Under dark-field examination, the various materials making up the structure of the cell or microorganism

Under dark-field examination, the various materials making up the structure of the cell or microorganism under view cause it to appear to glow and emit its own light. Since fine structures often cannot be seen when they appear in front of a bright background, illuminating them from the side and viewing them on a black background lights them up and provides contrast and super fine resolution when plan achromat oil immersion iris diaphragm objectives are used. The background is black because the direct or transmitted light from the condenser is passing around the objective and not directly into it. Read more