Learn how to set Koehler illumination on any microscope. Teach yourself, or teach others. The app simulates your microscope's controls and the images generated at the eyepieces, acting as a virtual microscope. The locations of the controls on your microscope stand are shown, and the correct way to use them is explained. Their effect on the image at the eyepieces is demonstrated. Remembering all of the steps required to set Koehler illumination can be tricky, and this app will serve as a useful reminder whenever you wish to check that the configuration of your instrument is correct. Setting Koehler illumination generates an evenly illuminated field of view, reduces stray light, and allows you to set the balance between resolution and contrast.