Bokeh is a term that photographers use a lot. It refers to the shape and quality of the area that is not focused on a photo. It is most noticeable in how speculative highlights and spotlights are reproduced, but it is 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 is much more nuanced than that. In 1997, “h” was added by Photo technology editor, Mike Johnston, so the written form was more similar to the pronunciation.
There is equal stress on both syllables – it is not “boke” (rhymes with poke) or “boh-kee.” “Boh-kay” is quite close because Japanese, like all languages, also has regional variations. You can check out this video to hear the right (and almost all wrong) way of saying bokeh.
Field depth and Bokeh
Bokeh is really a subjective quality assessment of the objectively focused areas in an image. An image where the areas that are not in focus look good and increase the aesthetics are said to have “good bokeh.”
An image where the area that is not in focus distracts or impairs the aesthetic can be said to have “bad bokeh.” But again, since this is subjective, people can not agree on whether a photo has good or bad bokeh.
Since bokeh is only relevant when large parts of an image are out of focus, it is usually associated with photography where a shallow depth of field is desired, such as portraits or certain nature photography. It is also associated with macro and sports photography as it can be a side effect of the tool or the circumstances.
Of course, a picture taken for all types of photography can have bokeh. We’ll learn more about bokeh quality later, but let’s talk about depth of field now.
Depth of field is the amount of focus plane that is acceptably sharp to the viewer. It is what determines what is in or out of focus in an image. In an image with a short depth of field, like the portrait on the left above, only a small part (in this case only a few millimeters) of the focus plane is in focus. You notice that the model’s ears are also blurred.
In an image with a large depth of field, like the image to the right above, everything is in focus. 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 sensor size of the camera.
What matters to bokeh is not so much that images have out-of-focus areas, but rather how they are rendered. When something falls outside the depth of field, instead of being reproduced exactly on the camera sensor, it is reproduced as a blurred circle.
This phenomenon is called a “circle of confusion.” It is clearest with point light sources, which is why light and other speculative highlights are so visible when they are out of focus.
Like everything that has to do with optics, however, it is a little more nuanced than that. Spot light sources are only theoretically represented as circles. What they actually look like is determined by the design and construction of the lens. So that is also what determines the bokeh quality.
Factors Affecting Bokeh
Several lens design elements affect what bokeh looks like. The first is the number of aperture blades in the lens. Those with fewer aperture blades produce 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 lens’ aperture also affects bokeh. A wider aperture produces a larger, rounder bokeh. With narrower openings, the shape of the iris is more defined, whether it is a circle or a polygon, and the circles of confusion become smaller.
Spherical aberration occurs in all photographic lenses. The steps you take to correct for it also affect the bokeh of the image. A lens that strongly corrects for spherical aberration will have circles of confusion that are brighter around the outside than in the center, 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 pale edges.
The angle at which light enters the lens also affects bokeh. Towards the edge of an image, circles of confusion are often rendered more like ellipses than circles, which is called a “cat’s eye” effect. With some lenses, the cat’s eye effect is so heavy that the bokeh looks like it is swirling in a circle.
Good Bokeh, Bad Bokeh, Ugly Bokeh
It’s probably pretty clear now, but photographers have gone crazy deep on bokeh. There is a lot of discussion about what makes good or bad bokeh, but there are some points that are worth emphasizing.
Bokeh is a subjective quality assessment of the objectively focused areas of an image. Good bokeh does not necessarily make a good photo. A boring motif with appealing bokeh will still make a boring photo, areas that are not in focus just look decent.
Avoid always using the widest aperture just to chase bokeh and think it will enhance your photos – there is much more 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. In general, however, smooth, circular bokeh is considered more attractive because it is least likely to distract from the subject.
In our opinion, the picture above has what we consider to be good bokeh, while the picture below has bad. The areas that are not in focus are far too structured and eye-catching, and the soap bubble effect is very in-your-face.
Capture Bokeh in your photos
While we generally do not recommend just taking pictures of blurred backgrounds (it’s a bit of a cliché at this point). There are a few things you can do if you want to increase the quality of bokeh in your photos or at least have more creative control over it.
Using a primary lens with a wide maximum aperture tends to give you more comfortable bokeh than consumer zoom lenses, especially if they are designed for portrait or macro photography.
Shoot with the largest possible aperture that still keeps your subject in focus. Sometimes it means wide open, but others you have to use a slightly narrower aperture to get everything you want sharp.
Also think about your background. Spotlights and bright mirror highlights (like raindrops reflected from leaves) give the most defined bokeh, while dark shadows tend to blur.
Making the distance between the subject and the background as large as possible gives you the most blurred background and thus a softer bokeh. Longer telephoto lenses will also increase this effect, as long as you can keep a good distance between the subject and the background.
It is also important to learn to focus the camera precisely. Some situations that lead to good bokeh are difficult for the camera’s autofocus system.
Experiment and play. Catching good bokeh is one of the things you can really only learn by doing because it is subjective.
Why Your Smartphone Must Forge Bokeh
Most modern smartphones have a portrait mode that, among other things, blurs backgrounds to mimic bokeh from a lens with a wide aperture. Whether the effect looks good or not is up to you, but why it must be falsified is interesting.
Again, to achieve good bokeh, an image needs parts of the front or background out of focus. As we covered above, 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 is very short (generally between 2-6 mm). Since they also have very small sensors, the crop factor means that they have the same point of view as wide-angle lenses or normal lenses on a full-frame DSLR.
Here, however, is the catch: the cropping factor only affects the apparent field of view, not the depth of field. It is the actual focal length of the lens that matters, and on smartphones the lenses have very short focal lengths. This in turn means that there is a very large depth of field and thus no bokeh.