Inner Centration Error on Aspheres. Season 1/ Part 4
Innner centration error is a lens error that occurs even when no external references are in effect.?One of these references is usually the lens edge cylinder.?This internal centering error does not exist with spherical lenses, since a centering error can only ever be defined via the external reference.?The two centers of curvature always result in a clear optical axis, for which the lens edge cylinder can also be correctly processed later (left image) by center grinding or center turning in the frame.?With aspheres like plan-asphere (see season 1/1 and season 1/2), asphere-sphere or double asphere, there is always an innner centration error after processing the second optical surface, since both surfaces are overdetermined and no clear optical axis?can be defined.?
Middle image: Aspherical axis and normal of the plane surface cannot coincide because they are not parallel.?
Right picture: Sphere's center of curvature is not on the asphere's axis.
Further case: double asphere with inclined and laterally shifted asphere axes (not shown here).