Dark Field Microscope Disadvantages

Dark Field illumination is a technique used to observe unstained samples causing them to appear brightly lit against a dark, almost purely black, background.

Pictured right: Highly magnified image of sugar crystals using darkfield microscopy technique

When light hits an object, rays are scattered in all azimuths or directions. The design of the dark field microscope is such that it removes the dispersed light, or zeroth order, 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.

Dark Field

These specimens often have similar refractive indices as their surroundings, making them hard to distinguish with other illumination techniques.

You can use dark field to study marine organisms such as algae and plankton, diatoms, insects, fibers, hairs, yeast and protozoa as well as some minerals and crystals, thin polymers and some ceramics.

You can also use dark field in the research of live bacterium, as well as mounted cells and tissues.

It is more useful in examining external details, such as outlines, edges, grain boundaries and surface defects than internal structure.

Dark field microscopy is often dismissed for more modern observation techniques such as phase contrast and DIC, which provide more accurate, higher contrasted images and can be used to observe a greater number of specimens.

Recently, dark field has regained some of its popularity when combined with other illumination techniques, such as fluorescence, which widens its possible employment in certain