What does the iris diaphragm adjust?

The iris diaphragm is a crucial component in microscopy that adjusts the diameter of the light cone reaching the specimen. By changing the size of the opening, the diaphragm controls how much light passes through the condenser and onto the slide. This adjustment is vital for optimizing illumination conditions, as it helps to enhance contrast and resolution in the observed image.

When the diaphragm is opened wider, more light enters, which can be beneficial for viewing transparent specimens. Conversely, closing the diaphragm narrows the light cone, allowing for increased contrast and better detail visibility, particularly for thicker or more opaque samples. Thus, its primary function revolves around controlling the amount and angle of light that illuminates the specimen, making it an essential tool for effective microscopy.