Final answer:
The purpose of the iris diaphragm on a microscope is to regulate light intensity, allowing for better contrast and clarity in the image, especially at higher magnifications.
Step-by-step explanation:
The purpose of the iris diaphragm on a microscope is to regulate light intensity. By adjusting the iris diaphragm, you can control how much light passes through a specimen, which is crucial for achieving the desired contrast and clarity in the microscope's image. When you increase the magnification, the amount of light per unit area of image decreases, making the image dimmer. To counteract this, you may need more intense lighting. This can be achieved by adjusting the light intensity of the illuminator or by manipulating the iris diaphragm to allow more or less light through. It's important to experiment with these adjustments to create the best possible image when using various objective lenses and magnifications.