We calculate the partially coherent images of an edge in one dimension by the method of adding intensities, that is, by modeling the illumination as an array of mutually incoherent plane waves incident over a range of angles. In order to visualize the transition between coherent and incoherent imaging, we display images that result from such off‐axis plane waves; these images change considerably as the angle of illumination changes. The calculations are easily carried out on a microcomputer with a high‐level mathematics program. The results shed light on off‐axis and dark‐field illumination as well. Finally, we elucidate a distinction between imaging with the aperture stop in the transform plane and imaging with the aperture stop distant from the transform plane.