A microscopy system and a microscopy method are provided for observing a fluorescent substance accumulated in a tissue. The microscopy system comprises a filter allowing to observe the tissue at a same time both with visible light and with fluorescent light. It is possible to observe a series of previously recorded fluorescent light images in superposition with the visible light images. An end of the series of images may be automatically determined. A thermal protective filter may be inserted into a beam path of an illuminating system at such automatically determined end of the series.