The shutter release is the 'go' button on a camera.
The shutter-release button on a camera is the final act in taking a photograph with an single-lens reflex camera (SLR) or digital single-lens reflex camera (DSLR). After the aperture, shutter speed, ISO and focusing have all been set, that button is the "go" or "record" button of the camera.
Shutter
A camera shutter can be thought of exactly like a window shutter on a house; it is responsible for blocking out or letting in the light. In a DSLR camera, the shutter is a thin sheet that covers the digital sensor that acts as the film of the camera. The photographer is responsible for setting how long the shutter stays up or open with each shot. The greater the shutter speed, the less exposure time; the lower the shutter speed, the greater the exposure, meaning that more light is let in.
Shutter-Release Button
The shutter-release button allows the physical act of taking a photograph. It is the button, usually top right on the camera, that the photographer presses when she is ready to take the shot. When pressed, the shutter is released, that is it is moved out of the way to allow light to enter the camera and produce an image or the photograph on the camera's sensor. The shutter release performs the same function in a film camera, when the button is pressed, the plastic shutter moves out of the way to allow light to enter and expose the film.
Mirror Flip
All SLR and DSLR cameras contain mirrors that allow the photographer to view the framed image in the view finder. Without a mirror, the photographer would have to shoot blindly. The mirror is placed directly in front of the shutter, so it can bounce the image up and out of the viewfinder. As the mirror is in front of the shutter, it must be moved in order for the shutter to open and allow light to enter the camera. When the shutter release button is pressed, the mirror flips upward and out of the way simultaneously with the shutter opening and closing. The mirror flipping along with the shutter opening and closing are what are responsible for the audible "click" noise that occurs upon pressing the shutter release button. Unfortunately, however, as the mirror must "move" it unavoidably causes added movement (blur) to the photograph.
Shutter Speed
The shutter speed (SS) is how the photographer goes about setting the amount of time the shutter is open. The SS is expressed in fractions of seconds: 1/30, 1/25, 1/60, 1/250, 1/8,000. The smaller the fraction (the greater the number on the underside of the fraction bar) the faster the SS. A faster SS means the shutter is open for less time, and, therefore, the likelihood of blur is decreased. On film SLR cameras, the SS is set using the top right dial on the camera body. In a DSLR, the SS is usually set through a thumb dial on the back of the camera body.
Obtaining a Fast SS
A faster SS means less blur, but a faster SS also implies less light is being let in, so in low-light situations, sometimes a fast SS cannot be used. In order to obtain the fastest speed your lighting situation allows for, there are three adjustments you must make to your camera. The first is stopping down your aperture to the widest possible (lowest number), the second is bumping up the film speed ISO to as high as you are comfortable with (the only drawback with a high ISO is that it increases graininess) and the third is steadying your camera with a tripod or resting your body and arms against a wall, table, chair or anything that can add extra grounding for the camera in order to reduce blur.
