Aspheric Lenses
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Types of Aspheric Lens
An aspheric lens may have any of a number of geometries. Most aspheric lenses are rotationally symmetric but have a more complex front surface. Unlike a spherical lens, the curvature changes with the distance from the optical axis. Another way of putting this would be to say that the radius of curvature varies radially from the center of the lens.
Typically, the further from the optic axis, the weaker the curvature. A lens that does not have these symmetries is typically called a free-form optic.
Aspheric lenses are defined by their surface profile (sag of the surface parallel to the optical axis) or by means of orthogonal coefficients Qbfs and Qcon. Qbfs quantifies the RMS slope departure of your aspheric lens from a best fit sphere, and Qcon quantifies the sag departure from a base conic.