circle of least confusion

The finest focal spot that can be created by an optical system given the presence of astigmatism and spherical aberration.

Synonyms: circle of confusion, disk of confusion, circle of indistinctness, blur circle, blur spot

See also: astigmatism, spherical aberration, aberration

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Depth of Field and Depth of Focus

Fundamentals of the axial or longitudinal properties of microscope objectives.