Before you can take great photos, you need to understand the qualities of light and how to read them. Robert Keeley looks at the most fundamental element of photography, the impact of light.
The most
important element in every image you’ll ever make is light – without it, you
can’t make a photograph. Understanding the effect of light on your pictures,
how it works, and how you can make it work for you, is vital to creating better
photos. Arguably it’s the most important element. You must learn to ‘see’ the
light which is available to you in the way a camera’s sensor ‘sees’ it. They
are not the same – most digital camera sensors have much less dynamic range
(that is the ability to record both dark shadows and the brightest highlights)
than our eyes do.
Dynamic range is the range of
light intensities any sensor (or film) can capture at the same time. Within
that dynamic range different exposure latitudes can be captured. For a given
recording medium (a sensor or type of film) exposure latitude is the range of
exposures which will produce an acceptable result – whether the scene is
slightly underexposed or overexposed. What this means is that you really need
to ‘see the light’ when assessing any scene you want to photograph. You need to
try to see the ‘intensity’ of that light and then work out how dark the darkest
shadows are, and how light the brightest spots are, as well as the overall
luminance of the light on your scene. To do that you have to educate your eyes,
and measure.
A series of images illustrating different exposure latitudes within the Dynamic Range of this particular DSLR. Top image: Canon EOS 1D Mk IV, 16-35mm lens @ 35mm, 1/30s @ f/4.5, ISO 200; Middle image: 1/30s @ f/13, ISO 200; Bottom image: 1/30s @ f/14, ISO 200.
MEASURING LIGHT
Before you
can use the available light, your camera needs some system for measuring it. Light
can be measured either via a handheld light meter or more often these days by a
meter built into your camera (which offers a ‘reflected’ light reading – that
is reflected off your subject). Metering is achieved in two ways, either by
measuring the amount of light falling on to a scene (an incident reading via a
handheld meter) or the amount of light reflected off a scene (the previously
mentioned reflected reading). But in-camera metering - which almost all enthusiasts
and amateurs rely upon - can be tricked because it relies on reflected light
readings. Scenes which are too bright (a snowman on a field of snow on a sunny
day) or too dark (a black dog in an unlit alleyway at night) will fool the
camera into trying to balance that scene out to give a ‘correct’ exposure for
an 18 percent grey card – the mid-point between the lightest and darkest areas
which can be captured.
The result in either of the above examples will be an
image which doesn’t show the colours and tones as you see them. Your camera
works out its metering based on the focal length and the metering pattern being
used (which may include spot, partial, centre-weighted or matrix, and these all
put more value on the light measured in certain parts of the scene). But the
photographer can override the camera’s suggested meter reading using exposure compensation,
and sometimes you’ll want to do this to achieve a certain creative impact.
Using the examples above, for instance, the snowman in the snowfield will probably
require at least +1 exposure compensation to counteract the camera’s suggested
exposure setting, and the black dog in the unlit alley will need at least -1
exposure compensation, because in both cases the camera will be trying to
automatically set the correct exposure for an 18 percent grey card.
So the
metering of the ‘snowman’ scene will be measured as extremely bright, and the
metering system will subsequently try to underexpose the scene (and thus need
to be counteracted), while the black dog in the alleyway scene will be metered
as dark, setting the camera towards overexposure (which will also need to be
counteracted). You will need to override these metering effects to get an image
as you see it (assuming that’s what you’re after!).
A handy rule of thumb is to
open up a stop for bright white subjects (though sometimes in really bright
snow it will still pay to underexpose slightly after that to reveal some
surface detail), and then close down a stop for darker or black subjects. Your
selection of a metering pattern (spot, partial, centre-weighted or matrix) and
how it will measure the light can also affect how your camera will set its
exposure if you’re using any semi-automated mode.
A typical midday scene where a range of shadows and highlights makes creating a successful image very difficult. Where possible it would be worth shooting this scene early in the morning or late in the afternoon, depending on where shadows may fall at each of those times. EOS 1D Mk IV, 16-35mm lens @ 16mm, 1/200s @ f/5.6, ISO 200.
In part two of this series, we look at the impact of colour
temperature, and how to use natural light to best effect in creating your
images. Click here.
In the final part of this series, we look at special
lighting situations, including how to use 'window light' and night shooting. Click here.