
Aspheric surface
The aspheric surface is a surface of revolution whose sag is given by the sum of the standard conicoid sag expression plus an even polynomial in the radius r=(x2+y2)1/2:

By setting the curvature c to zero, this surface may be used as a general power series surface of even order.
At its vertex, surface has curvature c+2a2
The polynomial coefficients are entered in the parameters section of the surface data editor.
Parameters
- a2, a4,..., a20
- Aspheric coefficients for surface sag