Fluorescence correlation spectroscopy is a method that analyses the fluctuations in the fluorescence of a low number of fluorophores providing information on the amplitude and time scale of the fluctuations. The fluctuations originate from motion and photo physical or chemical processes. If just one focus is used, the direction of the motion cannot be derived. Therefore, we use 4 spatially distributed foci enabling the determination of the motion of the molecules in 3 dimensions.