Focusing Knobs
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The focusing knobs are the set of two large knobs at the left. The knob on the right is the condenser height adjustment knob. In this view of the other side of the microscope, the focusing knobs are on the right. The long, silver knobs on the left are the stage adjustment knobs.
At left is the set of two focusing knobs close-up. Always start with the stage set at its lowest point. Put the slide in place using, the slide clips on the stage, swing the revolving nosepiece around so that the lowest power lens is over the slide, look through the ocular lens(es) and begin to raise the stage slowly, using the outer, or coarse, focusing knob. Once the specimen is fairly clear, use the inner, or fine, focusing knob to further adjust the focus.

On a parfocal microscope, you may only have to adjust the fine focus when switching between objective lenses.