mm
Visual Acuity
Limited by:
 chromatic aberration ( 5-10 mm)
 Foveal cone size (6 mm)
 Diffraction (4 – 8 mm)
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The Resolution of a Microscope
Limited by diffraction which means by the
wavelength of light
Optical and Electron Micrographs of e. coli
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1.22
 1=
D
CRT – Corneal Refractive Therapy
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