Photonics Dictionary

blur circle

A blur circle refers to the out-of-focus region in an image captured by an optical system. When an object in a scene is not in perfect focus, its image is spread out into a circular shape on the camera sensor or film. This circular area is known as the blur circle.

Several factors contribute to the size and characteristics of a blur circle, including:

Aperture size: A larger aperture (smaller f-number) in a camera allows more light to enter and can result in smaller, softer blur circles.

Distance from the focal plane: Objects at different distances from the focal plane will produce blur circles of different sizes.

Lens characteristics: The optical design of a lens, including the presence of aberrations, can influence the shape and appearance of blur circles.

Blur circles are a common phenomenon in photography, and the aesthetic quality of the blur, often referred to as "bokeh," is a consideration in the field of photography. Photographers may intentionally use a shallow depth of field to create pleasing and artistic blur effects in the out-of-focus areas of an image.

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