Shutter and Aperture: A Balancing Act
This is a topic that has been explained, illustrated, or diagrammed in every way possible to make it simple. A good explanation certainly helps, but full comprehension of shutter and aperture seems to only come through practice.
This controls how long light is able to enter the camera for. It’s basically a curtain that opens and closes based on the camera settings. When the curtain is open, the camera records an image onto its sensor. So, the longer the curtain is open, the more light enters the camera. The importance in shutter speed comes into play when capturing motion. A slower shutter speed makes moving objects appear blurry, a fast shutter speed freezes subjects in motion.
Measuring Shutter Speed: Fractions of a Second
Shutter speed is measured in fractions of a second. 1/4000th is usually the highest speed on a DSLR, while the slowest is 30 seconds (or unlimited with the ‘bulb’ setting). The slowest speed that one can shoot at without a tripod is about usually 1/60th of a second (more or less depending on skill or environment).
This can best be compared to the pupil of an eye. In a dim room, it opens up to allow in more light. In bright daylight, it contracts. On the camera this is measured in ‘F-Stops.’
Depth of Field
Aperture also determines depth of field, which is the range where the lens sees objects in focus. The smaller the hole is, the bigger the range of focus. A large hole makes the focus range smaller.
Making the hole larger will decrease the range of vision, making it smaller will increase it.
Measuring Aperture: F-Stops
This is where everybody gets tipped up. The method of measuring aperture seems to defy common logic. The size of the hole (aperture) is measured in F-stops, and the higher the F-stop is, the smaller the hole (F-16). A low F-stop indicates a larger hole (F-2.8).
The Balancing Act
Simply put, shutter speed is used to create blur or a sense of motion in pictures, while aperture controls the range of focus.
When shooting on manual mode, a photographer has to strike the perfect balance between both shutter and aperture to create a properly exposed image, as well as one that conveys the desired effect.
Since this concept is usually hard for newbies to grasp, here’s link to a couple of graphics that explain it in a better form than I can.