Bokeh

In photography, bokeh (/ˈboʊkə/ BOH-kə or /ˈboʊkeɪ/ BOH-kay; Japanese: ) is the aesthetic quality of the blur produced in the out-of-focus parts of an image produced by a lens. Bokeh has been defined as 'the way the lens renders out-of-focus points of light'. Differences in lens aberrations and aperture shape cause some lens designs to blur the image in a way that is pleasing to the eye, while others produce blurring that is unpleasant or distracting ('good' and 'bad' bokeh, respectively).Bokeh occurs for parts of the scene that lie outside the depth of field. Photographers sometimes deliberately use a shallow focus technique to create images with prominent out-of-focus regions. Bokeh is often most visible around small background highlights, such as specular reflections and light sources, which is why it is often associated with such areas. However, bokeh is not limited to highlights; blur occurs in all out-of-focus regions of the image. The term comes from the Japanese word boke (暈け or ボケ), which means 'blur' or 'haze', or boke-aji (ボケ味), the 'blur quality'. The Japanese term boke is also used in the sense of a mental haze or senility. The term bokashi (暈かし) is related, meaning intentional blurring or gradation. The English spelling bokeh was popularized in 1997 in Photo Techniques magazine, when Mike Johnston, the editor at the time, commissioned three papers on the topic for the May/June 1997 issue; he altered the spelling to suggest the correct pronunciation to English speakers, saying 'it is properly pronounced with bo as in bone and ke as in Kenneth, with equal stress on either syllable'.The spellings bokeh and boke have both been in use since at least 1996, when Merklinger had suggested 'or Bokeh if you prefer.'The term bokeh has appeared in photography books as early as 1998.It is sometimes pronounced /ˈboʊkə/ (boke-uh). Though difficult to quantify, some lenses have subjectively more pleasing out-of-focus areas. 'Good' bokeh is especially important for macro lenses and long telephoto lenses, because they are typically used in situations that produce shallow depth of field. Good bokeh is also important for medium telephoto lenses (typically 85–150 mm on 35 mm format). When used in portrait photography (for their 'natural' perspective), the photographer usually wants a shallow depth of field, so that the subject stands out sharply against a blurred background. Bokeh characteristics may be quantified by examining the image's circle of confusion. In out-of-focus areas, each point of light becomes an image of the aperture, generally a more or less round disc. Depending on how a lens is corrected for spherical aberration, the disc may be uniformly illuminated, brighter near the edge, or brighter near the center. A well-known lens that exhibited the latter 'soap-bubble' characteristic was that produced by Hugo Meyer & Co., more recently revived by Meyer Optik Görlitz. Lenses that are poorly corrected for spherical aberration will show one kind of disc for out-of-focus points in front of the plane of focus, and a different kind for points behind. This may actually be desirable, as blur circles that are dimmer near the edges produce less-defined shapes which blend smoothly with the surrounding image.The shape of the aperture has an influence on the subjective quality of bokeh as well. For conventional lens designs (with bladed apertures), when a lens is stopped down smaller than its maximum aperture size (minimum f-number), out-of-focus points are blurred into the polygonal shape formed by the aperture blades. This is most apparent when a lens produces hard-edged bokeh. For this reason, some lenses have many aperture blades and/or blades with curved edges to make the aperture more closely approximate a circle rather than a polygon. Minolta has been on the forefront of promoting and introducing lenses with near-ideal circular apertures since 1987, but most other manufacturers now offer lenses with shape-optimized diaphragms, at least for the domain of portraiture photography. In contrast, a catadioptric telephoto lens renders bokehs resembling doughnuts, because its secondary mirror blocks the central part of the aperture opening. Recently, photographers have exploited the shape of the bokeh by creating a simple mask out of card with shapes such as hearts or stars, that the photographer wishes the bokeh to be, and placing it over the lens.