A fiber optics illuminator was incorporated in an illuminator designed for dispersion staining. The fiber optics illuminator was provided with a collection lens which has an adjustable sleeve and a field diaphram that enables it to produce a highly intense, axial beam of Köhler illumination which is needed for dispersion staining. This illumination system permits the microscopist to obtain bright, easily detectable, near monochromatic dispersion staining colors with small colorless particles.