Final answer:
It is best to adjust the focus using the coarse focusing knob before using the fine focusing knob because the coarse focusing knob allows for large-scale movements, while the fine focusing knob allows for small-scale movements.
Step-by-step explanation:
It is best to adjust the focus using the coarse focusing knob before using the fine focusing knob because the coarse focusing knob allows for large-scale movements, while the fine focusing knob allows for small-scale movements. By using the coarse focusing knob first, you can quickly bring the image into rough focus, and then use the fine focusing knob to make small adjustments and bring the image into sharp focus.
Example: If you are trying to focus on a specimen under high magnification, using the fine focusing knob directly might cause you to overshoot the focus point due to its sensitivity, which would make it difficult to bring the image into clear focus. However, by using the coarse focusing knob first to get the image close to the focus point, you can then use the fine focusing knob to make precise adjustments and achieve a clear and sharp image.