The propagation geometry. The partially coherent source with a source size σ and coherence length ξ is positioned at z0. Partially coherent radiation with the beam size , coherence length and radius of curvature RL is incident on the lens at zL. The beam size and the radius of curvature are modified by the transmission through the lens. The beam is focused at the focal position zF with the focus size and coherence length ξF. The beam parameters at an arbitrary position z1 downstream of the lens are determined.