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Microscopes
• Light microscopes were first developed in the
1500s.
• One of the earliest inventors of
microscopes was the Dutch lens grinder
Anton van Leeuwenhoek. “Father of
Microscopy”
• His microscopes were mostly single lens
magnifiers with a place to attach a specimen.
He is credited with producing over 250
different microscopes.
• The first compound light microscope was
designed by the Jansens in 1590, even
before van Leeuwenhoek.
• The compound light microscope design
allowed biologists to view specimens
through a series of two lenses. This gives
a greater amount of magnification. The
total magnification possible is a product of
the two lenses used.
Electron Microscopes:
Light microscopes can only produce sharp
images of objects when the objects are larger
than 0.2 micrometers (2 ten thousandths of a
millimeter), or about 1/50th of the diameter of the
typical cell.
Electron microscopes focuses a
beam of electrons on specimens, and
can form images 1000 times smaller
than those visible under the light
microscope.
How can Electron microscopes see
much smaller objects than light?
• Light wave lengths are too large for some
very tiny objects and do not reflect from
them.
• Electron beams have much
smaller wavelengths and can
reflect back from the smaller
objects. (Images cannot be
viewed directly as with light microscopes.)
Two Major types of electron microscopes:
• TEM – TRANSMISSION ELECTRON
MICROSCOPE
• An electron beam
shines through very
thin specimens. It
produces a
two-dimensional image.
It can only be used
to view dead specimens.
(They can magnify
200,000 times.)
SEM – SCANNING ELECTRON MICROSCOPE
• An electron beam scans back and forth across
the surface of a specimen to provide a threedimensional image of the object’s surface.
(They can magnify 100,000 times.)
• Images of the electron microscope can be seen on a
monitor, rather than directly, as with the light microscope.
THE COMPOUND LIGHT MICROSCOPE
Compound Light Microscope –
this microscope uses a beam of light that
passes through two lenses to provide an
enlarged view of structures that are too small to
be seen with the unaided eye.
Magnification – this refers to the microscope’s
ability to increase an object’s apparent size.
Resolution- this refers to the ability of a
microscope to show details clearly.
Total Magnification- this is calculated by
multiplying the ocular lens x the objective
lens over the slide.
• scanning lens
• (ocular 10x)(objective 4x)
= 40x total
• low power
• (ocular 10x)(objective 10x)
= 100x total
• high power
• (ocular 10x)(objective 40x)
= 400x total
• Field of View – the area of the specimen
that is seen when looking through the
ocular lens. As the total magnification
increases, the field of view decreases.
• Depth of Field – the ability to focus
through different depths or “layers” within
a specimen.
• Parafocal – the characteristic of a
microscope that maintains focus when
switched to another objective lens
Put away the microscope
properly:
• 1) Remove your slide
• 2) Clean the stage
• 3) Lower the stage (Some microscopes only)
• 4) Place the lowest power objective in place.
• 5) Wrap the cord around the supports on the
microscope
• 6) Place the cover on the microscope