The examination of unstained biological specimens with light microscopy methods often suffers from poor contrast and, hence, poor visibility of the object to be examined. This renders many applications e.g. performing electrophysiological experiments, investigating cell growth or simply judging the current health state of cells, almost impossible. To improve the visibility of living unstained biological specimens, several contrasting methods have been developed. One of the most frequently used contrasting methods is phase contrast, developed in the 1930s by Frits Zernike. Since their invention, phase contrast microscopes are part of almost every biological laboratory.

In this tutorial the principle of phase contrast imaging is described taking the example of an inverted research microscope. Additionally, the alignment of the components needed for phase contrast is shown in the interactive part of the tutorial.