Understanding Depth of Field

Depth of field is the zone of sharp focus in your image. It extends in front of and behind your subject. You may be focused on a person’s face, yet with deep depth of field, things in front of and behind the person will be in focus too. With shallow depth of field, only your subject will be in focus.

You will control the aperture, and the resulting depth of field, by turning your aperture control, either a wheel on the camera body or a ring on the lens. Refer to your camera’s user’s manual to learn where the aperture control lives. This will be one of the most used controls on your camera!

Depth of field is extremely important to photographers who shoot landscape images and portraits. It is controlled by the size of the aperture opening. When you use a large aperture opening, such as f/1.4, the only thing that will be sharp in your image is the exact area where you have focused the camera. Nothing else will be sharp in front or behind the subject. Instead, the surroundings will have a blurry look. That can be a good thing for portraits.

Figure 4.5: Very shallow depth of field at f/1.4. Only the subject’s cute face is sharp.

In figure 4.5 you’ll see a portrait of a tiny person with very shallow depth of field. I took the portrait next to a lake and wanted to blur the background so that the young lady was emphasized. I used a large aperture, in this case f/1.4 on my 50mm lens. When you look at the image, the blurry background immediately draws attention to the face of the child in the image. Your eye is naturally attracted to the sharpest, clearest thing in a picture. If you want a portrait to make a person stand out, use shallow depth of field by opening your camera’s aperture to a large opening (big hole). The large aperture will cause the subject’s surroundings to fade into blurriness, while the subject remains sharp.

A View from Cherohala Skyway in late October at the peak of the Autumn leaf color season. This National Scenic Byway runs between Tellico Plains, Tennessee and Robbins, North Carolina, USA.

Figure 4.6: Deep depth of field. From foreground to background is sharp

On the other hand, when out shooting beautiful nature images, you will want to have deep depth of field by using a smaller aperture opening, such as f/8 or f/11. This makes not only the point of focus sharp, but also everything surrounding the spot where you focused the camera. Figure 4.6 shows an image where I used a small aperture to make nearly everything in focus. In the image of the autumn mountain, I focused about 1/3 of the way into the scene, and let depth of field from the small aperture cover both the foreground and background.

Tip: In figure 4.6 I wanted to simulate a 3D look. A picture is two dimensional (flat) so a scenic, although pretty, can often look flat and even uninteresting. If you add a foreground object to the image—as I did with the trees on the left and right sides—it causes a viewer’s brain to detect depth, when a 2D image really has no depth. If you want your landscape images to look even better, try to include a foreground object in the the image. You will need lots of depth of field (a small aperture) in order to make sure the foreground object is acceptably sharp. How can you do that? Let’s see how!

Now, let’s use a series of images that show how depth of field, or the zone of sharp focus, changes whenever you change the aperture size. You will learn to control depth of field so that you can include or exclude sharpness for certain objects in your image.

Let’s say you are taking a picture of a friend who is standing 6 feet (2 m) away from you. About 6 feet behind your friend is another person. There’s also a third person standing about 6 feet behind the second person. Three people total, each about 6 feet apart, with the friend wearing a red blouse in front (figure 4.7).

You are shooting with a 50mm f/1.8 lens (f/1.8 is the maximum aperture, and f/22 is the minimum aperture). You focus on your friend’s face, the young lady in red, and take a picture. It looks like the picture in figure 4.7.

Figure 4.7: Three young people at f/1.8, shutter speed at 1/6000s, 100 ISO

Figure 4.7: Three young people at f/1.8, shutter speed at 1/6000s, 100 ISO

A big aperture like f/1.8 has very shallow depth of field. Notice how the girl in red in figure 4.7 is sharp, but the two young people behind her are not. The background has been de-emphasized, while the young girl in red has been emphasized. It looks a bit strange in this image because there are several people. It would look better if we extended the depth of field (zone of sharpness) to cover them too. We can do that, as we’ll soon see, by simply closing down (stopping down) the aperture without changing where the camera is focused (on the young lady in red’s face).

The girl standing behind the young lady in red, to the right, is not in focus, nor is the young lad even farther away to the left. Only the girl in front is in focus at f/1.8. Not much else is in focus, so there is very shallow depth of field. The depth of field in this picture is about 1.5 feet (.45m).

What would happen if you stopped down to a medium-sized aperture like f/8? Figure 4.8 shows what that does to the depth of field.

Figure 4.8: Three young people at f/8, shutter speed at 1/500s, 100 ISO

Figure 4.8: Three young people at f/8, shutter speed at 1/500s, 100 ISO

Remember, you are focused on the girl in front, and at f/1.8 (a big hole) the others were out of focus. Without changing your focus in any way, you adjusted your aperture to f/8. Something changed! Even though the camera is focused on the girl in front, now the girl to the right is sharp too.

Figure 4.8 shows that the depth of field now extends past the girl in front and covers the girl in back. It got deeper. Since the girl to the right is about 6 feet (2 m) behind the girl in red, the depth of field is at least six feet, but it is probably more like 9 feet (2.75 m) because it extends toward the camera too. Interestingly, depth of field extends farther behind the subject than it does in front of the subject.

However, also notice that the boy to the left is still not in focus. The background is not in focus either. The depth of field is deeper, but still not deep enough to cover all your subjects. This image is the result of a medium aperture opening (f/8), not big (f/1.8), and not small (f/22). Now, let’s consider what happens if we stop down, or close the aperture to a small opening like f/22 (see figure 4.9).

Figure 4.9 – Three young people at f/22, shutter speed at 1/40s, 100 ISO

Figure 4.9 – Three young people at f/22, shutter speed at 1/40s, 100 ISO

Aha! Now everything in the picture is in focus (figure 4.9). An aperture as small as f/22 makes it easy to get sharp focus. Remember, you focused on the girl in front in all these pictures. At first, only the girl in red was in focus (f/1.8), and as the aperture got smaller, more and more of the surroundings came into sharp focus (f/8 and f/22), without changing where the camera was focused.

So, as mentioned several times for emphasis, depth of field is simply the zone of sharp focus. It extends in front of and behind your focused subject, and gets deeper in both directions, toward the camera and away from it, as you stop down your lens.

If you set your camera to the aperture priority setting (usually A or Av) on the mode dial or manual mode (M on the dial), you can adjust the aperture to help control how deep the focus is in your pictures. I was using aperture priority, which let me set the aperture while the camera automatically adjusted the shutter speed for me (half automation is convenient).

We are going to discuss shutter speed next, so you’ll need to notice how the camera chose to change the shutter speed. In figure 4.7 the shutter speed started off at 1/6000s because it was a sunny day and I was using a large aperture (aperture = how much light comes in).

With such a big aperture opening, lots of light was coming into the camera. Since I was using aperture priority (A or Av) mode, the camera was able to select an appropriately fast shutter speed to let all that light in for only a very short period of time. Otherwise, the image would have been overexposed from too much light.

I was using 100 ISO for these pictures so they would be noise free. Yet, even at that relatively insensitive ISO setting, because I was using a large aperture opening and a lot of light was coming in, the camera needed to limit that light by using a very fast shutter speed of 1/6000s (shutter speed = how long light comes in).

Later, as I stopped down the aperture to let in less light (smaller hole), the camera compensated by letting the light come in a little longer with a slower shutter speed (figure 4.8 shows the speed as 1/500s).

Finally, in the last image (figure 4.9), I stopped the lens all the way down to f/22 (tiny hole), which obviously limited the amount of light coming in considerably. The camera compensated by using a very slow shutter speed of 1/40s to let the light come in for a much longer time.

If I had been using manual mode instead of aperture priority, I would have had to adjust both the aperture and shutter speed myself. Aperture priority made it easier for me by adjusting the shutter speed automatically when I changed the aperture. I like semi automation because it works very well in today’s cameras. We’ll talk more about semi automation in the next chapter.

These pictures were fairly easy to take under sunny skies with stationary subjects, but you can see where the shutter speed exposure compensations could get troublesome if these three subjects were playing ball or jumping around. 1/40s will not stop action very well.

This is when the experienced photographer takes advantage of motion control (next section) and becomes less concerned about depth of field. Sometimes you have to make a trade off (speed over depth). When there is action you want to freeze involved, depth of field cannot take absolute priority in action shooting because the slow shutter speed resulting from using a small aperture will not stop action. So, the emphasis must switch from the aperture control to the shutter speed control. Shutter speed provides motion control.

Tip: I could have used manual mode to take these images, setting the aperture and shutter speed manually, but I’m a believer in using technology to help myself when it is appropriate to do so. I controlled what I wanted to control, the aperture, and let the camera save me time by automatically adjusting the shutter speed. My purpose was to effectively control and extend the depth of field in these three images, using the aperture (depth of field control), not the shutter speed (motion control). I was not overly concerned about the shutter speed, except for that last one of 1/40s (figure 4.9). With the lens I was using, the shutter speed of 1/40s is getting awfully slow and my picture could have started getting blurry from camera vibrations. Please refer to the upcoming section called Reciprocal Focal Length Shutter Speed Rule to get a better understanding of why you have to pay careful attention to shutter speed when handholding your camera.

Assignment: Set your camera to 800 ISO and aperture priority mode (A or Av). Take a picture of an outdoor subject with your camera’s largest aperture opening (f/1.4 to f/4), as close as your camera’s lens will focus. Include some background and try to make the background look blurry (shallow depth of field with a large aperture). If you are using a kit lens with a maximum aperture of f/3.5, it will be a little harder to blur the background, but if you get close to your subject, the background will blur. Now, shoot a second picture of the same subject at your lens’s minimum aperture (usually f/22). Compare the two pictures on your computer monitor at 100 percent zoom in. Pay careful attention to how the depth of field difference between the maximum and minimum aperture affects the subject and the background. Does the subject look any different? Does the background look any different?

Beyond Point-And-Shoot

Note: This article is an excerpt from a chapter of my book, Beyond Point-and-Shoot: Learning to Use a Digital SLR or Interchangeable-Lens Camera. Please review the book here: http://www.pictureandpen.com/BeyondPS.asp

Keep on capturing time…
Darrell Young

Darrell Young

Darrell Young is an active member of the Nikonians User Community, Nikon Professional Services (NPS), Professional Photographers of America (PPA), North American Nature Photography Association (NANPA), and the author of 18 photography books from NikoniansPress and Picture and Pen Press, through Rocky Nook. You may review a few of Darrell’s books here. He has been an avid photographer since 1968 when his mother gave him a Brownie Hawkeye camera. Here is one of Darrell’s nature image portfolios.

His website, www.PictureAndPen.com, was created to support the readers of his educational books, photography students, and clients. Visitors to his website will find articles and reviews designed to inform, teach, and help you enjoy your photographic journey.

Join Darrell on FacebookTwitter, and Google+

3 Comments

Leave a Reply

Your email address will not be published. Required fields are marked *