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circle of confusion
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Diagram illustrating spherical aberration, showing parallel light rays passing through a lens and failing to converge at a single focal point, resulting in a blurred image represented by the circle of least confusion.
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circle of confusion

optics
Also known as: circle of least confusion
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Quick Summary

Diagram illustrating spherical aberration, showing parallel light rays passing through a lens and failing to converge at a single focal point, resulting in a blurred image represented by the circle of least confusion.

The "circle of confusion" in optics refers to the indistinct circular patch created by a lens when it forms an out-of-focus image of a single object point. This phenomenon is also known as a "blur circle".1

In contrast, the "circle of least confusion" is a physics term describing the smallest cross-section of a symmetrical bundle of rays that do not converge to a single focal point due to spherical aberration.2

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2 Britannica Sources
  1. circle of confusion
  2. circle of least confusion

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