Depth of field is an important concept in photography. It gives information about the part of the space around the plane of focus, in which objects are of sufficiently high sharpness, virtually indistinguishable from that of the main object in which the focus is set.

Depth of field depends mainly on the lens' focal length, the aperture and the distance to the object which is in focus. The larger the focal length of the lens, the less depth of field. Mighty tele lenses with focal length of 400-500 mm have a very small depth of field, while with the wide-angle 20-28 mm, it is big. Corelation between aperture and depth of field is also inversely proportional.

As aperture is smaller (more closed), the depth of field is greater and vice versa. Using a blend of around 22, can provide a huge depth of field, but it is not 100% guarantee for sharp image, as in such apertures diffraction starts to show up and the image becomes softer. Biggest sharpness is usually achieved in 8-11 aperture. Finally, the distance to the object is just as important - the closer the object which is in focus, the less depth of field and vice versa.

We can not determine whether good depth of field is small or large one. In some cases small is better, while in others - large. So when shooting a close-up portrait, you should use a lens with higher focal length and with aperture wide open, in order to get a nice blurry background, without distracting objects irritating the eye. Most suitable lenses for portraits are from 85 to 135 millimeters. These lenses convey proper perspective, without the typical wide-angle lens distortion.