Download Geometrical Optics

Geometrical Optics
Chapter 24 + Other Tidbits
1
On and on and on …
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This is a short week.
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Schedule follows
So far, no room available for problem
session. Still working on it.
Today we try to complete lenses.
Quiz on Friday?
November 2009
SUNDAY
22
MONDAY
TUESDAY
23
WEDNESDAY
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COMPLETE
THIN
LENS
THURSDAY
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Interference
& Diffraction
FRIDAY
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SATURDAY
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THANKSGIVING THANKSGIVING
HOLIDAY
PROBLEMS
SOLVING
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Interference
Diffraction
December 2009
SUNDAY
MONDAY
TUESDAY
1
REVIEW
SESSION
If Room is
Available
NO ROOM
AVAILAVLE
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7
OVERVIEW OF
COURSE
LAST DAY OF
CLASS
3
8
WEDNESDAY
THURSDAY
FRIDAY
SATURDAY
2
3
EXAMINATION
#4
4
5
INTERFERENCE
&
DIFFRACTION
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11
10
12
FINAL
EXAM
Most important case: converging lens
Object to left of F1
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Most important case: converging lens
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Most important case: converging lens
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Most important case: converging lens
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Most important case: converging lens
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Aberrations are imperfections in the optical image formed by a
spherical lens (or optical mirror). There are five main aberrations:
1. Chromatic aberration. The refractive index of glass varies with wavelength.
This results in different focal lengths and image magnifications for different
colours.
2. Spherical aberration. Lenses with spherical surfaces have a shorter focal
length at their periphery than at their centre.
3. Coma. The various circular zones of a lens produce an image of an off-axis
point that is distorted radially into a comet shape known as a coma patch.
4. Curvature of field. The focal surface is not a plane but a bowl shape.
5. Astigmatism. Because a lens appears asymmetric to an off-axis beam, the
image of a point is not a point but a short line radial from, or tangential to, the
optic axis of the lens. These images are formed in different planes.
6. Distortion. The image magnification is greater towards the edges of the field
(pincushion distortion) or less (barrel distortion) than at its centre.
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Remember the Spectrum?
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Dispersion

Index of refraction
depends on the
wavelength, or color.
1
1  1
(n  1)   
 R1 R2  f

f depends on the index
of refraction.
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Chromatic Aberration
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Example
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Correction : achromatic lens couple
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Spherical Aberration
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Results from the assumption of paraxial conditions.
Real lenses need a wider opening, larger apertures.
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Spherical Aberration - Correcting
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Barrel Distortion
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Coma
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Some useful stuff
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Diaphram
Intensity~Area
Change D by 2 will double area
Fixed f stops will therefore
go by factors of 2
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Camera
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The intensity of the light striking the film or CCD array is
proportional to the area of the lens.
This is adjusted by the photographer by means of the
aperture or diaphragm control.
f-number is defined by
focallength
f
f  num ber

aperturediameter d

Ex: A lens of focal length f=50mm and an aperture
diameter of 25mm has an f number of 2, often written
as “f/2”
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f stops
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Multiplier
sqrt(2)
Designation
sqrt(2)^2
2.0
f/2
sqrt(2)^3
2.8
f/2.8
sqrt(2)^4
4.0
f/4
sqrt(2)^5
5.6
f/5.6
sqrt(2)^6
8.0
f/8
sqrt(2)^7
11.1
f/11
sqrt(2)^8
16.0
f/16
More on Camera
24
The Microscope
25