What holds the eyepiece and objective lens at the correct distance for proper focusing?

In a microscope, the eyepiece and objective lens are held at the correct distance for proper focusing by the body tube or the optical tube assembly. This structure maintains the necessary distance between the lenses to achieve the correct magnification and focus. Additionally, the stage and focusing mechanisms, such as coarse and fine focus knobs, allow for precise adjustments to ensure clarity of the observed specimen.