Final answer:
The condenser in a phase-contrast microscope is located just below the stage and is essential for focusing light on the specimen and adjusting contrast. An annular stop in the condenser creates a hollow cone of light that, together with the phase plate in the objective lens, allows for visualization of live, unstained specimens with enhanced contrast.
Step-by-step explanation:
If your microscope has phase-contrast optics, the condenser is housed just below the stage. Light from an illuminator is focused on the object by the condenser lens, which is adjustable with the condenser adjustment knob. In phase-contrast microscopes, an annular stop within the condenser creates a hollow cone of light that is focused on the specimen before it reaches the objective lens.
This setup, including the phase plate in the objective, allows for the visualization of live, unstained specimens with significant contrast due to the manipulation of light wave phases.
For optimal imaging, the condenser is raised or lowered depending on the objective lens used. The appropriate use of the condenser and the iris diaphragm helps in creating a perfect image with the desired contrast.
As such, it is critical to position the condenser correctly to maximize the effectiveness of the phase-contrast microscopy technique, especially for specimens examined at higher magnifications.