Darkfield illumination is one of the various methods of lighting used in microscopy to capture the small, and make it large. This method illuminates the subject through the use of oblique angle lighting to create a glowing and unique presentation of a subject. Oblique lighting eliminates the zero order of illumination which is what sets this method apart from Brightfield illumination. The visible light consists of rays refracted from the subject into the imaging system.
In order to create Darkfield illumination, a microscopist requires a Brightfield objective and a Darkfield condenser. When executing Darkfield, it is important to have the disc stop equal to the numerical aperture of the objective at the location of the aperture diaphragm exit pupil. Additionally, one must open the field stop fully to ensure the the light is unfocused. Then the operator will raise and lower the substage condenser until the apex of illumination reaches the sample plane.
Advantages of Darkfield Illiminated Photomicrographs
- Effective for semi transparent subjects
- Useful for delineating edges of subjects
- Can reveal internal structures not seen with Brightfield illumination