Edges of the cell membrane are revealed in this darkfield image of a living fibroblast growing in monolayer tissue culture. This technique is useful for capturing details in difficult specimens that cannot be imaged using other methods.

Darkfield Cell Specimen: Fibroblast in Culture Technique: Darkfield

Darkfield illumination requires blocking out of the central light which ordinarily passes through and around (surrounding) the specimen, allowing only oblique rays from every azimuth to "strike" the specimen mounted on the microscope slide. The top lens of a simple Abbe darkfield condenser is spherically concave, allowing light rays emerging from the surface in all azimuths to form an inverted hollow cone of light with an apex centered in the specimen plane. If no specimen is present and the numerical aperture of the condenser is greater than that of the objective, the oblique rays cross and all such rays will miss entering the objective because of their obliquity. The field of view will appear dark, while the specimen will appear in bright contrast.