Botany online 1996-2004. No further update, only historical document of botanical science!
Effects of an amplitude and a phase preparation. The middle picture shows an uninfluenced beam of light. The upper part of the picture demonstrates that the light intensity decreases after the beam's passage through the preparation (grey block). The observer is under the impression that the light becomes dimmer.
The lower part of the picture indicates how the phase displacement changes the light beam. The change cannot be perceived with the naked eye though it is used in the image generation of phase contrast microscopes (according to D. GERLACH, 1985).