BY SUZANNE WILLIAMS
Depth of field is the amount of subject matter in a photograph that is in focus. It can be greater, where much of the scene is in focus, or shallow, where very little of the scene is in focus. The amount of depth of field changes because of a number of factors - the type of lens, the angle of your camera, and the distance to the objects in the scene. It is also greatly dependent on aperture.
Remember, aperture is the size of the opening in the camera's lens. A small aperture is expressed by a larger number - F16 or F25, for instance. Therefore, a large aperture is expressed with a smaller number - F2.8 or F4. (It helps to think of apertures as fractions. In a fraction, the larger the denominator the smaller the fraction.)
Where depth of field is concerned, a large aperture will give less depth of field, and a small aperture will give greater depth of field. With this knowledge, a photographer can control the look and feel of his photograph. In other words, he or she can take the same photo and achieve extremely different results.
Look at my first example. In these two photographs, we have the same flower, same camera angle, and same lighting. However, the aperture in the photo on the left was smaller than the photo on the right. This causes the photo to retain more of the texture of the grass. However, in the image on the right the grass appears softer and less in focus. The shallower depth of field better directs the viewer's eye to the flower.
There are times when a larger depth of field is more desirable. The biggest example would be in wide-angle, or landscape, photography. In these instances, it is best for much of the scene to be in focus. In landscape scenes, you have many objects, all at differing distances from your camera lens. Greater depth of field, therefore, through the use of a smaller aperture, causes these objects to be in focus together.
(The use of smaller aperture also resulted in the "star" effect in this image.)
Another reason to have a greater depth of field can be seen in the photograph below. In this photograph, I wanted more detail in the surrounding butterflies and hanging chrysalis. Because each was at a slightly different distance from my lens and because I was taking a macro (or close-up) photograph, my general depth of field was shallow. By choosing F22 as the aperture, I was able to create greater depth of field than I would normally have had.
(Always remember when dealing with apertures that the smaller the aperture the longer your shutter speed.)
Something must be said now about depth of field as it relates to macro (or close-up) photography. Generally speaking, the closer you are to the object you are photographing, the shallower your depth of field will be. With extremely shallow depths of field, time and care must be taken to achieve proper focus.
In the photograph below, this dragonfly was perhaps 2" in length. Because of its small size, my close distance to the object, and also because the object was not complete horizontal to my lens, several areas of the dragonfly's body appear out of focus. My greatest concern in creating this image was, therefore, the eyes of the insect. With careful attention to the eyes remaining on focus, I was still able to obtain a clean, sharp picture.
Depth of field is another of those areas of photography that it is essential to understand. With knowledge of how to create and therefore, control depth of field, a photographer can achieve the exact results he or she desires.
Suzanne Williams Photography
Suzanne Williams is a native Floridian, wife, and mother, with a penchant for spelling anything, who happens to love photography.