Microscopes
• Microscope, instrument used to obtain a
magnified image of minute objects or minute
details of objects.
•
OPTICAL MICROSCOPES
The most widely used microscopes are
optical microscopes, which use visible
light to create a magnified image of an
object.
Early Microscopes
• The first microscopes were of two kinds: simple and
compound.
• A simple microscope has just one lens (or lens
combination)—a magnifying glass can be thought of
as such a microscope.
• Simple microscopes are capable of extremely fine
work. Those made by the great Dutch microscopist
Anton van Leeuwenhoek (1632-1723) were small
enough to fit in one's palm, but they enabled him to
see cells, bacteria, and single-celled animals
Microscopes
• Paramecium
Early Microscopes
• This drawing shows a compound
microscope used in 18th-century
France. First developed in the late 16th
century, compound microscopes use
two or more sets of lenses to achieve
high magnification.
• Culver Pictures
– "Microscope, 18th Century," Microsoft® Encarta®
Encyclopedia 99. © 1993-1998 Microsoft
Corporation. All rights reserved.
Early Microscopes
• English scientist Robert Hooke built
this microscope in the 17th century
and used it to conduct pioneering
research. He discovered the cell
structure of plants by observing a
thin slice of cork under his
microscope.
• Cecil Fox/Science Source/Photo Researchers, Inc.
– "Hooke’s Microscope," Microsoft® Encarta®
Encyclopedia 99. © 1993-1998 Microsoft
Corporation. All rights reserved.
Compound Microscope
• The compound microscope uses two lenses, an
objective lens and an ocular lens, mounted at
opposite ends of a closed tube, to provide greater
magnification than is possible with a single lens. The
total magnification of a compound microscope is
determined by the two lens systems and can be more
than 2000 times.
• We will use compound microscopes.
Compound Microscope
Ocular Lens
(Eye Piece)
Objective Lens
Objective Lenses
Compound Microscopes
• Two key characteristics affect the quality of a microscope—
magnification and resolving power.
•
A compound microscope's magnification is
determined by multiplication: it is equal to the
magnification produced by the ocular times the
magnification produced by the objective.
• Viewing an object with a 10X ocular lens (a lens that magnifies
things ten times) and a 100X objective lens produces an
enlarged image that is 1,000X—that is, it appears to be a
thousand times larger.
Compound Microscopes
• Today, a typical compound microscope can resolve
better than 1 micrometer (one-thousandth of a
millimeter; 1 m equals one-millionth of a meter, a
meter being about 39.37 inches).
• Most bacteria are about 1 m long; by comparison,
human hair is around 100 m thick. An atom is much
smaller than that—about 0.1 nanometer (a
nanometer is only a billionth of a meter).
Microscopes
Bacteria
Compound Microscopes
• Optical microscopes have a firm stand with a flat stage
to hold the material examined and some means for
moving the microscope tube toward and away from the
specimen to bring it into focus: course and fine
adjustment knobs.
• Ordinarily, specimens are transparent and are mounted
on slides—thin, rectangular pieces of clear glass
that are placed on the stage for viewing.
Compound Microscopes
Stage Clips
Course Adjustment
Fine Adjustment
Base
Stage
Compound Microscope
• The stage has a small hole through which light can
pass from a light source mounted underneath the
stage—either a mirror that reflects natural light or a
special electric light that directs light through the
specimen.
• A revolving diaphram regulates how much light is
allowed to pass through to the slide.
Compound Microscope
Diaphram
Light Source
Microscopes
• In photomicrography, the process of taking photographs
through a microscope, a camera is mounted directly
above the microscope's eyepiece. Normally the camera
does not contain a lens because the microscope itself
acts as the lens system.
• Microscopes used for research have a number of
refinements to enable a complete study of the
specimens. Because the image of a specimen is highly
magnified and inverted, manipulating the specimen by
hand is difficult.
•
You will find this out for yourself, so be patient!
Microscopes
• The stages of high-powered research microscopes can
by moved by micrometer screws. You will use these if
you take Med. Tech. or Bio II. In some microscopes,
the stage can also be rotated.
• Research microscopes are also equipped with three or
more objective lenses, mounted on a revolving head,
so that the magnifying power of the microscope can be
varied.
• Our microscopes are equipped with a revolving head
and three objective lenses.
Microscopes
Arm
Revolving Head
Microscopes
• In this class you will have hands-on experience with a
microscope.
• A miniature world will be opened up as you slip a glass
slide under the instrument and peer at all sorts of
interesting things.These images will be exciting and fun!
• Sophisticated research microscopes can provide even
more.
Seeing the Invisible: The New Microscope
• By Samuel H. Cohen
• Recent years have seen ingenious refinements of the
traditional microscope that relies on visible light.
• Innovative types of electron microscopes—which
rely on electrons—have appeared as well. It was the
electron microscope (whose development in the
1930s eventually earned its inventor, German
physicist Ernst Ruska, a Nobel Prize) that brought
the human eye into contact with the world of
molecules and atoms.
Seeing the Invisible: The New Microscope
• Within the last decade scientists have also devised
new types of microscopes that can look even further
into the hidden structure of reality.
• To get an idea of the smallness of the features that
these microscopes can detect (smaller than an atom),
think of it this way: about 100 billion atoms could be
fitted into the period at the end of this sentence.
Electron Microscopes
• The electron microscope, which works like a light
microscope but uses a beam of electrons instead of a
beam of light.
• The electron beam is deflected and focused by
means of magnetic lenses.
• Using an electron microscope, scientists, for the first
time, could peer into the structure of crystals and
fibers and explore the world of viruses, DNA, and
objects of like scale.
Electron Microscopes
This false color image of the head of a fruit fly
illustrates the level of detail that electron
microscopes are capable of resolving. The
magnification of this image is about 200 times.
Electron microscopes achieve much greater
magnifications than light microscopes by using
electrons with wavelengths considerably shorter
than those associated with visible light. Light
microscopes are capable of maximum
magnifications of about 2,000 times, whereas
magnifications approaching 1,000,000 times are
Oliver Meckes/Photo Researchers, Inc.
possible with electron microscopes.
"Image of a Fruit Fly," Microsoft®
Encarta® Encyclopedia 99. © 19931998 Microsoft Corporation.
All rights reserved.