Announcements 3/16/11
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Prayer
Exam 2 being graded, hopefully scores available
tomorrow.
Term project progress report due Saturday night
Still missing slinkies from a few of you.
I’ll be out of town Mon & Wed of next week. Will
have Dr. Peatross and Dr. Durfee substitute
Running out of liquid helium tomorrow… my
regular office hours will resume Friday. (Well,
except for next Mon & Wed, because I’ll be out of
town.)
Quick writing
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Draw the ray diagram for this situation:
Converging lens, f = 20 cm, p = 80 cm
Quick writing
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Draw the ray diagram for this other situation:
Converging lens, f = 20 cm, p = 15 cm
Quick writing
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Draw the ray diagram for this third situation:
Diverging lens, f = -20 cm, p = 5 cm
Reading Quiz
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What’s the term used to refer to rays failing to
focus because a lens is shaped incorrectly?
a. elliptical aberration
b. hyperbolic aberration
c. parabolic aberration
d. spherical aberration
Spherical Aberration
Credit: the next several slides were produced by Dr. Durfee
Reducing Spherical Aberration with
Aperture
Spherical Aberration
Reducing Spherical Aberration by
Reversing Lens
Coma
0 Degree Tilt
10 Degree Tilt
20 Degree Tilt
30 Degree Tilt
40 Degree Tilt
40 Degree Tilt + Aperture
Thought question
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Chromatic Aberration
Red light coming from O produces an image at I.
Where will blue light coming from O form an
image?
Lens-makers’ eqn:
a. same place
 1
1
1 
b. closer to the lens
  n  1  

f
 R1 R2 
c. farther from lens
How does a camera work?
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Simplest picture
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What if you leave out the lens?
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What’s a pinhole camera?
Reading Quiz
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What is the f-number of a lens?
a. The focal length in meters
b. The focal length in inches
c. One over the focal length in meters
d. The focal length divided by the diameter of
the lens
e. The focal length divided by 25 cm
Thought question
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How does the f-number of a
lens relate to the half-angle
of the “light cone” formed by
parallel light entering the
lens?
a. q  2cos1 
1


f-number


b. q  sin 1  f-number 
1



 f-number 
c. q  sin 1 
d. q  tan 1  f-number 
1 
1

e. q  tan 

2

f-number


q
Cameras: f-stops
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Which has the higher f-number?
What’s the advantage of one over the other?
Thought question
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If you have trouble seeing things far away
but can see close objects well, you are “nearsighted”. What kind of lenses do you need in
your glasses?
a. Converging lenses
b. Diverging lenses
Near point vs. Far point
Near point: how close can you see things
comfortably
a. Regular person: np  25 cm
b. Farsighted person: np = much larger
 Far point: how far away can you focus on
things
a. Regular person: fp = infinity
b. Nearsighted person: fp = much smaller
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– For me, my fp  1 m (right eye), 0.5 m (left
eye)