Depth of Field, Focal Lengths, and Distance
When you photograph a scene with a wide-angle lens, you always get a larger depth of field than you would with a longer focal length. The figure shows an example of a scene photographed with a 24mm lens.
There’s a wide variety of lenses out there, each suited for specific tasks. Lenses fall into the following categories:
super wide-angle lenses that have a focal length from 10mm to 20mm
wide-angle lenses that have a focal length from 20mm to 35mm
normal lenses with a focal length of 50mm and that are close to the range of vision of the human eye
short telephoto lenses with a focal length from 85mm to105mm
long telephoto lenses that have a focal length of 150mm or greater
A short focal length captures a wider view of what’s in front of the lens. A long focal length zooms in on your subject, capturing a narrow angle of view. Telephoto lenses are ideal for taking pictures of subjects you can’t get close to, such as birds and wildlife.
Telephoto lenses are also great for capturing details of a scene. When you photograph a scene with a telephoto lens, you end up with a shallower depth of field than you would when photographing with a lens with a shorter focal length. Remember this when you photograph subjects like birds and animals.
Another way to control your depth of field is to get closer to your subject with a telephoto lens, which brings your subject into clear focus. The combination of being close to your subject, shooting it with a telephoto or macro lens, and using a large aperture (small f-stop number) yields an extremely shallow depth of field. Notice that the butterfly’s head and antennae, and the flower are in focus, but the tips of the insect’s wings are not.