Darkfield illumination with reflected light enables visualisation of grain boundaries, surface defects, and other features that are difficult or impossible to detect with brightfield illumination. The technique relies on an opaque occluding disk, which is placed in the path of the light traveling through the vertical illuminator so that only the peripheral rays of light reach the deflecting mirror. These rays are reflected by the mirror and pass through a hollow collar surrounding the objective to illuminate the specimen at highly oblique angles.