Bokeh

Bokeh is a Japanese-derived term used in photography to describe the aesthetic quality of blur in out-of-focus areas of an image. It is distinct from the quantity of blur — how much background separation occurs — and instead refers to how that blur looks: whether highlights render as smooth circles or show harsh edges, whether gradients between focused and unfocused areas are gentle or abrupt, and whether the overall character of the blur is visually pleasing. Bokeh quality is subjective, but lenses with smooth, rounded aperture blades and specific optical designs tend to be more consistently regarded as having pleasing bokeh.

The physical factors that determine how much blur is produced are aperture, focal length, subject distance, and distance from subject to background. A wider aperture produces shallower depth of field and more blur. A longer focal length compresses perspective and produces more background separation at the same aperture. Getting closer to the subject reduces depth of field. Putting more distance between the subject and background increases how much the background defocuses. On Micro Four Thirds, the 2x crop factor means that achieving equivalent background blur to a full-frame camera requires opening the aperture two stops wider. A 50mm f/1.8 full-frame lens is equivalent in field of view and depth of field to a 25mm f/0.9 lens on M43 — a combination that does not exist natively. However, lenses like the Voigtlander Nokton 25mm f/0.95 approach this.

For portrait photography on M43, the lenses most commonly cited for bokeh quality include the Olympus 45mm f/1.8, Olympus 75mm f/1.8, Panasonic Leica 42.5mm f/1.2, and Olympus 45mm f/1.2 Pro. The f/1.2 lenses produce more background separation than the f/1.8 lenses at the cost of higher price and larger size. The 75mm f/1.8 at 150mm equivalent on M43 is particularly well regarded for portrait bokeh within the system, offering a longer focal length and close focusing distance that combine to produce strong background separation.