A camera is basically a light tight box, and in order to expose an image, there must be a way of letting in a controlled amount of light.
An aperture is simply a hole that lets in light.
Adjusting the size of the aperture controls the amount of light that enters the camera during exposure.
The size of the aperture opening is measured in f-stops.
Starting with f/1.0 we have a series of numbers that represent full stops.
Auto exposure controls the amount of light that is used to expose the camera’s image sensor. It does this by adjusting the aperture and the shutter speed.
Proper exposure is basically determined by averaging the amount of light needed to produce an image with good highlights, middle tones, and shadows.
The camera has a built in light meter that evaluates the total amount of light reflected from the subject. It then averages this light and sets the correct exposure.
Digital cameras can have more than one type of metering system however. So it is important to learn how your particular camera meter measures light as well as any options to change the way it does this.
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