Which focus knob should be used when using higher power lenses?

When using higher power lenses, the fine focus knob should be used. Higher power lenses have a narrower field of view, making precise focusing crucial. The fine focus knob allows for small adjustments that help achieve a clear image without overshooting the focus. It is important to avoid using the coarse focus knob at high magnifications, as it can lead to potential damage to the slide or lens.