***To get the most out of this tutorial you really need a camera that allows at least some manual control over exposure. Ideally it should have spot metering and manual control of both aperture and shutter speed settings, but at a push any camera with a lightmeter and exposure compensation will do.***
Correct exposure is essential to successful photography, and an understanding of exposure and light metering is a core skill for anyone wishing to explore the art of photography.
Most photographers rely almost exclusively on the automatic lightmeter in their camera to produce an accurate exposure, and under most circumstances this is not a problem. The through-the-lens (TTL) multi-segment evaluative lightmeters found on most modern good quality cameras are very sophisticated, and can cope with most situations quite adequately. However even the best meter can be fooled by unusual lighting conditions or very high contrast scenes into producing under- or over-exposed images.
For example, if youâ€™ve ever take a photograph of someone standing in front of a brightly lit window, youâ€™ll probably have found that you can see the pattern on the curtains but that the subject is far too dark. This is because the lightmeter was fooled by the bright light from the window and the shot was under-exposed.
Similarly if youâ€™ve ever taken a photo of something light against a dark background youâ€™ve probably found that the background looked lighter than it should and the main subject was pale and burned out. Again the lightmeter has been confused by the unusual background, but this time the shot is over-exposed.
In order to understand how this happens and accurately correct it, it is necessary to know how lightmeters operate, and the rules by which exposure is calculated. Donâ€™t worry, thereâ€™s no maths involved, and itâ€™s a lot simpler than you might think.