Figure 2.14 An opaque light stop inserted into a brightfield microscope is used to produce a darkfield image. The
light stop blocks light traveling directly from the illuminator to the objective lens, allowing only light reflected or
refracted off the specimen to reach the eye.
Darkfield microscopy can often create high-contrast, high-resolution images of specimens without the use of stains,
which is particularly useful for viewing live specimens that might be killed or otherwise compromised by the stains.
For example, thin spirochetes likeTreponema pallidum, the causative agent of syphilis, can be best viewed using a
darkfield microscope (Figure 2.15).
Figure 2.15 Use of a darkfield microscope allows us to view living, unstained samples of the spirocheteTreponema
pallidum. Similar to a photographic negative, the spirochetes appear bright against a dark background. (credit:
Centers for Disease Control and Prevention/C.W. Hubbard)
- Identify the key differences between brightfield and darkfield microscopy.
Chapter 2 | How We See the Invisible World 47