Microscope Notes


  • One of the most widely used tools in Biology
  • An instrument that produces an enlarged image of an object
  • Magnification – the increase in an object’s apparent size
  • Resolution – the power of a microscope to clearly show detail


Compound Light Microscope  

  • LM  
  • With this type of microscope the thin sliced (enough to be transparent) and sometimes stained specimen is mounted on a glass slide to be viewed
  • The slide is placed on the stage and a light source (a light bulb or mirror in the base) directs the light upward
  • Light passes through the specimen and through the objective lens, which is positioned directly above the specimen
  • A set of objective lenses is located on the rotating nosepiece enlarges the image of the specimen with different powers of magnification
  • The most powerful objective lens produces an image 40 times (40X) the actual size of the specimen
  • From the objective lens, the magnified image is projected up through the body tube to the ocular lens in the eyepiece where it is magnified further (10X)
  • To compute the total magnification of a microscope, multiply the power of magnification of the lens being used (40X, 100X) by the power of magnification of the ocular or eyepiece lens (10X) example: 40 X 10 = 400X total power of magnification
  • The Resolution power of LM’s is limited by the physical characteristics of light (At powers of magnification beyond about 2000X, the image of the specimen becomes blurry.)


Electron Microscopes  

  •   Used to view extremely small objects  
  •  Beam of Electrons, rather than light, produces an enlarged image  
  • Electron microscopes are more powerful than LM’s  
  • There are several types of electron microscopes

Transmission Electron Microscope  

  • Can magnify objects up to 200,000 times  
  • Projects image onto a screen or photographic plate  
  • Used to produce greatly magnified images of internal details of a specimen
  • Can not be used to view living specimens  


Scanning Electron Microscope (SEM)

  • Produces a 3 dimensional image  
  •  Specimens aren’t sliced but are sprayed with a fine metal coating  
  • A beam of electrons is passed over the surface of the metal coating to emit a shower of electrons
  • Showered electrons are projected onto a fluorescent screen or photographic plate  
  • SEM’s produce greatly magnified image of surface details of specimens
  • Can magnify up to 100,000 times
  •   Can not be used to view living specimens