In my last post, I looked at why your camera will sometimes get the exposure wrong and some of the simple steps you can take to improve things. But there’s more to exposure than just how dark or light your pictures are.
Essentially, the exposure is controlled by balancing the aperture (the size of the hole that lets light into the camera) and the shutter speed (the amount of time this hole is open). These variables affect more than just the exposure though, they'll have a profound effect on the look and feel of your picture.
The shutter-speed affects how movement is rendered in your picture, whether it's blurred or frozen. These options were handled in my post on shooting action. If there's no significant movement in your picture, then the most creative thing that you can do is to vary the aperture.
The aperture controls depth of field: the amount on either side of the thing you focus on that is also sharp. You really have two options: a shallow depth of field where only a part of the picture is in focus, or a broad depth of field where most, if not all of your picture is in focus.
A shallow depth of field is easier to perceive. This is given by using a wider aperture (the smaller numbers on the aperture scale). If you shoot a portrait and use a wide aperture, you can make sure that only the subject is in focus and the background is blurred. This avoids a distracting background and helps to concentrate the attention of the person looking at the picture.
By having just a part of the picture in focus, you can, in effect, tell them where to look, and what you think is important in the picture. It can be a bit like standing next to them and pointing at something.
A picture with a broad depth of field is more difficult to recognise, but anyone looking at the picture should be struck by an overall feeling of quality. Whether you're shooting a landscape or a cityscape, what you want to achieve is a picture where everything, from the foreground to as far as the eye can see, is in focus. To achieve this, you'll need to use one of the smallest apertures (using one of the larger numbers on the aperture scale). This might involve using a relatively slow shutter-speed and so you might need to use a tripod to avoid camera shake.
Other factors that influence the depth of field are focal length and sensor size. A telephoto lens has much less depth of field at any given aperture than a wideangle lens. The smaller sensors and lack of control over aperture in compact cameras make it much more difficult to achieve a shallow depth of field, but using a telephoto setting and selecting a sport or action picture scene mode will help.
If you want a broad depth of field, using a wider zoom setting and selecting the landscape picture scene mode will easily achieve this.
One important thing to remember is that if you're not using an automatic mode then you'll have to balance any aperture selection with a corresponding shutter-speed otherwise you will affect the exposure.
All photos © Steve Davey. Header image: Buddha statue, Chiang Mai, Thailand: Choosing a wide aperture and using a telephoto lens has given a very shallow depth of field, and a pleasing out of focus background.
Join Steve on a photography tour to the high altitude landscape of Ladakh in India, and visit a Tibetan Monastery festival. More information on http://www.bettertravelphotography.com/phototours/
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