Definitions for "Spherical Aberration"
An optical defect caused 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 center (negative aberration); when the outer zone has a longer focal length than the center, the aberration is said to be positive.
the failure of a lens system to image the central and peripheral rays at the same focal point.
Comes to existence when light rays meet an optical element near its egde. These light rays are focused in a different distance than light rays which meet the optical element in its middle part. The consequence is a blurred image. In optical systems consisting of several lenses, this aberration can be reduced by a useful combination of several lens surfaces.