Category Archives: Nature of Science

The third and last theme of the Readings.

Microscopy Today

Cells were not discovered until the seventeenth century, when the microscope was invented.

Three different microscopes produce images for different purposes:

  • Compound: for viewing by human eye.
  • Transmission Electron (TEM): for photographic film.
  • Scanning Electron (SEM): three dimensions.

Magnification, Resolution and Contrast

  • Magnification…The path of light rays and electrons moving through space is wavelike but the wavelength of electrons is much shorter than the wavelength of light.
  • Resolution… is the minimum distance between two objects that allows them to be seen as two separate objects.
  • Contrast… a difference in the shading of an object compared to its background.

Illumination, Viewing, and Recording

The human eye can view microscopic images when:

  • Light rays are bent (refracted) and brought to focus as they pass through glass lenses.
  • Electrons are directed toward a screen that are sensitive to their presence.

Confocal Microscopy… can create a three-dimensional image from a laser beam scanning across a specimen and producing a series of optical sections.

Video-enhanced Contrast Microscopy… a television camera converts the light image into an electronic image, which can be entered into a computer.  The computer makes the darkest areas of the original image darker and the lightest areas of the original much lighter.