It can be a challenge to form an artefact-free, high contrast image which faithfully reproduces the colour of your sample, with a microscope. The most critical step in forming such an image is properly aligning the condenser of your microscope.
This video shows how to align an Abbe-style condenser to produce Kholer illumination – an illumination pattern which limits artefacts and enhances the contrast and colour of your sample. This video demonstrates this procedure and explains the basic physics achieved by Kholer illumination. A much more detailed description of the goal, physics and outcome of Kholer illumination can be found over at Microcourses.