Phase-Contrast and Dark Field Microscopy

A main obstacle in the microscopy of biological objects is their poor contrast. Only where a contrast exists or where it can be achieved by contrast-enhancing dyes, structures can be made visible. Light-absorbing parts of a preparation weaken the amplitude of the light waves that pass through them. It is thus also spoken of amplitude preparations. The change of stronger and feebler light is perceived by the eye as a difference in brightness. The invisible parts of the preparation are went through by the light without a change of amplitude, but the phase of the light may be changed depending on the consistency of the material. This change is due to the altered speed of the lightwaves. Differences in phase can be perceived neither by the eye nor by a photographical film. Read more