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.