Many a vacationer has relied on the Auto Mode; and many a professional has relied on the light meter of their camera. One must understand that light tends to be moody, and can deceive the photographer’s equipment. Just like a navigator needs to know how much, how long and how fast to navigate his or her ship in order to safely reach their destination, a good photographer also needs to know how to guide the available light through the aperture and shutter of their camera before letting it reach the film or digital sensor.
Understanding exposure is not rocket-science. Too much light passing through the lens will give your picture a flat look. On the other hand, less light will give you dark pictures. If you don’t believe it let’s see how easy it is.
When it comes to understanding exposure, there are three factors that one must understand, especially while using an SLR camera: How much, how long and how fast?
How much? Exposure is a measure of how much light falls on your film or digital sensor. This depends on the aperture size and the shutter speed in combination. An aperture is nothing but an adjustable hole through which light passes through your camera; and a shutter is a flap that opens and closes. If the aperture size is small a slower shutter speed must be used and if the aperture size is big, a faster shutter speed must be used. Aperture size is measured by the f-factor or the f-number. A smaller f-factor (f-1.8) means that the aperture opens wider, allowing more light and a bigger f-factor(f-22) means that the aperture size is very small, allowing less light to pass through it.
How long? The shutter speed is a measure of how long the shutter stays open to allow light through it. Shutter speed is measured in fractions of a second. For example, 1/30 means a slow shutter speed, allowing light to pass through for a longer time, and 1/400 means a faster shutter speed, allowing light to pass through for a shorter time.
How fast? Your film speed is an important factor in understanding exposure. The ISO setting tells you how sensitive your film is to light. A 100 ISO film is best for outdoor shots in bright sunlight whereas a 1600 ISO film is very sensitive and is best for darker environments. By adjusting the ISO settings on your digital camera you can adjust your sensor’s sensitivity to light. A faster ISO means a faster shutter speed and a shorter exposure.
While understanding exposure, we must also try to understand how the aperture size, shutter speed and the ISO speed affect other factors.
Another function of the aperture size is the depth of field (dof). An aperture size of 1.8 (bigger) will give a shallow depth of field. This means that the camera is focused on a limited area and you may not be able to see the background. An aperture size of 22 (smaller) will give a large depth of field, bringing the surrounding area into focus.
A slow shutter speed may help you expose your film long enough in dark light conditions, but just a little jerk can give you blurry pictures. Some photographers deliberately use a slow shutter speed in order to capture action like that of a moving car or a waterfall. In order to avoid the blur while photographing moving objects you will need to increase the shutter speed.
Photography is an art, and understanding exposure can make an artist out of you.