Nikon Metrology / Download / Darkfield

Darkfield | Darkfield

Key Words: brightfield

Definition:Dark field microscopy is a contrast technique where only light diffracted from the specimen is used to form the image. The specimen appears bright against a dark background

TECHNOLOGY:

Darkfield microscopy creates contrast in transparent unstained specimens such as living cells. It depends on controlling specimen illumination so that central light which normally passes through and around the specimen is blocked. Rather than light illuminating the sample with a full cone of light (as in brightfield microscopy) the condenser forms a hollow cone with light travelling around the cone rather than through it.

This form of illumination allows only oblique rays of light to strike the specimen on the microscope stage and the image is formed by rays of light scattered by the sample and captured in the objective lens. When there is no sample on the microscope stage the view is completely dark.

Care should be taken in preparing specimens as features above and below the plane of focus can also scatter light and compromise image quality (for example, dust, fingerprints). In general, thin specimens are better because the possibility of diffraction artefacts is reduced.

APPLICATIONS:

In darkfield microscopy, contrast is created by a bright specimen on a dark background. It is ideal for revealing outlines, edges, boundaries, and refractive index gradients but does not provide a great deal of information about internal structure. Ideal subjects include living, unstained cells (where darkfield illumination provides information not visible with other techniques), although fixed stains cells can also be imaged successfully. Darkfield imaging is particularly useful in haematology for the examination of fresh blood. Non-biological specimens include minerals, chemical crystals, colloidal particles, inclusions and porosity in glass, ceramics, and polymer thin sections.

MICROSCOPE CONFIGURATION:

Almost any brightfield laboratory microscope can be easily converted for use with darkfield illumination using special darkfield condensers (dry or oil type).

RECOMMENDED SYSTEM:

Consult Nikon

LINKS:

Darkfield illumination for stereomicroscopy

Associated Products


Choose Region/Language