Blurry Background on a Budget: Settings That Work Without a $2000 Lens
The question comes up on every beginner forum: how do I get a blurred background without an expensive lens? The honest answer has two halves. Aperture is only one of the things that control blur, and the others cost nothing. But a kit lens still has a ceiling, and it helps to know where it sits.
The numbers
For a head-and-shoulders portrait with the background far away, the size of one out-of-focus point of light, as a share of the frame height, is about the focal length divided by 700 times the f-number. Here is what that gives:
| Lens and aperture | Blur disc, % of frame height |
|---|---|
| Kit zoom, 18 mm at f/3.5 | 0.7 |
| Kit zoom, 35 mm at f/4.5 | 1.1 |
| Kit zoom, 55 mm at f/5.6 | 1.4 |
| 50 mm f/1.8 prime | 4.0 |
| 85 mm f/1.8 prime | 6.7 |
So the long end of a kit zoom blurs about twice as much as the wide end, and a cheap 50 mm f/1.8 blurs nearly three times as much as the kit zoom at 55 mm. The free techniques below can take a kit lens from the first row to the third, and they cost nothing. They do not make it equal to a fast prime, and an inexpensive 50 mm f/1.8 is the best-value upgrade if you want more.
Push the background away
This is the most powerful free lever. The numbers above assume a background at infinity, and real backgrounds are closer. Take the 55 mm kit lens framing a head-and-shoulders portrait from about 1.1 m. A background 1 m behind the subject gets you about half of the full blur. At 3 m behind, about three quarters. At 10 m behind, about 90 percent. Standing someone against a wall wastes most of what the lens can do, and moving them a few metres in front of a distant background costs nothing.
Use the long end of the zoom
Zoom to the longest focal length and step back to keep the framing. Blur grows with focal length for the same framing, so 55 mm at f/5.6 gives double the blur of 18 mm at f/3.5. Be clear about what changes. At the same framing the zone in focus on your subject stays about the same, which is the point of the aperture versus distance post. It is the background that gets blurrier and looks larger and closer, which is also the effect described in the telephoto compression post.
Fill the frame
Getting closer, so the subject fills more of the frame at the same focal length, increases the magnification, and the blur grows with it. It also shrinks the zone in focus very quickly. With a 50 mm lens at f/5.6, the zone is about 1.2 m deep at 3 m but only about 28 cm at 1.5 m, a quarter, not a half. That is what makes a close subject separate from its background. Near a lens's minimum focusing distance you cannot go closer, so check it.
Stacking the three
Put the subject well in front of an open background, zoom to the longest focal length, fill the frame, and use the widest aperture available at that zoom, usually f/5.6 on a kit lens. Compare the best case with other options. A kit lens at 55 mm and f/5.6, with a background 10 m behind, gives about 1.3 percent of the frame height. A 50 mm f/1.4 with a wall only 1 m behind still gives about 2.6 percent. So technique helps a kit lens a lot, and it still does not beat a fast prime used lazily.
What a fast prime buys
A fast prime gives more blur where distance cannot be improved, such as in tight rooms or with close backgrounds. It also gathers far more light, which matters in low light, and it makes extreme selective focus possible. For plain outdoor portraits against a distant background, a kit lens used well is often enough. And if you have no other lens, the post on portrait mode versus real bokeh explains what your phone does instead.
A test to run
Photograph a subject at 18 mm from close range, then at 55 mm from further back, keeping the subject the same size in the frame, at the widest aperture each setting allows. The background should be clearly blurrier in the second picture. Then repeat with the subject against a wall, and again 5 m in front of a distant background, to see how much the background distance matters. It takes a few minutes and teaches you more than any chart.
To see the zone in focus for your own lens and distance, use the calculator. The bokeh guide explains the blur numbers in more detail.
Related reading: Background Blur (Bokeh): How to Maximize It, Aperture vs Distance: What Affects DOF More?, Portrait DOF: Choosing the Right Aperture.