Perhaps most fruitful in the study of cellular organization is the electron microscope, a device employing a beam of electrons rather than light.
The electron microscope requires a vacuum chamber, since electron beams are dissipated by air. A magnified image from the electron beam is visualized on a fluorescent screen and may also be permanently recorded on a photographic plate. The preparation of the specimen for electron microscopy is more tedious and requires even greater care than that for light microscopy.
The utility of an optical instrument such as the microscope can be characterized by its resolution or resolving power. The resolving power represents a measure of the minimum distance by which two closely spaced objects can be clearly elucidated and identified. The resolving power of a light microscope is 0.25mm. By comparison, the resolving power of the human eye is 0.2 mm. The use of electrons permits a resolution (separation of neighboring particles) that is more than 1000 times better than that of the light microscope. Thus, two points that are only 0.2 nm apart can be seen distinctly with the electron microscope.