Biology 206L Class website

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Biology 206L Class website

• www.bio.utexas.edu/courses/bio206/

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Test of CPS System

• A question will be posed
• Are you here today?
• Yes
• No

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Microscopy

• Why do we use a microscope?

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Microscopy

• Why do we use a microscope?
• To enable use to see (i.e.image) objects
  that are small.

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Microscopy

• Why do we use a microscope?
• To enable use to see (i.e.image) objects
  that are small.
• What is the problem here?

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Microscopy

• Why do we use a microscope?
• To enable use to see (i.e.image) objects
  that are small.
• What is the problem here?
• Our eyes contain light a sheet of light
  detectors. In order to discern the parts of an
  object, light from different parts of that object
  must fall on different light detectors.

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Microscopy

• Why do we use a microscope?
• To enable use to see (i.e.image) objects
  that are small.
• What is the problem here?
• Our eyes contain light a sheet of light
  detectors. In order to discern the parts of an
  object, light from different parts of that object
  must fall on different light detectors.
• The most common issue one thinks about
  MAGNIFICATION

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LAB 1 MicroscopyObjectives

1. Learn parts and become comfortable using a light
   microscope in a proper fashion
2. Learn concepts of magnification, contrast,
   resolution
3. Learn how to use your condenser (Köhler
   illumination)
4. Learn about phase contrast
5. Examine stage of mitosis in onion root tip

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3 major concepts in light microscopy

• Magnification can we enlarge objects to see
  them?
• Contrast can we see what we enlarge?
• Resolution exactly how small a part can we
  see?

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Lenses and Magnification
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Note principle here

• The position of light in the focal plane
  determines the angle of light emerging from the
  other side of the lens.

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Question

• If we place an object at the focal plane of an
  lens, will an image form on the other side?
• Yes
• No

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Note principle here

• The angle of light rays entering a lens
  determines the position these rays have in the
  focal plane on the other side of the lens.

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Conjugate Planes

• Planes are conjugate if an image focused in one
  is focused in the other.

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The Condenser
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The Condenser
What do you use it for? Control illumination
Desire is to get uniform illumination
Condenser moves up and dow racking the
condenser You need to know where to put it.
This process is called setting
Kohler Condenser has two diaphragms Field
diaphragm Aperture diaphragm

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The Field DiaphragmControls the positions within
the specimen plane that are illuminated. The
Aperture DiaphragmControls the angles of light
passing through the specimen plane.
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Problem of contrast
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Problem of contrast
Problem Even if we magnify an object so its
different parts fall on different detectors on
the back of our eye, if those parts are of the
same intensity, we will see nothing. There have
to be differences in intensity between the parts
of the image (i.e. contrast) to see an image.
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What is the most common way to handle the problem
of contrast?Stain the specimen--hope that its
parts take up the stain differently
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Aperture diaphragmIf we restrict the angles of
light coming into the specimen by stopping down
the aperture, the contrast in the specimen goes
up because more light is scattered. This is
called scattering contrast.
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Phase Contrast
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Phase ContrastInvolves manipulating differences
in the phase of lightcreated even in a low
contrast specimen and convertingthese phase
differences into intensity differences.
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Question

• What is the maximum magnification with a light
  microscope?
• 100X
• 1000X
• Infinite, that is, not limited

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Resolution
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ResolutionWhat do we mean by Resolution?
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Home experiment to seethe consequences of
diffraction of light in imaging systems like the
microscopeAiry Disk
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The aperture diaphragm affects both contrast and
resolution.