Learning how to control the Depth of Field in your photos is probably the single biggest way that you can make an artistic impact, other than maybe changing the composition of the photo itself.
I love playing with the depth of field to achieve different effects, whether it’s producing a soft, blurred background to really bring all the attention to my subject, or when shooting landscapes, making sure that everything is in sharp, precise, focus, from that tree branch in the foreground, to those mountain peaks 20 miles away.
Today I’m going to share with you how to control the depth of field in your photos. But first, what is the depth of field precisely?
To put it simply, depth of field is the amount of physical space within your photograph that is in sharp focus. A deep (large) depth of field means that many, if not all, of the objects in your photograph are in focus. On the other hand, a shallow (small) depth of field means that only part of your photo is in focus.
Let’s look at the extremes. With a very deep depth of field, you might have nearly everything in focus. At the other end of the spectrum, a person’s nose may be in focus with the rest of their face blurred (very shallow depth of field).
The depth of field is best illustrated by example. Look at the two photos below to get a better understanding of deep vs. shallow depth of field.
This first image of a railroad line was shot using a very deep depth of field. Notice how everything is in focus from the closest rail slat to the concrete walls in the distance. This photo was taken with a small aperture.
The photo of the snake is an example of a very shallow depth of field. Even though the snake’s head is in sharp focus, its body, just a few inches further away, is blurred. This photo was taken using a very large aperture and telephoto lens (also good for keeping distance from the snake!).
Now I’m going to show you how to control the depth of field using the settings and positioning of your DSLR camera. There are three ways to do this, or some combination thereof.
Aperture is a camera setting you can use to control the size of the opening in your lens. Making this opening larger allows more light in, which allows you to use a faster shutter speed, but more interesting for us, it also has the effect of reducing the depth of field.
Aperture is measured in f-stops, and might for example range from f/1.8 to f/16 in a typical lens. The smaller the f-number, the larger the aperture and vice versa. So for a very shallow depth of field, you would want to use a number like 1.8 while high f-numbers would be used to try to keep as much in focus as possible. A middle f-number of something around 8 would be useful for keeping the majority of the foreground in focus, but the background a bit blurry.
The easiest way to control aperture on your DSLR camera is to use aperture priority mode. This is the A setting on Nikon cameras, or the Av setting on Canon cameras. Aperture priority mode will allow you to set the aperture to whatever you want within the limits of the lens you are using, and the camera will select a shutter speed accordingly to give you a proper exposure.
Distance to your subject
Another means of controlling the depth of field in your photos is to change the distance to the person or object you are photographing.
The Depth of field becomes much more shallow when focusing on subjects that are very close to the camera, whereas if you are focusing on something some distance away, the depth of field is much wider, allowing more of the scene to be in focus overall.
This photo of cherry blossoms in bloom was shot with a combination of large f/1.8 aperture, and at very close range, only a foot or two away from the flowers. Notice how the buildings in the background are completely blurred out for nice effect.
Focal length can also be used to control the depth of field. Focal length is essentially the “zoom” factor you are using in your lens and is specified in mm. A typical zoom lens might have a variable focal length of 18-55 mm, for example.
With all other things equal, increasing focal length tends to make the depth of field more shallow, and vice versa for short focal lengths. That 300mm telephoto lens is going to have a super shallow depth of field compared to your 14mm prime lens!
In actual practice you’ll want to use various combinations of the above three methods to control the depth of field depending on the look you are going for in your photo.
If you’re shooting a subject that you really want to stand out, you’ll want to use a small aperture, get as close as possible, and use a relatively long lens. On the other hand, if you’re shooting a landscape shot where you want a very wide depth of field, you can use a wide angle lens and high aperture — and you probably have no choice but to be far away!
Since aperture is generally the easiest to control, you’ll usually want to choose your lens and shooting position first, while using aperture to fine tune more precisely the depth of field that you want.
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