Creating portraits like the featured image above that have that beautiful background blur is actually much easier than you think.
There's really no secret or trick to it - it's simply understanding the factors at play.
Some of those factors are mechanical and have to do with your lens.
Others simply have to do with distance.
In total, there are four elements that influence the extent of blur in a portrait. Let's examine each!
First things first: if you aren't sure what aperture is, it's the size of the hole through which light passes into your camera's lens. That hole is created by a diaphragm like the one shown above. I'll quickly summarize aperture below, but for a more detailed look, check out this guide.
Naturally, the smaller the hole, the less light that enters the lens and larger the hole, the more light that enters your lens.
Aperture values are denoted in f-stops, like f/4, f/8 and f/11.
What gets a little confusing is the manner in which the aperture values relate to the size of the aperture. That is, f/2 indicates a very large aperture and f/16 indicates a very small aperture.
At first, you'd think that the larger number should indicate the larger aperture, but the f-number is a fraction. So, f/2 would become 1/2 and f/16 would become 1/16. Seen as a fraction, it's easy to see that 1/2 is larger than 1/16, and therefore f/2 is a larger aperture than f/16.
The size of the aperture also determines the depth of field. In a nutshell, depth of field refers to the area of the photo that's in sharp focus.
The larger the aperture, the shallower the depth of field. So, if you're shooting at f/2, the background will be more blurry than it would be at f/11 because at f/2 the depth of field is shallower.
To get a blurry background: Use a large aperture, say, in the range of f/2 to f/4.
Distance Between Subject and Background
A second determinant of how blurry your portrait backgrounds appear is the distance between the subject and the background.
This one is simple to understand because as the distance increases between the subject and the background, the amount of blur also increases.
That means if your portrait just doesn't have the level of blur you'd like to see, move your subject further away from the background.
In the image above, you can see that the background is a fair distance away, which helps create that nice blurriness that sets the subject apart in the shot.
To get a blurry background: Increase the distance between your subject and the background.
DISTANCE BETWEEN SUBJECT AND Your Lens
How far the subject is from your lens is yet another factor at play when striving for a blurry background.
In this case, the closer your lens is to the subject, the blurrier the background will be.
The image above demonstrates this concept well.
Note how close the subject is to the lens, and how the background is nicely blurred. That blur occurs even though the background isn't all that far away!
To get a blurry background: Decrease the distance between you and the subject.
Focal length is a fairly complex technical term that refers to the distance from your camera's sensor to the point of convergence of light in your lens.
For practical purposes, focal length indicates how long a lens is, and by virtue of that, how "zoomed in" the resulting image appears.
As an example, a 24mm wide-angle lens is a short focal length. As such, it produces images like the one above that capture more of the scene and appear "zoomed out," thus the name wide-angle.
Wide-angle lenses produce the least amount of background blur due to this zoomed out appearance. Notice in the image above how there's very little background blur. That's why wide-angle lenses are a favorite of landscape photographers because they aid in getting everything in the scene from foreground to background in focus.
On the other hand, longer focal length lenses, like a 200mm telephoto, produce the zoomed in look you see in the image above.
Because longer focal lengths get you closer to the subject, it has the effect of blurring the background.
That means that two photographers, one with a 24mm lens and one with a 200mm lens, standing side-by-side taking a portrait of the same person, will get vastly different results. The photographer with the 24mm lens will not have a blurry background where the photographer with the 200mm lens will.
To get a blurry background: Use a longer focal length lens.
Putting It All Together
In the introduction, I said that creating blurry portrait backgrounds is a lot simpler that it seems at first.
I hope you agree.
After all, two of the four factors are simply distance related - how far you are from the subject and how far the subject is from the background. To increase blur, move closer to the subject and move the subject further away from the background.
The other two elements are simple to resolve as well.
To increase blur, use a larger aperture.
Likewise, avoid shooting portraits with a wide-angle lens in favor of a longer focal length. That doesn't mean you need to go buy the largest telephoto lens you can afford. Even moving from a 24mm wide-angle to a 50mm standard lens will get you markedly improved background blur.
To see all these factors in action, check out the video below by Tom Greenwood of Sydney Portraits. Then, use these portrait photography tips to help you create gorgeous portraits of the people in your life.