# Köhler  Illumination

**Köhler Illumination for Brightfield**

Köhler illumination is a method for evenly illuminating the sample with white light. This method is very important for brightfield imaging in widefield microscopy, and for using the T-PMT for confocal imaging. Brightfield illumination from light source focuses onto the sample via condenser, as a result extra steps are necessary to ensure the light-path is focused on the sample.

1. Bring the sample into focus
2. Close the field diaphragm (<span style="color: #ff0000;">**2**</span>) until you can see at least one edge
3. Adjust condenser height <span style="color: #0000ff;"><span style="color: #000000;">(</span>**3**</span>) until the edges of the diaphragm are crisp. You’ll see an octagon.
4. Center the diaphragm (**<span style="color: #008000;">4</span>**) mage using the two centering screws
5. Open the field diaphragm (2) just until the image fills the field of view (FOV)

[![kohler illumination.png](https://www-app.igb.illinois.edu/core-docs/uploads/images/gallery/2022-06/scaled-1680-/kohler-illumination.png)](https://www-app.igb.illinois.edu/core-docs/uploads/images/gallery/2022-06/kohler-illumination.png)

Link for setting up Köhler illumination

ZEISS Microscopy How-to: Set up Köhler Illumination on your ZEISS Axio Imager (Upright):

[https://www.youtube.com/watch?v=Qk8dbT-N1xw ](https://www.youtube.com/watch?v=Qk8dbT-N1xw "ZEISS Microscopy How-to: Set up Köhler Illumination on your ZEISS Axio Imager")

MicroscopyU has a great interactive on guide for Köhler illumination: [https://www.microscopyu.com/tutorials/kohler](https://www.microscopyu.com/tutorials/kohler "Guide for Köhler Illumination")