Optics instrumens Eye Eye Lup Lup Microscoope Microscoope Teropong Teropong.
GEK1532 Optics of the Eye
-
Upload
givena2ndchance -
Category
Documents
-
view
225 -
download
0
Transcript of GEK1532 Optics of the Eye
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 1/42
GEK1532
Introduction to optics to
understand the eye
Thorsten Wohland
Dep. Of ChemistryS8-03-06
Tel.: 6516 1248
E-mail: [email protected]
http://micro.magnet.fsu.edu/primer/anatomy/
components.html
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 2/42
Total internal reflection
E
F
n1 n2
n1 < n2
E
F
n1 n2
n1 > n2
Total internal reflection (TIR) can happen only when light propagates in a
denseer medium and comes to a interface with a less dense medium:
Example: TIR happens from glass to air or water to air, but not from air to
water or air to glass.
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 3/42
Interference describes the superposition of two or more em waves resulting
in an amplification (constructive interference) or an attenuation
(destructive interference) of the amplitudes of the em field and thus in
intensities.
Interference
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 4/42
Revision: pigmentsPigment
Class
Compound
Type
Colors
Porphyrin chlorophyll green
Carotenoid carotene
and
lycopenexanthophyll
yellow,
orange,
redyellow
Flavonoid flavone
flavonol
anthocyanin
yellow
yellow
red, blue,
purple,
magenta
http://webexhibits.org/causesofcolor/1B.html
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 5/42
Scattering and Pigmentation
Rayleigh scattering,
stronger for blue light
(note: sometimesRayleigh scattering is
refered to as Tyndall
scattering)Retina
Iris
Absorption of red
and green light
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 6/42
Yellow pigment (blueis absorbed)
Scattering Layer
(RayleighScattering)
Scattering and Pigmentation
Pictures from Andrew Parker¶s³Seven Deadly Colors´ (Free Press)
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 7/42
Whiteness or Silveriness
Snow, foam, chalk, paper all are examples of
materials that scatter and reflect light in some
way at many surfaces. The resulting color inall cases is white.
This white though can vanish when the air
spaces are filled with some liquid (see oily
paper, or wet chalk).
random structures -> matt appearance
Regular structures -> shiny appearance
(sometimes silverish)
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 8/42
Interference colors
As in bubbles interference can as well work in feathers and wings.
Insect wings shimmer in many colors due to interference. A special
example here is the peacock:
http://webexhibits.org/causesofcolor/15C.html
One can see very fine branches on the
feathers. These are responsible for the multiple
reflections and the interference effects of thepeacock¶s feathers.
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 9/42
Is it really interference?
Seen under different
angles the color of thepeacock feather changes:
a characteristic of
interference colors
Albino peacocks do not possessany melanin thus most white light
is reflected instead of absorbed.
The white light is much stronger
than the interference color and
the peacock seems to be white.
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 10/42
Violet as an interference color
Ridges are 100 nm in size
White bar is 1/10 of a millimeter
Structure in the wings responsible for the color
Pictures from Andrew Parker¶s ³SevenDeadly Colors´ (Free Press)
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 11/42
Examples of bioluminescence
UV light can be absorbed will then be given off at a longer wavelength.
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 12/42
Snake, Benham¶s disk
http://www.michaelbach.de/ot/col_benham/index.html
Picture from Andrew Parker¶s ³SevenDeadly Colors´ (Free Press)
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 13/42
The eye
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 14/42
Mirrors, Virtual Images
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 15/42
Mirrors, Virtual Images
For the eye it looks like the light
rays come from behind themirror.
We call this a virtual image
since the light does not reallyoriginate from the image.
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 16/42
Spherical Mirrors
Seeing the light, Fig 3.6
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 17/42
Optics: Lenses
f f
xxOA
positive lenses:
Bi-convex
f f
xxOA
negative lenses:
Bi-concave
Plano-Convex lens
Plano-Concave lens
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 18/42
The function of lenses is based on
refraction
E
F
n1 n2
n1 < n2
E
F
n1 n2
n1 > n2
Snell¶s law: The difference between E and Fis the bigger, the bigger the
difference is between n1 and n2.
(n1sinE = n2sin F
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 19/42
Lenses: Refraction
E1
F1 E2 F2
na ng
na < ng (ref arctive indeces of air=1 and glass =1.5)
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 20/42
Lenses: Refraction for a Plano
Convex lens
ng
na < ng (ref arctive indeces of air=1 and glass =1.5)
E1
F1
na
E2
F2
The same processes
happen as well at the Bi-
concave and Plano-
concave lenses
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 21/42
Parallel incident rays will pass the
focal point after passing a lens «
f
xx
f
f
x
f
f
xx
f
Incident rays passing
the focus will be
parallel after passing
the lens.
« and we say the lens
has a focal length of
³f´.
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 22/42
Rays passing the center of the lens
pass undisturbed
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 23/42
One ray will follow both rules: the
optical axis
OA
f
x
f
x
OA
f
x
f
x
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 24/42
Image Formation
f f
xx
OA
Object
Image
f f
xx
OA
Object
Image
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 25/42
Image Formation
f f xx
OA
Object
Image
Real images (all light rays are converging on the image) are upside down
compared to the object.
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 26/42
Can we calculate the image
position?
f f xx
si
so
io s s f
111
!Yes, with the so called
lens equation:
distanceimage
1
distanceobject
1
distanceocal
1!
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 27/42
Can we calculate the size of the
image?
f f xx
si
so
o
i
s
s
M !
distanceobject
distanceimageionmagni icat !
Magnif ication:
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 28/42
Negative or concave lenses
f f
xxOA
Parallel incidents rays
diverge and look like as if
they would come from the
back focal point. The lens
has a focal length of ³-f´
f
f
xxOA
Rays thorough the
center of the lens pas
undisturbed.
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 29/42
Image formation for a negative lens
f f xx
OA
Object
Image
Virtual images (the light rays are not converging on the image) are upright.
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 30/42
Image formation for a negative lens
f
f xx
OA
ObjectImage
io s s f
111!
o
i
s
s!
si
so
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 31/42
Example
oio s s s f
2111!!
ios s f
111!
oi s s !
When do we get an image that is equal in size to the object?
1!!
o
i
s
s
f s s io 2!!
Magnification is 1!
si
so
xf x
f xx
2f
2f
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 32/42
The picture on the retina
The eye has a positive lens that creates a real picture on the retina.
One of the facts that was unimaginable for many people is that the
picture on the retina is as well upside down as we have seen for positive
lenses.
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 33/42
Camera pictures
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
si
so
A camera uses a lens (or a combination of lenses) to produce an image
on a film.
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 34/42
Some special topics: Fresnel Lens
E1
F1 E2 F2
na ng
Light is refracted at surfaces between two
materials. So only the surface of the lens is
the active part.
So can we reduce the weight of a lens and
thus the material needed?
Seeing the light, Fig 3.29
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 35/42
Lens combinations
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 36/42
A single-lens reflex camera
http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 37/42
Summary
� Negative, positive lenses and description by lensequation
� Reversibility of light paths
� Lens combination (different back and front focallength)
� Image formation (real, virtual)
� Change in refractive index or lens curvature can
change focal length� Cameras (camera obscura, reflex camera)
� The eye, defects and corrections
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 38/42
Remember this experiment
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 39/42
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 40/42
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 41/42
Large slit: additive color mixing
between spectra from both sides
8/6/2019 GEK1532 Optics of the Eye
http://slidepdf.com/reader/full/gek1532-optics-of-the-eye 42/42
Additive primary colors mix to yield
subtractive primary colors