User:Nadiezda Fernandez-Oropeza/Notebook/Notebook/2010/11/19

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Personal notes on Kohler Illumination

  • This entry contains the some tips on Kohler Illumination procedure.

Kohler Illumination

This topic was already discussed on the entry of 09/15/2010. See the following link: Kohler Illumanation

In the section Set up for Kohler Illumination, a number of steps are listed. I will just add a couple of notes in some of them.

  1. Switch on the light source.
  2. Place the sample on the stage and then open the field diaphragm to its maximum aperture and notice whether or not the sample is illuminated.
  3. Focus the sample.

This is done first by placing the objective at the correct distance from the sample slid. If the refractive index is greater than 1, a good amount of a thick oil needs to be placed between the objective and the sample slide.

Then, center the slid by adjusting the knobs that move the slide left or right and away or toward the observer.

  1. Close the field diaphragm to its maximum and with the condenser focusing knobs bring the diaphragm edges to best focus possible.

This is the most difficult part of the process. Therefore, it would be best to follow these upcoming instructions to get better results.

Bring the condenser down, closer to the sample.

If the intensity of light has changed, then play with the condenser’s focusing knobs until you find a bright spot.

If the intensity of the light has not changed, close the diaphragm a little more until the view gets dimmer. Then play with the condenser’s focusing knobs until you find a bright spot.

Repeat the process until the image of the edge of the diaphragm is best focused.

  1. Center the image with the edges of the field diaphragm within the FOV.
  2. When it is centered, open the field diaphragm until its edge is outside the field.
  3. To reduce glare adjust the condenser diaphragm.
    • Steve Koch 22:16, 1 December 2010 (EST): These are great notes! For this last item, do you mean "field diaphragm" by "condenser diaphragm? There is also an iris behind the condenser (I usually called it the "condenser iris", not sure its official name). That iris is used to adjust the numerical aperture of the illuminating light. It can sometimes help with contrast, but reducing its size reduces the resolution.


This is a very tedious process. It requires a lot of practice and tolerance. So be patient.