Article

Application of Depth of Field

See also Depth of Field DOF Explained.

Managing Depth Of  Field is an essential art for all photographers.

By managing depth of field we mean being in control and selecting the depth of field, making changes in the way we take photographs in terms of settings, lenses and position, plus sometimes using special techniques or software, rather than just taking what comes or merely adjusting the aperture.

We need to start by considering what we want to achieve, it may be that we want to throw the background out of focus, as with some wildlife photographs such as bird studies, we don't want the distraction of the background. With portraits and some other images we may also want to achieve the same thing. To throw the background out of focus, we want to use a combination of a longer focal length and larger aperture (towards f2) and getting closer to our subject. Each of these acts will limit the depth of field, combining them has a greater affect.

We may want to extend the depth of field so that everything is sharp over a longer distance, then the opposite to the above applies, a combination of a smaller aperture (towards f32), going further away and using a wider angle lens. Combining these has a greater impact.

As we have a number of options to create the effect we want, we mix these requirements with others that we may have, such as a need for a higher shutter speed to stop movement. To expand the range of options we can adjust the ISO sensitivity and where we have too much light to achieve what we want, for example greater depth of field and movement as with waterfalls, we can use Neutral Density filters. 

We can expand the amount the depth of field in three ways, by the use of a split focus filter attachment, by editing together several photographs and by using slicing.

• A Split focus filter is a filter that has only a lens in one half, so that the area covered by the lens focuses closer than the remaining part. This works with flowers in the foreground against items beyond or turned on the side can allow nearby hedges or fences to be in focus running into the distance. Looking carefully you can sometimes see the photo going from in focus to out of focus to 'in' focus again, but with a sufficiently small aperture (i.e. f22) you may get enough depth of field that the depth of field from the two areas are able to overlap and merge. These filters were at one time in quite wide use but are now not so widely used. This, although far from ideal, is the only one of the approaches that is really practical with moving subjects and still images.

• Editing together several photographs involves taking a number of photographs with the camera in one position and then putting one over the other in Photoshop or similar and erasing the out of focus areas, allowing in focus areas in a shot behind to become visible. This can be more difficult than it sounds because as the focus is changed the image size changes slightly.

• The slicing approach also uses a number of images, but can be a much larger number, and using software that extracts from each image the sharpest items building a sharp image from the best of all the photographs.  Usually this is done with a set of still images, with the camera on a tripod so no movement is possible, but there is also a program that can build a sharp image out of a collection of video frames, allowing, in theory, an image from a moving subject. See also Introducing Slicing,   and the many other articles that we have, including sets of slices for you to experiment with on this topic.

The amount of extra depth of field that we add is controllable, so we may for example with a food photograph wish to have a plate and food fully in focus and throw the glasses and other items behind it on the table out of focus.

In the studio or at home you can, may be able to, control your camera from a computer allowing you to both see what is in focus and finely control the camera focus, this is particularly useful when looking at macro, close up, product or food photography and using the slicing approach.  Capturing slices with a Nikon DSLR covers this in depth, including screen displays.

The start point for advanced application of depth of field for landscape and similar is either to use a calculator on a  computer, a calculator device or depth of field tables. In the field the tables and calculator device are applicable, my preference being the tables, although I carry both with me. You can then refine the effects you want using the depth of field preview and taking test shots and looking at a magnified version of the image.  The use of accessories like the Delkin professional pop-up shade and Hoodman Loupe  can make it far easier to see what is happening, especially when you are outdoors. The loupe not only cuts out the light, but also magnifies the image that you see.

See also

Depth of Field DOF Explained