Final answer:
The lens located just below the stage, which concentrates light on the specimen, is called the condenser.
Step-by-step explanation:
The condenser is a crucial component in a microscope, positioned beneath the stage to focus and direct light onto the specimen. Its primary function is to gather and concentrate light, creating a well-illuminated field for observation. By adjusting the condenser, users can control the intensity and uniformity of the light, optimizing the visibility of the specimen.
This optical element plays a key role in enhancing the quality of the image produced, making it an essential part of microscopy that contributes to the clarity and precision of observations.