Microscopy with Transmitted and Refracted Light

Brightfield microscopy is Kohler-illuminated transmitted light microscopy without other contrast-generating optics. Darkfield illumination microscopy is best at visualizing highly refractile objects, objects that do a good job of bending light. When illuminated with a darkfield condenser, these objects refract the light, and the objectives only collect this refracted light, leaving the rest of the field dark. Rheinberg illumination is a variant of darkfield microscopy. Instead of an outer clear or open annulus and an opaque center stop in the front focal plane of the condenser, Rheinberg illumination uses an outer colored ring that is a different color from a transparent, colored central disk. Polarized light microscopy, differential interference contrast microscopy (a form of polarized light microscopy), and phase contrast microscopy all generate contrast by wave interference within (polarized light) or between (phase contrast) these two wave trains. Compensators are devices on polarization microscopes that introduce a known amount of phase difference, or retardation.