Advanced Techniques January 12, 2026 4 min read

Background Blur (Bokeh): How to Maximize It

Three things decide how blurry a background gets: how long the lens is, how wide the aperture is, and how far the background sits behind your subject. Everything else people argue about, sensor size, lens brand, "bokeh quality", works on top of those.

What bokeh means

The word comes from the Japanese boke, "blur" or "haze". Strictly it describes how the out-of-focus areas look, smooth or busy, discs or smears, rather than how much blur there is. In practice people use it for both, so this page covers both: how to get more blur, and a little about what makes it pleasant. The shape side has its own post, on aperture blades and bokeh shape.

How much blur a lens gives you

For a fixed framing, the size of the blur on a distant background is proportional to focal length divided by f-number. An 85 mm lens at f/1.8 blurs far more than a 50 mm at f/1.8, and a 135 mm at f/2 more again. Here is what that looks like for a head-and-shoulders portrait on full frame with the background far away, expressed as the width of one out-of-focus point of light compared with the height of the picture.

Lens and aperture	Blur disc, % of frame height
24 mm f/2.8	1.2
35 mm f/1.8	2.8
50 mm f/1.8	4.0
55 mm f/5.6 (kit zoom, long end)	1.4
85 mm f/2.8	4.3
85 mm f/1.8	6.7
135 mm f/2	9.6
200 mm f/2.8	10.2

Two things stand out. A kit zoom at 55 mm and f/5.6 gives about a fifth of the blur of an 85 mm f/1.8. And an 85 mm at f/2.8 matches a 50 mm at f/1.8, so extra focal length can make up for a slower aperture. The numbers are tied to the framing, not the distance: step back and zoom in to keep the same framing and the same maths holds.

How far behind the subject the background needs to be

The table assumes a background at infinity. Real backgrounds are closer, and the blur falls off quickly. Take the 85 mm at f/1.8 shooting a head-and-shoulders portrait from about 1.7 m. A background 1 m behind the subject gets you a bit over a third of the full blur. At 3 m behind, about two thirds. At 10 m behind, about 85 percent. Most of the gain arrives in the first few metres, so the cheapest improvement in most portraits is moving the person away from the wall, not buying a faster lens.

Wider aperture also means a thinner slice in focus

With the same 85 mm f/1.8, the zone that is acceptably sharp is about 1.4 m deep when the subject is 10 m away, 35 cm at 5 m, and about 5 cm at 2 m. At f/1.2 or f/1.4 from two metres, the nose and the eyes can end up in different places. Faces tend to look better at f/2 to f/2.8 for that reason, which the portrait aperture guide goes into. Keep f/1.4 for the moments when you can afford a missed focus.

Sensor size

All of the above is for full frame. On APS-C, multiply the f-number by about 1.5 to compare like with like, so f/1.8 on APS-C gives roughly the blur of f/2.7 on full frame at the same framing. For Micro Four Thirds, multiply by 2. The full frame versus crop sensor post goes through why. A phone is the extreme case, and its blur is made differently, as the post on portrait mode versus real bokeh explains.

Lenses

If you are buying for blur, a 50 mm f/1.8 is the cheap way in, an 85 mm f/1.8 is where most people end up, and a 135 mm at f/1.8 or f/2 is the next step if you have room to stand back. Wildlife and sports photographers get their blur from 300 to 600 mm lenses, where even f/4 or f/5.6 smears a distant background. An f/2.8 zoom is fine, just not as strong as the fast primes. If you only own a kit lens, the post on getting blur on a budget covers what you can still do.

Lots of blur can still look bad

A busy background, branches, signs, patterned fences, blurs into a mess of bright shapes that fights the subject. Plain, dark or evenly lit backgrounds work best, and bright points of light are best kept out of the frame unless you want them as discs. Some lenses draw bright edges on those discs, or an "onion ring" pattern inside them. A test shot of a string of lights at wide aperture shows it quickly, and it is worth doing before buying second-hand glass.

To see what a particular lens, distance and aperture will do before you shoot, put them into the calculator and look at the near and far limits.