You photograph a portrait with glowing lights in the background, review the image, and notice something unexpected.
Instead of soft, circular bokeh, some blurred lights look hexagonal, seven-sided, octagonal, or slightly angular.
Nothing is necessarily wrong with your lens.
Those geometric highlights are usually revealing something that normally stays hidden inside the lens: the shape of its aperture diaphragm.
Each bright point of light that falls far enough outside the focus plane can expand into a visible blur disc. Under the right conditions, that disc begins to resemble the opening the light traveled through.
When the opening is close to circular, the bokeh looks round.
When aperture blades form a visible polygon, the bokeh can reproduce that geometry.
Understanding this relationship makes polygonal bokeh much easier to diagnose, control, and even use creatively.
For a broader explanation of how defocused areas are created, please read What Is Bokeh in Photography.
What Is Polygonal Bokeh?
Polygonal bokeh describes out-of-focus highlights whose outer edges form noticeable straight sides rather than smooth circles.
Depending on the lens, you might see:
- Hexagons
- Heptagons
- Octagons
- Nonagons
- Slightly rounded polygons
- Almost circular shapes with faint flat edges
These shapes become easiest to recognize when small bright lights are strongly defocused.
Think about holiday lights, nighttime traffic, sunlight reflecting from water, illuminated windows, metallic reflections, raindrops catching light, or distant streetlights.
Ordinary blurred foliage might not make the shape obvious.
A bright point against a dark background will.
Most importantly, polygonal bokeh describes the outer shape of the blur disc. It does not describe rings, texture, or patterns inside it.
Your Bokeh Can Reveal the Shape of the Aperture
Most photographic lenses contain an adjustable diaphragm made of overlapping blades.
Changing your f-stop changes the size of the opening those blades create.
At a very wide aperture, the opening may be almost completely open, with the blades largely withdrawn from the light path. Under those conditions, out-of-focus highlights often appear relatively round.
Stop the lens down, and the blades move inward.
Now their edges begin defining the opening.
With six straight blades, the opening may look approximately hexagonal.
Seven blades can produce a seven-sided shape.
Eight may produce an octagon.
Nine blades create nine sides, although curved blade designs can make those sides considerably harder to notice.
That is why one lens can produce beautifully round highlights at one aperture and visibly geometric highlights only a stop or two later.
Your photograph is effectively giving you a tiny visual clue to the physical shape of the aperture.
Why Does Bokeh Often Look Round When the Lens Is Wide Open?
Maximum aperture frequently produces the roundest highlights a lens can create.
Consider a 50mm f/1.8 lens.
At f/1.8, the aperture diaphragm may open so wide that the blade edges have little influence on the central opening.
Photograph the same lights at f/2.8, f/4, and f/5.6, however, and the diaphragm gradually becomes more visible.
The result can be a progression from circles to subtly angular shapes and eventually to obvious polygons.
This is one reason photographers sometimes notice that bokeh looks smoother in one photo even when they use the same lens.
The lens did not change.
The aperture did.
If you need help understanding how aperture fits into the rest of your bokeh settings, please check out Best Camera Settings for Bokeh.
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Does the Number of Aperture Blades Matter?
Yes, although blade count is only part of the story.
A lens with relatively few straight blades tends to reveal its geometric shape more easily once you stop it down.
More blades create more sides, so the resulting opening more closely approximates a circle.
Compare a six-sided polygon with an eleven-sided one. Even before considering curvature, the eleven-sided opening resembles a circle much more closely.
Still, blade count alone doesn’t tell you whether a lens will produce beautiful bokeh.
Blade curvature matters too.
Modern lenses often use rounded diaphragm blades to keep the aperture more circular across a wider range of f-stops.
Two nine-blade lenses can therefore render highlights differently: one with highly curved blades, the other with a more obvious polygon.
Optical design, aberrations, highlight edges, focusing distance, and other factors also shape how the background looks.
Why Does My Bokeh Shape Change at Different F-Stops?
The aperture is not one fixed shape that becomes smaller.
As the blades move, their relationship to one another changes.
At one setting, the opening might appear almost circular. Several clicks later, you may see the flatter blade edges more easily.
That means you should not assume there is one universal f-stop where every lens suddenly develops polygonal bokeh.
Test the actual lens.
You might discover that f/2 produces beautifully rounded highlights, f/2.8 shows only slight geometry, and f/4 creates clearly defined polygons.
Another lens may behave differently.
Even a one-stop adjustment can noticeably change the background.
Polygonal Bokeh vs Cat-Eye Bokeh vs Onion-Ring Bokeh
These three characteristics can appear in similar photographs, but they are not the same optical effect.
Polygonal bokeh turns the outer highlight into a many-sided shape because the aperture diaphragm shapes the light.
Cat-eye bokeh usually makes highlights near the edges of the photograph look compressed or oval rather than round.
Onion-ring bokeh produces visible concentric texture inside the highlight.
One photograph can show more than one of these characteristics.
For example, a highlight near the corner might be slightly cat-eye shaped while also showing polygonal edges.
Another disc could look polygonal on the outside while containing faint onion-ring texture inside.
Diagnosing the correct feature matters because changing the aperture may help one problem while doing little for another.
How to Test Your Lens for Polygonal Bokeh
You can see exactly how your lens behaves with a simple test.
Arrange several small lights in the background. String lights, decorative LEDs, or distant lamps work particularly well.
Place another object much closer to the camera and focus accurately on that object.
Start at your lens’s maximum aperture.
Take one photograph.
Next, close the aperture by approximately one stop and photograph the identical scene.
Continue through several settings, perhaps f/1.8, f/2.8, f/4, f/5.6, and f/8, depending on the lens.
Keep the camera position, subject, focus point, and background lights as consistent as possible.
Compare the resulting highlights side by side.
Look specifically at:
- How round the highlights appear
- When straight edges first become visible
- How many sides you can identify
- Whether the corners differ from the center
- Whether the highlight edge becomes stronger or softer
- How the overall background changes as the aperture closes
This exercise tells you much more about your particular lens than memorizing a general rule.
How to Make Polygonal Bokeh Look Rounder
The simplest solution is often to open the aperture.
Move from f/4 to f/2.8, for example, and inspect the highlights again.
Going wider can reduce how strongly the blade geometry appears.
Changing bokeh size also helps.
Increase the distance between your subject and background, move closer to the subject when composition permits, or choose a longer focal length. Larger blur discs can create a stronger bokeh effect, though aperture geometry may still show through.
Background choice matters as well.
Isolated white bulbs against a nearly black background make every edge easy to inspect. Softer highlights mixed with foliage, color, reflections, or ambient illumination can make subtle polygons far less noticeable.
Finally, reconsider whether the shape is actually hurting the photograph.
View the full image rather than zooming in on one bokeh disc to 300%.
Sometimes the geometry disappears completely at a normal viewing size.
Does Polygonal Bokeh Mean You Need a Better Lens?
Not automatically.
A lens can produce polygonal highlights and still be exceptionally sharp, beautifully built, fast to focus, compact, lightweight, or excellent in low light.
Bokeh is only one aspect of lens rendering.
Still, photographers who frequently shoot portraits against lights may reasonably prioritize diaphragm design.
If round highlights are a major priority, look for lens specifications like rounded diaphragm blades, a 9-blade aperture, or an 11-blade aperture.
Also check out Top 8 Best Lenses for Bokeh Photography for more lens ideas.
Polygonal Bokeh Can Be a Creative Choice
Round bokeh is popular, but not required.
Geometric highlights can give an image a distinctive visual rhythm.
Older lenses, in particular, may create recognizable hexagonal or angular backgrounds that feel very different from the ultra-smooth rendering many modern optics produce.
Nighttime city scenes can work beautifully with this effect.
Defocused traffic lights, illuminated windows, café lights, reflections, or decorative bulbs can become repeating geometric shapes throughout the frame.
Instead of hiding them, intentionally place several polygons around the subject.
For locations and subjects where bright points of light are easy to find, please read Summer Night Photography Ideas.
Another creative approach is to use those geometric highlights as a separate layer in experimental photography. For ideas on combining defocused lights with another exposure, check out How To Create Multiple Exposure Photography With Light and Bokeh.
Once the shape becomes intentional, what initially looked like an optical flaw can become part of the photograph’s character.
Can You Fix Polygonal Bokeh in Editing?
Editing can soften distracting highlights, but completely rebuilding dozens of angular bokeh discs into convincing circles can become surprisingly time-consuming.
Local blur, healing, masking, or selective retouching may work when only one or two highlights are distracting.
Heavy correction is rarely the best first choice.
If you notice the effect while shooting, changing the aperture or composition usually yields a more natural result than redesigning the background afterward.
Another option is to reduce the prominence of one troublesome highlight. Darken it slightly, lower its contrast, or crop it from the edge if the composition still works.
The purpose of editing should be to keep attention on the photograph, not to make every blur disc mathematically perfect.
Check Geometric Highlights Before Making a Large Print
Polygonal highlights that seem insignificant on a phone can become stronger graphic elements once an image is enlarged.
Finish your crop first, then use the Print Size Converter to check how the remaining pixel dimensions relate to the print size you are considering.
For the rest of the print workflow, Printing Photos Perfectly: File Formats, DPI, and Print Quality explains how resolution, DPI, file format, sharpening, and export decisions affect the transition from a digital photograph to a finished print.
Assessing the image at or near its intended output size can also keep you from rejecting a photograph over details viewers may never notice.
Why Does My Bokeh Look Polygonal Instead of Round?
Polygonal bokeh usually appears because out-of-focus highlights are revealing the shape created by your lens’s aperture blades.
The effect often becomes more visible as you stop down.
Blade count determines the number of sides, while curved blades help the aperture stay closer to circular across a wider range of settings.
None of this automatically means the lens is defective.
Start by photographing the same lights at several apertures.
Watch how the shapes change.
Decide whether the geometry actually distracts from the photograph.
When rounder highlights matter, opening the aperture, adjusting distances, changing the background, or choosing a lens with a more circular diaphragm can help.
When the polygons look interesting, keep them.
Bokeh doesn’t need to be perfectly round to be beautiful.
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