Pardon my French.
Bokeh is a Japanese word for the soft, painterly, out-of-focus effect provided by a telephoto lens; or the shallow DOF (depth of field) you can achieve by shooting “wide-open” with fast glass; e.g., the Nikon 85mm f/1.4.
I shot the tree and barn photos on this page with a 300mm lens and a 2x teleconverter, which doubled the focal length to an extreme 600mm. (1/640 sec at f/8.0, 1/3 EV, ISO 200). Click on the photos for large view.
I spot metered the tree and everything in the immediate foreground and background became an abstract blur—ideal for shooting portraits with no backdrop required. You can thus transform a “busy” b.g. into a swash of colors to compliment and emphasize your subject.
Bokeh is a common effect in Hollywood films, and one advantage of shooting movies with a DSLR is the ability to achieve shallow DOF with the appropriate lens.
Of course there are plug-ins that mimic the effect, or you could use Photoshop’s Lens Blur filter (see the before and after shot below),but do all this extra work? Besides, the software solution can look artificial and wind up a distraction.
Barn shot, 600mm.
Below, a cropped enlargement (detail) of the background with natural bokeh.
Now compare the original to the version below where, in Photoshop, I used Pixel Bender and applied the Oil Paint filter.
Nice… yet it’s no longer a photo.
Much better to be able to say “Look, Ma, no post-processing!”
Fast glass / long lens does the trick.