Who Invented the first microscope?
Who Invented the first microscope?
? Credit for the first microscope is usually given to Zacharias Jansen, in Middleburg, Holland, around the year 1595.
Minor White
1
Magnification ~ 9x (barely qualifies as a microscope) 2
Robert Hooke
~1670
Anton von Leeuwenhoek
Discovered the cell (looking at cork)
3
Dutch tradesman 1632-1723 -no higher education
Discovered: bacteria, sperm cells, blood cells...
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1
Anton von Leeuwenhoek
? Single tiny lens
"these little animals were, to my eye, more than ten thousand times smaller than the animalcule which Swammerdam has portrayed, and called by the name of Waterflea, or Water-louse, which you can see alive and moving in water with the bare eyes."
- letter to Royal Society 1678
Magnification ~ 270X
5
Anton von Leeuwenhoek
an unbelievably great company of living animalcules, a-swimming more nimbly than any I had ever seen up to this time. The biggest sort. . . bent their body into curves in going forwards. . . Moreover, the other animalcules were in such enormous numbers, that all the water. . . seemed to be alive.
Discovery of bacteria In the mouth of old man who had never brushed his teeth!
Magnification ~ 270X
6
Compound Microscope
? Structure: Made of two lenses, Objective and eyepiece ? Objective: The object being viewed is placed just outside the focal length of the objective lens. The intermediate image thus formed is real, inverted, and enlarged.
7
An example
? Suppose the focal length of the objective is 12mm, and the object is placed at 13mm. The image is then 156mm away from the lens and the magnification is 156/13 = 12 X
1/si = 1/f - 1/so
8
2
? Eyepiece: Work as a magnifying glass, used to view the real intermediate image formed by the objective lens.
? To view the image with a relaxed eye (so the light rays entering the eye is parallel), the image must be located at the focal point of the eyepiece.
? Shorter the focal length, larger the magnification.
9
10
Microscope eyepiece
Same principle as magnifying glass
No lens
With lens
~ 250 mm
f
Magnification = 250/f (in mm)
11
Compound microscope
Total magnification = Mobj X Meyepiece = si/fobj X 250/feyepiece Si = 160 mm for standard microscopes
Example - fobj = 1.6mm, feyepiece =25 mm M = 100 X 10 = 1000
12
3
13
14
Oil immersion objective
- high magnification -> short focal length - big angles
Oil with n = 1.5
15
Confocal microscopy
16
4
Optical limitation
? Light cannot be focused to less than ~
-due to diffraction (coming up later in course)
Solutions - use short wavelength (e.g. x-rays) - use something other than light
17
18
neuron
Fruit fly
Cat flea
Black ant
19
Scanning Tunneling Microscope
Electrical current depends sensitively on distance
20
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