What is Bokeh in Photography?

Introduction: What is (and Isn’t) Bokeh?

If you’ve spent any time around pho­tog­ra­phy forums, work­shops, or social media, you’ve prob­a­bly heard some­one say, “This lens has so much bokeh,” or “Why can’t I get enough bokeh in my shots?” As some­one who teach­es photography—and some­one who enjoys nuance—I can’t help but cringe a lit­tle. The term “bokeh” is often used as though it’s syn­ony­mous with blur, specif­i­cal­ly the amount of it. Tech­ni­cal­ly, this isn’t cor­rect, but here’s where it gets inter­est­ing: this wide­spread mis­use is evolv­ing our lan­guage in real time. At this rate, “bokeh” might end up just mean­ing “blur,” and every­one will still know what’s being said.

I get the appeal of this con­fla­tion. As a term, blur is ambiguous—it can mean motion blur, opti­cal aber­ra­tions, or just gen­er­alised soft­ness in an image. But in this con­text, we’re specif­i­cal­ly talk­ing about the parts of an image ren­dered out of focus because they fall out­side the depth of field. Unfor­tu­nate­ly, there isn’t a sin­gle Eng­lish word that exclu­sive­ly describes those areas. Terms like “out-of-focus areas” or “defo­cus blur” are accu­rate, but they’re clunky and awk­ward in casu­al use. This is where “bokeh” shines—it’s suc­cinct, pre­cise, and has a cer­tain ele­gance. But sim­plic­i­ty comes at a cost. When “bokeh” is used to mean any blur, we lose its unique and nuanced mean­ing: the aes­thet­ic and tech­ni­cal qual­i­ties of the defo­cused areas in an image.

Blur vs. Bokeh

Let’s clar­i­fy an impor­tant dis­tinc­tion: blur refers to the amount and degree of out-of-focus ren­der­ing in a pho­to, while bokeh describes the qual­i­ty and char­ac­ter of that blur. The two con­cepts are close­ly relat­ed but not inter­change­able.

What is Blur?

Blur is a broad term that encom­pass­es any lack of sharp­ness in an image. It can result from sev­er­al fac­tors, includ­ing:

• Motion blur: This type of blur occurs when either the sub­ject or the cam­era moves dur­ing an expo­sure.
• Lens aber­ra­tions: Opti­cal imper­fec­tions in lens design can intro­duce blur by caus­ing dis­tor­tion, uneven sharp­ness, or soft­ness across parts of the frame.
• Defo­cus blur: The inten­tion­al or unin­ten­tion­al blur cre­at­ed when parts of a scene fall out­side the depth of field.

What is Bokeh?

Bokeh refers to the aes­thet­ic qual­i­ties of defo­cus blur—the char­ac­ter and visu­al appeal of the areas in an image that are inten­tion­al­ly out of focus. Unlike blur, which describes the amount of soft­ness, bokeh is about how that soft­ness looks and feels. It gen­er­al­ly con­sid­ers the fol­low­ing aspects:

• Tran­si­tion smooth­ness: Good bokeh is dis­tin­guished by how smooth­ly the focus rolls off into blur. Lens­es that ren­der grad­ual tran­si­tions from focused to out-of-focus areas are favoured.
• Ren­der­ing of high­lights: Bokeh is notice­able in out-of-focus high­lights. Depend­ing on the lens, these high­lights might appear smooth and cir­cu­lar, or they could take on harsh, uneven shapes with dis­tract­ing edges.
• Over­all har­mo­ny: Pleas­ing bokeh com­ple­ments your sub­ject. A back­ground with pleas­ant bokeh draws atten­tion to the sub­ject, while dis­tract­ing or “busy” bokeh can pull the viewer’s eye away.

The dis­tinc­tion is impor­tant because more blur doesn’t auto­mat­i­cal­ly mean bet­ter bokeh. Two lens­es might cre­ate the same amount of blur, but the ren­der­ing could be vast­ly dif­fer­ent. One might pro­duce smooth­ly ren­dered back­grounds that draw atten­tion to your sub­ject, while the oth­er cre­ates harsh, jit­tery, or ner­vous tex­tures or dis­tract­ing halos that are off­putting.

What Influences Bokeh?

Bokeh is shaped by a lens’s design, phys­i­cal con­struc­tion, and inter­ac­tion with light. While depth of field deter­mines the amount of blur, the char­ac­ter of that blur depends on spe­cif­ic design choic­es in the lens. Here’s how var­i­ous fac­tors shape bokeh.

Optical Design and Aberrations

The opti­cal design of a lens plays a lead­ing role in deter­min­ing bokeh qual­i­ty. Spher­i­cal aber­ra­tions are par­tic­u­lar­ly impor­tant. Lens­es with well-con­trolled spher­i­cal aber­ra­tion pro­duce smooth, even­ly lit out-of-focus high­lights. Over-cor­rec­tion leads to harsh, well-defined edges that make defo­cused regions look busy and dis­tract­ing. Con­verse­ly, under-cor­rec­tion cre­ates a Gauss­ian effect, where high­lights are bright­est at the cen­tre and fade soft­ly toward the edges.

Axi­al chro­mat­ic aber­ra­tion also impacts bokeh by intro­duc­ing magen­ta and green fring­ing in defo­cused areas, which is often called bokeh fring­ing. This aber­ra­tion occurs because dif­fer­ent wave­lengths of light focus at slight­ly dif­fer­ent dis­tances. High-qual­i­ty lens­es mit­i­gate these effects with extra-low dis­per­sion (ED) or flu­o­rite lens ele­ments, which aim to pro­duce a more colour-neu­tral bokeh.

Zoom vs. Prime Lenses and Bokeh

There’s a com­mon assump­tion that prime lens­es pro­duce inher­ent­ly more har­mo­nious bokeh than zoom lens­es. While primes often offer larg­er max­i­mum aper­tures and shal­low­er depth of field, mod­ern zoom lens­es can also deliv­er aes­thet­i­cal­ly pleas­ing bokeh. Dr. Ste­fan Ball­mann, Senior Sci­en­tist at ZEISS and expert in opti­cal design, explains:

“Peo­ple often assume that zoom lens­es will pro­duce a less har­mo­nious bokeh than fixed focal length lens­es. But that’s not nor­mal­ly true, at least as far as mod­ern zoom lens­es are con­cerned. That assump­tion basi­cal­ly stems from the fact that the out-of-focus high­light areas of cer­tain zooms are not con­sid­ered to be as ‘aes­thet­i­cal­ly pleas­ing’ as those of a fixed focal length lens. But it is true that prime lens­es usu­al­ly have a high­er max. aper­ture than zoom lens­es. There­fore, prime lens­es show a shal­low­er depth-of-field and thus demon­strate a faster tran­si­tion from focus to out-of-focus areas.”

Thus, while prime lens­es offer cer­tain advan­tages, mod­ern zoom lens­es are ful­ly capa­ble of ren­der­ing excel­lent bokeh. Can you deter­mine which of the fol­low­ing three pho­tos is the zoom?

I used the Canon RF 28–70mm F2.8 IS STM at 35mm for the sec­ond pho­to. The Fuji­film XF 23mm F1.4 R LM WR cap­tured the first, and the Canon EF 35mm F1.4 L USM cap­tured the third.

Aspherical Lenses and Onion Ring Bokeh

Aspher­i­cal lens­es, designed to reduce spher­i­cal aber­ra­tions and some forms of astig­ma­tism, can cre­ate unwant­ed pat­terns in defo­cused high­lights. These have com­plex sur­faces that allow for pre­cise light con­trol, par­tic­u­lar­ly at wide aper­tures. How­ev­er, their man­u­fac­tur­ing process has a draw­back.

Most mod­ern aspher­i­cal lens­es are cre­at­ed by press­ing molten glass into pre-shaped met­al moulds. These moulds are cre­at­ed with lath­es that leave micro­scop­ic con­cen­tric ridges on their sur­faces. When the lens is formed, these ridges are trans­ferred to its sur­face. While invis­i­ble in the focused areas of an image, they become vis­i­ble in defo­cused high­lights, appear­ing as con­cen­tric cir­cles, or “onion rings.”

Apodization Filters

Apodiza­tion fil­ters are an advanced fea­ture in some lens­es, such as Sony’s Smooth Trans Focus (STF) series, designed specif­i­cal­ly to enhance bokeh. These fil­ters are essen­tial­ly radi­al den­si­ty fil­ters built into the lens. They are dark­er at the edges and grad­u­al­ly light­en toward the cen­tre, soft­en­ing the edges of out-of-focus high­lights and pro­duc­ing excep­tion­al­ly smooth tran­si­tions.

The results are unre­al. Apodiza­tion fil­ters cre­ate bokeh with an almost per­fect Gauss­ian light dis­tri­b­u­tion, where out-of-focus high­lights fade grace­ful­ly into their sur­round­ings. How­ev­er, this Gauss­ian per­fec­tion comes with trade-offs. First, apodiza­tion fil­ters reduce light trans­mis­sion, mean­ing a lens with an f/2.8 max­i­mum aper­ture might only trans­mit light equiv­a­lent to f/4. This makes apodiza­tion lens­es less ver­sa­tile in low-light con­di­tions.

On a per­son­al note, while the bokeh from apodiza­tion lens­es is unde­ni­ably smooth, it often looks like some­thing gen­er­at­ed by a soft­ware defo­cus effect—almost arti­fi­cial in its flaw­less­ness. There’s an irony here: com­put­er-gen­er­at­ed imagery (CGI) tries to repli­cate the quirks and imper­fec­tions of real-world lens­es, such as onion rings and chro­mat­ic aber­ra­tions, to make scenes feel authen­tic. Mean­while, apodiza­tion fil­ters make real-world images look like flaw­less CGI.

Mirror Lenses and Doughnut Bokeh

Mir­ror lens­es, also called cata­diop­tric lens­es, are known for their char­ac­ter­is­tic dough­nut-shaped bokeh. Like con­sumer-grade tele­scopes, these lens­es use a com­bi­na­tion of mir­rors and glass to achieve long focal lengths in com­pact pack­ages that are more afford­able than refrac­tive lens­es fea­tur­ing sim­i­lar reach. Their unique opti­cal design is the key to both their size and their quirks.

Mir­ror lens­es typ­i­cal­ly fea­ture two mir­rors: a pri­ma­ry con­cave mir­ror locat­ed deep with­in the lens and a sec­ondary mir­ror mount­ed at the cen­tre of opti­cal­ly clear glass at the front. Unlike the front ele­ments of tra­di­tion­al lens­es, this glass doesn’t refract light—it sim­ply sup­ports the sec­ondary mir­ror. Light enters the lens, reflects off the pri­ma­ry mir­ror at the rear, bounces off the sec­ondary mir­ror, and then pass­es back through a hole in the pri­ma­ry mir­ror to reach the cam­era sen­sor. How­ev­er, because the sec­ondary mir­ror blocks the cen­tre of the opti­cal path and the pri­ma­ry mir­ror has a cen­tral hole, only light from the out­er edges of the mir­rors con­tributes to out-of-focus high­lights, cre­at­ing the dis­tinc­tive dough­nut-shaped bokeh asso­ci­at­ed with these lens­es.

Optical Vignetting: Catseye and Swirly Bokeh

Opti­cal vignetting is com­mon in many lens­es and occurs when light enter­ing the lens at steep angles near the edges of the frame is par­tial­ly blocked by the phys­i­cal struc­ture of the lens, such as the iris diaphragm, bar­rel, or inter­nal ele­ments. This restric­tion reduces the bright­ness toward the edges of the image and alters the shape of out-of-focus high­lights, mak­ing them resem­ble the shape of a cat’s eye or gib­bous Moon as they approach the frame’s edge.

The effect is most notice­able at large aper­tures and is reduced by increas­ing the F‑number. Anoth­er relat­ed effect is swirly bokeh, often seen in vin­tage lens­es like the Helios 44–2. This effect occurs when opti­cal vignetting com­bines with field cur­va­ture to cre­ate a spi­ralling dis­tor­tion in the defo­cused back­ground, giv­ing the image what some pro­po­nents call a “dream-like” qual­i­ty. While some pho­tog­ra­phers seek this aes­thet­ic, I find the swirls are dis­tract­ing and over­pow­er the sub­ject rather than com­ple­ment it.

Dust and Artifacts

One over­looked fac­tor that can sig­nif­i­cant­ly impact bokeh qual­i­ty in out-of-focus high­lights is lens clean­li­ness. Dust and debris inside the lens, and on the front or rear ele­ments can cre­ate vis­i­ble arti­facts in defo­cused high­lights. When light pass­es through these par­ti­cles, it scat­ters uneven­ly, pro­duc­ing faint spots or shad­ows in the blurred areas of an image. You can avoid or min­i­mize these arti­facts by keep­ing the front and rear ele­ments of your lens­es clean.

Simulating Background Blur in Post-Processing

Dri­ven by the influ­ence of smart­phone pho­tog­ra­phy, many soft­ware appli­ca­tions have made it pos­si­ble to enhance bokeh or sim­u­late shal­low focus dur­ing post-pro­cess­ing. These tools let you take your images beyond what your cam­era ini­tial­ly cap­tured. They can either com­ple­ment and refine the nat­ur­al bokeh of an image’s out-of-focus regions or sim­u­late shal­low focus in pho­tos unin­ten­tion­al­ly cap­tured with a large depth of field.

Enhancing Natural Bokeh

Appli­ca­tions like Adobe Light­room and Pho­to­shop pro­vide tools to enhance nat­ur­al bokeh. You can use masks to select the out of focus back­ground and adjust its expo­sure, con­trast, clar­i­ty, or sat­u­ra­tion to empha­size your sub­ject. For instance, you can select the blur­ry back­ground, slight­ly reduce its bright­ness and clar­i­ty to har­mo­nize the colours and con­trast, and use a grad­u­at­ed lin­ear fil­ter to blend it seam­less­ly into the fore­ground, improv­ing the over­all cohe­sion of your pho­to as I did in the fol­low­ing pic­ture (scroll over the pho­to to view the result).

Faking Bokeh with AI Tools

When shal­low focus isn’t achiev­able in-cam­era, AI-pow­ered tools can deliv­er sur­pris­ing­ly con­vinc­ing results—assuming you don’t look too close­ly. Fea­tures like Photoshop’s Neur­al Fil­ters or Lightroom’s Lens Blur use advanced sub­ject detec­tion and depth map­ping to sim­u­late shal­low depth of field. By iso­lat­ing the sub­ject from the back­ground, these tools apply a grad­u­at­ed blur to mim­ic the effect of a wide-aper­ture lens.

How­ev­er, these tools often strug­gle with fine and errat­ic details. Fly­aways, frizzy hair, scrag­gly beards, and ani­mal whiskers are fre­quent­ly trimmed or blurred awk­ward­ly. Glass­es and trans­par­ent objects present addi­tion­al challenges—sometimes they’re ful­ly or par­tial­ly blurred, while oth­er times the back­ground seen through them appears unnat­u­ral­ly sharp. Ear­li­er imple­men­ta­tions had dif­fi­cul­ty with spaces between fin­gers or limbs, con­fus­ing the algo­rithms and leav­ing sharp patch­es of back­ground that break the illu­sion.

AI-gen­er­at­ed bokeh also tends to suf­fer from uni­for­mi­ty issues, lack­ing the sub­tle nuances of opti­cal blur. Real bokeh is shaped by lens design, cre­at­ing imper­fec­tions like cat­s­eye high­lights or onion rings that add char­ac­ter. In con­trast, AI blur often appears over­ly smooth and ster­ile. Addi­tion­al­ly, elec­tron­ic noise in high-ISO images is often smoothed out in defo­cused regions while remain­ing intact on the sub­ject, cre­at­ing a jar­ring dis­par­i­ty. The qual­i­ty of results varies sig­nif­i­cant­ly across tools and imple­men­ta­tions, but these lim­i­ta­tions can make soft­ware-gen­er­at­ed bokeh a dead give­away to trained eyes.

The fol­low­ing pho­to­graph was tak­en using my ultra-wide angle Fuji­film XF8mmF3.5 R WR. Move your cur­sor over the pic­ture to see the attempt of Pho­to­shop’s “neur­al fil­ters” to iso­late the sub­ject and ren­der an arti­fi­cial­ly shal­low depth of field effect. Then pay atten­tion to how the fil­ter trim’s the tufts of fur and fine hairs around the ears.

Striking a Balance

Post-pro­cess­ing is a pow­er­ful tool, whether you’re enhanc­ing opti­cal blur or cre­at­ing it from scratch. When used thought­ful­ly, it can com­ple­ment the sub­ject and over­all com­po­si­tion, ele­vat­ing the image. While soft­ware may nev­er ful­ly repli­cate the quirks and imper­fec­tions of opti­cal defo­cus, it offers you the cre­ative flex­i­bil­i­ty to refine your images in once-impos­si­ble ways.

Conclusion

Bokeh is more than just blur—it’s a defin­ing char­ac­ter­is­tic of how a lens ren­ders out-of-focus areas, shap­ing the mood and impact of your image. Under­stand­ing the fac­tors that influ­ence bokeh and how to refine or sim­u­late it through post-pro­cess­ing gives you greater con­trol over your cre­ative vision. Whether you’re embrac­ing the quirks of opti­cal bokeh or explor­ing the pos­si­bil­i­ties of AI tools, mas­ter­ing bokeh is a small but pow­er­ful step toward ele­vat­ing your pho­tog­ra­phy.