Table-top ultrafast X-ray sources are a promising tool in physics of matter as well as in biology and medicine. An intriguing feature of these sources is that they can be easily operated in the soft X-ray region, by exploiting continuum Bremsstrahlung as well as discrete line emission from neutral atoms and ions. As an example, this spectral region is of large interest for the characterization of thin films [1] or for the study of biological samples by using techniques like soft x-ray diffraction imaging or microscopy [2], In this kind of experiments the coherence properties of the radiation source play a key role. Table-top ultrafast soft X-ray sources are characterized by a partial spatial coherence, which is related to a non-zero angular source size, and by a limited temporal coherence which is a consequence of the spectral richness of the produced radiation.