halo

An artifact common to phase contrast microscopy of large phase objects, where dark objects will appear to have a bright border and bright objects will appear to have a dark border. It is caused by weakly diffracted light traveling through the objective phase ring.

Synonyms: halo effect

Related MicroscopyU Article

Apodized Phase Contrast

In apodized phase contrast microscopy, halo attenuation and an increase in specimen contrast can be obtained by the utilization of selective amplitude filters located adjacent to the phase film in the phase plates built into the objective at the rear focal plane. These amplitude filters consist of neutral density filter thin films applied to the phase plate surrounding the phase film as illustrated in the tutorial window.