How Digital Cameras Work: The Shutter
One of the key elements that allow a camera to work is the shutter. This element serves one of the most basic functions of the entire camera. The shutter allows light passed through the lens to expose the image sensor (or film). The shutter is located on the actual camera body or in the lens assembly. Shutters usually follow two designs, a focal plane shutter or leaf shutter. The focal plane shutter is designed to have two covers that open horizontally or vertically, while the leaf shutter is designed to open in a spiral function.
Parts of the Shutter
The shutter is comprised of a two main parts. The first main part of the shutter is the curtain, typically made of metal or plastic. The curtain is the part of the shutter that closes and opens to either prevent or allow light to pass through. The focal-plane shutter is the most common when dealing with SLR cameras. This type of shutter has two curtains that will open and close exposing the image sensor. The other and less common type of shutter is the leaf shutter, which is compromised of several curtains that close together in unison.
The second main component of the shutter is the driving device. This is the component of the shutter that actually manipulates the curtain of the shutter. The driving device not only opens and closes the shutter, but also syncs the shutter with the rest of the camera. This is what changes the speed that your shutter opens at, and aids in syncing your shutter to your flash.
How the Shutter Works
The shutter is one of the least complicated components in a camera, but still one of the most crucial. The basic function of the shutter is to allow light to expose the image sensor. The manner in which this is done is pretty simple.
Once light passes through the lens it reaches the shutter. The shutter will open for a brief period of time, depending on your shutter speed. During this brief opening the light is allowed to pass through and expose the image sensor (or film). In a DSLR camera the shutter will open either vertically or horizontally usually, but not fully. DSLR cameras typically have a shutter that will open fully from one side and close from an opposite side. For example if your camera has a horizontal shutter the shutter will typically open from the bottom by dropping the shutter down, and close from the top after the shutter speed has been reached.
The length of time your shutter stays open is the shutter speed. The speed of the shutter is typically derived in fractions of a second (1/100, 1/200, 1/800). An additional function of the shutter in most SLR style cameras is the bulb function. This is a special shutter speed that has no time limit. With the bulb function as long as you hold down the capture button the shutter will stay open until you release it.