What Is Bokeh? The Character of Out-of-Focus Blur

You look at a portrait where the background melts into something creamy and you say “beautiful bokeh.” In another frame the background is just as blurred, but the blur is restless, jagged, tiring to look at. Both images have shallow depth of field. The difference isn’t in the amount — it’s in the character. That’s exactly what bokeh means.

Let’s settle the distinction up front: depth of field tells you how much of the frame is sharp. Bokeh describes how the unsharp part looks. One is quantity, the other is quality. Shoot the same scene at the same aperture with two different lenses and the depth of field will be nearly identical — yet the background can look completely different.

Where the word comes from

The Japanese word boke (暈け) means “blur” or “haze.” The term entered English photography writing in 1997 via Photo Techniques magazine, where the editor added an “h” to keep people from mispronouncing it — and the spelling “bokeh” stuck.

The origin tells you something useful: Japanese lens designers took this idea seriously long before the West did. “Good bokeh” isn’t a measurable sharpness figure, it’s a deliberate design choice — some lenses give up a little resolution specifically to render blur more beautifully.

How bokeh is physically formed

A lens renders only one distance in perfect sharpness at a time. Every point outside that plane lands on the sensor not as a point but as a small disc — the circle of confusion from the depth of field guide.

The blur you see in a scene is simply countless such discs overlapping. So a lens’s bokeh identity is set by two things:

1. The shape of the disc — round, polygonal, clipped at the edges?
2. The brightness distribution inside the disc — bright in the middle, or bright at the rim?

Both come entirely from the lens’s optical and mechanical design. Your camera brand, sensor and megapixel count don’t determine bokeh directly. The lens does.

What sets the shape of bokeh balls

Aperture blades

Wide open, the opening is essentially circular, so bokeh balls come out round. The moment you stop down, the blades take over the shape: a 7-blade lens produces 7-sided polygons, a 9-blade lens 9-sided ones. This is why modern lenses use rounded blades — so the shape stays close to a circle even when stopped down.

For anyone who knows the f-stop scale this is directly actionable: want round bokeh balls, stay wide open; want sunstars, stop down. You cannot have both in the same frame.

Cat’s eye (mechanical vignetting)

You’ve probably noticed bokeh balls near the edges of the frame getting clipped into lemon or cat’s-eye shapes. The cause isn’t the aperture, it’s the lens barrel: oblique ray bundles coming from off-axis get cut off by the front and rear openings. This is called mechanical vignetting.

Onion rings

Some bokeh balls show concentric rings inside them. That’s the manufacturing signature of an aspherical element: microscopic steps left by moulding or grinding get reproduced as concentric rings in the out-of-focus disc. You can see this texture clearly in the larger discs in the photo at the top of this page.

Soap bubble

If the disc has a pronounced bright ring at its rim and a duller centre, that’s soap-bubble bokeh. It comes from overcorrected spherical aberration. Some classic lenses — and modern designs deliberately imitating them — build their entire character on this effect.

Creamy bokeh versus nervous bokeh

Shape aside, what really creates the “beautiful” or “ugly” impression is the edge transition of the disc. The deciding factor is how spherical aberration has been corrected:

• In an undercorrected lens, background discs fade out softly toward the rim → creamy, calm bokeh. The price is that foreground blur turns harsh.
• In an overcorrected lens, the rim of the disc hardens into a distinct ring. Thin branches in the background split into two separate lines — Japanese calls this nisen bokeh, “double-line bokeh.” The eye reads it as restless.

There’s a colour side too. Green or magenta fringes around out-of-focus edges come from longitudinal chromatic aberration (LoCA): blur in front of the focus plane picks up one colour cast, blur behind it the opposite one. Stopping down one or two stops reduces it markedly, and it can be partly cleaned up in editing.

Bokeh isn’t only the lens’s job — you choose the background

In practice, the thing that ruins bokeh most often isn’t an inexpensive lens, it’s the wrong background. The same lens behaves completely differently in two scenes:

• Hard scene: Thin sunlit branches, shrubbery, broken reflections on water. That’s countless small high-contrast points — each becomes a disc, they tangle into each other, and the frame turns restless.
• Easy scene: A plain wall in shade, a distant single-toned mass of foliage, point lights at night. Few sources, soft transitions.

So the right reflex in the field isn’t to swap lenses, it’s to take two steps sideways. Changing the background is free. We covered what this looks like in practice in natural light portraits.

A practical recipe for beautiful bokeh

We want to underline step four. Doubling the distance between subject and background usually does more than one extra stop of aperture. Do it with a cheap 50mm f/1.8 and the result is surprising — we explained why that lens gets recommended so relentlessly in your first prime lens.

If you’re wondering which focal length gives the most flattering separation for faces, see the comparison in choosing a portrait lens; the effect of focal length on perspective and background magnification is covered in the focal length guide.

Shooting bokeh balls on purpose

Bokeh balls don’t just happen — you set the scene up for them:

Drop the subject entirely, shoot distant lights out of focus, and you get a pure bokeh frame like the one at the top of this page. A city at night offers endless opportunities for this; night street photography explains how to set exposure in that environment.

Why does phone portrait mode look different?

Phone sensors are too small to produce this separation optically, so portrait mode adds the blur in software. A depth map is generated, the background is blurred, and synthetic bokeh discs are drawn on top.

Three things usually give it away: masking errors around fine detail like stray hair and glasses arms, blur that starts abruptly at the subject’s outline (real optics transition gradually), and discs around bright points that look too uniform, too computed. Why sensor size creates this gap is compared in full frame vs APS-C.

Common mistakes

• Confusing bokeh with depth of field: There’s no such thing as “more bokeh.” There’s shallower depth of field. Bokeh is character, not quantity.
• Shooting everything wide open: At f/1.2 the sharp band is so thin that one eye lands and the other misses. For most faces f/2 - f/2.8 is both safe and creamy enough.
• Never thinking about the background: A branchy, speckled background makes even the most expensive lens look nervous.
• Calling every kind of blur bokeh: Camera shake and motion blur aren’t bokeh; we gathered the causes in why photos come out blurry.
• Judging bokeh from a small screen preview: Nisen bokeh, onion rings and colour fringing only show up at 100%.