M1. TYPES OF MICROSCOPE

• Brightfield: Oldest, most common illumination system used
• Principal type of Microscopy in clinical lab?

  bRIGHTFIELD
• In brightfield DARK specimen, BRIGHT background
• Brightfield today: Kohler illumination
• Phase-contrast: Variations in refractive index → variations in light intensity or contrast
• Phase-contrast Specimen: light to dark with haloes of varying intensity related to the thickness of the component
• Ideal for viewing low-refractile elements/living cells?

  Phase-contrast
• examples of low-refractile elements/living cells?

  Hyaline casts, Mucus threads
• Refraction: bending of light as it passes from one medium to another
• Diffraction: bending of light as it passes an obstacle or through an aperture or an opening
• Conversion of Brightfield to Phase-Contrast Microscope?

  Condenser: Annular diaphragm or light annulus

  Objective: Phase-shifting element or dark annulus
• Polarized: The direction of light has one direction with one plane of direction of vibration
• Identify and classify birefringent substances that shine

  brillianty against a dark background?

  Polarized
• “Birefringent” = ability of substance to refract light in

  2 directions (at 90 ̊)
• Positive Birefringence: Clockwise rotation of polarized light
• Negative Birefringence: Counterclockwise rotation of polarized light
• Red compensator of Positive Birefringence = BLUE-GREEN
• example of Positive Birefringence?

  Calcium pyrophosphate
• Red compensator of Negative Birefringence = YELLOW
• example of negative birefringence?

  Monosodium urate
• Red Compensator: indicates the type of birefringence if it is positive or negative
• Conversion of Brightfield to Polarizing?

  Below condenser: Polarizing filter, East-West direction

  for light vibration

  Between Objective and Eyepiece: Analyzer, North-South

  direction
• Interference Contrast is more superior than polarized because it has optical sectioning
• Interference Contrast: The difference in optical light paths through the specimen is converted into intensity differences in the specimen

  image
• 3D images of high contrast and resolution are obtained

  without haloing?

  Interference Contrast
• Interference contrast is Excellent for detailed viewing of unstained specimens
• Superior visualization of all components?

  Interference Contrast
• Useful for microscopic exam of wet preparations?

  Interference contrast
• Modulator has 3

  regions: dark, gray,

  and bright regions
• Determines intensity

  gradients of light to

  dark observed in the

  3D image?

  Modulation or Hoffman
• Produces 3D image

  through birefringent

  crystal prisms as

  beam splitters:

  ➢ 2 Wollaston

  prisms?

  Differential or Nomarski
• Darkfield is Inexpensive, beneficial in clarifying edges and boundaries but not good for structural detail
• Darkfield Special condenser: presents only oblique light rays to specimen
• Darkfield is preferred for ID spirochetes
• Conversion of Brightfield to Darkfield Microscope?

  Condenser: replace with special darkfield condenser