Why you should set up Koehler illumination: A correctly set up Koehler illumination delivers a homogeneous illumination across your specimen.

It maximizes image contrast, minimizes stray light, and makes optimum use of the illumination intensity. Good Koehler illumination is needed for achieving best image resolution, reproducibility, and image quality as well as a prerequisite for other transmitted light contrasting methods. Recheck regularly to ensure that your system is set up correctly for Koehler Illumination. The openings of the FD and AD need to be adjusted for each objective.