Darkfield Microscopes

Darkfield microscopes employ a special contrast enhancing technique known as dark field illumination to produce beautiful images of normally difficult-to-observe biological specimens. Similar to the phenomenon of being able to see stars at night but not during the day, darkfield illumination is most often used with samples that are not easily imaged against a light background, and results in samples that appear bright against a dark background. The darkfield effect is achieved via an opaque, circular central stop, usually located in the sub-stage condenser or inserted as a filter, which blocks out the central part of the path of illumination, only allowing light to pass through the sample at oblique angles. These oblique light rays enter the objective lens after being reflected and diffracted off of the features of the sample to yield the characteristic light-against-dark image. Darkfield microscopy is a very common and economical contrast technique to equip a microscope with, especially for low magnification use. The dark field microscope has found considerable use within the the field of live blood microscopy (sometimes referred to as live cell microscopy or darkfield analysis of live blood). However, dark field illumination is just as useful on an inverted metallurgical microscope, as well as for diatoms, small aquatic organisms and many other biological and metallurgical samples.