Surface Profile
While in principle aspheric surfaces can take a wide variety of forms, aspheric lenses are often designed with surfaces of the form
where the optic axis is presumed to lie in the z direction, and is the sag—the z-component of the displacement of the surface from the vertex, at distance from the axis. The coefficients describe the deviation of the surface from the axially symmetric quadric surface specified by and .
If the coefficients are all zero, then is the radius of curvature and is the conic constant, as measured at the vertex (where ). In this case, the surface has the form of a conic section rotated about the optic axis, with form determined by :
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Conic section hyperbola parabola ellipse (surface is a prolate spheroid) sphere ellipse (surface is an oblate spheroid)
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