Microscope Notes

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Microscope Notes

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Microscopy

• Three goals
• produce a magnified image of the specimen,
• separate the details in the image,
• render the details visible to the human eye or
  camera.
• Multiple-lens designs with objectives and
  condensers (compound)
• Simple single lens devices that are often
  hand-held, such as a magnifying glass.

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Microscopy History
Simple
Compound
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Microscopy History
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Microscopy History
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Types of Microscopes

• Simple
• Compound
• Stereoscopic
• Electron

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Simple Microscope

• Similar to a magnifying glass and has only one
  lense.

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A Lense

• Enlarges an image and bends the light toward your
  eye.

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Microscope

• One or more lenses that makes an enlarged image
  of an object.

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Compound Microscope
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The Compound Microscope

• It is made of a series of lenses that allow you
  to magnify objects to about a maximum
  magnification of 2000X.
• This magnification is not enough to see all cells
  and certainly not all the organelles that are
  present in some cells.
• Due to the nature of light the compound
  microscope has a resolving power of only 2µm.  As
  a result if you are looking at two objects that
  are less than 2µm apart the light waves that
  bounce back to your eye would make it appear as
  only one object.  You would loose much of the
  detail!

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Compound Microscope

• Lens closest to the objectobjective.
• Light from condenser, forms light cone
  concentrated onto the object (specimen).
• Light passes through the specimen and into the
  objective
• projects a real, inverted, and magnified image of
  the specimen to a fixed plane within the
  microscope intermediate image plane

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Eyepiece Lense

• Usually has a power of 10 x

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• Eyepiece Lense
• X
• Objective Lense
• Total Magnification

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Objective Lenses

• Low Power 4 x
• Medium Power 10 x
• High Power 40 x

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Stereoscopic Microscope

• Gives a three dimensional view of an object.
  (Examples insects and leaves)

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New Technology

• Another approach is needed if you wish to see
  greater detail within the cell.  In fact you
  would have to use a medium (other than light) as
  a vehicle to see objects that are smaller than
  2µm.  That vehicle is the electron.  The
  wavelength for electrons is much shorter than for
  light and the resolution can be less than 0.2µm. 
  There are two kinds of electron microscopes.

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Electron Microscope
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Transmission Electron Microscope

• Early TEM had a maximum magnification of only
  400X, much less than light microscopes.
• Two Canadians developed the first TEM that could
  magnify up to 7000X (James Hillier and Albert
  Prebus)
• They found that the tiny grains that were viewed
  under conventional microscopes were actually
  complex organelles.
• TEM like light microscopes produce 2D images only.

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TEM (cont)

• Cells viewed under TEM must be very thin 1µm.  To
  accomplish this, the specimen is set in plastic
  material and cut with a special instrument.  The
  specimen must be dead and sophisticated equipment
  is required.

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TEM
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TEM Pics
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Scanning Electron Microscope

• The SEM passes a narrow beam of electrons over
  the surface of a specimen.
• The specimens must be coated with a very thin
  film of metal.  As electrons bounce off the
  specimen a television screen picks up the image.
• The SEM has a lower resolution than the TEM but
  they have the advantage of producing a 3D image.

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SEM

• Specimens viewed under the SEM must be fixed
  (killed), cleaned and coated with metal.  The
  metal of choice is gold because it will not allow
  electrons to pass through it.  Again
  sophisticated equipment is needed to use and
  prepare these samples.

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SEM
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