Depth of field (DOF) refers to the area of detail in a photograph that is in focus. There are 2 types shallow and deep. Deep DOF is usually seen in landscape photography where you want objects in the foreground, middle and background to be in sharp focus. Shallow DOF can be used to isolate your subject from the background, causing the background and sometimes the foreground to be blurred there by reducing distractions in a photo.
Learning to control Depth of field is a skill very photographer should learn. Before taking a photo one of the first questions you should ask your self what is the subject and can the subject stand on its own to hold the viewers interest or do you need to have more information to help support the subject in the photograph.
Lets first talk about Deep DOF the kind used in most landscape photography. you will need to understand lens choice, aperture setting and subject distance.
Deep Depth of field we will use a wider then normal focal length lens in most cases.
1. Lens choice 35mm or wider will help keep focus throughout the whole photo
2. Small Aperture (larger number) like f16, f22 or higher if your lens supports smaller aperture
3. Your subject distance is usually far from you.
Focusing about 1/3 of the way into a scene with a wide angle lens and a small aperture selected on your lens will yield a photograph with good sharpness front to back.
Shallow Depth of field is the opposite, you are looking to single out an area of a picture, isolate a subject, or remove a distracting background or foreground in a photograph. This technique is usually used in portraits by getting sharp focus on the persons eyes.
For shallow DOF you will need.
1. Lens choice longer then normal (normal lenses are considered to be 50mm)
2. Large Aperture (small number) like f2.8, f3.5 or f5.6
3. Distance to subject is usually rather close for the focal length you are using.
These are just two extreme examples, the land scape deep depth of field and a portrait . In reality there are many times you will have subjects that fall somewhere in-between This is when you have to decide how you want the photograph to be taken and what is the true subject.
Practice is the best way to learn. take 3 objects place them on a table Water glasses or coffee mugs will work and shoot photos of these objects at different aperture settings using a wide angle lens and then a telephoto lens. look at the results and you will get a good understanding of how the aperture relates to Depth of field. The more you practice the sooner it will start to become second nature.
Practice photos below: Shot hand held so on the F16 70mm you will notice some camera shake this shows the importance of using a tripod when doing serious photography
Photo 1 is shot at 70mm and f16 sharpness noted front to back (except camera shake noticed on the front mug).