There are a lot of concepts that you need to study and understand as a beginning photographer. Composition, lighting, and camera settings, for example, all have a great deal of impact on the images you take.
One of the most important photography concepts to understand is also one of the most complex: depth of field. In short, depth of field is the range within an image that is in sharp focus. But simplistic definitions aside, there is a volume of considerations that go into determining depth of field and using it to enhance your images.
Quick Examples of Depth of Field
One of the easiest ways to illustrate the concept of depth of field is to provide examples. Look at the image below, and notice how everything in the background is blurry:
The blurry background indicates that a shallow depth of field was used. Shallow depth of field is a technique often used in portraits because it produces nice bokeh effects (the blurry circle shapes in the background created by a wide aperture) that helps draw attention to the primary subject. In this case, the three children are in very sharp focus, but with a blurred background, the attention of our eyes isnâ€™t distracted â€“ we maintain focus on the kids.
Conversely, landscape images tend to benefit from a large depth of field, like in this image:
Notice how everything in the scene is in sharp focus. This helps our eyes move through the scene, from the rocks in the foreground to the river in the middle to the hills and trees in the background. A large depth of field thus facilitates greater movement of the viewerâ€™s eye such that they can soak up all there is to see in the scene.
Depth of field can be as little as a few millimeters, as is often the case in macro photography, or it can be a few miles, as is often the case when shooting landscapes. Nevertheless, the term depth of field refers to that area â€“ however large or small â€“ that is in sharp focus.
Depth of field is not an exact area either, in that it is a continuous range. There isnâ€™t a line of demarcation between perfectly in focus pixels and blurry pixels â€“ it happens gradually. Depth of field is also unevenly distributed in front of and behind the subject. The distances may vary, but a good rule of thumb is that for most situations, about one-third of the area of focus falls in front of your subject, with the other two-thirds of focus falling behind the subject. However, as the focal length increases, these distances shift more toward an equal distribution.
So, now that youâ€™ve seen examples, itâ€™s time to learn how to manipulate depth of field. There are several critical components that go into determining how deep or shallow depth of field will be.
Factor #1: Aperture
The aperture of your camera refers to the size of the hole through which light enters your cameraâ€™s lens. The larger the aperture opening, the more light thatâ€™s allowed in; the smaller the aperture opening, the less light your lens will be able to collect.
Aperture is denoted using f-stops, which, for beginners is a bit confusing because f-stops are inversely related to the size of the aperture, like so:
Large f-stop number = small aperture
Small f-stop number = large aperture
So, examining the chart above, at f/4 (a small f-stop number) you have a large aperture opening. At f/22 (a large f-stop number) you have a small aperture opening. This can be extraordinarily confusing at first for a beginner to remember, so try thinking of f-stops like fractions:
F/4 would be converted to 1/4; F/22 would be converted to 1/22. Which is bigger? Obviously, 1/4 is bigger than 1/22, so f/4 represents a larger aperture opening than f/22.
Now, the lower the f-stop, the shallower the depth of field. When shooting a portrait, a photographer might use f/2.8, for example. Conversely, when photographing a landscape, a photographer might use f/16 because the higher the f-stop, the larger the depth of field.
In short: The smaller the f-stop, the shallower the depth of field. Move towards larger f-stops to increase your depth of field.
Factor #2: Distance
There are two distance elements that factor into depth of field: the distance from the camera to the subject and the distance between the subject and the background.
The closer your camera is to the subject, the shallower the depth of field. So, again, using portraits as an example, the photographer will generally be quite close to his or her subject, thus making it relatively easy to get a shallow depth of field. On the other hand, since landscape photography is generally done from afar to capture the expanse of the landscape, depth of field is quite deep, even if a smaller than normal aperture is used. Consider this:
At a distance of 10 feet, an aperture of f/4 will result in a shallow depth of field with a blurry background. But that same aperture of f/4 at a distance of half a mile will result in a comparatively large depth of field.
The second distance factor at play here is the distance between the subject and the background. In this case, the farther the subject is from the background, the more blurred it will be. In a portrait, for example, placing the model at 15 feet away, with a background at 20 feet away, will result in a background that is more in focus than it the model is 15 feet away and the background is 45 feet away.
In short: The shorter the distance between you and your subject, the shallower the depth of field. Additionally, the further your subject is from the background, the shallower the depth of field.
Factor #3: Focal Length
Focal length refers to the size of your cameraâ€™s lens and its ability to magnify a subject. Basically, the longer your lens, the shallower the depth of field will be.
For example, if youâ€™ve got an 18-200mm zoom lens, the depth of field at 18mm at f/4 will be much greater than it would be at 200mm at the same f/4 aperture.
In short: The longer your lens, the shallower the depth of field. To maximize depth of field, use a shorter focal length like a wide-angle lens.
Camera Settings for Depth of Field
As weâ€™ve discussed, you will need to use your aperture, in part, to control depth of field. But manipulating your aperture also means manipulating other settings.
For example, if you set a small aperture, say f/16, you limit the amount of light that enters your lens. Without as much light, you run the risk of underexposing your image. In other words, your image will be dark.
To compensate for this, you could slow down your shutter speed, say from 1/200 seconds to 1/50 seconds, thus giving the lens longer to collect the available light. You could also use a higher ISO setting, say, ISO 800 instead of ISO 400. Remember that ISO refers to the level of sensitivity of your cameraâ€™s sensor to light, with the higher the number indicating an increasing sensitivity to light.
However, if youâ€™re a beginner, making all of these adjustments can be a bit overwhelming. Fortunately, many DSLRs and even point-and-shoot cameras have presets you can use to streamline the process.
In short: Adjusting the aperture to get the desired depth of field will require changes to your shutter speed and ISO. The smaller the aperture, the slower the shutter speed and the higher the ISO needed for a well-exposed image.
Camera Presets for Depth of Field
By Graphic: Althepal Derivative work: Mehdi (ModeDial.svg) [CC BY-SA 2.5 (http://creativecommons.org/licenses/by-sa/2.5)], via Wikimedia Commons
One of the simplest ways to manipulate depth of field and still get a well-exposed image is to use your cameraâ€™s Aperture Priority mode, which, depending on the manufacturer of your camera may be indicated with an A or AV on the camera mode dial.
Aperture Priority mode gives you control over the aperture while the camera retains control over the shutter speed. Thus, if you want a shallow depth of field, dial in an appropriate aperture, say, f/4, and the camera will select an appropriately fast shutter speed for a properly exposed image. If you want a large depth of field, shoot at f/16 and the camera will select the appropriately slow shutter speed to get a good exposure.
Of course, there are limits to the ability of the camera to adjust the shutter. For example, if youâ€™ve got a very small aperture like f/22 and there isnâ€™t much available light, the camera might struggle to select a shutter speed that remains fast enough for you to hold your camera in your hand. For most people, shutter speeds at or below 1/30 of a second are too slow, or else camera shake ruins the picture. As a result, always have your tripod handy in case you need to slow the shutter significantly.
If youâ€™ve got a point and shoot camera, donâ€™t worry â€“ you can still manipulate depth of field too. If you look on the mode dial on your camera, you should see a little mountain figure. Shooting in that mode â€“ landscape â€“ selects a narrower aperture and faster shutter speed to get you the large depth of field typically required for landscape shots. Look for the little head icon â€“ portrait mode â€“ and the camera will select settings more conducive to a shallow depth of field. These shooting modes are also often found on DSLRs in the shooting mode menu.
In short: Use your cameraâ€™s presets â€“ Aperture Priority mode on a DSLR and portrait or landscape mode on a point and shoot â€“ to control depth of field without having to make as many on-camera adjustments.
Why Depth of Field is Important
As discussed above, depth of field is a great tool for portraiture and landscape photography because in the former, you can use a shallow depth of field to separate your subject from the background, thus forcing viewersâ€™ eyes to inspect your subject longer. In the latter, a large depth of field opens the entire photo for viewing and gives a better impression of the full landscape.
Depth of field is also useful for wildlife photography, because like portraits, itâ€™s easier to view animals if they are separated from the background, as is the case in the image above. Sports photographs also benefit from a shallow depth of field, again, to help make the primary subject stand out from all the action thatâ€™s going on around him or her. Street photography, on the other hand, is a great place to use a large depth of field so that viewers have a good sense of the environment surrounding the primary subject.
Depth of field is also an excellent tool to help you create more artistic images. Knowing how to make certain parts of an image sharp or blurry will help you better define your subjects, mask background details you donâ€™t want to be seen, and create images that have much more mood and visual interest.
In short: Portraits, wildlife photography, and sports photography all benefit from a shallow depth of field that draws attention to the primary subject. Landscape photography and street photography often benefit from a large depth of field that gives viewers a better understanding of the larger surroundings.
Easy Ways to Check Depth of Field
Learning how to control depth of field can be quite the undertaking, but checking depth of field is really quite simple. Try these methods to check your images for the desired focus:
Checking your shots on your cameraâ€™s LCD will give you a much better look at your image than what you see through the viewfinder. Use the zoom function to zoom in and closely inspect various parts of the image to see whatâ€™s in focus and what isnâ€™t.
If youâ€™re shooting in a studio (or anywhere else where itâ€™s convenient to have your laptop attached to your camera), you can view your images directly on your computer screen after taking them. This affords you a large, crystal-clear view of whatâ€™s happening in the image regarding depth of field.
Depth of Field Preview
By Mauritsvink (Own work) [Public domain], via Wikimedia Commons
If youâ€™ve got a DSLR, chances are that itâ€™s got a depth of field preview button. The depth of field button is usually located on the front of the camera near the lens, close enough that you can easily depress the button with your thumb or forefinger. In the image above, the depth of field button is the small, round button nearest the 500D label.
This handy feature will give you a preview of what the depth of field looks like at the aperture you have set. This is useful because the viewfinder actually shows you what the depth of field looks like at the cameraâ€™s widest aperture. This is done to give you the brightest view of the scene, thus making it easier to compose shots, but obviously making it more difficult to determine depth of field.
In short: Easily check depth of field by using your cameraâ€™s LCD, tethering your camera to your laptop, or using your DSLRâ€™s depth of field preview function.