When things get tricky

We’ve explained that camera exposure systems could adapt to a degree to ‘difficult’ lighting, but that they have no sense of the intrinsic lightness or darkness of specific subjects. But does this really make much difference? Indeed it does. If any of your digital camera shots come out badly exposed, it’s often the intrinsic brightness of the subject that’s caused the problem, not ‘difficult’ lighting, or any error on your part. Just to show you how much difference intrinsic subject brightness does make, we’ve arranged a series of still-life experiments…

The black background and dark subject fooled our camera’s meter. Left to its own devices, it overexposed by 2 EV.

Metering for dark tones/black

We used a black background for this shot of an ornamental elephant, which itself was a mixture of dark red and black. The camera didn’t know any of this, of course. All it could do was measure the amount of light it ‘saw’. Not surprisingly, this wasn’t very much! As a result, the camera increased the exposure. Remember, all it can do is attempt to render the subject as an overall 18% grey tone, because while you and I might realise the elephant and the background are black, the camera doesn’t have the cognitive powers of the human brain. It’s dark, so increase the exposure – that’s the limit of its thinking. The result isn’t too hard to predict: an 18% grey elephant against an 18% grey background.

Watch out for highlights

Our elephant shot reveals something else that’s interesting, too. In the overexposed version, look at the dried flowers in the foreground – they’re actually close to an average 18% grey tone in real life, but because the camera’s increased the exposure, they’ve been almost completely burned out. However, by manually overriding the exposure, and reducing it by 2 EV, we’ve not only restored the elephant and the background to a ‘proper’ black, we’ve restored the correct tones to the dried flowers. The same will apply if you’re photographing black birds with bright beaks, for example; when you’re photographing dark-toned subjects, the camera will often increase the exposure and lose highlight detail in other parts of the scene. The subject’s darkness doesn’t have to be as extreme as that in our example; if you’re shooting dark-toned vegetation, for example, reducing the exposure by between 0.7 EV and 1 EV to preserve the depth of colour and highlight detail is often a good idea.

No adjustment

+0.3 EV

These vegetables are lighter-toned than the average 18% grey looked for by the camera’s meter, so we needed to apply EV compensation to produce a realistic level of brightness.

No adjustment.

+2 EV

Metering for light tones

Unusually dark-toned subjects are not an everyday problem. Light-toned subjects are far more common, and they typically distort the camera’s meter reading to a greater degree. Our still life shot demonstrates this well. The ginger, onions and squash are all fairly light-toned, along with the cloth beneath them, but even so you might expect the camera to expose them correctly without any help. The result, though, is distinctly dull and gloomy. Only by reshooting with +0.3 EV compensation were we able to restore a realistic-looking brightness to the shot. At first you might need to experiment a great deal to find appropriate EV compensation values for light or dark-toned subjects. But with practice, and a growing understanding of your camera’s behaviour, it gets a lot easier to work out when to override the camera, and by how much.If you’re photographing anything white, beware! Your camera’s meter will attempt to reproduce it as a muddy grey, so you need to intervene. This shot required +2 EV exposure compensation to look ‘right’.