Questions: Which focus knob should be used at the 10X objective and above?

The answer is the fine focus knob.

Explanation:

• The fine focus knob is used for precise focusing adjustments, especially when using higher magnification objectives like the 10X and above. It allows for small, incremental changes to the focus, which is necessary to achieve a clear image at higher magnifications.
• The coarse focus knob, on the other hand, is typically used for initial focusing at lower magnifications (such as 4X or 10X) because it moves the stage or objective lens more significantly. However, at higher magnifications, using the coarse focus knob can result in overshooting the focus point, making it difficult to achieve a sharp image.

In summary, for objectives at 10X and above, the fine focus knob should be used to ensure precise and clear focusing.