The field diaphragm controls how much light enters the substage condenser and, consequently, the rest of the microscope. Instructions about how to use this tutorial appear below the window.
To operate the tutorial, use your mouse cursor to drag the slider to open and close the field diaphragm. The image of a deer tick in the viewfield will react to the diaphragm settings. As the diaphragm is closed, the unfocused image of the diaphragm closes down on the deer tick in the viewfield. When completely closed, the diaphragm does not allow any light to enter the microscope.