The Why and What of Koehler Illumination

Many explanations of the role of the condenser lens in microscopes state that the condenser focuses light on to the sample. The truth is really that the condenser concentrates the light on the sample with perfectly de-focuses light. And that was the huge benefit at the time. Today, with advanced light sources and efficient diffusers, even cheap microscopes can produce sufficiently homogeneous illumination without focusable condensers and field diaphragms, and the added advantages of Koehler illumination are reserved for research microscopes.
Sources:
Koehler, A (1893). Ein neues belichtungsverfahren fur mikrophongraphische Zwecke. Zeitschr. f./ Wiss. Mikroskopie, 10, 443-440. Translated to English by ‪@PUMAMicroscope‬
PUMA Microscope (2021). Kohler Illumination. How to build, collimate, and use the Kohler Illuminator for the PUMA Microscope. • Köhler Illumination - ...
Waters, J (2019). Microscope alignment for optimal image quality: Koehler Illumination. • Microscope alignment f...
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[@copernicus6420]

This is a very beautiful explanation. Thank you sir

[@lotharmayring6063]

Wieso muss denn beim Koehlern der Kondensor zentriert werden. Seine optisch Achse sollte doch in jedem Fall
mit der optischen Achse des Objektives uebereinstimmen und nicht mehr veraendert werden. Wohl aber
sollte die Leuchtfeldblende zentrierbar sein.
Das bedingt auch immer eine zentrierbare Punktlichtquelle.