Apodized phase contrast
viewing images with large phase difference with high clarity and detail without 'halo' effects
The 'halo' effect is an artefact in phase contrast imaging and occurs in specimens with large phase shifts. The development of objectives with a phase ring configuration has significantly reduced this problem.
A traditional phase plate has a thin ring of neutral density material (termed a phase film) on the surface, which retards direct light passing through the specimen by one quarter wavelength to allow constructive and destructive interference with diffracted light at the intermediate image plane. In an apodized phase contrast objective, two concentric areas of semi-transparent neutral density material surround the phase film on the phase plate. These reduce the intensity of light diffracted from the specimen at small angles. The result is a clearer image, improved contrast and reduced halo effects.
Phase contrast imaging is applicable to many transparent subjects, such as living cells in culture, micro-organisms, thin tissue slices, lithographic patterns, fibres, latex dispersions, glass fragments, and subcellular particles (including nuclei and other organelles) where the technique reveals structure that is not visible in brightfield imaging. An advantage of phase contrast microscopy is that living cells can be imaged in detail without the need for staining or use of fluorophores.
Phase contrast capability can be added to almost any brightfield microscope with appropriate phase contrast accessories (annulus in substage condenser and phase contrast objectives). Nikon's apodized phase contrast objectives can be used with Nikon's upright and inverted research and educational microscopes.
Apodized phase contrast|
Halo Reduction with Apodized Phase Contrast