Bokeh is a term photographers throw around a lot. It refers to the shape and quality of the out-of-focus area in a photo. It’s most noticeable in how specular highlights and point lights are rendered, but it’s present everywhere.
How to Pronounce “Bokeh”
Pronounced “boh-keh,” this term comes from the Japanese word “boke,” which means something close to blur or haze, although it’s a lot more nuanced than that. In 1997, the “h” was added by Photo Techniques editor, Mike Johnston, so the written form more closely resembled the pronunciation.
There’s equal stress on both syllables—it’s not “boke” (rhyming with poke) or “boh-kee.” “Boh-kay” is pretty close as, like every language, Japanese also has regional variations. You can check out this video to hear the right (and just about every wrong) way to say bokeh.
Depth of Field and Bokeh
Bokeh is really a subjective quality judgment of the objectively out-of-focus areas of an image. An image in which the out-of-focus areas look good and add to the aesthetic is said to have “good bokeh.”
An image in which the out-of-focus area distracts or detracts from the aesthetic can be said to have “bad bokeh.” Again, though, because this is subjective, people might disagree on whether a photo has good or bad bokeh.
Because bokeh is only relevant when large portions of an image are out of focus, it’s usually associated with photography in which a shallow depth of field is desired, like portrait or some wildlife photography. It’s also associated with macro and sports photography because it can be a side effect of the gear or circumstances.
Of course, an image shot for any style of photography can have bokeh. We’ll get more into bokeh quality later, but for now, let’s talk about depth of field.
The depth of field is the amount of the focal plane that’s acceptably sharp to the viewer. It’s what determines what is in or out of focus in an image. In an image with a shallow depth of field, like the portrait on the left above, only a small part (in this case, just a few millimeters) of the focal plane is in focus. You’ll notice that even the model’s ears are slightly blurred.
In an image with a large depth of field, like the photo on the right above, everything is in focus. The depth of field is affected by the focal length of the lens, the aperture to which the lens is set, the distance the subject is from the camera, and the size of the camera sensor.
What matters for bokeh isn’t so much that images have out-of-focus areas, but rather, how they’re rendered. When something falls outside the depth of field, instead of being reproduced exactly on the camera sensor, it’s reproduced as a blurry circle.
This phenomenon is called a “circle of confusion.” It’s most apparent with point light sources, which is why lights and other specular highlights are so visible when they’re out of focus.
However, like everything to do with optics, there’s a little more nuance to it than that. Point light sources are only theoretically rendered as circles. How they actually appear is determined by the design and construction of the lens. So, that’s also what determines the bokeh quality.
Factors That Affect Bokeh
Several lens design elements affect how bokeh appears. The first is the number of aperture blades in the lens. Those with fewer aperture blades will render more polygonal circles of confusion. For example, a lens with seven aperture blades produces heptagons, while a lens with nine (or more) produces more rounded bokeh.
The aperture of the lens also affects bokeh. A wider aperture will produce bigger, rounder bokeh. At narrower apertures, the shape of the iris is more defined, whether it be a circle or a polygon, and the circles of confusion will be smaller.
Spherical aberration is present in all photographic lenses. The steps you take to correct for it also affect the bokeh of an image. A lens that heavily corrects for spherical aberration will have circles of confusion that are brighter around the outside than in the middle, which is called the “soap bubble” effect. A lens that corrects less for spherical aberration will have the opposite effect: circles of confusion with bright centers and faded edges.
The angle at which light enters the lens also affects bokeh. Toward the edge of an image, circles of confusion are often rendered more as ellipses than circles, which is called a “cat’s eye” effect. With some lenses, the cat’s eye effect is so heavy, the bokeh looks like it’s swirling in a circle.
Good Bokeh, Bad Bokeh, Ugly Bokeh
It’s probably pretty clear by now, but photographers have gone crazy deep on bokeh. There’s a lot of discussion over what makes good or bad bokeh, but there are a few points worth stressing.
Bokeh is a subjective judgment of quality about the objectively out-of-focus areas of an image. Good bokeh doesn’t necessarily make a good photo. A boring subject with pleasing bokeh will still make a boring photo, the out-of-focus areas will just look decent.
Avoid always using the widest aperture just to chase bokeh, thinking it will improve your images—there’s a lot more to it than that.
The photographer is what makes bokeh good or bad. Some people hate the soap bubble effect, while others buy lenses specifically to create it. Generally, though, smooth, circular bokeh is considered better looking because it’s the least likely to distract from the subject.
In our opinion, the image above has what we consider good bokeh, while the image below has bad. The out-of-focus areas are just too textured and eye-catching, and the soap bubble effect is very in-your-face.
Capturing Bokeh in Your Images
While we don’t generally recommend just taking photos of blurry backgrounds (it’s a bit of a cliché at this point). There are some things you can do if you want to increase the quality of the bokeh in your images or, at least, have more creative control over it.
Using a prime lens with a wide maximum aperture tends to give you more pleasing bokeh than consumer zoom lenses, especially if they’ve been designed for portrait or macro photography.
Shoot at the widest aperture possible that still keeps your subject fully in focus. Sometimes, that means wide open, but others, you’ll need to use a slightly narrower aperture to get everything you want sharp.
Think about your background, too. Point lights and bright specular highlights (like raindrops reflected off of leaves) provide the most defined bokeh, while dark shadows tend to render indistinctly.
Also, if you make the distance between your subject and background as large as possible, this gives you the blurriest background, and thus, smoother bokeh. Longer telephoto lenses will also increase this effect, as long as you can maintain a good distance between the subject and background.
It’s also important to learn how to accurately focus your camera. Some situations that lead to good bokeh are hard on your camera’s autofocus system.
Experiment and play around. Capturing good bokeh is one of those things you can really only learn by doing because it’s subjective.
Why Your Smartphone Has to Fake Bokeh
Most modern smartphones have a portrait mode that, among other things, blurs backgrounds to emulate the bokeh of a wide-aperture lens. Whether the effect looks good or not is up to you, but why it has to be faked is interesting.
Again, to achieve good bokeh, an image needs parts of the fore- or background to be out of focus. As we covered above, the aperture, focal length, and sensor size all affect the depth of field.
While smartphone cameras have wide fixed apertures (often f/1.8 or f/2.0), the focal length of the lenses are really short (generally, between 2-6mm). Because they also have very small sensors, the crop factor means they have the same angle of view as that of wide-angle or normal lenses on a full-frame DSLR.
Here’s the catch, though: the crop factor only affects apparent field of view, not the depth of field. It’s the actual focal length of the lens that matters, and on smartphones, the lenses have very short focal lengths. This, in turn, means there’s a very large depth of field, and thus, no bokeh.
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