Lab

1
Lab 4 Microscopes

• J. Ellen Lathrop-Davis

2
Types of Microscopes

• Light Microscopes
• Use visible light to illuminate specimen
• Different types for different uses
• Stereo dissecting microscopes for large or
  thick objects
• Compound microscopes for small objects
  (Phase-contrast, Interference, Dark field,
  Reflecting, X-ray, Fluorescent, UV)
• Electron Microscopes
• Use electrons to view specimen

3
Compound Light Microscope - Components

• Arm
• Base
• Stage
• Ocular
• Objective
• Light source
• Condenser
• Coarse focus
• Fine focus

4
Magnification and Focus

• Magnification
• Objective X ocular
• 4x X 10x 40x
• Lenses are par focal when object is in focus at
  one magnification, it should be roughly in focus
  at the next
• Use coarse focus knob at low magnification
• Use fine focus knob at higher magnifications

5
Resolution

• Ability to distinguish two points as separate
• Increases with increased magnification
• Limited by wavelength of light
• Limits magnification that can be used with light
  microscope to 1000X
• Oil emersion uses oil to increase resolution
• Electron microscope uses electrons (shorter
  wavelength)
• Scanning EM for surface features
• Transmission EM for internal features

http//www.triroc.com/sunnen/topics/virology.htm
6
Field of View

• Amount in focus under present magnification
• Decreases as magnification increases
• Depth of Field top to bottom
• Width of Field side to side

7
Working Distance

• Distance between specimen and objective
• Decreases with increased magnification
• Dissecting microscope used for larger objects
  (e.g., whole insects)
• Lower magnification
• Greater field of view
• Greater working distance

8
Conversion and Dosage Bonus

• Convert 2.5 g to mg
• A patient needs 0.5 g of a medication available
  in 250 mg tablets. How many tablets should the
  patient receive?