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How to Set Kohler Illumination on your Microscope

How to Set Kohler Illumination on your Microscope

A step by step guide to setting Kohler Illumination on your microscope 

Setting Kohler illumination is an important process to make sure you have a clean and evenly illuminated field of view on your microscope.  Also, it helps with parfocality of objectives.  Parfocality is when there is little to no adjustment of the focus when switching between objectives

First things first turn your microscope on and get comfortable.  Check and make sure your eyepiece diopters are set to zero and rotate in the 10X objective. Then bring your specimen into focus.  Now you are ready to get busy with the kohler alignment!

  1. Make sure the condenser is adjusted in a higher position (close to the stage). If it’s a fliptop condenser, you will want to make sure the top element is flipped in.
  2. Now that your condenser is close to where it needs to be, you want to close down the field diaphragm, also known as a field stop. While looking through the microscope, slowly close the diaphragm. This is usually a rotatable ring around where your light comes up from the bottom of the microscope.  You can find the field stop adjustment by checking your manual if it’s not where I just described.  
  3. Once the diaphragm is closed you will want to bring the condenser to the correct height.  By raising and lowering the condenser you will notice the edges of the diaphragm (it will look like an octagon) start to become very sharp.  
  4. After the condenser is at the correct height, use the centering keys to move the diaphragm to the center of the FOV (field of view). Centering keys are typically located under the stage where the condenser is mounted. 
  5. With the diaphragm in the center of the field, slowly open the diaphragm until it is fully open. 
  6. BOOM! Kohler illumination. Sit back and enjoy that bright and evenly illuminated field. Was that easier than you thought?  

Below is a helpful video on how to set Kohler Illumination on an Olympus BX microscope.  


Feel free to reach out to anyone on our team at Munday Scientific.  You can reach us at

By Chad Potts, 08-12-22

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