Boke Blur

Boke Blur

Racking focus in this manner generates camera blur that is
accurate relative to the plane of focus, but it does not truly
create the look of a defocused lens, because the lens itself
is a major participant in that look.
Boke connotes the phenomenon whereby points of light
become discs of light (also called circles of confusion) that
take on the character of the lens itself as they pass through
the camera lens and aperture. Like lens fl ares (covered in
Chapter 12) these are purely a phenomenon of the camera
lens, not human vision; they can add beauty and suspense
to a shot.
Illuminated out of focus elements in a shot are, after all,
mysterious. Visual intrigue is created as the shot resolves in
or out of a wash of color and light.

A perfect lens passes a defocused point of light to the
back of the camera as a soft, spherical blur. A bright point
remains bright, but is larger and softer. Ordinary blur of a
low-dynamic-range image in 8 or 16 bit per channel color
mode instead merely dims the highlights.

Most camera lenses are not perfect, so instead of perfect
blurred spheres, boke spheres may be brighter toward the
edges than in the middle. An anamorphic lens will show
squashed spheres, and as with lens fl ares, the shape of the
aperture itself may be visible in the circles, making them
hexagonal (or pentagonal, and so on, depending on the
number of blades in the opening).