Bokeh (BOH-key)

Have you ever wondered what the poetic blur in those beautiful shallow depth of field photos is called? The term is Bokeh (pronounced BOH-kay, from the Japanese word boke which means blur, or haze).  

In photography, bokeh is the aesthetic quality of the blur produced in the out-of-focus parts of an image, also defined as "the way the lens renders out-of-focus points of light". Different lenses render this effect in different ways depending on the shape of the lens, aperture, and lens aberrations. (Lens aberration “refers to a defect in a lens such that light is not focused to a point, but is spread out over some region of space, and hence an image formed by a lens with aberration is blurred or distorted, with the nature of the distortion depending on the type of aberration”.) Differences in lens aberrations and aperture shape cause some lens designs to blur the image in a way that is pleasing to the eye. Bokeh occurs for parts of the scene that lie outside the depth of field. I often enjoy deliberately using a shallow depth of field to create images with prominent out-of-focus regions. The shallower the depth of field (i.e. f2.0, or f1.8) the more prominent the bokeh will appear. 

This technique can be incredibly beautiful and useful when making portraits. By focusing on the prominent features of your subject, like the eyes, you can really draw the viewers attention into the gaze of the subject while eliminating distracting background information.