The transmission electron microscope works much like a light microscope--even looks like one if you stand the LM on its head. The biggest difference is the source of illumination: the light microscope uses a beam of light, the electron microscope uses a beam of electrons, to illuminate the sample. Because the wavelength of electrons is so much smaller than the wavelength of visible light, we can observe much smaller objects in the transmission electron microscope. In the TEM, the resolution is limited by the illuminating wavelength and the quality of the image forming and magnifying lenses. In the LM, light is focused and images are magnified by glass lenses--if you want a larger image, you must switch from a weaker objective lens to a stronger objective lens. In the electron microscope, the lenses are electromagnetic and by changing the electric current to the lenses, it is possible to change the strength of the lens and thereby change the magnification of the image. In operation, a beam of electrons is focused to a large spot and transmitted through a thin, stained slice of sample. The stained section differentially absorbs or scatters the transmitted electrons, forming an image of light and dark areas. This image of the slice is then magnified thousands of times by powerful electromagnetic lenses and projected on a small viewing screen. The operator, sitting in the dark, observes the image on the low resolution viewing screen though binocular eyepieces. The screen can be lifted out of the way and a high resolution image recorded on photographic film.