Coarse and fine focus control
The focus controls occur on
each side of the microscope stand. The inner knurled knob is the fine
focus control, the
outer one is the coarse focus control. The outer ring has a white
reference line on it (the arrow points to the line) and the inner ring, is
graduated from 0 to 350, and approximates to microns (m).
This can be used to
gauge the approximate thickness of your section.
Get into the habit of focusing through the specimen, that you are examining, and also of adjusting the aperture of the condenser lens as well, as both will enable you to establish a good focal plane.