I shot this photograph with my camera's aperture set to f/5.6. The aperture of a camera lens controls how much light enters the camera by opening and closing a diaphragm within the lens. A low f-number (also known as f-stop), such as f/3.5 or f/5.6, means that more light is able to enter the camera. One consequence of a lower f-stop is that only objects at a certain distance from your lens will be in focus. Objects farther or closer than this distance will be thrown out of focus, as in this shot where the worm is sharp but the background and foreground are blurry. This concept is known as "depth of field". A large (or "deep") depth of field simply means that both the nearest and farthest objects in your field of view will be sharply in focus. This can be achieved by increasing the f-stop on your camera and letting in less light (most cameras will go up to at least f/8 or f/11, while many professional lenses can reach f/35 or greater). Conversely, a small (or "shallow") depth of field is what we find in this photo, where only objects at the same distance as the worm will be in focus. This can be a good photo-taking strategy if you want to highlight one particular object, such as the worm. The lower your f-stop, the shallower your field of view will be.