Canon is one of the very few manufacturers of digital cameras that makes its own sensors. Their sensors come in three sizes: APS-C, APS-H, and Full Size. Full size refers to the size of standard 35 mm film which has been around for nearly a century.
The figure above shows the dimensions of the sensors along with the crop factor. The crop factor is the comparison of each of the sensors against a full size sensor. The crop factor is an important measure measurement, since it affects the focal length of a lens. For example, a 50 mm lens is equivalent to a 80 mm lens when used on a camera with an APS-C sensor. The same 50 mm lens on an APS-H sensor camera is equivalent to a 65 mm lens.