Introduction to Microscopes
"Two Stones on the Water“
Best Optical Micrograph
From ancient times, man has wanted to see things far
smaller than could be perceived with the naked eye.
This led to the construction, in the 16th century, of a
magnifier composed of a single convex lens, and
this, in turn, led to the eventual development of the
microscope.
Perhaps the most earliest pioneers in the history of
the microscope are Thomas Digges of England and
Hans and Zacharias Janssens of Holland.
Zacharias Janssens and his father Hans,
a pair of Dutch spectacle makers built
the first compound light microscope by
mounting a lens at each end of a tube.
Their microscopes had a magnification
around 3X to 9X
But it was Anton van Leeuwenhoek who became the first man to make and use
a real microscope. Leeuwenhoek ground and polished a small glass ball into a
lens with a magnification of 270X, and used this lens to make the world's first
practical microscope.
Because it had only one lens, Leeuwenhoek's microscope is now
referred to as a single-lens microscope. Its convex glass lens was
attached to a metal holder and was focused using screws.
Today, the term "microscope" is generally used to
refer to this type of compound microscope.
In the compound microscope, the lens closer to the
object to be viewed is refers to as the "objective",
while the lens closer to the eye is called the
"eyepiece“ or “ocular lens”.
Since its invention, the compound microscope has made tremendous
contributions to the progress of science. Using a compound microscope
that he had built himself, the 17th-century Englishman Robert Hooke
discovered the fact that living things are composed of regularly shaped
structures he called cells.
Robert Hooke (1635 – 1703) was the
first to publish detailed drawings of
objects observed through his compound
light microscope
Hooke’s detailed drawings made his
book very popular.
Hooke’s microscope.
Hooke’s drawing of thin
sections of cork, from an oak
tree. Hooke observed these
regularly-shaped structures in
many different living things.
He used the word “cell” to
describe them, since they
resembled the monastic cells
(rooms) used by monks in a
monastery.
Schleiden and Schwann were major contributors to the Cell Theory
Matthias Schleiden
1804 – 1881
Botanist
Theodore Schwann
1810 – 1882
Zoologist
Schleiden and Schwann
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1830’s
Mathias Schleiden identified the first plant cells
He viewed a wide variety of plant specimens with a
microscope and concluded that all plants are made
up of cells.
Thomas Schwann made the same conclusion about
animal cells.
Magnification
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The ability to increase the appearance of an object
The total magnification is the product of the
magnification of the ocular lens (10X) and the objective
lens being used (4 – 100x)
d’Youville’s compound microscopes have three
objective lenses, producing the following magnifications:
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40X (low power or scanning lens)
100X (medium power)
400X (high power)
Magnification
Resolution
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The ability to distinguish between two closely
spaced objects
Can be described as the sharpness or clarity of
the image
For light microscopes, as magnification
increases, the resolution decreases
Resolution
As magnification
increases…
…resolution
decreases.
Magnification vs. Resolution
Depth of Field
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The area of a specimen that is in focus at
one time
At higher magnifications, the depth of field
be comes shallower
Less of a specimen will be in focus at one
time
Depth of field
Limitations for light microscopes
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The smallest objects that can be viewed with a
light microscope are about 200 nm, which is
determined by the wavelength of visible light
Light waves pass over very small objects without
being affected by them, like a wave of water
passing over sand (small objects) compared to
rocks (larger objects)
In order to view very small objects with good
resolution, a different type of wave must be
used – electron beams!
Further scientific advancements
lead to the development of the
first electron microscope in the
1930s. This enabled scientists
to view the world from a
completely different perspective.
The first practical electron
microscope was built by Eli
Franklin Burton and his students
at the University of Toronto in
1938.
Types of Electron Microscopes
• Transmission Electron Microscope
• Scanning Electron Microscope
• Scanning Tunneling Microscope
Transmission Electron Microscope
Electron microscopes
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Specimens for transmission electron microscopes
are encased in wax, then sliced in ultra-thin
samples and placed on a metal grid
Specimens are therefore not alive
Beam of electrons are sent through the specimen
and a sensor below captures an image which is
displayed on a monitor
Transmission Electron Micrographs
Chloroplast located in spinach leaf
Mitochondrion in an animal cell
Scanning Electron Micrographs
Human Head Louse
Fruit Fly Head
Most Bizarre Micrograph
Magnification: 100,000X
Title: The Debutantes' Ball
"At the debutante's ball, young nano-women gather in their finery at the
edge of the stage to weep because the nano-boys won't dance with
them.“ This is an image of a section of an anti-reflective coating (the
nano-women) on a silicon base (the stage).
Spiders Make the Best Ever Post it Notes!
A scanning electron microscope (SEM) micrograph of the foot of the jumping
spider E. arcuata. The very fine fringes at the base of it’s feet cause it to be
very “sticky” against flat surfaces.