Rotation of the small knob at its tip, raises and lowers the condenser to achieve focus. Swinging Lens D irectly above this at a right angle to the condenser adjusting knob you will find a rod which controls a lens which can be swung in or out of place. Failure to use this lens properly is the most common mistake that most people make. If you fail to use this properly you will not be able to see much, especially when we use thick sections or whole mounts. Aperture Iris Diaphragm F inally, there is a lever which controls the aperture iris.
L ocate all of the controls for the condenser.
It passes through the field iris diaphragm. The size of the field diaphragm is controlled by rotating a knurled ring which is concentric with it. The field diaphragm controls the area of illumination. L ocate the field diaphragm and its knurled ring. To change objectives you rotate the nosepiece, starting with the 4X objective.