 The two settings determine the exposure value (EV), a measure of how much light is recorded during the exposure.There is a direct relationship between the exposure times and aperture settings so that if the exposure time is lengthened one step, but the aperture opening is also narrowed one step, the amount of light exposing the film or sensor is the same.In most modern cameras, the amount of light entering the camera is measured using a built-in light meter or exposure meter.