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.