Starting in the 17th century, light microscopes, which use a set of lenses to magnify tiny objects, have been an important scientific tool for studying crystals, bacteria, forensic evidence and many other things too small for the naked eye. In the 20th century, technology created the electronic microscope, which could enlarge things more than a light microscope would ever be able to.
How They Illuminate an Object
In a light microscope, a beam from a light source hits a condenser lens which focuses the light on whatever object has been placed under the microscope. With an electron microscope, a filament generates a stream of electrons which are channelled through metal apertures and magnetic lenses to strike the target.
How You See The Object
With a light microscope, light glancing off or passing through the object is magnified by a series of curved lenses. With a transmission electron microscope, the electrons strike and interact with the object, then the microscope transmits the results to a phosphor screen to create a visible image. With a scanning electron microscope, instruments in the microscope detect the interactions as the beam scans the object, then build up a picture out of pixels on a cathode-ray tube.
What They Can Do
A light microscope can magnify objects under the lens by up to 1,000 times. The beam of an electron microscope can magnify objects up to 10,000 times. The electron microscope was developed because 1,000x magnification wasn't enough to study the fine details of cellular structures such as the nucleus.
Good light microscopes can cost £65 or more. Even used electron microscopes cost thousands of dollars, and new ones can run well over £65,000.