Laboratory microscopes are devices designed to magnify a small area of an object or image in order to see features that are otherwise too small to be seen. Traditional optical microscopes are lens assemblies typically featuring an (often interchangeable) objective lens that focuses light from an object to form an image inside the microscope and a second arrangement of
lenses known as an eyepiece, which refocuses the light to create a larger, inverted image beyond the eyepiece. Electron microscopes (both Travelling - TEM and Scanning - SEM) and X-ray microscopes work on similar principles to optical microscopes, except that they use high energy electrons focussed by electrostatic and electromagnetic lenses rather than photons focussed by glass lenses. Another class of laboratory microscopes is scanning probes, which are passed over the surface of a sample, interacting with different parts of a surface. Examples include scanning acoustic microscopes that use sound waves to measure changes in acoustic impedance (similar to sonar) and scanning tunnelling microscopes that provide highly accurate measurements of object surfaces by exploiting the exponential reduction in quantum tunnelling rates with distance from a surface.