A microscope is an instrument that produces an enlarged image of an object. Biologists use microscopes to study things that are too small to be seen with the unaided eye. Most microscopes are called light microscopes because they accomplish their task by using lenses to bend light rays. Resolution allows the viewer to see two objects that are very close together as two objects rather than as one.
Compound microscopes use multiple lenses to produce an increase in magnification.
A rotating head that has the objective lenses attached to it. This adjustment is used to make large adjustments in focusing by moving the lenses up and down. Never use this adjustment when using the 40X objective. This adjustment is used to make small adjustments in focusing. It has a limited amount of movement and is most efficiently used after focusing with the 4X objective and coarse focus, then increasing magnification and making final adjustments with the fine focus knob.