In photography, depth of field refers to how big of a slice of reality is in focus when you take a picture. I know it is at first a confusing concept, so think about this analogy. Pretend you are standing beside a pond on a farm and a leaf is floating on top of the water. For our example, let's say the pond is brackish. When you look at the leaf can you see the bottom of the pond? No. Now pretend you are standing beside a well-maintained swimming pool and a leaf is floating on the water (just landed and the pool boy hasn't been able to skim it out yet). When you look at the leaf can you see the bottom of the pool? Yes. Now instead of visibility (whether or not you can see the bottom), think of sharp focus. Depth of field refers to how much both behind and in front of an object (the one you are focusing on) will be in focus. There are a couple of terms associated with this effect, and you should memorize their meanings. Forget about my analogy at this point because these terms are not referring to water!
Shallow Depth of Field - the camera will only deliver a sharp picture of the object it has focused on. The objects behind and in front of the object of focus will be rendered blurry.
Deep Depth of Field - the camera will deliver a sharp picture of the object of focus and the objects behind and in front of the object of focus.
Let's use a couple of examples. Let's say you take a photograph of a cala lily. Only part of the flower appears sharp in the photograph. Everything else is blurred. That is shallow depth of field. Here is an example I photographed.
Now lets say you have an object 200 feet from a house and you want to take a photograph that renders both the house and the object in focus. Here is an example that I photographed that illustrates this scenario.
Notice that the house is not in perfect focus. However, if I had used a similar camera setting as the one I chose for the cala lily, you would not even be able to tell that there was a building behind that chair.
What are the settings? Depth of field is controlled by what we refer to in photography as the aperture setting. These settings are represented by a number preceded by a lowercase f, such as f 4.5.
What does it mean? For our purposes, just know that, 1) the larger the number, the greater the depth of field, and 2) the larger the number, the lesser amount of light coming through the lens. I'll discuss point 2 in a minute. Regarding point 1, the picture of the chair was probably taken with the camera set to f 16, and the cala lily was probably photographed with the camera set to f 2.8.
I really should say camera lens was set to f 2.8 or f 16 because, and this is important, the aperture also refers to the diameter of the device in the lens that controls the amount of light that is allowed to strike the film or digital sensor (point 2). Shutter speed is one of the variables used to control proper exposure and aperture is another. Therefore, you cannot just arbitrarily select a high number like f 11 of f 16 when you want everything in focus. You must also select a slower shutter speed so that the photograph will be properly exposed.
There are a couple of other factors that affect depth of field. I won't try to explain the physics behind these factors because it would make your head hurt , and I'm not all that familiar with the reasons myself. Fortunately, the explanations don't matter in terms of practicality. Just know the following:
Things That Control Depth of Field
1. A small aperture such as f 16 will render things if focus that are behind and in front of the object the camera focuses on. The opposite is true. A large aperture such as f 2.8 will only render the object the camera focuses on as sharp.
NOTE: The confusing thing is the fact that a small aperture is f 16 and a large aperture is f 2.8. Of course, 16 is a greater number than 2.8, so the logic here seems backwards. It is, so just memorize these facts.
2. A wide angle lens has a greater depth of field than a normal lens. A telephoto lens has shallower depth of field than a normal lens.
3. Photographing things close up yields a shallower depth of fiels than does photographing things at a distance.
Confused? I hope not, but if you are leave a comment.
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