tangential

Definition: Adjective: ~ rays, ~ line: that which lies parallel to a line just touching an imaginary circle (e.g. outer rim of lens) drawn at right-angles to the optical axis. * An off-axis fan of rays or image line parallel to the tangent of a circle normal to the optical axis. * Synonymous with meridional (since the locus of intersections of tangents defines the meridian). * Compare with sagittal.

Related Terms: astigmatism

Previous Term: Talbot  Next Term: T-number