A microscopy system has a detection system, which is configured to detect light of a first channel in a detection region and convert it to a first fluorescent light signal, to detect light of a second channel in a second detection region and convert it to a first correction signal, and to detect light of a third channel in a third detection region and convert it to a second correction signal. The system further includes a controller, which is configured to determine an approximation value for the spatial distribution of the concentration of the fluorescent dye in an object region using the first fluorescent light signal, the first correction signal, and the second correction signal. A first part of the emission spectrum of the fluorescent dye is detected in the first detection region.