Depth of field is the commonly uses term to describe how much of an image is in focus and is predominantly determined by the size of the camera’s aperture. This effect can easily be explained and replicated by just looking around you. If you focus your vision on an object near to you, it is sharp, but objects in your peripheral vision are not. However, if you look at the subject in the middle or far distance – say, the view over your garden – the whole scene tends to look sharper overall.

Photography does the same thing, but it is more pronounced, principally because you are capturing a three-dimensional subject on a two dimensional medium. The degree of sharpness in an image depends on a number of correlated factors: the focal length of the lens, the focus distance and the aperture. While there are a host of formulae and equations to aid you in determining this, for most people, the easiest way to learn is by experimenting; photography is about creativity as much as it is about science.