what does the diaphragm do on a microscope

The diaphragm on a microscope has different functions depending on its location. The condenser aperture diaphragm controls the angle of the illuminating light cone and the numerical aperture of the microscope. The field diaphragm controls how much light enters the substage condenser and, consequently, the rest of the microscope. The iris diaphragm controls the amount of light that reaches the specimen, while the disc diaphragm varies both the intensity and size of the cone of light that is projected upward into the prepared slide. In summary, the diaphragm on a microscope regulates the amount of light passing through the specimen, controls the angle and numerical aperture of the microscope, and varies the intensity and size of the cone of light that is projected upward into the prepared slide.