The primary purpose of a microscope condenser is to control and direct the illumination of the specimen. It plays a crucial role in:  

l Focusing Light: The condenser gathers and focuses light from the light source onto the specimen. This concentrated light is essential for achieving high-resolution images.  

l Controlling Light Intensity: The condenser incorporates an aperture diaphragm that regulates the amount of light reaching the specimen. This allows the user to adjust the intensity and contrast of the image.  

l Enabling Koehler Illumination: Many condensers are designed to enable Koehler illumination, a technique that ensures even and uniform illumination across the field of view.

There is a guide about How to Adjust the Condenser for the Microscope you might also want to get.