Sophisticated modern technology has
brought us cameras that are capable of making technical decisions about
photography completely unaided. Gently press the shutter release of an
autofocus SLR, and the landscape snaps into sharp focus in the
viewfinder. Press harder and the camera assesses light levels, focal
length and perhaps even subject contrast before setting the aperture
and shutter speed and taking the picture. The result is technically
perfect: correctly exposed and needle-sharp.
But let's take a closer look at what we
mean by "technically perfect". Cameras are designed to cope best with
average scenes: those that are an approximately equal mix of dark and
light areas, with the most important subject in the middle of the
frame. If you point the camera at a scene that's widely different from
this rather arbitrary "average", you may not be so happy with the
For example, even simple cameras can cope
adequately with a riverside landscape that features trees, pale rocks
and water in roughly equal proportions. The brightness of the rocks
compensates for the dark trees and, taken overall, the scene conforms
to our hypothetical "average". A ploughed field fringed with yew trees
presents a different problem, though. The whole of the subject is dark,
and reflects perhaps only a third as much light as the average scene.
Even the most advanced camera has no way of knowing this, and will
blindly set what it thinks is the "correct" exposure. In practice this
is the exposure which will produce an average print or transparency.
Unless you intervene and actively control the camera, all parts of the
picture will turn out to be too light. In this example, you will wish
to set the camera manually in order to take a picture that more closely
resembles the original landscape. But often you'll want instead to use
photographic controls to create an image that expresses how you felt
about the landscape. There's no way to literally capture searing heat
in a picture, but by slightly overexposing a desert scene, you can at
least suggest the blinding glare and soaring mercury of an equatorial
To really get a feel for how each of
these controls affects the image, you need to go out and take pictures.
To avoid confusing the effects of several different factors, you may
find it helpful to take several pictures of the same scene, changing
just one control at a time. After all, it just takes some clicks.