This tutorial explores how focus can be varied on thick samples to selectively bring different focal planes into view.

	Interactive Java Tutorial
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The tutorial simulates a differential interference contrast (DIC) microscope viewing samples either with or without a retardation plate. The retardation plate can be inserted by using the radio buttons at the bottom right of the microscope port. To operate the tutorial, use the pull-down menu bar to select a sample, and then adjust the slider to bring various parts of the specimen into focus.