A transmitted light microscope will typically be of little use to anyone wanting to examine the structure of metallic samples, the surface of ceramics, integrated circuits, or printed paper documents. As a result, the reflected light microscope has been developed for these purposes. Reflected light microscopy is often referred to as incident light, epi-illumination, or metallurgical microscopy, and is the method of choice for fluorescence and for imaging specimens that remain opaque even when ground to a thickness of 30 micrometers. Much like the fluorescence microscope, in reflected brightfield microscopy the sample is illuminated from above through the objective. The Köhler illumination principle applies in cases where the objective with its pupil plane is also utilized as the condenser.

The range of specimens falling into this category is enormous and includes most metals, ores, ceramics, many polymers, semiconductors (unprocessed silicon, wafers, and integrated circuits), slag, coal, plastics, paint, paper, wood, leather, glass inclusions, and a wide variety of specialized materials. Because light is unable to pass through these specimens, it must be directed onto the surface and eventually returned to the microscope objective by either specular or diffused reflection. As mentioned above, such illumination is most often referred to as episcopic illumination, epi-illumination, or vertical illumination (essentially originating from above), in contrast to diascopic (transmitted) illumination that passes through a specimen. Several reflected light specimens are presented in Figure 1. The surface of an integrated circuit is shown using reflected light differential interference contrast (DIC) in Figure 1(a), while the jewel bearing of a watch mechanism captured in brightfield is presented in Figure 1(b). Darkfield is another useful reflected light technique, as evidenced by the image revealing surface structure of a superconducting wire cable in Figure 1(c). Finally, a magnetic thin film (Figure 1(d)) can be imaged using polarized reflected light microscopy to examine surface defects (blisters) that affect the homogeneity of the film.