This tutorial explores how the substage condenser diaphragm controls the numerical aperture of the light cone that illuminates the objective.

	Interactive Java Tutorial
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To operate the tutorial, simply move the slider up or down to change numerical aperture (this moves in a pre-determined set of steps). Note that changes in the condenser aperture diaphragm size result in modification of the size and angle of the illuminating light cone. This controls the numerical aperture of the microscope and regulates the quantity of light that enters the objective front lens.