Basic knowledge in optics and contrasting methods is fundamental for microscopic imaging. The precise setup of an optical microscope including correct Koehler illumination improves image quality – the base for further image analysis. Within light microscopy we differentiate between stained and unstained samples influencing the amplitude and the phase of the light waves traversing the sample. For the human eye, differences in the amplitude are visible as brightness differences. Contrasting methods like phase contrast, modulation contrast, differential interference contrast, often used in living samples, convert phase shifts into intensity. Staining and fluorescence techniques, like immunofluorescence or the use of fluorescent proteins, are used to make selected structures or proteins visible. Thus, to optimize the use of a microscope it is reasonable to learn more about its basic characteristics.