studying cells

• Microscopes are a topic frequently requested for help with in tutoring, covering magnification calculation, conversion of units, and calibration of the eyepiece graticule
• Magnification


  How many times larger the image is compared to the actual size of the object
• Resolution/Resolving power


  The minimum distance between two objects which they can still be viewed as separate
• Types of microscopes


  • Optical/light microscope
  • Transmission electron microscope
  • Scanning electron microscope
• Optical microscope


  • Uses a beam of light
  • Lower resolution and magnification
  • Can view living samples and get color images
• Electron microscope


  • Uses a beam of electrons
  • Higher resolution and magnification
  • Requires a vacuum and can only get black and white images
• Optical microscopes cannot see the inside of organelles in detail or some small organelles at all
• Transmission electron microscope


  Beam of electrons passes through the specimen, creating a 2D black and white image
• Scanning electron microscope


  Beam of electrons scatters and reflects off the surface, creating a 3D image
• Converting units


  Millimeters to micrometers: multiply by 1000

  Micrometers to millimeters: divide by 1000
• Calculating magnification from a micrograph


  Measure the image size of the scale bar in mm

  2. Convert the image size to micrometers

  3. Divide the image size by the actual size of the scale bar (in micrometers)
• Eyepiece graticule


  A glass disc within the eyepiece with a scale etched on it, used to measure the size of objects
• Calibrating the eyepiece graticule


  Line up the eyepiece graticule with the stage micrometer scale

  2. Count how many divisions on the eyepiece graticule fit into 1 division on the stage micrometer

  3. Use the known value of 1 stage micrometer division (10 micrometers) to calculate the value of 1 eyepiece graticule division
• The value of 1 eyepiece graticule division changes with different magnifications
• To measure the size of a structure, count the number of eyepiece graticule divisions it covers and multiply by the calibrated value of 1 division