The examination of live unstained biological specimens often suffers from poor contrast and therefore bad visibility of the specimen. Thick specimens in particular, such as brain slices, show up as nothing more than light grey structures instead of single cells. This tutorial explains the optical elements in the light path and the operating mode of DIC (differential interference contrast) on the example of an inverted and motorized high-end research light microscope which can be used for transmitted light contrasting methods and fluorescence microscopy.