Köhler

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Proper Köhler illumination is a prerequesite to yield bright, high-contrast pictures. Especially when using DIC you should always take care that your sample is illuminated as good as possible.

Thus, do the following:

  • With the 10x objective, focus your sample. The field iris aperture (the thing over the lamp house that can be opened and closed) should be fully open while focussing.
  • Now close the field iris until you only see a tiny spot of light.
  • With the sample still focussed, move the condensor up and down until the edge of the iris also appears perfectly focussed. (The condensor is the lens system directly beneath the sample tray)
  • Now open the iris just as far that the entire field is illuminated.
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