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One of the most useful skills you can wield in your arsenal is using Depth of Field. The ability to focus in on any one or all objects. It's both useful and appealing. In my opinion, though this may be argued, it is one of the most prominent skills that distinguishes amateur from professional photography. Properly using it can be difficult and sometimes expensive. Though when used correctly Depth of Field can help produce amazing results.

What is Depth of Field?

The definition of Depth of Field (DOF) is the distance in front of and beyond the subject that appears to be in focus.

What does that mean exactly?
It's commonly misunderstood that the out of focus or blurry part of the photo is the Depth of Field. In truth, the in-focus or sharp part of the photograph is the Depth of Field. Having a larger field of depth means more is in focus while having a smaller field of depth means less is in focus. The depth of field is completely controllable using your lens, focus, and aperture.

Advantages of Depth of Field

Once you learn how to properly control your cameras depth of field, you can use it for both composition and artistic reasons. As well, and this may be more important, knowing and controlling the depth of field will keep your images sharp and in-focus. You can always fix exposure and framing in Photoshop if need be, but you can't fix a blurry image. In all circumstances, a broad depth of field is useful. It will ensure that everything in frame will be sharp. It's the safe bet. This is most useful in landscape photography as you want everything to be in focus for quite a distance. Using a shallow depth of field allows you to control a busy scene. For example, if you want to focus your picture on one person sitting across a table you can blur out everyone else and the background. You want to capture the environment but you want peoples eye to focus on the one person.

How your lens effects Depth of Field

Your lens is a primary contributor to the depth of field. All lenses have a length or size. For example most stock lenses are 24mm - 55mm. As an SLR owner you can purchase additional longer or shorter lenses that you can swap out. Unfortunately, the same can't be said for Compact cameras. The length of your lens is what controls how shallow and how broad the depth of field is. The longer the lens is (ex. 200mm) the narrower your depth of field will be. A longer lens is better for snapping portrait pictures or sports. A shorter lens (16mm) has a much broader depth of field which is better for scenic pictures.

Aperture

Aperture has a significant effect on the depth of field. By increasing or decreasing the aperture size, you are changing how shallow or broad the depth of field is. The larger the aperture (or the smaller the f-number) the more shallow the field will be. The smaller the aperture (or the larger the f-number) the broader it will be.

Below are three images that show how reducing the f-number can effect the depth of field.

As you can see, the background becomes less blurry the smaller the aperture is. The focal length stayed the same, the only other change was the shutter speed which has no effect on the depth of field. This balances the exposure as the aperture size decreases.

What does this all mean?

By utilizing both your lens length and your aperture you can control how much is in focus. Generally when you are shooting portraits you want to blur out the background. The only time you don't want to use some sort of shallow depth of field is when you are shooting a landscape. Then you want to broaden your depth of field as much as possible.

Now that you know what controls it and how to increase and decrease it. Experiment with it. It is the best way to put to practice what you learn. The more you play with it the more your personal style will emerge.

Examples

This will be a fun yet challenging assignment. I want you to photograph your subject with a series of field depth.

1. A shallow depth of field, very little should be in focus. Your goal is to direct the viewers attention to the main subject.
2. A large depth of field, everything should be in focus. Use the whole frame in this photo. Everything is important in this picture. The challenge here will be controlling the scene and making sure your subject isn't overcome by what is around it.
3. A shallow depth of field, the challenge here is your main subject has to be out of focus and something else in the photo has be to in focus. How can you still compose a scene where your main subject is out of focus? That's the challenge!

   
   Post your assignment in the comments below. Remember, be creative and experimental. Photography is an art.
   
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