Exposure
The exposure (brightness) of photographs is determined by the amount of light that falls on the image sensor (CCD) while the shutter is open. Two factors that determine exposure are shutter speed and aperture.
Aperture refers to the size of the opening through which the light passes. The larger the aperture, the greater the amount of light that passes through the opening and the brighter the exposure. Smaller apertures mean less light and darker exposures. The camera displays show aperture in
Shutter speed determines how long the shutter is open. The slower the shutter speed, the longer the image sensor is exposed to light and the brighter the exposure. Faster shutter speeds mean that the image sensor is exposed to light for less time, producing darker exposures.
The relationship between shutter speed and aperture can be likened to filling a cup from a tap. In this analogy, the amount of water needed to fill the cup is the amount of light needed for optimal exposure. If the cup overflows, the picture will be overexposed. If the cup doesn’t fill, the picture will be underexposed. The amount the tap is opened is the aperture, and the length of time the tap is opened the shutter speed. Open up the tap and the cup will fill in less time; tighten the tap and more time will be needed to fill the cup.
Just as a cup can be filled in different times using different tap settings, different combinations of shutter speed and aperture can be used to produce the same exposure. The results, however, will be very different: fast shutter speeds and larger apertures freeze moving objects and soften background details, while slow shutter speeds and small apertures blur moving objects and bring out background details.
Fast shutter speed (/ s) | Slow shutter speed (1 s) |
Small aperture (f/36)Large aperture (f/3)
(Remember, the larger the
smaller the aperture.)