A composite microscope is an optical instrument composed essentially of a tube bounded at its ends by converging spherical lenses, forming an association of separate lenses.
The lens closest to the observed object is called objective, and is a lens with focal length in the order of millimeters. The lens next to the viewer is called eyepiece, and is a lens with focal length in the order of centimeters.
The operation of a compound misoscope is quite simple. The lens provides a true, inverted image larger than the subject. This image acts as an object for the eyepiece, which acts as a magnifying glass, providing a larger, direct virtual final image.
That is, the object is enlarged twice, making very small objects better observed.
This compound microscope is also called Optical Microscope being able to enlarge up to 2,000 times the observed object. There are also Electron Microscopes capable of providing magnifications up to 100,000 times and Scanning Microscopes that produce magnifications greater than 1 million times.