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Köhler illumination is a microscope alignment technique, most often used for transmitted light, that ensures images are evenly illuminated and at maximum resolution. The microscope should be adjusted for Köhler illumination before transmitted light imaging, phase contrast and especially differential interference contrast (DIC), which is highly sensitive to incorrect alignment.
Condenser Components
Before adjusting for Köhler you need to know where the relevant condenser components are on the microscope. This varies between manufacturers and models. The image below gives some examples of where to find the field diaphragm, iris aperture, etc. If in doubt, please as a member of light microscopy staff.
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