Phase Contrast Microscope Operating Guide

Phase contrast microscopy allows better viewing of unstained specimens, making use of small differences in the refractive index of the specimen. In addition to being "bent," light passing through a substance is slowed so that it is out of phase with light that did not pass through the specimen. The difference between the diffracted, or slowed, light and the direct light is difficult to detect in a microscope without phase contrast objectives and a phase contrast sub-stage condenser.

In a phase contract microscope the difference between the direct and diffracted light is increased. A ring in the sub-stage condenser of the phase contrast microscope focuses a hollow cone of light on the specimen. Undiffracted light, or direct light, in this cone speeds up as it passes through a phase-shifting element in the objective lens. Light passing through the specimen (and diffracted) is combined with direct light that passed through the phase-shifting element. The result of combining the two beams of light, is a darker or brighter spot in the image, depending on the difference in the phases of the two light beams.

Phase Contrast Microscope Operating Guide: light pathways

 

To learn more about phase contrast microscopy, see the following website. By selecting this link you will open a new browser tab that is not connected to the Micro eGuide. http://www.olympusmicro.com/primer/techniques/phasecontrast/phaseindex.html

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