Exposure is the amount of light that is allowed to the image sensor while taking a photo. Exposure can be computed from exposure value (EV).

The 3 main aspects that determines the exposure are

• Apperture
• Shutter speed
• Film sensitivity or sensor sensitivity

Aperture

An aperture is an opening in a lens that limits the amount of light passing through it to the camera body. The term aperture is also often used to describe the diameter of that opening. It is usually adjustable, most often by turning an “aperture ring” on the outside of the lens body

The image above shows the different measures of lens opening for different apertures.

This image is a pictorial presentation of what actually happens when the aperture is increased and decreased. The amount of light let into the camera is more when the aperture opening is more and less when aperature opening is less.

The lens aperture is usually specified as an f-number, the ratio of focal length to effective aperture diameter.A lens typically has a set of marked “f-stops” that the f-number can be set to. A lower f-number denotes a greater aperture opening which allows more light to reach the film or image sensor (The f-number and the aperture opening are inversely proportional). The specifications for a given lens typically include the minimum and maximum apertures. These refer to the maximum and minimum f-numbers the lens can be set respectively.

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