Petzval curvature

Petzval curvature

[′pets·väl ′kər·və·chər]
(optics)
The axial curvature of the image of a plane object produced by an optical system, equal to the sum over all the optical surfaces in the system of R (1/ n′- 1/ n), where R is the curvature of the surface, and n and n′ are the refractive indices before and after the surface. Also known as Petzval sum.