To operate this tutorial, use the mouse cursor to click on the Outside button and reveal internal details about the microscope optical train. Light entering the common main objective is divided into two parallel "bundles" that travel through separate optical trains, one for each eye. The zooming system is equipped with an aperture diaphragm to adjust depth of focus and to improve contrast for observation and photomicrography. Use the Aperture Diaphragm slider to open and close the iris diaphragm and observe how this affects the light beam traveling through the microscope.