Whether you have a DSLR with several lenses, or a compact camera with a zoom, you’ll need to make decisions about whether to use a wide angle lens, a telephoto lens, or a lens somewhere in between.
So what factors will affect your decision? There are lots of differences in the way lenses behave, but the main ones are listed here:
1. Field of view
We all know that the wide angle lens includes a wide view, while the telephoto lens brings distant objects closer. But the angle of view also affects the background to your subject. In this diagram below (which is very approximate!), the green lines represent the field of view you might get at the wide end of your telephoto lens, the red lines show the field of view somewhere in the mid-range of your lens, and the blue lines represent the telephoto field of view.
So you can see that if you were photographing the foreground flower, the amount of background that you would include behind it would vary considerably depending on the focal length of the lens that you used.
A wide angle lens will exaggerate the perspective in a scene, making foreground objects appear larger, and pushing distant objects further away. A telephoto lens, on the other hand, compresses the perspective, reducing the apparent space between near and far objects. Compare these two photos of a hyacinth field above, both taken from the same position, the first with a wide angle lens, and the second with a telephoto.
3. Depth of field
If you photograph the same subject from the same place with different lenses, a telephoto lens will give you a shallower depth of field than a standard or wide angle lens. So if you want to throw the background to your subject out of focus, this will be easier with a longer lens.
When you take all those factors into consideration, you can see how they might affect your choice of lens in any particular situation. Take portrait photography, for instance.
A wide angle lens will exaggerate the size of nearer objects – so a close up portrait taken with a wide angle lens will make your subject’s nose look large, and generally result in an unflattering image! A medium telephoto will usually be better, allowing a bit of distance between the photographer and the subject, while still giving a frame filling portrait - with a normal-sized nose!
For landscape photography, you will probably have use for the whole range of focal lengths. Wide angle photos will give a great feeling of space and depth in a landscape, with plenty of depth of field; while longer lenses can be used to pick out just part of a landscape for a tighter photograph.
Wildlife photographers will often use long lenses when their subjects are too shy to approach closely. A flower photographer will often use a longer lens because of the benefits of having an out of focus background – but may also use a wide angle lens to show a flower growing in its environment.