what does the fine adjustment knob do on a microscope

The fine adjustment knob on a microscope is used to make small, precise adjustments to the focus of the microscopes objective lens. It is typically used after the coarse adjustment knob has been used to bring the specimen into rough focus. The fine adjustment knob moves the stage or the objective lens a millimeter at a time, allowing for finer details of the specimen to be brought into focus. At higher magnifications, the fine adjustment knob is especially useful for achieving a clear image with higher resolution.