Features

Picture perfect

20070615 [Computer Shopper]

Exposure modes

Modern cameras have a wealth of exposure modes and options, which at first seems a little odd since they already know the 'perfect' exposures for a wide variety of lighting conditions.

The reason we have this choice is because photography is about more than just getting the right amount of light into the camera. Certain subjects benefit from different combinations of shutter speed and aperture, and of course you might not agree with your camera about the perfect exposure.

The shutter speed and lens aperture can be used to control the exact amount of light entering your camera and striking its sensor. While there's a typical combination, which your camera will suggest for a given situation, it's also possible to achieve the same exposure by increasing one and decreasing the other to compensate. For example, if you doubled the shutter speed and therefore let in half as much light, you could open the aperture to let in twice as much to compensate, or vice versa. You would do this to record certain subjects better or achieve creative effects.

The most popular exposure mode is Automatic, often indicated by a green symbol. This automatically chooses a shutter speed and aperture for the given conditions, but it won't have anything creative in mind; indeed, it often hides a lot of your camera's advanced options. Automatic modes also tend to fire your flash when they think you need it, although you may prefer they didn't.

The next exposure mode is Program, or P for short. Program mode is also fully automatic, with your camera selecting an aperture and shutter. In addition, it will reveal the settings hidden in Auto mode. Program normally also lets you choose when the flash goes off. Consequently, Program mode is like Automatic for discerning photographers, and we'd recommend it for general use.

Better digital compacts and all digital SLRs offer Aperture and Shutter Priority modes, normally labelled A and S respectively, although Canon refers to them as Av and Tv. Aperture Priority lets you choose the aperture and the camera will automatically select a shutter speed to match. Conversely, Shutter Priority lets you choose the shutter speed with the camera selecting an aperture to match. So they're still automatic, but with a little more control.

Most models also offer a Manual exposure mode that lets you choose the shutter speed and aperture, with the camera warning you if it thinks you'll under- or overexpose as a result.

All but the most professional cameras also offer scene presets, which optimise the settings for certain conditions, such as portraits, landscapes or night shots. These are a great way of achieving creative results without delving into the technicalities.

Let there be light: Using exposure compensation

While modern cameras are packed with technology, sometimes they misjudge a scene and under- or overexpose it. Then again, the camera could make a technically perfect exposure, but you'd prefer it to look a little brighter or darker.

Luckily, it's simple to tweak the exposure without worrying about apertures, shutter speeds or metering systems. Virtually every digital camera these days is equipped with exposure-compensation controls, which allow you to make the picture brighter or darker than the camera suggests.

To use exposure compensation, you use a button that is usually labelled with a plus and minus symbol. This should present a scale on your screen from +2 to -2 in units called EV.

A setting of +1 EV will double the brightness, while -1 EV will halve it.

If you're photographing the inside of a room and light streaming through a window is fooling your camera into underexposing the picture, you can experiment with a setting of +1 or even +2 EV. If your subject is very bright - for example, a distant mountain or canyon vista - consider using a setting of -1 EV to darken it.

Minus settings also work very well with sunsets and can render foreground objects into attractive silhouettes. Whatever you do, though, remember to return the scale to 0 afterwards or all your photos will come out too bright or dark.