Soft X-ray Tomographic (TomoX) microscopy has become a reality in the last years. The resolution range of this technique nicely fits between confocal and electron microscopies and will play a key role in the elucidation of the organization between the molecular and the organelle levels. In fact, it offers the possibility of imaging three-dimensional structures of hydrated biological specimens near their native state without chemical pre-treatment. Ideally, TomoX reconstructs the specimen absorption coefficients from projections of this specimen, but, unfortunately, X-ray micrographs are only an approximation to projections of the specimen, resulting in inaccuracies if a tomographic reconstruction is performed without explicitly incorporating these approximations. In an attempt to mitigate some of these inaccuracies, we develop in this work an image formation model within the approximation of assuming incoherent illumination.