bokeh

The visible circular slices of cones of converging light that are captured on a camera sensor are known as bokeh. It is caused by light entering the lens and being focused in front or behind the sensor, where rather than being focused to a point, the converging cone-shaped light is intersected and appears more spread out. Bokeh gets bigger and changes shape based on the size and shape respectively of the aperture stop. Cameras with fixed, circular apertures have circular bokeh, while adjustable apertures reflect the inner edge of the aperture stop. Overall lens construction also determines bokeh shape—some lenses can reduce, eliminate, or emphasize bokeh; while older, poorly constructed, or intentionally designed lenses and filters can have swirly, uneven, or shaped bokeh. Exposure can also play a role, emphasizing the brighter parts of bokeh the more exposed the image is, or becoming less defined if the source of the bokeh is moving or the lens is unstable.