While using microscopes, one need to take many precautions.
To view any slide on higher resolution, all the focal adjustments should be done with scanning lens. After adjusting the focus with the scanning lens, turn the lens knob to higher resolution. Make sure, you move the lens in such a way that it does not break the slide.
in case, the view of the slide is not clear, then use fine adjustments only. On higher power lens, do not try to adjust focus adjustment knob, as it can break the slide. Before keeping the slide on a microscope, make sure all lenses are clean and the platform is also clean.