How to use a light microscope - Kohler illumination

Even the best stained slides can appear quite ordinary unless your microscope is adjusted properly for Kohler illumination. This video addresses the basics before demonstrating how to achieve correct illumination across a range of different microscopes.

[@pauljmeyer1]

Thank you for showing the finer points of gaining the best image quality using this system.

[@kerriestevenson124]

Thanks Damien, what perfect timing. I was just saying to my histopathology lecturer that I was looking for good video on Kohler illumination when notification of this video popped up. Exactly what I needed.

[@damienharkin]

You are most welcome Kerrie. I've been trying to find the time to create this video for a while now, so I'm glad that you found it useful. Please let me know if there are any other topics that you would like covered.

[@BritishBeachcomber]

Great video. I've just upgraded to a similar microscope so I'll be running through the procedure soon. Just one thing. After each adjustment it would be useful if you could show the "before" image alongside, so we can see the improvement.

[@damienharkin]

Yes, good idea. I thought about doing this but wasn’t sure that the difference would be as obvious when viewed on RUclips. I do notice a discernible difference by eye when looking down the scope. Let me know how you go.

[@SynthAddict]

nice demo, thanks
I couldn't afford a proper Koehler condenser yet and this will do the trick
it's shocking how in years of micro study in college something this simple and important was never covered :-( at least I know it now

[@damienharkin]

You are most welcome. Thanks for the positive feedback.

[@harp6198]

Thank you for this video!
How would one achieve Köhler illumination at 400, 600 or 1000x magnification where the edges of the hexagon can barely be seen?

[@damienharkin]

Hi Harp, If you adjust for Kohler illumination at lower powers then you should be reasonably close to where you need to be, but if needing to be more accurate then would suggest using the pen/pencil technique as displayed in my video.
Best wishes
Damien

[@harp6198]

@@damienharkin Thank you very much! It is much appreciated :)

[@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.

[@damienharkin]

A centred light source enables more even illumination of the area of interest. Since the condenser lens focuses light from the light source, then it should be centred. Closing the field iris diaphragm provides an approximate focal point to achieve this.

[@lotharmayring6063]

@@damienharkin first the light source has to be centered to his iris. Diffusing filters can make the source more even. The condenssor iris should be in the middle of the picture centering it. The condensor iris should be als closed as possible , because we all will prefer interference microscopy. At least the lightfield-iris can be centered to so called Keohler-iris. But in many cases it gives a better image using oblique DIC-like illumination. Koehler-illumination is only usefull for the factory aligning and testing their optics not for good microscopers

[@damienharkin]

Thanks for the feedback.