Light microscopes

• Cells range in size:

  • most animal cells are between 0.01 mm - 0.05 mm
  • most plant cells are between 0.01 mm - 0.10 mm
• Compound microscope

  • uses two lenses, the objective lens and the eyepiece
  • the very short focal length objective lens produces a greatly-magnified image
  • the short focal length eyepiece magnifies this further
  • used in a school laboratory
• Features of a compound microscope

  • eyepiece
  • coarse focus
  • fine focus
  • objective lenses
  • arm
  • stage clip
  • stage
  • condenser
  • mirror
• Calculating the magnification of the microscope


  magnification of the microscope = magnification of eyepiece x magnification of the objective
• Calculating the magnification of an image


  magnification = size of image/real size of object
• Light microscope developments

  • 1590s - Dutch spectacle makers Janssen experimented with putting lenses in tubes. They made the first compound microscope. They are thought to have magnified from x3 to x9
  • 1660s - British scientist, Robert Hooke - also famous for his law of elasticity in Physics - observed and drew cells using a compound microscope
  • Late 1600s - Dutch scientist Antonie van Leeuwenhoek constructed a microscope with a single spherical lens. It magnified up to x275
  • 1800s - the optical quality of lenses increased and microscopes are similar to the ones used today
• Maximum magnification


  around x1500 to x2000
• Resolution

  • the fineness of detail that can be seen in an image
  • the higher the resolution of an image, the more detail it holds
  • computing terms - resolution is measured in dots per inch (dpi)
• Limits of the light microscope

  • the resolution of a light microscope is around 0.2 μm or 200 nm
  • it cannot distinguish two points closer than 200 nm
  • one μm is one billionth of a metre (1/1000000000 m, or in standard form as 1 × 10-9 m)