Definition of Depth Of Field

Depth of Field is the area in a photograph that is in focus.

What effects Depth Of Field

The contributing factors to depth of field are:

• lens aperture
• distance from subject
• focal length

These three items are what you can control to change your depth of field

Depth Of Field and Aperture:

By changing your aperture you change how large your depth of field is. The larger your aperture (smaller f-number) will give you a smaller depth of field. If you use a smaller aperture (larger f-number) you will have a larger depth of field. Although you can change the size of the depth of field through aperture, the amount of change will be dependent on the other two factors, distance from subject and focal length.

The example on the right was done with a 50 mm lens and a shoots were taken from about a foot and a half a way. The number on the top left of each image is the f-stop. As you can see, the top image with a small f-stop (large aperture) shows only the center object in focus where as a large f-stop (small aperture) means that nearly all the objects are in focus.

Depth Of Field and Distance From Subject

The closer your subject is to your lens the less depth of field you will have. If your subject is really close and in focus your background is more likely to be out of focus.

The reverse is also true. If you take a photo of a subject far away both the subject and its background will be in focus, even if the background is a long distance back from the subject.

Once again this also depends on the other two factors of aperture and focal length.

Depth Of Field and Focal Length

Changing your lens for a normal length (like a 50mm lens) to a wide angle lens (like a 24mm lens) is similar to moving the subject from near your lens to further away from your lens. Therefore changing focal length should have the same effect as changing your distance from the subject.

If you use a wide angle lens you will have a larger depth of field but if you use a telephoto lens you will have a smaller depth of field. Of course, like the other factors, the depth of field will also depend on aperture and distance from subject.

Why should you control your Depth Of Field?

If you want to remove distracting backgrounds or have people focus only on the subject you can accomplish this through a narrow depth of field. Portraits for example are a common place where photographers will use a narrow depth of field. On the other hand, for landscapes you many want to use a wide depth of fields so that everything from near by trees to far away mountains are in focus.

This is not a rule. It all depends on what you want to accomplish and your personal preferences are. Learning how to use depth of field will help greatly controlling what your view sees in your photographs.

Conclusion

Depth of field is the amount of the area that is in focus. This is determined by aperture, distance from subject and focal length.

To increase your depth of field you can do one or all of the following:

• increase your aperture (use a smaller f-number)
• increase your distance from the subject
• decrease your focal length

To decrease your depth of field you can do one or all of the following:

• decrease your aperture (use a smaller f-number)
• decrease your distance from the subject
• increase your focal length