Almost every camera has a shutter, the mechanism that controls how long light hits the sensor, but not all shutters work the same way. Among mechanical shutters, there are two main designs, the leaf shutter and the focal plane shutter, and the difference between them is not trivia. It determines how fast you can sync a flash, how quiet your camera is, how big and expensive your lenses get, and which kind of photography each system is best suited to. If you have ever wondered why a small fixed-lens camera can do something your big mirrorless body cannot, the shutter is often the reason. There are electronic shutter modes too, which we will come to, but the mechanical pair is where the story starts.