Getting the correct amount of light onto the sensor (or film!) is an essential aspect of photography. It is controlled by the aperture of the lens, the sensitivity setting of the sensor, the shutter speed. Adjust each of these will adjust the exposure and it is a trade-off between all the settings. Each of these settings has other effects as well that need to be considered.
- Presentation seen 4th February 2016 from Roger Crocombe ARPS, “Exposure Matters” [pdf]