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History of the microscope

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History of the microscope
Ancient History
From ancient times, man has wanted to see things far smaller than could be
perceived with the naked eye. Although the first use of a lens is a bit of a
mystery, it's now believed that use of lenses is more modern than previously
thought.
However, it has been known for over 2000 years that glass bends light. In the
2nd Century BC, Claudius Ptolemy described a stick appearing to bend in a pool
of water, and accurately recorded the angles to within half a degree. He then
very accurately calculated the refraction constant of water.
During the 1st century AD (year 100), glass had been
invented and the Romans were looking through the glass
and testing it. They experimented with different shapes of
clear glass and one of their samples was thick in the middle
and thin on the edges.
They discovered that if you held one of these "lenses" over
an object, the object would look larger. These early lenses
were called magnifiers or burning glasses. The word lens is
actually derived from the Latin word lentil, as they were
named because they resembled the shape of a lentil bean.
At the same time, Seneca described actual magnification by a globe of water.
"Letters, however small and indistinct, are seen enlarged and more clearly
through a globe of glass filled with water." The lenses were not used much until
the end of the 13th century when spectacle makers were producing lenses to be
worn as glasses. Then, around 1600, it was discovered that optical instruments
could be made by combining lenses.
The First Microscopes
The early simple "microscopes" which were only magnifying
glasses had one power, usually about 6x - 10x. One thing
that was very common and interesting to look at, were fleas
and other tiny insects, hence these early magnifiers called
"flea glasses".
Sometime, during the 1590's, two Dutch spectacle makers,
Zaccharias Janssen and his father Hans started
experimenting with these lenses. They put several lenses in a tube and made a
very important discovery. The object near the end of the tube appeared to be
greatly enlarged, much larger than any simple magnifying glass could achieve by
itself!
Their first microscopes were more of a novelty than a scientific tool since
maximum magnification was only around 9X and the images were somewhat
blurry. Although no Jansen microscopes survived, an instrument made for Dutch
royalty was described as being composed of "3 sliding tubes, measuring 18
inches long when fully extended, and two inches in diameter". The microscope
was said to have a magnification of 3x when fully closed, and 9x when fully
extended.
It was Antony Van Leeuwenhoek (1632-1723), a Dutch draper and scientist, and
one of the pioneers of microscopy who in the late 17th century became the first
man to make and use a real microscope.
He made his own simple microscopes, which had a single lens and were handheld. Van Leeuwenhoek achieved greater success than his contemporaries by
developing ways to make superior lenses, grinding and polishing a small glass
ball into a lens with a magnification of 270x, the finest known at that time (other
microscopes of the time were lucky to achieve 50x magnification). He used this
lens to make the world's first practical microscope.
Leeuwenhoek's microscope used a single convex glass lens attached to a metal
holder and was focused using screws. Anthony Leeuwenhoek became more
involved in science and with his new improved microscope was able to see
things that no man had ever seen before. He saw bacteria, yeast, blood cells and
many tiny animals swimming about in a drop of water. People did not realize that
magnification might reveal structures that had never been seen before - the idea
that all life might be made up of tiny components unseen by the unaided eye was
simply not even considered.
Compound Microscopes
To increase the power of a single-lens microscope, the
focal length has to be reduced. However, a reduction in
focal length necessitates a reduction of the lens diameter,
and after a point, the lens becomes difficult to see
through.
To solve this problem, the compound microscope system was invented in the
17th century. This type of microscope incorporates more than one lens so that
the image magnified by one lens can be further magnified by another.
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 referred to as the "objective", while the lens closer to the eye is called
the "eyepiece".
The function of any microscope is to enhance resolution. The microscope is used
to create an enlarged view of an object such that we can observe details not
otherwise possible with the human eye. Because of the enlargement, resolution
is often confused with magnification, which refers to the size of an image. In
general, the greater the magnification, the greater the resolution, but this is not
always true. There are several practical limitations of lens design, which can
result in increased magnification without increased resolution. The reason for a
dichotomy between magnification and resolution is the ability of the human eye to
see two objects.
Englishman Robert Hooke is credited with the microscopic milestone of
discovering the basic unit of all life, the cell. In the mid 17th century, Hooke saw a
structural mesh while studying a sample of cork that reminded him of the small
monastic rooms called cells (Micrographia). Hooke is also credited with being the
first to use the basic three-lens configuration that is still used in microscopes
today.
Later Developments
All the early microscopists saw quite distorted images due to the low quality of
the glass and imperfect shape of their lenses. Little was done to improve the
microscope until the middle of the 19th century when great strides were made
and quality instruments like today's microscope emerged. Companies in
Germany like Zeiss and an American company founded by Charles Spencer
began producing fine optical instruments. We can also mention Ernst Abbe, who
carried out a theoretical study of optical principles, and Otto Schott, who
conducted research on optical glass.
In order for light microscopes to achieve better resolution, three basic problems
had to be overcome:

Chromatic aberration: the unequal bending of different colours of light that occur in a
lens. This problem was first solved by Chester Hall in the 1730's. He discovered that if
he used a second lens of different shape and light bending properties he could realign
the colours without losing all of the magnification of the first lens.
Top - a photograph taken with a good quality lens.
Bottom - a photograph taken with a wide angle lens showing
visible chromatic aberration (especially at the dark edges on
the right).
Spherical aberration: the unequal bending of light that hits different parts of a lens.
Joseph Jackson Lister solved this problem in 1830. He discovered that by putting lenses
at precise distances from each other, the aberration from all but the first lens could be
eliminated. Low power low curvature lenses could be made with minimal aberration and
by using a lens of this type for the first in a series, the problem could be virtually
eliminated.
A perfect lens (top) focuses all incoming rays to a point on
the optic axis. A real lens with spherical surfaces (bottom)
suffers from spherical aberration: it focuses rays more tightly
if they enter it far from the optic axis than if they enter closer
to the axis. It therefore does not produce a perfect focal
point.
The third problem is that
physically possible, it
as wide as possible. Ernst
this problem in the
laws that govern the
and maximised this
immersion lenses. The
was able to achieve is
resolution Leeuwenhoek
earlier. This resolution of
physical limit imposed by
for a microscope, to be as good as
must collect a cone of light that is
Abbe worked out the solution to
1870's. He determined the physical
collection of light by an objective
collection by using water and oil
maximum resolution that Abbe
about 10 times better than the
had achieved about 100 years
0.2 microns or 200 nanometers is a
the wavelength of light.
Modern Day Microscopes
In recent times, the development of the microscope has slowed, since optical principles
are well understood and to an extent, the optical limits have been reached. The majority
of microscopes follow the same structural principles that describe monocular, monobinocular and stereo-binocular microscopes.
While the technical limits of design have been reached, Vision Engineering has taken the
approach of developing the practical day-to-day user friendliness of the microscope.
Patented Technology
Vision Engineering's patented Dynascope™ technology removes the need for
conventional eyepieces by expanding the image exiting the eyepieces from 3mm,
obtained using traditional microscopes, to 100mm. This has the major advantage of
freedom of head and body movement for the operator. Practical implications include
more efficient and easier use of quality microscope instruments in every application.
At the heart of Vision Engineering's patented technology lies a rotating multi-lenticular
[multi-lens] disc, composed of millions of lenticules [lenses], which act as independent
image forming surfaces with diameters of a few microns each. The disks spin at high
speed to merge the millions of individual optical paths into an aberration-free, highclarity image. The result is a system which has unrivalled levels of operator comfort,
reducing fatigue and increasing quality and productivity.
History of the Microscope
There is no clear agreement on who first invented the microscope. Some say that Zacharias Janssen first
invented the microscope in the 1590s. Zacharias and his father, Hans, were actually Dutch eyeglass
makers. It's believed that, together, they began experimenting with ways to use different lenses. When they
put a lens at the end of a small tube, they discovered that objects near the end were magnified more than
the lens by itself could achieve, and thus began their development of a microscope with multiple lenses.
Others believe that the true inventor was German-Dutch Hans Lippershey, also an eyeglass maker. He
also created some of the earliest microscopes, and while he may have invented his own separately of
Janssen, some argue that Lippershey actually stole designs for the microscope from Janssen.
In the late 1600s and early 1700s, Dutch scientist Anton van Leeuwenhoek worked to create stronger
lenses that vastly improved the microscope, allowing people to see incredibly small things. He was one of
the first scientists able to observe bacteria, movement in water droplets, and blood in capillaries.
The microscope had many uses right away. One of the most significant uses is by British scientist Robert
Hooke. In 1665, he published his microscopic observations in his book Micrographia. It was the first book to
include illustrations of plants and animals seen through a microscope. With the magnifying powers of a
microscope, Hooke was also the first to use the term 'cell.'
History of the Microscope
During the 1590s, the two spectacle-makers, Hans and Zacharias Jansen began experimenting. They put
lenses in a tube and made a very important discovery. They discovered that objects near the end of the
tube appeared to be enlarged, much larger than any simple magnifying glass could achieve alone. In the
1660’s Robert Hooke began looking at all kinds of objects with his microscope. He put all of his drawings in
a book called Micrographia He is credited with naming cells but also studied items like fleas under his
microscope. Anton van Leeuwenhoek was very good at grinding and polishing lenses. These lenses led to
the building of his microscope which was considered the first practical microscope. In 1674 Anton Van
Leeuwenhoek was the first to see and describe bacteria. Another huge advance in microscopes didn’t
occur until German physicist Ernst Ruska and the electrical engineer Max Knoll constructed the prototype
electron microscope in 1931, capable of four-hundred-power magnification. Electron microscopes uses
accelerated electrons in order to view objects. Modern electron microscopes can magnify objects up to 10
million times
Early Light Microscopes Developed
During the 1590s, two Dutch spectacle producers further experimented with these early
lenses. Zaccharias Janssen and his father Hans Janssen realised that if you put a small
object in a tube containing several lenses, the object would appear very large when at
the end of the tube and was much more enlarged than when a simple magnifying glass
was used.
The pair only achieved a magnification of 9x and these early microscopes were more
novelties than scientific instruments.
In the late 17th Century, Anthony von Leeuwenhoek from Holland invented a single
lens, hand-held microscope that could achieve a magnification of 270x.
Using this lens, he went on to develop the first microscope that could actually be made
use of. Leeuwenhoek found he was able to see structures that noone had seen before
such as blood cells and bacteria.
In the same century, Englishman Robert Hooke was acknowledged as having
discovered the smallest most basic unit of an organism – the cell.
He was also recognised as the first person to use a microscope with three lenses, the
configuration used in today’s microscopes.
Microscopes go into Large Scale Production
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There were few further developments made to the microscope until the middle of the
19th century, when sophisticated microscopes such as the ones we use today were
developed. The German company Zeiss started to manufacture these refined devices.
During these early years, scientists worked to solve various problems with the
microscopes, such as the unequal bending of light that hits the lens in different places.
In 1830, Joseph Lister, realized that placing the lenses at specific distances from one
another resolved this problem for all but the first in the series of lenses.
For the first lens, use of a low power lens with low curvature minimized this unequal
light bending to the extent that the problem was almost eliminated.
Phase-Contrast Microscope Developed
Frits Xernicke developed the phase-contrast microscope in 1932. This device enabled
researchers to study transparent biological materials.
Electron Microscope Appears
The use of visible light in microscopy limits the resolution that could be achieved, but
this was problem was overcome in 1931 when two German scientists Max Knoll and
Ernst Ruska discovered that beams of electrons could be used instead of light. The
electron microscope could to be used to observe objects that were not visible using light
microscopes.
Scientists working for corporations competed to develop the first commercial electron
microscope and Ernst Ruska, working for Siemens, eventually achieved this in 1938. By
the late 1930s, microscopes had been developed that could achieve resolutions as low
as 10nm and by the mid 1940s, resolutions as low as 2nm had been achieved.
The main competitors in Europe were Siemens, Philips and Carl Zeiss. In the late
1930s, the scientists in Japan formed the Japan Electron Optics Laboratory that
eventually manufactured the greatest variety of electron microscopes among all of the
companies.
The early versions of electron microscopes used transmission electron microscopy. The
first scanning electron microscope hit the market in 1965, which revolutionized the world
of material science.
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