DARK FIELD MICROSCOPE

 DARK FIELD MICROSCOPE

·       Dark field microscopes are named because the microscopic “field” is dark, while the object being viewed is bright.

·       Instead of the normal condenser, a dark field microscope uses a Dark field condenser that contains an Opaque disk.

Principle

·       The Opaque disk blocks light that would enter the Objective lens directly. Only light that is reflected off (turned away from) the specimen enters the objective lens and reach the eye through Ocular lens or Eye piece. Because there is no direct background light, the specimen appears light against a black background-the dark field.

Uses

·       Dark field microscope is used to examine live microorganisms that are

ü  Invisible in the ordinary light microscope

ü  Cannot be stained by standard methods, or are so distorted by staining that their characteristics then cannot be identified.

·       Dark field microscope is also used for the observation of thin Spirochetes such as Treponema pallidum which is the causative agent of Syphilis and Leptospira sp.

·       Used for the Observation of microbial motility; tufts of bacterial flagella can often be seen in unstained cells.

·       Used for the observation of internal structure in larger eukaryotic microorganisms such as algae, yeasts, etc.