A microscope illumination system includes a first light source configured to provide light along an optical axis and an aperture device including an aperture wheel that is rotatable about an axis of rotation. The aperture wheel includes a plurality of apertures of varying size disposed circumferentially on the aperture wheel. The aperture wheel is rotatable so as to dispose each of the apertures in a position that is centered on the optical axis so as to generate an illumination beam path that extends in a centered relationship with respect to the optical axis, and so as to dispose each of the apertures in a position that is off-center from the optical axis and that is within a defined region around the optical axis so as to generate an illumination beam path that extends off-center from the optical axis for oblique incident illumination.