Definition: Bokeh

Bokeh

In photography anything that is outside the ‘Depth of Field‘ will be out of focus. Any part of the image that is out of focus exhibits ‘bokeh’. This Japanese word is pronounced BOK-kay. It is the blur or out-of-focus component of the image.

Bokeh is created by a combination of the lens and aperture. The lens creates out of focus areas of the image when the circle of confusion is large enough to cause the sharpness to be lost. The aperture forms the shape of the circles of confusion. Its shape determines the shape of the light beams that pass through the lens.

All lenses create bokeh. However, the bokeh that any individual photographic lens creates is the result of the unique characteristics of that particular lens. Its shape, any optical aberrations it exhibits; its situation in the photographic lens-set and the aperture all affect the shape of the bokeh. This combination of factors may create bokeh that is pleasing to the eye, or not. Photographic lenses that create more pleasing bokeh have higher sales value. Manufacturers therefore expend research and development resources to ensure that the bokeh produced by a lens is pleasing.

Bokeh is an important component of photographic composition. Photographers frequently create shallow focus so the out-of-focus area of the image does not draw the eye. This points the attention of the viewer to the area of the picture in focus emphasizing the important aspects of the image. Bokeh can be a very pleasing part of an image, or it can be simply ignorable. In either case it creates an atmosphere and can modify the content of the picture in a positive or negative way. As a controllable aspect of photography it is an effective mechanism for affecting the viewers understanding of the image.

The picture above was taken, out of focus, with an eight second exposure at night. All the bright highlights are shown as ‘circular’ spots (except the ones that merge or were moving lights). Bokeh is often visible around strong highlights like light sources. Many people assume that these highlights are the bokeh. In fact bokeh is not only the highlights. Any out-of-focus blur is bokeh. The highlights are only more prominent because of the intensity of the light that created them.

Bokeh tends to form a circle only when the aperture is at it widest. In some photographic lenses when the aperture is at its widest the iris is withdrawn behind the circular fixed aperture set into the diaphragm. At other aperture sizes the iris blades form the shape of the aperture and they do not form a perfect circle. Instead the blades form a shape which has sides corresponding to the number of blades. It is this shape which forms the bokeh shape of the most prominent highlights. In the picture above, taken at f8, if you look carefully, you can see that the bokeh of the highlights have eight sides (click here to see the image enlarged). This lens has circular bokeh at f 1.2 (wide open).

The tendency that bokeh has to form near circles is because of the shape of the aperture. However, it is possible to create bokeh of different shapes. For example, cut a heart shape into a piece of card and held on the front of the lens. Now shoot an image that will create bokeh. You will produce heart-shaped bokeh highlights. This Google images page on ‘shaped bokeh‘ demonstrates the point.

It is the way that bokeh looks that gives it its character. Each spot of light in a photograph is really a tiny near-circle. The aberrations in the lens never allow a perfect point of focus. So it is the look of the point of focus that provides the quality of the bokeh in the image. Of course, depending on your view point and the type of image you want to produce, the quality of the bokeh may be important.

The bokeh circles made by a lens will have specific characteristics. Other lenses will vary. One type is a well formed circle with a fringing edge (see diagram: type 1) and can have sharp edges and strong fringes. This represents a lens with poor focus. A more neutral form is where the bokeh circle forms an evenly lit disc (type 2). The edge is defined by the absence of any more light in that circle. The graduated bokeh circle is one that has a more intense central light gradually diminishing to the edge. The graduated form of bokeh creates softer, less discordant bokeh for most purposes. It will blend easily with other bokeh circles around it. In most cases bokeh is designed to be ignored or to help the viewer to find the sharp, well defined, parts of the image. If bokeh is harsh and obvious it will distract the eye.

As with all compositional elements judgement is with the viewer. Success with bokeh is dependent on the photographers skills to use the bokeh that their lens produces to make the best photograph possible. Some forms of the bokeh circle may not be right for the photograph in production. However, that is part of the creative decision-making of lens choice and the making of the photograph. However, your lens purchasing choice should consider the quality of the bokeh.

Bokeh has an infinity of uses and ways to help the photographer express their creativity. Getting to know how to control bokeh takes practice with your equipment and is the result of understanding it and skillfully creating the image you want with it.