Once you know the bits and pieces of your digital camera, you're ready to move into a bold new territory. Automatic mode? Out the window. Let the camera do the work for you? Forget it. We're going fully manual — welcome to the world of exposure.
What is exposure?
You've probably come across the terminology "obtaining a correct exposure" in your photographic travels. Exposure is the measure of light that reaches the image sensor in order to capture an image. There are three main elements that determine how either a camera (in automatic modes) or a photographer (in manual modes) determines exposure.
Exposure is made up of three elements, working together. (Credit: CBSi)
Back in the old days of film, each roll would have an ASA or ISO rating, which meant how fast or how sensitive to light it was. Digital cameras work on the same principle, but this time, replace film with the image sensor. ISO is the sensitivity level, so an ISO of 100 is relatively slow, and an ISO of 400 and above is considered fast.
You would use a "slow" ISO when there is a lot of light so the image sensor is less sensitive, and a "fast" ISO when there is less light and it is difficult to get a decent exposure without introducing camera shake into your images.
Think of aperture like the pupil in your eye. Aperture is a measure of how much light is let into the camera through the lens. Like your pupil, the lens can open up (widen its aperture) to let more light in, or close down (narrow its aperture) to let less light in. Aperture is measured in f/ stops and affects depth of field.
Using a wide aperture (small f/ stop) will produce an image with a blurred background and sharp foreground, or area of focus, and a small aperture (large f/ stop) will produce an image with sharpness across more of the image. This will be explained further when we discuss depth of field.
The lens on the left is stopped down to f/22 (letting in the least amount of light), in the middle is f/8, and on the right, f/2.8. (Credit: CBSi)
The length of time the shutter is open, measured in fractions of a second. A fast shutter speed will let in less light than a slower shutter speed. For example, a shutter speed of 1/60 will let in more light than a shutter speed of 1/125.
In the following sequence, each shutter speed lets in half the amount of light than the one that came before.
1/8, 1/15, 1/30, 1/60, 1/125, 1/250, 1/500
The same principle applies for aperture, but when you change the measure it's called "stopping up" or "stopping down", or just a stop.
f/2.8, f/4, f/5.6, f/8, f/11/, f/16, f/22
The same exposure can be reached through a combination of apertures and shutter speeds. For example, an exposure of f/8 at 1/125 is equivalent to f/5.6 at f/250.