Dark Field microscopy is a microscope illumination technique used to observe unstained samples causing them to appear brightly lit against a dark, almost purely black, background.
When light hits an object, rays are scattered in all directions. The design of the dark field microscope is such that it removes the dispersed light so that only the scattered beams hit the sample.
The introduction of a condenser and/or stop below the stage ensures that these light rays will hit the specimen at different angles, rather than as a direct light source above/below the object.
The result is a “cone of light” where rays are diffracted, reflected and/or refracted off the object, ultimately, allowing you to view a specimen in dark field.
A dark field microscope is ideal for viewing objects that are unstained, transparent and absorb little or no light.
These specimens often have similar refractive indices as their surroundings, making them hard to distinguish with other illumination techniques.
Dark field can be used to study marine organisms such as algae and plankton, diatoms, insects, fibres, hairs, yeast, live bacterium, protozoa as well as cells and tissues and is ideal for live blood analysis enabling the practitioner to see much more than is possible with other lighting methods.