Spherical Aberration

A defect caused by grinding the surface of a lens or mirror to a spherical rather than a parabolic shape.

Negative Aberration

When rays of light passing through the curved surface of a lens near its edge converge at a point closer to the lens than those passing through its centre.

Positive Aberration

Wwhen the outer zone has a longer focal length than the centre.

See also: Aberration, Aspherical.

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