Camera diaphragm
A camera is made up of many different elements that all work simultaneously together to produce photos. Whether a digital or film camera, most of the camera components are the same. There are a few key elements of a camera that are essential to proper exposure and perfect photos: shutter speed, ISO and aperture.
Definition of Aperture
Aperture is essentially the amount of light allowed in to expose either the film or the image sensor. This is controlled by a part of the camera call the diaphragm. The opening in the diaphragm is called the f-stop. By controlling the collimation or paralleling of light, the diaphragm controls the image sharpness as well (i.e., smaller opening, sharper image). This also allows for some control over image aberrations or the distortion of color.
How Aperture Works
Aperture works in one of two separate ways, depending on the type of camera and lens being used. The basic workings although are the same for both methods. Similar to the iris in an eye, the diaphragm opens and closes, making either a large opening or a small opening to allow incoming light to be collimated. With manual focus lenses this is done by adjusting the aperture ring on the lenses, while in most digital cameras this is done using the aperture wheel on the camera body.
F-Stops
The term f-stop is derived from a mathematical calculation. The focal length over the diameter of the diaphragm's opening is equal to the aperture (N = f/d). This is were the f-stop or f-number is drawn from. These numbers are typically represented by "f" over the diameter (i.e., f/2, f/4, f/8) in digital cameras and by the aperture number (N) in manual focus lenses (i.e., 22, 16, 11). A larger f-number, or larger aperture number, represents a smaller opening (i.e., f/2 is larger the f/8, and 11 is larger the 16).
Exposures
The two main functions for determining a good exposure are the shutter speed (in fractions of a second) and aperture (in f-stops). These two elements will make a greater difference in image quality then any other. Typically these two elements are dependent on each other. When increasing the f-stop, the shutter speed needs to be reduced and vice versa (i.e., switching from f/8, with a shutter speed of 125, to f/4, the shutter speed needs to be increased to 500).
Auto Aperture
Although aperture once was done mostly manually by an aperture ring that controlled the diaphragm on the lens in film photography, the progression of technology has allowed many changes. Most notable are the aperture priority and auto modes that have become popular with digital cameras. In these modes, the camera's computer-operated sensors adjust the diaphragm according to the best specifications as it sees fit. Although this is useful, real control over an image and its quality are still maintained through manual setup.
