Koehler Illumination

Koehler microscope illumination produces illumination on the specimen that is uniform in brightness and free from glare. It is especially helpful when performing photo microscopy. Koehler illumination was first introduced in 1893 by August Kohler, who was working for the Carl Zeiss corporation.

When using Koehler illumination it is important to align the condenser lens for optimal illumination. Here are a few simple steps to follow:

1. Focus on your sample in brightfield mode.
2. Close the field diaphragm (your image will now have a dark cirlce around it and may be slightly out of focus at the edges).
3. Focus the diaphragm so the edges of your image are crisp and sharp, the black circle still remains around the image.
4. Center the image using the two centering screws. (The image with the dark circle around it should now be in the center of your field of view).
5. Open up the field diaphragm again so the entire specimen fills the field of view and the dark circle disappears.

The Motic BA310 microscope is an example of a microscope with Koehler illumination.