Definitions:

1. A microscope that used bright illumination against a black background to view small particles. NOUN
   • Using an ultramicroscope, researchers can examine the intricate structures of viruses and other nonoscopic organisms.
2. A specialized optical microscope designed to observe particles too small to be seen with standard light microscopes, by detecting the light they scatter, rather than light they reflect or absorb. NOUN
   • With the ultramicroscope, objects as small as 10 nanometers become visible.

Synonyms:

• dark-field microscope
• nanoscope