The light from the thing that we want to see is magnified with lenses in a microscope and we see a virtual image of that tiny thing. The smallest thing that we can see with a ‘light’ microscope is about 500 nanometers. A nanometer is one-billionth (that’s 1,000,000,000th) of a meter. So the smallest thing that you can see with a light microscope is about 200 times smaller than the width of a hair. Bacteria are about 1000 nanometers in size. The reason we can’t see anything smaller is because these microscopes use light. We don’t think about light as having a size, but visible light is about 500-800 nanometers. To see anything smaller we need a more powerful microscope.
Electron microscopes ‘see’ things using electrons instead of light. Electrons are much smaller than the wavelength of visible light and so much smaller things can be seen with these electron microscopes. The pictures that you get from an electron microscope are black and white because we need visible light to have colors. Sometimes we see electron microscope pictures that have colors. Those colors are added by scientists, like Dennis Kunkel to help point out important things or sometimes because they just look cool.
The world’s most powerful microscopes don’t see things with light or even electrons. They see things by feeling, feeling with a very sharp tip on the end of something that looks like a needle. Sometimes scientists put carbon nanotubes on the end to make them even sharper. A tip so sharp it is only a few atoms wide. A tip so sharp that as it is moved across something it feels its shape. The very powerful microscopes are called atomic force microscopes, because they can see things by the forces between atoms. So with an atomic force microscope you can see things as small as a strand of DNA or even individual atoms. These microscopes use computers to help convert the information from tapping on the sample to make a three-dimensional view of the object. So with the world’s most powerful microscope, scientists have been able to ‘see’ DNA and report that it is a double helix just like Watson and Crick showed over 50 years ago!