The Exposure Triangle
There are three main elements that need to be taken into consideration when looking for correct exposure. The three elements that make up the exposure triangle are ISO, Aperture and Shutter Speed. They relate to light and how it enters and interacts with the camera.
ISO stands for International Organisation for Standardisation. In digital photography it measures the sensitivity of the image sensor. The lower the ISO number the less sensitive the camera is to light. The higher the ISO the more grain you will have in your image, the lower the number the less sensitive your camera is to light and the finer the grain. A high ISO will allow you to make your picture brighter but a low ISO will give you a sharp and crisp image with little or no grain.
Aperture is the size of the opening in the lens when a picture is taken. The aperture that you set impacts the size of that hole. The larger the hole the more light that gets in – the smaller the hole the less light. It is measured in f/stops and will affect how much light your image is exposed to. A wide Aperture like f/2 will let in lots of light and give a shallow depth of field. A narrow aperture like f/22 will let in less light but keep everything in focus.
Shutter Speed relates to the amount of time that the shutter is open. Shutter speed is measured in seconds and fractions of seconds. The bigger the denominator the faster the speed so a shutter speed on 1/2000 is faster than 1/125. A fast shutter speed will freeze action and a low shutter speed with create motion blur. When taking portraits it is best to keep your shutter speed at at least 1/125th of a second to ensure an image without motion blur.