What is darkfield microscopy?

Answer 1

A Dark Field microscope is one that has a special condensor (light source) that illuminates the specimen in such a way as to enhance the contrast even if it is unstained. When you look at a specimen in a dark field scope, it looks bright, but it is visible against a black background -- the 'dark field.'

Answer 2

The dark-field microscope allow a viewer to observe living, unstained cells and organisms by simply the way in the specimen in which they are illuminated. A hollow cone of light is focused on the specimen in such a way that unreflected and unrefracted rays do not enter the objective. Only light that has been reflected or refracted by the specimen forms an image. The field surrounding the specimen appears black, while the object itself is brightly illuminated. The dark field microscope reveal considerable internal structure in larger eucaryotic microorganisms. A phase-contrast microscope is used when an investigator wants to view living cells in order to observe a dynamic process such as movement or phagocytosis. A phase contrast microscope converts slight difference in refractive index and cell density into easily detected variations in light intensity and is an excellent way to pbserve living cells.

Answer 3

In dark field microscopy the condenser is designed to form a hollow cone of light, as apposed to bright field microscopy that illuminates the sample with a full cone of light. In dark field microscopy, the objective lens sits in the dark hollow of this cone and light travels around the objective lens, but does not enter the cone shaped area. The entire field of view appears dark when there is no sample on the microscope stage. However, when a sample is placed on the stage it appears bright against a dark background. It is similar to back-lighting an object that may be the same colour as the background it sits against - in order to make it stand out.