Depth of field

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.

In this aspect we should not be fooled by the equivalent focal lengths of small amateur digital cameras, but we need to look their actual focal lengths. A digital camera lens with focal length 20 mm, although equivalent to a 100 mm film camera, is not ideal for where we want to achieve blurry background. It is good to have a lens with focal length 40-50 mm and at least 1:2 aperture to fully enjoy this effect. For the picture you see in the example is used 200 millimeters lens with aperture 2.8.


Sometimes we can get interesting close-up portraits, even when using lenses with small focal length. This depends on the objectives we had set. For example, if our goal is to capture the colors of the landscape behind the person we shoot, we will use wide-angle lens and a closed diaphragm.


The photo was taken with 18 millimeters wide angle lens with aperture 11.

Most often we strive for greater depth of field when shooting landscapes or group portraits in which we want to achieve sharp background. Then you have to choose a wide angle lens and use a closed aperture. Thus we make sure that everything in the picture will be in focus.

To know the dependencies between the aperture, the focal length and depth of field is essential. This gives us a preliminary idea of how much of what we see will be in the area of focus. You should know that the area of focus for each DOF is about one-third before the point in which we are focused and about two thirds after. So if focus on an object 1.3 meters from us and the DOF 1 meter focus will fall on all sites from one to two meters.

Knowing these dependencies, whether shooting a portrait of a friend, a beautiful landscape or sports competition, in every situation we can choose the appropriate lens or using the zoom settings to get the best picture possible.