Exposure
ISO, Aperture, and Shutter Speed Explained
In photography, exposure is a critical element that determines what is actually recorded on a camera's image sensor. There are three adjustable elements that control the exposure - ISO, Aperture, and Shutter Speed.
ISO Speed is how sensitive your camera’s sensor is to light, each value of the rating represents a “stop” of light, and each incremental ISO number (up or down) represents a doubling or halving of the sensor’s sensitivity to light.
Aperture controls the lens’ diaphragm, which controls the amount of light traveling through the lens to the film plane. The aperture setting is indicated by the f-number, whereas each f-number represents a “stop” of light.
Shutter Speed indicates the speed in which the curtain opens then closes. This is essentially how long light is permitted to hit your camera’s sensor once you hit the shutter-release button. Each shutter speed value also represents a “stop” of light. The shutter speed is measured in fractions of a second.
When these three elements are combined, they represent a given exposure value (EV) for a given setting.
Any change in any one of the three elements will have a measurable and specific impact on how the remaining two elements react to expose the film frame or image sensor and how the image ultimately looks.
For example, if you increase the f-stop, you decrease the size of the lens’ diaphragm thus reducing the amount of light hitting the image sensor, but also increasing the DOF (depth of field) in the final image.
Reducing the shutter speed affects how motion is captured, in that this can cause the background or subject to become blurry. However, reducing shutter speed (keeping the shutter open longer) also increases the amount of light hitting the image sensor, so everything is brighter.
Increasing the ISO, allows for shooting in lower light situations, but you increase the amount of digital noise inherent in the photo. It is impossible to make an independent change in one of the elements and not obtain an opposite effect in how the other elements affect the image, and ultimately change the EV.
