Bokeh
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In photography, Bokeh is a Japanese word - the transliteration of a Japanese word for "blur" - describing the subjective aesthetic quality of out-of-focus areas of an image projected by a camera lens. For example, in some images the background may be deliberately caused to be out-of-focus to reduce distractions and to emphasize the primary subject.
Some lenses are thought to produce more pleasing out-of-focus areas that enhance the over-all quality of the image. Bokeh is a quite subjective quality that is difficult to quantify and is sometimes debated.
Bokeh characteristics may be quantified by the circle of confusion. In out-of-focus areas, each point of light becomes a disc. In 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 far 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 as 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. 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 it is retracted away behind the lens opening.
The other characteristics of a lens that cause it to produce pleasing bokeh are complicated. Most photographers do not 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 macro lenses and long telephoto lenses becauses they're 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, to make the subject stand out.
See also
External link
- Bokeh explained by Harold Merklinger (http://www.luminous-landscape.com/essays/bokeh.shtml)de:Bokeh