This tutorial explores how a changes in the size of the opaque stop in a simple Abbe darkfield illumination condenser affects light cone shape and numerical aperture.

	Interactive Java Tutorial
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To operate the tutorial, move the slider to effect a change in the size of the opaque stop. The default size is a stop that produces a numerical aperture of 0.4, intended for use with a 10x objective. As the size of the opaque stop is changed, the numerical aperture of the hollow light cone also changes to produce a new light cone of different numerical aperture. The condenser numerical aperture is given for each light cone along with the suggested objective magnification.