Final answer:
The fine focus control is used to focus the image when using the high-power objective (45x) on a compound microscope.
Step-by-step explanation:
When using the high-power objective (45x), the fine focus control is used to focus the image. The fine focus control allows for small-scale movements and is especially useful with high magnification objectives like the 45x. The coarse focus control is used for large-scale movements with lower magnification objectives.