Bokeh

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This article is about the photographic usage of the term "Bokeh". For other uses of the term, please refer to Bokeh (disambiguation)

Image:Josefina with Bokeh.jpg Bokeh (from the Japanese boke ぼけ, "blur"Template:Ref) is a photographic term describing the subjective aesthetic qualities of out-of-focus areas in an image produced by a camera lens. For example, causing an out-of-focus background image may reduce distractions and emphasize the primary subject.

Although difficult to quantify, and hence open to debate, some lenses are believed to enhance overall image quality by producing more subjectively pleasing out-of-focus areas (bokeh).

Bokeh characteristics may be quantified by examining the image's circle of confusion. In out-of-focus areas, each point of light becomes a disc. In images taken by some lenses, that disc is uniformly illuminated, for others it is brighter near the edge, and for others it is brighter near the center. Some lenses show one kind of disc for out-of-focus points closer to the camera, and a different kind for points farther from the camera. Traditionally speaking, an out-of-focus point of light with a more illuminated center and a dimmer outer edge is considered to be more desirable than an evenly illuminated disc or one with brighter edges than center. A circle of confusion with darker edges has a less defined shape which allows it to blend with the surrounding image. A hard edge would tend to bring the eye away from the in-focus subject and toward the out-of-focus element.

The shape of the aperture is known to have a great influence on bokeh. Mirror lenses produce a "doughnut" bokeh that is generally considered unpleasant. Some lenses will show a many-sided shape rather than a circle, depending on the blades in their diaphragm. Generally lenses with more blades in the diaphragm tend to produce more "round" bokeh. Some lenses' diaphragms have blades with curved edges to make the aperture more closely approximate a circle rather than a polygon. It is important to keep in mind that this only comes into effect when the lens is stopped down to something other than its maximum aperture. When the lens is set to its maximum aperture, the aperture blades do not have any influence on the shape of the circle of confusion since they are retracted away behind the lens opening.

The degree to which the lens is corrected for chromatic aberration also affects bokeh. Highly over-corrected lenses (like some video lenses) produce out-of-focus highlights, a bright, sharp edge and a dark center. Older lenses tend to be less aggressively corrected for chromatic aberration. Bokeh can thus be seen largely as a function of modulation transfer function characteristics.

The other characteristics of a lens that cause it to produce pleasing bokeh are complicated. Some lens designs are known to produce a certain kind of bokeh, but most photographers do not fully understand how the lens design influences bokeh; they merely note whether a lens produces results that please them.

Bokeh is especially important for large-aperture lenses, macro lenses and long telephoto lenses because they are typically used with a narrow depth of field.

Bokeh is also important for "portrait lenses" (typically medium telephoto — 85–150 mm on 35-mm format) because the photographer would typically select a shallow depth of field (wide aperture) to have an out of focus background and make the subject stand out.

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Notes

  • Template:Note Mike Johnston, former editor of Photo Techniques magazine, claims to have coined the "bokeh" spelling to suggest the correct pronunciation to English speakers; see his Bokeh in Pictures article referenced below.
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External links

de:Bokeh fr:Bokeh pl:Bokeh ru:Боке

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