Modern cameras have accurate and reliable exposure systems. They judge light levels well and produce nice, punchy shots under a wide variety of conditions. But they are not perfect, and a few simple steps can quickly increase your “hit rate” for well-exposed pictures. Despite advances in technology, there are situations that remain a challenge to automatic exposure. Backlit, high contrast and relatively dark subjects in a large bright area; light subjects against a dark ground; reflective surfaces like glass or water; areas with some glare on them; pictures where the subject is not in the centre of the picture; subjects with a very wide range of light from dark, through mid-tones to highlights.
The solutions to these problem pictures depends a bit on your equipment and the effect you want to achieve, so I will include various methods of addressing each one, and try to indicate how the solution will affect the final image.
Backlit Subjects have the light coming from behind them. If the light is very bright or if the subject is small relative to a bright background, your exposure metre may read the average light and you will get a silhouette or a badly underexposed foreground. If you want a silhouette but got a muddy subject, point the camera towards the brightest area, depress the shutter half way, recompose and finish pressing the button.
If you did not want a silhouette, either focus on a dark area, excluding the background, lock the exposure, recompose and shoot as above. With this method, you will have to be careful that you lock exposure on something the same distance away as the subject, because focus and exposure are usually taken from the same point (the camera assumes that what you focus on should be properly exposed). This is not much of a problem for landscapes and other distant objects. For portraits and other close subjects, you have other options.
“Fill-flash” will light your subject and balance the exposure with the background. Most cameras give you options to turn the flash to auto, always off, always on plus other combinations with red-eye reduction. Set it to ‘always on’. This works well within the range of the flash; up to say 2 metres. To extend the range, increase the sensor’s ISO.
If you don’t want to have the foreground and background exposures balanced, your camera may have a “partial” or “spot” metering option. Look in the menu. This feature takes the meter reading from a small area in the centre of the image, ignoring anything else. You can guarantee that the area you are interested will be well exposed, though the rest of the picture may not. Remember to return the camera to evaluative, centre weighted or matrix metering afterwards.
High Contrast Scenes are often just normal days in the country or the seaside to us: we wonder why the sky is washed out instead of the rich blue we remember from our day out. Cameras just cannot capture the full range of tones, or levels of brightness in a scene that our human eyes see. Their compromise usually results in a well exposed foreground (the mid-tones like grass), and an overexposed sky, washed out and bland.
Using a graduated filter is a simple way of reducing the contrast between the sky and the land, is to use a graduated filter, which fits over the lens and has a grey top half, fading to clear towards the bottom (check out my recent Intel on Filters).
Relying on auto exposure in the snow almost always disappoints. The exposure meter in your camera is calibrated to correctly expose an 18% grey surface. This works surprisingly well, because human skin, grass and foliage, road surfaces and rock all reflect about this level of light. But not snow; not ice; not sand on a sunny beach… these are all much better reflectors than a grey card! As a result, the camera thinks the scene is a lot brighter than it really is, and compensates by reducing the exposure. It makes the snow look grey, the beach dull. The reverse is also true: A black dog often comes out grey when we use automatic exposure. Since the camera assumes that every subject reflects 18% of the light falling on it, we have to control it.
It isn’t hard to increase the exposure in the snow scene, or reduce it for very dark objects that take up a large part of the scene. The tool built into your camera to do this is called, logically enough, “exposure compensation”. Exposure compensation (check in your manual) is measured in “stops”. + stops give more exposure, - stops give less. Every +stop doubles the exposure, every –stop halves it.
For a snowy of beach scene, try adding +1 stop, then try a little more or less until you get the exposure just right. With a dark scene, do the same thing with – stops.
Exposure compensation isn’t just useful for snow or black dogs: any time you find your photo too dark (underexposed) reshoot with 1 or more stops added. If it is too pale, try again with -1 or more stops dialled in. You will soon recognise subjects that will benefit from more or less exposure in this way.
Haze and Glare also trick the meter. A little moisture in the air or sitting on a leaf will have the camera overexposing and washing out the subject. Your beautifully saturated greens and blues become just pale imitations… exposure compensation is less help, here. Shading the lens from extraneous light will help, since light falling on the glass can make the meter less able to define the subject and will always rob the image of definition. Glare filters and Polarising filters are reliable ways of improving exposure in these situations. They do not directly affect exposure, but by reducing reflected light and haze, they increase contrast and definition, which results in more accurate results.
Not all cameras are designed to accept filters; however, a number of companies now make holders and brackets to permit them to be used with a much wider range of cameras.
Cameras may not be able to deal with every exposure situation automatically, but with a little forethought, we can help them along considerably.
