Final answer:
To move the objective lens up and down, you would turn the coarse focusing knob for large adjustments or the fine focusing knob for precise focus, depending on the desired magnification.
Step-by-step explanation:
To move the objective lens up and down on a microscope, you would turn the coarse focusing knob for large-scale movements with lower magnification objectives (like 4x and 10x). For higher magnification objectives (like 40x or 100x), you would use the fine focusing knob to make small-scale adjustments and ensure precise focus. These two mechanisms work together to provide the necessary focusing ability for observing specimens at different magnifications.
The objective lens plays a crucial role in the initial magnification of the specimen, forming a larger image within the focal length of the eyepiece, which further magnifies the image to create what we see through the microscope. The total magnification is the product of the magnifications of both the ocular lens and the objective lens.