Resolution depends on the wavelength and numerical aperture. Light microscopes work through bending light. In a compound light microscope, two or more sets of glass lenses bend incoming rays to form an enlarge image of a cell or specimen. It helps if the cell parts differ in color and density and in many cases stains are used. Transmission Electron microscope is based on accelerating the flow of streams of electrons that have wavelengths of about 0.005 manometer that is about 100,000 times shorter than visible light.
Electrons are particles, but they behave like waves.
Electrons cannot pass through glass lenses, but they can be bent from their paths and focused by a magnetic field. In a transmission electron microscope, such a field is the lens. Scanning Electron Microscope has a narrow beam of electrons that moves back and forth across a specimen thinly coated with metal. The metal responds by emitting some of its own electrons. A detector connected to electronic circuitry transforms the electron energy into an image of the specimen on a screen.