The darkfield condenser is used for the darkfield microscopy technique. Darkfield microscopy is used for studying unstained transparent samples. Such samples absorb light weakly and, therefore, they are indistinguishable when observed using the brightfield microscopy technique.
The N.A. of the darkfield condenser must exceed the N.A. of the objective and, therefore, the condenser works with dry objectives with magnifications ranging from 4x to 60x with apertures less than 0.9.
The darkfield condenser is mounted in the arm instead of the Abbe condenser.
In order to get a contrast image of the sample using the darkfield microscopy technique, it is recommended to use a cover glass 0.17mm thick and a slide 1-1.2mm thick.