You can use your camera’s Aperture Priority Mode to control the depth of field  (the area of sharpness) within your photograph.

Introduction

The term “depth of field” refers to the area of an image in which the subject matter will appear acceptably sharp. It is measured from front to back. The smaller the aperture eg F/16, the larger the area of sharpness; the larger the aperture eg F/2.8, the shorter the depth of field, and the shorter the area of sharpness.

Depth of field is best illustrated through examples. The following pictures will show how depth of field affects the overall appearance of your pictures.

Smaller apertures such as f/11 and f/16 will result in more of your photograph being in clear focus. In this example, using an aperture of f/16, the flowers in the foreground, the caves in the middle and the distant sky are all in focus.

Larger Area of Sharpness
F/11	F/16
Small Aperture

Cappadocia (Turkey)

This is another example of a photograph shot with a small aperture, f/16. The tea vendors in the foreground, the trees in the middle and the Blue Mosque in the background are all in focus.

To get the maximum depth of field, you must use the camera’s optics to your advantage.  Optics tell us that the depth of field extends from 1/3^rd of the way in front of the point focus to 2/3^rd’s of the way behind it. Therefore to keep the most amount of space in your picture in focus, you should focus 1/3^rd of the way in front of your image. In this image, the results came from focusing on the faces of the tea vendors.

 

Larger Area of Sharpness
F/11	F/16
Small Aperture

Tea Vendors (Turkey)

Medium apertures with f-numbers such as f/5.6 and f/8 are used when depth of field is not an important element in the composition. A medium aperture will give you the best quality picture that your camera’s optics are capable of.

In this image, the monk is the only subject that needs to be sharp and depth of field – area in focus – is not important.

 

Average Area of Sharpness
F/5.6	F/8
Med. Aperture

Monk at Corridor (Cambodia)

Large apertures such as f/2.8 and f/4 reduce the depth of the area in your photograph that will appear in focus. In this image, the area of sharpness is limited to the mother and calf. The grass in the foreground and the sky in the background are both out of focus in terms of tone and shape. This prevents the foreground and background from competing with the main subject for the viewer’s attention.  

 

Smaller Area of Sharpness
F/2.8	F/4
Large Aperture

Fawn Nursing (Kenya)

Again, here a shallow depth of field left the egret and branches in focus with the trees and water in the background out of focus. The large aperture also resulted in the faster shutter speed required to freeze the action of the egret.

Smaller Area of Sharpness
F/2.8	F/4
Large Aperture

Great Egret Taking Off  (Florida, US)

Conclusion

A mastery of depth of field can produce dramatic and widely varied results. A small aperture enables the photographer to keep virtually everything in the picture in focus while a large aperture makes it possible to isolate the specific portion of the picture you wish the viewer to focus upon.