- Brightfield microscopyis commonly used to observe color and light intensity
(brightness) information from a stained specimen. The entire specimen section
being examined is illuminated and appears bright to the viewer. Most specimens
are fairly transparent under the microscope and consequently are difficult to
analyze visually against a plain white background. Thus,cell stainingcan be
used to add color to the picture, thereby making objects such as cells and their
components much easier to see. Through the use of different stains, certain cell
components (e.g., a nucleus, a cell wall, or the entire cell) can be selectively or
preferentially stained to examine the component structure. Staining may also be
used to highlight metabolic processes or to differentiate between live and dead
cells in a sample. However, it is important to note that because the specimen is
stained prior to being viewed under a microscope, the observed colors are not
necessarily those of the actual specimen.
Turret with
objective lenses
Stage plate
Light source
Eyepiece
Specimen holder
(e.g., petri dish)
Light path
Fig. 8.3 Example of an
inverted microscope
Rotating objectives
Stage plate
Stereo
eyepiece
Specimen (plant,
zebra fish, mouse)
Bottom illumination
Top illumination
Stereo head
Fig. 8.4 Example of a
stereomicroscope
238 8 Microscopy