Bokeh
The aesthetic quality of out-of-focus blur in an image. Derived from the Japanese word for blur, it evaluates how pleasing defocused areas appear rather than simply measuring blur amount.
Bokeh refers to the aesthetic quality of out-of-focus areas in a photograph. From the Japanese "暈け" (boke, meaning blur), the term is said to have come into wider use in English-language photography circles around the 1990s. Unlike defocus measurement, bokeh evaluates how pleasing the blur appears - a subjective quality assessment of lens rendering.
Bokeh shape and character depend on lens optical design. Point-light bokeh discs offer one clue to a lens's bokeh characteristics.
- Aperture blade influence: More blades increase the number of polygon sides and bring discs closer to a circle; 9 or more is one design example. Fewer blades (5-6) create polygonal shapes. Rounded blade designs are used to keep discs closer to circular at wider apertures
- Spherical aberration: Under-corrected spherical aberration affects luminance distribution within bokeh discs. Soft, even background bokeh is valued in some evaluations
- Mechanical vignetting: At frame edges, barrel obstruction deforms discs into lemon (
cat's eye) shapes. Stopping down 1-2 stops reduces this - Onion ring bokeh: Concentric ring patterns; manufacturing marks on aspherical elements are cited as one cause in some modern lenses
Computational photography approximates bokeh through depth maps and kernel simulation. Smartphone portrait modes are one example, applying a modeled blur in post-processing (as of 2026). CG rendering allows custom aperture shapes for anamorphic or vintage lens effects.