The diaphragm on a microscope is used to regulate the amount of light passing through the specimen. There are different types of diaphragms on a microscope, including the luminous-field diaphragm, aperture diaphragm, field diaphragm, and iris diaphragm. The luminous-field diaphragm determines which portion and size of the specimen is illuminated, while the aperture diaphragm of the condenser regulates the illumination of the pupil of the objective. The field diaphragm controls only the width of the bundle of light rays reaching the condenser. The iris diaphragm is located under the stage and can be adjusted to vary the intensity and size of the cone of light that is projected through the slide. The main function of the iris diaphragm is to control the amount of light that reaches the specimen, which comes from the microscopes light source and is gathered by the condenser before being regulated by the diaphragm. The use of a diaphragm in controlling illumination and thereby regulating the contrast is especially important in intermediate and high magnifications of a specimen under the microscope.